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 27, 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 3.01 Notice of Delisting or Failure to Satisfy a Continued Listing Rule or Standard; Transfer of Listing.

On July 27, 2022, Rubius Therapeutics, Inc. (the “Company”) received a deficiency letter from the Listing Qualifications Department (the “Staff”) of The Nasdaq Stock Market LLC (“Nasdaq”) notifying the Company that, for the last 30 consecutive business days, the bid price for the Company’s common stock had closed below the $1.00 per share minimum bid price requirement for continued inclusion on the Nasdaq Global Select Market pursuant to Nasdaq Listing Rule 5450(a)(1) (the “Minimum Bid Price Requirement”). The Nasdaq deficiency letter has no immediate effect on the listing of the Company’s common stock, and its common stock will continue to trade on the Nasdaq Global Select Market under the symbol “RUBY” at this time.

In accordance with Nasdaq Listing Rule 5810(c)(3)(A), the Company has been provided a period of 180 calendar days, or until January 23, 2023, to regain compliance with the Minimum Bid Price Requirement. If, at any time ending January 23, 2023, the bid price for its common stock closes at $1.00 or more for a minimum of 10 consecutive business days as required under the applicable rule, the Staff will provide written notification to the Company that it has regained compliance with the Minimum Bid Price Requirement, unless the Staff exercises its discretion to extend this ten-day period pursuant to Nasdaq Listing Rule 5810(c)(3)(H).

If the Company does not regain compliance with the Minimum Bid Price Requirement by the applicable date, the Company may be eligible for an additional 180 calendar day compliance period. To qualify, the Company would need to transfer the listing of its common stock to the Nasdaq Capital Market, provided that it meets the continued listing requirement for market value of publicly held shares and all other initial listing standards of the Nasdaq Capital Market, with the exception of the Minimum Bid Price Requirement. To effect such a transfer, the Company would also need to pay an application fee to Nasdaq and provide written notice to the Staff of its intention to cure the deficiency during the second compliance period by effecting a reverse stock split if necessary. As part of its review process, the Staff will make a determination of whether it believes the Company will be able to cure the deficiency. Should the Staff conclude that the Company will not be able to cure the deficiency, the Staff will provide written notification to the Company that its common stock will be subject to delisting. At that time, the Company may appeal the Staff’s delisting determination to a Nasdaq Listing and Hearing Review Panel. However, there can be no assurance that, if the Company receives a delisting notice and appeals the delisting determination by the Staff to the panel, such appeal would be successful.

The Company intends to monitor the closing bid price of its common stock and may, if appropriate, consider available options to regain compliance with the Minimum Bid Price Requirement. However, there can be no assurance that the Company will be able to regain compliance with the Minimum Bid Price Requirement.

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.