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We have developed and characterized an anti-idiotype (Id) antibody, designated 6D12 (IgG1,k), which mimics a distinct and specific epitope of HER2/Neu and can be used as a surrogate antigen for HER2/Neu. Anti-Id 6D12 (Ab2) was raised against the murine mAb 4D5 (Ab1), which is the parental Ab for Herceptin (also called Trastuzumab). In this study, anti-Id 6D12 was evaluated for its ability to prevent the spontaneous development of HER2/Neu-overexpressing mammary tumors in rat neu transgenic (Tg) mice. Rat neu is 80% homologous with human HER2/Neu and the epitope targeted by 6D12 is conserved in rat neu. Immunization of 12 weeks old neu Tg mice with anti-Id 6D12 elicited antibodies which inhibited the binding of Ab1 to Ab2 and Ab1 to antigen-positive cells suggesting that these antibodies were true anti-anti-idiotypic (Ab3) in nature. Flow cytometry assays were used to directly assess the binding of the induced Ab3 (Ab1′) antibodies to HER2/Neu transfected murine cell line EL4-HER and non-transfected parental cell line EL4. Immune sera reacted significantly with EL4-HER cells and did not bind to EL4 cells. Induction of anti-HER2/Neu Ab was an indication of immune response to HER2/Neu in the otherwise tolerant host. mAb 4D5 was used as a positive control in this assay. These Ab3 antibodies elicited by 6D12 immunization inhibited the proliferation of human HER2/Neu-overexpressing breast cancer cells SK-BR-3 in vitro and lysed antigen-positive cells by antibody-dependent cell mediated cytotoxicity (ADCC). Furthermore, immunization with anti-Id 6D12 significantly delayed the spontaneous development of HER2/Neu-overexpressing mammary tumors in this model as compared to control anti-Id vaccine treated neu Tg mice. These results suggest that anti-Id 6D12 may be useful as a potential network Ag for the treatment of HER2/Neu-positive human cancer. Supported by the NIH grant RO1CA 91878.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA