COMPARISON OF HUMORAL IMMUNE-RESPONSES AND TUMOR-IMMUNITY IN MICE IMMUNIZED WITH RECOMBINANT SV40 LARGE TUMOR-ANTIGEN AND A MONOCLONAL ANTIIDIOTYPE

We compared the humoral immune responses induced in BALB/c mice by imm unization with recombinant SV40 large tumor antigen (T-ag) with those induced by a monoclonal anti-idiotype (anti-Id), designated 58D, that is specific for SV40 T-ag-induced Id network components. We also chall enged immunized mice with a lethal dose of SV40-transformed cells to a ssess in vivo tumor immunity. Two biweekly immunizations with either S V40 T-ag or anti-Id 58D induced humoral responses that recognized both SV40 T-ag and anti-Id 58D. Four biweekly immunizations with SV40 T-ag increased the antigen-specific antibody titers and decreased the resp onse to anti-Id 58D, while four biweekly immunizations of anti-Id 58D increased antibody titers to both itself and SV40 T-ag. Comparison of specific T-ag epitope and idiotope specificities indicated that SV40 T -ag and anti-Id 58D immunization generated responses that recognized a similar epitope on SV40 T-ag and expressed a shared idiotope recogniz ed by anti-Id 58D. SV40 T-ag immunized mice challenged with a lethal d ose of SV40-transformed cells were completely protected and no tumors were observed. This is despite the fact that little or no SV40 T-ag-sp ecific cytotoxic T-lymphocyte activity was detectable. In contrast, on ly 3 of 10 mice immunized with anti-Id 58D were protected from a letha l challenge. These results indicate that, although monoclonal anti-Id immunization can induce responses that recognize similar SV40 T-ag epi topes and express shared idiotopes associated with antibodies to SV40 T-ag, the recombinant antigen itself induces superior in vivo tumor im munity.