Primary but not metastatic human melanomas expressing DR antigens stimulate autologous lymphocytes

Lymphocytes from melanoma patients were stimulated in mixed culture with autologous tumor cells (MLTC) in order to evaluate lymphocyte proliferation and subsequent cytotoxicity on autologous melanoma cells. It was found that melanoma cells from lymph node metastases were unable to induce autologous tumor-cytotoxic cells in 21 cases examined, in 15 of which MLTC also failed to induce lymphocyte proliferation. Patients' lymphocytes, however, were significantly stimulated by allogeneic irradiated lymphocytes and by interleukin 2. To investigate whether the lack of autologous stimulation was restricted to metastatic cells, the immune response of patients with only primary lesions of malignant melanoma was evaluated. It was found that primary melanoma cells were able to induce proliferation in 7 out of 9 (77%) patients, whereas positive cytotoxicity was obtained in 2 out of 4 patients tested. In order to see whether the presence of DR molecules was important for the stimulatory activity, melanoma cells were examined for the expression of DR antigens by indirect immunofluorescence with monoclonal antibodies. Positive autologous MLTC was found in all of six DR+ primary melanomas, whereas the two DR-tumors were unable to stimulate autologous lymphocytes. An anti-DR but not an anti-DC monoclonal antibody was able to block the proliferation of lymphocytes induced by an autologous primary melanoma. Neither MLTC nor cell-mediated killing was obtained with either DR+ or DR-metastatic melanoma. In 60% of the cases tested, however, DR+ metastatic melanoma cells were able to stimulate allogeneic lymphocytes of normal individuals. Increased expression of DR antigens was induced by in vitro treatment with human gamma-interferon in metastatic tumor cells; this caused an increase in the proliferation of allogeneic but not autologous lymphocytes. These findings indicate that primary but not metastatic DR+ melanoma cells are able to activate the proliferation and cytotoxicity of autologous peripheral blood lymphocytes, suggesting a potential role of DR antigens in regulating tumor-host relationships in melanoma patients.