The present invention relates to the identification of antibodies which are specific
to human B7.1 antigen (CD80) and which are capable of inhibiting the binding of
B7.1 to a CD28 receptor and which are not capable of inhibiting the binding of
B7.1 to a CTLA-4 receptor. Two of these antibodies, 16C10 and 7C10, significantly
inhibit the production of IL-2, in spite of the existence of a second activating
ligand B7.2 (CD86). Blocking of the primary activation signal between CD28 and
B7.1 (CD80) with these antibodies while allowing the unimpaired or coincident interaction
of CTLA-4 and B7.1 and/or B7.2 represents a combined antagonistic effect on positive
co-stimulation with an agonistic effect on negative signalling. These antibodies,
or B7.1-binding fragments thereof, may be used as for the treatment of Crohn's disease.
