Disclosed is a composition for inhibiting the interactions of B7-1 and B7-2 with their natural ligands. Such compositions comprise an antibody specific for B7-2 and an antibody specific for B7-1, in a pharmaceutically acceptable carrier. The composition may be formulated for either separate or combined administration of the antibody components. The antibodies may be monoclonal antibodies, or humanized antibodies. Preferred antibodies are disclosed.