Gregory Lee, Anthony P. Cheung, Bixia Ge, Mingang Zhu, Peter P. Li, Eric Hsu and Teng-Kai Huang
Background: RP215 monoclonal antibody (Mab) was shown to react specifically with the unique carbohydrate associated epitope located in the variable regions of cancer cell-expressed immunoglobulins known as CA215. This Mab was shown to inhibit the growth of a variety of cancer cells in vitro or in vivo. Anti-idiotype (anti-id) Mabs against RP215 were generated and characterized for future development of epitope-specific anti-cancer vaccines in humans. Results: Following successful immunization of rats with F(ab’)2 fragments of RP215, rat anti-id Mabs were established for biochemical and immunological characterization. Subsequent immunizations of mice with purified rat anti-id Mab revealed significant anti-anti-id antibody (Ab3) responses. In immunohistochemical studies, both Ab3 and RP215 reacted positively with various cancer cells lines and with comparable staining intensities. Both RP215 and Ab3 inhibited significantly the growth of cancer cells in vitro by means of TUNEL assay. To document that the RP215-specific epitope is carbohydrate-associated, the absence of RP215-epitope expressions upon culturing of cancer cells in serumfree medium was demonstrated. Experiments confirmed that the expression of RP215-specific epitope was dependent on the presence of carbohydrate precursors in culture media. Conclusion: Judging from these observations, anti-id Mabs which carry the internal image of RP215-specific carbohydrate-associated epitope can be suitable candidates for anti-cancer vaccine development in humans.