MULTIPLE LINEAGES OF TUMORS EXPRESS A COMMON TUMOR-ANTIGEN, P1A, BUT THEY ARE NOT CROSS-PROTECTED

Whether tumors of different lineages share common Ags is a critical is sue for understanding anti-tumor immune responses and for designing Ag -specific tumor immunotherapy. Because of lack of cross-protection amo ng individually derived tumors, it has been proposed that tumor Ags ar e specific for individual tumors. Here we show that lack of cross-prot ection is not due to lack of a shared tumor Ag. Thus, a plasmocytoma J 558 transfected with the costimulatory molecule B7-activates a cross-r eactive CTL response in vivo. The major Ag recognized by the cross-rea ctive CTL is P1A, which is expressed in mastocytoma P815, plasmocytoma J558, and fibrosarcoma Meth A. Surprisingly, no significant cross-pro tection can be detected among P1A-expressing tumors after immunization with either P1A-expressing or B7-transfected P815 cells. Our results demonstrate that multiple lineages of tumors are not cross-protected e ven though they share a tumor Ag that can be recognized by CTL. These results have important implications for tumor immunotherapy.