Patients with metastatic melanoma have a very poor prognosis. In many cases, the tumor recurs after surgical excision. Therefore, it might be beneficial for cancer patients to induce an immune attack against the tumor by inserting a cytokine gene into the tumor cells. Here, 14 primary cell cultures could be established from 45 patients with malignant melanoma. Primary cell cultures were transfected via electroporation with the gene encoding for human interleukin-7 (IL-7). Transfection resulted in the production of biologically active IL-7 with an average of 850 pg/mL per 10(6) cells per 24 hours. Irradiation with 10,000 cGy, which inhibited tumor cell growth in vitro, increased the amount of released IL-7 to an average amount of 1050 pg/mL per 10(6) cells per 24 hours. No significant differences in the phenotype were observed in the IL-7-transfected cells compared with nontransfected cells. The expression of HLA class I and II, ICAM-1, and of a melanoma-associated antigen remained unaltered. Transfection with IL-7 had no significant effect on the proliferation of melanoma cells as measured in a MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay. There was no significant change in the cytokine profile after transfection or irradiation of the cells, but one cell culture expressed a high amount of IL-6 (about 2 ng/mL). IL-6 was expressed in nontransfected cells and was not altered by transfection. Interestingly, transfected cells from primary melanoma cultures possessed a higher sensitivity to immunologic effector cells compared with nontransfected cells. This was true for allogeneic as well as autologous melanoma cells. Our results show the feasibility of a gene transfer into primary human melanoma cells, different from retroviral transduction. IL-7-transfected cells might be of value in vaccination protocols for melanoma patients.