Induction of protective antitumor immune response against a murine plasmacytoma not curable by alkylating-drug treatment

Immunization with viable tumor cells followed by subsequent administration of glutaraldehyde-treated tumor cells induced a protective antitumor immune response in the host toward the alkylating-drug resistant RPC-5 plasmacytoma. This was proven by resistance to challenge with RPC-5 tumor cells, neutralization in Winn tests, by effectiveness of combined chemotherapy with melphalan plus immunotherapy with spleen cells from RPC-5 immunized mice and in vitro by cytotoxicity tests. The specificity of the immune response was ascertained in vivo by comparison with the response toward MOPC-315 plasmacytoma. However, in vitro cytotoxicity tests revealed the occurrence of shared antigens between the RPC-5 and MOPC-315 tumor cells. It is concluded that the ineffectiveness of alkylating-drug treatment toward the RPC-5 tumor is not due to the inability of this tumor to induce a specific antitumor immune response, and that cross-antigenic relationship as revealed by in vitro cytotoxicity tests does not necessarily reflect cross-protection between various plasmacytomas.