UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

PURSUANT TO SECTION 13 OR 15(d)

OF THE SECURITIES EXCHANGE ACT OF 1934

Date of Report (Date of earliest event reported): May 21, 2020

RUBIUS THERAPEUTICS, INC.

(Exact name of registrant as specified in its charter)

(617) 679-9600

(Registrant’s telephone number, including area code)

N/A

(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

¨ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 203.425)

¨ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

¨ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

¨ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

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

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 or Rule 12b-2 of the Securities Exchange Act of 1934.

Emerging growth company     x

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.     ¨

Item 5.07 – Submission of Matters to a Vote of Security Holders.

On May 21, 2020, Rubius Therapeutics, Inc. (the “Company”) held its annual meeting virtually (the “Annual Meeting”) of stockholders. The following proposals were submitted to the stockholders at Annual Meeting:

(i) To elect three Class II directors to the Company’s board of directors, to serve until the 2023 annual meeting of stockholders and until his or her successor has been duly elected and qualified, or until his or her earlier death, resignation or removal; and

(ii) To ratify the appointment of PricewaterhouseCoopers LLP as the Company’s independent registered public accounting firm for the fiscal year ending December 31, 2020.

The proposals are described in detail in the Company’s Proxy Statement filed with the Securities and Exchange Commission on April 9, 2020.

The number of shares of common stock entitled to vote at the Annual Meeting was 80,428,403.  The number of shares of common stock present or represented by valid proxy at the Annual Meeting was 70,122,531.  All matters submitted to a vote of the Company’s stockholders at the Annual Meeting were approved and all director nominees were elected.

The number of votes cast for and against and the number of abstentions and broker non-votes with respect to each matter voted upon are set forth below:

There were 7,342,591 broker non-votes regarding the election of directors.

Stockholders ratified the appointment of PricewaterhouseCoopers LLP as the Company’s independent registered public accounting firm for the fiscal year ending December 31, 2020.  The results of the voting included 70,112,667 votes for, 8,798 votes against and 1,066 votes abstained. There were no broker non-votes regarding this proposal.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.