CD80 and neoplasm: Since immunization with cells expressing B7.1 alone showed different protective T-cell mediated immune responses between a virally infected cell system and a gene-transfected cell system at a dose of 5×106 cells per mouse immunization, we speculated that virally derived antigens affect presentation of TAP-independent intrinsic tumor antigens, thereby decreasing the capacity of tumor cells for T-cell priming.