Achilles Therapeutics (ACHL) 20-F 1 Mar 22 2021 FY Annual report (foreign) Financial data

Document and Entity Information

Document and Entity Information	12 Months Ended
	Dec. 31, 2021shares
Document Information [Line Items]
Document Type	20-F
Amendment Flag	false
Document Period End Date	Dec. 31, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Entity Registrant Name	Achilles Therapeutics plc
Entity Central Index Key	0001830749
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Well-known Seasoned Issuer	No
Entity Common Stock, Shares Outstanding	40,603,489
Entity Shell Company	false
Entity Emerging Growth Company	true
Entity File Number	001-40299
Entity Incorporation, State or Country Code	X0
Entity Address, Address Line One	245 Hammersmith Road
Entity Address, City or Town	London
Entity Address, Country	GB
Entity Address, Postal Zip Code	W6 8PW
Document Annual Report	true
Document Transition Report	false
Document Shell Company Report	false
Document Registration Statement	false
Document Accounting Standard	U.S. GAAP
Entity Ex Transition Period	false
ICFR Auditor Attestation Flag	false
Auditor Name	KPMG, LLC
Auditor Location	Reading, United Kingdom
Auditor Firm ID	1118
Business Contact
Document Information [Line Items]
Contact Personnel Name	Daniel C.C. Hood
Entity Address, Address Line One	245 Hammersmith Road
Entity Address, City or Town	London
Entity Address, Country	GB
Entity Address, Postal Zip Code	W6 8PW
City Area Code	+44
Local Phone Number	(0)20 8154 4600
Contact Personnel Email Address	legal@achillestx.com
American Depository Shares
Document Information [Line Items]
Trading Symbol	ACHL
Title of 12(b) Security	American Depositary Shares, each representing one ordinary share, nominal value of £0.001 per share
Security Exchange Name	NASDAQ
Ordinary Shares
Document Information [Line Items]
Title of 12(b) Security	Ordinary shares, nominal value £0.001 per share
Security Exchange Name	NASDAQ
No Trading Symbol Flag	true

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 266,319	$ 177,849
Prepaid expenses and other current assets	18,430	9,948
Total current assets	284,749	187,797
Non-current assets:
Property and equipment, net	17,743	13,369
Operating lease right of use assets	11,048	14,740
Deferred tax assets	26	4
Restricted cash	33
Other assets	3,507	3,008
Total non-current assets	32,357	31,121
TOTAL ASSETS	317,106	218,918
Current liabilities:
Accounts payable	3,722	6,314
Income taxes payable		7
Accrued expenses and other liabilities	10,906	6,590
Operating lease liabilities—current	4,482	3,712
Total current liabilities	19,110	16,623
Non-current liabilities:
Operating lease liabilities-non-current	7,777	12,271
Other long-term liability	691	652
Total non-current liabilities	8,468	12,923
Total liabilities	27,578	29,546
Commitments and contingencies (Note 13)
Shareholders' equity:
Ordinary shares, £0.001 par value; 40,603,489 and 4,389,920 shares authorized, issued and outstanding at December 31,2021 and 2020, respectively	54	6
Deferred shares, £92,451.851 par value, one share authorized, issued and outstanding at December 31, 2021; Deferred shares, £0.001 par value; 30,521 shares issued and outstanding at December 31,2020	128
Additional paid in capital	401,821	234,922
Accumulated other comprehensive income	6,636	12,322
Accumulated deficit	(119,111)	(58,012)
Total shareholders’ equity	289,528	189,372
TOTAL LIABILITIES AND SHAREHOLDERS’ EQUITY	$ 317,106	218,918
Convertible Preferred Shares
Shareholders' equity:
Convertible preferred shares, £0.001 par value; no shares authorized, issued and outstanding as of December 31, 2021; 104,854,673 shares authorized, issued and outstanding at December 31, 2020		$ 134

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical)	Dec. 31, 2021£ / sharesshares	Dec. 31, 2021$ / sharesshares	Dec. 31, 2020£ / sharesshares	Dec. 31, 2020$ / sharesshares
Ordinary shares, par value | (per share)	£ 0.001	$ 0.001	£ 0.001	$ 0.001
Ordinary shares, shares authorized	40,603,489	40,603,489	4,389,920	4,389,920
Ordinary shares, shares issued	40,603,489	40,603,489	4,389,920	4,389,920
Ordinary shares, shares outstanding	40,603,489	40,603,489	4,389,920	4,389,920
Deferred shares, par value | £ / shares	£ 92,451.851		£ 0.001
Deferred shares, shares authorized	1	1
Deferred shares, shares issued	1	1	30,521	30,521
Deferred shares, shares outstanding	1	1	30,521	30,521
Convertible Preferred Shares
Convertible preferred shares, par value | £ / shares	£ 0.001		£ 0.001
Convertible preferred shares, shares authorized	0	0	104,854,673	104,854,673
Convertible preferred shares, shares issued	0	0	104,854,673	104,854,673
Convertible preferred shares, shares outstanding	0	0	104,854,673	104,854,673

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
OPERATING EXPENSES:
Research and development	$ 42,224	$ 22,629	$ 9,072
General and administrative	21,971	11,098	4,703
Total operating expenses	64,195	33,727	13,775
Loss from operations	(64,195)	(33,727)	(13,775)
OTHER INCOME (EXPENSE), NET:
Other income (expense)	3,133	531	(215)
Total other income (expense), net	3,133	531	(215)
Loss before provision for income taxes	(61,062)	(33,196)	(13,990)
Provision for income taxes	(37)	(3)
Net loss	(61,099)	(33,199)	(13,990)
Other comprehensive income:
Foreign exchange translation adjustment	(5,686)	4,213	8,504
Comprehensive loss	$ (66,785)	$ (28,986)	$ (5,486)
Net loss per share attributable to ordinary shareholders—basic and diluted	$ (2.13)	$ (31.14)	$ (21.79)
Weighted average ordinary shares outstanding—basic and diluted	28,654,760	1,066,208	642,169

Consolidated Statements of Shar

Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Ordinary Shares	Deferred Shares	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Series A Convertible Preferred Shares	Series A Convertible Preferred SharesAdditional Paid-in Capital	Series B Convertible Preferred Shares	Series B Convertible Preferred SharesAdditional Paid-in Capital	Series C Convertible Preferred Shares	Series C Convertible Preferred SharesAdditional Paid-in Capital
Beginning balance at Dec. 31, 2018	$ 12,673	$ 2		$ 23,866	$ (395)	$ (10,823)
Beginning balance, shares at Dec. 31, 2018							17,850,000
Beginning balance at Dec. 31, 2018							$ 23
Beginning balance, shares at Dec. 31, 2018		1,407,925	71,431
Issuance of convertible preferred shares, net of issuance costs							$ 13		$ 43
Issuance of convertible preferred shares, net of issuance costs, shares							10,400,000		34,794,714
Issuance of convertible preferred shares, net of issuance costs							$ 13,254	$ 13,241	$ 80,188	$ 80,145
Issuance of ordinary shares (Note 7)		$ 2		(2)
Issuance of ordinary shares (Note 7), shares		1,358,765
Conversion of ordinary shares into deferred shares			$ 1	(1)
Conversion of ordinary shares into deferred shares, share		(232,483)	920,434
Share-based compensation expense	719			719
Unrealized gain on foreign currency translation	8,504				8,504
Net loss	(13,990)					(13,990)
Ending balance at Dec. 31, 2019	101,348	$ 4	$ 1	117,968	8,109	(24,813)
Ending balance, shares at Dec. 31, 2019							28,250,000		34,794,714
Ending balance at Dec. 31, 2019							$ 36		$ 43
Ending balance, shares at Dec. 31, 2019		2,534,207	991,865
Issuance of convertible preferred shares, net of issuance costs									$ 23		$ 32
Issuance of convertible preferred shares, net of issuance costs, shares									17,397,356		24,412,603
Issuance of convertible preferred shares, net of issuance costs									$ 44,124	$ 44,101	$ 69,894	$ 69,862
Issuance of ordinary shares (Note 7)		$ 2		(2)
Issuance of ordinary shares (Note 7), shares		1,993,503
Conversion of ordinary shares into deferred shares			$ 1	(1)
Conversion of ordinary shares into deferred shares, share		(137,790)	548,040
Repurchase of deferred shares			$ (2)	2
Repurchase of deferred shares, shares			(1,509,384)
Share-based compensation expense	2,992			2,992
Unrealized gain on foreign currency translation	4,213				4,213
Net loss	(33,199)					(33,199)
Ending balance at Dec. 31, 2020	$ 189,372	$ 6		234,922	12,322	(58,012)
Ending balance, shares at Dec. 31, 2020	104,854,673						28,250,000		52,192,070		24,412,603
Ending balance at Dec. 31, 2020	$ 230,931						$ 36		$ 66		$ 32
Ending balance, shares at Dec. 31, 2020		4,389,920	30,521
Issuance of ordinary shares (Note 7)	160,624	$ 14		160,610
Issuance of ordinary shares (Note 7), shares		9,750,000
Conversion of ordinary shares into deferred shares, share		(18,262)	78,537
Effect of corporate reorganization including conversion of preferred share to ordinary share		$ 34	$ 128	(28)
Effect of Corporate Reorganization including Conversion of Preferred Share to Ordinary Share, shares							(28,250,000)		(52,192,070)		(24,412,603)
Effect of corporate reorganization including conversion of preferred share to ordinary share							$ (36)		$ (66)		$ (32)
Effect of Corporate Reorganization including Conversion of Preferred Share to Ordinary Share, shares		26,481,831	(109,057)
Share-based compensation expense	6,317			6,317
Unrealized gain on foreign currency translation	(5,686)				(5,686)
Net loss	(61,099)					(61,099)
Ending balance at Dec. 31, 2021	$ 289,528	$ 54	$ 128	$ 401,821	$ 6,636	$ (119,111)
Ending balance, shares at Dec. 31, 2021	0
Ending balance, shares at Dec. 31, 2021		40,603,489	1

Consolidated Statements of Sh_2

Consolidated Statements of Shareholders' Equity (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Series B Convertible Preferred Shares
Issuance costs	$ 20	$ 283
Series C Convertible Preferred Shares
Issuance costs	$ 187

Consolidated statements of cash

Consolidated statements of cash flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (61,099)	$ (33,199)	$ (13,990)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization	3,288	772	302
Loss on disposal of property and equipment	156		14
Changes in right of use assets and operating lease liabilities, net	(18)	1,179	(9)
Non-cash loss on foreign currency remeasurement	3		0
Non-cash share-based compensation	6,317	2,992	719
Changes in operating assets and liabilities
Prepaid expenses and other current assets	(9,771)	(3,120)	(2,566)
Accounts payable	(2,572)	5,258	548
Income taxes payable	(7)	7
Accrued expenses and other liabilities	4,937	3,045	873
Other long-term liability	47	614
Deferred tax assets	(22)	(4)
Other assets	(543)	(2,796)	(33)
Net cash used in operating activities	(59,284)	(25,252)	(14,142)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(7,634)	(11,847)	(942)
Net cash used in investing activities	(7,634)	(11,847)	(942)
CASH FLOWS FROM FINANCING ACTIVITIES:
Issuance of ADRs in initial public offering, net of issuance costs	160,755
Proceeds of issuance of convertible preferred shares, net of issuance costs		113,825	93,622
Payments of initial public offering costs		(121)
Net cash provided by financing activities	160,755	113,704	93,622
Effect of exchange rate changes on cash equivalents and restricted cash	(5,334)	3,650	8,373
Net increase in cash	88,503	80,255	86,911
Cash, cash equivalents and restricted cash, beginning of year	177,849	97,594	10,683
Cash, cash equivalents and restricted cash, end of year	266,352	177,849	97,594
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Right of use assets obtained in exchange for new operating lease liabilities	314	15,846	457
Property and equipment purchases in accrued expenses	726	285	343
Issuance costs of convertible preferred shares included in accounts payable			192
Deferred offering costs included in accrued expenses		826
Cash and cash equivalents	266,319	$ 177,849	$ 97,594
Restricted cash	$ 33

Nature of the Business

Nature of the Business	12 Months Ended
	Dec. 31, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Nature of the Business	1. Achilles Therapeutics plc (formerly Achilles TX Limited) and subsidiaries, or the Company, is a biopharmaceutical company developing transformative The Company is a public limited company originally incorporated pursuant to the laws of England and Wales in November 2020 as a private limited company named Achilles TX Limited, with nominal assets and liabilities, for the purposes of becoming the ultimate holding company for Achilles Therapeutics UK Limited (formerly Achilles Therapeutics Limited) and consummating the corporate reorganization described below. Achilles Therapeutics UK Limited was incorporated in May 2016 under the laws of England and Wales and its registered office and principal place of business is currently 245 Hammersmith Road, London W6 8PW. Achilles TX Limited and Achilles Therapeutics Holdings Limited (a wholly owned direct subsidiary of Achilles TX Limited formed in November 2020 for the purpose of becoming the direct holding company of Achilles Therapeutics UK Limited and Achilles Therapeutics US, Inc.) have not conducted any operations prior to the corporate reorganization other than activities incidental to their formation. The corporate reorganization and initial public offering, or IPO, took place in several steps which were completed on April 6, 2021. • Exchange of Achilles Therapeutics UK Limited Shares for Achilles TX Limited Shares : In December 2020 all shareholders of Achilles Therapeutics UK Limited (except for the holders of deferred shares) exchanged each of the shares held by them for shares of Achilles TX Limited to result in them holding the same number and class of newly issued shares of £1.20 nominal value of Achilles TX Limited and, as a result, Achilles TX Limited became the sole shareholder of Achilles Therapeutics UK Limited. • Reduction of the share capital of Achilles TX Limited: Achilles TX Limited reduced its share capital by way of a reduction of the nominal value of each share in the capital of Achilles TX Limited from £1.20 to £0.001 in order to satisfy the net asset test requirement in section 92 of the Companies Act 2006 for re-registration as a public limited company and to create distributable reserves. • Re-registration of Achilles TX Limited as Achilles Therapeutics plc: In February 2021, Achilles TX Limited was re-registered as a public limited company pursuant to section 92 of the UK Companies Act 2006 and renamed Achilles Therapeutics plc. The Company adopted new Articles of Association appropriate for a public limited company. As a result of the above Achilles TX Limited is the successor to Achilles Therapeutics UK Limited (the “Predecessor”) and the financial information for the period prior to the incorporation of Achilles TX Limited represents that of the Predecessor. On April 6, 2021, the Company completed the initial public offering, or IPO. In connection with the IPO, the Company sold an aggregate of 9,750,000 ADSs representing the same number of ordinary shares, at a public offering price of $18.00 per ADS. Net proceeds were $160.6 million, after deducting underwriting discounts and commissions and other offering expenses. Upon completion of the IPO, the Company adopted new articles suitable for a listed public limited company. On April 6, 2021, the Company effected a one-for-0.2526 (rounded to four decimal places) reverse share split of its issued and outstanding ordinary shares except for N ordinary shares and a proportional adjustment to the existing conversion ratios for each class of the Company’s convertible preferred shares, and a one-for-0.1792 (rounded to four decimal places) reverse share split of its issued and outstanding N ordinary shares. Accordingly, all share and per share amounts for all periods presented in the consolidated financial statements and notes thereto have been adjusted retroactively, where applicable, to reflect this reverse share split and adjustment of the preferred share conversion ratios. Two shareholders elected to receive a number of Class A non-voting ordinary shares rather than their full entitlement of ordinary shares following the reverse share split. As part of this reverse share split, a single deferred share with a nominal value of £ 92,451.851 in the capital of the Company was created. The Company has devoted its efforts principally to research and development since formation. The Company has not yet completed product development, filed for or obtained regulatory approvals for any products, nor verified the market acceptance and demand for such products. As a result, the Company is subject to risks that are common to emerging companies in the biotech industry, including the uncertainties of the product discovery and development process, dependence on key individuals, development of the same or similar technological innovations by the Company’s competitors, protection of proprietary technology, compliance with government regulations and approval requirements, the Company’s ability to access capital and uncertainty of market acceptance of products. Going In accordance The December 31 The As of December 31, 2021, the Company had cash and cash equivalents of $266.3 million. The Directors have reviewed the financial projections of the Company for the 12 months subsequent to the date of issuance of these financial statements including consideration of severe but plausible scenarios that may affect the Company in that period. These show that the Company will be able to pay (or otherwise discharge) its debts as they fall due immediately following the date of signing of this Balance Sheet and for the period considered by the forecast. Accordingly, the

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Basis The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America or U.S. GAAP and are presented in U.S. dollars. . Use The Segment Operating The Company operates in a single segment, focusing on researching, developing and commercializing potentially novel cancer immunotherapies targeting clonal neoantigens. Consistent with its operational structure, its chief operating decision maker, the Company’s chief executive officer, views and manages the Company’s operations and manages its business as a single operating segment. All material long-lived assets of the Company reside in the UK Foreign The gains of 2021, For (loss)/ Cash The In connection with a lease, the Company maintains a required minimum balance, currently less than $0.1 million in connection with a letter of credit issued for the benefit of the landlord for its commercial facility used as a security deposit for the lease. The total amount is classified as Restricted Cash and has been classified as a non-current asset in the Consolidated Balance Sheets. Deferred Initial Public Offering Costs The Company capitalized deferred initial public offering, or IPO, costs, which primarily consist of direct, incremental legal, professional accounting and other third-party fees relating to the Company’s IPO, within prepaid expenses and other current assets. The deferred IPO costs were offset against IPO proceeds upon the consummation of the offering. The Company recorded $ 1.0 million of deferred IPO costs as of December 31, 2020. The Company did no t record any deferred IPO costs as of December 31, 2021 and 2019. Fair The fair value hierarchy as Level 1 as there are quoted prices in active markets for identical assets. See Note 3, Fair Value of Financial Instruments. Concentrations Financial Property Property Estimated useful life Lab equipment 5 years Fixture and fittings 5 years Office equipment and computers 3 years Leasehold improvements Shorter of useful life or remaining lease term Upon Impairment The Company evaluates assets for potential impairment when events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Recoverability is measured by comparing the book values of the assets to the expected future net undiscounted cash flows that the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the book values of the assets exceed their fair value. The Company recognized an impairment loss of $0.1 million in the year ended December 31, 2021. The Company did not recognize any impairment losses in the years ended December 31, 2020 and 2019. Research Research Research The Asset Retirement and Environmental Obligations Pursuant to ASC 410, Asset Retirement and Environmental Obligations, an asset retirement obligation (“ARO” or “AROs”) is recorded when there is a legal obligation associated with the retirement of a tangible long-lived asset and the fair value of the liability can reasonably be estimated. Upon initial recognition, AROs are recorded as a liability at their estimated present value, with an offsetting increase to the carrying amount of the long-lived asset. Over time, the liabilities are accreted for the change in their present value through charges to operations costs. If the fair value of the estimated ARO changes, an adjustment is recorded to both the ARO and the asset retirement cost. Revisions in estimated liabilities can result from revisions of estimated inflation rates, escalating retirement costs, and changes in the estimated timing of settling ARO liabilities. Total ARO consists of amounts for decommissioning and restoration of rented facilities to be performed in the future. The Company computes the liability for AROs based on assumptions from third-party estimates of the total restoration costs, adjusted for inflation. These values are discounted to present value using our credit adjusted incremental borrowing rate of the related rental facility and recorded ARO in other long-term liabilities. Periodic accretion of the discount on the ARO is recorded as part of accretion expense. Share-based compensation The commitments Effective Compensation—Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting There have been no performance conditions attached to the share options granted by the Company to date. The fair value of each share option grant is estimated on the date of grant using the Black-Scholes option pricing model. See Note 8, “Share-based compensation,” for the Company’s assumptions used in connection with option grants made during the periods covered by these consolidated financial statements. Assumptions used in the option pricing model include the following: Expected volatility. As Achilles became a listed, public company in April 2021, the Company has limited company-specific historical and implied volatility information for its ordinary shares. Therefore, it estimates its expected share volatility based on the historical volatility of publicly traded peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded share price. Expected term. The expected term of the Company’s share options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options as there is a limited trading history of our ordinary shares. Risk-free interest rate. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods that are approximately equal to the expected term of the award. Expected dividend. Expected dividend yield of zero is based on the fact that the Company has never paid cash dividends on ordinary shares and does not expect to pay any cash dividends in the foreseeable future. Effective Compensation—Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting There have been no performance conditions attached to the share options granted by the Company to date. The fair value of each share option grant is estimated on the date of grant using the Black-Scholes option pricing model. See Note 8, “Share-based compensation,” for the Company’s assumptions used in connection with option grants made during the periods covered by these consolidated financial statements. Assumptions used in the option pricing model include the following: Expected volatility. As Achilles became a listed, public company in April 2021, the Company has limited company-specific historical and implied volatility information for its ordinary shares. Therefore, it estimates its expected share volatility based on the historical volatility of publicly traded peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded share price. Expected term. The expected term of the Company’s share options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options as there is a limited trading history of our ordinary shares. Risk-free interest rate. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods that are approximately equal to the expected term of the award. Expected dividend. Expected dividend yield of zero is based on the fact that the Company has never paid cash dividends on ordinary shares and does not expect to pay any cash dividends in the foreseeable future. Given the absence of an active market for the Company’s ordinary shares prior to the IPO, the Valuation of Privately-Held-Company Equity Securities Issued as Compensation price valuation as an input to the determination of share-based compensation. After IPO, the fair value of ordinary shares is determined by reference to the closing price of ADSs on the Nasdaq Global Select Market on the date of grant. The Leases Effective Lease Operating Income The future and to the extent management believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies. The The 2021, Research The The As The Unsurrendered UK Comprehensive Comprehensive Net The Government grants The Group receives certain government grants that support specific research and development activities. Income in respect of grants also includes contributions towards the costs of research and development. Income is recognized when costs under each grant are incurred in accordance with the terms and conditions of the grant and the collectability of the receivable is reasonably assured. Government grants relating to costs are deferred and recognized in the income statement over the period necessary to match them with the costs they are intended to compensate. The Group recognizes income from government grants under 'Other income—net' in the Company’s consolidated statement of comprehensive loss. Recent Recently In December 2019, the FASB issued ASU 2019-12, “ Income Taxes—Simplifying the Accounting for Income Taxes In November 2021, the FASB issued ASU 2021-10, “ Government Assistance – Topic 832 – Disclosures by Business Entities about Government Assistance 15, 2021; however, early adoption is permitted. The new guidance was adopted on January 1, 2022 and will be effective for the year ended December 21, 2022. This guidance is not expected to have a material impact on the Company’s financial statements and related disclosures.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	12 Months Ended
	Dec. 31, 2021
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	3. Fair Value of Financial Instruments The following tables show assets measured at fair value on a recurring basis as of December 31, 2021 (in thousands): December 31, 2021 Level 1 Level 2 Level 3 Cash equivalents: Money market funds $ 40,224 $ — $ — $ 40,224 $ — $ — There were no liabilities measured at fair value on a recurring basis as of December 31, 2021. There were no assets or liabilities measured at fair value on a recurring basis as of December 31, 2020.

Prepaid Expenses and Other Curr

Prepaid Expenses and Other Current Assets	12 Months Ended
	Dec. 31, 2021
Prepaid Expense And Other Assets Current [Abstract]
Prepaid Expenses and Other Current Assets	4. Prepaid December 31, 2021 2020 UK R&D tax credit $ 10,523 $ 6,214 Prepaid research and development 3,608 751 Prepaid insurance 1,525 21 VAT recoverable 650 1,125 Deferred offering costs — 1,007 Other current assets 2,124 830 $ 18,430 $ 9,948

Property and Equipment, Net

Property and Equipment, Net	12 Months Ended
	Dec. 31, 2021
Property Plant And Equipment [Abstract]
Property and Equipment, Net	5. Property and Equipment, net Property and equipment, net consisted of the following (in thousands): December 31, 2021 2020 Lab equipment $ 7,505 $ 4,644 Leasehold improvements 7,021 6,960 Office equipment and computers 1,561 1,168 Fixtures and fittings 757 706 Assets under construction 5,351 1,275 22,195 14,753 Less: Accumulated depreciation (4,452 ) (1,384 ) $ 17,743 $ 13,369 Depreciation $3.3 million, 2021,

Accrued Expenses and Other Liab

Accrued Expenses and Other Liabilities	12 Months Ended
	Dec. 31, 2021
Payables And Accruals [Abstract]
Accrued Expenses and Other Liabilities	6. Accrued December 31, 2021 2020 Compensation and benefits $ 2,649 $ 1,494 External research and development expenses 2,985 2,201 Facility costs 2,629 868 Property and equipment 712 303 Professional services 663 1,222 Other liabilities 1,268 502 $ 10,906 $ 6,590

Shareholders_ Equity

Shareholders’ Equity	12 Months Ended
	Dec. 31, 2021
Stockholders Equity Note [Abstract]
Shareholders’ Equity	7. Ordinary As of December 31, 2021 and 2020, the Company had the following number of ordinary shares with a par value £0.001 (equivalent to $0.001) issued and outstanding December 31, 2021 2020 Ordinary shares 38,987,122 — Class A non-voting ordinary shares 1,616,367 — B Ordinary shares — 505,108 D Ordinary shares — 155,669 E Ordinary shares — 80,007 F Ordinary shares — 327,084 G Ordinary shares — 194,261 H Ordinary shares — 88,871 I Ordinary shares — 48,391 J Ordinary shares — 262,478 L Ordinary shares — 1,207,670 M Ordinary shares — 811,436 N Ordinary shares — 708,945 Deferred Shares 1 30,521 Total ordinary and deferred shares 40,603,490 4,420,441 As of December 31, 2020 and 2019, the Company issued various classes of ordinary shares as Employee Shares (See Note 8). Each holder of B ordinary shares was entitled to one vote per B ordinary share and, to receive dividends declared with Investor Majority consent and any such dividend as determined by the board of directors of the Company acting with investor director consent, provided that the preferred shares and the B ordinary shares shall, subject to the 2019 Articles and 2020 Articles, rank equally in all respects for the purpose of any dividend that is declared or paid. All other classes of ordinary shares do not have voting rights. All ordinary shares, including B shares, have a liquidation preference that is junior to Preferred Shares. On April 6, 2021, all the Employee Shares, Convertible Preferred Shares (see below) and B ordinary shares were converted into ordinary shares or Class A non-voting ordinary shares. Please refer to the details in Note 1. Class A non-voting ordinary shares have same rights and privileges as ordinary shares, except for the voting rights. As of December 31, 2021, the Company has not declared any dividends. Deferred shares As of December 31, 2020 and 2019, deferred shares were a unit of equity in the Company. Deferred shares can be repurchased at any time by the Company for £1.00 for all the deferred shares registered in the name of any holder. Deferred shares have effectively no voting or economic rights attached to them. On April 6, 2021, all the deferred shares were cancelled. In addition, a single deferred share with a nominal value of £92,451.851 in the capital of the Company was created as part of the Company’s reorganization (Note 1). As of December 31, 2021, the Company had one deferred share which could be repurchased at any time by the Company for nil consideration. Convertible The As of December 31, 2020, Convertible Preferred Shares consisted of the following (in thousands, except share data): Shares Liquidation Carrying Authorized Outstanding preference value Series A preferred shares 28,250,000 28,250,000 $ 36,725 $ 36,725 Series B preferred shares (1) 52,192,070 52,192,070 124,615 124,312 Series C preferred shares 24,412,603 24,412,603 70,081 69,894 104,854,673 104,854,673 $ 231,421 $ 230,931 (1) The liquidation preference amount of Series B preferred shares as of December 31, 2020 illustrated in the above tables represents the liquidation amount under the initial public offering. The liquidation preference amount of Series B preferred shares will be different under other situations. On April 6, 2021, all the Convertible Preferred Shares were converted into ordinary shares or Class A non-voting ordinary shares. There are no Convertible Preferred Shares outstanding as of December 31, 2021. The rights, preferences, and privileges of Convertible Preferred Shares were as follows as of December 31, 2020 Conversion At the option of the holder, Convertible Preferred Shares are convertible into an equivalent number of B ordinary shares at any time at conversion ratio of 1:1 In the event the Company issues additional new securities at a price equal to or less than £1.916 per share, the Company shall, unless and to the extent that the holders of 80% of the Series B preferred shares and Series C preferred shares waived, issue to each holder of Series B preferred shares and Series C preferred shares a number of new Series B preferred shares and Series C preferred shares in accordance with the anti-dilution protections within the articles of association. In the event the Company issues additional new securities at a price equal to or less than £2.1589 per share but higher than £1.916 per share, the Company shall, unless and to the extent that the holders of 80% of the Series C preferred shares waived, issue to each holder of Series C preferred shares a number of new Series C preferred shares in accordance with the anti-dilution protections within the articles of association. Dividends Subject to consent of 60% of holders of the Convertible Preferred Shares, dividends may be paid to the holders of Convertible Preferred Shares and B ordinary shares as determined by the board of directors of the Company. Through December 31, 2021, no dividends have been declared or paid. Voting rights The holders of the Convertible Preferred Shares were entitled to vote, together with the holders of B ordinary shares, at all general meetings of the Company and to receive and vote on proposed written resolutions of the Company. The Convertible Preferred Shares carried the right to one vote per Convertible Preferred Share held. Liquidation In the event of any voluntary or involuntary liquidation, dissolution or winding up of the Company, each holder of the then-outstanding Convertible Preferred Shares would be entitled to an amount equal to 100%, 106% and 100% of the subscription price of Series A preferred shares held, Series B preferred shares held and Series C preferred shares held, respectively. After Convertible Preferred Shares, holders of deferred shares would be paid a total of £1.00 for the entire class of deferred shares. Any remaining surplus after liquidation preference to the holders of the Convertible Preferred Shares and deferred shares would then be distributed to the holders of vested ordinary shares (as if they constituted one and the same class) pro rata to the number of vested ordinary shares held. If the amount each Convertible Preferred Share holder was entitled to by participating in the liquidation event as an ordinary share holder on an as-converted basis (regardless of whether such holder converted its Convertible Preferred Shares to B ordinary shares) was greater than the amount to which the holder was entitled as a Convertible Preferred Share holder, the entitlement of the Convertible Preferred Share holder would be calculated on an as-converted ordinary share basis and is ranked equal to the rights of ordinary shareholders. If upon any such liquidation, dissolution, or winding-up, the assets available for distribution to shareholders were insufficient to pay the holders of the Convertible Preferred Shares the full amounts to which they were entitled, the holders of Convertible Preferred Shares were to share ratably in any distribution of the assets available for distribution in proportion to the respective amounts which would otherwise be payable in respect of the Convertible Preferred Shares held by them upon such distribution if all amounts payable on or with respect to such shares were paid in full.

Share-based Compensation

Share-based Compensation	12 Months Ended
	Dec. 31, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Share-based Compensation	8. Employee Shares and Options Under the Company’s shareholder and subscription agreements, which were effective until the date of IPO, the Company was authorized to grant equity awards to individuals including a director of and/or a person who is employed by or who directly or indirectly provides consultancy services to the Company, in the form of D, E, F, G, H, I, J, K, L, M and N ordinary shares , collectively referred to as Employee Shares and share options. All Employee Shares converted into ordinary shares in accordance with the reverse share split implemented on IPO (see Note 1 , “Nature of business,” to our financial statements appearing at the end of this Annual Report ). The share options were granted pursuant to the terms of the 2020 Share Omnibus Plan, or the 2020 Plan. Upon and following closing of the IPO, no further equity awards were granted under the 2020 Plan. To the extent outstanding options granted under the 2020 Plan are cancelled, forfeited or otherwise terminated without being exercised and would otherwise have been returned to the share reserve under the 2020 Plan, the number of shares underlying such awards will be available for future grant under the Company’s 2021 Omnibus Plan (see below). In anticipation of IPO, the holders of Employee Shares and the Company entered into individual vesting agreements, or Vesting Agreements, which apply the same terms to vesting of Employee Shares as applied prior to IPO under the Company’s pre-IPO Articles of Association, except that following the IPO Employee Shares that would pre-IPO have converted to deferred shares, will be transferred back to the Company and cancelled within twelve months of an employee leaving the Company. 2021 Share Omnibus Plan In March 2021, the Company’s board of directors adopted, and the Company’s shareholders approved, the 2021 Share Omnibus Plan, or the 2021 Plan, which became effective upon the effectiveness of the Company’s Registration Statement on Form F-1 in connection with the IPO. The 2021 Plan allows the remuneration committee to make equity-based and cash-based incentive awards to our officers, employees, directors and other key persons (including consultants). The Company initially reserved 2,572,558 of its ordinary shares for the issuance of awards under the 2021 Plan. The 2021 Plan provides that the number of shares reserved and available for issuance under the plan will automatically increase each January 1, beginning on January 1, 2022, by 4% of the outstanding number of ordinary shares on the immediately preceding December 31, or such lesser number of shares as determined by our remuneration committee. This number is subject to adjustment in the event of a sub-division, consolidation, share dividend or other change in our capitalization. The total number of ordinary shares that may be issued under the 2021 Plan was 2,572,558 shares as of December 31, 2021, of which 1,578,993 shares remained available for future grant. 2021 Employee Share Purchase Plan The Company’s 2021 Employee Share Purchase Plan, or ESPP, was adopted by the Board in March 2021 and approved by shareholders in March 2021 and became effective upon the effectiveness of the Company’s Registration Statement on Form F-1 in connection with the IPO. The ESPP initially reserves and authorizes the issuance of up to a total of 467,738 ordinary shares to participating employees. The ESPP provides that the number of shares reserved and available for issuance will automatically increase each January 1, beginning on January 1, 2022 and each January 1 thereafter through January 1, 2022, by the least of (i) 1% of the outstanding number of ordinary shares on the immediately preceding December 31; (ii) 467,738 ordinary shares or (iii) such number of shares as determined by the remuneration committee. The number of shares reserved under the ESPP is subject to change in the event of a share split, share dividend or other change in our capitalization. The total number of ordinary shares that may be issued under the ESPP was 467,738 shares as of December 31, 2021, of which 467,738 shares remained available for future grant. As of December 31, 2021, the initial purchase period under the ESPP has not yet commenced. Employee Shares The Company typically grants incentive shares which vest over a four-year Unvested Employee Shares are forfeited upon the giving or receiving of notice of termination of employment or service relationship in accordance with the Articles of the Company (prior to IPO, and in accordance with the Vesting Agreements post-IPO) and 2020 Plan. Before IPO, the forfeited shares were converted into deferred shares, with a repurchase right for a nominal amount in favor of the Company. As of December 31, 2020, the Company repurchased 1,509,384 deferred shares with the consideration of £0.01 to each holder for all of the deferred shares held by that holder. As part of the Company’s reorganization, 109,058 outstanding deferred shares immediately before the IPO were cancelled upon IPO, and a single deferred share with a nominal value of £92,451.851 in the capital of the Company was created. As of December 31, 2021, the Company had one deferred share which could be repurchased by the Company at any time for nil consideration. The Company measures all share-based awards using the fair value on the date of grant and recognizes compensation expense for those awards over the requisite service period, which is generally the vesting period of the respective award. The Company has granted Employee Shares to employees and non-employees with service-based conditions and records expense for these awards using the straight-line method. A Number of Weighted unvested average ordinary grant date shares fair value Unvested ordinary shares as of December 31, 2019 1,727,874 $ 2.96 Granted 1,993,503 $ 7.58 Vested (746,095 ) $ 3.44 Forfeited (137,790 ) $ 3.46 Unvested ordinary shares as of December 31, 2020 2,837,492 $ 6.38 Granted — — Vested (916,172 ) $ 5.61 Forfeited (18,262 ) $ 6.80 Unvested ordinary shares as of December 31, 2021 1,903,058 $ 6.43 As of 2021 and 2.6 Share Options The following table summarizes the Company’s share options activity for the year ended December 31, 2021: Number of Options Weighted Average Exercise Price Weighted Average Remaining Contractual Term (Years) Aggregate Intrinsic Value (in thousands) Outstanding as of December 31, 2020 240,584 $ 6.75 4.84 $ 313 Granted 1,164,778 $ 13.83 Exercised — — Forfeited (47,515 ) $ 12.98 Outstanding as of December 31, 2021 1,357,847 $ 8.95 8.58 $ 10 Exercisable as of December 31, 2021 102,424 $ 6.99 4.37 $ — Unvested as of December 31, 2021 1,255,423 $ 9.11 8.92 $ 10 The weighted average grant-date fair value of share options granted during the year ended December 31, 2021 and 2020 was $5.42 and $3.33 per share, respectively. As of Share Option Valuation The weighted-average assumptions used in the Black-Scholes option pricing model to determine the fair value of the share options granted to employees during the year ended December 31, 2021 and 2020 were as follows: Year Ended December 31, Year Ended December 31, 2021 2020 Expected term (in years) 6.02 Years 3.21 Years Expected volatility 72.15 % 73.81 % Expected dividend yield 0.00 % 0.00 % Risk free interest rate 1.07 % 0.20 % Fair value of underlying ordinary shares $ 9.53 $ 6.35 Share-based Compensation Expense Share-based Years Ended December 31, 2021 2020 2019 Research and development $ 3,362 $ 1,331 $ 332 General and administrative 2,955 1,661 387 $ 6,317 $ 2,992 $ 719

Leases

Leases	12 Months Ended
	Dec. 31, 2021
Leases [Abstract]
Leases	9. Leases As of December 31, 2021, the Company had seven operating leases of real property for office and laboratory use, for which the Company recorded right-of-use assets and leases liabilities as of the ASU 2016-02 effective date or lease commencement date, if later. In addition, three of the Company’s leases met the short-term exception, having lease terms of 12 months or less, and are therefore not recorded on the Company’s balance sheet. The Company’s leases do not include purchase options. Where the Company’s leases contain options to extend the lease term, the extended lease term is only included in the measurement of the lease when it is reasonably certain to remain in the lease beyond the non-cancelable term. The Company’s leases contain variable lease costs, which pertain to common area maintenance and other operating charges, that are expensed as incurred. Operating leases On July 8, 2016, the Company entered into a Master Service Agreement with Royal Free London NHS Foundation Trust, which included access rights to the laboratory space at the Royal Free Hospital, Pond Street, London, with a 5-year term. The Master Service Agreement was due to expire on August 31, 2020. On June 1, 2020, the Master Service Agreement was renewed and will expire on August 31, 2023. On February 1, 2019, the Company entered into six agreements with Stevenage Bioscience Catalyst to lease office and laboratory suites at Gunnels Wood Road, Stevenage, Hertfordshire, which were due to expire on January 31, 2021. In February 2021, the Company renewed six agreements which will expire on July 31, 2022. On January 10, 2020, the Company entered into a non-cancellable operating lease in relation to office and laboratory premises at Gunnels Wood Road, Stevenage, Hertfordshire for a period of 2 years. The future minimum lease payments committed to in relation to this lease less any landlord incentives to be recognized up to the break total £0.2 million or $0.2 million. On February 21, 2020, the Company entered into a non-cancellable operating lease in relation to office premises at Hammersmith Road, London for a period of 10 years, with a break clause at 5 years. The future minimum lease payments committed to in relation to this lease less any landlord incentives to be recognized up to the break total £5.4 million or $7.0 million. On February 28, 2020, the Company entered into a 4-year manufacturing services collaboration agreement for laboratory space access at Gunnels Wood Road, Stevenage, Hertfordshire, with cancellation penalties of up to £2.2 million or $2.7 million should the Company terminate without due cause. In December 2020, the Company entered into a new lease of a warehouse in west London, United Kingdom for a period of 10 years, with a break clause at 5 years. The Company expects to construct a flexible GMP modular facility to scale up its manufacturing footprint at these premises. The future minimum lease payments to be committed to in relation to this lease up to the break date are £3.8 million or $4.9 million. In June 2021, the Company entered into a new lease of office premises in London, United Kingdom for a period of 3 years, with a break clause at 2 years. The future minimum lease payments to be committed to in relation to this lease up to the break date are £0.1 million or $0.1 million. On October 1, 2021, the Company entered into a non-cancellable operating lease in relation to office and laboratory premises in Philadelphia, Pennsylvania in the United States for a period of 38 months. The right-of-use asset and lease liability will be recorded on the lease commencement date, which is in January 2022. In connection with this lease, the Company maintains a required minimum balance, currently less than $0.1 million in connection with a letter of credit issued for the benefit of the landlord for its commercial facility used as a security deposit for the lease. The total amount is classified as Restricted Cash and has been classified as a non-current asset on the Consolidated Balance Sheets. The letter of credit expires on September 30, 2022. However, it automatically extends for additional one-year Summary of lease costs recognized under ASU 2016-02 The following table contains a summary of the lease costs recognized under ASU 2016-02 and other information pertaining to the Company’s operating leases for the years ended December 31, 2021, 2020 and 2019 (dollars in thousands): Years ended December 31, 2021 2020 2019 Lease cost Operating lease cost $ 4,718 $ 2,927 $ 564 Variable lease cost 5,022 2,891 31 Short-term lease cost 65 49 88 $ 9,805 $ 5,867 $ 683 Other information: Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows used in operating leases $ 4,736 $ 1,844 $ 574 Right of use assets obtained in exchange for new operating lease liabilities $ 314 $ 15,846 $ 457 Weighted average remaining lease term (in years) 3.1 years 4.0 years 0.9 years Weighted average discount rate 4.86 % 4.85 % 5.01 % Variable lease cost is determined based on usage in accordance with the contractual agreements. Pursuant to the terms of the Company’s non-cancelable lease agreements in effect at December 31, 2021, the following table summarizes the Company’s maturities of operating lease liabilities as of December 31, 2021 (in thousands): December 31, 2021 Operating lease liabilities payment 2022 $ 4,974 2023 4,322 2024 3,046 2025 815 Total lease payments $ 13,157 Less: imputed interest (898 ) Present value of lease liability $ 12,259

License Agreements

License Agreements	12 Months Ended
	Dec. 31, 2021
License Agreements [Abstract]
License Agreements	10. License agreements CRT license In May 2016, the Company entered into a License Agreement, or the License Agreement, with Cancer Research Technology Limited, or CRT, pursuant to which the Company obtained access rights to intellectual property and know-how from the TRACERx Study. Under the License Agreement, the Company is granted an exclusive, sublicensable license to the TRACERx patents and bioinformatic data for use in: (i) the therapeutic field of neoantigen cell therapies and adoptive cell transfer; and (ii) the neoantigen diagnostic field, for use in research and the potential development of products for commercialization. The Company is further granted, during the vaccine option period, an exclusive license to the TRACERx patents and the bioinformatic data in the private neoantigen therapeutic vaccine field for research and development but not in the development of products for commercial sale, and a non-exclusive license to the same in the public neoantigen therapeutic vaccine field. The Company also obtained a non-exclusive license to the TRACERx bioinformatic pipeline, patient sequencing and medical data, know-how, and materials. CRT additionally granted the Company certain rights to new patent applications filed by the Founding Institutions in respect of inventions resulting from the TRACERx study through February 2023, including automatic exclusive licenses to patent rights relating to non-severable improvements of technology covered by the original TRACERx patents and non-exclusive rights to severable improvements. CRT granted the Company the right of first negotiation to license certain patents rights generated by the Company’s founders outside of the TRACERx study which relate to the licensed technology. In July 2017, the Company obtained a non-exclusive license to the LOHHLA patent under the License Agreement. In October 2018, the Company obtained an exclusive license to the LOHHLA patent under an addendum to the License Agreement. Under the License Agreement, the Company holds an option to exploit products in the therapeutic vaccine field (the “Vaccine Option”). In March 2021, the Company extended the Vaccine Option from May 2021 to May 2023 with a payment of less than £0.1 million or $0.1 million. In May 2018, the Company entered into an amendment to the License Agreement that created an additional sample period through July 2020 and specified additional patient tumor and blood materials to be subject to the License Agreement related to the immunology side study. The License Agreement was subsequently amended in July 2020, November 2020 and March 2021. Upon execution of the License Agreement the Company granted CRT 396,125 B ordinary shares and 67,793 C ordinary shares. The C ordinary shares granted to CRT were forfeited and transferred to the deferred shares during the year ended December 31, 2019, as the applicable performance conditions were not met. The B ordinary shares granted to CRT were converted into ordinary shares upon IPO. The Company recorded $0.3 million of IP research and development expense in 2016. The Company is obligated to pay CRT milestone success payments up to an aggregate of £6.5 million for therapeutic products, and milestone success payments up to an aggregate £0.8 million for non-therapeutic products, as well as sub-single digit to low-single digit percentage royalty on net sales of products that utilize the licensed intellectual property, subject to certain customary reductions. The royalty obligations continue on a product-by-product and country-by-country basis until the later of: (i) the date there ceases to be a valid patent claim covering such product in the country in which it is sold; or (ii) with respect to contribution royalty products, ten years from the first commercial sale of the product, and with respect to a patent royalty product, five years from the first commercial sale of the product. On a product-by-product basis, the Company may also elect to provide other cash consideration at fair market value and forgo the milestone or royalty payment. Unless terminated earlier, the term of the agreement continues until the later of the expiration of the royalty term in each country and such time as no further milestone payments are due, and upon such termination, the licenses granted shall become fully-paid, royalty-free, irrevocable, and perpetual. The Company has the right to terminate the license agreement for convenience in its entirety upon 90 days’ notice. Each party may terminate the agreement if the other party is in material breach subject to a 90 day remedy period. The Company has the right to acquire ownership of the TRACERx patents upon either: (i) the occurrence of a royalty product for use in the therapeutic field; (ii) CRT shareholders cease to hold any ordinary shares in the Company; (iii) the Company undergoes an initial public offering; or (iv) the Company is acquired by a third party for more than £25.0 million. Upon IPO, the Company gave notice to CRT to exercise the option to acquire the TRACERx patents with no consideration in accordance with the terms of the License Agreement. The acquisition was not finalized as of December 31, 2021. Less than $0.1 million of expenses were recorded for the year ended December 31, 2021 related to the CRT License Agreement. No expenses were recorded for the years ended December 31, 2020 and 2019 related to the CRT License Agreement. Secarna license On October 20, 2021, the Company entered into an agreement, or Secarna Agreement with Secarna Pharmaceuticals GmbH & Co. KG or Secarna, whereby Secarna granted to the Company a non-exclusive worldwide license under certain patent and other intellectual property rights, to use the Secarna technology in the ex vivo manufacture of a T cell pharmaceutical product. The Company is obligated to pay Secarna development milestone payments up to a maximum aggregate of €6.5 €26 million ($29.4 Unless terminated earlier, the term of the agreement continues until the later of the expiration of the royalty term in each country and such time as no further milestone payments are due, and upon such termination, the licenses granted shall become fully-paid, royalty-free, irrevocable, and perpetual. The Company has the right to terminate the license agreement for convenience in its entirety upon 90 days’ notice. Each party may terminate the agreement if the other party is in material breach subject to a 60 day remedy period.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Income Taxes	11. The Company is domiciled in the United Kingdom and is primarily subject to taxation in that country. During the years ended December 31, 2021, 2020 and 2019, the Company recorded no income tax benefits for the net operating losses incurred in the UK in each period due to its uncertainty of realizing a benefit from those items. During the year ended December 31, 2021, 2020 and 2019, the Company recorded a tax provision related to income tax obligations of its operating company in the U.S., which generates a profit for tax purposes. Loss before provision for income taxes consisted of the following (in thousands): December 31, 2021 2020 2019 United Kingdom $ (61,182 ) $ (33,204 ) $ (13,990 ) Foreign 120 8 — $ (61,062 ) $ (33,196 ) $ (13,990 ) The income tax provision for the years ended December 31, 2021, 2020 and 2019 is comprised of the following (in thousands): December 31, 2021 2020 2019 Current expense: United Kingdom $ — $ — $ — Foreign 59 7 — Total current expense: 59 7 — Deferred expense (benefit): United Kingdom — — — Foreign (22 ) (4 ) — Total deferred expense (benefit): (22 ) (4 ) — Total income tax expense: $ 37 $ 3 $ — The 2021, 2020 A Year Ended December 31, 2021 2020 2019 Income taxes at UK statutory rate 19.00 % 19.00 % 19.00 % R&D expenditure (6.67 )% (6.69 )% (12.37 )% Change in valuation allowance (20.12 )% (13.12 )% (6.85 )% Change in UK tax rate 7.64 % — — Other (0.13 )% 0.80 % 0.22 % (0.28 )% (0.01 )% — Significant 2021, December 31, 2021 2020 2019 Deferred tax assets Net operating loss carryforwards $ 17,742 $ 7,065 $ 2,475 Depreciation (1,311 ) (983 ) (243 ) Non-cash share-based compensation 2,328 769 161 Other 329 241 (2 ) Total deferred tax assets $ 19,088 $ 7,092 $ 2,391 Valuation allowance (19,062 ) (7,088 ) (2,391 ) Net deferred tax assets $ 26 $ 4 $ — As of Changes December 31, 2021 2020 2019 Valuation allowance at beginning of year $ 7,088 $ 2,391 $ 1,342 Increases recorded to income tax provision 7,624 4,628 996 Exchange difference (313 ) 69 53 Change in tax rate 4,663 — — Valuation allowance at end of year $ 19,062 $ 7,088 $ 2,391 Future The The The During the second quarter of 2021, the Finance Act 2021 (the Act) was enacted in the United Kingdom. The Act increases the corporate income tax from 19% to 25% effective April 1, 2023 and enhances the first-year capital allowance on qualifying new plant and machinery assets effective April 1, 2021. The effects on the Company’s existing deferred tax balances have been recorded and is offset by the valuation allowance maintained against the Company’s UK net deferred tax assets. As of December 31, 2021 and 2020, income taxes on undistributed earnings of the Company’s U.S. subsidiary have not been provided for as the Company plans to indefinitely reinvest these amounts in the U.S. The cumulative undistributed foreign earnings were not material as of December 31, 2021 and 2020.

Net Loss Per Share

Net Loss Per Share	12 Months Ended
	Dec. 31, 2021
Earnings Per Share [Abstract]
Net Loss Per Share	12. Basic Year ended December 31, 2021 2020 2019 Numerator Net loss $ (61,099 ) $ (33,199 ) $ (13,990 ) Net loss attributable to ordinary shareholders—basic and diluted $ (61,099 ) $ (33,199 ) $ (13,990 ) Denominator Weighted-average number of ordinary shares used in net loss per share—basic and diluted 28,654,760 1,066,208 642,169 Net loss per share—basic and diluted $ (2.13 ) $ (31.14 ) $ (21.79 ) The 2021, Year ended December 31, 2021 2020 2019 Series A preferred shares (as converted into ordinary shares) — 7,134,644 7,134,644 Series B preferred shares (as converted into ordinary shares) — 13,181,515 8,787,851 Series C preferred shares (as converted into ordinary shares) — 6,165,672 — Unvested ordinary shares 1,903,058 2,837,492 1,727,874 Share options 1,357,847 240,584 — Total 3,260,905 29,559,907 17,650,369

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2021
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	13. Commitments Commitment The In June 2021, the Company entered into an obligation to take on a new lease of lab and office premises in Stevenage, Hertfordshire, United Kingdom for a period of 10 years, with a break clause at 3 and 7 years. The future minimum lease payments to be committed to in relation to this lease up to the break date are £0.6 million or $0.8 million. As of December 31, 2021, the lease was not commenced and no right of use assets and operating lease liabilities were recognized related to that lease agreement. Asset Retirement Obligations The following is a reconciliation of our beginning and ending asset retirement obligation balances for 2021 and 2020 (in thousands): 2021 2020 Balance, beginning of the year $ 652 $ — Additions in estimates 652 Accretion of discount $ 38 — Balance, end of year $ 690 $ 652 The Company’s asset retirement obligations relate to post-closure reclamation costs for a lease of office and laboratory space. Legal From Indemnification In In accordance with the indemnification agreements entered into with relevant individuals in accordance with the Company’s Articles of Association, the Company has indemnification obligations to its officers and directors, officers and members of senior management for certain events or occurrences, subject to certain limits, while they are serving at the Company’s request in such capacity. There have been no claims to date, and the Company has director and officer insurance that may enable it to recover a portion of any amounts paid for future potential claims.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Related Party Transactions	14. The 2021, During the year ended December 31, 2019, $0.1 million was charged to the company by Syncona Investment Management Limited for management fees and other costs incurred on behalf of the Company. No such transaction was incurred during the year ended December 31, 2021 and 2020. Syncona Investment Management is a subsidiary of Syncona Limited.

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2021
Compensation And Retirement Disclosure [Abstract]
Employee Benefit Plans	15. In the United Kingdom, the Company makes contributions to private defined contribution pension schemes on behalf of its employees. The contributions to this scheme are expensed to the statement of operations as they fall due. The Company paid $1.8 million, $1.0 million and $0.5 in contributions in the year ended December 31, 2021, 2020 and 2019, respectively. In the United States, the Company established a defined contribution savings plan under Section 401(k) of the Internal Revenue Code. This plan covers substantially all U.S. employees who meet minimum age and service requirements and allows participants to defer a portion of their annual compensation on a pre-tax basis. The Company paid less than $0.1

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2021
Subsequent Events [Abstract]
Subsequent Events	16. The Company has completed an evaluation of all subsequent events through March 1, 2022, the date on which the financial statements were issued, to ensure that these financial statements include appropriate disclosure of events both recognized in these financial statements as of December 31, 2021, and events which occurred subsequently but were not recognized in these financial statements. On February 2, 2022, the Company issued 1,044,410 options with an exercise price of $3.62.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Going Concern	Going In accordance The December 31 The As of December 31, 2021, the Company had cash and cash equivalents of $266.3 million. The Directors have reviewed the financial projections of the Company for the 12 months subsequent to the date of issuance of these financial statements including consideration of severe but plausible scenarios that may affect the Company in that period. These show that the Company will be able to pay (or otherwise discharge) its debts as they fall due immediately following the date of signing of this Balance Sheet and for the period considered by the forecast. Accordingly, the
Basis of Presentation	Basis The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America or U.S. GAAP and are presented in U.S. dollars. .
Use of Estimates	Use The
Segment Information	Segment Operating The Company operates in a single segment, focusing on researching, developing and commercializing potentially novel cancer immunotherapies targeting clonal neoantigens. Consistent with its operational structure, its chief operating decision maker, the Company’s chief executive officer, views and manages the Company’s operations and manages its business as a single operating segment. All material long-lived assets of the Company reside in the UK
Foreign Currency Translation	Foreign The gains of 2021, For (loss)/
Cash and Cash Equivalents	Cash The In connection with a lease, the Company maintains a required minimum balance, currently less than $0.1 million in connection with a letter of credit issued for the benefit of the landlord for its commercial facility used as a security deposit for the lease. The total amount is classified as Restricted Cash and has been classified as a non-current asset in the Consolidated Balance Sheets.
Deferred Initial Public Offering Costs	Deferred Initial Public Offering Costs The Company capitalized deferred initial public offering, or IPO, costs, which primarily consist of direct, incremental legal, professional accounting and other third-party fees relating to the Company’s IPO, within prepaid expenses and other current assets. The deferred IPO costs were offset against IPO proceeds upon the consummation of the offering. The Company recorded $ 1.0 million of deferred IPO costs as of December 31, 2020. The Company did no t record any deferred IPO costs as of December 31, 2021 and 2019.
Fair Value of Financial Instruments	Fair The fair value hierarchy as Level 1 as there are quoted prices in active markets for identical assets. See Note 3, Fair Value of Financial Instruments.
Concentrations of Credit Risk and Off-Balance Sheet Risk	Concentrations Financial
Property and Equipment	Property Property Estimated useful life Lab equipment 5 years Fixture and fittings 5 years Office equipment and computers 3 years Leasehold improvements Shorter of useful life or remaining lease term Upon
Impairment of Long-Lived Assets	Impairment The Company evaluates assets for potential impairment when events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Recoverability is measured by comparing the book values of the assets to the expected future net undiscounted cash flows that the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the book values of the assets exceed their fair value. The Company recognized an impairment loss of $0.1 million in the year ended December 31, 2021. The Company did not recognize any impairment losses in the years ended December 31, 2020 and 2019.
Research and Development Costs	Research Research
Research Contract Costs and Accruals	Research The
Asset Retirement and Environmental Obligations	Asset Retirement and Environmental Obligations Pursuant to ASC 410, Asset Retirement and Environmental Obligations, an asset retirement obligation (“ARO” or “AROs”) is recorded when there is a legal obligation associated with the retirement of a tangible long-lived asset and the fair value of the liability can reasonably be estimated. Upon initial recognition, AROs are recorded as a liability at their estimated present value, with an offsetting increase to the carrying amount of the long-lived asset. Over time, the liabilities are accreted for the change in their present value through charges to operations costs. If the fair value of the estimated ARO changes, an adjustment is recorded to both the ARO and the asset retirement cost. Revisions in estimated liabilities can result from revisions of estimated inflation rates, escalating retirement costs, and changes in the estimated timing of settling ARO liabilities. Total ARO consists of amounts for decommissioning and restoration of rented facilities to be performed in the future. The Company computes the liability for AROs based on assumptions from third-party estimates of the total restoration costs, adjusted for inflation. These values are discounted to present value using our credit adjusted incremental borrowing rate of the related rental facility and recorded ARO in other long-term liabilities. Periodic accretion of the discount on the ARO is recorded as part of accretion expense.
Share-Based Compensation	Share-based compensation The commitments Effective Compensation—Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting There have been no performance conditions attached to the share options granted by the Company to date. The fair value of each share option grant is estimated on the date of grant using the Black-Scholes option pricing model. See Note 8, “Share-based compensation,” for the Company’s assumptions used in connection with option grants made during the periods covered by these consolidated financial statements. Assumptions used in the option pricing model include the following: Expected volatility. As Achilles became a listed, public company in April 2021, the Company has limited company-specific historical and implied volatility information for its ordinary shares. Therefore, it estimates its expected share volatility based on the historical volatility of publicly traded peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded share price. Expected term. The expected term of the Company’s share options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options as there is a limited trading history of our ordinary shares. Risk-free interest rate. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods that are approximately equal to the expected term of the award. Expected dividend. Expected dividend yield of zero is based on the fact that the Company has never paid cash dividends on ordinary shares and does not expect to pay any cash dividends in the foreseeable future. Effective Compensation—Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting There have been no performance conditions attached to the share options granted by the Company to date. The fair value of each share option grant is estimated on the date of grant using the Black-Scholes option pricing model. See Note 8, “Share-based compensation,” for the Company’s assumptions used in connection with option grants made during the periods covered by these consolidated financial statements. Assumptions used in the option pricing model include the following: Expected volatility. As Achilles became a listed, public company in April 2021, the Company has limited company-specific historical and implied volatility information for its ordinary shares. Therefore, it estimates its expected share volatility based on the historical volatility of publicly traded peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded share price. Expected term. The expected term of the Company’s share options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options as there is a limited trading history of our ordinary shares. Risk-free interest rate. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods that are approximately equal to the expected term of the award. Expected dividend. Expected dividend yield of zero is based on the fact that the Company has never paid cash dividends on ordinary shares and does not expect to pay any cash dividends in the foreseeable future. Given the absence of an active market for the Company’s ordinary shares prior to the IPO, the Valuation of Privately-Held-Company Equity Securities Issued as Compensation price valuation as an input to the determination of share-based compensation. After IPO, the fair value of ordinary shares is determined by reference to the closing price of ADSs on the Nasdaq Global Select Market on the date of grant. The
Leases	Leases Effective Lease Operating
Income Taxes	Income The future and to the extent management believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies. The The 2021,
Research and Development Tax Credit	Research The The As The Unsurrendered UK
Comprehensive Income (Loss)	Comprehensive Comprehensive
Net Loss Per Share	Net The
Government Grants	Government grants The Group receives certain government grants that support specific research and development activities. Income in respect of grants also includes contributions towards the costs of research and development. Income is recognized when costs under each grant are incurred in accordance with the terms and conditions of the grant and the collectability of the receivable is reasonably assured. Government grants relating to costs are deferred and recognized in the income statement over the period necessary to match them with the costs they are intended to compensate. The Group recognizes income from government grants under 'Other income—net' in the Company’s consolidated statement of comprehensive loss.
Recent Accounting Pronouncements	Recent Recently In December 2019, the FASB issued ASU 2019-12, “ Income Taxes—Simplifying the Accounting for Income Taxes In November 2021, the FASB issued ASU 2021-10, “ Government Assistance – Topic 832 – Disclosures by Business Entities about Government Assistance 15, 2021; however, early adoption is permitted. The new guidance was adopted on January 1, 2022 and will be effective for the year ended December 21, 2022. This guidance is not expected to have a material impact on the Company’s financial statements and related disclosures.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Summary of Property and Equipment	Property Estimated useful life Lab equipment 5 years Fixture and fittings 5 years Office equipment and computers 3 years Leasehold improvements Shorter of useful life or remaining lease term Property and equipment, net consisted of the following (in thousands): December 31, 2021 2020 Lab equipment $ 7,505 $ 4,644 Leasehold improvements 7,021 6,960 Office equipment and computers 1,561 1,168 Fixtures and fittings 757 706 Assets under construction 5,351 1,275 22,195 14,753 Less: Accumulated depreciation (4,452 ) (1,384 ) $ 17,743 $ 13,369

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2021
Fair Value Disclosures [Abstract]
Summary of Assets Measured at Fair Value on Recurring Basis	The following tables show assets measured at fair value on a recurring basis as of December 31, 2021 (in thousands): December 31, 2021 Level 1 Level 2 Level 3 Cash equivalents: Money market funds $ 40,224 $ — $ — $ 40,224 $ — $ —

Prepaid Expenses and Other Cu_2

Prepaid Expenses and Other Current Assets (Tables)	12 Months Ended
	Dec. 31, 2021
Prepaid Expense And Other Assets Current [Abstract]
Summary of Prepaid Expenses and Other Current Assets	Prepaid December 31, 2021 2020 UK R&D tax credit $ 10,523 $ 6,214 Prepaid research and development 3,608 751 Prepaid insurance 1,525 21 VAT recoverable 650 1,125 Deferred offering costs — 1,007 Other current assets 2,124 830 $ 18,430 $ 9,948

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	12 Months Ended
	Dec. 31, 2021
Property Plant And Equipment [Abstract]
Summary of Property and Equipment	Property Estimated useful life Lab equipment 5 years Fixture and fittings 5 years Office equipment and computers 3 years Leasehold improvements Shorter of useful life or remaining lease term Property and equipment, net consisted of the following (in thousands): December 31, 2021 2020 Lab equipment $ 7,505 $ 4,644 Leasehold improvements 7,021 6,960 Office equipment and computers 1,561 1,168 Fixtures and fittings 757 706 Assets under construction 5,351 1,275 22,195 14,753 Less: Accumulated depreciation (4,452 ) (1,384 ) $ 17,743 $ 13,369

Accrued Expenses and Other Li_2

Accrued Expenses and Other Liabilities (Tables)	12 Months Ended
	Dec. 31, 2021
Payables And Accruals [Abstract]
Schedule of Accrued Expenses and Other Liabilities	Accrued December 31, 2021 2020 Compensation and benefits $ 2,649 $ 1,494 External research and development expenses 2,985 2,201 Facility costs 2,629 868 Property and equipment 712 303 Professional services 663 1,222 Other liabilities 1,268 502 $ 10,906 $ 6,590

Shareholders_ Equity (Tables)

Shareholders’ Equity (Tables)	12 Months Ended
	Dec. 31, 2021
Stockholders Equity Note [Abstract]
Summary of Ordinary Shares Issued and Outstanding	As of December 31, 2021 and 2020, the Company had the following number of ordinary shares with a par value £0.001 (equivalent to $0.001) issued and outstanding December 31, 2021 2020 Ordinary shares 38,987,122 — Class A non-voting ordinary shares 1,616,367 — B Ordinary shares — 505,108 D Ordinary shares — 155,669 E Ordinary shares — 80,007 F Ordinary shares — 327,084 G Ordinary shares — 194,261 H Ordinary shares — 88,871 I Ordinary shares — 48,391 J Ordinary shares — 262,478 L Ordinary shares — 1,207,670 M Ordinary shares — 811,436 N Ordinary shares — 708,945 Deferred Shares 1 30,521 Total ordinary and deferred shares 40,603,490 4,420,441
Summary of Convertible Preferred Shares	As of December 31, 2020, Convertible Preferred Shares consisted of the following (in thousands, except share data): Shares Liquidation Carrying Authorized Outstanding preference value Series A preferred shares 28,250,000 28,250,000 $ 36,725 $ 36,725 Series B preferred shares (1) 52,192,070 52,192,070 124,615 124,312 Series C preferred shares 24,412,603 24,412,603 70,081 69,894 104,854,673 104,854,673 $ 231,421 $ 230,931

Share-based compensation (Table

Share-based compensation (Tables)	12 Months Ended
	Dec. 31, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Changes in Unvested Ordinary Shares	A Number of Weighted unvested average ordinary grant date shares fair value Unvested ordinary shares as of December 31, 2019 1,727,874 $ 2.96 Granted 1,993,503 $ 7.58 Vested (746,095 ) $ 3.44 Forfeited (137,790 ) $ 3.46 Unvested ordinary shares as of December 31, 2020 2,837,492 $ 6.38 Granted — — Vested (916,172 ) $ 5.61 Forfeited (18,262 ) $ 6.80 Unvested ordinary shares as of December 31, 2021 1,903,058 $ 6.43
Summary of Share Options Activity	The following table summarizes the Company’s share options activity for the year ended December 31, 2021:
Summary of Weighted-Average Assumptions Used in Black-Scholes Option Pricing Model	The weighted-average assumptions used in the Black-Scholes option pricing model to determine the fair value of the share options granted to employees during the year ended December 31, 2021 and 2020 were as follows: Year Ended December 31, Year Ended December 31, 2021 2020 Expected term (in years) 6.02 Years 3.21 Years Expected volatility 72.15 % 73.81 % Expected dividend yield 0.00 % 0.00 % Risk free interest rate 1.07 % 0.20 % Fair value of underlying ordinary shares $ 9.53 $ 6.35
Summary of Share-based Compensation Expense	Share-based Years Ended December 31, 2021 2020 2019 Research and development $ 3,362 $ 1,331 $ 332 General and administrative 2,955 1,661 387 $ 6,317 $ 2,992 $ 719

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2021
Leases [Abstract]
Summary of Lease Costs Recognized and Other Information Pertaining to Operating Leases	The following table contains a summary of the lease costs recognized under ASU 2016-02 and other information pertaining to the Company’s operating leases for the years ended December 31, 2021, 2020 and 2019 (dollars in thousands): Years ended December 31, 2021 2020 2019 Lease cost Operating lease cost $ 4,718 $ 2,927 $ 564 Variable lease cost 5,022 2,891 31 Short-term lease cost 65 49 88 $ 9,805 $ 5,867 $ 683 Other information: Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows used in operating leases $ 4,736 $ 1,844 $ 574 Right of use assets obtained in exchange for new operating lease liabilities $ 314 $ 15,846 $ 457 Weighted average remaining lease term (in years) 3.1 years 4.0 years 0.9 years Weighted average discount rate 4.86 % 4.85 % 5.01 %
Summary of Maturities of Operating Lease Liabilities	Pursuant to the terms of the Company’s non-cancelable lease agreements in effect at December 31, 2021, the following table summarizes the Company’s maturities of operating lease liabilities as of December 31, 2021 (in thousands): December 31, 2021 Operating lease liabilities payment 2022 $ 4,974 2023 4,322 2024 3,046 2025 815 Total lease payments $ 13,157 Less: imputed interest (898 ) Present value of lease liability $ 12,259

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Summary of Loss Before Provision for Income Taxes	Loss before provision for income taxes consisted of the following (in thousands): December 31, 2021 2020 2019 United Kingdom $ (61,182 ) $ (33,204 ) $ (13,990 ) Foreign 120 8 — $ (61,062 ) $ (33,196 ) $ (13,990 )
Summary of Income Tax Provision	The income tax provision for the years ended December 31, 2021, 2020 and 2019 is comprised of the following (in thousands): December 31, 2021 2020 2019 Current expense: United Kingdom $ — $ — $ — Foreign 59 7 — Total current expense: 59 7 — Deferred expense (benefit): United Kingdom — — — Foreign (22 ) (4 ) — Total deferred expense (benefit): (22 ) (4 ) — Total income tax expense: $ 37 $ 3 $ —
Schedule of Reconciliation of Income Tax Expense Computed at Statutory UK Income Taxes	A Year Ended December 31, 2021 2020 2019 Income taxes at UK statutory rate 19.00 % 19.00 % 19.00 % R&D expenditure (6.67 )% (6.69 )% (12.37 )% Change in valuation allowance (20.12 )% (13.12 )% (6.85 )% Change in UK tax rate 7.64 % — — Other (0.13 )% 0.80 % 0.22 % (0.28 )% (0.01 )% —
Summary of Significant Component of Deferred Tax Assets and Liabilities	Significant 2021, December 31, 2021 2020 2019 Deferred tax assets Net operating loss carryforwards $ 17,742 $ 7,065 $ 2,475 Depreciation (1,311 ) (983 ) (243 ) Non-cash share-based compensation 2,328 769 161 Other 329 241 (2 ) Total deferred tax assets $ 19,088 $ 7,092 $ 2,391 Valuation allowance (19,062 ) (7,088 ) (2,391 ) Net deferred tax assets $ 26 $ 4 $ —
Summary of Changes in Valuation Allowance for Deferred Tax Assets	Changes December 31, 2021 2020 2019 Valuation allowance at beginning of year $ 7,088 $ 2,391 $ 1,342 Increases recorded to income tax provision 7,624 4,628 996 Exchange difference (313 ) 69 53 Change in tax rate 4,663 — — Valuation allowance at end of year $ 19,062 $ 7,088 $ 2,391

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	12 Months Ended
	Dec. 31, 2021
Earnings Per Share [Abstract]
Summary of Basic and Diluted Net Loss Per Share Attributable to Ordinary Shareholders	Basic Year ended December 31, 2021 2020 2019 Numerator Net loss $ (61,099 ) $ (33,199 ) $ (13,990 ) Net loss attributable to ordinary shareholders—basic and diluted $ (61,099 ) $ (33,199 ) $ (13,990 ) Denominator Weighted-average number of ordinary shares used in net loss per share—basic and diluted 28,654,760 1,066,208 642,169 Net loss per share—basic and diluted $ (2.13 ) $ (31.14 ) $ (21.79 )
Summary of Antidilutive Securities Excluded from Computation of Earnings Per Share	The 2021, Year ended December 31, 2021 2020 2019 Series A preferred shares (as converted into ordinary shares) — 7,134,644 7,134,644 Series B preferred shares (as converted into ordinary shares) — 13,181,515 8,787,851 Series C preferred shares (as converted into ordinary shares) — 6,165,672 — Unvested ordinary shares 1,903,058 2,837,492 1,727,874 Share options 1,357,847 240,584 — Total 3,260,905 29,559,907 17,650,369

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2021
Commitments And Contingencies Disclosure [Abstract]
Summary of Asset Retirement Obligation	The following is a reconciliation of our beginning and ending asset retirement obligation balances for 2021 and 2020 (in thousands): 2021 2020 Balance, beginning of the year $ 652 $ — Additions in estimates 652 Accretion of discount $ 38 — Balance, end of year $ 690 $ 652

Nature of the Business - Additi

Nature of the Business - Additional Information (Details) £ / shares in Units, $ / shares in Units, $ in Thousands	Apr. 06, 2021USD ($)Stockholder$ / sharesshares	Apr. 06, 2021GBP (£)£ / sharesshares	Dec. 31, 2020USD ($)£ / shares	Dec. 31, 2021USD ($)shares	Dec. 31, 2020USD ($)shares	Dec. 31, 2019USD ($)shares
Disclosure Of Nature Of Business [Line Items]
Nominal value of newly issued share | £ / shares		£ 0.001	£ 1.20
Reverse share split, nominal value of deferred share | £		£ 92,451.851
Accumulated Deficit			£ 58,012	$ 119,111	$ 58,012
Cash and cash equivalents			£ 177,849	$ 266,319	$ 177,849	$ 97,594
Ordinary Shares
Disclosure Of Nature Of Business [Line Items]
Issuance of ordinary shares (Note 7), shares | shares				9,750,000	1,993,503	1,358,765
Reverse stock split				one-for-0.2526
Convertible Preferred Shares
Disclosure Of Nature Of Business [Line Items]
Reverse stock split				one-for-0.1792
Class A Non Voting Ordinary Share
Disclosure Of Nature Of Business [Line Items]
Number of shareholders elected to receive shares | Stockholder	2
IPO | American Depository Shares
Disclosure Of Nature Of Business [Line Items]
Issuance of ordinary shares (Note 7), shares | shares	9,750,000	9,750,000
Price per share | $ / shares	$ 18
Net proceeds from sale	$ 160,600

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2021USD ($)Segment	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Summary Of Significant Accounting Policy [Line Items]
Number of operating Segment | Segment	1
Foreign exchange gains	$ 2,500,000	$ 400,000	$ 100,000
Deferred IPO costs		1,007,000
Impairment loss	100,000	0	0
Accrued interest or penalties	0	0	0
IPO
Summary Of Significant Accounting Policy [Line Items]
Deferred IPO costs	0	$ 1,000,000	$ 0
Maximum
Summary Of Significant Accounting Policy [Line Items]
Required minimum balance maintained in connection with lease	$ 100,000
Percentage of qualifying research and development expenditure	33.35%
Percentage of subcontracted qualifying research and development expenditure	21.67%

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Summary of Property and Equipment Recorded at Cost and Depreciation Using Straight-Line Method (Details)	12 Months Ended
	Dec. 31, 2021
Lab Equipment
Summary Of Significant Accounting Policy [Line Items]
Property and equipment estimated useful life	5 years
Fixture and Fittings
Summary Of Significant Accounting Policy [Line Items]
Property and equipment estimated useful life	5 years
Office Equipment and Computers
Summary Of Significant Accounting Policy [Line Items]
Property and equipment estimated useful life	3 years
Leasehold Improvements
Summary Of Significant Accounting Policy [Line Items]
Property plant and equipment depreciation methods	Shorter of useful life or remaining lease term

Fair Value of Financial Instr_3

Fair Value of Financial Instruments - Summary of Assets Measured at Fair Value on Recurring Basis (Details) - Level 1 $ in Thousands	Dec. 31, 2021USD ($)
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents	$ 40,224
Money Market Funds
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents	$ 40,224

Fair Value of Financial Instr_4

Fair Value of Financial Instruments - Additional Information (Details) - Recurring Basis - USD ($)	Dec. 31, 2021	Dec. 31, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Liabilities measured at fair value on recurring basis	$ 0	$ 0
Assets measured at fair value on recurring basis		$ 0

Prepaid Expenses and Other Cu_3

Prepaid Expenses and Other Current Assets - Summary of Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Prepaid Expense And Other Assets Current [Abstract]
UK R&D tax credit	$ 10,523	$ 6,214
Prepaid research and development	3,608	751
Prepaid insurance	1,525	21
VAT recoverable	650	1,125
Deferred offering costs		1,007
Other current assets	2,124	830
Total	$ 18,430	$ 9,948

Property and Equipment, Net - S

Property and Equipment, Net - Summary of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Property Plant And Equipment [Line Items]
Property and equipment, Gross	$ 22,195	$ 14,753
Less: Accumulated depreciation	(4,452)	(1,384)
Property and equipment, net	17,743	13,369
Lab Equipment
Property Plant And Equipment [Line Items]
Property and equipment, Gross	7,505	4,644
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, Gross	7,021	6,960
Office Equipment and Computers
Property Plant And Equipment [Line Items]
Property and equipment, Gross	1,561	1,168
Fixture and Fittings
Property Plant And Equipment [Line Items]
Property and equipment, Gross	757	706
Asset under Construction
Property Plant And Equipment [Line Items]
Property and equipment, Gross	$ 5,351	$ 1,275

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Property Plant And Equipment [Abstract]
Depreciation expense	$ 3.3	$ 0.8	$ 0.3

Accrued Expenses and Other Li_3

Accrued Expenses and Other Liabilities - Schedule of Accrued Expenses and Other Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Payables And Accruals [Abstract]
Compensation and benefits	$ 2,649	$ 1,494
External research and development expenses	2,985	2,201
Facility costs	2,629	868
Property and equipment	712	303
Professional services	663	1,222
Other liabilities	1,268	502
Accrued expenses and other liabilities	$ 10,906	$ 6,590

Shareholders' Equity - Addition

Shareholders' Equity - Additional Information (Details)	Apr. 06, 2021£ / shares	Dec. 31, 2021USD ($)Vote	Dec. 31, 2021£ / sharesshares	Dec. 31, 2021$ / sharesshares	Dec. 31, 2020£ / sharesshares	Dec. 31, 2020$ / sharesshares	Dec. 31, 2019£ / shares
Class Of Stock [Line Items]
Ordinary shares, par value | (per share)			£ 0.001	$ 0.001	£ 0.001	$ 0.001
Description of voting rights of ordinary shares		Each holder of B ordinary shares was entitled to one vote per B ordinary share and, to receive dividends declared with Investor Majority consent and any such dividend as determined by the board of directors of the Company acting with investor director consent, provided that the preferred shares and the B ordinary shares shall, subject to the 2019 Articles and 2020 Articles, rank equally in all respects for the purpose of any dividend that is declared or paid. All other classes of ordinary shares do not have voting rights.
Convertible preferred shares outstanding | shares			0	0	104,854,673	104,854,673
Description of conversion		All Convertible Preferred Shares will automatically convert into an equivalent number of B ordinary shares upon either: (i) the notice of 60% of Convertible Preferred Shareholders that such conversion shall occur; or (ii) immediately upon an initial public offering in which the per share net public offering is at least 1.15 times £2.1589 (subject to appropriate adjustment in the event of any share dividend, share split, combination or other similar recapitalization)
Percentage of convertible preferred shareholders		60.00%
Initial public offering net offering			£ 2.1589
Net aggregate proceeds of offering | $		$ 160,755,000
Dividends declared or paid | $		$ 0
Description of voting rights of preferred shares		The Convertible Preferred Shares carried the right to one vote per Convertible Preferred Share held.
Amount of deferred shares paid after convertible preferred shares			£ 1
Deferred Shares
Class Of Stock [Line Items]
Deferred shares repurchase price per share					£ 1		£ 1
Deferred shares nominal value per share	£ 92,451.851
Deferred shares repurchase | shares			1	1
B Ordinary Shares
Class Of Stock [Line Items]
Number of vote per share | Vote		1
Convertible preferred shares, conversion ratio		100.00%
Series B Preferred Shares and Series C Preferred Shares
Class Of Stock [Line Items]
Percentage of preferred shares waived		80.00%
Series C Preferred Shares
Class Of Stock [Line Items]
Convertible preferred shares outstanding | shares					24,412,603	24,412,603
Percentage of preferred shares waived		80.00%
Percentage of outstanding convertible preferred shares		100.00%
Convertible Preferred Shares
Class Of Stock [Line Items]
Number of vote per share | Vote		1
Series A Preferred Shares
Class Of Stock [Line Items]
Convertible preferred shares outstanding | shares					28,250,000	28,250,000
Percentage of outstanding convertible preferred shares		100.00%
Series B Preferred Shares
Class Of Stock [Line Items]
Convertible preferred shares outstanding | shares					52,192,070	52,192,070
Percentage of outstanding convertible preferred shares		106.00%
Minimum
Class Of Stock [Line Items]
Net aggregate proceeds of offering | $		$ 75,000,000
Minimum | Series C Preferred Shares
Class Of Stock [Line Items]
Issuance price of additional new securities			£ 1.916
Maximum | Series B Preferred Shares and Series C Preferred Shares
Class Of Stock [Line Items]
Issuance price of additional new securities			1.916
Maximum | Series C Preferred Shares
Class Of Stock [Line Items]
Issuance price of additional new securities			£ 2.1589

Shareholders' Equity - Summary

Shareholders' Equity - Summary of Ordinary Shares Issued and Outstanding (Details) - shares	Dec. 31, 2021	Dec. 31, 2020
Class Of Stock [Line Items]
Ordinary shares, shares issued	40,603,489	4,389,920
Ordinary shares, shares outstanding	40,603,489	4,389,920
Ordinary Shares
Class Of Stock [Line Items]
Ordinary shares, shares issued	38,987,122
Ordinary shares, shares outstanding	38,987,122
Ordinary and Deferred Shares
Class Of Stock [Line Items]
Ordinary shares, shares issued	40,603,490	4,420,441
Ordinary shares, shares outstanding	40,603,490	4,420,441
Class A Non Voting Ordinary Share
Class Of Stock [Line Items]
Ordinary shares, shares issued	1,616,367
Ordinary shares, shares outstanding	1,616,367
B Ordinary Shares
Class Of Stock [Line Items]
Ordinary shares, shares issued		505,108
Ordinary shares, shares outstanding		505,108
D Ordinary Shares
Class Of Stock [Line Items]
Ordinary shares, shares issued		155,669
Ordinary shares, shares outstanding		155,669
E Ordinary Shares
Class Of Stock [Line Items]
Ordinary shares, shares issued		80,007
Ordinary shares, shares outstanding		80,007
F Ordinary Shares
Class Of Stock [Line Items]
Ordinary shares, shares issued		327,084
Ordinary shares, shares outstanding		327,084
G Ordinary Shares
Class Of Stock [Line Items]
Ordinary shares, shares issued		194,261
Ordinary shares, shares outstanding		194,261
H Ordinary Shares
Class Of Stock [Line Items]
Ordinary shares, shares issued		88,871
Ordinary shares, shares outstanding		88,871
I Ordinary Shares
Class Of Stock [Line Items]
Ordinary shares, shares issued		48,391
Ordinary shares, shares outstanding		48,391
J Ordinary Shares
Class Of Stock [Line Items]
Ordinary shares, shares issued		262,478
Ordinary shares, shares outstanding		262,478
L Ordinary Shares
Class Of Stock [Line Items]
Ordinary shares, shares issued		1,207,670
Ordinary shares, shares outstanding		1,207,670
M Ordinary Shares
Class Of Stock [Line Items]
Ordinary shares, shares issued		811,436
Ordinary shares, shares outstanding		811,436
N Ordinary Shares
Class Of Stock [Line Items]
Ordinary shares, shares issued		708,945
Ordinary shares, shares outstanding		708,945
Deferred Shares
Class Of Stock [Line Items]
Ordinary shares, shares issued	1	30,521
Ordinary shares, shares outstanding	1	30,521

Shareholders' Equity - Summar_2

Shareholders' Equity - Summary of Convertible Preferred Shares (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Class Of Stock [Line Items]
Shares Authorized		104,854,673
Shares Outstanding	0	104,854,673
Liquidation preference		$ 231,421
Carrying value		$ 230,931
Series A Preferred Shares
Class Of Stock [Line Items]
Shares Authorized		28,250,000
Shares Outstanding		28,250,000
Liquidation preference		$ 36,725
Carrying value		$ 36,725
Series B Preferred Shares
Class Of Stock [Line Items]
Shares Authorized		52,192,070
Shares Outstanding		52,192,070
Liquidation preference		$ 124,615
Carrying value		$ 124,312
Series C Preferred Shares
Class Of Stock [Line Items]
Shares Authorized		24,412,603
Shares Outstanding		24,412,603
Liquidation preference		$ 70,081
Carrying value		$ 69,894

Share-based Compensation - Addi

Share-based Compensation - Additional Information (Details) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2021USD ($)$ / sharesshares	Dec. 31, 2020USD ($)£ / sharesshares	Dec. 31, 2020USD ($)$ / sharesshares	Mar. 31, 2021shares	Dec. 31, 2020£ / shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period	4 years
Remaining vesting period	3 years
Unrecognized compensation costs related to unvested employee shares outstanding | $	$ 11.3	$ 17.4	$ 17.4
Weighted-average period	2 years 7 months 6 days	3 years 1 month 6 days	3 years 1 month 6 days
Weighted average grant-date fair value of share options granted | $ / shares	$ 5.42		$ 3.33
Unrecognized compensation cost related to share options outstanding | $	$ 5.4
Share Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average period	3 years 3 months 18 days
Deferred Shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Deferred share repurchased	1	1,509,384	1,509,384
Stock repurchase price per share | £ / shares		$ 0.01
Number of outstanding shares cancelled		109,058	109,058
Price per share | £ / shares					£ 92,451.851
Vesting on First Anniversary
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting percentage	25.00%
2021 Share Omnibus Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Ordinary shares reserved for future issuance				2,572,558
Increase of reserved shares, percent of common stock outstanding	4.00%
Ordinary shares issued	2,572,558
Shares available for future grant	1,578,993
2021 Employee Share Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Increase of reserved shares, percent of common stock outstanding	1.00%
Ordinary shares issued	467,738
Shares available for future grant	467,738
2021 Employee Share Purchase Plan | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Ordinary shares authorized for issuance				467,738

Share-based Compensation - Summ

Share-based Compensation - Summary of Changes in Unvested Ordinary Shares (Details) - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Beginning balance	2,837,492	1,727,874
Number of unvested ordinary shares, Granted		1,993,503
Number of unvested ordinary shares, Vested	(916,172)	(746,095)
Number of unvested ordinary shares, Forfeited	(18,262)	(137,790)
Ending balance	1,903,058	2,837,492
Beginning balance	$ 6.38	$ 2.96
Weighted average grant date fair value, Granted		7.58
Weighted average grant date fair value, Vested	5.61	3.44
Weighted average grant date fair value, Forfeited	6.80	3.46
Ending balance	$ 6.43	$ 6.38

Share-based Compensation - Su_2

Share-based Compensation - Summary of Share Options Activity (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021USD ($)$ / sharesshares
Share Based Compensation Arrangement By Share Based Payment Award Options Additional Disclosures [Abstract]
Number of Options, Beginning Balance | shares	240,584
Number of Options, Granted | shares	1,164,778
Number of Options, Forfeited | shares	(47,515)
Number of Options, Ending Balance | shares	1,357,847
Number of Options, Exercisable | shares	102,424
Number of Options, Unvested | shares	1,255,423
Weighted Average Exercise Price, Beginning Balance | $ / shares	$ 6.75
Weighted Average Exercise Price, Granted | $ / shares	13.83
Weighted Average Exercise Price, Forfeited | $ / shares	12.98
Weighted Average Exercise Price, Ending Balance | $ / shares	8.95
Weighted Average Exercise Price, Exercisable | $ / shares	6.99
Weighted Average Exercise Price, Unvested | $ / shares	$ 9.11
Weighted Average Remaining Contractual Term	4 years 10 months 2 days
Weighted Average Remaining Contractual Term, Exercisable	4 years 4 months 13 days
Weighted Average Remaining Contractual Term, Unvested	8 years 11 months 1 day
Aggregate Intrinsic Value, Beginning Balance | $	$ 313
Aggregate Intrinsic Value, Ending Balance | $	10
Aggregate Intrinsic Value, Unvested | $	$ 10

Share-based Compensation - Su_3

Share-based Compensation - Summary of Weighted-Average Assumptions Used in Black-Scholes Option Pricing Model (Details) - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Expected term (in years)	6 years 7 days	3 years 2 months 15 days
Expected volatility	72.15%	73.81%
Expected dividend yield	0.00%	0.00%
Risk free interest rate	1.07%	0.20%
Fair value of underlying ordinary shares	$ 9.53	$ 6.35

Share-based Compensation - Shar

Share-based Compensation - Share-based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	$ 6,317	$ 2,992	$ 719
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	3,362	1,331	332
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	$ 2,955	$ 1,661	$ 387

Leases - Additional Information

Leases - Additional Information (Details)

Oct. 01, 2021USD ($)

Jun. 01, 2020

Feb. 28, 2020USD ($)

Feb. 28, 2020GBP (£)

Feb. 21, 2020USD ($)

Feb. 01, 2019

Jul. 08, 2016

Jun. 30, 2021USD ($)

Feb. 28, 2021

Dec. 31, 2020USD ($)

Dec. 31, 2021USD ($)Lease

Jun. 30, 2021GBP (£)

Dec. 31, 2020GBP (£)

Feb. 21, 2020GBP (£)

Jan. 10, 2020USD ($)

Jan. 10, 2020GBP (£)

Lease Disclosure [Line Items]

Number of operating leases | Lease

7

Number of leases met short-term exception | Lease

3

Future minimum lease payments

$ 13,157,000

Maximum

Lease Disclosure [Line Items]

Required minimum balance maintained in connection with lease

$ 100,000

Master Service Agreement

Lease Disclosure [Line Items]

Lease term

5 years

Lease expiration date

Aug. 31, 2020

Lease renewal expiration date

Aug. 31, 2023

Six Agreements

Lease Disclosure [Line Items]

Lease expiration date

Jan. 31, 2021

Lease renewal expiration date

Jul. 31, 2022

Non-cancellable Operating Lease

Lease Disclosure [Line Items]

Lease term

38 months

10 years

10 years

2 years

2 years

Lease term, break clause period

5 years

Letter of credit expiration date

Sep. 30, 2022

Letter of credit extended term

1 year

Non-cancellable Operating Lease | Maximum

Lease Disclosure [Line Items]

Future minimum lease payments

$ 7,000,000

£ 5,400,000

$ 200,000

£ 200,000

Required minimum balance maintained in connection with lease

$ 100,000

Manufacturing Services Collaboration Agreement

Lease Disclosure [Line Items]

Lease term

4 years

4 years

Manufacturing Services Collaboration Agreement | Maximum

Lease Disclosure [Line Items]

Collaboration agreement cancellation penalty amount

$ 2,700,000

£ 2,200,000

Lease of Warehouse

Lease Disclosure [Line Items]

Lease term

10 years

10 years

Lease term, break clause period

5 years

Lease of Warehouse | Maximum

Lease Disclosure [Line Items]

Future minimum lease payments

$ 4,900,000

£ 3,800,000

Lease of Office Premises

Lease Disclosure [Line Items]

Lease term

3 years

3 years

Lease term, break clause period

2 years

Lease of Office Premises | Maximum

Lease Disclosure [Line Items]

Future minimum lease payments

$ 100,000

£ 100,000

Leases - Summary of Lease Costs

Leases - Summary of Lease Costs Recognized and Other Information Pertaining to Operating Leases (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Lease cost
Right of use assets obtained in exchange for new operating lease liabilities	$ 314	$ 15,846	$ 457
ASU 2016-02
Lease cost
Operating lease cost	4,718	2,927	564
Variable lease cost	5,022	2,891	31
Short-term lease cost	65	49	88
Total lease cost	9,805	5,867	683
Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows used in operating leases	4,736	1,844	574
Right of use assets obtained in exchange for new operating lease liabilities	$ 314	$ 15,846	$ 457
Weighted average remaining lease term (in years)	3 years 1 month 6 days	4 years	10 months 24 days
Weighted average discount rate	4.86%	4.85%	5.01%

Leases - Summary of Maturities

Leases - Summary of Maturities of Operating Lease Liabilities (Details) $ in Thousands	Dec. 31, 2021USD ($)
Leases [Abstract]
2022	$ 4,974
2023	4,322
2024	3,046
2025	815
Total lease payments	13,157
Less: imputed interest	(898)
Present value of lease liability	$ 12,259

License Agreements - Additional

License Agreements - Additional Information (Details) € in Millions	1 Months Ended		12 Months Ended
	Mar. 31, 2021USD ($)	Mar. 31, 2021GBP (£)	Dec. 31, 2021USD ($)€ / shares	Dec. 31, 2021GBP (£)€ / shares	Dec. 31, 2021EUR (€)€ / shares	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)shares	Dec. 31, 2016USD ($)
License Agreements [Line Items]
IP research and development expense			$ 42,224,000			$ 22,629,000	$ 9,072,000
Minimum | TRACERx Patents
License Agreements [Line Items]
Acquisition price | £				£ 25,000,000
CRT License
License Agreements [Line Items]
IP research and development expense								$ 300,000
Contribution period of royalty products			10 years	10 years	10 years
Patent period of royalty products			5 years	5 years	5 years
Expenses related to license agreement						$ 0	$ 0
CRT License | B Ordinary Shares
License Agreements [Line Items]
Shares granted | shares							396,125
CRT License | C Ordinary Shares
License Agreements [Line Items]
Shares granted | shares							67,793
CRT License | Therapeutics Products
License Agreements [Line Items]
Aggregate milestone payments | £				£ 6,500,000
CRT License | Non Therapeutics Products
License Agreements [Line Items]
Aggregate milestone payments | £				£ 800,000
CRT License | Maximum
License Agreements [Line Items]
Payment for vaccine option	$ 100,000	£ 100,000
Expenses related to license agreement			$ 100,000
Secarna License
License Agreements [Line Items]
Aggregate milestone payments			$ 7,400,000		€ 6.5
Patent period of royalty products			10 years	10 years	10 years
Rate of aggregate milestone payments | € / shares			1.132	1.132	1.132
Commercial milestone payments			$ 29,400,000		€ 26
Rate of commercial milestone payments | € / shares			1.132	1.132	1.132
License expense			$ 800,000		€ 0.7
Average rate of license expense | € / shares			1.183	1.183	1.183

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	Apr. 01, 2023	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Line Items]
Income tax benefits		$ 37,000	$ 3,000
Net operating loss carryforwards		$ 71,000,000	37,100,000	$ 13,000,000
Tax positions settlement		50.00%
Uncertain tax positions		$ 0	0	$ 0
Uncertain tax positions accrued interest or penalties		0	0
Uncertain tax positions accrued interest or penalties recognized in statement of operations		$ 0	$ 0
Corporate income tax rate		19.00%	19.00%	19.00%
Scenario Forecast
Income Tax Disclosure [Line Items]
Corporate income tax rate	25.00%
United Kingdom
Income Tax Disclosure [Line Items]
Income tax benefits		$ 0	$ 0	$ 0

Income Taxes - Summary of Loss

Income Taxes - Summary of Loss Before Provision for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
United Kingdom	$ (61,182)	$ (33,204)	$ (13,990)
Foreign	120	8
Loss before provision for income taxes	$ (61,062)	$ (33,196)	$ (13,990)

Income Taxes - Summary of Incom

Income Taxes - Summary of Income Tax Provision (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Current expense:
Foreign	$ 59	$ 7
Total current expense:	59	7
Deferred expense (benefit):
Foreign	(22)	(4)
Total deferred expense (benefit):	(22)	(4)
Total income tax expense:	$ 37	$ 3

Income Taxes - Schedule of Reco

Income Taxes - Schedule of Reconciliation of Income Tax Expense Computed at Statutory UK Income Taxes (Details)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income taxes at UK statutory rate	19.00%	19.00%	19.00%
R&D expenditure	(6.67%)	(6.69%)	(12.37%)
Change in valuation allowance	(20.12%)	(13.12%)	(6.85%)
Change in UK tax rate	7.64%
Other	(0.13%)	0.80%	0.22%
Effective income tax rate reconciliation	(0.28%)	(0.01%)

Income Taxes - Summary of Signi

Income Taxes - Summary of Significant Component of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets
Net operating loss carryforwards	$ 17,742	$ 7,065	$ 2,475
Depreciation	(1,311)	(983)	(243)
Non-cash share-based compensation	2,328	769	161
Other	329	241	(2)
Total deferred tax assets	19,088	7,092	2,391
Valuation allowance	(19,062)	(7,088)	$ (2,391)	$ (1,342)
Net deferred tax assets	$ 26	$ 4

Income Taxes - Summary of Chang

Income Taxes - Summary of Changes in Valuation Allowance for Deferred Tax Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Valuation allowance at beginning of year	$ 7,088	$ 2,391	$ 1,342
Increases recorded to income tax provision	7,624	4,628	996
Exchange difference	(313)	69	53
Change in tax rate	4,663
Valuation allowance at end of year	$ 19,062	$ 7,088	$ 2,391

Net Loss Per Share - Summary of

Net Loss Per Share - Summary of Basic and Diluted Net Loss Per Share Attributable to Ordinary Shareholders (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Earnings Per Share [Abstract]
Net loss	$ (61,099)	$ (33,199)	$ (13,990)
Net loss attributable to ordinary shareholders—basic and diluted	$ (61,099)	$ (33,199)	$ (13,990)
Weighted-average number of ordinary shares used in net loss per share—basic and diluted	28,654,760	1,066,208	642,169
Net loss per share attributable to ordinary shareholders—basic and diluted	$ (2.13)	$ (31.14)	$ (21.79)

Net Loss Per Share - Summary _2

Net Loss Per Share - Summary of Antidilutive Securities Excluded from Computation of Earnings Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	3,260,905	29,559,907	17,650,369
Series A Preferred Shares
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share		7,134,644	7,134,644
Series B Preferred Shares
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share		13,181,515	8,787,851
Series C Preferred Shares
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share		6,165,672
Unvested Ordinary Shares
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	1,903,058	2,837,492	1,727,874
Share Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	1,357,847	240,584

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) £ in Millions	1 Months Ended
	Jun. 30, 2021USD ($)	Dec. 31, 2021USD ($)	Jun. 30, 2021GBP (£)	Dec. 31, 2020USD ($)
Other Commitments [Line Items]
Unused purchase commitment		$ 7,400,000		$ 4,300,000
Future minimum lease payments		13,157,000
Operating lease right of use assets		11,048,000		$ 14,740,000
Present value of lease liability		12,259,000
Lease of Lab and Office Premises
Other Commitments [Line Items]
Lease term	10 years		10 years
Future minimum lease payments	$ 800,000		£ 0.6
Operating lease right of use assets		0
Present value of lease liability		$ 0
Break Clause One | Lease of Lab and Office Premises
Other Commitments [Line Items]
Period of break clause	3 years
Break Clause Two | Lease of Lab and Office Premises
Other Commitments [Line Items]
Period of break clause	7 years

Commitments and Contingencies_2

Commitments and Contingencies - Summary of Asset Retirement Obligation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Asset Retirement Obligation Roll Forward Analysis Roll Forward
Balance, beginning of the year	$ 652
Additions in estimates		$ 652
Accretion of discount	38
Balance, end of year	$ 690	$ 652

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Syncona Investment Management Limited
Related Party Transaction [Line Items]
Management fees and other costs incurred	$ 0	$ 0	$ 100,000

Employee Benefit Plans - Additi

Employee Benefit Plans - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
United Kingdom
Defined Contribution Plan Disclosure [Line Items]
Contributions paid	$ 1,800,000	$ 1,000,000	$ 0.5
United States | Maximum
Defined Contribution Plan Disclosure [Line Items]
Contributions paid	$ 100,000	$ 100,000

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) - $ / shares	Feb. 02, 2022	Dec. 31, 2021
Subsequent Event [Line Items]
Number of options issued		1,164,778
Exercise price of options issued		$ 13.83
Subsequent Event
Subsequent Event [Line Items]
Number of options issued	1,044,410
Exercise price of options issued	$ 3.62