Gene therapy for cancer is being tested in clinical trials using tumor-infiltrating lymphocytes (TIL) or tumor cells modified by the insertion of genes coding for interleukin 2 or tumor necrosis factor alpha. In the present study, we investigated the feasibility of transducing human tumor cells with genes coding for gamma-interferon (IFN gamma) or alpha-interferon (IFN alpha), which are two other cytokines that can enhance host antitumor immune responses. Tumor cells from 12 melanoma and 2 renal cell carcinoma patients were transduced with retroviral vectors containing the gene for IFN gamma. Northern blot analysis showed IFN gamma transcripts only in the IFN gamma gene-transduced cells. In both IFN gamma-secreting and non-secreting tumor lines, the cell surface expression of HLA class I and class II molecules increased following transduction. However, the magnitude of the increase in HLA expression appeared to be greater in tumor lines secreting IFN gamma. Two melanoma cell lines were successfully transduced with an IFN alpha retroviral vector. Melanoma cells transduced with the IFN alpha gene contained IFN alpha RNA transcripts and secreted large amounts of IFN alpha. In contrast to cells transduced with the IFN gamma gene, the expression of HLA class II molecules was not increased in the IFN alpha gene-transduced cells. Finally, we tested the ability of HLA.DR+ melanoma cells, which had been transduced with the IFN gamma gene, to stimulate specific cytokine release by autologous CD4+ TIL. Specific secretion of cytokine by TIL occurred when the TIL and IFN gamma gene-transduced tumor cells were cultured together but not when TIL were cultured alone or with control nontransduced tumor cells. These results suggest that molecules newly expressed on the transduced cells promoted antigen presentation and T-cell responses against the transduced tumor cells. The insertion of the IFN gamma gene into melanoma cells may be useful either for active immunization against melanoma or for the generation of TIL to be used in adoptive immunotherapy.