0001564590-22-008077 | 20-F | XBRL Viewer | Achilles Therapeutics PLC

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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 (Parenthetical)	Dec. 31, 2021 £ / shares shares	Dec. 31, 2021 $ / shares shares	Dec. 31, 2020 £ / shares shares	Dec. 31, 2020 $ / shares shares
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 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 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 Shares Additional Paid-in Capital	Series B Convertible Preferred Shares	Series B Convertible Preferred Shares Additional Paid-in Capital	Series C Convertible Preferred Shares	Series C Convertible Preferred Shares Additional 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 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 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

12 Months Ended

Dec. 31, 2021

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Nature of the Business

1. Nature of the business

Achilles Therapeutics plc (formerly Achilles TX Limited) and subsidiaries, or the Company, is a biopharmaceutical company developing transformative precision T cell therapies to treat multiple types of solid tumors. The Company is focused on advancing immuno-oncology therapeutics by exploiting its pioneering work in the field of tumor evolution and clonal neoantigens.

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 concern

In accordance with the Financial Accounting Standards Board, or FASB, Accounting Standards Update, or ASU, 2014-15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern (Subtopic 205-40), the Company has evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about the Company’s ability to continue as a going concern.

The Company has historically been loss making and anticipates that it will continue to incur losses for the foreseeable future and had an accumulated deficit of $119.1 million as of December 31, 2021. The Company has funded these losses principally through the issuance of ordinary and preferred shares. The Company expects to continue to incur operating losses and negative cash outflows until such time as it generates a level of revenue that is sufficient to support its cost structure.

The spread of COVID-19 has impacted the global economy and has impacted the Company’s operations, including the interruption of preclinical and clinical trial activities and potential interruption to supply chains. The Company has maintained operations at its GMP manufacturing and research and development sites through 2021 to date. The Company continues to assess the impact COVID-19 may have on its ability to advance the development of drug candidates or to raise financing to support the development of drug candidates, but no assurances can be given that this analysis will enable it to avoid part or all of any impact from the spread of COVID-19 or its consequences, including downturns in business sentiment generally or in its sector in particular.

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 financial statements have been prepared on a basis that assumes the Company will continue as a going concern and which contemplates the realization of assets and settlement of liabilities and commitments as they fall due in the ordinary course of business for at least 12 months from the date of issuance of the financial statements.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2021

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of significant accounting policies

Basis of presentation

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. All significant inter–company accounts and transactions between the Company and its subsidiaries have been eliminated upon consolidation.

Use of estimates

The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of income and expenses during the reporting periods. Significant estimates and assumptions reflected in these financial statements include, but are not limited to, the accrual for research and development expenses, the fair value of ordinary shares and incremental borrowing rate for leases. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results could differ materially from those estimates.

Segment information

Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker in deciding how to allocate resources and assess performance. 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

The functional currency of the Company is pound sterling which is its local currency. Monetary assets and liabilities denominated in currencies other than the functional currency are translated into the functional currency at rates of exchange prevailing at the balance sheet dates. Non-monetary assets and liabilities denominated in foreign currencies are translated into the functional currency at the exchange rates prevailing at the date of the transaction. Exchange gains or losses arising from foreign currency transactions are included in other expense, net in the Consolidated statement of operations and comprehensive loss. The Company recorded foreign exchange gains of $2.5 million, $0.4 million and $0.1 million for the years ended December 31, 2021, 2020 and 2019, respectively.

For financial reporting purposes, the financial statements of the Company have been presented in the U.S. dollar, the reporting currency. The financial statements of entities are translated from their functional currency into the reporting currency as follows: assets and liabilities are translated at the exchange rates at the balance sheet dates, revenue and expenses are translated at the average exchange rates and shareholders’ equity is translated based on historical exchange rates. Translation adjustments are not included in determining net loss but are included as a foreign exchange adjustment to accumulated other comprehensive (loss)/income, a component of shareholders’ equity.

Cash and cash equivalents

The Company considers all highly liquid investments that have maturities of three months or less when acquired to be cash equivalents. 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 not record any deferred IPO costs as of December 31, 2021 and 2019.

Fair value of financial instruments

The carrying values of the Company’s cash and cash equivalents, prepaid expenses and other current assets, accounts payable, and certain accruals approximate their fair value due to their short-term nature. The Company has a money-market fund that is measured under 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

Financial instruments that subject the Company to credit risk consist solely of cash and cash equivalents. The Company maintains cash balances in excess of amounts insured by the UK Government Financial Services Compensation Scheme in the United Kingdom. The Company has no significant off-balance-sheet risk or concentration of credit risk, such as foreign exchange contracts, options contracts, or other foreign hedging arrangements.

Property and equipment

Property and equipment are recorded at cost and depreciated using the straight-line method over the estimated useful lives of the respective assets, which are as follows:

		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 retirement or sale, the cost of assets disposed of and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is included in the statement of operations and other comprehensive loss. Expenditures for repairs and maintenance are charged to expense as incurred. Assets under construction are not depreciated until the asset is available and ready for use.

Impairment of long-lived assets

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 and development costs are expensed as incurred. Research and development expenses consist of costs incurred in performing research and development activities, including salaries, non-cash share-based compensation and benefits, depreciation expense, travel, third-party license fees, and external costs of outside vendors engaged to conduct clinical development activities, clinical trials, cost to manufacture clinical trial materials and net of tax credits associated with research and development activities.

Research contract costs and accruals

The Company has entered into various research and development-related contracts with research institutions and other companies. These agreements are generally cancelable, and related payments are recorded as research and development expenses as incurred. Accruals for research and development expenses typically include fees paid to vendors in conjunction with preclinical development activities, CROs and investigative sites in connection with preclinical and clinical activities and costs to manufacture clinical trial materials in connection with the manufacturing of drug formulations for use in preclinical and clinical activities. When estimating accruals for research and development expenses as of each balance sheet date, the Company analyzes progress of the preclinical activities or clinical trials, including the phase or completion of services performed relative to invoices received and contracted costs. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates of research and development expenses have not been materially different from the actual costs.

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 Company recognizes compensation expense for equity awards based on the grant date fair value of the award, which may include share options and restricted ordinary shares. For equity awards that vest based on a service condition, the share-based compensation expense is recognized on a straight-line basis over the requisite service period. The Company accounts for forfeitures as they occur. For equity awards with performance conditions, the Company recognizes share-based compensation expense using a straight-line basis over the requisite service commitments period when the achievement of a performance-based milestone is probable, based on the relative satisfaction of the performance condition as of the reporting date. The Company uses the fair value of its ordinary shares to determine the fair value of Employee Shares, C ordinary shares and K ordinary shares awarded to employees and directors.

Effective January 1, 2019, the Company adopted ASU No. 2018-07, Compensation—Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting (“ASU 2018-7”), which expands the scope of Topic 718 to include share-based payment awards to nonemployees. As a result, stock-based awards granted to nonemployees are accounted for in the same manner as awards granted to employees and directors as described above. The adoption of this new guidance did not have a material impact on the Company’s financial statements.

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 Company estimated the fair value of its ordinary shares with input from an independent third-party valuation specialist firm in accordance with the guidelines in the American Institute of Certified Public Accountants’ Accounting and Valuation Guide, Valuation of Privately-Held-Company Equity Securities Issued as Compensation (the “Practice Aid”). The Company’s valuations of ordinary shares were prepared using either a market approach based on precedent transactions in the ordinary and preferred shares or a market adjusted equity value method to estimate the Company’s total equity value, and using an option-pricing backsolve method (“OPM”) to allocate the equity value to each class of the Company’s securities. In some cases, the Company determined that there were no significant events occurring between a prior valuation date and a subsequent grant. As such, in these cases the Company used the most recent share

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 OPM backsolve method derives an equity value such that the value indicated for ordinary shares is consistent with the investment price, and it provides an allocation of this equity value to each of the Company’s securities. The OPM treats the various classes of ordinary shares and preferred shares as call options on the total equity value of a company, with exercise prices based on the value thresholds at which the allocation among the various holders of a company’s securities changes. Under this method, each class of ordinary shares has value only if the funds available for distribution to shareholders exceeded the value of the preferred share liquidation preferences at the time of the liquidity event. Key inputs into the OPM backsolve calculation included the valuation of equity, probability weighted expected time to liquidity and volatility. A reasonable discount for lack of marketability was applied to the total per share value to arrive at an estimate of the total fair value of an ordinary share on a non-marketable basis.

Leases

Effective January 1, 2019, the Company adopted ASU No. 2016-02, Leases (Topic 842), as amended, using the modified retrospective method and utilizing the effective date as its date of initial application, with prior periods presented in accordance with previous guidance under ASC 840, Leases (“ASC 840”). At the inception of an arrangement, the Company determines whether the arrangement is or contains a lease based on the unique facts and circumstances present in the arrangement. Leases with a term greater than one year are recognized on the balance sheet as right-of-use assets and current and non-current lease liabilities, as applicable. Entities may elect not to separate lease and non-lease components. The Company has elected to account for lease and non-lease components together as a single lease component for all underlying assets and to allocate all the contract consideration to the lease component only. All the Company’s leases are classified as operating leases.

Lease liabilities and their corresponding right-of-use assets are initially recorded based on the present value of lease payments over the expected remaining lease term. Certain adjustments to the right-of-use asset may be required for items such as incentives received. The interest rate implicit in lease contracts has not been readily determinable. As a result, the Company utilizes its incremental borrowing rate to discount lease payments, which reflects the fixed rate at which the Company could borrow on a collateralized basis the amount of the lease payments in the same currency, for a similar term, in a similar economic environment. As the Company does not have a rating agency-based credit rating, quotes were obtained from lenders to establish an estimated secured rate to borrow based on Company and market-based factors as of the respective lease measurement dates. The Company has elected not to recognize leases with an original term of one year or less on the balance sheet. The Company typically only includes the non-cancelable lease term in its assessment of a lease arrangement unless there is an option to extend the lease that is reasonably certain of exercise. Prospectively, the Company will adjust the right-of-use assets for straight-line rent expense or any incentives received and remeasure the lease liability at the net present value using the same incremental borrowing rate that was in effect as of the lease commencement or transition date.

Operating lease costs are recognized on a straight-line basis over the lease term, and they are categorized within research and development and general and administrative expenses in the statement of operations. The operating lease cash flows are categorized under net cash used in operating activities in the statement of cash flows.

Income taxes

The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the financial statements or in its tax returns. Deferred tax assets and liabilities are determined on the basis of the differences between the financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that deferred tax assets will be recovered in 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 Company uses a two-step approach for recognizing and measuring uncertain tax positions. The first step is to evaluate tax positions taken or expected to be taken in a tax return by assessing whether they are more likely than not sustainable, based solely on their technical merits, upon examination, and including resolution of any related appeals or litigation process. The second step is to measure the associated tax benefit for each position as the largest amount that the Company believes is more likely than not realizable. Differences between the amount of tax benefits taken or expected to be taken in the Company’s income tax returns and the amount of tax benefits recognized in the financial statements represent the Company’s unrecognized income tax benefits, which is either recorded as a liability or reduction of deferred tax assets.

The Company recognizes interest and penalties related to unrecognized tax benefits on the income tax expense line in the accompanying statement of operations. As of December 31, 2021, 2020 and 2019, no accrued interest or penalties have been incurred.

Research and development tax credit

The Company is subject to corporate taxation in the United Kingdom, or UK. Due to the nature of the business, the Company has generated losses since inception. The benefit from research and development (“R&D”) tax credits is recognized in the statements of operations and comprehensive loss as a reduction of research and development costs and represents the sum of the research and development tax credits recoverable in the UK.

The UK research and development tax credit is fully refundable to the Company and is not dependent on current or future taxable income. As a result, the Company has recorded the entire benefit from the UK research and development tax credit as a benefit which is included in net loss before income tax and accordingly, not reflected as part of the income tax provision. If, in the future, any UK research and development tax credits generated are needed to offset a corporate income tax liability in the UK, that portion would be recorded as a benefit within the income tax provision and any refundable portion not dependent on taxable income would continue to be recorded as a reduction of research and development costs.

As a company that carries out extensive research and development activities, the Company benefits from the UK research and development tax credit regime under the scheme for small or medium-sized enterprises (“SME”). Under the SME regime, the Company can surrender some of its trading losses that arise from qualifying research and development activities for a cash rebate of up to 33.35% of such qualifying research and development expenditure. Qualifying expenditures largely comprise employment costs for research staff, consumables, outsourced contract research organization costs and utilities costs incurred as part of research projects. Certain subcontracted qualifying research and development expenditures are eligible for a cash rebate of up to 21.67%. A large portion of costs relating to research and development, clinical trials and manufacturing activities are eligible for inclusion within these tax credit cash rebate claims.

The Company may not be able to continue to claim research and development tax credits under the SME regime in the future because it may no longer qualify as a small or medium-sized company.

Unsurrendered UK losses may be carried forward indefinitely to be offset against future taxable profits, subject to numerous utilization criteria and restrictions. The amount that can be offset each year is limited to £5.0 million plus an incremental 50% of UK taxable profits.

Comprehensive income (loss)

Comprehensive income (loss) includes net loss as well as other changes in shareholders’ equity that result from transactions and economic events other than those with shareholders.

Net loss per share

The Company has reported losses since inception and has computed basic net loss per share attributable to ordinary shareholders by dividing net loss attributable to ordinary shareholders by the weighted-average number of ordinary shares outstanding for the period, without consideration for potentially dilutive securities. For purpose of this calculation, unvested Employee Shares and convertible preferred shares are considered potential dilutive ordinary shares. The Company computes diluted net loss per ordinary share after giving consideration to all potentially dilutive ordinary shares, including unvested Employee Shares and convertible preferred shares, outstanding during the period determined using the treasury-stock and if-converted methods, except where the effect of including such securities would be antidilutive. Because the Company has reported net losses since inception, these potential ordinary shares have been anti-dilutive and basic and diluted loss per share were the same for all periods presented.

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

Recently adopted accounting standards

In December 2019, the FASB issued ASU 2019-12, “Income Taxes—Simplifying the Accounting for Income Taxes (Topic 740) (“ASU 2019-12”),” which simplifies the accounting for income taxes. The new guidance removes certain exceptions to the general principles in ASC 740 such as recognizing deferred taxes for equity investments, the incremental approach to performing intra-period tax allocation and calculating income taxes in interim periods. The standard also simplifies accounting for income taxes under U.S. GAAP by clarifying and amending existing guidance, including the recognition of deferred taxes for goodwill, the allocation of taxes to members of a consolidated group and requiring that an entity reflect the effect of enacted changes in tax laws or rates in the annual effective tax rate computation in the interim period that includes the enactment date. This guidance is effective for annual periods beginning after December 15, 2020, and interim periods thereafter; however, early adoption is permitted. The new guidance was adopted on January 1, 2021 and it did not have a material impact on the Company’s consolidated financial statements and related disclosures.

In November 2021, the FASB issued ASU 2021-10, “Government Assistance – Topic 832 – Disclosures by Business Entities about Government Assistance,” which increases the transparency of government assistance including the disclosure of (1) the types of assistance, (2) an entity’s accounting for the assistance, and (3) the effect of the assistance on an entity’s financial statements. The amendments in this Update require the following annual disclosures about transactions with a government that are accounted for by applying a grant or contribution accounting model by analogy: 1. Information about the nature of the transactions and the related accounting policy used to account for the transactions. 2. The line items on the balance sheet and income statement that are affected by the transactions, and the amounts applicable to each financial statement line item. 3. Significant terms and conditions of the transactions, including commitments and contingencies. ASU 2021-10 is effective for annual periods beginning after December

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 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.

- Definition

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

+ References + Details

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 expenses and other current assets

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

	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

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 expense was $3.3 million, $0.8 million and $0.3 million for the years ended December 31, 2021, 2020 and 2019, respectively.

Accrued Expenses and Other Liabilities

12 Months Ended

Dec. 31, 2021

Payables And Accruals [Abstract]

Accrued Expenses and Other Liabilities

6. Accrued expenses and other liabilities

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

	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

12 Months Ended

Dec. 31, 2021

Stockholders Equity Note [Abstract]

Shareholders’ Equity

7. Shareholders’ equity

Ordinary shares

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 preferred shares

The Company issued series A convertible preferred shares (“Series A”), series A-1 convertible preferred shares (“Series A-1”), series B preferred shares (“Series B”) and series C preferred shares (“Series C”) (collectively, “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

(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 (subject to appropriate adjustment in the event of any share dividend, share split, combination or other similar recapitalization). 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) and the net aggregate proceeds of the offering are at least £75 million.

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.

- Definition

The entire disclosure for shareholders' equity comprised of portions attributable to the parent entity and noncontrolling interest, including other comprehensive income. Includes, but is not limited to, balances of common stock, preferred stock, additional paid-in capital, other capital and retained earnings, accumulated balance for each classification of other comprehensive income and amount of comprehensive income.

+ References

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+ Details

Share-based Compensation

12 Months Ended

Dec. 31, 2021

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Share-based Compensation

8. Share-based compensation

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 service period with 25% of the award vesting on the first anniversary of the vesting commencement date, and the balance vesting periodically over the remaining three years.

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 summary of the changes in the Company’s unvested ordinary shares from December 31, 2019 through December 31, 2021 are as follows:

	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 December 31, 2021 and 2020, there was $11.3 million and $17.4 million of unrecognized compensation costs related to unvested Employee Shares outstanding, which is expected to be recognized over a weighted-average period of 2.6 years and 3.1 years, respectively.

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 December 31, 2021, there was $5.4 million of unrecognized compensation cost related to share options outstanding, which is expected to be recognized over a weighted-average period of 3.3 years.

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 compensation expense recorded as research and development and general and administrative expenses is as follows (in thousands):

	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

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 periods, without written amendment agreement, in each succeeding calendar year, through the lease expiration date.

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

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 million ($7.4 million using a rate of €1.132 at December 31, 2021) and one-time commercial milestone payments up to €26 million ($29.4 million using a rate of €1.132 at December 31, 2021), as well as tiered 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 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) ten years from the first commercial sale of the product. For the year ended December 31, 2021, the Company recorded expenses of €0.7 million ($0.8 million using an average rate of €1.183 for the year ended December 31, 2021) related to the Secarna license agreement.

Income Taxes

12 Months Ended

Dec. 31, 2021

Income Tax Disclosure [Abstract]

Income Taxes

11. Income taxes

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 provision for income taxes for the years ended December 31, 2021, 2020 and 2019 was computed at the United Kingdom statutory income tax rate.

A reconciliation of income tax expense computed at the statutory UK income tax rate to income taxes as reflected in the consolidated financial statements is as follows:

	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 components of the Company’s deferred tax assets and liabilities as of December 31, 2021, 2020 and 2019 consist of the following (in thousands):

	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 December 31, 2021, 2020 and 2019, the Company had UK net operating loss carryforwards of approximately $71.0 million, $37.1 million and $13.0 million, respectively, that can be carried forward indefinitely, respectively.

Changes in the valuation allowance for deferred tax assets during the years ended December 31, 2021, 2020 and 2019 related primarily to the increases in net operating loss carryforwards and research and development tax credit carryforwards were as follows (in thousands):

	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 realization of the tax benefits of existing temporary differences and net operating loss carryforwards ultimately depends on the existence of sufficient taxable income within the carryforward period. As of December 31, 2021, 2020 and 2019, the Company performed an evaluation to determine whether a valuation allowance was needed. The Company considered all available evidence, both positive and negative, which included the results of operations for the current and preceding years. The Company determined that it was not possible to reasonably quantify future taxable income and determined that it is more likely than not the net deferred tax assets will not be realized. Accordingly, the Company maintained a full valuation allowance as of December 31, 2021, 2020 and 2019.

The Company applies the authoritative guidance on accounting for and disclosure of uncertainty in tax positions, which requires the Company to determine whether a tax position of the Company is more likely than not to be sustained upon examination, including resolution of any related appeals of litigation processes, based on the technical merits of the position. For tax positions meeting the more likely than not threshold, the tax amount recognized in the financial statements is reduced by the largest benefit that has a greater than fifty percent likelihood of being realized upon the ultimate settlement with the relevant taxing authority. There were no material uncertain tax positions as of December 31, 2021, 2020 and 2019.

The Company will recognize interest and penalties related to uncertain tax positions in income tax expense when in a taxable income position. As of December 31, 2021 and 2020, the Company had no accrued interest or penalties related to uncertain tax positions and no amounts have been recognized in the Company’s statement of operations.

The Company files income tax returns in the UK Generally, the tax years through 2020 remain open to examination. To the extent the Company has tax attribute carryforwards, the tax years in which the attribute was generated may still be adjusted upon examination by the UK tax authorities, if such tax attributes are utilized in a future period.

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.

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 21
-URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32857-109319

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 11.C)
-URI http://asc.fasb.org/extlink&oid=122134291&loc=d3e330215-122817

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 17
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32809-109319

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 6.I.5.Q1)
-URI http://asc.fasb.org/extlink&oid=122134291&loc=d3e330036-122817

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 14
-URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32705-109319

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 270
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6424409&loc=d3e44925-109338

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-URI http://asc.fasb.org/topic&trid=2144680

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6424122&loc=d3e41874-109331

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h)(2))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

+ Details

Net Loss Per Share

12 Months Ended

Dec. 31, 2021

Earnings Per Share [Abstract]

Net Loss Per Share

12. Net loss per share

Basic and diluted net loss per share attributable to ordinary shareholders was calculated as follows (in thousands, except share and per share amounts):

	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 Company’s potentially dilutive securities, which include warrants to purchase ordinary shares, unvested Employee Shares and Convertible Preferred Shares, have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted-average number of ordinary shares outstanding used to calculate both basic and diluted net loss per share attributable to ordinary shareholders is the same. The Company excluded the following potential ordinary shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share attributable to ordinary shareholders for the year ended December 31, 2021, 2020 and 2019 because including them would have had an anti-dilutive effect:

	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

12 Months Ended

Dec. 31, 2021

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

13. Commitments and contingencies

Commitment with suppliers

The Company entered into several agreements with vendors that contain non-cancellable software arrangements and minimum purchase commitments of laboratory materials and consumables for the purpose of research and development activities as well as clinical development. The unused purchase commitment as of December 31, 2021 and 2020 was $7.4 million and $4.3 million, respectively.

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 proceedings

From time to time, the Company may be a party to litigation or subject to claims incident to the ordinary course of business. The Company was not a party to any litigation and did not have contingency reserves established for any liabilities as of December 31, 2021 and 2020.

Indemnification agreements

In the normal course of business, the Company enters into contracts and agreements that contain a variety of representations and warranties and provide for general indemnification. The Company’s exposure under these agreements is unknown because it involves claims that may be made against the Company in the future. To date, the Company has not paid any claims or been required to defend any action related to its indemnification obligations. However, the Company may record charges in the future as a result of these indemnification obligations.

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

12 Months Ended

Dec. 31, 2021

Income Tax Disclosure [Abstract]

Related Party Transactions

14. Related party transactions

The Company analyzed its transactions with related parties for the years ended December 31, 2021, 2020 and 2019, and determined it had the following material transactions that have not been described elsewhere in the financial statements.

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

12 Months Ended

Dec. 31, 2021

Compensation And Retirement Disclosure [Abstract]

Employee Benefit Plans

15. Employee benefit plans

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 million in contributions in the years ended December 31, 2021 and 2020, respectively.

- Definition

The entire disclosure for retirement benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
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-Name Accounting Standards Codification
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Subsequent Events

12 Months Ended

Dec. 31, 2021

Subsequent Events [Abstract]

Subsequent Events

16. Subsequent Events

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 Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2021

Accounting Policies [Abstract]

Going Concern

Going concern

Basis of Presentation

Basis of presentation

Use of Estimates

Use of estimates

Segment Information

Segment information

Foreign Currency Translation

Foreign currency translation

Cash and Cash Equivalents

Cash and cash equivalents

Deferred Initial Public Offering Costs

The Company recorded $1.0 million of deferred IPO costs as of December 31, 2020. The Company did not record any deferred IPO costs as of December 31, 2021 and 2019.

Fair Value of Financial Instruments

Fair value of financial instruments

Concentrations of Credit Risk and Off-Balance Sheet Risk

Concentrations of credit risk and off-balance sheet risk

Property and Equipment

Property and equipment

Property and equipment are recorded at cost and depreciated using the straight-line method over the estimated useful lives of the respective assets, which are as follows:

		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

Impairment of Long-Lived Assets

Impairment of long-lived assets

Research and Development Costs

Research and development costs

Research Contract Costs and Accruals

Research contract costs and accruals

Asset Retirement and Environmental Obligations

Share-Based Compensation

Share-based compensation

during the periods covered by these consolidated financial statements. Assumptions used in the option pricing model include the following:

Leases

Income Taxes

Income taxes

Research and Development Tax Credit

Research and development tax credit

The Company may not be able to continue to claim research and development tax credits under the SME regime in the future because it may no longer qualify as a small or medium-sized company.

Comprehensive Income (Loss)

Comprehensive income (loss)

Comprehensive income (loss) includes net loss as well as other changes in shareholders’ equity that result from transactions and economic events other than those with shareholders.

Net Loss Per Share

Net loss per share

Government Grants

Government grants

Recent Accounting Pronouncements

Recent accounting pronouncements

Recently adopted accounting standards

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2021

Accounting Policies [Abstract]

Summary of Property and Equipment

Property and equipment are recorded at cost and depreciated using the straight-line method over the estimated useful lives of the respective assets, which are as follows:

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

	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 (Tables)

12 Months Ended

Dec. 31, 2021

Property Plant And Equipment [Abstract]

Summary of Property and Equipment

Property and equipment are recorded at cost and depreciated using the straight-line method over the estimated useful lives of the respective assets, which are as follows:

		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 Liabilities (Tables)

12 Months Ended

Dec. 31, 2021

Payables And Accruals [Abstract]

Schedule of Accrued Expenses and Other Liabilities

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

	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)

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 (Tables)

12 Months Ended

Dec. 31, 2021

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Changes in Unvested Ordinary Shares

A summary of the changes in the Company’s unvested ordinary shares from December 31, 2019 through December 31, 2021 are as follows:

	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

	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 compensation expense recorded as research and development and general and administrative expenses is as follows (in thousands):

	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)

12 Months Ended

Dec. 31, 2021

Leases [Abstract]

Summary of Lease Costs Recognized and Other Information Pertaining to Operating Leases

	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

	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)

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 reconciliation of income tax expense computed at the statutory UK income tax rate to income taxes as reflected in the consolidated financial statements is as follows:

	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 components of the Company’s deferred tax assets and liabilities as of December 31, 2021, 2020 and 2019 consist of the following (in thousands):

	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

	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)

12 Months Ended

Dec. 31, 2021

Earnings Per Share [Abstract]

Summary of Basic and Diluted Net Loss Per Share Attributable to Ordinary Shareholders

Basic and diluted net loss per share attributable to ordinary shareholders was calculated as follows (in thousands, except share and per share amounts):

	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 Company excluded the following potential ordinary shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share attributable to ordinary shareholders for the year ended December 31, 2021, 2020 and 2019 because including them would have had an anti-dilutive effect:

	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 (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 - Additional Information (Details) £ / shares in Units, $ / shares in Units, $ in Thousands			1 Months Ended	12 Months Ended
	Apr. 06, 2021 USD ($) Stockholder $ / shares shares	Apr. 06, 2021 GBP (£) £ / shares shares	Dec. 31, 2020 USD ($) £ / shares	Dec. 31, 2021 USD ($) shares	Dec. 31, 2020 USD ($) shares	Dec. 31, 2019 USD ($) 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	$ 18.00
Net proceeds from sale	$ 160,600

Summary of Significant Accounting Policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2021 USD ($) Segment	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
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	$ 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 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 Instruments - Summary of Assets Measured at Fair Value on Recurring Basis (Details) - Level 1 $ in Thousands	Dec. 31, 2021 USD ($)
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 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 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 - 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 - 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 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 - Additional Information (Details)		12 Months Ended
Shareholders' Equity - Additional Information (Details)	Apr. 06, 2021 £ / shares	Dec. 31, 2021 USD ($) Vote	Dec. 31, 2021 £ / shares shares	Dec. 31, 2021 $ / shares shares	Dec. 31, 2020 £ / shares shares	Dec. 31, 2020 $ / shares shares	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			£ 1.00
Deferred Shares
Class Of Stock [Line Items]
Deferred shares repurchase price per share					£ 1.00		£ 1.00
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 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 - 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

- Definition

Carrying amount, attributable to parent, of an entity's issued and outstanding stock which is not included within permanent equity. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. Includes stock with a put option held by an ESOP and stock redeemable by a holder only in the event of a change in control of the issuer.

+ References + Details

Share-based Compensation - Additional Information (Details) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($) $ / shares shares	Dec. 31, 2020 USD ($) £ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares	Mar. 31, 2021 shares	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 - 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 - Summary of Share Options Activity (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021 USD ($) $ / shares shares
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 - 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 - 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 (Details)								1 Months Ended			12 Months Ended
Leases - Additional Information (Details)	Oct. 01, 2021 USD ($)	Jun. 01, 2020	Feb. 28, 2020 USD ($)	Feb. 28, 2020 GBP (£)	Feb. 21, 2020 USD ($)	Feb. 01, 2019	Jul. 08, 2016	Jun. 30, 2021 USD ($)	Feb. 28, 2021	Dec. 31, 2020 USD ($)	Dec. 31, 2021 USD ($) Lease	Jun. 30, 2021 GBP (£)	Dec. 31, 2020 GBP (£)	Feb. 21, 2020 GBP (£)	Jan. 10, 2020 USD ($)	Jan. 10, 2020 GBP (£)
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					$ 7,000,000.0									£ 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 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 of Operating Lease Liabilities (Details) $ in Thousands	Dec. 31, 2021 USD ($)
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 Information (Details) € in Millions	1 Months Ended		12 Months Ended
	Mar. 31, 2021 USD ($)	Mar. 31, 2021 GBP (£)	Dec. 31, 2021 USD ($) € / shares	Dec. 31, 2021 GBP (£) € / shares	Dec. 31, 2021 EUR (€) € / shares	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($) shares	Dec. 31, 2016 USD ($)
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 \| £				£ 25,000,000.0
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		€ 26.0
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 Information (Details) - USD ($)		12 Months Ended
	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		$ 71,000,000.0	37,100,000	$ 13,000,000.0
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 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)

- Definition

Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

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

- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References + Details

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 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 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 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)

- Definition

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

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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+ Details

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 - Additional Information (Details) £ in Millions	1 Months Ended
	Jun. 30, 2021 USD ($)	Dec. 31, 2021 USD ($)	Jun. 30, 2021 GBP (£)	Dec. 31, 2020 USD ($)
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 - 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 - 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 - 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	$ 0.5
United States \| Maximum
Defined Contribution Plan Disclosure [Line Items]
Contributions paid	$ 100,000	$ 100,000

Subsequent Events - Additional Information (Details) - $ / shares		12 Months Ended
	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