CD80 and neoplasm: Since immunization with a high dose of B7.1 or B7.1+TAP1 transfected cells dramatically protected mice from tumor challenge (Fig. 2C left), we determined if immunization of mice with γ-irradiated CMT.64 cells infected with VV-B7.1+VV-CR19 (wild-type virus) or VV-B7.1+VV-TAP1 have protection similar to mice immunized with gene-transfected tumor cells.