Share-based compensation (Tables)

12 Months Ended

Dec. 31, 2020

Share-based compensation

Schedule of share based compensation expense

The Company recorded share‑based compensation expense in the following expense categories of its consolidated statements of operations and comprehensive loss (in thousands):

	Year Ended
	December 31,
	2020		2019		2018
Research and development expenses	$	2,603	$	1,286	$	513
General and administrative expenses		3,911		1,797		510
	$	6,514	$	3,083	$	1,023

Schedule of share option activity

				Weighted
		Weighted		Average	Aggregate
	Number of	Average		Contractual	Intrinsic
	Shares	Exercise Price		Term	Value
				(in years)	(in thousands)
Outstanding as of December 31, 2019	2,634,346	$	9.57	9.04	$	6,107
Granted	1,370,984		12.00	—		—
Exercised	(79,158)		3.42	—		—
Forfeited	(189,509)		11.10	—		—
Outstanding as of December 31, 2020	3,736,663	$	10.51	8.54	$	27,553
Vested and expected to vest as of December 31, 2020	3,736,663	$	10.51	8.54	$	27,553
Options exercisable as of December 31, 2020	1,518,721	$	8.81	7.90	$	13,729

Schedule of assumptions used to determine the fair value of share options granted

The following table presents, on a weighted average basis, the assumptions used in the Black‑Scholes option‑pricing model to determine the fair value of share options granted to employees and directors:The following table presents, on a weighted average basis, the assumptions used in the Black‑Scholes option‑pricing model to determine the fair value of share options granted to employees and directors:
	Year Ended
	December 31,
	2020		2019		2018
Risk-free interest rate	1.3	%	2.1	%	2.7	%
Expected volatility	74.8	%	77.9	%	78.6	%
Expected dividend yield	—		—		—
Expected term (in years)	5.98		5.86		6.07