0001564590-21-015517 | 10-K | XBRL Viewer

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2020	Mar. 22, 2021	Jul. 10, 2020
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Document Transition Report	false
Entity File Number	001-39370
Entity Registrant Name	Nkarta, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	47-4515206
Entity Address, Address Line One	6000 Shoreline Court
Entity Address, Address Line Two	Suite 102
Entity Address, City or Town	South San Francisco
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94080
City Area Code	415
Local Phone Number	582-4923
Title of 12(b) Security	Common Stock, $0.0001 par value per share
Trading Symbol	NKTX
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		32,791,817
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Central Index Key	0001787400
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	No
Entity Public Float			$ 657.5
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Portions of the registrant’s Definitive Proxy Statement for the 2021 Annual Meeting of Stockholders to be filed with the U.S. Securities and Exchange Commission pursuant to Regulation 14A within 120 days after the end of the fiscal year covered by this Annual Report on Form 10-K are incorporated by reference in Part III, Items 10-14 of this Annual Report on Form 10-K.

Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 96,692	$ 20,607
Short-term investments, available-for-sale	218,221	16,384
Prepaid expenses and other current assets	3,922	474
Total current assets	318,835	37,465
Restricted cash	413	268
Property and equipment, net	9,350	3,080
Operating lease right-of-use assets	8,505	7,144
Other long-term assets	547	455
Total assets	337,650	48,412
Current liabilities:
Accounts payable	1,176	1,882
Operating lease liabilities, current portion	1,402	1,516
Preferred stock purchase right liability		1,478
Accrued and other current liabilities	6,253	3,289
Total current liabilities	8,831	8,165
Operating lease liabilities, net of current portion	7,517	5,780
Other long-term liabilities	82	134
Total liabilities	16,430	14,079
Commitments and contingencies (Note 7)
Convertible preferred stock, $0.0001 par value; no shares and 54,350,179 shares authorized at December 31, 2020 and 2019, respectively; no shares and 27,283,973 shares issued and outstanding at December 31, 2020 and 2019, respectively		59,815
Stockholders' equity (deficit):
Preferred stock, $0.0001 par value; 54,350,179 shares and no shares authorized at December 31, 2020 and 2019, respectively; no shares issued and outstanding at December 31, 2020 and 2019
Common stock, $0.0001 par value; 100,000,000 and 71,919,982 shares authorized at December 31, 2020 and 2019, respectively; 32,627,963 and 1,600,601 shares issued and outstanding at December 31, 2020 and 2019, respectively	3	1
Additional paid-in capital	439,235	1,179
Accumulated other comprehensive loss	3	(2)
Accumulated deficit	(118,021)	(26,660)
Total stockholders' equity (deficit)	321,220	(25,482)
Total liabilities, convertible preferred stock and stockholders' equity (deficit)	$ 337,650	$ 48,412

Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Convertible preferred stock, par value	$ 0.0001	$ 0.0001
Convertible preferred stock, shares authorized	0	54,350,179
Convertible preferred stock, shares issued	0	27,283,973
Convertible preferred stock, shares outstanding	0	27,283,973
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	54,350,179	0
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	100,000,000	71,919,982
Common stock, shares issued	32,627,963	1,600,601
Common stock, shares outstanding	32,627,963	1,600,601

Statements of Operations and Comprehensive Loss - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Statement [Abstract]
Collaboration revenue		$ 115,000
Operating expenses:
Research and development	$ 36,220,000	17,217,000
General and administrative	15,288,000	5,247,000
Total operating expenses	51,508,000	22,464,000
Loss from operations	(51,508,000)	(22,349,000)
Other income (expense), net:
Change in fair value of preferred stock purchase right liability	(40,163,000)	1,318,000
Change in fair value of derivative liability		858,000
Loss from extinguishment of debt		(752,000)
Interest income	313,000	304,000
Interest expense		(473,000)
Other income (expense), net	(3,000)	18,000
Total other income (expense), net	(39,853,000)	1,273,000
Net loss	(91,361,000)	(21,076,000)
Comprehensive loss:
Net loss	(91,361,000)	(21,076,000)
Other comprehensive loss:
Unrealized loss on securities	5,000	(2,000)
Comprehensive loss	$ (91,356,000)	$ (21,078,000)
Net loss per share, basic and diluted	$ (5.44)	$ (14.41)
Weighted-average number of common shares used in net loss per share, basic and diluted	16,806,262	1,462,511

Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss	Convertible Preferred Stock
Temporary Equity, Beginning Balance, Shares at Dec. 31, 2018						6,170,349
Temporary Equity, Beginning Balance at Dec. 31, 2018						$ 12,709
Beginning Balance, Shares at Dec. 31, 2018		1,231,840
Beginning Balance at Dec. 31, 2018	$ (5,396)	$ 1	$ 187	$ (5,584)
Temporary equity, beneficial conversion feature upon issuance of convertible						261
Temporary equity, reacquisition of beneficial conversion feature upon settlement of promissory notes						(145)
Temporary equity, issuance of Series B convertible preferred stock upon conversion of promissory notes						$ 6,237
Temporary equity, issuance of Series B convertible preferred stock upon conversion of promissory notes, Shares						2,621,181
Temporary equity, Issuance of Series B convertible preferred stock, net of issuance costs						$ 43,548
Temporary equity, Issuance of Series B convertible preferred stock, net of issuance costs, Shares						18,492,443
Temporary equity, series B preferred stock purchase right (liability) upon issuance of Series B convertible preferred stock						$ (2,795)
Vesting of shares of common stock subject to repurchase	42		42
Vesting of shares of common stock subject to repurchase, Shares		354,632
Issuance of common stock upon exercise of stock option, net of repurchase	3		3
Issuance of common stock upon exercise of stock option, net of repurchase, Shares		14,129
Share-based compensation expense	947		947
Unrealized loss on securities	(2)				$ (2)
Net loss	$ (21,076)			(21,076)
Temporary Equity, Ending Balance, Shares at Dec. 31, 2019	27,283,973					27,283,973
Temporary Equity, Ending Balance at Dec. 31, 2019	$ 59,815					$ 59,815
Ending Balance, Shares at Dec. 31, 2019		1,600,601
Ending Balance at Dec. 31, 2019	(25,482)	$ 1	1,179	(26,660)	(2)
Temporary equity, Issuance of Series B convertible preferred stock, net of issuance costs						$ 64,321
Temporary equity, Issuance of Series B convertible preferred stock, net of issuance costs, Shares						27,066,206
Reclassification of preferred stock purchase right liability to equity upon issuance of convertible preferred stock						$ 41,641
Temporary equity, conversion of convertible preferred stock to common stock						$ (165,777)
Temporary equity, conversion of convertible preferred stock to common stock, Shares						(54,350,179)
Conversion of convertible preferred stock to common stock	165,777	$ 1	165,776
Conversion of convertible preferred stock to common stock, Shares		14,689,215
Issuance of common stock upon initial public offering, net of issuance costs	265,096	$ 1	265,095
Issuance of common stock upon initial public offering, net of issuance costs, Shares		16,100,000
Vesting of shares of common stock subject to repurchase	50		50
Vesting of shares of common stock subject to repurchase, Shares		85,304
Issuance of common stock upon exercise of stock option, net of repurchase	387		387
Issuance of common stock upon exercise of stock option, net of repurchase, Shares		152,843
Share-based compensation expense	6,748		6,748
Unrealized loss on securities	5				5
Net loss	$ (91,361)			(91,361)
Temporary Equity, Ending Balance, Shares at Dec. 31, 2020	0					0
Ending Balance, Shares at Dec. 31, 2020		32,627,963
Ending Balance at Dec. 31, 2020	$ 321,220	$ 3	$ 439,235	$ (118,021)	$ 3

Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
Statements of Cash Flows - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net loss	$ (91,361)	$ (21,076)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation expense	6,748	947
Depreciation and amortization expense	786	401
Accretion of discount and amortization of premium on investments, net	738	(19)
Non-cash lease expense	262	152
Change in fair value of preferred stock purchase right liability	40,163	(1,318)
Change in fair value of derivative liability		(858)
Non-cash loss from extinguishment of debt		752
Non-cash interest expense		473
Others	(14)
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(3,645)	(463)
Accounts payable and accrued and other liabilities	2,817	2,642
Net cash used in operating activities	(43,506)	(18,367)
Cash flows from investing activities:
Purchases of available-for-sale securities	(222,570)	(16,367)
Proceeds from maturities of available-for-sale securities	20,000
Purchase of property and equipment	(7,511)	(1,928)
Net cash used in investing activities	(210,081)	(18,295)
Cash flows from financing activities:
Proceeds from issuance of convertible preferred stock, net of issuance costs	64,321	43,548
Proceeds from initial public offering, net of issuance costs	265,096
Proceeds from stock option exercises	387	3
Proceeds from early exercise of stock options	13	44
Proceeds from issuance of convertible notes, net of issuance costs		5,986
Net cash provided by financing activities	329,817	49,581
Net increase in cash and cash equivalents	76,230	12,919
Cash, cash equivalents and restricted cash at beginning of year	20,875	7,956
Cash, cash equivalents and restricted cash at end of year	97,105	20,875
Reconciliation of cash, cash equivalents and restricted cash to the balance sheets:
Cash and cash equivalents	96,692	20,607
Restricted cash	413	268
Total cash, cash equivalents and restricted cash	97,105	20,875
Supplemental disclosures of non-cash investing and financing activities:
Acquisitions of property and equipment	$ 455	265
Deferred offering costs included in accrued and other current liabilities		$ 104

Basis of Presentation and Significant Accounting Policies

12 Months Ended

Dec. 31, 2020

Accounting Policies [Abstract]

Basis of Presentation and Significant Accounting Policies

2. Basis of Presentation and Significant Accounting Policies

Basis of Presentation

The accompanying financial statements have been prepared in accordance with U.S. generally accepted accounting principle (“U.S. GAAP”).

Certain prior period amounts reported in the Company’s financial statements have been reclassified to conform to the current period presentation, with no impact on previously reported operating results or financial position.

Reverse Stock Split

On July 1, 2020, the Company effected a 1-for-3.7 reverse stock split (the “Reverse Stock Split”) of its issued and outstanding common stock. Accordingly, the conversion ratio for the Company’s outstanding convertible preferred stock was proportionately adjusted such that the common stock issuable upon conversion of such preferred stock was decreased in proportion to the Reverse Stock Split. The par value of the common stock was not adjusted as a result of the Reverse Stock Split. All references to common stock, options to purchase common stock, early exercised options, share data, per share data, convertible preferred stock (to the extent presented on an as-converted to common stock basis) and related information contained in these financial statements have been retrospectively adjusted to reflect the effect of the Reverse Stock Split for all periods presented.

COVID-19 Pandemic

On March 11, 2020, the World Health Organization declared the outbreak of a novel strain of coronavirus, COVID-19, as a global pandemic, which continued to spread throughout the United States and around the world in the fourth quarter of 2020. Multiple variants of the virus that causes COVID-19 are also circulating globally. The COVID-19 pandemic is contributing to a general slowdown in the global economy and may affect the Company’s business, results of operations, financial condition, and future strategic plans. The extent of the impact of the COVID-19 pandemic on the Company’s operational and financial performance will depend on certain developments, including the duration and spread of the outbreak, the effectiveness of actions taken in the United States and other countries to contain, vaccinate against, and treat the disease, and its impact on the Company’s planned preclinical studies and clinical trials, employees and vendors, all of which are uncertain and cannot be predicted. The Company has taken certain precautionary measures to minimize exposure of the Company’s employees to the virus and to comply with directives from public health officials. This includes work from home policies for employees as well as enhanced safety measures for scientists who are in labs and manufacturing facility. Some of the third-party vendors that the Company uses have experienced disruptions during this pandemic. However, COVID-19 did not materially impact the timelines the Company previously announced for the filing of the NKX101 IND or the dosing of the first patient in the NKX101 clinical trial, and the Company does not expect COVID-19 to have a material impact on the current timeline for the filing of the NKX019 IND. At this time, the extent to which the COVID-19 pandemic may impact the Company’s financial condition or results of operations is uncertain and these precautionary measures may negatively impact productivity, and cause disruptions or delays to the Company’s activities and timelines. In response to the pandemic, the Coronavirus Aid, Relief and Economic Security Act (the “CARES Act”) was signed into law on March 27, 2020. The CARES Act, among other things, includes tax provisions relating to refundable payroll tax credits, deferment of employer’s social security payments, net operating loss utilization and carryback periods, modifications to the net interest deduction limitations and technical corrections to tax depreciation methods for qualified improvement property. The CARES Act had no impact on the Company’s income tax provision for the year ended December 31, 2020. The Company continues to evaluate the impact of the CARES Act on its financial position, results of operations and cash flows. The Company currently does not expect to apply for loans or grants under the CARES Act.

Use of Estimates

The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the Company’s financial statements and accompanying notes. On an ongoing basis, management evaluates its estimates, including those related to preclinical studies, fair value of assets and liabilities, convertible preferred stock, share-based compensation and income taxes. Management bases its estimates on historical experience, knowledge of current events and actions it may undertake in the future that management believes to be reasonable under the circumstances. Actual results may differ from these estimates and assumptions.

Concentration of Credit Risk

Financial instruments, which potentially subject the Company to concentration of credit risk, consist primarily of cash, cash equivalents and short-term investments. The Company maintains cash, cash equivalents and short-term investments with various high credit quality and are invested through banks and other financial institutions in the United States. Such deposits may be in excess of federally insured limits. Management believes that the Company is not exposed to significant credit risk due to the financial position of the depository institutions in which those deposits are held. The Company has not experienced any losses on deposits since inception.

Comprehensive Loss

Comprehensive loss consists of net loss and unrealized gains or losses on available-for-sale investments. The Company displays comprehensive loss and its components as part of the statements of operations and comprehensive loss.

Fair Value of Financial Instruments

The accounting guidance defines fair value, establishes a consistent framework for measuring fair value, and expands disclosure for each major asset and liability category measured at fair value on either a recurring or nonrecurring basis. Fair value is defined as an exit price representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, the accounting guidance establishes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value as follows:

Level 1: Observable inputs such as quoted prices in active markets;

Level 2: Inputs, other than the quoted prices in active markets, that are observable either directly or indirectly; and

Level 3: Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions.

The carrying amounts of prepaid expenses and other current assets, accounts payable, accrued liabilities and other current liabilities are reasonable estimates of their fair value due to the short-term nature of these accounts.

Cash, Cash Equivalents, Short-term Investments and Restricted Cash

Cash and Cash Equivalents

The Company considers all highly liquid investments with insignificant interest rate risk and an original maturity of three months or less at the date of purchase to be cash equivalents. Cash includes demand deposits held in readily available checking accounts at a federally insured financial institution. Cash equivalents consist of money market funds.

Short-term Investments

Short-term investments consist of commercial debt securities, commercial paper and U.S. Government securities, classified as available-for-sale securities and have maturities of greater than three months but less than one year. The Company has classified all of its available-for-sale investment securities as current assets on the balance sheets because these are considered highly liquid securities and are available for use in current operations. The Company carries these securities at fair value, and reports unrealized gains and losses as a separate component of accumulated other comprehensive loss. The cost of debt securities is adjusted for amortization of purchase premiums and accretion of discounts to maturity. Such amortization and accretion is included in interest income in the statements of operations and comprehensive loss. Realized gains and losses on sales of securities are determined using the specific identification method and recorded in other income (expense), net in the statement of operations and comprehensive loss.

Restricted Cash

The Company is required to maintain a letter of credit related to its office and lab space lease. This cash is the collateral for that letter of credit and per the terms of the lease must remain in place until two months after the termination of the lease. As the remaining term of the lease as of December 31, 2020 is greater than one year, the related restricted cash has been classified as non-current.

Property and Equipment, Net

Property and equipment, which consist of leasehold improvements, furniture and fixtures, research equipment, computers and software and construction-in-progress are stated at cost less accumulated depreciation. Depreciation and amortization is calculated using the straight-line method over the estimated useful lives of the assets, which ranges from three to five years. Leasehold improvements are amortized over the remaining life of the lease for leasehold improvements at the time the asset is placed into service.

Impairment of Long-Lived Assets

The carrying value of long-lived assets, including property and equipment, are reviewed for impairment whenever events or changes in circumstances indicate that the asset may not be recoverable. An impairment loss is recognized when the total of estimated future undiscounted cash flows, expected to result from the use of the asset and its eventual disposition, are less than its carrying amount. Impairment, if any, would be assessed using discounted cash flows or other appropriate measures of fair value. Through December 31, 2020, there has been no such impairment losses recorded by the Company.

Deferred Offering Costs

Deferred offering costs that consisted of legal, accounting, printing and other fees and costs directly attributable to the IPO were capitalized. Upon the completion of the IPO in July 2020, the total deferred offering costs of $4.4 million were offset against the proceeds from the IPO and reclassified to additional paid-in capital on the balance sheets.

Preferred Stock Purchase Right Liability

The Company at times enters into convertible preferred stock financings where, in addition to the initial closing, investors agree to buy, and the Company agrees to sell, additional shares of that convertible preferred stock at a fixed price in the event that certain agreed upon milestones are achieved or at the election of investors. The Company evaluates this purchase right and assesses whether it meets the definition of a freestanding instrument and, if so, determines the fair value of the purchase right liability and records it on the balance sheets with the remainder of the proceeds raised being allocated to convertible preferred stock. The preferred stock purchase right liability is revalued at each reporting period with changes in the fair value of the liability recorded as change in fair value of preferred stock purchase right in the statements of operations and comprehensive loss. A final revaluation adjustment of preferred stock purchase right liability was recorded at settlement in July 2020 and the resultant fair value was then reclassified to convertible preferred stock at that time.

Convertible Preferred Stock

The Company recorded all shares of convertible preferred stock at their respective issuance price less issuance costs on the dates of issuance. Convertible preferred stock was previously classified outside of stockholders’ equity (deficit) on the balance sheets as events triggering redemption were not solely within the Company’s control because the preferred stockholders had the ability to effect a liquidation event, as they have majority of the Company’s Board seats.

Immediately prior to the closing of the Company’s IPO in July 2020, all outstanding shares of the Company’s convertible preferred stock converted into the Company’s common stock. There were no outstanding shares of the Company’s convertible preferred stock as of December 31, 2020.

Revenue Recognition

Revenue is recognized in accordance with ASC 606 when a customer obtains control of promised goods or services. The Company applies the following five steps to recognize revenue: (i) identify the contract with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to performance obligations in the contract; and (v) determine the recognition period. The Company evaluates its performance obligations to determine whether each item represents a good or service that is distinct or has the same pattern of transfer as other deliverables. A deliverable is considered distinct if the customer can benefit from the good or service independently of other goods/services either in the contract or that can be obtained elsewhere, and the entity’s promise to transfer the good or service to the customer is separately identifiable from other promises in the contact. If the deliverable is not considered distinct, the Company combines such deliverables and accounts for them as a single performance obligation. The Company allocates the consideration to each deliverable at the inception of the arrangement based on the transaction price.

In April 2017, the Company entered into the Collaboration and License Agreement (the “Collaboration Agreement”) with GlaxoSmithKline Intellectual Property Development Limited and Glaxo Group Limited (together, “GSK”) to research and develop therapeutics using Engineered NK Cells as carriers for target programs. On December 10, 2018, the Collaboration Agreement with GSK was terminated. Nominal revenue of $0.1 million was recognized for the year ended December 31, 2019 in connection with the wind-down activities through the termination of the Collaboration Agreement in December 2018. There was no revenue recorded for the year ended December 31, 2020.

Research and Development Costs

Research and development costs are expensed as incurred. Research and development costs consist primarily of salaries and other benefits of research and development personnel, including associated share-based compensation, costs related to research activities, preclinical studies, clinical trial, drug manufacturing and allocated overhead and facility-related expenses. The Company accounts for non-refundable advance payments for goods or services that will be used in future research and development activities as expenses when the goods have been received or when the service has been performed rather than when the payment is made.

Clinical trial costs are a component of research and development expenses. The Company expenses costs for its clinical trial activities performed by third parties, including clinical research organizations and other service providers, as they are incurred, based upon estimates of the work completed over the life of the individual study in accordance with associated agreements. The Company uses information it receives from internal personnel and outside service providers to estimate the clinical trial costs incurred.

Commitments

The Company recognizes a liability with regard to loss contingencies when it believes it is probable a liability has occurred and the amount can be reasonably estimated. If some amount within a range of loss appears at the time to be a better estimate than any other amount within the range, the Company accrues that amount. When no amount within the range is a better estimate than any other amount the Company accrues the minimum amount in the range. There has been no such liabilities recorded by the Company as of December 31, 2020.

Leases

At the commencement date of a lease, the Company recognizes lease liabilities which represent its obligation to make lease payments, and right-of-use assets (“ROU assets”) which represent its right to use the underlying asset during the lease term. The lease liability is measured at the present value of lease payments over the lease term. As the Company’s leases typically do not provide an implicit rate, the Company uses an incremental borrowing rate based on the information available at the lease commencement date. The ROU asset is measured at cost, which includes the initial measurement of the lease liability and initial direct costs incurred by the Company and excludes lease incentives. ROU assets are recorded in operating lease ROU assets and lease liabilities are recorded in operating lease liabilities, current and noncurrent in the balance sheets.

Lease terms may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. Operating lease expense is recognized on a straight-line basis over the lease term. Lease agreements that contain both lease and non-lease components are generally accounted for separately. The Company does not recognize lease liabilities and ROU assets for short-term leases with terms of twelve months or less.

Share-Based Compensation

Share-based compensation expense represents the cost of the grant-date fair value of employee, officer, director, and non-employee stock option grants, estimated in accordance with the applicable accounting guidance, recognized using the straight-line method over the vesting period for service-based options and using the graded vesting method for performance-based options. The vesting period generally approximates the expected service period of the awards. Forfeitures are recognized and accounted for as they occur.

The fair value of stock options is estimated using a Black-Scholes option pricing model on the date of grant. This method requires certain assumptions be used as inputs, such as the fair value of the underlying common stock, expected term of the option before exercise, expected volatility of the Company’s common stock, expected dividend yield, and a risk-free interest rate. Options granted during the year have a maximum contractual term of ten years. The Company has limited historical stock option activity and therefore estimates the expected term of stock options granted using the simplified method, which represents the average of the contractual term of the stock option and its weighted-average vesting period. The expected volatility of stock options is based upon the historical volatility of a number of publicly traded companies in similar stages of clinical development. The Company has historically not declared or paid any dividends and does not currently expect to do so in the foreseeable future. The risk-free interest rates used are based on the U.S. Department of Treasury (“U.S. Treasury”) yield in effect at the time of grant for zero-coupon U.S. Treasury notes with maturities approximately equal to the expected term of the stock options.

Income Taxes

Income taxes have been accounted for using the asset and liability method. Under the asset and liability method, deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and tax credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates applicable to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. A valuation allowance against deferred tax assets is recorded if, based upon the weight of all available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized.

Segment Reporting

The Company’s chief operating decision maker, its President and Chief Executive Officer, manages its operations and business as one operating segment for the purposes of allocating resources, makes operating decisions and evaluates financial performance. No product revenue has been generated since inception and all assets are held in the United States.

Net Loss Per Share

Basic net loss per share is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of common shares outstanding for the period, without consideration of potential dilutive securities. Diluted net loss per share is computed by dividing the net loss attributable to common stockholders by the sum of the weighted average number of common shares plus the potential dilutive effects of potential dilutive securities outstanding during the period. Potential dilutive securities are excluded from diluted earnings or loss per share if the effect of such inclusion is antidilutive. The Company’s potentially dilutive securities, which include convertible preferred stock prior to the conversion of such shares to common stock, unvested common stock, and outstanding stock options under the Company’s equity incentive plan, have been excluded from the computation of diluted net loss per share as they would be anti-dilutive to the net loss per share. For all periods presented, there is no difference in the number of shares used to calculate basic and diluted shares outstanding due to the Company’s net loss position.

Recent Accounting Pronouncements

Adopted Accounting Pronouncements

Financial Instruments. In June 2016, the FASB issued ASU 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, which amends the impairment model by requiring entities to use a forward-looking approach based on expected losses to estimate credit losses on certain types of financial instruments, including available-for-sale debt securities. The Company adopted this standard in the first quarter of 2020. The adoption of this standard did not have a material impact on the Company’s financial statements.

Fair Value Measurements. In August 2018, the FASB issued ASU 2018-13—Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement, which eliminates, adds and modifies certain disclosure requirements for fair value measurement. The amendments in ASU 2018-13 that relate to changes in unrealized gains and losses, the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements and the narrative description of measurement uncertainty should be applied prospectively for only the most recent interim or annual period presented in the initial fiscal year of adoption. All other amendments in ASU 2018-13 should be applied retrospectively to all periods presented upon their effective date. The Company adopted this standard in the first quarter of 2020. The adoption of this standard did not have a material impact on the Company’s disclosures.

Accounting Pronouncements Not Yet Adopted

Income Taxes. In December 2019, the FASB issued ASU 2019-12—Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes, which simplifies the accounting for income taxes by eliminating certain exceptions to the guidance in Topic 740 related to the approach for intra-period tax allocation, the methodology for calculating income taxes in an interim period and the recognition of deferred tax liabilities for outside basis differences. The new guidance also simplifies aspects of the accounting for franchise taxes and enacted changes in tax laws or rates. This standard is effective for fiscal years beginning after December 15, 2020, with early adoption permitted. The Company will adopt this standard in the first quarter of 2021 and the adoption is not expected to have a material impact on the Company’s financial statements.

There were no other significant updates to the recently issued accounting standards other than as disclosed herewith. Although there are several other new accounting pronouncements issued or proposed by the FASB, the Company does not believe any of those accounting pronouncements have had or will have a material impact on its financial position or operating results.

Fair Value of Financial Instruments

12 Months Ended

Dec. 31, 2020

Fair Value Disclosures [Abstract]

Fair Value of Financial Instruments

4. Fair Value of Financial Instruments

The following tables summarize the fair value of the Company’s financial instruments (in thousands):

			Fair Value Measurements Using
	December 31, 2020		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents:
Money market funds	$	94,631	$	94,631	$	—	$	—
Short-term investments:
Corporate debt securities	$	48,614	$	—	$	48,614	$	—
Commercial paper		63,445		—		63,445		—
U.S. Government securities		106,162		—		106,162		—
Total short-term investments	$	218,221	$	—	$	218,221	$	—
Total	$	312,852	$	94,631	$	218,221	$	—

			Fair Value Measurements Using
	December 31, 2019		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents:
Commercial paper	$	2,395	$	—	$	2,395	$	—
Short-term investments:
Corporate debt securities	$	6,027	$	—	$	6,027	$	—
Commercial paper		10,357		—		10,357		—
Total short-term investments		16,384		—		16,384		—
Total	$	18,779	$	—	$	18,779	$	—
Liabilities:
Preferred stock purchase right liability	$	1,478	$	—	$	—	$	1,478

Cash Equivalents and Short-Term Investments

Financial assets measured at fair value on a recurring basis consist of the Company’s cash equivalents and short-term investments. Cash equivalents consisted of money market funds and short-term investments consisted of commercial paper, corporate debt securities and U.S. Government securities. The Company obtains pricing information from its investment manager and generally determines the fair value of investment securities using standard observable inputs, including reported trades, broker/dealer quotes, and bids and/or offers.

Investments are classified as Level 1 within the fair value hierarchy if their quoted prices are available in active markets for identical securities. Investments in money market funds of $94.6 million included in cash equivalents as of December 31, 2020 were classified as Level 1 instruments.

Investments in corporate debt securities, commercial paper and U.S. Government securities included in short-term investments are valued using Level 2 inputs. Level 2 securities are initially valued at the transaction price and subsequently valued and reported upon utilizing inputs other than quoted prices that are observable either directly or indirectly, such as quotes from third-party pricing vendors. Fair values determined by Level 2 inputs, which utilize data points that are observable such as quoted prices, interest rates and yield curves, require the exercise of judgment and use of estimates, that if changed, could significantly affect the Company’s financial position and results of operations.

The following tables summarize the Company’s short-term investments as of December 31, 2020 and December 31, 2019 (in thousands):

		December 31, 2020
	Maturity (in years)	Amortized Cost		Unrealized Losses			Unrealized Gains		Estimated Fair Value
Corporate debt securities	1 year or less	$	48,616	$	(6	)	$	4	$	48,614
Commercial paper	1 year or less		63,445		—			—		63,445
U.S. Government securities	1 year or less		106,157		(7	)		12		106,162
Total		$	218,218	$	(13	)	$	16	$	218,221

		December 31, 2019
	Maturity (in years)	Amortized Cost		Unrealized Losses			Unrealized Gains		Estimated Fair Value
Corporate debt securities	1 year or less	$	6,029	$	(2	)	$	—	$	6,027
Commercial paper	1 year or less		10,357		—			—		10,357
Total		$	16,386	$	(2	)	$	—	$	16,384

Prior to 2020, the Company followed the guidance in ASC 320 Investments—Debt and Equity Securities in determining whether unrealized losses were other than temporary. The Company adopted Topic 326 on January 1, 2020, and now considers whether unrealized losses have resulted from a credit loss or other factors. The unrealized losses on the Company’s available-for-sale securities as of December 31, 2020 and December 31, 2019 were caused by fluctuations in market value and interest rates as a result of the economic environment. The Company concluded that an allowance for credit losses was unnecessary as of December 31, 2020 and that there were no impairments as of December 31, 2019 considered as other-than-temporary because the decline in the market value was attributable to changes in market conditions and not credit quality, and that it is neither management’s intention to sell nor is it more likely than not that the Company will be required to sell these investments prior to recovery of their cost basis or recovery of fair value. There was no realized gain or loss on available-for-sale securities in the periods presented.

The Company elected the practical expedient to exclude accrued interest from both the fair value and the amortized cost basis of the available-for-sale debt securities for the purposes of identifying and measuring an impairment and to not measure an allowance for expected credit losses for accrued interest receivables. Accrued interest receivable is written off through net realized investment gains (losses) at the time the issuer of the bond defaults or is expected to default on payment. The Company made an accounting policy election to present the accrued interest receivable balance as part of prepaid expenses and other current assets in the balance sheets. Accrued interest receivable related to short-term investments was $1.1 million and $41,000 as of December 31, 2020 and 2019, respectively.

Preferred Stock Purchase Right Liability

In August 2019, the Company entered into a Series B Preferred Stock Purchase Agreement (see Note 10) that contained future purchase rights that were required to be accounted for as liabilities and remeasured to fair value at each reporting date, with any change in the fair value reported as a component of other expense, net. On July 1, 2020, the Company completed the Series B Milestone Closing and issued 27,066,206 shares of its Series B convertible preferred stock for aggregate gross proceeds of $64.4 million. Upon the exercise of the preferred stock purchase right on July 1, 2020, the preferred stock purchase right liability was revalued at an estimated fair value of $41.6 million and was reclassified to additional paid-in capital in the balance sheets. See Note 10 for further details on preferred stock purchase right liability.

The estimated fair value of the preferred stock purchase right liability at July 1, 2020 and December 31, 2019 was determined using a valuation model that incorporated the probability of the occurrence of the Series B Milestone Closing in addition to the factors considered at issuance. To determine the fair value of preferred stock purchase right as of July 1, 2020, an intrinsic value model was used. The assumptions used to determine the fair value of the preferred stock purchase right liability as of December 31, 2019 and upon its issuance in August 2019 included an estimated probability of occurrence of the Series B Milestone Closing of 90%, an assumed discount rates of 1.6% and 1.8%, respectively, and an estimated time period the preferred stock purchase right liability would be outstanding of 0.8 years and 1.1 years, respectively. As certain of these inputs are not observable in the market, the preferred stock purchase right liability is classified as a Level 3 instrument.

The following table provides the change in preferred stock purchase right liability for the year ended December 31, 2020 (in thousands):

	Preferred Stock Purchase Right Liability
Balance, December 31, 2019	$	1,478
Change in fair value of preferred stock purchase right		40,163
Reclassification of preferred stock purchase right liability to equity upon issuance of convertible preferred stock		(41,641	)
Balance, December 31, 2020	$	—

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Balance Sheet Components

12 Months Ended

Dec. 31, 2020

Balance Sheet Related Disclosures [Abstract]

Balance Sheet Components

5. Balance Sheet Components

Prepaid Expenses and Other Current Assets

Prepaid expenses and other current assets are comprised of the following (in thousands):

	December 31,
	2020		2019
Prepaid expenses	$	2,586		407
Other current assets		1,336		67
Total prepaid expenses and other current assets	$	3,922	$	474

Property and Equipment, Net

Property and equipment, net is comprised of the following (in thousands):

	December 31,
	2020			2019
Leasehold improvements	$	1,984		$	287
Furniture and fixtures		322			265
Research equipment		4,892			2,929
Computers and software		124			61
Construction-in-progress		3,459			183
Total property and equipment		10,781			3,725
Less accumulated depreciation and amortization		(1,431	)		(645	)
Total property and equipment, net	$	9,350		$	3,080

Depreciation and amortization expense were $0.8 million and $0.4 million for the years ended December 31, 2020 and 2019, respectively.

Accrued and Other Current Liabilities

Accrued and other current liabilities are comprised of the following (in thousands):

	December 31,
	2020		2019
Accrued compensation	$	3,534	$	1,678
Accrued research and development costs		1,675		702
Accrued property and equipment		117		214
Deferred offering costs		—		104
Other accrued and current liabilities		927		591
Total accrued and other liabilities	$	6,253	$	3,289

Leases

12 Months Ended

Dec. 31, 2020

Leases [Abstract]

Leases

6. Leases

The Company has operating leases for its corporate office, laboratory space and dedicated space in a vivarium in South San Francisco, California.

The components of lease expense were as follows (in thousands):

	Year Ended December 31,
	2020		2019
Operating lease expense	$	1,856		1,315
Variable lease expense ⁽¹⁾		178		126
Short-term lease expense		14		—
Total lease expense	$	2,048	$	1,441

⁽¹⁾ Variable lease expense for the periods presented primarily included common area maintenance charges.

Supplemental information related to operating leases were as follows (in thousands):

	Year Ended December 31,
	2020		2019
Cash paid for amounts included in the measurement of lease liabilities
Operating cash flows used for operating leases	$	1,705	$	1,180

Lease liabilities arising from obtaining right-of-use assets
Operating leases	$	2,401	$	5,107

The weighted-average remaining lease term was 8.1 years for the corporate office and laboratory space leases and 0.3 years for the vivarium lease as of December 31, 2020. The corporate office lease includes an option to renew for an additional seven years. However, the renewal option was not included in the lease term for calculating the lease liability, as the renewal option allow the Company to maintain operational flexibility, and the Company was not reasonably certain that it would exercise the renewal option at the time of the lease commencement. The weighted-average discount rate was 10% as of December 31, 2020.

Maturities of operating lease liabilities under existing operating leases as of December 31, 2020 were as follows (in thousands):

Year ending December 31,	Amount
2021	$	1,461
2022		1,452
2023		1,503
2024		1,556
2025		1,610
2026 and thereafter		5,371
Total future minimum lease payments		12,953
Less imputed interest		(4,034	)
Present value of net minimum lease payments	$	8,919
Operating lease liabilities:
Current		1,402
Non-current		7,517
Total lease liability	$	8,919

In May 2020, the Company signed a second amendment to its corporate office and laboratory facilities lease. The amended lease provides for an eight-year non-cancelable lease of additional office and laboratory space in the same building. The lease for additional office and laboratory space provides for abatement of rent during the first three months of the lease and contains rent escalations during the term of the lease. The lease for this additional space is expected to commence in the first quarter of 2021 and expires in 2029. The lease amendment also includes an extension of the lease term for the existing office and laboratory space beginning on May 1, 2020 through the first quarter of 2029. The lease agreement includes an option to extend the lease for an additional seven-year term.

Subsequently, in January 2021, the Company signed a third amendment to its corporate office and laboratory facilities lease which provides for lease of additional space in the same building. The lease of this additional space is expected to commence in the second quarter of 2021 and expires in March 2024. The other terms of the existing lease remain unchanged.

Total minimum lease payments of $4.5 million and $0.7 million related to the lease of additional space under the second and third amendment, respectively, were excluded from the table above as the lease agreement had not yet commenced as of December 31, 2020.

Convertible Preferred Stock and Stockholders’ Equity (Deficit)

12 Months Ended

Dec. 31, 2020

Equity [Abstract]

Convertible Preferred Stock and Stockholders’ Equity (Deficit)

10. Convertible Preferred Stock and Stockholders’ Equity (Deficit)

Under the Amended and Restated Certificate of Incorporation dated August 26, 2019, the Company had a total of 126,270,161 shares of capital stock authorized for issuance, consisting of 71,919,982 shares of common stock, par value of $0.0001 per share, and 54,350,179 shares of convertible preferred stock, par value of $0.0001 per share. Of the 54,350,179 shares of convertible preferred stock, 6,170,349 were designated Series A convertible preferred stock and 48,179,830 were designated Series B convertible preferred stock.

In connection with the Reverse Stock Split on July 1, 2020, the Company filed a certificate of amendment to its certificate of incorporation, which provided 100,000,000 authorized shares of common stock with a par value of $0.0001 per share and 54,350,179 authorized shares of preferred stock with a par value of $0.0001 per share.

Series A Convertible Preferred Stock

In December 2017, the Company sold and issued in a private placement 3,866,602 shares of Series A convertible preferred stock at $2.07 per share (the “Series A Financing”). Upon the closing of the Series A Financing, the convertible notes outstanding at that date were converted into 2,011,114 shares of Series A convertible preferred stock at 80% of the $2.07 price per share (the “Series A Original Issue Price”) paid by the Series A Financing investors. The GSK Convertible Note converted into 292,633 shares of Series A convertible preferred stock at 85% of the Series A Original Issue Price. In connection with the convertible notes, the Company recorded a beneficial conversion feature of $0.9 million which was recognized as a debt discount and accreted to interest expense over the term of the note using the effective interest method.

Series B Convertible Promissory Notes

In May 2019, the Company entered into Series B Convertible Promissory Notes (the “Convertible Notes”) whereby the Company agreed to issue and certain existing Series A investors (the “Noteholders”) agreed to purchase $6,000,000 in Convertible Notes. The Convertible Notes accrued interest at a contractual rate of 7.5% per year and had an original maturity date of one year from their issuance date. The Convertible Notes were to automatically convert into Series B convertible preferred stock at 85% or 80% of the price per share paid by other investors upon certain qualified financing events, with the percent discount based on the timing of the financing, or through a voluntary option to convert upon certain non-qualified financing events. In addition, if the maturity date were to occur prior to the conversion or repayment of the Convertible Notes, the Noteholders had the right to convert the outstanding principal amount of the Convertible Notes, and all accrued and unpaid interest, into Series A convertible preferred stock at the Series A original issuance price.

As the Convertible Notes contained various settlement outcomes, the Company evaluated each scenario for accounting purposes. The settlement into Series A convertible preferred stock scenario resulted in the Company recording a beneficial conversion feature of $0.3 million upon the issuance of the Convertible Notes, as the fair value of the Series A convertible preferred stock on the date of issuance was greater than the original Series A issuance price. The conversion discounts were considered to be redemption features and were evaluated as an embedded derivative and bifurcated from the Convertible Notes, due to the substantial premium to be paid upon redemption. Upon bifurcating the redemption features, the Company recorded a derivative instrument of $1.3 million. The derivative instrument and beneficial conversion feature were recorded as a debt discount at inception and were being amortized to interest expense using the effective interest method over the one-year term of the debt.

In August 2019, in connection with the Series B convertible preferred stock financing, the Convertible Notes terms were modified so that the Noteholders received a conversion benefit equal to an annual effective interest rate of 7.5% on the outstanding principal on the Convertible Notes, rather than the originally stated 85% price. The change in the conversion benefit resulted in an adjustment to the derivative instrument of $0.9 million. In addition, as the Convertible Notes contained an embedded beneficial conversion feature and were extinguished before conversion, the Company allocated a portion of the settlement to the repurchase of the beneficial conversion feature, using the intrinsic value on the extinguishment date. This resulted in a reduction to the previously recorded beneficial conversion feature of $0.1 million. Additionally, the Company recorded a loss on extinguishment of debt of $0.8 million, representing the write-off on the unamortized debt issuance costs on the date the Convertible Notes converted into Series B convertible preferred stock.

During the year ended December 31, 2019, the Company recorded $0.1 million of interest expense related to the stated interest for the Convertible Notes and $0.4 million using the effective-interest method in relation to the debt discounts described above. The annual effective-interest rates for the Convertible Notes was 30.4%.

Series B Convertible Preferred Stock

On August 27, 2019, the Company entered into a Series B Preferred Stock Purchase Agreement (the “Stock Purchase Agreement”). The Stock Purchase Agreement contained provisions that obligated the Company to sell, outside of its control, an additional 27,066,206 shares of Series B convertible preferred stock at the Series B Original Issue Price per share, for expected gross proceeds of $64.4 million, upon the achievement of a milestone, or by election of the holders of at least one-third of the Company’s Series B convertible preferred stock at any time prior to the completion of the Company’s initial public offering if the milestone was not achieved (the “Series B Milestone Closing”). If the shares were not purchased prior to the completion of the Company’s initial public offering, then the right to purchase these shares would have automatically expired. In the event that an Initial Series B Closing purchaser, or its affiliates or transferees, failed to purchase their required shares in the Series B Milestone Closing, then all the Series B convertible preferred stock held by such initial Series B purchaser would have been automatically converted into one share of common stock for each ten shares of Series B convertible preferred stock.

On July 1, 2020, the Company completed the Series B Milestone Closing pursuant to a milestone waiver by the holders of the Series B convertible preferred stock, and issued 27,066,206 shares of Series B convertible preferred stock for gross proceeds of $64.4 million. On July 14, 2020, upon the closing of the Company’s IPO, all outstanding shares of the Company’s convertible preferred stock converted into 14,689,215 shares of the Company’s common stock. There were no outstanding shares of the Company’s convertible preferred stock as of December 31, 2020.

The Company determined its obligation to issue additional shares of the Company’s Series B convertible preferred stock in the Series B Milestone Closing represented a freestanding financial instrument that required liability accounting. This freestanding preferred stock purchase right liability was initially recorded at fair value, with fair value changes recognized in the statements of operations and comprehensive loss. At the time the Stock Purchase Agreement was entered into in August 2019, the initial estimated fair value of the preferred stock purchase right liability was $2.8 million, and was revalued at $1.5 million as of December 31, 2019. On July 1, 2020, the preferred stock purchase right liability was revalued at an estimated fair value of $41.6 million and was reclassified to additional paid-in capital upon the exercise of the preferred stock purchase right. The Company recorded the change in the fair value of the Series B convertible preferred stock purchase right liability of $40.2 million as other expense and $1.3 million as other income for the years ended December 31, 2020 and 2019, respectively, in the statements of operations and comprehensive loss.

Common Stock

In conjunction with the Company’s July 2020 IPO closing, the Company issued and sold 16,100,000 shares of its common stock, including 2,100,000 shares pursuant to the full exercise of the underwriters' option to purchase additional shares, at a public offering price of $18.00 per share, for aggregate net proceeds of $265.1 million after deducting underwriting discounts and commissions and other offering costs. In connection with this offering, all outstanding shares of the Company’s convertible preferred stock converted into 14,689,215 shares of common stock.

The following is a summary of the rights and privileges of the holders of common stock as of December 31, 2020:

Liquidation Preference: In the event of liquidation, dissolution or winding up, holders of common stock will be entitled to share ratably in the net assets legally available for distribution to stockholders after the payment of all debts and other liabilities and the satisfaction of any liquidation preference granted to the holders of any then-outstanding shares of preferred stock.

Dividends: Subject to preferences that may be applicable to any then-outstanding preferred stock, holders of common stock are entitled to receive ratably those dividends, if any, as may be declared from time to time by the Board out of legally available funds. As of December 31, 2020, no cash dividends have been declared or paid.

Voting Rights: Each holder of common stock is entitled to one vote for each share on all matters submitted to a vote of the stockholders, including the election of directors. Under the Company’s amended and restated certificate of incorporation and amended and restated bylaws, stockholders will not have cumulative voting rights. Because of this, the holders of a majority of the shares of common stock entitled to vote in any election of directors can elect all of the directors standing for election, if they should so choose.

Rights and Preferences: Holders of common stock have no preemptive, conversion or subscription rights and there are no redemption or sinking fund provisions applicable to the common stock. The rights, preferences and privileges of the holders of common stock are subject to, and may be adversely affected by, the rights of the holders of shares of any series of preferred stock that the Company may designate in the future.

Share-Based Compensation

12 Months Ended

Dec. 31, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Share-Based Compensation

11. Share-Based Compensation

Equity Incentive Plan

2015 Equity Incentive Plan

The Company granted options under its 2015 Equity Incentive Plan (the “2015 Plan”) until July 2020 when it was terminated as to future awards, although it continues to govern the terms of options that remain outstanding under the 2015 Plan. The 2015 Plan allows for the grant of incentive stock options, non-statutory stock options, stock appreciation rights, restricted stock unit awards and other stock awards. Awards can be made to officers, directors, employees, non-employee directors, and consultants of the Company. In connection with the Board of Directors’ and stockholders’ approval of the 2020 Plan, the 2015 Plan was terminated as to future awards and any options or awards outstanding under the 2015 Plan remain outstanding and effective. As of December 31, 2020, there were an aggregate of 2,211,562 shares of common stock issuable upon the exercise of outstanding options under the 2015 Plan.

2020 Performance Incentive Plan

The Company’s 2020 Performance Incentive Plan (the “2020 Plan”) which was adopted by the Company’s board of directors in June 2020 and approved by the Company’s stockholders in July 2020, became effective upon the consummation of the IPO. Upon the effectiveness of the 2020 Plan, no further grants may be made under the Company’s 2015 Plan. The Company’s 2020 Plan allows for the grant of incentive stock options, non-qualified stock options, stock appreciation rights, stock bonuses, restricted stock, stock units and other forms of awards including cash awards to its officers, directors, employees, consultants and advisors.

As of December 31, 2020, a total of 2,660,371 shares of the Company’s common stock were authorized for issuance with respect to awards granted under the 2020 Plan. The share limit will automatically increase on the first trading day in January of each year (commencing in 2021) by an amount equal to the lesser of (1) 5% of the total number of outstanding shares of the Company’s common stock on the last trading day in December in the prior year, or (2) such lesser number as determined by the Company’s board of directors. Any shares subject to awards granted under the 2020 Plan or the 2015 Plan that are not paid, delivered or exercised before they expire or are canceled or terminated, or otherwise fail to vest, as well as shares used to pay the purchase or exercise price of such awards or related tax withholding obligations, will become available for new award grants under the 2020 Plan. A total of 1,542,532 options had been granted and 1,390,402 shares was available for issuance under the 2020 Plan for the year ended December 31, 2020.

The following table summarizes the stock option activity during the year ended December 31, 2020 (in thousands, except number of shares, exercise prices and contractual term):

	Number of shares			Weighted-average exercise price		Weighted-average remaining contractual term (in years)		Aggregate Intrinsic Value
Outstanding at December 31, 2019		2,329,516		$	3.59		9.6	$	668
Granted		1,782,794			19.52
Exercised		(183,287	)		2.18
Forfeited		(288,308	)		9.40
Outstanding at December 31, 2020		3,640,715		$	11.00		9.0	$	183,742
Exercisable at December 31, 2020		654,195		$	5.34		8.6	$	36,717
Vested and expected to vest at December 31, 2020		3,640,715		$	11.00		9.0	$	183,742

The aggregate intrinsic value represents the difference between the exercise price of stock options and the quoted market price of the Company’s common stock for all in-the-money stock options.

Additional information related to the Company’s stock options is summarized below (in thousands, except per share amounts):

	Year Ended December 31,
	2020		2019
Weighted-average grant-date fair value of stock option grants per share	$	12.84	$	2.70

Intrinsic value of options exercised	$	1,444	$	104
Fair value of options vested	$	2,664	$	656

Employee Stock Purchase Plan

The Company’s 2020 Employee Stock Purchase Plan (the “ESPP”), which was adopted by the Company’s board of directors in June 2020 and approved by the Company’s stockholders in July 2020, became effective upon the consummation of the IPO. A total of 295,599 shares of the Company’s common stock is initially available for issuance under the ESPP. The ESPP allows eligible employees to purchase shares of the Company’s common stock at a discount through payroll deductions of up to 15% of their eligible compensation, subject to any plan limitations. The ESPP provides for six-month offering periods, and at the end of each offering period, employees are able to purchase shares at 85% of the lower of the fair market value of the Company’s common stock on the first trading day of the offering period or on the last trading day of the offering period. As of December 31, 2020, no shares had been issued under the ESPP, and the full number of shares authorized under the ESPP Plan was available for issuance purposes upon the effectiveness of the ESPP.

Liability for Early Exercise of Restricted Stock Options

Certain individuals were granted the ability to early exercise their stock options. The shares of common stock issued from the early exercise of unvested stock options are restricted and continue to vest in accordance with the original vesting schedule. The Company has the option to repurchase any unvested shares at the original purchase price upon any voluntary or involuntary termination. The shares purchased by the employees and non-employees pursuant to the early exercise of stock options are not deemed, for accounting purposes, to be outstanding until those shares vest. The cash received in exchange for exercised and unvested shares related to stock options granted is recorded as a liability for the early exercise of stock options on the accompanying balance sheets and will be transferred into common stock and additional paid-in capital as the shares vest. Shares subject to repurchase by the Company were 77,393 shares and 132,249 shares, with the related liability of $0.1 million and $0.1 million as of December 31, 2020 and 2019, respectively, recorded under other long-term liabilities in the balance sheets.

Common Stock Reserved for Future Issuance

As of December 31, 2020, the Company had reserved the following shares of common stock for future issuance:

	December 31, 2020
Common stock options granted and outstanding		3,640,715
Reserved for future equity award grants		1,390,402
Reserved for future ESPP issuances		295,599
		5,326,716

Share-Based Compensation Expense

Share-based compensation expense for the years ended December 31, 2020 and 2019 were as follows (in thousands):

	Year Ended December 31,
	2020		2019
Research and development	$	1,871	$	376
General and administrative		4,877		571
Total share-based compensation expense	$	6,748	$	947

The total unrecognized compensation cost related to unvested share-based awards was $22.2 million, which is expected to be recognized over a weighted-average remaining service period of 3.4 years as of December 31, 2020.

In October 2020, the Company recorded share-based compensation expense of $2.3 million related to the modification of certain stock option granted to its former Chief Financial Officer, Matthew Plunkett, under a Separation and Release Agreement that was executed on October 2, 2020 (the “Termination Date”). In addition, the Company recorded severance benefits expense of $0.3 million in October 2020 that is payable within the 6 months after the Termination Date.

In September and November of 2019, the Company granted options subject to both a service-based condition and a performance-based condition that require the achievement of a Series B Milestone Closing (Note 10) before the options can be eligible for service vesting conditions. The performance-based condition was achieved in the third quarter of fiscal year 2020.

Fair Value Disclosures

The fair value of stock options was estimated on the date of grant using the Black-Scholes option pricing model with the following range of assumptions:

	Year Ended December 31,
	2020	2019
Common stock fair value	$4.29 - $61.47	$3.40 - $4.77
Risk-free interest rate	0.4% - 0.5%	1.5% - 2.3%
Expected volatility	74.8% - 81.4%	80.2% - 81.9%
Expected term (in years)	5.5 - 6.1	5.6 - 6.1
Expected dividend yield	—	—

The Company recognizes compensation costs related to stock options granted to employees and nonemployees based on the estimated fair value of the awards on the date of grant, net of forfeitures. The Company generally recognizes grant-date fair value of stock options granted to employees and non-employee service providers on a straight-line basis over the requisite service period, which is generally the vesting term of the respective awards. The Company determines the fair value of stock options with a service and performance condition, or performance-based options, based on the fair value of the Company’s common stock on the date of grant. The Company accounts for the impact of forfeitures as they occur. For purposes of calculating share-based compensation, the Company estimates the fair value of stock options issued using a Black-Scholes option-pricing model. The determination of the fair value of share-based payment awards utilizing the Black-Scholes option-pricing model is affected by the Company’s stock price and a number of assumptions, including expected volatility, expected life, risk-free interest rate and expected dividends.

Expected term. The Company opted to use the “simplified method” for estimating the expected term of employee options, whereby the expected term equals the average of the vesting term and the original contractual term of the option (generally 10 years).

Expected volatility. Due to the Company’s limited operating history and a lack of company specific historical and implied volatility data, the Company based its estimate of expected volatility on the historical volatilities of the common stock of comparable publicly traded biopharmaceutical companies over a period equal to the expected term of the stock option grants. The comparable companies were chosen based on their similar size, stage in the life cycle, and financial leverage to the Company.

Risk-free interest rate. The risk-free rate assumption is based on the U.S. Treasury instruments with maturities similar to the expected term of the stock options.

Expected dividend yield. The Company has not issued any dividends and do not expect to issue dividends over the life of the options, as a result the estimated dividend yield is zero.

Income Taxes

12 Months Ended

Dec. 31, 2020

Income Tax Disclosure [Abstract]

Income Taxes

12. Income Taxes

Due to the Company’s net losses for the years ended December 31, 2020 and 2019, and since the Company has a full valuation allowance against deferred tax assets, there was no tax provision or benefit for income taxes recorded in the years presented other than minimum amounts required for state tax purposes.

A reconciliation on income taxes to the amount computed by applying the statutory federal income tax rate to the net loss is summarized as follows (in thousands):

	Year Ended December 31,
	2020			2019
Income tax benefit at statutory rates	$	(19,186	)	$	(4,426	)
State income tax, net of federal benefit		(3,929	)		(1,959	)
Permanent items		749			245
Research and development credits		(1,264	)		(627	)
Other		231			2
Change in valuation allowance		14,965			7,287
Change in fair value of derivative liabilities		8,434			(522	)
Income tax expense	$	—		$	—

Significant components of the Company’s deferred tax assets are shown below (in thousands):

	December 31,
	2020			2019
Deferred tax assets:
Net operating loss carry forwards	$	17,674		$	6,897
Depreciation and amortization		265			200
Research and development credits		3,986			1,316
Accrued expenses		983			459
Lease liability		2,496			2,042
Other, net		891			3
Total deferred tax assets		26,295			10,917
Valuation allowance for deferred tax assets		(23,696	)		(8,731	)
Deferred tax assets, net of valuation allowance		2,599			2,186
Deferred tax liabilities:
Right-of-use asset		(2,382	)		(2,036	)
Depreciation and amortization		(217	)		(150	)
Net deferred tax assets	$	—		$	—

The Company has a net operating loss and has provided a valuation allowance against net deferred tax assets due to uncertainties regarding the Company’s ability to realize these assets. The valuation allowance increased by $15.0 million and $7.3 million as of December 31, 2020 and 2019, respectively.

In assessing the realizability of deferred tax assets, the Company considers whether it is more likely than not that some portion or all of the deferred tax assets will not be realized. The ultimate realization of deferred tax assets is dependent upon the generation of future taxable income during the periods in which the temporary differences representing net future deductible amounts become deductible. Due to the Company’s history of losses, and lack of other positive evidence, the Company has determined that it is more likely than not that its net deferred tax assets will not be realized, and therefore, the net deferred tax assets are substantially offset by a valuation allowance at December 31, 2020 and 2019. The $2.6 million net deferred tax asset is realizable as a result of utilizing the deferred tax liabilities associated with the Company’s leases as a source of income. The deferred tax assets were primarily comprised of federal and state tax net operating losses and tax credit carryforwards.

As of December 31, 2020, the Company had net operating loss (“NOL”) carryforwards of approximately $63.3 million and $62.7 million, available to reduce future taxable income, if any, for federal and California state income tax purposes, respectively. Of the $63.3 million federal NOL carryforwards, $0.2 million and $3.0 will begin expiring in 2035 and 2036, respectively, if not utilized, while $60.1 million can be carried forward indefinitely. The state NOL carryforwards will begin expiring in 2036, if not utilized.

The Company also had federal and state research and development credit carry forwards of approximately $3.2 million and $1.9 million, respectively, at December 31, 2020. The federal credits will begin expiring in 2035 if not utilized. The California credits have no expiration date.

Utilization of the NOL and research and development credit carryforwards may be subject to a substantial annual limitation due to ownership change limitations that may have occurred or that could occur in the future, as required by Section 382 of the Internal Revenue Code of 1986, as amended (the “Code”), as well as similar state provisions. The future utilization of the Company’s NOL and tax credit carryforwards to offset future taxable income may be subject to a substantial annual limitation as a result of changes in ownership by stockholders that hold 5% or more of the Company’s common stock. An assessment of such ownership changes under Section 382 was not completed through December 31, 2019. To the extent that an assessment is completed in the future, the Company’s ability to utilize tax attributes could be restricted on a year-by-year basis and certain attributes could expire before they are utilized. The Company will examine the impact of any potential ownership changes in the future.

The Company has not been audited by the Internal Revenue Service or any state income or franchise tax agency. As of December 31, 2020, its federal and state returns for the years ended 2015 through the current period are still open to examination. In addition, all of the net operating losses and research and development credit carryforwards that may be used in future years are still subject to inquiry given that the statute of limitation for these items would begin in the year of the utilization. The balance of gross unrecognized tax benefits as of December 31, 2020 and 2019 was approximately $0.8 million and $0.3 million, respectively, all of which would affect the Company’s income tax expense if recognized, before consideration of the Company’s valuation allowance. The Company does not expect its unrecognized tax benefits to change significantly over the next 12 months. The Company recognizes interest and penalties accrued on any unrecognized tax benefits as a component of income tax expense. There was no interest and penalties for the years ended December 31, 2020 and 2019. The Company files income tax returns in the United States federal jurisdiction and the State of California and is not currently under examination by any taxing authority for any open tax year. Due to net operating loss carryforwards, all years remain open for income tax examination. To the extent the Company has tax attribute carryforwards, the tax years in which the attribute was generated may still be adjusted upon examination by the IRS or state tax authorities to the extent utilized in a future period. No federal or state tax audits are currently in process.

The following table summarizes the changes in the Company’s gross unrecognized tax benefits (in thousands):

	December 31,
	2020		2019
Balance at the beginning of the year	$	270	$	73
Additions for tax positions taken in prior years		14		5
Additions for tax positions taken in current year		493		192
Balance at the end of the year	$	777	$	270

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References + Details

Basis of Presentation and Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying financial statements have been prepared in accordance with U.S. generally accepted accounting principle (“U.S. GAAP”). Certain prior period amounts reported in the Company’s financial statements have been reclassified to conform to the current period presentation, with no impact on previously reported operating results or financial position.
Reverse Stock Split	Reverse Stock Split On July 1, 2020, the Company effected a 1-for-3.7 reverse stock split (the “Reverse Stock Split”) of its issued and outstanding common stock. Accordingly, the conversion ratio for the Company’s outstanding convertible preferred stock was proportionately adjusted such that the common stock issuable upon conversion of such preferred stock was decreased in proportion to the Reverse Stock Split. The par value of the common stock was not adjusted as a result of the Reverse Stock Split. All references to common stock, options to purchase common stock, early exercised options, share data, per share data, convertible preferred stock (to the extent presented on an as-converted to common stock basis) and related information contained in these financial statements have been retrospectively adjusted to reflect the effect of the Reverse Stock Split for all periods presented.
COVID-19 Pandemic	COVID-19 Pandemic On March 11, 2020, the World Health Organization declared the outbreak of a novel strain of coronavirus, COVID-19, as a global pandemic, which continued to spread throughout the United States and around the world in the fourth quarter of 2020. Multiple variants of the virus that causes COVID-19 are also circulating globally. The COVID-19 pandemic is contributing to a general slowdown in the global economy and may affect the Company’s business, results of operations, financial condition, and future strategic plans. The extent of the impact of the COVID-19 pandemic on the Company’s operational and financial performance will depend on certain developments, including the duration and spread of the outbreak, the effectiveness of actions taken in the United States and other countries to contain, vaccinate against, and treat the disease, and its impact on the Company’s planned preclinical studies and clinical trials, employees and vendors, all of which are uncertain and cannot be predicted. The Company has taken certain precautionary measures to minimize exposure of the Company’s employees to the virus and to comply with directives from public health officials. This includes work from home policies for employees as well as enhanced safety measures for scientists who are in labs and manufacturing facility. Some of the third-party vendors that the Company uses have experienced disruptions during this pandemic. However, COVID-19 did not materially impact the timelines the Company previously announced for the filing of the NKX101 IND or the dosing of the first patient in the NKX101 clinical trial, and the Company does not expect COVID-19 to have a material impact on the current timeline for the filing of the NKX019 IND. At this time, the extent to which the COVID-19 pandemic may impact the Company’s financial condition or results of operations is uncertain and these precautionary measures may negatively impact productivity, and cause disruptions or delays to the Company’s activities and timelines. In response to the pandemic, the Coronavirus Aid, Relief and Economic Security Act (the “CARES Act”) was signed into law on March 27, 2020. The CARES Act, among other things, includes tax provisions relating to refundable payroll tax credits, deferment of employer’s social security payments, net operating loss utilization and carryback periods, modifications to the net interest deduction limitations and technical corrections to tax depreciation methods for qualified improvement property. The CARES Act had no impact on the Company’s income tax provision for the year ended December 31, 2020. The Company continues to evaluate the impact of the CARES Act on its financial position, results of operations and cash flows. The Company currently does not expect to apply for loans or grants under the CARES Act.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the Company’s financial statements and accompanying notes. On an ongoing basis, management evaluates its estimates, including those related to preclinical studies, fair value of assets and liabilities, convertible preferred stock, share-based compensation and income taxes. Management bases its estimates on historical experience, knowledge of current events and actions it may undertake in the future that management believes to be reasonable under the circumstances. Actual results may differ from these estimates and assumptions.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments, which potentially subject the Company to concentration of credit risk, consist primarily of cash, cash equivalents and short-term investments. The Company maintains cash, cash equivalents and short-term investments with various high credit quality and are invested through banks and other financial institutions in the United States. Such deposits may be in excess of federally insured limits. Management believes that the Company is not exposed to significant credit risk due to the financial position of the depository institutions in which those deposits are held. The Company has not experienced any losses on deposits since inception.
Comprehensive Loss	Comprehensive Loss Comprehensive loss consists of net loss and unrealized gains or losses on available-for-sale investments. The Company displays comprehensive loss and its components as part of the statements of operations and comprehensive loss.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The accounting guidance defines fair value, establishes a consistent framework for measuring fair value, and expands disclosure for each major asset and liability category measured at fair value on either a recurring or nonrecurring basis. Fair value is defined as an exit price representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, the accounting guidance establishes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value as follows: Level 1: Observable inputs such as quoted prices in active markets; Level 2: Inputs, other than the quoted prices in active markets, that are observable either directly or indirectly; and Level 3: Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions. The carrying amounts of prepaid expenses and other current assets, accounts payable, accrued liabilities and other current liabilities are reasonable estimates of their fair value due to the short-term nature of these accounts.
Cash, Cash Equivalents, Short-term Investments and Restricted Cash	Cash, Cash Equivalents, Short-term Investments and Restricted Cash Cash and Cash Equivalents The Company considers all highly liquid investments with insignificant interest rate risk and an original maturity of three months or less at the date of purchase to be cash equivalents. Cash includes demand deposits held in readily available checking accounts at a federally insured financial institution. Cash equivalents consist of money market funds. Short-term Investments Short-term investments consist of commercial debt securities, commercial paper and U.S. Government securities, classified as available-for-sale securities and have maturities of greater than three months but less than one year. The Company has classified all of its available-for-sale investment securities as current assets on the balance sheets because these are considered highly liquid securities and are available for use in current operations. The Company carries these securities at fair value, and reports unrealized gains and losses as a separate component of accumulated other comprehensive loss. The cost of debt securities is adjusted for amortization of purchase premiums and accretion of discounts to maturity. Such amortization and accretion is included in interest income in the statements of operations and comprehensive loss. Realized gains and losses on sales of securities are determined using the specific identification method and recorded in other income (expense), net in the statement of operations and comprehensive loss. Restricted Cash The Company is required to maintain a letter of credit related to its office and lab space lease. This cash is the collateral for that letter of credit and per the terms of the lease must remain in place until two months after the termination of the lease. As the remaining term of the lease as of December 31, 2020 is greater than one year, the related restricted cash has been classified as non-current.
Property and Equipment, Net	Property and Equipment, Net Property and equipment, which consist of leasehold improvements, furniture and fixtures, research equipment, computers and software and construction-in-progress are stated at cost less accumulated depreciation. Depreciation and amortization is calculated using the straight-line method over the estimated useful lives of the assets, which ranges from three to five years. Leasehold improvements are amortized over the remaining life of the lease for leasehold improvements at the time the asset is placed into service.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The carrying value of long-lived assets, including property and equipment, are reviewed for impairment whenever events or changes in circumstances indicate that the asset may not be recoverable. An impairment loss is recognized when the total of estimated future undiscounted cash flows, expected to result from the use of the asset and its eventual disposition, are less than its carrying amount. Impairment, if any, would be assessed using discounted cash flows or other appropriate measures of fair value. Through December 31, 2020, there has been no such impairment losses recorded by the Company.
Deferred Offering Costs	Deferred Offering Costs Deferred offering costs that consisted of legal, accounting, printing and other fees and costs directly attributable to the IPO were capitalized. Upon the completion of the IPO in July 2020, the total deferred offering costs of $4.4 million were offset against the proceeds from the IPO and reclassified to additional paid-in capital on the balance sheets.
Preferred Stock Purchase Right Liability	Preferred Stock Purchase Right Liability The Company at times enters into convertible preferred stock financings where, in addition to the initial closing, investors agree to buy, and the Company agrees to sell, additional shares of that convertible preferred stock at a fixed price in the event that certain agreed upon milestones are achieved or at the election of investors. The Company evaluates this purchase right and assesses whether it meets the definition of a freestanding instrument and, if so, determines the fair value of the purchase right liability and records it on the balance sheets with the remainder of the proceeds raised being allocated to convertible preferred stock. The preferred stock purchase right liability is revalued at each reporting period with changes in the fair value of the liability recorded as change in fair value of preferred stock purchase right in the statements of operations and comprehensive loss. A final revaluation adjustment of preferred stock purchase right liability was recorded at settlement in July 2020 and the resultant fair value was then reclassified to convertible preferred stock at that time.
Convertible Preferred Stock	Convertible Preferred Stock The Company recorded all shares of convertible preferred stock at their respective issuance price less issuance costs on the dates of issuance. Convertible preferred stock was previously classified outside of stockholders’ equity (deficit) on the balance sheets as events triggering redemption were not solely within the Company’s control because the preferred stockholders had the ability to effect a liquidation event, as they have majority of the Company’s Board seats. Immediately prior to the closing of the Company’s IPO in July 2020, all outstanding shares of the Company’s convertible preferred stock converted into the Company’s common stock. There were no outstanding shares of the Company’s convertible preferred stock as of December 31, 2020.
Revenue Recognition	Revenue Recognition Revenue is recognized in accordance with ASC 606 when a customer obtains control of promised goods or services. The Company applies the following five steps to recognize revenue: (i) identify the contract with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to performance obligations in the contract; and (v) determine the recognition period. The Company evaluates its performance obligations to determine whether each item represents a good or service that is distinct or has the same pattern of transfer as other deliverables. A deliverable is considered distinct if the customer can benefit from the good or service independently of other goods/services either in the contract or that can be obtained elsewhere, and the entity’s promise to transfer the good or service to the customer is separately identifiable from other promises in the contact. If the deliverable is not considered distinct, the Company combines such deliverables and accounts for them as a single performance obligation. The Company allocates the consideration to each deliverable at the inception of the arrangement based on the transaction price. In April 2017, the Company entered into the Collaboration and License Agreement (the “Collaboration Agreement”) with GlaxoSmithKline Intellectual Property Development Limited and Glaxo Group Limited (together, “GSK”) to research and develop therapeutics using Engineered NK Cells as carriers for target programs. On December 10, 2018, the Collaboration Agreement with GSK was terminated. Nominal revenue of $0.1 million was recognized for the year ended December 31, 2019 in connection with the wind-down activities through the termination of the Collaboration Agreement in December 2018. There was no revenue recorded for the year ended December 31, 2020.
Research and Development Costs	Research and Development Costs Research and development costs are expensed as incurred. Research and development costs consist primarily of salaries and other benefits of research and development personnel, including associated share-based compensation, costs related to research activities, preclinical studies, clinical trial, drug manufacturing and allocated overhead and facility-related expenses. The Company accounts for non-refundable advance payments for goods or services that will be used in future research and development activities as expenses when the goods have been received or when the service has been performed rather than when the payment is made. Clinical trial costs are a component of research and development expenses. The Company expenses costs for its clinical trial activities performed by third parties, including clinical research organizations and other service providers, as they are incurred, based upon estimates of the work completed over the life of the individual study in accordance with associated agreements. The Company uses information it receives from internal personnel and outside service providers to estimate the clinical trial costs incurred.
Commitments	Commitments The Company recognizes a liability with regard to loss contingencies when it believes it is probable a liability has occurred and the amount can be reasonably estimated. If some amount within a range of loss appears at the time to be a better estimate than any other amount within the range, the Company accrues that amount. When no amount within the range is a better estimate than any other amount the Company accrues the minimum amount in the range. There has been no such liabilities recorded by the Company as of December 31, 2020.
Leases	Leases At the commencement date of a lease, the Company recognizes lease liabilities which represent its obligation to make lease payments, and right-of-use assets (“ROU assets”) which represent its right to use the underlying asset during the lease term. The lease liability is measured at the present value of lease payments over the lease term. As the Company’s leases typically do not provide an implicit rate, the Company uses an incremental borrowing rate based on the information available at the lease commencement date. The ROU asset is measured at cost, which includes the initial measurement of the lease liability and initial direct costs incurred by the Company and excludes lease incentives. ROU assets are recorded in operating lease ROU assets and lease liabilities are recorded in operating lease liabilities, current and noncurrent in the balance sheets. Lease terms may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. Operating lease expense is recognized on a straight-line basis over the lease term. Lease agreements that contain both lease and non-lease components are generally accounted for separately. The Company does not recognize lease liabilities and ROU assets for short-term leases with terms of twelve months or less.
Share-Based Compensation	Share-Based Compensation Share-based compensation expense represents the cost of the grant-date fair value of employee, officer, director, and non-employee stock option grants, estimated in accordance with the applicable accounting guidance, recognized using the straight-line method over the vesting period for service-based options and using the graded vesting method for performance-based options. The vesting period generally approximates the expected service period of the awards. Forfeitures are recognized and accounted for as they occur. The fair value of stock options is estimated using a Black-Scholes option pricing model on the date of grant. This method requires certain assumptions be used as inputs, such as the fair value of the underlying common stock, expected term of the option before exercise, expected volatility of the Company’s common stock, expected dividend yield, and a risk-free interest rate. Options granted during the year have a maximum contractual term of ten years. The Company has limited historical stock option activity and therefore estimates the expected term of stock options granted using the simplified method, which represents the average of the contractual term of the stock option and its weighted-average vesting period. The expected volatility of stock options is based upon the historical volatility of a number of publicly traded companies in similar stages of clinical development. The Company has historically not declared or paid any dividends and does not currently expect to do so in the foreseeable future. The risk-free interest rates used are based on the U.S. Department of Treasury (“U.S. Treasury”) yield in effect at the time of grant for zero-coupon U.S. Treasury notes with maturities approximately equal to the expected term of the stock options.
Income Taxes	Income Taxes Income taxes have been accounted for using the asset and liability method. Under the asset and liability method, deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and tax credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates applicable to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. A valuation allowance against deferred tax assets is recorded if, based upon the weight of all available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized.
Segment Reporting	Segment Reporting The Company’s chief operating decision maker, its President and Chief Executive Officer, manages its operations and business as one operating segment for the purposes of allocating resources, makes operating decisions and evaluates financial performance. No product revenue has been generated since inception and all assets are held in the United States.
Net Loss Per Share	Net Loss Per Share Basic net loss per share is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of common shares outstanding for the period, without consideration of potential dilutive securities. Diluted net loss per share is computed by dividing the net loss attributable to common stockholders by the sum of the weighted average number of common shares plus the potential dilutive effects of potential dilutive securities outstanding during the period. Potential dilutive securities are excluded from diluted earnings or loss per share if the effect of such inclusion is antidilutive. The Company’s potentially dilutive securities, which include convertible preferred stock prior to the conversion of such shares to common stock, unvested common stock, and outstanding stock options under the Company’s equity incentive plan, have been excluded from the computation of diluted net loss per share as they would be anti-dilutive to the net loss per share. For all periods presented, there is no difference in the number of shares used to calculate basic and diluted shares outstanding due to the Company’s net loss position.
Recent Accounting Pronouncements	Recent Accounting Pronouncements Adopted Accounting Pronouncements Financial Instruments. In June 2016, the FASB issued ASU 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, which amends the impairment model by requiring entities to use a forward-looking approach based on expected losses to estimate credit losses on certain types of financial instruments, including available-for-sale debt securities. The Company adopted this standard in the first quarter of 2020. The adoption of this standard did not have a material impact on the Company’s financial statements. Fair Value Measurements. In August 2018, the FASB issued ASU 2018-13—Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement, which eliminates, adds and modifies certain disclosure requirements for fair value measurement. The amendments in ASU 2018-13 that relate to changes in unrealized gains and losses, the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements and the narrative description of measurement uncertainty should be applied prospectively for only the most recent interim or annual period presented in the initial fiscal year of adoption. All other amendments in ASU 2018-13 should be applied retrospectively to all periods presented upon their effective date. The Company adopted this standard in the first quarter of 2020. The adoption of this standard did not have a material impact on the Company’s disclosures. Accounting Pronouncements Not Yet Adopted Income Taxes. In December 2019, the FASB issued ASU 2019-12—Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes, which simplifies the accounting for income taxes by eliminating certain exceptions to the guidance in Topic 740 related to the approach for intra-period tax allocation, the methodology for calculating income taxes in an interim period and the recognition of deferred tax liabilities for outside basis differences. The new guidance also simplifies aspects of the accounting for franchise taxes and enacted changes in tax laws or rates. This standard is effective for fiscal years beginning after December 15, 2020, with early adoption permitted. The Company will adopt this standard in the first quarter of 2021 and the adoption is not expected to have a material impact on the Company’s financial statements. There were no other significant updates to the recently issued accounting standards other than as disclosed herewith. Although there are several other new accounting pronouncements issued or proposed by the FASB, the Company does not believe any of those accounting pronouncements have had or will have a material impact on its financial position or operating results.

Fair Value of Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2020

Summary of Fair Value of Financial Instrument

The following tables summarize the fair value of the Company’s financial instruments (in thousands):

			Fair Value Measurements Using
	December 31, 2020		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents:
Money market funds	$	94,631	$	94,631	$	—	$	—
Short-term investments:
Corporate debt securities	$	48,614	$	—	$	48,614	$	—
Commercial paper		63,445		—		63,445		—
U.S. Government securities		106,162		—		106,162		—
Total short-term investments	$	218,221	$	—	$	218,221	$	—
Total	$	312,852	$	94,631	$	218,221	$	—

			Fair Value Measurements Using
	December 31, 2019		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents:
Commercial paper	$	2,395	$	—	$	2,395	$	—
Short-term investments:
Corporate debt securities	$	6,027	$	—	$	6,027	$	—
Commercial paper		10,357		—		10,357		—
Total short-term investments		16,384		—		16,384		—
Total	$	18,779	$	—	$	18,779	$	—
Liabilities:
Preferred stock purchase right liability	$	1,478	$	—	$	—	$	1,478

Schedule of Change in Preferred Stock Purchase Right Liability

The following table provides the change in preferred stock purchase right liability for the year ended December 31, 2020 (in thousands):

	Preferred Stock Purchase Right Liability
Balance, December 31, 2019	$	1,478
Change in fair value of preferred stock purchase right		40,163
Reclassification of preferred stock purchase right liability to equity upon issuance of convertible preferred stock		(41,641	)
Balance, December 31, 2020	$	—

Short-term investments

Schedule of Short-term Investments

The following tables summarize the Company’s short-term investments as of December 31, 2020 and December 31, 2019 (in thousands):

		December 31, 2020
	Maturity (in years)	Amortized Cost		Unrealized Losses			Unrealized Gains		Estimated Fair Value
Corporate debt securities	1 year or less	$	48,616	$	(6	)	$	4	$	48,614
Commercial paper	1 year or less		63,445		—			—		63,445
U.S. Government securities	1 year or less		106,157		(7	)		12		106,162
Total		$	218,218	$	(13	)	$	16	$	218,221

		December 31, 2019
	Maturity (in years)	Amortized Cost		Unrealized Losses			Unrealized Gains		Estimated Fair Value
Corporate debt securities	1 year or less	$	6,029	$	(2	)	$	—	$	6,027
Commercial paper	1 year or less		10,357		—			—		10,357
Total		$	16,386	$	(2	)	$	—	$	16,384

Balance Sheet Components (Tables)

12 Months Ended

Dec. 31, 2020

Balance Sheet Related Disclosures [Abstract]

Schedule of Prepaid Expenses and Other Current Assets

Prepaid expenses and other current assets are comprised of the following (in thousands):

	December 31,
	2020		2019
Prepaid expenses	$	2,586		407
Other current assets		1,336		67
Total prepaid expenses and other current assets	$	3,922	$	474

Schedule of Property and Equipment, Net

Property and equipment, net is comprised of the following (in thousands):

	December 31,
	2020			2019
Leasehold improvements	$	1,984		$	287
Furniture and fixtures		322			265
Research equipment		4,892			2,929
Computers and software		124			61
Construction-in-progress		3,459			183
Total property and equipment		10,781			3,725
Less accumulated depreciation and amortization		(1,431	)		(645	)
Total property and equipment, net	$	9,350		$	3,080

Schedule of Accrued and Other Current Liabilities

Accrued and other current liabilities are comprised of the following (in thousands):

	December 31,
	2020		2019
Accrued compensation	$	3,534	$	1,678
Accrued research and development costs		1,675		702
Accrued property and equipment		117		214
Deferred offering costs		—		104
Other accrued and current liabilities		927		591
Total accrued and other liabilities	$	6,253	$	3,289

Leases (Tables)

12 Months Ended

Dec. 31, 2020

Leases [Abstract]

Components of Lease Expense

The components of lease expense were as follows (in thousands):

	Year Ended December 31,
	2020		2019
Operating lease expense	$	1,856		1,315
Variable lease expense ⁽¹⁾		178		126
Short-term lease expense		14		—
Total lease expense	$	2,048	$	1,441

⁽¹⁾ Variable lease expense for the periods presented primarily included common area maintenance charges.

Schedule of Supplemental Information related to Operating Leases

Supplemental information related to operating leases were as follows (in thousands):

	Year Ended December 31,
	2020		2019
Cash paid for amounts included in the measurement of lease liabilities
Operating cash flows used for operating leases	$	1,705	$	1,180

Lease liabilities arising from obtaining right-of-use assets
Operating leases	$	2,401	$	5,107

Schedule of Maturities of Operating Lease Liabilities

Maturities of operating lease liabilities under existing operating leases as of December 31, 2020 were as follows (in thousands):

Year ending December 31,	Amount
2021	$	1,461
2022		1,452
2023		1,503
2024		1,556
2025		1,610
2026 and thereafter		5,371
Total future minimum lease payments		12,953
Less imputed interest		(4,034	)
Present value of net minimum lease payments	$	8,919
Operating lease liabilities:
Current		1,402
Non-current		7,517
Total lease liability	$	8,919

Share-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock Option Activity

The following table summarizes the stock option activity during the year ended December 31, 2020 (in thousands, except number of shares, exercise prices and contractual term):

	Number of shares			Weighted-average exercise price		Weighted-average remaining contractual term (in years)		Aggregate Intrinsic Value
Outstanding at December 31, 2019		2,329,516		$	3.59		9.6	$	668
Granted		1,782,794			19.52
Exercised		(183,287	)		2.18
Forfeited		(288,308	)		9.40
Outstanding at December 31, 2020		3,640,715		$	11.00		9.0	$	183,742
Exercisable at December 31, 2020		654,195		$	5.34		8.6	$	36,717
Vested and expected to vest at December 31, 2020		3,640,715		$	11.00		9.0	$	183,742

Summary of Additional Information Related to Stock Options

Additional information related to the Company’s stock options is summarized below (in thousands, except per share amounts):

	Year Ended December 31,
	2020		2019
Weighted-average grant-date fair value of stock option grants per share	$	12.84	$	2.70

Intrinsic value of options exercised	$	1,444	$	104
Fair value of options vested	$	2,664	$	656

Summary of Common Stock Reserved For Future Issuance

As of December 31, 2020, the Company had reserved the following shares of common stock for future issuance:

	December 31, 2020
Common stock options granted and outstanding		3,640,715
Reserved for future equity award grants		1,390,402
Reserved for future ESPP issuances		295,599
		5,326,716

Summary of Share-based Compensation Expense

Share-based compensation expense for the years ended December 31, 2020 and 2019 were as follows (in thousands):

	Year Ended December 31,
	2020		2019
Research and development	$	1,871	$	376
General and administrative		4,877		571
Total share-based compensation expense	$	6,748	$	947

Schedule of Fair Value of Stock Options Estimated on Date of Grant Using Black-Scholes Option Pricing Model

The fair value of stock options was estimated on the date of grant using the Black-Scholes option pricing model with the following range of assumptions:

	Year Ended December 31,
	2020	2019
Common stock fair value	$4.29 - $61.47	$3.40 - $4.77
Risk-free interest rate	0.4% - 0.5%	1.5% - 2.3%
Expected volatility	74.8% - 81.4%	80.2% - 81.9%
Expected term (in years)	5.5 - 6.1	5.6 - 6.1
Expected dividend yield	—	—

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2020

Income Tax Disclosure [Abstract]

Reconciliation on Income Taxes Amount Computed by Applying Statutory Federal Income Tax Rate to Net Loss

A reconciliation on income taxes to the amount computed by applying the statutory federal income tax rate to the net loss is summarized as follows (in thousands):

	Year Ended December 31,
	2020			2019
Income tax benefit at statutory rates	$	(19,186	)	$	(4,426	)
State income tax, net of federal benefit		(3,929	)		(1,959	)
Permanent items		749			245
Research and development credits		(1,264	)		(627	)
Other		231			2
Change in valuation allowance		14,965			7,287
Change in fair value of derivative liabilities		8,434			(522	)
Income tax expense	$	—		$	—

Significant Components of Deferred Tax Assets

Significant components of the Company’s deferred tax assets are shown below (in thousands):

	December 31,
	2020			2019
Deferred tax assets:
Net operating loss carry forwards	$	17,674		$	6,897
Depreciation and amortization		265			200
Research and development credits		3,986			1,316
Accrued expenses		983			459
Lease liability		2,496			2,042
Other, net		891			3
Total deferred tax assets		26,295			10,917
Valuation allowance for deferred tax assets		(23,696	)		(8,731	)
Deferred tax assets, net of valuation allowance		2,599			2,186
Deferred tax liabilities:
Right-of-use asset		(2,382	)		(2,036	)
Depreciation and amortization		(217	)		(150	)
Net deferred tax assets	$	—		$	—

Summary of Changes in Gross Unrecognized Tax Benefits

The following table summarizes the changes in the Company’s gross unrecognized tax benefits (in thousands):

	December 31,
	2020		2019
Balance at the beginning of the year	$	270	$	73
Additions for tax positions taken in prior years		14		5
Additions for tax positions taken in current year		493		192
Balance at the end of the year	$	777	$	270

Description of Business - Additional Information (Details) $ / shares in Units, $ in Thousands			12 Months Ended
	Jul. 14, 2020 USD ($) $ / shares shares	Jul. 01, 2020 USD ($) shares	Dec. 31, 2020 USD ($) Segment shares	Dec. 31, 2019 USD ($) shares
Class Of Stock [Line Items]
Number of operating segments \| Segment			1
Shares issued during period			32,627,963	1,600,601
Net proceeds after deducting underwriting discounts,commissions and other offering costs \| $			$ 265,096
Accumulated deficit \| $			118,021	$ 26,660
Cash, cash equivalents, restricted cash and short-term investments \| $			$ 315,300
Temporary equity, shares issued			0	27,283,973
Series B Convertible Preferred Stock
Class Of Stock [Line Items]
Proceeds from issuance of redeemable convertible preferred stock, net of issuance costs \| $		$ 64,400
Temporary equity, shares issued		27,066,206
IPO
Class Of Stock [Line Items]
Shares issued during period	16,100,000
Shares issued, price per share \| $ / shares	$ 18.00
Net proceeds after deducting underwriting discounts,commissions and other offering costs \| $	$ 265,100	$ 265,100
Underwriters Option to Purchase Additional Shares
Class Of Stock [Line Items]
Shares issued during period	2,100,000
Common Stock
Class Of Stock [Line Items]
Conversion of convertible preferred stock to common stock			14,689,215
Common Stock \| IPO
Class Of Stock [Line Items]
Conversion of convertible preferred stock to common stock	14,689,215
Net proceeds after deducting underwriting discounts,commissions and other offering costs \| $	$ 265,100

Basis of Presentation and Significant Accounting Polices - Additional Information (Details)	6 Months Ended	12 Months Ended
	Dec. 31, 2020 USD ($) shares	Dec. 31, 2020 USD ($) Segment shares	Dec. 31, 2019 USD ($) shares	Jul. 31, 2020 USD ($)	Dec. 31, 2018 shares
Accounting Policies [Line Items]
Reverse stock split, conversion ratio		3.7
Description of the reverse stock split		On July 1, 2020, the Company effected a 1-for-3.7 reverse stock split (the “Reverse Stock Split”) of its issued and outstanding common stock. Accordingly, the conversion ratio for the Company’s outstanding convertible preferred stock was proportionately adjusted such that the common stock issuable upon conversion of such preferred stock was decreased in proportion to the Reverse Stock Split. The par value of the common stock was not adjusted as a result of the Reverse Stock Split. All references to common stock, options to purchase common stock, early exercised options, share data, per share data, convertible preferred stock (to the extent presented on an as-converted to common stock basis) and related information contained in these financial statements have been retrospectively adjusted to reflect the effect of the Reverse Stock Split for all periods presented.
Impairment losses on long-lived assets		$ 0
Deferred offering costs				$ 4,400,000
Outstanding shares \| shares	0	0	27,283,973
Product revenue	$ 0		$ 115,000
Liability regard to loss contingencies	$ 0	$ 0
Contractual term of options granted		10 years
Number of operating segments \| Segment		1
ASU 2016-13
Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]	true	true
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Mar. 31, 2020	Mar. 31, 2020
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]	true	true
ASU 2018-13
Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]	true	true
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Mar. 31, 2020	Mar. 31, 2020
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]	true	true
Collaboration and License Agreement \| GSK
Accounting Policies [Line Items]
Product revenue		$ 0	$ 100,000
Convertible Preferred Stock
Accounting Policies [Line Items]
Outstanding shares \| shares	0	0	27,283,973		6,170,349
Minimum
Accounting Policies [Line Items]
Estimated useful lives of assets		3 years
Maximum
Accounting Policies [Line Items]
Estimated useful lives of assets		5 years
Contractual term of options granted		10 years

Net Loss Per Share - Computation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Numerator:
Net loss	$ (91,361)	$ (21,076)
Denominator:
Weighted average common shares outstanding	16,918,664	1,712,639
Less: weighted average unvested common stock issued upon early exercise of common stock options	(112,402)	(165,589)
Less: weighted average unvested founder shares of common stock		(84,539)
Weighted average shares used to compute net loss per share, basic and diluted	16,806,262	1,462,511
Net loss per share, basic and diluted	$ (5.44)	$ (14.41)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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+ Details

Convertible Preferred Stock and Stockholders' Equity (Deficit) - Additional Information (Details)				1 Months Ended			12 Months Ended
	Jul. 14, 2020 USD ($) $ / shares shares	Jul. 01, 2020 USD ($) $ / shares shares	Aug. 27, 2019 USD ($) shares	Aug. 31, 2019 USD ($)	May 31, 2019 USD ($)	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares	Aug. 26, 2019 $ / shares shares	Dec. 31, 2018 shares
Class Of Stock [Line Items]
Capital stock, shares authorized									126,270,161
Common stock, shares authorized		100,000,000					100,000,000	71,919,982	71,919,982
Common stock, par value \| $ / shares		$ 0.0001					$ 0.0001	$ 0.0001	$ 0.0001
Convertible preferred stock, shares authorized							0	54,350,179
Convertible preferred stock, par value \| $ / shares							$ 0.0001	$ 0.0001	$ 0.0001
Preferred stock, shares authorized		54,350,179					54,350,179	0
Preferred stock, par value \| $ / shares		$ 0.0001					$ 0.0001	$ 0.0001
Loss on extinguishment of debt \| $								$ 752,000
Number of shares converted into shares							0	27,283,973
Estimated fair value of preferred stock purchase right liability \| $		$ 41,600,000		$ 2,800,000				$ 1,478,000
Change in fair value of purchase right liability \| $							$ (40,163,000)	1,318,000
Net proceeds after deducting underwriting discounts,commissions and other offering costs \| $							265,096,000
Cash dividends declared or paid \| $							$ 0
Common stock, voting rights							Each holder of common stock is entitled to one vote for each share on all matters submitted to a vote of the stockholders, including the election of directors.
Common stock entitled, number of vote for each share \| $							1
IPO
Class Of Stock [Line Items]
Net proceeds after deducting underwriting discounts,commissions and other offering costs \| $	$ 265,100,000	$ 265,100,000
Common Stock
Class Of Stock [Line Items]
Stock issued and sold							16,100,000
Conversion of preferred stock, Shares							14,689,215
Common Stock \| IPO
Class Of Stock [Line Items]
Stock issued and sold	16,100,000
Conversion of preferred stock, Shares	14,689,215
Stock public offering price \| $ / shares	$ 18.00
Net proceeds after deducting underwriting discounts,commissions and other offering costs \| $	$ 265,100,000
Common Stock \| Underwriters Option to Purchase Additional Shares
Class Of Stock [Line Items]
Stock issued and sold	2,100,000
Series B Convertible Promissory Notes
Class Of Stock [Line Items]
Convertible notes, beneficial conversion feature \| $					$ 300,000
Convertible notes accrued interest per year				7.50%
Percentage of convertible notes automatically convert into Series B convertible preferred stock price per share				85.00%
Derivative instrument \| $					$ 1,300,000
Amortization term of interest expense using effective interest method					1 year
Change in conversion benefit resulted in adjustment to derivative instrument \| $				$ 900,000
Loss on extinguishment of debt \| $				800,000
Interest expense related to stated interest \| $								100,000
Effective-interest relation to debt discounts \| $								$ 400,000
Annual effective-interest rates								30.40%
Series B Convertible Promissory Notes \| Previously Recorded
Class Of Stock [Line Items]
Convertible notes, beneficial conversion feature \| $				$ (100,000)
Series A investors \| Series B Convertible Promissory Notes
Class Of Stock [Line Items]
Number of convertible promissory notes issued \| $					$ 6,000,000
Convertible notes accrued interest per year					7.50%
Convertible notes original maturity date from issuance date					1 year
Series A investors \| Series B Convertible Promissory Notes \| Maximum
Class Of Stock [Line Items]
Percentage of convertible notes automatically convert into Series B convertible preferred stock price per share					85.00%
Series A investors \| Series B Convertible Promissory Notes \| Minimum
Class Of Stock [Line Items]
Percentage of convertible notes automatically convert into Series B convertible preferred stock price per share					80.00%
Convertible Preferred Stock
Class Of Stock [Line Items]
Convertible preferred stock, shares authorized									54,350,179
Sale of preferred stock, net of issuance costs, Shares							27,066,206	18,492,443
Number of shares converted into shares							0	27,283,973		6,170,349
Convertible Preferred Stock \| Common Stock \| IPO
Class Of Stock [Line Items]
Conversion of preferred stock, Shares	14,689,215
Series A Convertible Preferred Stock
Class Of Stock [Line Items]
Convertible preferred stock, shares authorized									6,170,349
Stock issued and sold						3,866,602
Convertible preferred stock price per share \| $ / shares						$ 2.07
Convertible notes, beneficial conversion feature \| $						$ 900,000
Series A Convertible Preferred Stock \| GSK Convertible Note
Class Of Stock [Line Items]
Convertible notes outstanding shares converted into convertible preferred stock						292,633
Percentage of outstanding convertible notes into convertible preferred stock						85.00%
Series A Convertible Preferred Stock \| Series A Financing investors
Class Of Stock [Line Items]
Convertible preferred stock price per share \| $ / shares						$ 2.07
Convertible notes outstanding shares converted into convertible preferred stock						2,011,114
Percentage of outstanding convertible notes into convertible preferred stock						80.00%
Series B Convertible Preferred Stock
Class Of Stock [Line Items]
Convertible preferred stock, shares authorized									48,179,830
Convertible notes outstanding shares converted into convertible preferred stock			1
Number of shares converted into shares			10
Sale of preferred stock, net of issuance costs, Shares		27,066,206
Proceeds from issuance of redeemable convertible preferred stock, net of issuance costs \| $		$ 64,400,000
Series B Convertible Preferred Stock \| Stock Purchase Agreement
Class Of Stock [Line Items]
Number of convertible preferred stock sold and issued during the period			27,066,206
Gross proceed from convertible preferred stock \| $			$ 64,400,000

Share-Based Compensation - Additional Information (Details) - USD ($)	1 Months Ended	12 Months Ended
	Oct. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of common stock available for issuance		5,326,716
Other long-term liabilities		$ 82,000	$ 134,000
Unrecognized compensation cost		$ 22,200,000
Unrecognized compensation cost, expected to be recognized over weighted average remaining service period		3 years 4 months 24 days
Share-based compensation		$ 6,748,000	$ 947,000
Contractual term of options granted		10 years
Dividends issued for options		$ 0
Dividends expected to be issued over life of options		$ 0
Estimated dividend yield		0.00%
Separation and Release Agreement \| Matthew Plunkett
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation	$ 2,300,000
Severance benefits expense	$ 300,000
Agreement execution date	Oct. 02, 2020
Period in which severance benefits payable after termination date	6 months
Restricted Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares subject to repurchase		77,393	132,249
Other long-term liabilities		$ 100,000	$ 100,000
2020 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares issued		0
Number of common stock available for issuance		295,599
Maximum percentage of employee compensation eligible for plan		15.00%
Offering period		6 months
Commons stock purchase price as percentage of fair value		85.00%
2015 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares issued		2,211,562
2020 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of common stock authorized for issuance		2,660,371
Increase in share limit as percentage of outstanding shares of common stock on last trading day in prior year		5.00%
Number of awards granted		1,542,532
Number of common stock available for issuance		1,390,402

Share-Based Compensation - Summary of Stock Option Activity (Details) - 2020 Plan and 2015 Plan - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares, outstanding beginning balance	2,329,516
Number of shares, granted	1,782,794
Number of shares, exercised	(183,287)
Number of shares, forfeited	(288,308)
Number of shares, outstanding ending balance	3,640,715	2,329,516
Number of shares, exercisable	654,195
Number of shares, vested and expected to vest	3,640,715
Weighted-average exercise price, outstanding beginning balance	$ 3.59
Weighted-average exercise price, granted	19.52
Weighted-average exercise price, exercised	2.18
Weighted-average exercise price, forfeited	9.40
Weighted-average exercise price, outstanding ending balance	11.00	$ 3.59
Weighted-average exercise price, exercisable	5.34
Weighted-average exercise price, vested and expected to vest	$ 11.00
Weighted-average remaining contractual term (in years), outstanding balance	9 years	9 years 7 months 6 days
Weighted-average remaining contractual term (in years), exercisable	8 years 7 months 6 days
Weighted-average remaining contractual term (in years), vested and expected to vest	9 years
Aggregate intrinsic value, outstanding balance	$ 183,742	$ 668
Aggregate intrinsic value, exercisable	36,717
Aggregate intrinsic value, vested and expected to vest	$ 183,742

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Taxes [Line Items]
Provision or benefit for income taxes	$ 0	$ 0
Increase in valuation allowance of net deferred tax assets	15,000,000	7,300,000
Net deferred tax asset	2,599,000	2,186,000
Gross unrecognized tax benefits	777,000	270,000	$ 73,000
Unrecognized tax benefits, penalties and interest expense	0	$ 0
Net Operating Loss and Tax Credit Carryforwards to Offset \| Minimum
Income Taxes [Line Items]
Changes in ownership by stockholders holding percentage		5.00%
Federal
Income Taxes [Line Items]
Net operating loss carryforwards	63,300,000
Federal \| Research and Development Credit Carry Forwards
Income Taxes [Line Items]
Tax credit carryforwards	$ 3,200,000
Tax credit carryforwards, expire	2035
Federal \| 2035
Income Taxes [Line Items]
Net operating loss carryforwards	$ 200,000
Net operating loss carryforwards, expire	2035
Federal \| 2036
Income Taxes [Line Items]
Net operating loss carryforwards	$ 3,000,000
Net operating loss carryforwards, expire	2036
Federal \| Carry Forward Indefinitely
Income Taxes [Line Items]
Net operating loss carryforwards	$ 60,100,000
California State
Income Taxes [Line Items]
Net operating loss carryforwards	$ 62,700,000
Net operating loss carryforwards, expire	2036
California State \| Research and Development Credit Carry Forwards
Income Taxes [Line Items]
Tax credit carryforwards	$ 1,900,000

Net Loss Per Share - Summarizes the Outstanding Potentially Dilutive Securities Excluded in Calculation of Diluted Net Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	3,718,108	9,835,799
Common Stock Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	3,640,715	2,329,516
Unvested Common Stock Upon Early Exercise of Common Stock Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	77,393	132,249
Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share		7,374,034

Fair Value of Financial Instruments - Schedule of Short-term Investments (Details) - Short-term investments - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available for sale securities, Amortized Cost	$ 218,218	$ 16,386
Available for sale securities, Unrealized Losses	(13)	(2)
Available for sale securities, Unrealized Gains	16
Available for sale securities,Estimated Fair Value	218,221	16,384
Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available for sale securities, Amortized Cost	63,445	10,357
Available for sale securities,Estimated Fair Value	$ 63,445	$ 10,357
Commercial Paper \| Maximum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Maturity (in years)	1 year	1 year
U.S. Government Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available for sale securities, Amortized Cost	$ 106,157
Available for sale securities, Unrealized Losses	(7)
Available for sale securities, Unrealized Gains	12
Available for sale securities,Estimated Fair Value	$ 106,162
U.S. Government Securities \| Maximum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Maturity (in years)	1 year
Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available for sale securities, Amortized Cost	$ 48,616	$ 6,029
Available for sale securities, Unrealized Losses	(6)	(2)
Available for sale securities, Unrealized Gains	4
Available for sale securities,Estimated Fair Value	$ 48,614	$ 6,027
Corporate Debt Securities \| Maximum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Maturity (in years)	1 year	1 year

Leases - Additional Information (Details) - USD ($) $ in Millions	1 Months Ended		12 Months Ended
	Jan. 31, 2021	May 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Lessee Lease Description [Line Items]
Weighted-average discount rate			10.00%
Operating lease not yet commenced minimum lease payments			$ 4.5	$ 0.7
Corporate Office and Laboratory Space
Lessee Lease Description [Line Items]
Weighted-average remaining lease term			8 years 1 month 6 days
Renewal term			7 years
Operating lease, existence of option to extend			true
Vivarium
Lessee Lease Description [Line Items]
Weighted-average remaining lease term			3 months 18 days
Corporate Office and Laboratory Facilities
Lessee Lease Description [Line Items]
Operating lease, existence of option to extend		true
Lease term		8 years
Lease expiration year		2029
Lessee option to extend description			The lease amendment also includes an extension of the lease term for the existing office and laboratory space beginning on May 1, 2020 through the first quarter of 2029. The lease agreement includes an option to extend the lease for an additional seven-year term.
Corporate Office and Laboratory Facilities \| Subsequent Event
Lessee Lease Description [Line Items]
Operating lease, description	The lease of this additional space is expected to commence in the second quarter of 2021 and expires in March 2024. The other terms of the existing lease remain unchanged.
Lease expiration month and year	2024-03

Commitments and Contingencies - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Loss Contingencies [Line Items]
Liabilities recorded for agreements	$ 0	$ 0
Agreement with Financial Institution
Loss Contingencies [Line Items]
Letters of credit outstanding amount	$ 400,000
Letter of credit notice period by financial institution before annual expiration date	30 days

University of Singapore and St. Jude Children's License Agreement - Additional Information (Details)	1 Months Ended		12 Months Ended
	Aug. 31, 2016 USD ($) shares	Aug. 31, 2016 SGD ($) shares	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
License Agreement [Line Items]
Research and development costs			$ 36,220,000	$ 17,217,000
NUS and St. Jude \| License Agreement
License Agreement [Line Items]
Upfront payment	$ 31,800	$ 42,750
Upfront payment, shares issued \| shares	250,000	250,000
Fair value of common stock issued	$ 2,500
Annual license maintenance fee		$ 25,000
Potential milestone payments		$ 5,000,000
Percentage of licensors royalties	2.50%	2.50%
Milestone payment			100,000
NUS and St. Jude \| License Agreement \| License Maintenance Fees
License Agreement [Line Items]
Research and development costs			$ 37,000	$ 37,000
NUS and St. Jude \| License Agreement \| After Year Two of the Agreement
License Agreement [Line Items]
Annual license maintenance fee		$ 50,000
NUS and St. Jude \| License Agreement \| Minimum
License Agreement [Line Items]
Percentage of sublicensing income	7.50%	7.50%
NUS and St. Jude \| License Agreement \| Maximum
License Agreement [Line Items]
Percentage of sublicensing income	20.00%	20.00%
License agreement term	120 months	120 months

Fair Value of Financial Instruments - Summary of Fair Value of Financial Instrument (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Jul. 01, 2020	Dec. 31, 2019
Assets:
Money market funds	$ 94,631
Total short-term investments	218,221		$ 16,384
Total	312,852		18,779
Commercial paper			2,395
Liabilities:
Preferred stock purchase right liability		$ 41,600	1,478
Commercial Paper
Assets:
Total short-term investments	63,445		10,357
Corporate Debt Securities
Assets:
Total short-term investments	48,614		6,027
U.S. Government Securities
Assets:
Total short-term investments	106,162
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Money market funds	94,631
Total	94,631
Significant Other Observable Inputs (Level 2)
Assets:
Total short-term investments	218,221		16,384
Total	218,221		18,779
Commercial paper			2,395
Significant Other Observable Inputs (Level 2) \| Commercial Paper
Assets:
Total short-term investments	63,445		10,357
Significant Other Observable Inputs (Level 2) \| Corporate Debt Securities
Assets:
Total short-term investments	48,614		6,027
Significant Other Observable Inputs (Level 2) \| U.S. Government Securities
Assets:
Total short-term investments	$ 106,162
Significant Unobservable Inputs (Level 3)
Liabilities:
Preferred stock purchase right liability			$ 1,478

Fair Value of Financial Instruments - Additional Information (Details) - USD ($)		1 Months Ended		12 Months Ended
	Jul. 01, 2020	Dec. 31, 2019	Aug. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Impairments					$ 0
Realized gain or loss on available-for-sale securities				$ 0
Temporary equity, shares issued		27,283,973		0	27,283,973
Preferred stock purchase right liability	$ 41,600,000	$ 1,478,000			$ 1,478,000
Fair value of preferred stock purchase right liability percentage		90.00%	90.00%
Fair value of preferred stock purchase right liability discount rate		1.60%	1.80%
Fair value of preferred stock purchase right liability outstanding term		9 months 18 days	1 year 1 month 6 days
Series B Convertible Preferred Stock
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Temporary equity, shares issued	27,066,206
Proceeds from issuance of convertible preferred stock	$ 64,400,000
Short-term investments
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Accrued interest receivable		$ 41,000		$ 1,100,000	$ 41,000
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Money Market Funds
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Investments				$ 94,600,000

Balance Sheet Components - Schedule of Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Balance Sheet Related Disclosures [Abstract]
Prepaid expenses	$ 2,586	$ 407
Other current assets	1,336	67
Total prepaid expenses and other current assets	$ 3,922	$ 474

Balance Sheet Components - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property Plant And Equipment [Line Items]
Total property and equipment	$ 10,781	$ 3,725
Less accumulated depreciation and amortization	(1,431)	(645)
Total property and equipment, net	9,350	3,080
Leasehold Improvements
Property Plant And Equipment [Line Items]
Total property and equipment	1,984	287
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Total property and equipment	322	265
Research Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	4,892	2,929
Computers and Software
Property Plant And Equipment [Line Items]
Total property and equipment	124	61
Construction in Progress
Property Plant And Equipment [Line Items]
Total property and equipment	$ 3,459	$ 183

Balance Sheet Components - Schedule of Accrued and Other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Balance Sheet Related Disclosures [Abstract]
Accrued compensation	$ 3,534	$ 1,678
Accrued research and development costs	1,675	702
Accrued property and equipment	117	214
Deferred offering costs		104
Other accrued and current liabilities	927	591
Total accrued and other liabilities	$ 6,253	$ 3,289

Leases - Components of Lease Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Lease, Cost [Abstract]
Operating lease expense	$ 1,856	$ 1,315
Variable lease expense	178	126
Short-term lease expense	14
Total lease expense	$ 2,048	$ 1,441

Leases - Schedule of Supplemental Information Related to Operating Leases (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Cash paid for amounts included in the measurement of lease liabilities
Operating cash flows used for operating leases	$ 1,705	$ 1,180
Lease liabilities arising from obtaining right-of-use assets
Operating leases	$ 2,401	$ 5,107

Leases - Schedule of Maturities of Operating Lease Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
2021	$ 1,461
2022	1,452
2023	1,503
2024	1,556
2025	1,610
2026 and thereafter	5,371
Total future minimum lease payments	12,953
Less imputed interest	(4,034)
Present value of net minimum lease payments	8,919
Operating lease liabilities:
Current	1,402	$ 1,516
Non-current	7,517	$ 5,780
Total lease liability	$ 8,919

Employee Benefits - Additional Information (Details) - 401 (K) Plan - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, description	On January 1, 2018, the Company adopted a defined contribution 401(k) plan that is available to eligible employees
Employer contribution, percent	3.00%
Expense contribution plan	$ 0.3	$ 0.2

Share-Based Compensation - Summary of Share-based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	$ 6,748	$ 947
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	1,871	376
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	$ 4,877	$ 571

Income Taxes - Significant Components of Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Net operating loss carry forwards	$ 17,674	$ 6,897
Depreciation and amortization	265	200
Research and development credits	3,986	1,316
Accrued expenses	983	459
Lease liability	2,496	2,042
Other, net	891	3
Total deferred tax assets	26,295	10,917
Valuation allowance for deferred tax assets	(23,696)	(8,731)
Deferred tax assets, net of valuation allowance	2,599	2,186
Deferred tax liabilities:
Right-of-use asset	(2,382)	(2,036)
Depreciation and amortization	$ (217)	$ (150)