IMMUNOHISTOLOGICAL REACTION-MECHANISM OF ANTI-MONOSIALOGANGLIOSIDE MONOCLONAL-ANTIBODY, MAB-202, SHOWING PREDOMINANT CYTOTOXICITY FOR MALIGNANT-MELANOMA

Mouse monoclonal IgM antibody (MAb 202) can cause melanoma cell necros is in vivo. We analysed its immune mechanism in three melanoma patient s to whom MAb 202 was administered. After the MAb 202 administration, histopathological analysis showed necrosis of melanoma cells expressin g only GM3 in two patients. Another patient carrying both GM3 and GD3 showed infiltration of lymphocytes within the tumor nest but no tumor cells or nest necrosis. Immunohistological examination using anti-mous e IgM antibody revealed MAb, 202 bound on the surface of melanoma cell s in two patients but not in the third (positive for both GM3 and GD3) . In vitro, MAb, 202 reacted with the melanoma cells of the same two p atients, but not with any other tissues of these individuals. We found no reaction of MAb 202 to non-melanoma cells including normal melanoc ytes and glia cells. Our trials suggest, 1) MAb 202 reacts directly to monosialogangliosides on the melanoma cell surface and then leads to the cytotoxicity reaction, or 2) MAb 202 induces lymphocyte infiltrati on and possibly then promotes the secretion of some cytokines.