Human high molecular weight-melanoma associated antigen mimicry by an anti-idiotypic antibody : characterization of the immunogenicity and the immune response to the mouse monoclonal antibody Imel-1

The mouse anti-idiotype (anti-id) monoclonal antibody (mAb) IMel-1 recognizes an idiotope in the antigen combining site of the immunizing anti-human high molecular weight melanoma-associated antigen (HMW-MAA) mAb 225.28. The mAb IMel-1 is able to induce an immune response against self cross-reacting HMW-MAA in rabbits that express HMW-MAA in normal tissues. Most of the rabbit anti-anti-id antibodies recognize a spatially distant determinant(s) from that defined by anti-HMW-MAA mAb 225.28. The immunogenicity of mAb IMel-1 is enhanced by its administration with the muramyl dipeptide-derived adjuvant. Anti-HMW-MAA antibodies were not detected in sera from rabbits immunized with HMW-MAA bearing cultured human melanoma cells. The differential immunogenicity of mAb IMel-1 and cell membrane bound HMW-MAA may account for the ability of anti-id mAb to induce anti-HMW-MAA immunity in patients who have not mounted such a response to HMW-MAA present in their lesions. Rabbit anti-HMW-MAA antibodies induced by anti-id mAb IMel-1 inhibited interactions of melanoma cells with elements of extracellular matrix. This may represent an additional mechanism by which anti-HMW-MAA immunity may affect the biology of melanoma cells in patients with melanoma immunized with anti-id mAb IMel-1.