Human monoclonal antibodies directed against melanoma tumor-associated antigens.

To analyze the humoral immune response to melanoma, human-mouse hybridomas were generated by the fusions of regional lymph node lymphocytes of patients with the mouse myeloma cell line M5. Six stable hybridomas were cloned from six separate lymphocyte parents obtained from three patients. Ascites were obtained from nude mice after i.p. injection with cultured hybridoma cells. The monoclonal antibodies, four immunoglobulin Gs and two pentameric immunoglobulin Ms, were partially purified to remove mouse immunoglobulin and then conjugated to biotin for immunocytochemical and immunohistochemical studies. With the avidin:biotin:peroxidase complex method to detect and amplify binding by the biotin-conjugated human monoclonal antibodies, we found the six antibodies to be reactive against cytoplasmic determinants in five short-term melanoma cultures and formalin-fixed paraffin-embedded melanoma tumors from four patients. The antigenic target of the antibodies identified was not carcinoembryonic antigen. Two antibodies, 2-139-1 and 6-26-3, were studied in more detail. Each stained 25 of 25 specimens of melanomas. Little or no reactivity was detected against fixed sections of normal skin, which included tissues such as epidermis, dermis, monocytes, lymphocytes, and vascular endothelium. More striking was the absence of binding to melanocytes in the basal layer of the skin or to pigmented nevus cells. Both antibodies showed cross-reactivity against other tumors, in particular colonic and prostatic carcinomas. In the normal colon, reactivity was restricted to the surface of the columnar epithelium; no reactivity was detected against normal prostatic epithelium. Reactivity was also not observed against liver and lung. However, the epithelia of the renal tubules, pancreatic ducts, and salivary ducts were all reactive. These human monoclonal antibodies identify cytoplasmic melanoma-associated tumor antigens that appear different from the membrane antigens defined by serological approaches and by most mouse monoclonal antibodies.