Inhibition of in vitro tumor cell growth by RP215 monoclonal antibody and antibodies raised against its anti-idiotype antibodies

RP215 monoclonal antibody (Mab) was shown to recognize carbohydrate-associated epitope(s) in the heavy chains of cancer cell-expressed immunoglobulins, designated in general as CA215 pan cancer marker. Growth inhibitions of tumor cells in vitro by RP215 Mab and antibodies against its anti-idiotype (anti-id) antibodies were investigated. Polyclonal rabbit anti-id antibodies and the corresponding rat anti-id Mabs were generated and characterized. Following immunizations in mice, antisera raised against anti-id antibodies were analyzed by typical immunoassays. It was observed that mouse anti-anti-id sera (Ab3) revealed binding affinity and specificity to CA215 that are comparable to those of RP215. Both RP215 and Ab3 were shown to induce apoptosis of cultured cancer cells in vitro by TUNEL and MTT assays. These experimental observations were consistent with that of in vivo tumor growth inhibition by RP215 in previous nude mouse experiments. Therefore, heterologous or homologous anti-id antibodies of RP215 that contain the internal image of its specific epitope in CA215 may serve as effective anti-cancer vaccines for therapeutic treatments of various cancers in humans. The relative stability of RP215-specific carbohydrate-associated epitope was compared to that of human IgG at extreme pH’s (≤2 or ≥12) or following NaIO4 treatments. The major molecular forms of CA215 were further documented with various enzyme immunoassays and found to have similar secondary structures to those of normal human immunoglobulin G.