IA-LIKE ANTIGENS ON FRESHLY EXPLANTED HUMAN-MELANOMA

Human Ia-like antigens were unexpectedly found on human melanoma cells maintained in long-term culture. Since these antigens may play a role in the biology of melanoma and in the tumor interaction with the host''s immune system, tissues surgically removed from 16 patients in different stages of the disease were tested in indirect immunofluorescence with monoclonal antibodies and operationally specific xenoantisera to framework determinants of Ia-like antigens. All samples which included primary, metastatic and recurrent lesions specifically reacted with anti Ia-like antigen antibodies. Melanoma cells can synthesize Ia-like antigens since they reappeared on cells cultured in vitro following treatment with pronase. The number of Ia-like antigen-positive cells in the melanoma lesions ranged from 15-90% and was unrelated to the presence of melanine and to the clinical stage of the disease: a low number of Ia-like antigen-bearing cells was found in primary tumors with high levels of invasivity (Clark''s staging) and in lesions from patients with massive metastatic spreading. Intradermic nevi surgically removed from 14 patients did not react with anti Ia-like antigen xenoantibodies. If these results are confirmed with a large number of lesions then testing of tumor biopsies for Ia-like antigens may aid to solve controversial diagnosis of melanoma.