Under the Company’s historical shareholder and subscription agreements, the Company was authorized to issue restricted shares, restricted share units, as well as options, as incentives to its employees, non-employees and members of its board of directors. To the extent such incentives were in the form of share options, the options were granted pursuant to the terms of the 2017 Equity Incentive Plan, or the 2017 Plan. In July 2019, the Company’s board of directors adopted the 2017 Plan. The 2017 Plan provided for the grant of Enterprise Management Incentive, or EMI, options, to its UK employees, for the grant of options to its U.S. employees and non-employees of the Company. The 2017 Plan was administered by the board of directors.

Options granted under the 2017 Plan, typically vest over a three or four-year service period with 33.3% and 25% respectively, of the award vesting on the first anniversary of the commencement date and the balance vesting monthly over the remaining years. Options granted under the 2017 Plan generally expire 10 years from the date of grant. Restricted share units granted under the 2017 Plan typically vest over a four-year service period with 25% of the award vesting on the first anniversary of the commencement date and quarterly thereafter.

The options granted on June 30, 2020 were subject to 25% vesting upon the earlier occurrence of (i) the one year anniversary of the date of grant, or (ii) the date of the listing of the Company's ordinary shares on any stock exchange, followed by straight line vesting for three years for the remaining 75% of the allocation until vested in full.

The restricted share units granted on June 30, 2020 were subject to 25% vesting upon the earlier of (i) the one year anniversary of the date of grant, or (ii) the first day following the six-month anniversary of the listing of the Company's ordinary shares on any stock exchange on which the closing price of the shares is 20% higher than the listing price for at least five consecutive trading days.

As of December 31, 2025, the Company was authorized to issue a total of 417,254 ordinary shares underlying outstanding options granted under the 2017 Plan prior to our initial public offering, or IPO.

The Company’s 2020 Employee Share Purchase Plan, or 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 termination of the 2020 Plan, by the lesser of (i) 1% of the outstanding number of ordinary shares on the immediately preceding December 31, (ii) 510,080 ordinary shares or (iii) such lesser number of ordinary shares as determined by the plan administrator. 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.

On October 1, 2021, the Company launched the SIP and the ESPP, through which employees can purchase shares at a discounted price. At the end of six months, shares will automatically be purchased at the lower of the opening and closing price of the shares for the saving period minus a 15% discount.

The Company’s 2020 Share Option and Incentive Plan, or the 2020 Plan, allows the compensation and leadership development committee to make equity-based, including options and restricted share units, and cash-based incentive awards to the Company’s officers, employees, directors and other key persons (including consultants).

Options granted under the 2020 Plan generally expire 10 years from the date of grant and typically vest over a 4 year service period with 25% of the options vesting on the first anniversary of the commencement date and the balance vesting monthly over the remaining years.

The Company initially reserved 2,074,325 of its ordinary shares for the issuance of awards under the 2020 Plan. The 2020 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 up to 4% of the outstanding number of ordinary shares on the immediately preceding December 31, or such lesser number of shares as determined by the Company’s compensation and leadership development committee. The total number of ordinary shares that were authorized for issuance under the 2020 Plan is 10,680,217 shares as of December 31, 2025, of which 3,184,218 shares remained available for future grant.

The options granted in 2025 under the 2020 Plan to employees generally expire 10 years from the date of grant. There are three potential vesting terms for the 2025 grants including: (i) 25% per year over four year service period, (ii) four year service period with 25% of the vesting on the first anniversary of the commencement date and the balance vesting monthly over the remaining years; and (iii) monthly vesting over four year service period.

During 2022, the Company granted a non-qualified share option to purchase up to 600,000 ordinary shares as an inducement grant to our chief executive officer. The non-qualified share option has a 10 year term and one-fourth vested on August 1, 2023 and the remaining three-fourths will vest in equal monthly installments over the following 36 months. The non-qualified share option has other terms that mirror those of non-qualified share options granted under the Company’s 2020 Plan and the Company’s standard form of non-qualified share option agreement.


	Number of Shares	Weighted Average Grant Date Fair Value
Unvested and Outstanding as of December 31, 2024	658,553	$	10.96
Granted	531,110	3.76
Vested	(189,174)	11.21
Forfeited	(226,062)	8.12
Unvested and Outstanding as of December 31, 2025	774,427	$	6.79

As of December 31, 2025 and 2024, there was $3.8 million and $5.5 million of unrecognized compensation cost related to unvested restricted share units, respectively, which is expected to be recognized over a weighted-average period of 2.5 years and 2.8 years, respectively. The exercise price of restricted share units is at a nominal value less than £0.01 per share.


	Number of Shares	Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (Years)	Aggregate Intrinsic Value (in thousands)
Outstanding as of December 31, 2024	8,235,619	$	12.01	6.95	$	6,009
Granted	2,581,977	$	6.19
Exercised	(925,179)	$	0.08
Cancelled or forfeited	(2,289,124)	$	15.13
Outstanding as of December 31, 2025	7,603,293	$	10.52	6.87	$	10,972
Exercisable as of December 31, 2025	4,492,506	$	13.58	5.67	$	3,950
Unvested as of December 31, 2025	3,110,787	$	6.11	8.62	$	7,022

The aggregate intrinsic value of options exercised during the years ended December 31, 2025, and 2024 was $3.5 million and $1.2 million, respectively.

The aggregate intrinsic value of share options is calculated as the difference between the exercise price of the share options and the fair value of the Company’s ordinary shares for those share options that had exercise prices lower than the fair value of the Company’s ordinary shares.

The weighted average grant-date fair value of share options granted was $2.48 and $7.00 per share during the years ended December 31, 2025 and 2024.

As of December 31, 2025 and 2024, there was $15.0 million and $25.5 million of unrecognized compensation cost related to unvested share options, which is expected to be recognized over a weighted-average period of 2.2 years and 2.4 years, respectively.

The weighted-average assumptions used in the Black-Scholes option pricing model to determine the fair value of the share options granted to employees and directors during the years ended December 31, 2025 and 2024 were as follows:


	Year Ended December 31,
	2025		2024
Expected option life (years)	5.0 years		5.1 years
Expected volatility	89.42	%	86.05	%
Risk-free interest rate	4.06	%	4.12	%
Expected dividend yield	—	%	—	%


	Year Ended December 31,
	2025		2024
Research and development	5,088		10,309
General and administrative	8,502		9,208
Total share-based compensation expense	$	13,590	$	19,517