	Three Months March 31,
	2019		2018
	(in thousands)
Cost of product revenue	$	27	$	15
Research and development		72		49
Sales and marketing		108		43
General and administrative		205		166
Total stock-based compensation	$	412	$	273

The Company estimates the grant-date fair value of the Company’s option awards using the Black-Scholes option pricing model. The assumptions for the Black-Scholes model for the three months ended March 31, 2019 and 2018 were as follows:

On June 17, 2009, the Company adopted the 2009 Equity Incentive Plan (the “2009 Plan”) under which the Board had the authority to issue stock options to employees, directors and consultants.

In February 2019, the Company adopted the 2019 Stock Option and Incentive Plan (the “2019 Plan”), which became effective in connection with the IPO. As a result, effective as of March 6, 2019, the Company may not grant any additional awards under the 2009 Plan. The 2009 Plan will continue to govern outstanding equity awards granted thereunder. The Company has initially reserved 2,000,430 shares of common stock for the issuance of awards under the 2019 Plan. In addition, the number of shares of common stock reserved for issuance under the 2019 Plan will automatically increase on the first day of January for a period of up to ten years, commencing on January 1, 2020, in an amount equal to 3% 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. As of March 31, 2019, there were 1,694,114 shares available for issuance under the 2019 Plan.

	Shares Available for Grant			Number of Shares			Weighted- Average Exercise Price Per Share		Weighted- Average Remaining Term		Aggregate Intrinsic Value
									(in years)		(in thousands)
Balance, December 31, 2018		392,299			3,636,358		$	3.54		7.79	$	11,267
Awards authorized		2,000,430			—
2009 Plan shares expired		(293,953	)		—
Options granted		(425,983	)		425,983			14.08
Options exercised		—			(80,515	)		2.12
Options cancelled		21,321			(21,321	)		3.12
Balance, March 31, 2019		1,694,114			3,960,505		$	4.67	7.87		$	114,058
Vested and exercisable, March 31, 2019					1,716,874		$	2.78	6.59		$	52,691
Vested and expected to vest, March 31, 2019					3,960,505		$	4.67	7.87		$	114,058

In February 2019, the Company adopted the 2019 Employee Stock Purchase Plan (“ESPP”), which became effective as of March 6, 2019. The Company has initially reserved 300,650 shares of common stock for purchase under the ESPP. Each offering to the employees to purchase stock under the ESPP will begin on each September 1 and March 1 and will end on the following February 28 or 29 and August 30, respectively. The first offering period is expected to begin on September 1, 2019 and end on February 29, 2020. On each purchase date, which falls on the last date of each offering period, ESPP participants will purchase shares of common stock at a price per share equal to 85% of the lesser of (1) the fair market value per share of the common stock on the offering date or (2) the fair market value of the common stock on the purchase date. The occurrence and duration of offering periods under the ESPP are subject to the determinations of the Company’s Compensation Committee, in its sole discretion.