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 17, 2018

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:

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

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

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

o 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     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.     o

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

As previously disclosed in the Registration Statement on Form S-1 (File No. 333-225840) (the “Registration Statement”) of Rubius Therapeutics, Inc. (the “Company”), on July 20, 2018 and in connection with the consummation of the initial public offering of the Company’s common stock (the “IPO”), the Company filed an amended and restated certificate of incorporation (the “Restated Certificate”) with the Secretary of State of the State of Delaware. The Board of Directors of the Company (the “Board”) and the Company’s stockholders previously approved the Restated Certificate to be filed in connection with, and to be effective upon, the consummation of the IPO. The Restated Certificate amends and restates the Company’s existing amended and restated certificate of incorporation in its entirety to, among other things: (i) authorize 150,000,000 shares of common stock; (ii) eliminate all references to the previously-existing series of preferred stock; and (iii) authorize 10,000,000 shares of undesignated preferred stock that may be issued from time to time by the Board in one or more series.

The foregoing description of the Restated Certificate is qualified by reference to the Restated Certificate, a copy of which is attached hereto as Exhibit 3.1 and is incorporated herein by reference.

In addition, as previously disclosed in the Registration Statement, on July 17, 2018, the amended and restated bylaws of the Company (the “Amended and Restated ByLaws”), previously approved by the Board and the Company’s stockholders to become effective immediately upon effectiveness of the Registration Statement, became effective. The Amended and Restated ByLaws amend and restate the Company’s bylaws in their entirety to, among other things: (i) eliminate the ability of the Company’s stockholders to take action by written consent in lieu of a meeting and call special meetings of stockholders; (ii) establish procedures relating to the presentation of stockholder proposals at stockholder meetings; (iii) establish procedures relating to the nomination of directors; and (iv) conform to the amended provisions of the Restated Certificate.

The foregoing description of the Amended and Restated ByLaws is qualified by reference to the Amended and Restated ByLaws, a copy of which is attached hereto as Exhibit 3.2 and is incorporated herein by reference.

Item 8.01 Other Events

On July 20, 2018, the Company completed its IPO of 12,055,450 shares of Common Stock at a price to the public of $23.00 per share for gross proceeds of approximately $277.3 million before deducting underwriting discounts and commissions and estimated offering expenses. This includes the exercise in full by the underwriters of their option to purchase 1,572,450 additional shares of Common Stock from the Company at the public offering price, less underwriting discounts and commissions.

Item 9.01. Financial Statements and Exhibits.

(d)              Exhibits.

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INDEX TO EXHIBITS

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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.

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