0001789769-21-000067 | 10-Q | XBRL Viewer

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Cover - shares	9 Months Ended
Cover - shares	Sep. 30, 2021	Nov. 12, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2021
Document Transition Report	false
Entity File Number	001-40215
Entity Registrant Name	Instil Bio, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	83-2072195
Entity Address, Address Line One	3963 Maple Avenue, Suite 350
Entity Address, City or Town	Dallas
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	75219
City Area Code	972
Local Phone Number	499-3350
Title of 12(b) Security	Common Stock, $0.000001 par value per share
Trading Symbol	TIL
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	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		128,926,778
Amendment Flag	false
Entity Central Index Key	0001789769
Current Fiscal Year End Date	--12-31
Document Fiscal Period Focus	Q3
Document Fiscal Year Focus	2021

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 20,400	$ 241,714
Marketable securities	494,958	0
Prepaid expenses and other current assets	7,729	4,424
Total current assets	523,087	246,138
Property, plant and equipment, net	103,690	55,341
Intangibles	10,104	10,104
Goodwill	5,722	5,722
Other long-term assets	4,794	1,707
Total assets	647,397	319,012
Current liabilities:
Accounts payable	5,254	3,495
Accrued expenses and other current liabilities	25,304	8,402
Contingent consideration, current portion	1,529	1,384
Total current liabilities	32,087	13,281
Contingent consideration, net of current portion	10,878	10,893
Deferred tax liabilities	1,475	2,471
Other long-term liabilities	1,537	0
Total liabilities	45,977	26,645
Commitments and contingencies (Note 7)
Convertible preferred stock, $0.000001 par value; 10,000,000 and 74,350,598 shares authorized as of September 30, 2021, and December 31, 2020, respectively; 0 and 70,176,046 shares issued and outstanding as of September 30, 2021, and December 31, 2020, respectively; $0 and $328,200 aggregate liquidation preference as of September 30, 2021, and December 31, 2020, respectively	0	331,966
Stockholders’ equity (deficit):
Common stock, $0.000001 par value; 300,000,000 and 111,000,000 shares authorized as of September 30, 2021, and December 31, 2020, respectively, 128,857,283 and 20,591,554 shares issued and outstanding as of September 30, 2021, and December 31, 2020, respectively	0	0
Additional paid-in capital	747,891	5,607
Accumulated other comprehensive loss	(104)	(283)
Accumulated deficit	(146,367)	(44,923)
Total stockholders’ equity (deficit)	601,420	(39,599)
Total liabilities, convertible preferred stock and stockholders’ equity (deficit)	$ 647,397	$ 319,012

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($)	Sep. 30, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Convertible preferred stock, par value (in dollars per share)	$ 0.000001	$ 0.000001
Convertible preferred stock, shares authorized (in shares)	10,000,000	74,350,598
Convertible preferred stock issued (in shares)	0	70,176,046
Convertible preferred stock outstanding (in shares)	0	70,176,046
Convertible preferred stock, liquidation preference	$ 0	$ 328,200,000
Common stock, par value (in dollars per share)	$ 0.000001	$ 0.000001
Common stock, shares authorized (in shares)	300,000,000	111,000,000
Common stock, shares issued (in shares)	128,857,283	20,591,554
Common stock, shares outstanding (in shares)	128,857,283	20,591,554

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Statement [Abstract]
Revenue	$ 0	$ 52	$ 0	$ 138
Operating expenses:
Research and development	29,064	4,908	64,674	9,152
General and administrative	13,960	2,855	37,134	7,153
Total operating expenses	43,024	7,763	101,808	16,305
Loss from operations	(43,024)	(7,711)	(101,808)	(16,167)
Interest and other (expense) income, net	(639)	449	(657)	(4,386)
Loss before income tax benefit	(43,663)	(7,262)	(102,465)	(20,553)
Income tax benefit	658	0	1,021	0
Net loss	(43,005)	(7,262)	(101,444)	(20,553)
Other comprehensive income (loss):
Foreign currency translation	124	17	197	(14)
Unrealized loss on available-for-sale securities, net	(18)	0	(18)	0
Net comprehensive loss	$ (42,899)	$ (7,245)	$ (101,265)	$ (20,567)
Net loss per share, basic (in dollars per share)	$ (0.33)	$ (0.43)	$ (1.03)	$ (1.32)
Net loss per share, diluted (in dollars per share)	$ (0.33)	$ (0.43)	$ (1.03)	$ (1.32)
Weighted-average shares used in computing net loss per share, basic (in shares)	128,794,142	16,928,831	98,256,027	15,616,389
Weighted-average shares used in computing net loss per share, diluted (in shares)	128,794,142	16,928,831	98,256,027	15,616,389

CONDENSED CONSOLIDATED STATEMENTS OF CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS’ EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Convertible preferred stock	Series A	Series B	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2019	15,000,000
Beginning balance at Dec. 31, 2019	$ 14,948
Ending balance (in shares) at Mar. 31, 2020	15,000,000
Ending balance at Mar. 31, 2020	$ 14,948
Beginning balance (in shares) at Dec. 31, 2019					11,199,980
Beginning balance at Dec. 31, 2019	(6,892)				$ 0	$ 293	$ 0	$ (7,185)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	62					62
Net loss	(4,089)							(4,089)
Foreign currency translation	(34)						(34)
Stock issued to acquire business (in shares)					5,640,000
Stock issued to acquire business	3,244					3,244
Ending balance (in shares) at Mar. 31, 2020					16,839,980
Ending balance at Mar. 31, 2020	$ (7,709)				$ 0	3,599	(34)	(11,274)
Beginning balance (in shares) at Dec. 31, 2019	15,000,000
Beginning balance at Dec. 31, 2019	$ 14,948
Ending balance (in shares) at Sep. 30, 2020	59,600,523
Ending balance at Sep. 30, 2020			$ 199,158
Beginning balance (in shares) at Dec. 31, 2019					11,199,980
Beginning balance at Dec. 31, 2019	$ (6,892)				$ 0	293	0	(7,185)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(20,553)
Foreign currency translation	(14)
Unrealized loss on available-for-sale securities, net	0
Ending balance (in shares) at Sep. 30, 2020					16,974,604
Ending balance at Sep. 30, 2020	$ (22,818)				$ 0	4,934	(14)	(27,738)
Beginning balance (in shares) at Mar. 31, 2020	15,000,000
Beginning balance at Mar. 31, 2020	$ 14,948
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of convertible preferred shares (in shares)			10,000,000	34,600,523
Issuance of convertible preferred shares			$ 14,366	$ 169,829
Ending balance (in shares) at Jun. 30, 2020	59,600,523
Ending balance at Jun. 30, 2020			$ 199,143
Beginning balance (in shares) at Mar. 31, 2020					16,839,980
Beginning balance at Mar. 31, 2020	$ (7,709)				$ 0	3,599	(34)	(11,274)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock from exercises of stock options (in shares)					9,374
Issuance of common stock from exercises of stock options	6					6
Stock-based compensation	899					899
Net loss	(9,202)							(9,202)
Foreign currency translation	3						3
Ending balance (in shares) at Jun. 30, 2020					16,849,354
Ending balance at Jun. 30, 2020	(16,003)				$ 0	4,504	(31)	(20,476)
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of convertible preferred shares (in shares)			1.00
Deferred financing costs for Series B	$ 15
Ending balance (in shares) at Sep. 30, 2020	59,600,523
Ending balance at Sep. 30, 2020			$ 199,158
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock from exercises of stock options (in shares)					125,250
Issuance of common stock from exercises of stock options	$ 99					99
Stock-based compensation	331					331
Net loss	(7,262)							(7,262)
Foreign currency translation	17						17
Unrealized loss on available-for-sale securities, net	0
Ending balance (in shares) at Sep. 30, 2020					16,974,604
Ending balance at Sep. 30, 2020	$ (22,818)				$ 0	4,934	(14)	(27,738)
Beginning balance (in shares) at Dec. 31, 2020	70,176,046		25,000,000	34,600,523
Beginning balance at Dec. 31, 2020	$ 331,966
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of convertible preferred shares (in shares)	4,174,551
Issuance of convertible preferred shares	$ 52,460
Conversion of redeemable convertible preferred stock (in shares)		(74,350,597)			(89,220,699)
Conversion of redeemable convertible preferred stock	$ (384,426)	$ (384,426)				(384,426)
Ending balance (in shares) at Mar. 31, 2021	0
Ending balance at Mar. 31, 2021	$ 0
Beginning balance (in shares) at Dec. 31, 2020					20,591,554
Beginning balance at Dec. 31, 2020	(39,599)				$ 0	5,607	(283)	(44,923)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common shares upon initial public offering net of underwriting discounts, commissions and offering costs (in shares)					18,400,000
Issuance of common shares upon initial public offering net of underwriting discounts, commissions and offering costs	339,174					339,174
Conversion of redeemable convertible preferred stock (in shares)		74,350,597			89,220,699
Conversion of redeemable convertible preferred stock	384,426	$ 384,426				384,426
Issuance of common stock from exercises of stock options (in shares)					530,870
Issuance of common stock from exercises of stock options	1,438					1,438
Stock-based compensation	2,812					2,812
Net loss	(23,128)							(23,128)
Foreign currency translation	30						30
Ending balance (in shares) at Mar. 31, 2021					128,743,123
Ending balance at Mar. 31, 2021	$ 665,153				$ 0	733,457	(253)	(68,051)
Beginning balance (in shares) at Dec. 31, 2020	70,176,046		25,000,000	34,600,523
Beginning balance at Dec. 31, 2020	$ 331,966
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of convertible preferred shares (in shares)	4,174,551
Ending balance (in shares) at Sep. 30, 2021	0
Ending balance at Sep. 30, 2021	$ 0
Beginning balance (in shares) at Dec. 31, 2020					20,591,554
Beginning balance at Dec. 31, 2020	$ (39,599)				$ 0	5,607	(283)	(44,923)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock from exercises of stock options (in shares)	3,820,528
Net loss	$ (101,444)
Foreign currency translation	197
Unrealized loss on available-for-sale securities, net	(18)
Ending balance (in shares) at Sep. 30, 2021					128,857,283
Ending balance at Sep. 30, 2021	$ 601,420				$ 0	747,891	(104)	(146,367)
Beginning balance (in shares) at Mar. 31, 2021	0
Beginning balance at Mar. 31, 2021	$ 0
Ending balance (in shares) at Jun. 30, 2021	0
Ending balance at Jun. 30, 2021	$ 0
Beginning balance (in shares) at Mar. 31, 2021					128,743,123
Beginning balance at Mar. 31, 2021	665,153				$ 0	733,457	(253)	(68,051)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	5,745					5,745
Net loss	(35,311)							(35,311)
Foreign currency translation	43						43
Deferred financing costs in connection with initial public offering	(158)					(158)
Ending balance (in shares) at Jun. 30, 2021					128,743,123
Ending balance at Jun. 30, 2021	$ 635,472				$ 0	739,044	(210)	(103,362)
Ending balance (in shares) at Sep. 30, 2021	0
Ending balance at Sep. 30, 2021	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock from exercises of stock options (in shares)					114,160
Issuance of common stock from exercises of stock options	121					121
Stock-based compensation	8,726					8,726
Net loss	(43,005)							(43,005)
Foreign currency translation	124
Other comprehensive income	106						106
Unrealized loss on available-for-sale securities, net	(18)
Ending balance (in shares) at Sep. 30, 2021					128,857,283
Ending balance at Sep. 30, 2021	$ 601,420				$ 0	$ 747,891	$ (104)	$ (146,367)

CONDENSED CONSOLIDATED STATEMENTS OF CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS’ EQUITY (DEFICIT) (Parenthetical) $ in Thousands	3 Months Ended
	Jun. 30, 2020 USD ($) $ / shares
Series A
Issuance costs \| $	$ 34
Series B
Shares issued, price per share (in dollars per share) \| $ / shares	$ 4.92

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash flows from operating activities:
Net loss	$ (101,444)	$ (20,553)
Adjustments to reconcile net loss to net cash used in operating activities:
Loss on issuance of Series A convertible preferred stock	0	4,400
Stock-based compensation	17,293	1,291
Foreign exchange remeasurement loss (gain)	602	(180)
Loss on change in fair value of contingent consideration	130	263
Depreciation and amortization	1,859	108
Accretion on marketable securities	12	0
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(2,877)	5
Other long-term assets	(3,160)	(29)
Accounts payable	3,750	(569)
Accrued expenses and current other liabilities	4,487	2,471
Net cash used in operating activities	(79,348)	(12,793)
Cash flows from investing activities:
Purchase of marketable securities	(699,987)	0
Maturities of marketable securities	205,000	0
Purchases of property, plant and equipment	(39,367)	(5,545)
Business acquisition, net of cash acquired	0	(306)
Net cash used in investing activities	(534,354)	(5,851)
Cash flows from financing activities:
Proceeds from initial public offering, net of issuance costs	339,016	0
Proceeds from issuance of convertible preferred stock, net of issuance costs	52,460	179,809
Proceeds from exercise of stock options	1,559	105
Other financing activities	(69)	63
Net cash provided by financing activities	392,966	179,977
Net (decrease) increase in cash and cash equivalents	(220,736)	161,333
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(128)	451
Cash, cash equivalents and restricted cash—beginning of period	241,764	8,895
Cash, cash equivalents and restricted cash—end of period	20,900	170,679
Supplemental disclosure of noncash information:
Conversion of preferred stock to common stock upon IPO	384,426	0
Purchases of property, plant and equipment in accounts payable and accrued liabilities	12,690	1,882
Business acquisition through issuance of common stock and contingent consideration payable	$ 0	$ 14,592

Organization and Description of Business	9 Months Ended
Organization and Description of Business	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Description of Business	Organization and Description of Business Instil Bio Inc. (the “Company” or “Instil Bio”) is headquartered in Dallas, Texas and was incorporated in the state of Delaware in August 2018. The Company is a clinical-stage biopharmaceutical company focused on developing an innovative cell therapy pipeline of autologous tumor infiltrating lymphocyte (“TIL”) therapies for the treatment of patients with cancer. Principal operations commenced during the first quarter of 2019 when the Company in-licensed its foundational TIL technology.

Summary of Significant Accounting Policies

9 Months Ended

Sep. 30, 2021

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

Basis of Presentation

The accompanying condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of the Company and its wholly owned subsidiaries Instil Bio (UK) Ltd. (formerly Immetacyte Ltd. (“Immetacyte”)) and Complex Therapeutics, LLC. Immetacyte was acquired on March 2, 2020 and Complex Therapeutics, LLC was incorporated on October 14, 2020. All intercompany balances and transactions have been eliminated in consolidation.

The unaudited condensed consolidated financial statements have been prepared on the same basis as the audited annual consolidated financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary for the fair statement of the Company’s financial position as of September 30, 2021, the condensed consolidated statements of operations and comprehensive loss for the three and nine months ended September 30, 2021 and 2020, the condensed consolidated statements of convertible preferred stock and stockholders' equity (deficit) for the three and nine months ended September 30, 2021 and 2020, and the results of its cash flows for the nine months ended September 30, 2021 and 2020. The financial data and other information disclosed in these notes related to the three and nine months ended September 30, 2021 and 2020 are also unaudited. The results for the three and nine months ended September 30, 2021 are not necessarily indicative of results to be expected for the year ending December 31, 2021, any other periods, or any future year period. The Company has evaluated subsequent events through the date the condensed consolidated financial statements were issued.

The accompanying unaudited condensed consolidated financial statements should be read in conjunction with the audited financial statements and the related notes thereto for the year ended December 31, 2020, which are included in the Company’s prospectus related to the initial public offering ("IPO"), filed with the Securities and Exchange Commission (“SEC”) on March 22, 2021 (the “Prospectus”), pursuant to Rule 424(b)(4) promulgated under the Securities Act of 1933, as amended (the “Securities Act”).

The preparation of condensed consolidated financial statements in conformity with GAAP and with the rules and regulations of the SEC requires management to make informed estimates and assumptions that affect the amounts reported in these condensed consolidated financial statements and accompanying notes. These amounts may materially differ from the amounts ultimately realized and reported due to the inherent uncertainty of any estimate or assumption.

Stock Split and Initial Public Offering

On March 12, 2021, the Company effected a 1.2-for-1 stock split of the Company’s common stock. The par value was not adjusted as a result of the stock split. The authorized shares as of March 12, 2021 were adjusted as a result of the stock split. All share and per share information included in the accompanying condensed consolidated

financial statements has been adjusted to reflect this stock split. The accompanying condensed consolidated financial statements and notes thereto give retroactive effect to the stock split for all periods presented.

On March 23, 2021, the Company completed its IPO through an underwritten sale of an aggregate of 18,400,000 shares of its common stock at a price of $20.00 per share. The aggregate net proceeds from the offering, inclusive of an additional 2,400,000 common shares sold upon the full exercise of the underwriter's purchase option, after deducting underwriting discounts and commissions and other offering expenses, was $339.0 million.

Concurrent with the IPO, all then-outstanding shares of the Company's convertible preferred stock outstanding (see Note 8) were automatically converted into an aggregate of 89,220,699 shares of common stock and were reclassified into permanent equity. Further, immediately following the closing of the IPO, the Company amended and restated its certificate of incorporation such that the total number of shares of common stock authorized to be issued was 300,000,000 and the total number of shares of preferred stock authorized to be issued was 10,000,000. Following the IPO, there are no shares of convertible preferred stock outstanding.

COVID-19 Pandemic

On March 11, 2020, the World Health Organization characterized the outbreak of COVID-19 as a global pandemic and recommended containment and mitigation measures. Since then, extraordinary actions have been taken by international, federal, state, and local public health and governmental authorities to contain and combat the outbreak and spread of COVID-19 in regions throughout the world. These actions include travel bans, quarantines, “stay-at-home” orders and similar mandates for many individuals to substantially restrict daily activities and for many businesses to curtail or cease normal operations. As a result of COVID-19, the Company has taken precautionary measures in order to minimize the risk of the virus to its employees and the communities in which it operates. Although the majority of the Company’s workforce now works remotely, there has been minimal disruption in the Company’s ability to ensure the effective operation of its business. While the broader implications of the COVID-19 pandemic on the Company’s results of operations and overall financial performance remain uncertain, including any implications from the spread of the new Delta variant of COVID-19, the COVID-19 pandemic has, to date, not had a material adverse impact on its results of operations or our ability to raise funds to sustain operations. The economic effects of the pandemic and resulting societal changes are currently not predictable, and the future financial impacts could vary from those foreseen.

Segments

Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business in one operating segment.

Cash, Cash Equivalents, Restricted Cash and Marketable securities

The Company considers all highly liquid investments purchased with original maturities of three months or less from the purchase date to be cash equivalents. Cash equivalents include amounts invested in money market accounts.

Restricted cash consists of a money market account which serves as collateral for the Company’s employee corporate credit cards and is classified within other long-term assets on the consolidated balance sheets.

Our short-term marketable securities have original maturities of less than a year at date of purchase. We classify and account for our marketable securities as available-for-sale securities, which are carried at their fair values based on the quoted market prices of the securities. Unrealized gains and losses are reported as accumulated other comprehensive loss. Realized gains and losses on available-for-sale securities are included in net loss in the period earned or incurred. As of September 30, 2021, marketable securities consisted of U.S. Treasury bills. The Company had no holdings of marketable securities as of December 31, 2020.

Short-term marketable securities are recorded at their estimated fair value. We periodically review whether our securities may be other-than-temporarily impaired, including whether or not (i) we have the intent to sell the security or (ii) it is more likely than not that we will be required to sell the security before its anticipated recovery. If one of these factors is met, we will record an impairment loss associated with our impaired investment. The impairment loss will be recorded as a write-down of investments in the condensed consolidated balance sheets and a realized loss within other expense in the condensed consolidated statements of operations.

The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the consolidated balance sheets that sum to the amounts shown in the consolidated statements of cash flows (in thousands):


	September 30, 2021		December 31, 2020
Cash and cash equivalents	$	20,400	$	241,714
Restricted cash	500		50
Cash, cash equivalents and restricted cash	$	20,900	$	241,764

Deferred Offering Costs

Costs that were directly related to the Company’s IPO were deferred for expense recognition and instead capitalized and recorded within other long-term assets on the accompanying condensed consolidated balance sheet. These costs consist of legal fees, accounting fees, and other applicable professional services. These deferred offering costs were reclassified to additional paid in capital upon the closing of the IPO. As of December 31, 2020, $0.5 million of deferred offering costs were capitalized.

Emerging Growth Company Status

The Company is an emerging growth company, as defined in the Jumpstart Our Business Startups Act of 2012 (the “JOBS Act”). Under the JOBS Act, emerging growth companies can delay adopting new or revised accounting standards issued subsequent to the enactment of the JOBS Act until such time as those standards apply to private companies. The Company has elected to avail itself of this extended transition period for complying with new or revised accounting standards that have different effective dates for public and private companies until the earlier of the date that it (i) is no longer an emerging growth company or (ii) affirmatively and irrevocably opts out of the extended transition period provided in the JOBS Act. As a result, these condensed consolidated financial statements may not be comparable to companies that comply with the new or revised accounting pronouncements as of public company effective dates.

Recent Accounting Pronouncements Not Yet Adopted

In December 2019, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. The standard simplifies the accounting for income taxes by removing certain exceptions to the general principles in Topic 740 and also improves consistent application by clarifying and amending existing guidance. The standard is effective for fiscal years beginning after December 15, 2021 and interim periods within fiscal years beginning after December 15, 2022. The Company currently is assessing the impact of this guidance and on its financial statements.

In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) which supersedes FASB ASC Topic 840, Leases (Topic 840) and provides principles for the recognition, measurement, presentation, and disclosure of leases for both lessees and lessors. The new standard requires the lessees to classify leases as either finance or operating leases based on the principle of whether or not the lease is effectively a financed purchase by the lessee, and such classification will determine whether lease expense is recognized based on an effective interest

method or on a straight-line basis over the term of the lease, respectively. A lessee is also required to record a right-of-use asset and a lease liability for all leases with a term of greater than twelve months regardless of classification. Leases with a term of twelve months or less will be accounted for similar to existing guidance for operating leases. In November 2019, the FASB issued ASU No. 2019-10, Financial Instruments—Credit Losses (Topic 326), Derivatives and Hedging (Topic 815), and Leases (Topic 842): Effective Dates, which revised the effective date for ASU No. 2016-02, Leases (Topic 842) for fiscal years beginning after December 15, 2020. In June 2020, the FASB issued ASU No. 2020-05, Revenue From Contracts With Customers (Topic 606) and Leases (Topic 842): Effective Dates for Certain Entities, further delaying the effective date for ASU No. 2016-02, Leases (Topic 842) to fiscal years beginning after December 15, 2021 and interim periods within fiscal years beginning after December 15, 2022. The Company immediately adopted ASU No. 2019-10 and ASU No. 2020-05 upon issuance by the FASB. The Company currently is assessing the impact of this guidance and on its financial statements.

Balance Sheet Components

9 Months Ended

Sep. 30, 2021

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Balance Sheet Components

Prepaid Expenses and Other Current Assets

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


	September 30, 2021		December 31, 2020
Prepaid research and development expenses	$	1,226	$	761
Prepaid general and administration expenses	2,859		420
Grant receivable	861		571
U.K. research and development tax and expenditure credits	2,299		799
Other receivables	484		1,803
Other current assets	—		70
Total prepaid expenses and other current assets	$	7,729	$	4,424

Property, Plant and Equipment, Net

Property, plant and equipment, net consist of the following (in thousands):


	September 30, 2021		December 31, 2020
Land	$	31,243	$	31,243
Building	6,309		6,309
Laboratory equipment	14,281		6,590
Manufacturing equipment	1,700		2,355
Office and computer equipment	2,182		1,510
Vehicles	64		—
Leasehold improvements	1,423		1,312
Construction work-in-progress	48,575		6,328
Total property, plant and equipment, gross	105,777		55,647
Less: accumulated depreciation	(2,087)		(306)
Total property, plant and equipment, net	$	103,690	$	55,341

Depreciation expense was $0.8 million and an immaterial amount for the three months ended September 30, 2021 and 2020, respectively, and was $1.9 million and an immaterial amount for the nine months ended September 30, 2021 and 2020, respectively, in the condensed consolidated statements of operations and comprehensive loss.

In October 2020, the Company acquired land inclusive of four buildings in Tarzana, California, for $37.6 million. The Company is in the process of developing this land for its United States ("U.S.") operations and

has capitalized $44.2 million in work in progress costs associated with this development project. The Company’s contractual commitments for this development project are limited to unreimbursed spend by the general contractor and as such, as of September 30, 2021, and December 31, 2020, $78.7 million and $6.3 million, respectively, is contractually committed to the development of this project. This acquisition is classified as an asset acquisition for which the Company records identifiable assets acquired at cost on a relative fair value basis. The most significant components of the allocation of fair value are four buildings as-if-vacant and land.

Other Long-term Assets

Other long-term assets consist of the following (in thousands):


	September 30, 2021		December 31, 2020
Deferred rent	$	2,088	$	509
Prepaid research and development expenses	2,024		603
Prepaid general and administration expenses	71		—
Security deposit	111		29
Restricted cash	500		50
Deferred offering costs	—		516
Total other long-term assets	$	4,794	$	1,707

Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consist of the following (in thousands):


	September 30, 2021		December 31, 2020
Accrued compensation and benefits	$	9,157	$	3,983
Accrued construction costs	11,178		302
Accrued research and development expenses	3,034		1,616
Accrued operational expenses	1,265		1,589
Current tax liabilities	436		631
Other current liabilities	234		281
Total accrued expenses and other current liabilities	$	25,304	$	8,402

Transactions with Immetacyte

9 Months Ended

Sep. 30, 2021

Business Combinations [Abstract]

Transactions with Immetacyte

License Agreement with Immetacyte

In February 2019, the Company entered into an Exclusive License & Research Services Agreement (the “License Agreement”) with Immetacyte, whose key founders are also shareholders of the Company, pursuant to which the Company obtained a worldwide license to Immetacyte’s proprietary technology, know-how and intellectual property for the research, development and manufacture of TIL therapies obtained from tumors using Immetacyte’s technology.

The payments made for the license of the TIL technology were accounted for as in-process research and development (“IPR&D”) as part of an asset acquisition and were expensed as it was determined that there was no alternative future use for the license. The Company accounts for contingent consideration payable upon achievement of certain development or commercial milestones when the underlying contingency is resolved. For the three months ended September 30, 2020, the Company recognized $0.6 million of IPR&D, which consisted of $0.3 million paid up front for the license and $0.3 million paid for achievement of a development milestone, which was recognized as a component of research and development expense in the Company’s statement of operations and comprehensive loss.

Additionally, the Company was obligated to make payments for the research and development, manufacturing, monitoring and general services which included: (i) research and development services payments of $1.9 million annually for each of the first three years, (ii) manufacturing services payments of $1.2 million for the first annual period and $1.6 million for two years thereafter, and (iii) $0.3 million for monitoring and general services.

For the nine months ended September 30, 2020, the Company recorded $0.6 million of research and development expense in the statement of operations and comprehensive loss as part of these services.

Upon the acquisition of Immetacyte, the License Agreement was terminated.

Acquisition of Immetacyte

In March 2020, the Company acquired 100% of the share capital of Immetacyte for $0.8 million in cash consideration, 5.6 million shares of common stock at an estimated fair value of $0.58 per share and up to an aggregate of $14.8 million of cash contingent consideration. The contingent consideration was additional cash consideration payable to the seller up until January 31, 2040 upon achievement of distinct product development milestones. The Company believes the acquisition, which includes the dedicated workforce of Immetacyte, will better position itself in developing an innovative cell therapy pipeline of autologous TIL therapies for the treatment of patients with cancer.

The fair value of consideration paid was as follows (in thousands):


Cash consideration	$	779
Common stock of 5,640,000 shares at an estimated fair value of $0.58 per share	3,243
Contingent consideration	11,349
Total consideration	$	15,371

The allocation of the purchase consideration was based on management’s estimate of the acquisition date fair values of the assets acquired and liabilities assumed, as follows (in thousands):


Assets acquired:
Net working capital	$	870
Property and equipment	690
Intangibles	10,104
Total assets acquired	11,664
Goodwill	5,722
Deferred tax liabilities	(2,015)
Total purchase price	$	15,371

The acquisition was accounted for as a business combination and, accordingly, the total fair value of purchase consideration was allocated to the tangible and intangible assets acquired and liabilities assumed based on their fair values on the acquisition date. Due to the Company’s pre-commercialization stage, many of the processes and methods used in the production of TILs were still in experimental development and pre-clinical stages and as such, resulted in a $10.1 million IPR&D asset. To value the IPR&D, the Company utilized the multi-period excess earnings method under the income approach. The method reflects the present value of the operating cash flows generated by this asset after taking into account the cost to realize the revenue, and an appropriate discount rate to reflect the time value and risk associated with the invested capital. These assumptions were applied to a relief-from-royalty model.

Within net working capital, was $0.8 million of acquired gross trade receivables, all of which has been collected. Goodwill is attributable to the assembled workforce and expected synergies from combining operations.

The goodwill recognized for this acquisition is not deductible for income tax purposes. From the acquisition date through September 30, 2021, there has been no change in the carrying amount of goodwill. Because the acquired IPR&D has an indefinite life, it is not amortized but rather evaluated for impairment. As of September 30, 2021 and, December 31, 2020 IPR&D was not impaired.The Company recognized acquisition costs of an immaterial amount and $0.9 million for the three and nine months ended September 30, 2020, which were expensed as incurred within general and administrative on the condensed consolidated statements of operations and comprehensive loss.

Fair Value Measurement

9 Months Ended

Sep. 30, 2021

Fair Value Disclosures [Abstract]

Fair Value Measurement

The fair value of cash and cash equivalents approximates carrying value since cash and cash equivalents consist of short-term highly liquid investments with maturities of less than three months at the time of purchase. Cash and cash equivalents are quoted market prices in active markets for identical assets and are therefore classified as Level 1 assets. Money market funds are open-end mutual funds that invest in cash, government securities, and/or repurchase agreements that are collateralized fully. To the extent that these funds are valued based upon the reported net asset value, they are categorized in Level 1 of the fair value hierarchy.

Short-term marketable securities comprised of U.S. Treasury bills that are classified within Level 2 of the fair value hierarchy are valued based on other observable inputs, including broker or dealer quotations, alternative pricing sources or U.S. Government Treasury yield of appropriate term.

The following tables provide information by level for assets and liabilities that are measured at fair value on a recurring basis:


	As of September 30, 2021
	Level 1		Level 2		Level 3		Total
	(In thousands)
Financial Assets
Money market funds	$	15,296	$	—	$	—	$	15,296
U.S. Treasury bills	—		494,958		—		494,958
Total	$	15,296	$	494,958	$	—	$	510,254
Financial Liabilities
Contingent consideration	$	—	—		12,407		$	12,407

	As of December 31, 2020
	Level 1		Level 2		Level 3		Total
	(In thousands)
Financial Assets
Money market funds	$	106,138	—		—		$	106,138
Financial Liabilities
Contingent consideration	$	—	—		12,277		$	12,277

There were no transfers in and out of Level 1, 2 and 3 measurements for the nine months ended September 30, 2021 and the year ended December 31, 2020. As of September 30, 2021 and December 31, 2020, there were no securities within Level 3 of the fair value hierarchy. The following table sets forth a summary of the changes in the fair value of the Company's Level 3 financial liabilities (in thousands):


	Nine Months Ended September 30, 2021
Fair value, beginning balance	$	12,277
Change in fair value	130
Fair value, ending balance	$	12,407


	Year Ended December 31, 2020
Fair value, beginning balance	$	—
Contingent consideration recorded as a result of Immetacyte acquisition	11,349
Change in present value of contingent consideration	928
Fair value, ending balance	$	12,277

The Company’s acquisition of Immetacyte involved the potential for the payment of future contingent consideration upon the achievement of (i) certain product development milestones including, approval of studies and commencement and completion of certain product trials, or (ii) various other performance conditions including, receipt of final approval for the first marketing authorization and first commercial sale in certain geographical markets. Contingent consideration is recorded at the estimated fair value of the contingent payments on the acquisition date. The fair value of the contingent consideration is remeasured at the estimated fair value at each reporting period with the change in fair value recognized as income or expense within research and development expense in the consolidated statements of operations and comprehensive loss.

During the nine months ended September 30, 2021, the change of fair value related to the contingent consideration is attributable to the change to present value unwinding, as well as expected dates and probabilities of milestone achievement revisions. During the nine months ended September 30, 2021, no contingent consideration payments were made by the Company.

During the year ended December 31, 2020, the Company determined the fair value of the contingent consideration by probability weighting scenarios of milestone achievements to determine the expected future contingent consideration payment, discounted to present value using an 8.5% discount rate based on the Company’s pre-tax cost of debt on the acquisition date. The probability of payments ranged from 20% to 100% and the timing of future payments ranged from 2020 to 2026. In determining the likelihood of milestone achievements which trigger payouts related to the contingent consideration, the probabilities for various scenarios, as well as the discount rate used in the Company’s calculations were based on internal unobservable projections. During the year ended December 31, 2020, no contingent consideration payments were made by the Company. As a result, as of December 31, 2020, the estimated future payments included the payment previously expected to be made in late 2020. As of December 31, 2020, the probability and timing of payments ranged from 20% to 100% and 2021 to 2026, respectively. As of December 31, 2020, the discount rate used in discounting the expected contingent consideration payments changed to 8% based on the Company’s pre-tax cost of debt, which increased the fair value of the contingent consideration by $0.9 million from the acquisition date.

- 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

Financial Instruments

9 Months Ended

Sep. 30, 2021

Investments, Debt and Equity Securities [Abstract]

Financial Instruments

Marketable securities classified as available-for-sale at September 30, 2021 consisted of the following (in thousands):


	Maturity	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
U.S. Treasury bills	Less than one year	$	494,976	$	—	$	(18)	$	494,958

As of September 30, 2021, all marketable securities had contractual maturities less than one year. We do not intend to sell our marketable securities and it is not likely that we will be required to sell these securities before recovery of their amortized cost bases. There were no marketable securities classified as available for sale at December 31, 2020.

Commitments and Contingencies

9 Months Ended

Sep. 30, 2021

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

Operating Leases

The Company leases various operating spaces in the U.S. and United Kingdom ("U.K.") under non-cancelable operating lease arrangements that expire on various dates through the end of 2026. These arrangements require the Company to pay certain operating expenses, such as service charges, taxes, repairs, and insurance and contain landlord or tenant incentives or allowances, renewal escalation causes. The Company recognizes rent expense under these arrangements on a straight-line basis over the term of the lease and records the difference between the rent paid and recognition of rent expense as a deferred rent liability. Total rent expense was $0.6 million and $0.2 million for the three months ended September 30, 2021 and 2020, respectively, and $1.8 million and $0.2 million for the nine months ended September 30, 2021 and 2020, respectively.

Future minimum lease payments under noncancellable operating leases as of September 30, 2021 were as follows (in thousands):


2021 (remaining three months)	$	597
2022	2,469
2023	2,352
2024	2,200
2025 and thereafter	3,182
Total	$	10,800

Legal Proceedings

From time to time, the Company may have certain contingent liabilities that arise in the ordinary course of its business activities. The Company accrues a liability for such matters when it is probable that future expenditures will be made and that such expenditures can be reasonably estimated. Significant judgment is required to determine both probability and the estimated amount. The Company does not expect that the resolution of these matters will have a material adverse effect on its financial position, results of operations or cash flows.

Commitments and Contingencies

Operating Leases

Future minimum lease payments under noncancellable operating leases as of September 30, 2021 were as follows (in thousands):


2021 (remaining three months)	$	597
2022	2,469
2023	2,352
2024	2,200
2025 and thereafter	3,182
Total	$	10,800

Legal Proceedings

Equity

9 Months Ended

Sep. 30, 2021

Equity [Abstract]

Equity

Common Stock

Each share of common stock has the right to one vote. The holders of common stock are also entitled to receive dividends whenever funds are legally available and if declared by the board of directors, subject to the prior rights of holders of all classes of stock outstanding having priority rights as to dividends. No cash dividends have been declared by the board of directors from inception.

In March 2020, the Company issued 5.6 million shares of its common stock at an estimated fair value of $0.58 per share to purchase Immetacyte (see Note 4).

In November 2020, the Company executed a limited recourse promissory note with its Chief Executive Officer (“CEO”), Bronson Crouch, in the amount of $1.1 million which was secured by a pledge of a total of 3.2 million shares of its common stock issued upon exercise of vested stock options. The note bore an interest rate of

2.5% per annum with a maturity date of the earlier of (i) five years from the date of the note or (ii) one business day prior to the filing or submission of the Company’s first registration statement covering the Company’s common stock with the SEC. The principal and interest under the note may be repaid at any time without penalty. Because the Company only has partial recourse under the promissory note, the Company deemed the note receivable to be non-substantive. As such, the note receivable was not reflected in the condensed consolidated financial statements and the related stock transaction will be recorded at the time the note receivable is settled in cash. As of December 31, 2020, the outstanding balance of the promissory note was $1.1 million. The promissory note was fully repaid in January 2021.

On March 23, 2021, the Company completed its IPO through an underwritten sale of an aggregate of an aggregate of 18,400,000 shares of its common stock at a price of $20.00 per share (see Note 2).

As of September 30, 2021, the Company had outstanding 128,857,283 shares of common stock.

Convertible Preferred Stock

As of December 31, 2020, there were 70,176,046 shares of preferred stock outstanding and the Company issued 4,174,551 shares of the Company Series C convertible preferred stock subsequent to December 31, 2020. Concurrent with the IPO, all then-outstanding shares of the Company's convertible preferred stock outstanding were automatically converted into an aggregate of 89,220,699 shares of common stock and were reclassified into permanent equity. Following the IPO, there are no shares of preferred stock outstanding.

Convertible preferred stock consisted of the following (in thousands, except shares):


	As of December 31, 2020
	Shares Authorized	Shares Issued and Outstanding	Aggregate Liquidation Preference
Series A	25,000,000	25,000,000	$	25,000
Series B	34,600,523	34,600,523	170,200
Series C	14,750,075	10,575,523	133,000
	74,350,598	70,176,046	$	328,200

All outstanding shares of convertible preferred stock were converted on a 1.2-for-1 conversion ratio of shares of common stock on March 23, 2021, the date of closing of the Company's IPO (see Note 2).

The Company classified the convertible preferred stock outside of total stockholders’ deficit because, in the event of certain deemed liquidation events that are not solely within the control of the Company, the shares would become redeemable at the option of the holders. The Company did not adjust the carrying values of the convertible preferred stock to the deemed liquidation values of such shares since a liquidation event was not probable of occurring at December 31, 2020. Subsequent adjustments to increase or decrease the carrying values to the ultimate liquidation values will be made only if, and when, it becomes probable that such a liquidation event will occur.

As of December 31, 2020, the holders of the Company’s convertible preferred stock had various rights, preferences and privileges as follows:

Voting Rights

The holders of convertible preferred stock were entitled to cast the number of votes equal to the number of shares of common stock into which the shares of convertible preferred stock held by such holder were convertible as

of the record date at any shareholder meeting of the Company. Except as provided by law or by the other provisions of the Company’s amended and restated certificate of incorporation, holders of convertible preferred stock and common stock were entitled to vote together as a single class. Holders of Series A convertible preferred stock, exclusively and as a separate class, were entitled to elect one member of the Company’s board of directors and holders of Series B convertible preferred stock, exclusively and as a separate class, were entitled to elect three members to the Company’s board of directors.

Dividends

Holders of convertible preferred stock were entitled to receive noncumulative cash dividends in an amount equal to 8% of their respective original (pre-split) issue price of $1.00, $4.92 and $12.58 for Series A, Series B and Series C convertible preferred stock, respectively, per annum per share (subject to appropriate adjustment in the event of any stock dividends, stock splits, stock combinations, recapitalizations or similar events), when and if declared by the Company’s board of directors, prior and in preference to the holders of common stock. As of September 30, 2021, no dividends had been declared.

Liquidation

In the event of any voluntary or involuntary liquidation, dissolution or winding up of the Company or deemed liquidation event, the holders of shares of Series C convertible preferred stock were entitled to receive, prior and in preference to any distribution to the holders of Series B convertible preferred stock, an amount equal to the greater of (i) $12.58 per share, plus any dividends declared but unpaid or (ii) such amount per share as would have been payable in respect of each share of Series C convertible preferred stock had all shares of Series C convertible preferred stock been converted into common stock immediately prior to such liquidation, dissolution, winding up or deemed liquidation event. After the required payment to Series C convertible stockholders, holders of shares of Series B convertible preferred stock were entitled to receive, prior and in preference to any distribution to the holders of Series A convertible preferred stock, an amount equal to the greater of (i) $4.92 per share, plus any dividends declared but unpaid or (ii) such amount per share as would have been payable in respect of each share of Series B convertible preferred stock had all shares of Series B convertible preferred stock been converted into common stock immediately prior to such liquidation, dissolution, winding up or deemed liquidation event. After the required payment to Series B convertible stock holders, holders of shares of Series A convertible preferred stock were entitled to receive, prior and in preference to any distribution to the holders of common stock, an amount equal to the greater of (i) $1.00 per share, plus any dividends declared but unpaid or (ii) such amount per share as would have been payable in respect of each share of Series A convertible preferred stock had all shares of Series A convertible preferred stock been converted into common stock immediately prior to such liquidation, dissolution, winding up or deemed liquidation event. After the required payment is made to the preferred stockholders, the remaining assets of the Company, if any, were to be distributed to the holders of common stock pro rata based on the number of shares held by each such holder.

Optional Conversion Rights

Each share of convertible preferred stock was convertible, at the option of the holder, into such number of shares of common stock as was determined by dividing the original issue price for that series by the conversion price for such series in effect at the time of conversion. The conversion price was $0.83, $4.10 and $10.48 per share with respect to the shares of Series A, Series B and Series C convertible preferred stock, respectively, and was subject to certain anti-dilution adjustments.

Mandatory Conversion

Each share of convertible preferred stock was to be automatically converted into shares of common stock at the then effective conversion ratio for such share upon the earlier of (i) the closing of the sale of shares of common stock to the public at a price of at least $12.58 per share (subject to appropriate adjustment in the event of any stock dividend, stock split, combination or other similar recapitalization) with the gross cash proceeds to the Company of at least $100 million, or (ii) the date and time, or the occurrence of an event, specified by vote or written consent of

the holders of at least a majority of outstanding shares of (a) Series B convertible preferred stock, (b) Series C convertible preferred stock not also holding Series B convertible preferred stock, and (c) all convertible preferred stock.

2021 Preferred Stock Activity

All currently outstanding shares of convertible preferred stock were converted into an aggregate of 89,220,699 shares of common stock on March 23, 2021, the closing date of the Company's IPO (see Note 2). After the completion of the IPO, the Company's current amended and restated certificate of incorporation authorizes the Company to issue up to 10,000,000 shares of preferred stock at $0.000001 par value per share. The board of directors are authorized to provide for the issue of the shares of the preferred stock in one or more series, and to fix the number of shares and to determine or alter for each such series, such voting powers, full or limited, or no voting powers, and such designation, preferences, and relative, participating, optional, or other rights and such qualifications, limitations, or restrictions thereof, as shall be stated and expressed in subsequent resolution or resolutions adopted by the board providing for the issuance of such shares. As of September 30, 2021, there have been no shares of preferred stock issued and outstanding by the Company.

Stock-Based Compensation

9 Months Ended

Sep. 30, 2021

Share-based Payment Arrangement [Abstract]

Stock-Based Compensation

2021 Equity Incentive Plan

In March 2021, the Company adopted the 2021 Equity Incentive Plan (the “2021 Plan”), which became effective in connection with the IPO. The 2021 Plan was approved by the Company’s board of directors and stockholders in March 2021. The 2021 Plan is an equity incentive plan pursuant to which the Company may grant the following awards: (i) incentive stock options; (ii) nonstatutory stock options; (iii) stock appreciation rights; (iv) restricted stock awards; (v) restricted stock unit awards; (vi) performance awards; and (vii) other forms of stock awards to employees, directors, and consultants, including employees and consultants of the Company’s affiliates. The 2021 Plan is a successor to the Company's 2018 Stock Incentive Plan (the “2018 Plan”). Following the effectiveness of the 2021 Plan, no further grants may be made under the 2018 Plan; however, any outstanding equity awards granted under the 2018 Plan will continue to be governed by the terms of the 2018 Plan.

The number of shares available for future issuance under the 2021 Plan is the sum of (1) 8,660,000 new shares of common stock, (2) 4,194,437 remaining shares of common stock reserved under the 2018 Plan that became available for issuance upon the effectiveness of the 2021 Plan and (3) the number of shares of common stock subject to outstanding awards under the 2018 Plan when the 2021 Plan became effective that thereafter expire or are forfeited, canceled, withheld to satisfy tax withholding or to purchase or exercise an award, repurchased by the Company or are otherwise terminated. The number of shares of common stock reserved for issuance under the 2021 Plan will automatically increase on January 1 of each year, for a period of ten years, from January 1, 2022 continuing through January 1, 2031, by 5% of the total number of shares of common stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares as may be determined by the Company’s board of directors. Stock options granted by the Company to employees generally vest over four years with a one year cliff.

As of September 30, 2021, 10,547,900 shares of common stock remained available for issuance under the 2021 Plan. As of September 30, 2021, the total number of shares authorized for issuance under the 2021 Plan was 12,854,437 shares.

The following summarizes option activity under the 2021 Plan:


	Shares Available for Grant	Shares Issuable Under Options	Weighted- Average Exercise Price		Weighted- Average Remaining Contract Term (in years)	Aggregate Intrinsic Value (in thousands)
Balance, December 31, 2020	10,217,237	15,331,923	$	0.80	9.22	$	78,857
Additional Shares Authorized	8,660,000
Options granted(1)	(8,604,737)	8,604,737	$	9.57
Options forfeited	275,400	(275,400)	$	2.92
Options exercised	—	(3,820,528)	$	0.41
Balance, September 30, 2021	10,547,900	19,840,732	$	4.65	8.99	$	265,567
Exercisable, September 30, 2021		4,249,857	$	1.69	8.52	$	68,914
Vested and expected to vest, September 30, 2021		4,369,857	$	1.67	8.52	$	70,960

______________________________________________________________

(1) Includes 2,252,137 stock options subject to performance conditions.

The aggregate intrinsic value disclosed in the above table is based on the difference between the exercise price of the stock option and the estimated fair value of the Company’s common stock as of the respective period-end dates. There were 3,820,528 stock options exercised during the nine months ended September 30, 2021. For the nine months ended September 30, 2021, the estimated weighted-average grant-date fair value of employee options granted was $11.57 per share.

The following table sets forth stock-based compensation included in the Company’s statement of operations and comprehensive loss (in thousands):


	Three Months Ended September 30,				Nine Months Ended September 30,
	2021		2020		2021		2020
Research and development expense	$	4,677	$	125	$	8,127	$	252
General and administrative expense	4,057		206		9,166		1,039
Total stock-based compensation expense	$	8,734	$	331	$	17,293	$	1,291

As of September 30, 2021, there was $68.7 million of total unrecognized compensation cost related to unvested stock options granted under the 2018 Plan (excluding performance awards), which is expected to be recognized over a weighted average period of 2.35 years.

The fair value of the Company’s stock option awards was estimated at the date of grant using a Black-Scholes option pricing model with the following assumptions:


	Nine Months Ended September 30,
	2021				2020
Expected term (in years)	5.77		—	6.24	5.27		—	6.08
Expected volatility	75.97	%	—	89.11%	69.69	%	—	82.64%
Risk-free interest rate	0.51	%	—	1.09%	0.42	%	—	1.76%
Fair value of common stock	$6.68		—	$26.44	$0.41		—	$1.38
Expected dividend yield	—%				—%

Prior to the Company's IPO in March 2021, the fair value of the shares of common stock underlying stock options has historically been determined by the Company’s board of directors. Because there has been no public market for the Company’s common stock, the board of directors has determined fair value of the common stock at the time of grant of the option by considering a number of objective and subjective factors including important

developments in the Company’s operations, contemporaneous valuations performed by an independent third party firm, sales of the Company’s convertible preferred stock, the Company’s operating results and financial performance, the conditions in the biotechnology industry and the economy in general, the stock price volatility of similar public companies and the lack of marketability of the Company’s common stock, among other factors. After the Company’s IPO in March 2021, the fair value of common stock is determined using the closing price of the Company’s common stock on the Nasdaq Global Select Market.

The Black-Scholes option pricing model requires the use of highly subjective assumptions which determine the fair value of stock-based awards. These assumptions include:

Expected term—The expected term represents the period that stock-based awards are expected to be outstanding and is determined as the average of the time-to-vesting and the contractual life of the awards.

Expected volatility—Since the Company is privately held and does not have any trading history for its common stock, the expected volatility was estimated based on the average volatility for comparable publicly traded biotechnology 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 or area of specialty.

Risk-free interest rate—The risk-free interest rate is based on the U.S. Treasury zero coupon issues in effect at the time of grant for periods corresponding with the expected term of awards.

Expected dividend yield—The Company has never paid dividends on its common stock and has no plans to pay dividends on its common stock. Therefore, the Company used an expected dividend yield of zero.

Performance Awards

During the nine months ended September 30, 2021, the Company granted 2,252,137 stock options to both employees and non-employees that are subject to a performance condition and will begin vesting upon the consummation of a strategic transaction by the Company prior to December 31, 2022, which is expected to be recognized over a weighted average period of 3.29 years. A strategic transaction has been defined as (a) a change in control, (b) the Company’s next capital raise or (c) an initial public offering of the Company’s shares, in which the Company receives at least $50.0 million in gross proceeds. As of September 30, 2021, this performance condition was determined to be achieved, and the Company has recognized $3.2 million stock-based compensation expense relating to these performance awards. As of September 30, 2021, the Company had $21.2 million of unrecognized compensation cost relating to these performance awards, calculated using the accelerated attribution method and the grant date fair value of the awards.

Employee Stock Purchase Plan

In March 2021, the Company adopted the Employee Stock Purchase Plan (the “ESPP”), which became effective in connection with the IPO. The ESPP was adopted by the Company’s board of directors and stockholders in March 2021. The ESPP initially provides participating employees with the opportunity to purchase up to an aggregate of 1,237,000 shares of common stock. The number of shares of common stock reserved for issuance will automatically increase on January 1st of each calendar year for a period of up to ten years, commencing on January 1, 2022 and ending on (and including) January 1, 2031, in an amount equal to the lesser of (i) one percent (1%) of the total number of shares of capital stock outstanding on the last day of the calendar month before the date of the automatic increase, and (ii) 2,474,000 shares of common stock. Notwithstanding the foregoing, the board may act prior to the first day of any calendar year to provide that there will be no January 1st increase in the share reserve for such calendar year or that the increase in the share reserve for such calendar year will be a lesser number of shares of common stock than would otherwise occur pursuant to the preceding sentence.

Net Loss Per Share

9 Months Ended

Sep. 30, 2021

Earnings Per Share [Abstract]

Net Loss Per Share

The following outstanding potentially dilutive shares have been excluded from the calculation of diluted net loss per share for the periods presented due to their anti-dilutive effect:


	September 30,
	2021	2020
Convertible preferred stock	—	59,600,523
Stock options to purchase common stock	19,840,732	14,343,832
Total	19,840,732	73,944,355

All outstanding shares of convertible preferred stock were converted on a 1.2-for-1 conversion ratio of shares of common stock on March 23, 2021, the date of the Company's IPO (see Note 2).

Summary of Significant Accounting Policies (Policies)	9 Months Ended
Summary of Significant Accounting Policies (Policies)	Sep. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of the Company and its wholly owned subsidiaries Instil Bio (UK) Ltd. (formerly Immetacyte Ltd. (“Immetacyte”)) and Complex Therapeutics, LLC. Immetacyte was acquired on March 2, 2020 and Complex Therapeutics, LLC was incorporated on October 14, 2020. All intercompany balances and transactions have been eliminated in consolidation. The unaudited condensed consolidated financial statements have been prepared on the same basis as the audited annual consolidated financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary for the fair statement of the Company’s financial position as of September 30, 2021, the condensed consolidated statements of operations and comprehensive loss for the three and nine months ended September 30, 2021 and 2020, the condensed consolidated statements of convertible preferred stock and stockholders' equity (deficit) for the three and nine months ended September 30, 2021 and 2020, and the results of its cash flows for the nine months ended September 30, 2021 and 2020. The financial data and other information disclosed in these notes related to the three and nine months ended September 30, 2021 and 2020 are also unaudited. The results for the three and nine months ended September 30, 2021 are not necessarily indicative of results to be expected for the year ending December 31, 2021, any other periods, or any future year period. The Company has evaluated subsequent events through the date the condensed consolidated financial statements were issued. The accompanying unaudited condensed consolidated financial statements should be read in conjunction with the audited financial statements and the related notes thereto for the year ended December 31, 2020, which are included in the Company’s prospectus related to the initial public offering ("IPO"), filed with the Securities and Exchange Commission (“SEC”) on March 22, 2021 (the “Prospectus”), pursuant to Rule 424(b)(4) promulgated under the Securities Act of 1933, as amended (the “Securities Act”). The preparation of condensed consolidated financial statements in conformity with GAAP and with the rules and regulations of the SEC requires management to make informed estimates and assumptions that affect the amounts reported in these condensed consolidated financial statements and accompanying notes. These amounts may materially differ from the amounts ultimately realized and reported due to the inherent uncertainty of any estimate or assumption.
COVID-19 Pandemic	COVID-19 Pandemic On March 11, 2020, the World Health Organization characterized the outbreak of COVID-19 as a global pandemic and recommended containment and mitigation measures. Since then, extraordinary actions have been taken by international, federal, state, and local public health and governmental authorities to contain and combat the outbreak and spread of COVID-19 in regions throughout the world. These actions include travel bans, quarantines, “stay-at-home” orders and similar mandates for many individuals to substantially restrict daily activities and for many businesses to curtail or cease normal operations. As a result of COVID-19, the Company has taken precautionary measures in order to minimize the risk of the virus to its employees and the communities in which it operates. Although the majority of the Company’s workforce now works remotely, there has been minimal disruption in the Company’s ability to ensure the effective operation of its business. While the broader implications of the COVID-19 pandemic on the Company’s results of operations and overall financial performance remain uncertain, including any implications from the spread of the new Delta variant of COVID-19, the COVID-19 pandemic has, to date, not had a material adverse impact on its results of operations or our ability to raise funds to sustain operations. The economic effects of the pandemic and resulting societal changes are currently not predictable, and the future financial impacts could vary from those foreseen.
Segments	Segments Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business in one operating segment.
Cash, Cash Equivalents and Restricted Cash	Cash, Cash Equivalents, Restricted Cash and Marketable securities The Company considers all highly liquid investments purchased with original maturities of three months or less from the purchase date to be cash equivalents. Cash equivalents include amounts invested in money market accounts. Restricted cash consists of a money market account which serves as collateral for the Company’s employee corporate credit cards and is classified within other long-term assets on the consolidated balance sheets.
Marketable securities	Our short-term marketable securities have original maturities of less than a year at date of purchase. We classify and account for our marketable securities as available-for-sale securities, which are carried at their fair values based on the quoted market prices of the securities. Unrealized gains and losses are reported as accumulated other comprehensive loss. Realized gains and losses on available-for-sale securities are included in net loss in the period earned or incurred. As of September 30, 2021, marketable securities consisted of U.S. Treasury bills. The Company had no holdings of marketable securities as of December 31, 2020. Short-term marketable securities are recorded at their estimated fair value. We periodically review whether our securities may be other-than-temporarily impaired, including whether or not (i) we have the intent to sell the security or (ii) it is more likely than not that we will be required to sell the security before its anticipated recovery. If one of these factors is met, we will record an impairment loss associated with our impaired investment. The impairment loss will be recorded as a write-down of investments in the condensed consolidated balance sheets and a realized loss within other expense in the condensed consolidated statements of operations.
Deferred Offering Costs	Deferred Offering CostsCosts that were directly related to the Company’s IPO were deferred for expense recognition and instead capitalized and recorded within other long-term assets on the accompanying condensed consolidated balance sheet. These costs consist of legal fees, accounting fees, and other applicable professional services. These deferred offering costs were reclassified to additional paid in capital upon the closing of the IPO.
Recent Accounting Pronouncements Not Yet Adopted	Recent Accounting Pronouncements Not Yet Adopted In December 2019, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. The standard simplifies the accounting for income taxes by removing certain exceptions to the general principles in Topic 740 and also improves consistent application by clarifying and amending existing guidance. The standard is effective for fiscal years beginning after December 15, 2021 and interim periods within fiscal years beginning after December 15, 2022. The Company currently is assessing the impact of this guidance and on its financial statements. In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) which supersedes FASB ASC Topic 840, Leases (Topic 840) and provides principles for the recognition, measurement, presentation, and disclosure of leases for both lessees and lessors. The new standard requires the lessees to classify leases as either finance or operating leases based on the principle of whether or not the lease is effectively a financed purchase by the lessee, and such classification will determine whether lease expense is recognized based on an effective interest method or on a straight-line basis over the term of the lease, respectively. A lessee is also required to record a right-of-use asset and a lease liability for all leases with a term of greater than twelve months regardless of classification. Leases with a term of twelve months or less will be accounted for similar to existing guidance for operating leases. In November 2019, the FASB issued ASU No. 2019-10, Financial Instruments—Credit Losses (Topic 326), Derivatives and Hedging (Topic 815), and Leases (Topic 842): Effective Dates, which revised the effective date for ASU No. 2016-02, Leases (Topic 842) for fiscal years beginning after December 15, 2020. In June 2020, the FASB issued ASU No. 2020-05, Revenue From Contracts With Customers (Topic 606) and Leases (Topic 842): Effective Dates for Certain Entities, further delaying the effective date for ASU No. 2016-02, Leases (Topic 842) to fiscal years beginning after December 15, 2021 and interim periods within fiscal years beginning after December 15, 2022. The Company immediately adopted ASU No. 2019-10 and ASU No. 2020-05 upon issuance by the FASB. The Company currently is assessing the impact of this guidance and on its financial statements.

- Definition

Disclosure of accounting policy for segment reporting.

+ References + Details

Summary of Significant Accounting Policies (Tables)

9 Months Ended

Sep. 30, 2021

Accounting Policies [Abstract]

Schedule of Cash, Cash Equivalents and Restricted Cash


	September 30, 2021		December 31, 2020
Cash and cash equivalents	$	20,400	$	241,714
Restricted cash	500		50
Cash, cash equivalents and restricted cash	$	20,900	$	241,764

Schedule of Cash, Cash Equivalents and Restricted Cash


	September 30, 2021		December 31, 2020
Cash and cash equivalents	$	20,400	$	241,714
Restricted cash	500		50
Cash, cash equivalents and restricted cash	$	20,900	$	241,764

Balance Sheet Components (Tables)

9 Months Ended

Sep. 30, 2021

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Schedule of Prepaid Expenses and Other Current Assets

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


	September 30, 2021		December 31, 2020
Prepaid research and development expenses	$	1,226	$	761
Prepaid general and administration expenses	2,859		420
Grant receivable	861		571
U.K. research and development tax and expenditure credits	2,299		799
Other receivables	484		1,803
Other current assets	—		70
Total prepaid expenses and other current assets	$	7,729	$	4,424

Schedule of Property, Plant and Equipment, Net

Property, plant and equipment, net consist of the following (in thousands):


	September 30, 2021		December 31, 2020
Land	$	31,243	$	31,243
Building	6,309		6,309
Laboratory equipment	14,281		6,590
Manufacturing equipment	1,700		2,355
Office and computer equipment	2,182		1,510
Vehicles	64		—
Leasehold improvements	1,423		1,312
Construction work-in-progress	48,575		6,328
Total property, plant and equipment, gross	105,777		55,647
Less: accumulated depreciation	(2,087)		(306)
Total property, plant and equipment, net	$	103,690	$	55,341

Schedule of Other Long-term Assets

Other long-term assets consist of the following (in thousands):


	September 30, 2021		December 31, 2020
Deferred rent	$	2,088	$	509
Prepaid research and development expenses	2,024		603
Prepaid general and administration expenses	71		—
Security deposit	111		29
Restricted cash	500		50
Deferred offering costs	—		516
Total other long-term assets	$	4,794	$	1,707

Schedule of Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consist of the following (in thousands):


	September 30, 2021		December 31, 2020
Accrued compensation and benefits	$	9,157	$	3,983
Accrued construction costs	11,178		302
Accrued research and development expenses	3,034		1,616
Accrued operational expenses	1,265		1,589
Current tax liabilities	436		631
Other current liabilities	234		281
Total accrued expenses and other current liabilities	$	25,304	$	8,402

Transactions with Immetacyte (Tables)

9 Months Ended

Sep. 30, 2021

Business Combinations [Abstract]

Schedule of Acquisition

The fair value of consideration paid was as follows (in thousands):


Cash consideration	$	779
Common stock of 5,640,000 shares at an estimated fair value of $0.58 per share	3,243
Contingent consideration	11,349
Total consideration	$	15,371

Schedule of Recognized Identified Assets Acquired and Liabilities Assumed

The allocation of the purchase consideration was based on management’s estimate of the acquisition date fair values of the assets acquired and liabilities assumed, as follows (in thousands):


Assets acquired:
Net working capital	$	870
Property and equipment	690
Intangibles	10,104
Total assets acquired	11,664
Goodwill	5,722
Deferred tax liabilities	(2,015)
Total purchase price	$	15,371

Fair Value Measurement (Tables)

9 Months Ended

Sep. 30, 2021

Fair Value Disclosures [Abstract]

Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis

The following tables provide information by level for assets and liabilities that are measured at fair value on a recurring basis:


	As of September 30, 2021
	Level 1		Level 2		Level 3		Total
	(In thousands)
Financial Assets
Money market funds	$	15,296	$	—	$	—	$	15,296
U.S. Treasury bills	—		494,958		—		494,958
Total	$	15,296	$	494,958	$	—	$	510,254
Financial Liabilities
Contingent consideration	$	—	—		12,407		$	12,407

	As of December 31, 2020
	Level 1		Level 2		Level 3		Total
	(In thousands)
Financial Assets
Money market funds	$	106,138	—		—		$	106,138
Financial Liabilities
Contingent consideration	$	—	—		12,277		$	12,277

Reconciliation of Level 3 Financial Liabilities

The following table sets forth a summary of the changes in the fair value of the Company's Level 3 financial liabilities (in thousands):


	Nine Months Ended September 30, 2021
Fair value, beginning balance	$	12,277
Change in fair value	130
Fair value, ending balance	$	12,407


	Year Ended December 31, 2020
Fair value, beginning balance	$	—
Contingent consideration recorded as a result of Immetacyte acquisition	11,349
Change in present value of contingent consideration	928
Fair value, ending balance	$	12,277

Financial Instruments (Tables)

9 Months Ended

Sep. 30, 2021

Investments, Debt and Equity Securities [Abstract]

Summary of Marketable Securities

Marketable securities classified as available-for-sale at September 30, 2021 consisted of the following (in thousands):


	Maturity	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
U.S. Treasury bills	Less than one year	$	494,976	$	—	$	(18)	$	494,958

Commitments and Contingencies (Tables)

9 Months Ended

Sep. 30, 2021

Commitments and Contingencies Disclosure [Abstract]

Schedule of Future Minimum Lease Payments

Future minimum lease payments under noncancellable operating leases as of September 30, 2021 were as follows (in thousands):


2021 (remaining three months)	$	597
2022	2,469
2023	2,352
2024	2,200
2025 and thereafter	3,182
Total	$	10,800

Equity (Tables)

9 Months Ended

Sep. 30, 2021

Equity [Abstract]

Schedule of Convertible Preferred Stock

Convertible preferred stock consisted of the following (in thousands, except shares):


	As of December 31, 2020
	Shares Authorized	Shares Issued and Outstanding	Aggregate Liquidation Preference
Series A	25,000,000	25,000,000	$	25,000
Series B	34,600,523	34,600,523	170,200
Series C	14,750,075	10,575,523	133,000
	74,350,598	70,176,046	$	328,200

Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2021

Share-based Payment Arrangement [Abstract]

Schedule of Option Activity

The following summarizes option activity under the 2021 Plan:


	Shares Available for Grant	Shares Issuable Under Options	Weighted- Average Exercise Price		Weighted- Average Remaining Contract Term (in years)	Aggregate Intrinsic Value (in thousands)
Balance, December 31, 2020	10,217,237	15,331,923	$	0.80	9.22	$	78,857
Additional Shares Authorized	8,660,000
Options granted(1)	(8,604,737)	8,604,737	$	9.57
Options forfeited	275,400	(275,400)	$	2.92
Options exercised	—	(3,820,528)	$	0.41
Balance, September 30, 2021	10,547,900	19,840,732	$	4.65	8.99	$	265,567
Exercisable, September 30, 2021		4,249,857	$	1.69	8.52	$	68,914
Vested and expected to vest, September 30, 2021		4,369,857	$	1.67	8.52	$	70,960

______________________________________________________________

(1) Includes 2,252,137 stock options subject to performance conditions.

Schedule of Stock-Based Compensation Expense

The following table sets forth stock-based compensation included in the Company’s statement of operations and comprehensive loss (in thousands):


	Three Months Ended September 30,				Nine Months Ended September 30,
	2021		2020		2021		2020
Research and development expense	$	4,677	$	125	$	8,127	$	252
General and administrative expense	4,057		206		9,166		1,039
Total stock-based compensation expense	$	8,734	$	331	$	17,293	$	1,291

Schedule of Valuation Assumptions

The fair value of the Company’s stock option awards was estimated at the date of grant using a Black-Scholes option pricing model with the following assumptions:


	Nine Months Ended September 30,
	2021				2020
Expected term (in years)	5.77		—	6.24	5.27		—	6.08
Expected volatility	75.97	%	—	89.11%	69.69	%	—	82.64%
Risk-free interest rate	0.51	%	—	1.09%	0.42	%	—	1.76%
Fair value of common stock	$6.68		—	$26.44	$0.41		—	$1.38
Expected dividend yield	—%				—%

Net Loss Per Share (Tables)

9 Months Ended

Sep. 30, 2021

Earnings Per Share [Abstract]

Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share

The following outstanding potentially dilutive shares have been excluded from the calculation of diluted net loss per share for the periods presented due to their anti-dilutive effect:


	September 30,
	2021	2020
Convertible preferred stock	—	59,600,523
Stock options to purchase common stock	19,840,732	14,343,832
Total	19,840,732	73,944,355

Summary of Significant Accounting Policies - Narrative (Details) $ / shares in Units, $ in Millions				9 Months Ended
	Mar. 23, 2021 USD ($) $ / shares shares	Mar. 19, 2021 shares	Mar. 12, 2021	Sep. 30, 2021 segment shares	Jun. 30, 2021 shares	Mar. 31, 2021 shares	Mar. 24, 2021 shares	Mar. 20, 2021 shares	Dec. 31, 2020 USD ($) shares	Sep. 30, 2020 shares	Jun. 30, 2020 shares	Mar. 31, 2020 shares	Dec. 31, 2019 shares
Subsidiary, Sale of Stock [Line Items]
Stock split (in shares)			1.2
Shares sold (in shares)	18,400,000
Price per share sold (in dollars per share) \| $ / shares	$ 20.00
Net proceeds from sale of stock \| $	$ 339.0
Shares issued upon conversion (in shares)	89,220,699	89,220,699
Common stock, shares authorized (in shares)		300,000,000		300,000,000					111,000,000
Convertible preferred stock, shares authorized (in shares)		10,000,000		10,000,000			10,000,000		74,350,598
Convertible preferred stock outstanding (in shares)				0	0	0		0	70,176,046	59,600,523	59,600,523	15,000,000	15,000,000
Number of segments \| segment				1
Security deposit \| $									$ 0.5
Underwriter purchase option
Subsidiary, Sale of Stock [Line Items]
Shares sold (in shares)	2,400,000

Summary of Significant Accounting Policies - Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Cash and cash equivalents	$ 20,400	$ 241,714
Restricted cash	500	50
Cash, cash equivalents and restricted cash	$ 20,900	$ 241,764	$ 170,679	$ 8,895

Balance Sheet Components - Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Prepaid research and development expenses	$ 1,226	$ 761
Prepaid general and administration expenses	2,859	420
Grant receivable	861	571
U.K. research and development tax and expenditure credits	2,299	799
Other receivables	484	1,803
Other current assets	0	70
Total prepaid expenses and other current assets	$ 7,729	$ 4,424

Balance Sheet Components - Property, Plant and Equipment, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	$ 105,777	$ 55,647
Less: accumulated depreciation	(2,087)	(306)
Total property, plant and equipment, net	103,690	55,341
Land
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	31,243	31,243
Building
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	6,309	6,309
Laboratory equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	14,281	6,590
Manufacturing equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	1,700	2,355
Office and computer equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	2,182	1,510
Vehicles
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	64	0
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	1,423	1,312
Construction work-in-progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	$ 48,575	$ 6,328

Balance Sheet Components - Narrative (Details) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Oct. 31, 2020 USD ($) building	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Depreciation expense		$ 800	$ 0	$ 1,900	$ 0
Number of buildings acquired \| building	4
Payments to acquire buildings	$ 37,600			39,367	$ 5,545
Work in progress		44,200		44,200
Contractual commitment		$ 78,700		$ 78,700		$ 6,300

Balance Sheet Components - Other Long-term Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Deferred rent	$ 2,088	$ 509
Prepaid research and development expenses	2,024	603
Prepaid general and administration expenses	71	0
Security deposit	111	29
Restricted cash	500	50
Deferred offering costs	0	516
Total other long-term assets	$ 4,794	$ 1,707

Balance Sheet Components - Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accrued compensation and benefits	$ 9,157	$ 3,983
Accrued construction costs	11,178	302
Accrued research and development expenses	3,034	1,616
Accrued operational expenses	1,265	1,589
Current tax liabilities	436	631
Other current liabilities	234	281
Total accrued expenses and other current liabilities	$ 25,304	$ 8,402

Transactions with Immetacyte - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Feb. 28, 2019
Business Acquisition [Line Items]
In-process research and development			$ 600
Upfront fee			300
Development milestone payment			300
Annual research and development services to be paid next three years						$ 1,900
Manufacturing services to be paid, first annual period						1,200
Annual manufacturing services to be paid next two years						1,600
Monitoring and general services to be paid						$ 300
Research and development		$ 29,064	4,908	$ 64,674	$ 9,152
Immetacyte
Business Acquisition [Line Items]
Percentage of share capital acquired	100.00%
Cash consideration	$ 779
Shares issued (in shares)	5,640,000
Shares issued, price per share (in dollars per share)	$ 0.58
Contingent consideration, maximum	$ 14,800
Intangibles	10,104
Gross trade receivables acquired	$ 800
Acquisition costs expensed			$ 0		900
License Agreement
Business Acquisition [Line Items]
Research and development					$ 600

Transactions with Immetacyte - Fair Value of Consideration (Details) - Immetacyte $ / shares in Units, $ in Thousands	1 Months Ended
	Mar. 31, 2020 USD ($) $ / shares shares
Business Acquisition [Line Items]
Cash consideration	$ 779
Common stock of 5,640,000 shares at an estimated fair value of $0.58 per share	3,243
Contingent consideration	11,349
Total consideration	$ 15,371
Shares issued (in shares) \| shares	5,640,000
Shares issued, price per share (in dollars per share) \| $ / shares	$ 0.58

Transactions with Immetacyte - Allocation of Purchase Consideration (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Mar. 31, 2020
Business Acquisition [Line Items]
Goodwill	$ 5,722	$ 5,722
Immetacyte
Business Acquisition [Line Items]
Net working capital			$ 870
Property and equipment			690
Intangibles			10,104
Total assets acquired			11,664
Goodwill			5,722
Deferred tax liabilities			(2,015)
Total purchase price			$ 15,371

Fair Value Measurement - Financial Assets and Liabilities (Details) - USD ($)	Sep. 30, 2021	Dec. 31, 2020
Financial Assets
U.S. Treasury bills		$ 0
U.S. Treasury bills
Financial Assets
U.S. Treasury bills	$ 494,958,000
Fair Value, Recurring
Financial Assets
Total	510,254,000
Financial Liabilities
Contingent consideration	12,407,000	12,277,000
Fair Value, Recurring \| U.S. Treasury bills
Financial Assets
U.S. Treasury bills	494,958,000
Fair Value, Recurring \| Level 1
Financial Assets
Total	15,296,000
Financial Liabilities
Contingent consideration	0	0
Fair Value, Recurring \| Level 1 \| U.S. Treasury bills
Financial Assets
U.S. Treasury bills	0
Fair Value, Recurring \| Level 2
Financial Assets
Total	494,958,000
Financial Liabilities
Contingent consideration	0	0
Fair Value, Recurring \| Level 2 \| U.S. Treasury bills
Financial Assets
U.S. Treasury bills	494,958,000
Fair Value, Recurring \| Level 3
Financial Assets
Total	0
Financial Liabilities
Contingent consideration	12,407,000	12,277,000
Fair Value, Recurring \| Level 3 \| U.S. Treasury bills
Financial Assets
U.S. Treasury bills	0
Money market funds \| Fair Value, Recurring
Financial Assets
Money market funds	15,296,000	106,138,000
Money market funds \| Fair Value, Recurring \| Level 1
Financial Assets
Money market funds	15,296,000	106,138,000
Money market funds \| Fair Value, Recurring \| Level 2
Financial Assets
Money market funds	0	0
Money market funds \| Fair Value, Recurring \| Level 3
Financial Assets
Money market funds	$ 0	$ 0

Fair Value Measurement - Level 3 Reconciliation (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	$ 12,277	$ 0
Contingent consideration recorded as a result of Immetacyte acquisition		11,349
Change in fair value	130	928
Fair value, ending balance	$ 12,407	$ 12,277

Fair Value Measurement - Narrative (Details)	9 Months Ended		12 Months Ended
Fair Value Measurement - Narrative (Details)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Contingent consideration payments			$ 0
Increase in fair value of contingent consideration	$ 130,000	$ 263,000	$ 900,000
Measurement Input, Discount Rate
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Measurement input			0.08	0.085
Minimum
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Payment probability			20.00%
Maximum
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Payment probability			100.00%

Financial Instruments - Summary of Investments (Details) - USD ($)	Sep. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Fair Value		$ 0
U.S. Treasury bills
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 494,976,000
Unrealized Gains	0
Unrealized Losses	(18,000)
Fair Value	$ 494,958,000

Commitments and Contingencies - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Commitments and Contingencies Disclosure [Abstract]
Rent expense	$ 0.6	$ 0.2	$ 1.8	$ 0.2

Commitments and Contingencies - Future Minimum Payments (Details) $ in Thousands	Sep. 30, 2021 USD ($)
Commitments and Contingencies Disclosure [Abstract]
2021 (remaining three months)	$ 597
2022	2,469
2023	2,352
2024	2,200
2025 and thereafter	3,182
Total	$ 10,800

Equity - Narrative (Details)			1 Months Ended		3 Months Ended			9 Months Ended	12 Months Ended
Equity - Narrative (Details)	Mar. 23, 2021 $ / shares shares	Mar. 19, 2021 shares	Nov. 30, 2020 USD ($) shares	Mar. 31, 2020 $ / shares shares	Mar. 31, 2021 shares	Sep. 30, 2020 shares	Jun. 30, 2020 $ / shares shares	Sep. 30, 2021 USD ($) vote $ / shares shares	Dec. 31, 2020 USD ($) board_member $ / shares shares	Jun. 30, 2021 $ / shares shares	Mar. 24, 2021 $ / shares shares	Mar. 20, 2021 shares	Dec. 31, 2019 shares
Class of Stock [Line Items]
Common stock, votes per share \| vote								1
Promissory note \| $			$ 1,100,000						$ 1,100,000
Promissory note secured by pledge, number of shares (in shares)			3,200,000
Interest rate			2.50%
Promissory note, term			5 years
Promissory note, days prior to filing of first registration statement			1 day
Shares sold (in shares)	18,400,000
Price per share sold (in dollars per share) \| $ / shares	$ 20.00
Common stock, shares outstanding (in shares)								128,857,283	20,591,554
Convertible preferred stock outstanding (in shares)				15,000,000	0	59,600,523	59,600,523	0	70,176,046	0		0	15,000,000
Issuance of convertible preferred shares (in shares)					4,174,551			4,174,551
Shares issued upon conversion (in shares)	89,220,699	89,220,699
Conversion ratio	1.2
Dividend rate									8.00%
Shares issued, price per share (in dollars per share) \| $ / shares										$ 12.58
Dividends declared \| $								$ 0
Mandatory conversion, common stock share price (at least) (in dollars per share) \| $ / shares									$ 12.58
Mandatory conversion, gross proceeds (at least) \| $									$ 100,000,000
Convertible preferred stock, shares authorized (in shares)		10,000,000						10,000,000	74,350,598		10,000,000
Convertible preferred stock, par value (in dollars per share) \| $ / shares								$ 0.000001	$ 0.000001		$ 0.000001
Convertible preferred stock issued (in shares)								0	70,176,046
Immetacyte
Class of Stock [Line Items]
Shares issued (in shares)				5,640,000
Shares issued, price per share (in dollars per share) \| $ / shares				$ 0.58
Series A
Class of Stock [Line Items]
Convertible preferred stock outstanding (in shares)									25,000,000
Issuance of convertible preferred shares (in shares)						1.00	10,000,000
Number of board members entitled to elect \| board_member									1
Shares issued, price per share (in dollars per share) \| $ / shares									$ 1.00
Liquidation preference per share (in dollars per share) \| $ / shares									1.00
Conversion price (in dollars per share) \| $ / shares									$ 0.83
Convertible preferred stock, shares authorized (in shares)									25,000,000
Convertible preferred stock issued (in shares)									25,000,000
Series B
Class of Stock [Line Items]
Convertible preferred stock outstanding (in shares)									34,600,523
Issuance of convertible preferred shares (in shares)							34,600,523
Number of board members entitled to elect \| board_member									3
Shares issued, price per share (in dollars per share) \| $ / shares							$ 4.92		$ 4.92
Liquidation preference per share (in dollars per share) \| $ / shares									4.92
Conversion price (in dollars per share) \| $ / shares									$ 4.10
Convertible preferred stock, shares authorized (in shares)									34,600,523
Convertible preferred stock issued (in shares)									34,600,523
Series C
Class of Stock [Line Items]
Convertible preferred stock outstanding (in shares)									10,575,523
Shares issued, price per share (in dollars per share) \| $ / shares									$ 12.58
Liquidation preference per share (in dollars per share) \| $ / shares									12.58
Conversion price (in dollars per share) \| $ / shares									$ 10.48
Convertible preferred stock, shares authorized (in shares)									14,750,075
Convertible preferred stock issued (in shares)									10,575,523

Equity - Preferred Stock (Details) - USD ($)	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Mar. 24, 2021	Mar. 20, 2021	Mar. 19, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Class of Stock [Line Items]
Convertible preferred stock, shares authorized (in shares)	10,000,000			10,000,000		10,000,000	74,350,598
Convertible preferred stock issued (in shares)	0						70,176,046
Convertible preferred stock outstanding (in shares)	0	0	0		0		70,176,046	59,600,523	59,600,523	15,000,000	15,000,000
Convertible preferred stock, liquidation preference	$ 0						$ 328,200,000
Series A
Class of Stock [Line Items]
Convertible preferred stock, shares authorized (in shares)							25,000,000
Convertible preferred stock issued (in shares)							25,000,000
Convertible preferred stock outstanding (in shares)							25,000,000
Convertible preferred stock, liquidation preference							$ 25,000,000
Series B
Class of Stock [Line Items]
Convertible preferred stock, shares authorized (in shares)							34,600,523
Convertible preferred stock issued (in shares)							34,600,523
Convertible preferred stock outstanding (in shares)							34,600,523
Convertible preferred stock, liquidation preference							$ 170,200,000
Series C
Class of Stock [Line Items]
Convertible preferred stock, shares authorized (in shares)							14,750,075
Convertible preferred stock issued (in shares)							10,575,523
Convertible preferred stock outstanding (in shares)							10,575,523
Convertible preferred stock, liquidation preference							$ 133,000,000

Stock-Based Compensation - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Mar. 31, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional shares authorized (in shares)	8,660,000			8,660,000
Shares available for future issuance (in shares)		10,547,900		10,547,900
Term to authorize additional shares				10 years
Percentage of outstanding capital stock				5.00%
Shares authorized (in shares)		12,854,437		12,854,437
Options exercised (in shares)				3,820,528
Options granted, weighted-average grant date fair value (in dollars per share)				$ 11.57
Unrecognized compensation cost		$ 68,700		$ 68,700
Options granted (in shares)				8,604,737
Strategic transaction, initial public offering, gross proceeds				$ 50,000
Total stock-based compensation expense		8,734	$ 331	$ 17,293	$ 1,291
Share-based Payment Arrangement, Tranche One
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period				4 years
Share-based Payment Arrangement, Tranche Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period				1 year
Stock options to purchase common stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost, recognition period				2 years 4 months 6 days
Expected dividend yield				0.00%	0.00%
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost		$ 21,200		$ 21,200
Options granted (in shares)				2,252,137
Total stock-based compensation expense				$ 3,200
Performance Shares \| Weighted Average
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period				3 years 3 months 14 days
Employee Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Term to authorize additional shares				10 years
Percentage of outstanding capital stock				1.00%
Shares authorized (in shares)	1,237,000
Minimum number of additional shares to be authorized (in shares)				2,474,000
2018 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future issuance (in shares)		4,194,437		4,194,437

Stock-Based Compensation - Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2021	Sep. 30, 2021	Dec. 31, 2020
Shares Available for Grant
Balance, December 31, 2020 (in shares)		10,217,237
Additional Shares Authorized (in shares)	8,660,000	8,660,000
Options granted (in shares)		(8,604,737)
Options forfeited (in shares)		275,400
Balance, June 30, 2021 (in shares)		10,547,900	10,217,237
Shares Issuable Under Options
Balance, December 31, 2020 (in shares)		15,331,923
Options granted (in shares)		8,604,737
Options forfeited (in shares)		(275,400)
Options exercised (in shares)		(3,820,528)
Balance, June 30, 2021 (in shares)		19,840,732	15,331,923
Exercisable, June 30, 2021 (in shares)		4,249,857
Vested and expected to vest, June 30, 2021 (in shares)		4,369,857
Weighted- Average Exercise Price
Balance, December 31, 2020 (in dollars per share)		$ 0.80
Options granted (in dollars per share)		9.57
Options forfeited (in dollars per share)		2.92
Options exercised (in dollars per share)		0.41
Balance, June 30, 2021 (in dollars per share)		4.65	$ 0.80
Exercisable, June 30, 2021, weighted-average exercise price (in dollars per share)		1.69
Vested and expected to vest, June 30, 2021, weighted-average exercise price (in dollars per share)		$ 1.67
Balance, weighted-average remaining contract term		8 years 11 months 26 days	9 years 2 months 19 days
Exercisable, weighted-average remaining contract term		8 years 6 months 7 days
Vested and expected to vest, weighted-average remaining contract term		8 years 6 months 7 days
Balance, aggregate intrinsic value		$ 265,567	$ 78,857
Exercisable, aggregate intrinsic value		68,914
Vested and expected to vest, aggregate intrinsic value		$ 70,960
Performance Shares
Shares Available for Grant
Options granted (in shares)		(2,252,137)
Shares Issuable Under Options
Options granted (in shares)		2,252,137

Stock-Based Compensation - Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation expense	$ 8,734	$ 331	$ 17,293	$ 1,291
Research and development expense
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation expense	4,677	125	8,127	252
General and administrative expense
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation expense	$ 4,057	$ 206	$ 9,166	$ 1,039

Stock-Based Compensation - Valuation Assumption (Details) - Stock option - $ / shares	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility, minimum	75.97%	69.69%
Expected volatility, maximum	89.11%	82.64%
Risk-free interest rate, minimum	0.51%	0.42%
Risk-free interest rate, maximum	1.09%	1.76%
Expected dividend yield	0.00%	0.00%
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	5 years 9 months 7 days	5 years 3 months 7 days
Fair Value of Common Stock (in dollars per share)	$ 6.68	$ 0.41
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	6 years 2 months 26 days	6 years 29 days
Fair Value of Common Stock (in dollars per share)	$ 26.44	$ 1.38

Net Loss Per Share (Details)		9 Months Ended
Net Loss Per Share (Details)	Mar. 23, 2021	Sep. 30, 2021 shares	Sep. 30, 2020 shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive shares (in shares)		19,840,732	73,944,355
Conversion ratio	1.2
Convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive shares (in shares)		0	59,600,523
Stock options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive shares (in shares)		19,840,732	14,343,832