6. Stock-based awards

2018 Stock option and grant plan

The Company’s 2018 Stock Option and Grant Plan (the “2018 Plan”) provided for the Company to grant incentive stock options or nonqualified stock options, restricted stock awards and other stock-based awards to employees, directors and consultants of the Company. The 2018 Plan was administered by the board of directors or, at the discretion of the board of directors, by a committee of the board of directors. The exercise prices, vesting and other restrictions were determined at the discretion of the board of directors, or its committee if so delegated.

The total number of shares of common stock that could have been issued under the 2018 Plan was 3,071,960 shares, of which 107,635 shares remained available for grant on June 18, 2019, the date that the Company’s 2019 Stock Option and Incentive Plan (the “2019 Plan”) became effective. Upon the effectiveness of the 2019 Plan, the 107,635 remaining shares available under the 2018 Plan were transferred and became available for issuance under the 2019 Plan. Shares of common stock underlying outstanding awards under the 2018 Plan that are forfeited, cancelled, held back upon exercise or settlement of an award to satisfy the exercise price or tax withholding, reacquired by the Company prior to vesting, satisfied without the issuance of stock, expire or are otherwise terminated (other than by exercise) will be added to the shares of common stock available for issuance under the 2019 Plan.

2019 Stock option and incentive plan

The 2019 Plan was adopted and approved by the Company’s board of directors in May 2019 and by the Company’s stockholders in June 2019. The 2019 Plan became effective on June 18, 2019 and replaced the Company’s 2018 Plan on that date. The 2019 Plan allows the board of directors or the compensation committee of the board of directors to make equity-based incentive awards to the Company’s officers, employees, directors or other key persons (including consultants). The number of shares initially reserved for issuance under the 2019 Plan is 2,572,457, which includes the 107,635 shares transferred from the 2018 Plan, and shall be cumulatively increased on January 1, 2020 and each January 1 thereafter by 4% of the number of shares of the Company’s common stock outstanding on the immediately preceding December 31 or such lesser number of shares determined by the Company’s board of directors or compensation committee of the board of directors.

The 2019 Plan is administered by the board of directors or, at the discretion of the board of directors, by a committee of the board of directors. The exercise prices, vesting and other restrictions are determined at the discretion of the board of directors, or its committee if so delegated, except that the exercise price per share of stock options may not be less than 100% of the fair market value of the share of common stock on the date of grant and the term of stock option may not be greater than ten years. All incentive options granted to any person possessing more than 10% of the total combined voting power of all classes of shares may not have an exercise price of less than 110% of the fair market value of the common stock on the grant date. Stock options granted to employees, officers, members of the board of directors and consultants will typically vest over a four-year period.

Shares that are expired, terminated, surrendered or canceled under the 2019 Plan without having been fully exercised will be available for future awards.

2019 Employee stock purchase plan

The 2019 Employee Stock Purchase Plan (the “2019 ESPP”) was adopted and approved by the Company’s board of directors in May 2019 and by the Company’s stockholders in June 2019. The 2019 ESPP became effective on June 18, 2019, at which time 273,869 shares were reserved for issuance. The 2019 ESPP provides that the number of shares reserved and available for issuance will automatically increase each January 1, beginning on January 1, 2020 and each January 1 thereafter through January 1, 2029, by the least of (i) 1% of the outstanding number of shares of the Company’s common stock on the immediately preceding December 31, (ii) 410,803 shares or (iii) such number of shares as determined by the compensation committee.

Stock option valuation

The assumptions that the Company used to determine the grant-date fair value of stock options granted to employees, directors and consultants were as follows, presented on a weighted average basis:


	Three Months Ended					Nine Months Ended
	September 30,					September 30,
	2019			2018		2019			2018
Expected term (in years)		n/a		5.87			6.04		5.87
Volatility		n/a		70.86	%		69.80	%	70.86
Risk-free interest rate		n/a		2.86	%		2.39	%	2.86
Dividend yield		n/a		0.00	%		0.00	%	0.00
Weighted average fair value of common stock		n/a	$	0.29		$	8.26		0.29

Stock options

The following table summarizes the Company’s stock option activity since December 31, 2018:


		Weighted-		Weighted-
		Average		Average	Aggregate
		Exercise		remaining	Intrinsic
	Number	Price per		contractual	Value
	of Options	Share		term (years)	(000's)
Balance Outstanding, December 31, 2018	1,839,913	$	0.61	9.74	$	10,577
Options granted	1,228,352	$	7.61
Options exercised	(651,031)	$	0.65
Balance Outstanding, September 30, 2019	2,417,234	$	4.16	9.23	$	44,931
Exercisable, September 30, 2019	72,910	$	3.43	9.11	$	1,409
Vested and expected to vest, September 30, 2019	2,417,234	$	4.16	9.23	$	44,931

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

The weighted average grant-date fair value per share of stock options granted during the nine months ended September 30, 2019 was $4.85.

Stock-based compensation

The Company recorded $34 in stock-based compensation expense for the three and nine months ended September 20, 2018, with $18 classified as research and development expense and $16 classified as general and administrative expense in the condensed consolidated statements of operations and comprehensive loss The Company recorded total stock-based compensation for options granted for the three and nine months ended September 30, 2019 of $483 and $1,100, with $125 and $301 classified as research and development expense and $358 and $799 classified as general and administrative expense, respectively, in the condensed consolidated statements of operations and comprehensive loss.

As of September 30, 2019, total unrecognized compensation cost related to the unvested stock-based awards was $6,235, which is expected to be recognized over a weighted average period of 3.11 years.

In April, June and July 2019, certain option holders early exercised options to purchase 491,207 shares of common stock, at an average exercise price of $0.65 per share, for cash proceeds of $321 (See Note 5). Stock-based compensation expense related to these options will continue to be recognized over the requisite service period of the awards based on the grant-date fair value which was determined using the Black-Scholes option-pricing model.