Gangliosides have been considered as potential targets for immunotherapy because they are overexpressed on the surface of melanoma cells. However, immunization with purified gangliosides results in a very poor immune response, usually mediated by IgM antibodies. To overcome this limitation, we immunized mice with R24, a monoclonal antibody (mAb) that recognizes the most tumor-restricted ganglioside (GD3); our goal was to obtain antiidiotype (Id) antibodies bearing the internal image of GD3. Animals produced anti-Id and anti-anti-Id antibodies. Both anti-Id and anti-anti-Id antibodies were able to inhibit mAb R24 binding to GD3. In addition, the anti-anti-Id antibodies were shown to recognize GD3 directly. Anti-Id and anti-anti-Id mAb were then selected from two fusion experiments for evaluation. The most interesting finding emerged from the characterization of the antianti-Id mAb 5.G8. It was shown to recognize two different GD3-expressing human melanoma cell lines in vitro and to mediate tumor cell cytotoxicity by complement activation and antibodydependent cellular cytotoxicity. The biological activity of the antianti-Id mAb was also tested in a mouse tumor model, in which it was shown to be a powerful growth inhibitor of melanoma cells. Thus, activity of the anti-anti-Id mAb 5.G8 matched that of the prototypic anti-GD3 mAb R24 both in vitro and in vivo. Altogether, our results indicate that the idiotype approach might produce high affinity, specific and very efficient antitumor immune responses. (Cancer Sci 2011; 102: 64-70) M elanomas and other tumors of neuroectodermal origin have a distinct profile of cell-surface ganglioside expression.(1) The relevance of these carbohydrate antigens as immune targets in cancer cells can be inferred from earlier studies that described the ability of monoclonal antibodies (mAb) raised against gangliosides to induce complement-dependent cytotoxicity (CDC) in melanoma, neuroblastoma, sarcoma and astrocytoma cell lines.(2) Generally, immunization with whole tumor cells or cell lysates induces low titer IgM antibodies to carbohydrate antigens, but the use of conjugated vaccines can produce high titers of IgM and IgG antibodies.(3) The best vaccine design involves the conjugation of the antigen to keyhole limpet hemocyanin (KLH) and the use of saponins QS-21 and GPI-0100 as adjuvants. In contrast to normal cells, transformed melanocytes abundantly express disialoganglioside 3 (GD3). R24 is a mouse mAb that specifically recognizes GD3 and mediates in vitro effector functions such as CDC and antibody-dependent cellular cytotoxicity (ADCC).(5) It also stimulates proliferation of GD3-expressing T cells derived from human peripheral blood (6) and was shown to enhance lymphocyte RNA expression of IL-4, IL-10 and IFN-c.(7) Normal melanocytes are not lysed by the R24-directed immune response due to their low GD3 expression. In contrast to the potent in vitro activity of R24, its effect in nu ⁄ nu mice bearing human melanoma grafts is much more modest; tumor inhibition was observed o...

No abstract