UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-K/A

(Amendment No. 1)

(Mark One)

For the fiscal year ended December 31, 2021

OR

FOR THE TRANSITION PERIOD FROM TO

Commission File Number 001-38663

Gritstone bio, Inc.

(Exact name of Registrant as specified in its Charter)

(510) 871-6100

Registrant’s telephone number, including area code

Securities registered pursuant to Section 12(b) of the Act:

Securities Registered Pursuant to Section 12(g) of the Act: None

Indicate by check mark if the Registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. Yes ☐ No ☒

Indicate by check mark if the Registrant is not required to file reports pursuant to Section 13 or 15(d) of the Act. Yes ☐ No ☒

Indicate by check mark whether the Registrant: (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the Registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes ☒ No ☐

Indicate by check mark whether the Registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the Registrant was required to submit such files). Yes ☒ No ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☒

Indicate by check mark whether the Registrant has filed a report on and attestation to its management assessment of the effectiveness of its internal control over financial reporting under Section 404(b) of the Sarbanes-Oxley Act (15 U.S.C. 7262(b)) by the registered public accounting firm that prepared or issued its audit report. ☐

Indicate by check mark whether the Registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act). Yes ☐ No ☒

The aggregate market value of the common stock held by non-affiliates of the registrant as of June 30, 2021 (the last business day of the registrant’s most recently completed second fiscal quarter) was approximately $419.0 million, based on the closing price of the registrant’s common stock, as reported by the Nasdaq Global Select Market on June 30, 2021 of $9.13 per share. Shares of the registrant’s common stock held by each executive officer, director, and holder of 5% or more of the outstanding common stock have been excluded in that such persons may deemed to be affiliates. This calculation does not reflect a determination that certain persons are affiliates of the registrant for any other purpose.

The number of shares of Registrant’s Common Stock outstanding as of March 7, 2022 was 72,708,342.

DOCUMENTS INCORPORATED BY REFERENCE

Portions of the Registrant’s Definitive Proxy Statement relating to the Annual Meeting of Shareholders, scheduled to be held on June 17, 2022, are incorporated by reference into Part III of this Annual Report on Form 10-K where indicated. Such Definitive Proxy Statement will be filed with the Securities and Exchange Commission on April 28, 2022.

EXPLANATORY NOTE

Gritstone bio, Inc. (the “Company”, “we”, “our” and “us”) is filing this Amendment No. 1 (the “Amendment No. 1”) solely to amend our Annual Report on Form 10-K for the fiscal year ended December 31, 2021 (the “Original Filing”), originally filed with the Securities and Exchange Commission (the “SEC”) on March 10, 2022 (the “Original Filing Date”). We are filing this Amendment No. 1 to amend clerical errors made in Part I of the Original Filing. The clerical errors were made in the third sentence and the title of Figure 8 included under the heading “Item 1. Business—New Developments—GRANITE updates”.

Item 1. Business.

New Developments

GRANITE updates

On January 13, 2022, we announced the first patient was enrolled for inclusion in the GRANITE -CRC-1L study, a Phase 2/3 trial evaluating our individualized neoantigen vaccine (GRANITE) for first line (1L) maintenance treatment of metastatic, microsatellite-stable colorectal cancer (MSS-CRC).

On January 13, 2022, we also announced updated interim data from the Phase 1/2 GRANITE trial evaluating individualized immunotherapy in combination with nivolumab (OPDIVO®) and ipilimumab (YERVOY®) in patients with advanced solid tumors. As of the January 5, 2022 data cutoff date, 6 out of 12 MSS-CRC patients treated in such GRANITE trial, who were alive at the time of our ESMO 2021 data presentation on September 17, 2021, remained alive, and the correlation between ctDNA and overall survival continued to be observed (Figure 8).

As of March 2022, the first patient was enrolled for inclusion in the GRANITE–CRC-ADJUVANT study, a randomized, controlled phase 2 trial of adjuvant GRANITE immunotherapy in MSS-CRC patients with stage II/III disease who are ctDNA+ after definitive surgery.

PART IV

Item 15. Exhibits and Financial Statement Schedules.

(a)(3) Exhibits

The documents listed in the Exhibit Index are filed with this report, in each case as indicated therein (numbered in accordance with Item 601 of Regulation S-K).

SIGNATURES

Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange Act of 1934, as amended, the Registrant has duly caused this Annual Report on Form 10-K/A to be signed on its behalf by the undersigned, thereunto duly authorized.

Pursuant to the requirements of the Securities Exchange Act of 1934, as amended, this Annual Report on Form 10-K/A has been signed below by the following persons on behalf of the Registrant in the capacities and on the dates indicated.