Nkarta (NKTX) 10-Q 13 May 21 2020 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2021	May 10, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
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		32,822,550
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Current Fiscal Year End Date	--12-31
Entity Central Index Key	0001787400

CONDENSED BALANCE SHEETS (Unaud

CONDENSED BALANCE SHEETS (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Current assets
Cash and cash equivalents	$ 62,608	$ 96,692
Short-term investments, available-for-sale	236,655	218,221
Prepaid expenses and other current assets	2,971	3,922
Total current assets	302,234	318,835
Restricted cash	413	413
Property and equipment, net	10,498	9,350
Operating lease right-of-use assets	11,873	8,505
Other long-term assets	674	547
Total assets	325,692	337,650
Current liabilities
Accounts payable	2,010	1,176
Operating lease liabilities, current portion	2,151	1,402
Accrued and other current liabilities	5,192	6,253
Total current liabilities	9,353	8,831
Operating lease liabilities, net of current portion	10,274	7,517
Other long-term liabilities	75	82
Total liabilities	19,702	16,430
Commitments and contingencies (Note 7)
Stockholders’ equity
Preferred stock
Common stock	3	3
Additional paid-in capital	443,347	439,235
Accumulated other comprehensive income	34	3
Accumulated deficit	(137,394)	(118,021)
Total stockholders’ equity	305,990	321,220
Total liabilities and stockholders’ equity	$ 325,692	$ 337,650

CONDENSED STATEMENTS OF OPERATI

CONDENSED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating expenses
Research and development	$ 13,539	$ 7,260
General and administrative	5,942	2,148
Total operating expenses	19,481	9,408
Loss from operations	(19,481)	(9,408)
Other income (expense), net:
Change in fair value of preferred stock purchase right liability		578
Interest income	110	124
Other expense, net	(2)
Total other income (expense), net	108	702
Net loss	(19,373)	(8,706)
Comprehensive loss:
Net loss	(19,373)	(8,706)
Other comprehensive gain (loss)	31	(1)
Comprehensive loss	$ (19,342)	$ (8,707)
Net loss per share, basic and diluted	$ (0.59)	$ (5.41)
Weighted average shares used to compute net loss per share, basic and diluted	32,739,610	1,609,184

CONDENSED STATEMENTS OF CONVERT

CONDENSED STATEMENTS OF CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive (Income) Loss	Accumulated Deficit	Convertible Preferred Stock
Beginning Balance at Dec. 31, 2019	$ (25,482)	$ 1	$ 1,179	$ (2)	$ (26,660)
Temporary Equity, Beginning Balance, Shares at Dec. 31, 2019						27,283,973
Temporary Equity, Beginning Balance at Dec. 31, 2019						$ 59,815
Beginning Balance, Shares at Dec. 31, 2019		1,600,601
Vesting of shares of common stock subject to repurchase	13		13
Vesting of shares of common stock subject to repurchase, Shares		17,494
Issuance of common stock upon exercise of stock option, net of repurchase	1		1
Issuance of common stock upon exercise of stock option, net of repurchase, Shares		2,871
Share-based compensation expense	482		482
Unrealized gain (loss) on short-term investments	(2)			(2)
Net loss	(8,706)				(8,706)
Ending Balance at Mar. 31, 2020	(33,694)	$ 1	1,675	(4)	(35,366)
Temporary Equity, Ending Balance, Shares at Mar. 31, 2020						27,283,973
Temporary Equity, Ending Balance at Mar. 31, 2020						$ 59,815
Ending Balance, Shares at Mar. 31, 2020		1,620,966
Beginning Balance at Dec. 31, 2020	321,220	$ 3	439,235	3	(118,021)
Beginning Balance, Shares at Dec. 31, 2020		32,627,963
Vesting of shares of common stock subject to repurchase	9		9
Vesting of shares of common stock subject to repurchase, Shares		15,802
Issuance of common stock upon exercise of stock option, net of repurchase	$ 756		756
Issuance of common stock upon exercise of stock option, net of repurchase, Shares	155,322	154,489
Share-based compensation expense	$ 3,347		3,347
Unrealized gain (loss) on short-term investments	31			31
Net loss	(19,373)				(19,373)
Ending Balance at Mar. 31, 2021	$ 305,990	$ 3	$ 443,347	$ 34	$ (137,394)
Ending Balance, Shares at Mar. 31, 2021		32,798,254

CONDENSED STATEMENT OF CASH FLO

CONDENSED STATEMENT OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash flows from operating activities
Net loss	$ (19,373)	$ (8,706)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation expense	3,347	482
Depreciation and amortization	301	141
Accretion and amortization of premium on investments, net	758	(28)
Non-cash lease expense	137	139
Change in fair value of preferred stock purchase right liability		(578)
Changes in operating assets and liabilities:
Prepaid expenses and other assets	825	(163)
Accounts payable and accrued and other liabilities	(642)	426
Net cash used in operating activities	(14,647)	(8,287)
Cash flows from investing activities
Purchases of property and equipment	(1,033)	(2,325)
Purchases of short-term investments	(35,161)	(3,578)
Maturities of short-term investments	16,000	10,800
Net cash provided by (used in) investing activities	(20,194)	4,897
Cash flows from financing activities
Proceeds from stock option exercises	756	1
Proceeds from early exercise of stock options	1	1
Payments of deferred offering costs		(711)
Net cash provided by (used in) financing activities	757	(709)
Net decrease in cash and cash equivalents	(34,084)	(4,099)
Cash, cash equivalents, and restricted cash beginning of period	97,105	20,875
Cash, cash equivalents, and restricted cash end of period	63,021	16,776
Reconciliation of cash, cash equivalents and restricted cash to the balance sheet:
Cash and cash equivalents	62,608	16,507
Restricted cash	413	269
Total cash, cash equivalents and restricted cash	$ 63,021	$ 16,776

Organization and Description of

Organization and Description of Business	3 Months Ended
	Mar. 31, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization and Description of Business	1. Organization and Description of Business Description of the Business Nkarta, Inc. (“Nkarta” or the “Company”) was incorporated in the State of Delaware in July 2015. The Company is a biopharmaceutical company developing engineered natural killer (“NK”) cells to fight cancer. The Company is focused on leveraging the natural potent power of NK cells to identify and kill abnormal cells and recruit adaptive immune effectors to generate responses that are specific and durable. Nkarta is combining its NK expansion platform technology with proprietary cell engineering technologies to generate an abundant supply of NK cells, engineer enhanced NK cell recognition of tumor targets, and improve persistence for sustained activity in the body for the treatment of cancer. Nkarta’s goal is to develop off-the-shelf NK cell therapy product candidates to improve outcomes for patients. The Company’s operations are based in South San Francisco, California and it operates in one segment. Liquidity and Management Plans The accompanying unaudited condensed financial statements have been prepared assuming that the Company will continue as a going concern. However, since inception, he Company has devoted substantially all of its efforts to organizing and staffing, business planning, raising capital, conducting preclinical studies and initiating clinical studies, and has not realized substantial revenues from its planned principal operations. In addition, the Company has a limited operating history, has incurred operating losses since inception and expects that it will continue to incur net losses into the foreseeable future as it continues its research and development activities. As of March 31, 2021, the Company had an accumulated deficit of $137.4 million and cash, cash equivalents, restricted cash and short-term investments of $299.7 million. Management plans to continue to incur substantial costs in order to conduct research and development activities and additional capital will be needed The Company intends to raise such capital through d ebt or equity financings or other arrangements to fund operations

Basis of Presentation and Signi

Basis of Presentation and Significant Accounting Policies	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Basis of Presentation and Significant Accounting Policies	2. Basis of Presentation and Significant Accounting Policies Basis of Presentation The accompanying unaudited condensed financial statements as of March 31, 2021 and for the three months ended March 31, 2021 and 2020 have been prepared in accordance with U.S. generally accepted accounting principle (“U.S. GAAP”) for interim financial information and pursuant to Article 10 of Regulation S-X of the Securities Act of 1933, as amended (the “Securities Act”). Accordingly, they do not include all of the information and notes required by U.S. GAAP for complete financial statements. These unaudited condensed financial statements include only normal and recurring adjustments that the Company believes are necessary to fairly state the Company’s financial position and the results of its operations and cash flows. The results for the three months ended March 31, 2021 are not necessarily indicative of the results expected for the full year or any subsequent interim period. The condensed balance sheet at December 31, 2020 has been derived from the audited financial statements at that date but does not include all disclosures required by U.S. GAAP for complete financial statements. Because all of the disclosures required by U.S. GAAP for complete financial statements are not included herein, these unaudited condensed financial statements and the notes accompanying them should be read in conjunction with the Company’s audited financial statements for the year ended December 31, 2020, contained in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020 filed by the Company with the SEC on March 25, 2021. 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 O n 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 first quarter of 2021. 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. At this time, the extent to which the COVID-19 pandemic may impact the Company’s financial condition or results of operations is uncertain. 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, 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. Net Loss Per Share Basic net loss per share is calculated by dividing the net loss 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 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 Income Taxes. In December 2019, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2019-12—Income Taxes (Topic 740): 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 adopted this standard in the first quarter of 2021 using the prospective method and the adoption did not 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 for the three months ended March 31, 2021. 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.

Net Loss Per Share

Net Loss Per Share	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Net Loss Per Share	3. Net Loss Per Share The following tables summarize the computation of the basic and diluted net loss per share (in thousands except share and per share data): Three Months Ended March 31, 2021 2020 Numerator: Net loss $ (19,373 ) $ (8,706 ) Denominator: Weighted average common shares outstanding 32,806,880 1,735,238 Less: weighted average unvested common stock issued upon early exercise of common stock options (67,270 ) (126,054 ) Weighted average shares used to compute net loss per share, basic and diluted 32,739,610 1,609,184 Net loss per share, basic and diluted $ (0.59 ) $ (5.41 ) The following table summarizes the outstanding potentially dilutive securities that have been excluded in the calculation of diluted net loss per share because their inclusion would be anti-dilutive: As of March 31, 2021 2020 Common stock options 4,185,431 2,487,763 Unvested common stock upon early exercise of common stock options 62,424 117,356 Convertible preferred stock — 7,374,034 4,247,855 9,979,153

Fair Value of Financial Instrum

Fair Value of Financial Instruments	3 Months Ended
	Mar. 31, 2021
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 March 31, 2021 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 $ 61,564 $ 61,564 $ — $ — Short-term investments: Corporate debt securities $ 55,299 $ — $ 55,299 — Commercial paper 60,462 — 60,462 — U.S. Government securities 120,894 — 120,894 — Total short-term investments 236,655 — 236,655 — Total $ 298,219 $ 61,564 $ 236,655 $ — 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 $ — 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, U.S. Government securities and corporate bonds. 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 $61.6 million and $94.6 million as of March 31, 2021 and December 31, 2020, respectively, were classified as Level 1 instruments and were included in cash and cash equivalents. Investments in marketable securities 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 marketable securities of $236.7 million and $218.2 million as of March 31, 2021 and December 31, 2020, respectively, were classified as Level 2 instruments and were included in short-term investments. Accrued interest receivable related to short-term investments were $0.8 million and $1.1 million as of March 31, 2021 and December 31, 2020, respectively, and included as part of prepaid expenses and other current assets in the balance sheets. The following tables summarize the Company’s short-term investments accounted for as available-for-sale securities as of March 31, 2021 and December 31, 2020 (in thousands): March 31, 2021 Maturity (in years) Amortized Cost Unrealized Losses Unrealized Gains Estimated Fair Value Corporate debt securities 1 year or less $ 55,308 $ (12 ) $ 3 $ 55,299 Commercial paper 1 year or less 60,462 — — 60,462 U.S. Government securities 1 year or less 120,851 43 120,894 Total $ 236,621 $ (12 ) $ 46 $ 236,655 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 The Company has classified all of its available-for-sale investment securities as current assets on the balance sheet based on the highly liquid nature of these investment securities and because these investment securities are considered available for use in current operations. The Company 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 March 31, 2021 and December 31, 2020 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 March 31, 2021 and that there were no impairments as of December 31, 2020. 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. Unrealized gains and losses are included in accumulated other comprehensive income There was no realized gain or loss on available-for-sale securities in the periods presented. The Company uses the specific identification method to determine the cost basis of investments sold.

Balance Sheet Components

Balance Sheet Components	3 Months Ended
	Mar. 31, 2021
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): March 31, 2021 December 31, 2020 Prepaid expenses $ 1,886 $ 2,586 Other current assets 1,085 1,336 Total prepaid expenses and other current assets $ 2,971 $ 3,922 Property and Equipment, Net Property and equipment, net is comprised of the following (in thousands): March 31, 2021 December 31, 2020 Leasehold improvements $ 1,990 $ 1,984 Furniture and fixtures 480 322 Research equipment 5,538 4,892 Computers and software 124 124 Construction in progress 4,098 3,459 Total property and equipment 12,230 10,781 Less accumulated depreciation and amortization (1,732 ) (1,431 ) Total property and equipment, net $ 10,498 $ 9,350 Depreciation and amortization expense were $0.3 million and $0.1 million for the three months ended March 31, 2021 and 2020, respectively. Accrued and Other Current Liabilities Accrued other current liabilities are comprised of the following (in thousands): March 31, 2021 December 31, 2020 Accrued compensation $ 2,086 $ 3,534 Accrued research and development costs 1,878 1,675 Accrued property and equipment 164 117 Other accrued and current liabilities 1,064 927 Total accrued and other liabilities $ 5,192 $ 6,253

Leases

Leases	3 Months Ended
	Mar. 31, 2021
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. Rent expense, which is recognized on a straight-line basis over the term of each lease, were $0.6 million and $0.4 million for the three months ended March 31, 2021 and 2020, respectively. The total cash paid for operating leases included in the operating cash flows were $0.4 million and $0.4 million for the three months ended March 31, 2021 and 2020, respectively. The weighted-average remaining lease term was 7.6 years for the corporate office and laboratory space leases as of March 31, 2021. The weighted-average discount rate was 9% as of March 31, 2021. In May 2020, the Company signed an amendment to its 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 commenced in January 2021 and expires in January 2029. The lease amendment also includes an extension of the lease term for the existing office and laboratory space beginning on May 1, 2020 and expiring in January 2029. The lease agreement includes an option to extend the lease for an additional seven-year term. 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 commenced in April 2021 and expires in March 2024. The other terms of the existing lease remain unchanged. Maturities of operating lease liabilities under existing operating leases as of March 31, 2021 were as follows (in thousands): Year ending December 31, Amount 2021 (remaining nine months) $ 1,674 2022 2,064 2023 2,053 2024 2,125 2025 2,200 2026 and thereafter 7,322 Total future minimum lease payments 17,438 Less imputed interest (5,013 ) Present value of net minimum lease payments $ 12,425 Operating lease liabilities: Current 2,151 Non-current 10,274 Total lease liability $ 12,425 Total minimum lease payments of $0.7 million related to the lease of additional space under the amendment were excluded from the table above as the lease agreement had not yet commenced as of March 31, 2021.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2021
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	7. Commitments & Contingencies Guarantee Agreement The Company has agreements whereby it indemnifies its officers and directors for certain events or occurrences while the officer or director is, or was, serving at the Company’s request in such capacity. The term of the indemnification period is for the officer’s or director’s lifetime. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is unlimited; however, the Company has a director and officer insurance policy that limits its exposure and enables the Company to recover a portion of any future amounts under certain circumstances and subject to deductibles and exclusions. The Company had no liabilities recorded for these agreements as of March 31, 2021 and December 31, 2020. Letters of Credit The Company has a $0.4 million letter of credit agreement with a financial institution that is used as collateral for the Company’s corporate headquarters’ operating lease. The letter of credit automatically renews annually without amendment unless cancelled by the financial institutions within 30 days of the annual expiration date.

Share-Based Compensation

Share-Based Compensation	3 Months Ended
	Mar. 31, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Share-Based Compensation	8. Share-Based Compensation Equity Incentive Plan The Company’s 2020 Performance Incentive Plan (the “2020 Plan”) 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 Equity Incentive Plan (the “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 March 31, 2021, there were an aggregate of 2,061,754 shares of common stock issuable upon the exercise of outstanding options under the 2015 Plan. Any options or awards outstanding under the 2015 Plan remain outstanding and effective A total of 4,295,638 shares of the Company’s common stock is 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 715,770 options had been granted under the 2020 Plan for the three months ended March 31, 2021, and 2,325,631 shares was available for issuance under the 2020 Plan as of March 31, 2021 . The following table summarizes the option activity under the 2020 Plan and 2015 Plan during the three months ended March 31, 2021: Number of shares Weighted- average exercise price Weighted- average remaining contractual term (in years) Outstanding at December 31, 2020 3,640,715 $ 11.00 9.0 Granted 715,770 53.39 Exercised (155,322 ) 4.87 Forfeited (15,732 ) 18.23 Outstanding at March 31, 2021 4,185,431 $ 18.45 9.0 Exercisable at March 31, 2021 745,999 $ 8.10 8.5 Vested and expected to vest at March 31, 2021 4,185,431 $ 18.45 9.0 The weighted-average grant date fair value of stock option grants was $36.29 per share for the three months ended March 31, 2021. Employee Stock Purchase Plan The Company’s 2020 Employee Stock Purchase Plan (the “ESPP”), became effective upon the consummation of the IPO. A total of 622,652 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 March 31, 2021 , no shares had been issued under the ESPP, and the full number of shares authorized under the ESPP Plan was available for issuance purposes Liability for Early Exercise of Restricted Stock Options Shares subject to repurchase by the Company were 62,424 shares and 77,393 shares, with the related liability of $0.1 million and $0.1 million recorded under other long-term liabilities in the balance sheets as of March 31, 2021 and December 31, 2020, respectively. Share-Based Compensation Expense Share-based compensation expense for the three months ended March 31, 2021 and 2020 were as follows (in thousands): Three Months Ended March 31, 2021 2020 Research and development $ 1,570 $ 192 General and administrative 1,777 290 Total share-based compensation $ 3,347 $ 482 The total unrecognized compensation cost related to unvested share-based awards was $44.6 million, which is expected to be recognized over a weighted-average remaining service period of 3.5 years as of March 31, 2021. The fair value of stock options was estimated on the date of grant using the Black-Scholes option pricing model with the following weighted-average assumptions: Three Months Ended March 31, 2021 2020 Common stock fair value $ 53.39 $ 4.29 Risk-free interest rate 0.69 % 0.51 % Expected volatility 79.86 % 87.78 % Expected term (in years) 6.0 6.0 Expected dividend yield — % — % Common Stock Reserved for Future Issuance As of March 31, 2021, the Company had reserved the following shares of common stock for future issuance: March 31, 2021 Common stock options granted and outstanding 4,185,431 Reserved for future equity award grants 2,325,631 Reserved for future ESPP issuances 622,652 7,133,714

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2021
Income Tax Disclosure [Abstract]
Income Taxes	9. Income Taxes There was no provision for income taxes recorded during the three months ended March 31, 2021 and 2020. The Company’s deferred tax assets continue to be fully offset by a valuation allowance .

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2020
Subsequent Events [Abstract]
Subsequent Events	10. Subsequent Events On May 5, 2021, the Company entered into a research collaboration agreement (the “CRISPR Agreement”) with CRISPR Therapeutics (“CRISPR”) to co-develop and co-commercialize an engineered CAR-NK product candidate targeting the CD70 tumor antigen. In addition, Nkarta will have non-exclusive rights to five CRISPR-Cas9 gene editing targets that can be engineered into an unlimited number of its own NK cell products. The companies will also bring together their complementary cell therapy engineering and manufacturing capabilities to advance the development of a novel NK plus T cell (“NK+T”) product candidate that will be the second collaboration product. CRISPR also has an option to co-develop and co-commercialize a future CAR-NK program. Under the terms of the agreement, the Company and CRISPR share equally all research and development costs and potential profits worldwide related to the collaboration products. For the NK+T program, CRISPR is responsible for gene-editing activities and T cell related activities, and Nkarta is responsible for NK cell related activities. For each non-collaboration product candidate incorporating a gene editing target licensed from CRISPR, the Company would retain worldwide rights and may be required to make potential future payments based on the achievement of development and regulatory approval milestones totaling less than mid-twenty million dollars

Basis of Presentation and Sig_2

Basis of Presentation and Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed financial statements as of March 31, 2021 and for the three months ended March 31, 2021 and 2020 have been prepared in accordance with U.S. generally accepted accounting principle (“U.S. GAAP”) for interim financial information and pursuant to Article 10 of Regulation S-X of the Securities Act of 1933, as amended (the “Securities Act”). Accordingly, they do not include all of the information and notes required by U.S. GAAP for complete financial statements. These unaudited condensed financial statements include only normal and recurring adjustments that the Company believes are necessary to fairly state the Company’s financial position and the results of its operations and cash flows. The results for the three months ended March 31, 2021 are not necessarily indicative of the results expected for the full year or any subsequent interim period. The condensed balance sheet at December 31, 2020 has been derived from the audited financial statements at that date but does not include all disclosures required by U.S. GAAP for complete financial statements. Because all of the disclosures required by U.S. GAAP for complete financial statements are not included herein, these unaudited condensed financial statements and the notes accompanying them should be read in conjunction with the Company’s audited financial statements for the year ended December 31, 2020, contained in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020 filed by the Company with the SEC on March 25, 2021.
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 O n 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 first quarter of 2021. 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. At this time, the extent to which the COVID-19 pandemic may impact the Company’s financial condition or results of operations is uncertain. 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, 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.
Net Loss Per Share	Net Loss Per Share Basic net loss per share is calculated by dividing the net loss 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 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 Income Taxes. In December 2019, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2019-12—Income Taxes (Topic 740): 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 adopted this standard in the first quarter of 2021 using the prospective method and the adoption did not 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 for the three months ended March 31, 2021. 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.

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Computation of Basic and Diluted Net Loss Per Share	The following tables summarize the computation of the basic and diluted net loss per share (in thousands except share and per share data): Three Months Ended March 31, 2021 2020 Numerator: Net loss $ (19,373 ) $ (8,706 ) Denominator: Weighted average common shares outstanding 32,806,880 1,735,238 Less: weighted average unvested common stock issued upon early exercise of common stock options (67,270 ) (126,054 ) Weighted average shares used to compute net loss per share, basic and diluted 32,739,610 1,609,184 Net loss per share, basic and diluted $ (0.59 ) $ (5.41 )
Summarizes the Outstanding Potentially Dilutive Securities Excluded in Calculation of Diluted Net Loss Per Share	The following table summarizes the outstanding potentially dilutive securities that have been excluded in the calculation of diluted net loss per share because their inclusion would be anti-dilutive: As of March 31, 2021 2020 Common stock options 4,185,431 2,487,763 Unvested common stock upon early exercise of common stock options 62,424 117,356 Convertible preferred stock — 7,374,034 4,247,855 9,979,153

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2021
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 March 31, 2021 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 $ 61,564 $ 61,564 $ — $ — Short-term investments: Corporate debt securities $ 55,299 $ — $ 55,299 — Commercial paper 60,462 — 60,462 — U.S. Government securities 120,894 — 120,894 — Total short-term investments 236,655 — 236,655 — Total $ 298,219 $ 61,564 $ 236,655 $ — 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 $ —
Short-term investments
Schedule of Short-term Investments	The following tables summarize the Company’s short-term investments accounted for as available-for-sale securities as of March 31, 2021 and December 31, 2020 (in thousands): March 31, 2021 Maturity (in years) Amortized Cost Unrealized Losses Unrealized Gains Estimated Fair Value Corporate debt securities 1 year or less $ 55,308 $ (12 ) $ 3 $ 55,299 Commercial paper 1 year or less 60,462 — — 60,462 U.S. Government securities 1 year or less 120,851 43 120,894 Total $ 236,621 $ (12 ) $ 46 $ 236,655 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

Balance Sheet Components (Table

Balance Sheet Components (Tables)	3 Months Ended
	Mar. 31, 2021
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): March 31, 2021 December 31, 2020 Prepaid expenses $ 1,886 $ 2,586 Other current assets 1,085 1,336 Total prepaid expenses and other current assets $ 2,971 $ 3,922
Schedule of Property and Equipment, Net	Property and equipment, net is comprised of the following (in thousands): March 31, 2021 December 31, 2020 Leasehold improvements $ 1,990 $ 1,984 Furniture and fixtures 480 322 Research equipment 5,538 4,892 Computers and software 124 124 Construction in progress 4,098 3,459 Total property and equipment 12,230 10,781 Less accumulated depreciation and amortization (1,732 ) (1,431 ) Total property and equipment, net $ 10,498 $ 9,350
Schedule of Accrued Other Current Liabilities	Accrued other current liabilities are comprised of the following (in thousands): March 31, 2021 December 31, 2020 Accrued compensation $ 2,086 $ 3,534 Accrued research and development costs 1,878 1,675 Accrued property and equipment 164 117 Other accrued and current liabilities 1,064 927 Total accrued and other liabilities $ 5,192 $ 6,253

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2021
Leases [Abstract]
Schedule of Maturities of Operating Lease Liabilities	Maturities of operating lease liabilities under existing operating leases as of March 31, 2021 were as follows (in thousands): Year ending December 31, Amount 2021 (remaining nine months) $ 1,674 2022 2,064 2023 2,053 2024 2,125 2025 2,200 2026 and thereafter 7,322 Total future minimum lease payments 17,438 Less imputed interest (5,013 ) Present value of net minimum lease payments $ 12,425 Operating lease liabilities: Current 2,151 Non-current 10,274 Total lease liability $ 12,425

Share-Based Compensation (Table

Share-Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Stock Option Activity	The following table summarizes the option activity under the 2020 Plan and 2015 Plan during the three months ended March 31, 2021: Number of shares Weighted- average exercise price Weighted- average remaining contractual term (in years) Outstanding at December 31, 2020 3,640,715 $ 11.00 9.0 Granted 715,770 53.39 Exercised (155,322 ) 4.87 Forfeited (15,732 ) 18.23 Outstanding at March 31, 2021 4,185,431 $ 18.45 9.0 Exercisable at March 31, 2021 745,999 $ 8.10 8.5 Vested and expected to vest at March 31, 2021 4,185,431 $ 18.45 9.0
Summary of Share-based Compensation Expense	Share-based compensation expense for the three months ended March 31, 2021 and 2020 were as follows (in thousands): Three Months Ended March 31, 2021 2020 Research and development $ 1,570 $ 192 General and administrative 1,777 290 Total share-based compensation $ 3,347 $ 482
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 weighted-average assumptions: Three Months Ended March 31, 2021 2020 Common stock fair value $ 53.39 $ 4.29 Risk-free interest rate 0.69 % 0.51 % Expected volatility 79.86 % 87.78 % Expected term (in years) 6.0 6.0 Expected dividend yield — % — %
Summary of Common Stock Reserved for Future Issuance	As of March 31, 2021, the Company had reserved the following shares of common stock for future issuance: March 31, 2021 Common stock options granted and outstanding 4,185,431 Reserved for future equity award grants 2,325,631 Reserved for future ESPP issuances 622,652 7,133,714

Organization and Description _2

Organization and Description of Business - Additional Information (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2021USD ($)Segment	Dec. 31, 2020USD ($)
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Number of operating segments | Segment	1
Accumulated deficit	$ 137,394	$ 118,021
Cash, cash equivalents restricted cash and short-term investments	$ 299,700

Basis of Presentation and Sig_3

Basis of Presentation and Significant Accounting Polices - Additional Information (Details)	Jul. 01, 2020	Mar. 31, 2021
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
ASU 2019-12
Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]		true
Change in Accounting Principle, Accounting Standards Update, Adoption Date		Mar. 31, 2021
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]		true

Net Loss Per Share - Computatio

Net Loss Per Share - Computation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Numerator:
Net loss	$ (19,373)	$ (8,706)
Denominator:
Weighted average common shares outstanding	32,806,880	1,735,238
Less: weighted average unvested common stock issued upon early exercise of common stock options	(67,270)	(126,054)
Weighted average shares used to compute net loss per share, basic and diluted	32,739,610	1,609,184
Net loss per share, basic and diluted	$ (0.59)	$ (5.41)

Net Loss Per Share - Summarizes

Net Loss Per Share - Summarizes the Outstanding Potentially Dilutive Securities Excluded in Calculation of Diluted Net Loss Per Share (Details) - shares	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	4,247,855	9,979,153
Common Stock Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	4,185,431	2,487,763
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	62,424	117,356
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 Instr_3

Fair Value of Financial Instruments - Summary of Fair Value of Financial Instrument (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Assets:
Money market funds	$ 61,564	$ 94,631
Total short-term investments	236,655	218,221
Total	298,219	312,852
Commercial Paper
Assets:
Total short-term investments	60,462	63,445
Corporate Debt Securities
Assets:
Total short-term investments	55,299	48,614
U.S. Government Securities
Assets:
Total short-term investments	120,894	106,162
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Money market funds	61,564	94,631
Total	61,564	94,631
Significant Other Observable Inputs (Level 2)
Assets:
Total short-term investments	236,655	218,221
Total	236,655	218,221
Significant Other Observable Inputs (Level 2) | Commercial Paper
Assets:
Total short-term investments	60,462	63,445
Significant Other Observable Inputs (Level 2) | Corporate Debt Securities
Assets:
Total short-term investments	55,299	48,614
Significant Other Observable Inputs (Level 2) | U.S. Government Securities
Assets:
Total short-term investments	$ 120,894	$ 106,162

Fair Value of Financial Instr_4

Fair Value of Financial Instruments - Additional Information (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Impairments		$ 0
Realized gain or loss on available-for-sale securities	$ 0
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	61,600,000	94,600,000
Significant Other Observable Inputs (Level 2) | Short-term investments
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Marketable securities	236,700,000	218,200,000
Accrued interest receivable	$ 800,000	$ 1,100,000

Fair Value of Financial Instr_5

Fair Value of Financial Instruments - Schedule of Short-term Investments Accounted as Available-for-sale Securities (Details) - Short-term investments - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available for sale securities, Amortized Cost	$ 236,621	$ 218,218
Available for sale securities, Unrealized Losses	(12)	(13)
Available for sale securities, Unrealized Gains	46	16
Available for sale securities,Estimated Fair Value	236,655	218,221
Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available for sale securities, Amortized Cost	60,462	63,445
Available for sale securities,Estimated Fair Value	$ 60,462	$ 63,445
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	$ 120,851	$ 106,157
Available for sale securities, Unrealized Losses		(7)
Available for sale securities, Unrealized Gains	43	12
Available for sale securities,Estimated Fair Value	$ 120,894	$ 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	1 year
Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available for sale securities, Amortized Cost	$ 55,308	$ 48,616
Available for sale securities, Unrealized Losses	(12)	(6)
Available for sale securities, Unrealized Gains	3	4
Available for sale securities,Estimated Fair Value	$ 55,299	$ 48,614
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

Balance Sheet Components - Sche

Balance Sheet Components - Schedule of Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Balance Sheet Related Disclosures [Abstract]
Prepaid expenses	$ 1,886	$ 2,586
Other current assets	1,085	1,336
Total prepaid expenses and other current assets	$ 2,971	$ 3,922

Balance Sheet Components - Sc_2

Balance Sheet Components - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Property Plant And Equipment [Line Items]
Total property and equipment	$ 12,230	$ 10,781
Less accumulated depreciation and amortization	(1,732)	(1,431)
Total property and equipment, net	10,498	9,350
Leasehold Improvements
Property Plant And Equipment [Line Items]
Total property and equipment	1,990	1,984
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Total property and equipment	480	322
Research Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	5,538	4,892
Computers and Software
Property Plant And Equipment [Line Items]
Total property and equipment	124	124
Construction in Progress
Property Plant And Equipment [Line Items]
Total property and equipment	$ 4,098	$ 3,459

Balance Sheet Components - Addi

Balance Sheet Components - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Balance Sheet Related Disclosures [Abstract]
Depreciation and amortization expense	$ 0.3	$ 0.1

Balance Sheet Components - Sc_3

Balance Sheet Components - Schedule of Accrued Other Current Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Balance Sheet Related Disclosures [Abstract]
Accrued compensation	$ 2,086	$ 3,534
Accrued research and development costs	1,878	1,675
Accrued property and equipment	164	117
Other accrued and current liabilities	1,064	927
Total accrued and other liabilities	$ 5,192	$ 6,253

Leases - Additional Information

Leases - Additional Information (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended
	Jan. 31, 2021	May 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Lessee Lease Description [Line Items]
Rent expense			$ 0.6	$ 0.4
Cash paid for operating leases			$ 0.4	$ 0.4
Weighted-average discount rate			9.00%
Operating lease not yet commenced minimum lease payments			$ 0.7
Corporate Office and Laboratory Space
Lessee Lease Description [Line Items]
Weighted-average remaining lease term			7 years 7 months 6 days
Renewal term		7 years
Corporate Office and Laboratory Facilities
Lessee Lease Description [Line Items]
Lease term		8 years
Lease expiration year		2029
Operating lease, existence of option to extend		true
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 and expiring in January 2029. The lease agreement includes an option to extend the lease for an additional seven-year term
Corporate Office and Laboratory Facilities | Third amendment
Lessee Lease Description [Line Items]
Lessee option to extend description			The lease of this additional space commenced in April 2021 and expires in March 2024. The other terms of the existing lease remain unchanged
Lease expiration month and year	2024-03

Leases - Schedule of Maturities

Leases - Schedule of Maturities of Operating Lease Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Leases [Abstract]
2021 (remaining nine months)	$ 1,674
2022	2,064
2023	2,053
2024	2,125
2025	2,200
2026 and thereafter	7,322
Total future minimum lease payments	17,438
Less imputed interest	(5,013)
Present value of net minimum lease payments	12,425
Operating lease liabilities:
Operating lease liabilities, current portion	2,151	$ 1,402
Operating lease liabilities, net of current portion	10,274	$ 7,517
Total lease liability	$ 12,425

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
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

Share-Based Compensation - Addi

Share-Based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of common stock available for issuance	7,133,714
Weighted average grant date fair value of stock option	$ 36.29
Other long-term liabilities	$ 75	$ 82
Unrecognized compensation cost	$ 44,600
Unrecognized compensation cost, expected to be recognized over weighted average remaining service period	3 years 6 months
Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares subject to repurchase	62,424	77,393
Other long-term liabilities	$ 100	$ 100
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	622,652
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	2,061,754
2020 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of common stock authorized for issuance	4,295,638
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	715,770
Number of common stock available for issuance	2,325,631

Share-Based Compensation - Summ

Share-Based Compensation - Summary of Stock Option Activity (Details) - $ / shares	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of shares, outstanding beginning balance	3,640,715
Number of shares, granted	715,770
Number of shares, exercised	(155,322)
Number of shares, forfeited	(15,732)
Number of shares, outstanding ending balance	4,185,431	3,640,715
Number of shares, exercisable	745,999
Number of shares, vested and expected to vest	4,185,431
Weighted-average exercise price, outstanding beginning balance	$ 11
Weighted-average exercise price, granted	53.39
Weighted-average exercise price, exercised	4.87
Weighted-average exercise price, forfeited	18.23
Weighted-average exercise price, outstanding ending balance	18.45	$ 11
Weighted-average exercise price, exercisable	8.10
Weighted-average exercise price, vested and expected to vest	$ 18.45
Weighted-average remaining contractual term (in years), outstanding balance	9 years	9 years
Weighted-average remaining contractual term (in years), exercisable	8 years 6 months
Weighted-average remaining contractual term (in years), vested and expected to vest	9 years

Share-Based Compensation - Su_2

Share-Based Compensation - Summary of Share-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	$ 3,347	$ 482
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	1,570	192
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	$ 1,777	$ 290

Share-Based Compensation - Sche

Share-Based Compensation - Schedule of Fair Value of Stock Options Estimated on Date of Grant Using Black-Scholes Option Pricing Model (Details) - $ / shares	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Common stock fair value	$ 53.39	$ 4.29
Risk-free interest rate	0.69%	0.51%
Expected volatility	79.86%	87.78%
Expected term (in years)	6 years	6 years

Share-Based Compensation - Su_3

Share-Based Compensation - Summary of Common Stock Reserved for Future Issuance (Details)	Mar. 31, 2021shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	7,133,714
Reserved for Future ESPP Issuances
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	622,652
Reserved for Future Equity Award Grants
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	2,325,631
Common Stock Options Granted and Outstanding
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	4,185,431

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income Tax Disclosure [Abstract]
Provision for income taxes	$ 0	$ 0

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) - Research Collaboration Agreement - CRISPR-Cas9	May 05, 2021	Mar. 31, 2021
Development and Regulatory Approval Milestones
Subsequent Event [Line Items]
Potential future payments		Totaling less than mid-twenty million dollars
Subsequent Event | NK Cell Products
Subsequent Event [Line Items]
Number of non-exclusive rights to gene editing targets	5