Exhibit 5.1

						Goodwin Procter LLP 100 Northern Avenue Boston, MA 02210   goodwinlaw.com   +1 617 570 1000

February 16, 2021

Adicet Bio, Inc.

500 Boylston Street, 13^th Floor

Boston, MA 02116

Re: Securities Registered under Registration Statement on Form S-3

We have acted as counsel to you in connection with your filing of a Registration Statement on Form S-3 (File No. 333-229499) (as amended or supplemented, the “Registration Statement”) filed on February 1, 2019 with the Securities and Exchange Commission (the “Commission”) pursuant to the Securities Act of 1933, as amended (the “Securities Act”), relating to the registration of the offering by Adicet Bio, Inc. (formerly known as resTORbio, Inc.), a Delaware corporation (the “Company”) of up to $175,000,000 of any combination of securities of the types specified therein (the “Shares”) of the Company’s Common Stock, $0.0001 par value share. Reference is made to our opinion letter dated February 1, 2019 and included as Exhibit 5.1 to the Registration Statement. We are delivering this supplemental opinion letter in connection with the prospectus supplement (the “Prospectus Supplement”) filed on February 11, 2021 by the Company with the Commission pursuant to Rule 424(b)(5) under the Securities Act. The Prospectus Supplement relates to the offering by the Company of (i) up to 10,575,513 shares (the “Shares”) of the Company’s common stock, par value $0.0001 per share (“Common Stock”) covered by the Registration Statement. The Shares include an over-allotment option granted to the underwriters of the offering to purchase 1,344,743 Shares. The Shares are being sold to the several underwriters named in, and pursuant to, an underwriting agreement among the Company and such underwriters (the “Underwriting Agreement”).

We have reviewed such documents and made such examination of law as we have deemed appropriate to give the opinion set forth below. We have relied, without independent verification, on certificates of public officials and, as to matters of fact material to the opinion set forth below, on certificates of officers of the Company.

The opinion set forth below is limited to the Delaware General Corporation Law.

Based on the foregoing, we are of the opinion that the Shares have been duly authorized and, upon issuance and delivery against payment therefor in accordance with the terms of the Underwriting Agreement, the Shares will be validly issued, fully paid and non-assessable.

Guggenheim Securities, LLC

February 16, 2021

Page 2

We hereby consent to the inclusion of this opinion as Exhibit 5.1 to the Registration Statement and to the references to our firm under the caption “Legal Matters” in the Registration Statement. In giving our consent, we do not admit that we are in the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations thereunder.