Modes of binding and internalization of monoclonal antibodies to human melanoma cell lines

The process of monoclonal antibody (MAb) binding to tumor cells is greatly influenced by the biology of the respective antigen. This was concluded from an analysis of binding and release of MAbs and MAb fragments to melanoma cells at different concentration levels and different temperatures. With an antigen known to be stably expressed at the cell surface (i.e., Mr 97,000 protein) rapid binding of MAbs was observed at both 0 degrees C and 37 degrees C, and this was reversed by treatment with isoosmolar acid buffer. With another group of antigens, MAb binding increased continuously up to considerable levels at 37 degrees C, but not at 0 degrees C. Concomitantly, the portion of radioactive MAb not desorbable by acid buffer treatment increased, pointing to temperature-dependent internalization. With still another group of (glycolipid) antigens, the highest MAb binding was obtained with fixed cells at 0 degrees C. In this situation MAb release was particularly rapid, thus pointing to a shedding process.