6. Redeemable convertible preferred stock

As of December 31, 2019 and 2018, 0 shares and 64,730,410 shares, respectively, of redeemable convertible preferred stock were issued and outstanding and were classified outside of stockholders' equity (deficit) because the shares contained redemption features that were not solely within the control of the Company.

Upon completion of the Company’s IPO on June 24, 2019, all outstanding shares of our Series A and Series B redeemable convertible preferred stock (the “Preferred Stock”) were converted into 21,056,136 shares of common stock and the related carrying value was reclassified to common stock and additional paid-in capital. Accordingly, there were no shares of redeemable convertible preferred stock outstanding as of December 31, 2019.

In June 2018, the Company entered into a Series A Preferred Stock Agreement ("2018 Series A Agreement"), which provided for a First Tranche Closing, Second Tranche Closing and a call option to purchase additional shares of Series A Preferred Stock.

In June 2018, the Company completed its First Tranche Closing, and issued and sold 15,000,000 shares of Series A Preferred Stock at a price of $1.00 ("2018 Series A Agreement Purchase Price") per share for aggregate proceeds of $14,784, net of issuance costs of $216. Upon the execution of the Company's license agreement with Amgen (see Note 9), the Company issued an additional 2,653,333 shares of Series A Preferred Stock to Amgen in June 2018 for a total value of $1,353.

The Second Tranche Closing was contingent upon the achievement of the Second Tranche Closing Milestone Event ("Milestone Event"), as reasonably determined by a majority of the Company's board of directors, prior to December 31, 2019 or waiver of the Milestone Event through written elections by a majority of the purchasers of shares of Series A Preferred Stock. Upon achievement or waiver of the Milestone Event, Amgen would be issued a number of additional shares for no consideration provided that Amgen's total holdings equal ten percent (10%) of the total outstanding and issued common stock of the Company on a fully diluted and as converted basis of the Second Tranche Closing. Additionally, the 2018 Series A Agreement contained a call option such that, following the Second Tranche Closing, the stockholders of Series A Preferred Stock have the right, but not the obligation, to purchase up to $20,000 of additional shares of Series A Preferred Stock at any time prior to January 14, 2022 at a price equal to the 2018 Series A Agreement Purchase Price.

The Company concluded that the rights to participate in the future issuance of Series A Preferred Stock met the definition of a freestanding financial instrument that was required to be recognized as a liability at fair value as (i) the instruments were legally detachable from the Series A Preferred Stock and (ii) required the Company to transfer equity instruments upon future closings of the Series A Preferred Stock. Upon the First Tranche Closing, the Company recognized a preferred stock tranche obligation of $7,350 with a corresponding reduction to the carrying value of the Series A Preferred Stock.

Upon the First Tranche Closing in June 2018, the initial carrying value of the Series A Preferred Stock was recorded at $8,787, equal to $15,000 of gross proceeds received by the Company and the fair value of $1,353 for the issuance of shares to Amgen, reduced by accrued issuance costs of $216 and the fair value of the preferred stock tranche obligation of $7,350.

Upon issuance of each tranche of Preferred Stock, the Company assessed the embedded conversion and liquidation features of the securities and determined that such features did not require the Company to separately account for these features. The Company also concluded that no beneficial conversion feature existed on the issuance date of each tranche of Preferred Stock.

In November 2018, upon the waiver of the Milestone Event through written elections by a majority of the shareholders of Series A Preferred Stock, the Company closed the second tranche of its Series A preferred financing through the issuance and sale of an aggregate of 25,000,001 shares of Series A Preferred Stock, at an issuance price of $1.00 per share, for proceeds of $25,000, before issuance costs of $4. In November 2018, in connection with the Company's issuance and sale of Series A Preferred Stock, the Company satisfied its obligation to issue additional shares under the Second Tranche Closing. Accordingly, the preferred stock tranche obligation associated with the future purchase obligation was adjusted to fair value immediately prior to the issuance of the Series A Preferred Stock, and upon issuance of the Series A Preferred Stock, the preferred stock tranche obligation associated with the future purchase obligation of $32,750, equal to then current fair value, was reclassified to the carrying value of the Series A Preferred Stock.

In November 2018, pursuant to the terms of the Amgen Agreement, the Company issued an additional 3,205,128 shares of Series A Preferred Stock valued at $7,404 to Amgen upon completion of the Series A Second Tranche Closing, satisfying its anti-dilution right under the Amgen Agreement.

In December 2018, the Company issued and sold 13,871,948 shares of Series B Preferred Stock, at an issuance price of $3.28 per share, for proceeds of $45,500 before issuance costs of $229. In connection with the Company's issuance and sale of Series B Preferred Stock, the Company terminated the option to purchase Series A Preferred Stock provided under the 2018 Series A Agreement.

As of December 31, 2018, redeemable convertible preferred stock consisted of the following:


		Preferred
	Preferred	stock					Common stock
	stock	issued and	Carrying		Liquidation		issuable upon
	authorized	outstanding	value		preference		conversion
Series A Preferred Stock	50,858,462	50,858,462	$	79,457	$	50,858	16,543,739
Series B Preferred Stock	13,871,948	13,871,948	$	45,271	$	45,500	4,512,397
	64,730,410	64,730,410	$	124,728	$	96,358	21,056,136