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): July 7, 2022

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))

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      ¨

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 5.03 Amendments to Articles of Incorporation or Bylaws; Change in Fiscal Year.

On July 7, 2022, at a special meeting of stockholders (the “Special Meeting”) of Rubius Therapeutics, Inc. (the “Company”), the Company’s stockholders approved an amendment to the Company’s Amended and Restated Certificate of Incorporation to increase the number of authorized shares of common stock of the Company from 150,000,000 to 300,000,000 (the “Amendment”). Also on July 7, 2022, following such approval, a Certificate of Amendment to the Company’s Amended and Restated Certificate of Incorporation effecting such increase was filed with the Secretary of State of the State of Delaware. The foregoing description of the Amendment is qualified in its entirety by reference to the copy of the Amendment filed as Exhibit 3.1 to this Form 8-K, which Amendment is incorporated by reference herein.

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

As noted above, the Amendment was submitted to the Company’s stockholders for approval at the Special Meeting. The proposal is described in detail in the Company’s definitive proxy statement filed with the Securities and Exchange Commission on June 21, 2022.

The number of shares of common stock entitled to vote at the Special Meeting was 90,357,032. The number of shares of common stock present or represented by proxy at the Special Meeting was 71,435,803.

Stockholders approved the proposal, with 70,818,240 votes cast for, 614,978 votes cast against and 2,585 votes abstained. There were 0 broker non-votes regarding the proposal.

Item 9.01. Financial Statements and Exhibits.

(d) Exhibits.

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.