Prior to the Conversion, the Company granted profit interest units under the 2014 Equity Incentive Plan (the Plan). Under the provisions of the Plan, the Board of Managers granted profit interest units (“PI Units”) to employees, managers, and consultants (collectively, the Participants). PI Units were Common Units that were issued to Participants with a threshold amount. In the event of a distribution by the Company, the proceeds distributed to the holder would be reduced by the threshold amount. PI Units were economically similar to a stock option award and vested based on time or performance-based milestones, as determined by the Board of Managers and stipulated in the grant agreements.

Profit interest units generally vested 25% after one-year with the remainder vesting monthly over the following three-year period. The Company has determined that the underlying terms and intended purpose of the PI Units are more akin to an equity-based compensation for employees and non-employees than a performance bonus or profit-sharing arrangement.

	Number of Units			Weighted- Average Grant Date Fair Value
Balance as of December 31, 2019		1,294,435		$	1.73
Granted		552,557			2.56
Cancelled/Forfeited		(22,657	)		2.35
Balance as of December 31, 2020		1,824,335			1.97
Granted		1,385,782			5.03
Cancelled/Forfeited		(47,227	)		2.63
Converted to vested and unvested common stock		(3,162,890	)		3.29
Balance as of December 31, 2021		—		$	—

Immediately prior to consummation of the IPO, all of the outstanding profit interest units were converted into 2,361,520 shares of common stock, of which 1,141,403 were subject to certain vesting conditions. The following table provides a summary of the unvested common stock activity for the year ended December 31, 2021:

	Number of Shares			Weighted- Average Grant Date Fair Value
Balance as of December 31, 2020		—		$	—
Conversion of profit interest units		1,141,403		$	6.62
Vested		(105,898	)	$	4.29
Forfeited		(7,116	)	$	3.11
Balance as of December 31, 2021		1,028,389		$	6.76

The estimated grant-date fair value of all the Company’s PI Units was calculated using the Black-Scholes option pricing model, based on the following assumptions:

	Year Ended December 31,
	2021	2020
Expected term (in years)	5.5 – 6.1		6.1
Expected volatility	75%	80%
Risk-free interest rate	0.74 – 1.10%	0.4 – 1.7%
Expected dividend rate	0%	0%

In September 2021, the Company’s board of directors and stockholders adopted and approved the 2021 Incentive Award Plan, or the 2021 Plan, and the Employee Stock Purchase Plan, or the ESPP, which became effective in connection with the IPO. The Company reserved 6,189,332 shares of common stock for future issuance under the 2021 Plan and 375,000 shares under the ESPP, respectively.

The number of shares of common stock reserved for issuance under the 2021 Plan automatically increase on the first day of January, commencing on January 1, 2022 and through 2031, in an amount equal to 5% of the total number of shares of the Company’s capital stock outstanding on the last day of the preceding year, or a lesser number of shares determined by the Company’s board of directors. In addition, any awards subject to the 2014 Plan which are forfeited or repurchased by the Company after the effective date of the 2021 Plan are added to the 2021 Plan reserve. Awards granted under the 2021 Plan expire no later than ten years from the date of grant. For the Incentive Stock Options, or ISOs, and Nonstatutory Stock Options, or NSOs, the option price shall not be less than 100% of the estimated fair value on the date of grant. Options granted typically vest over a four-year period but may be granted with different vesting terms. As of December 31, 2021, there were 4,715,520 shares available for issuance under the 2021 Plan.

	Number of Shares			Weighted- Average Exercise Price Per Share		Weighted- Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in thousands)
Balances as of December 31, 2020		—		$	—		—	$	—
Stock options granted		1,481,726			17.57
Stock options cancelled		(7,914	)		17.00
Balances as of December 31, 2021		1,473,812			17.57		9.71		11,711
Options vested and exercisable as of December 31, 2021		300,701			17.00		9.70		2,499

The intrinsic value is the difference between the fair value of the Company’s common stock at the time of exercise and the exercise price of the stock option.

The weighted-average grant date fair value of options granted to employees during the year ended December 31, 2021 was $11.01 per share.

The estimated grant-date fair value of the Company’s stock options was calculated using the Black-Scholes option pricing model, based on the following assumptions:

	Year Ended December 31,
	2021	2020
Expected term (in years)	5.0 - 6.7		—
Expected volatility	72% - 73%		—
Risk-free interest rate	0.79% - 1.34%		—
Dividend yield	0%		—

	Year Ended December 31,
	2021		2020
	(In thousands)
Research and development expenses	$	2,625	$	381
General and administrative expenses		2,956		175
Total share-based compensation	$	5,581	$	556

As of December 31, 2021, there was a total of $19.2 million of unrecognized compensation costs related to stock options and restricted stock awards that is expected to be recognized over a weighted-average period of approximately 3.2 years. The Company did not recognize incremental share-based compensation expense related to the conversion of the profit interest units to unvested common stock in accordance with the Conversion, as such exchange was at fair value.