In May 2019, the Company’s board of directors (the “Board”) adopted its 2019 Equity Incentive Plan (“2019 Plan”), which was subsequently approved by its stockholders and became effective on May 13, 2019. As a result, no additional awards under the Company’s 2016 Equity Incentive Plan, as amended (the “2016 Plan”) will be granted and all outstanding stock awards granted under the 2016 Plan that are repurchased, forfeited, expired, or are cancelled will become available for grant under the 2019 Plan in accordance with its terms. The 2016 Plan will continue to govern outstanding equity awards granted thereunder.

The 2019 Plan provides for the issuance of incentive stock options (“ISOs”) to employees, and for the grant of nonstatutory stock options, stock appreciation rights, restricted stock awards, restricted stock unit awards, performance stock awards, performance cash awards and other forms of stock awards to the Company’s employees, officers, and directors, as well as non- employees, consultants, and affiliates to the Company. Under the terms of the 2019 Plan, stock options may not be granted at an exercise price less than fair market value of the Company’s common stock on the date of the grant. The 2019 Plan is administered by the Compensation Committee of the Company’s Board.

Initially, subject to adjustments as provided in the 2019 Plan, the maximum number of the Company’s common stock that may be issued under the 2019 Plan was 4,530,000 shares, which is the sum of (i) 1,618,841 new shares, plus (ii) the number of shares (not to exceed 2,911,159 shares) that remained available for the issuance of awards under the 2016 Plan, at the time the 2019 Plan became effective, and (iii) any shares subject to outstanding stock options or other stock awards granted under the 2016 Plan that are forfeited, expired, or reacquired. The 2019 Plan provides that the number of shares reserved and available for issuance under the 2019 Plan will automatically increase each January 1, beginning on January 1, 2020, by 5% of the outstanding number of shares of common stock on the immediately preceding December 31 or such lesser number of shares as determined by the Board. Subject to certain changes in capitalization of the Company, the aggregate maximum number of shares of common stock that may be issued pursuant to the exercise of ISOs is equal to 13,000,000 shares of common stock. Stock options awarded under the 2019 Plan expire 10 years after grant and typically vest over four years.

As of September 30, 2024, there were 473,973 shares of common stock available for issuance under the 2019 Plan.

Total stock‑based compensation expense recorded for employees, directors and non‑employees:


	Three Months Ended				Nine Months Ended
	September 30,				September 30,
(in thousands)	2024		2023		2024		2023
Research and development	$	951	$	764	$	2,907	$	2,378
General and administrative		1,140		1,072		3,453		3,356
Total stock-based compensation expense	$	2,091	$	1,836	$	6,360	$	5,734

During the nine months ended September 30, 2024, the Company did not grant any stock options. For the three months ended September 30, 2024 and 2023, amortization of stock compensation of options amounted to $0.4 million and $1.1 million, respectively, and for the nine months ended September 30, 2024 and 2023, amortization of stock compensation of options amounted to $1.6 million and $3.9 million, respectively. As of September 30, 2024 and 2023, the total unrecognized stock‑based compensation expense for unvested options was $0.7 million and $3.7 million, respectively, which is expected to be recognized over 1.2 years and 1.8 years, respectively.

The following table summarizes the information about stock options outstanding at September 30, 2024:


						Weighted-Average
				Weighted-		Remaining
				Average		Contractual		Aggregate
(in thousands, except for share data)	Options Outstanding			Exercise Price		Term (in years)		Intrinsic Value
Outstanding at December 31, 2023		4,695,619		$	2.01		5.9	$	7,875
Options granted		—			—
Options exercised		(327,492	)		1.05
Forfeited		(58,123	)		1.05
Expired		—			—
Outstanding at September 30, 2024		4,310,004		$	2.09		5.0	$	27,613

Exercisable at September 30, 2024		4,168,686		$	2.13		5.0	$	26,561
Nonvested at September 30, 2024		141,318		$	1.05		7.2	$	1,052

The aggregate intrinsic value is calculated as the difference between the exercise price of all outstanding and exercisable stock options and the fair value of the Company’s common stock at September 30, 2024. The intrinsic value of stock options exercised during the three and nine months ended September 30, 2024, was zero and $1.1 million, respectively. The intrinsic value of stock options exercised during the three and nine months ended September 30, 2023, was $0.1 million. The total grant-date fair value of stock options vested during the three and nine months ended September 30, 2024 was $0.1 million and $0.2 million, respectively. The total grant-date fair value of stock options vested during the three and nine months ended September 30, 2023 was $0.1 million and $0.4 million, respectively.

During the nine months ended September 30, 2024, the Company granted 1,425,000 restricted stock units (“RSUs”). For the three months ended September 30, 2024 and 2023, amortization of stock compensation of RSUs amounted to $1.7 million and $0.7 million, respectively. For the nine months ended September 30, 2024 and 2023, amortization of stock compensation of RSUs amounted to $4.8 million and $1.8 million, respectively. As of September 30, 2024 and 2023, the unamortized compensation costs associated with non-vested restricted stock awards were $17.8 million and $4.5 million, respectively, with a weighted-average remaining amortization period of 2.6 years.

The following table summarizes the information about restricted stock units outstanding at September 30, 2024:


				Weighted-Average
				Grant Date
(in thousands, except for share data)	Shares			Fair Value
Outstanding at December 31, 2023		6,917,422		$	2.35
Awarded		1,425,000			5.71
Released		(1,256,626	)		1.86
Forfeited		(633,984	)		2.92
Outstanding at September 30, 2024		6,451,812		$	3.35
Nonvested at September 30, 2024		6,205,093		$	3.38

Weighted Average Remaining Recognition Period (in years)		2.6

In May 2019, the Company’s Board and its stockholders approved the 2019 Employee Stock Purchase Plan (the “ESPP”), which became effective as of May 13, 2019. The ESPP is intended to qualify as an “employee stock purchase plan” within the meaning of Section 423 of the U.S. Internal Revenue Code of 1986, as amended. The number of shares

of common stock initially reserved for issuance under the ESPP was 180,000 shares. The ESPP provides for an annual increase on the first day of each year beginning in 2020 and ending in 2029, equal to the lesser of (i) 1% of the shares of common stock outstanding on the last day of the calendar month before the date of the automatic increase and (ii) 360,000 shares; provided that prior to the date of any such increase, the Board may determine that such increase will be less than the amount set forth in clauses (i) and (ii). As of September 30, 2024, no shares of common stock had been issued under the ESPP. The first offering period will commence on November 15, 2024.