GOODWIN, PROCTER & HOAR LLP
                        COUNSELLORS AT LAW
                          EXCHANGE PLACE
                       BOSTON, MA 02109-2991

                                December 22, 2000


AVANT Immunotherapeutics, Inc.
119 Fourth Avenue
Needham, Massachusetts 02494
Attn: Dr. Una S. Ryan


         Re:      Legality of Securities to be Registered
                  under Registration Statement on Form S-3
                  ----------------------------------------

Ladies and Gentlemen:

         This opinion is delivered in our capacity as counsel to AVANT
Immunotherapeutics, Inc., a Delaware corporation (the "Company"), in
connection with the registration, pursuant to the Securities Act of 1933 (the
"Securities Act"), of 2,127,113 shares (the "Shares") of common stock, par
value $.001 per share, of the Company.

         In connection with rendering this opinion, we have examined the
Certificate of Incorporation and the Bylaws of the Company, each as amended to
date; such records of the corporate proceedings of the Company as we have deemed
material; a registration statement on Form S-3 under the Securities Act relating
to the Shares and the prospectus contained therein; and such other certificates,
receipts, records and documents as we considered necessary for the purposes of
this opinion.

         We are attorneys admitted to practice in The Commonwealth of
Massachusetts. We express no opinion concerning the laws of any jurisdiction
other than the laws of the United States of America and The Commonwealth of
Massachusetts and the Delaware General Corporation Law.

         Based upon the foregoing, we are of the opinion that the Shares are
duly authorized, legally issued, fully paid and nonassessable by the Company
under the Delaware General Corporation Law.

         The foregoing assumes that all requisite steps will be taken to comply
with the requirements of the Securities Act and applicable requirements of state
laws regulating the offer and sale of securities.




AVANT Immunotherapeutics, Inc.
December 22, 2000
Page 2


         We hereby consent to being named as counsel to the Company in the
Registration Statement, to the references therein to our firm under the caption
"Legal Matters" and to the inclusion of this opinion as an exhibit to the
Registration Statement.

                                           Very truly yours,

                                           /s/ Goodwin, Procter & Hoar LLP

                                           GOODWIN, PROCTER & HOAR LLP