VACCINATION WITH ANTIIDIOTYPE ANTIBODIES MIMICKING A RENAL-CELL CARCINOMA-ASSOCIATED ANTIGEN INDUCES TUMOR-IMMUNITY

We have previously isolated and characterized 6 different internal image mouse monoclonal anti-idiotype antibodies (Ab2) directed against the paratope of mouse monoclonal antibody G250 (MAbG250, Ab1), which specifically reacts with human renal cell carcinoma (RCC). These Ab2s (NUH31, 44, 51, 71, 82 and 91) demonstrated specificity for the combining site of Ab1, and appeared to recognize 2 partly overlapping idiotopes on Ab1. In this study. we further characterize the fine specificity of the Ab2, investigate whether the immunogenicity of Ab2 could be enhanced by conjugation to a carrier and investigate the anti-tumor efficacy of Ab3 sera in mice challenged with RCC. Immunization of animals with Ab2 conjugated to keyhole limpet hemocyanin as carrier protein resulted in a 2-fold increase in antigen-specific anti-anti-idiotype antibodies (Ab3) as compared with immunization using Ab2 alone. Specific reactivity was observed with antigen-positive cell lysates, and all Ab3 sera contained immunoglobulin resembling Ab1 (Ab1'), as shown by competitive Ab1-antigen binding assays. Fine-specificity studies of Ab3 sera revealed that the Ab2s can be divided into 4 mutually exclusive groups, showing that the 6 Ab2s recognize 4 slightly different idiotopes in the Ab1 binding pocket. Treatment of RCC-challenged mice with Ab3 sera resulted in significant tumor growth inhibition and lower tumor take rates as compared with control groups. Ab3 sera obtained from NUH-91-immunized animals showed superior characteristics as compared to the other Ab3 sera: no tumors remained after 5 weeks of Ab3-NUH91 treatment. Our findings indicate that the Ab2 elicit powerful anti-tumor effects in immune-competent animals. (C) 1994 Wiley-Liss, Inc.