Exhibit 1.1
                                                                     -----------

                             JOINT FILING AGREEMENT

The undersigned hereby agree that the Statement on this Schedule 13G/A, dated
February 14, 2003, (the "Schedule 13G/A"), with respect to the Common Stock, par
value $0.01 per share, of Immunomedics, Inc. is filed on behalf of each of us
pursuant to and in accordance with the provisions of Rule 13d-1(k) under the
Securities and Exchange Act of 1934, as amended, and that this Agreement shall
be included as an Exhibit to this Schedule 13G/A. Each of the undersigned agrees
to be responsible for the timely filing of the Schedule 13G/A, and for the
completeness and accuracy of the information concerning itself contained
therein. This Agreement may be executed in any number of counterparts, all of
which taken together shall constitute one and the same instrument.

        IN WITNESS WHEREOF, the undersigned have executed this Agreement as of
the 14th day of February, 2003.


                                                     OrbiMed Advisors Inc.

                                            By: /s/ Samuel D. Isaly
                                            ------------------------------
                                            Name:  Samuel D. Isaly
                                            Title: President

                                                     OrbiMed Advisors LLC

                                            By: /s/ Samuel D. Isaly
                                            ------------------------------
                                            Name:  Samuel D. Isaly
                                            Title: President of Managing
                                                   Member, OrbiMed Advisors Inc.


                                            By: /s/ Samuel D. Isaly
                                            ----------------------------
                                            Name:  Samuel D. Isaly