Two human melanoma lines were transduced by a retroviral vector with the gene of the human interleukin-2 (IL-2) and characterized for their immunological properties in comparison with the parental lines. Transduction resulted in the production of biologically active IL-2 in the average amounts of 2,282 and 2,336 pg/ml per 10(5) cells per 24 hr over 3 and 2 months by the Me14932/IL-2 and the Me1B6/IL-2 lines, respectively. Melanoma-transduced cells lost their tumorigenicity in nude mice. No major changes in the phenotype were observed in IL-2 gene-transduced lines. In fact, more than 90% of cells expressed class I and II(DR) HLA, adhesion molecules, integrins, and melanoma-associated antigens. Irradiation with 100-400 Gy, while inhibiting tumor cell growth in vitro, allowed the release of IL-2 by the transduced cells for at least 5 weeks. The two melanoma lines also maintained susceptibility to lysis by lymphokine-activated killer (LAK) cells and by a HLA-A2-restricted melanoma-specific cytotoxic T lymphocyte (CTL) clone recognizing the melanoma antigen (Melan-A). In a limiting dilution assay, transduced, but not parental melanoma lines unless added with an amount of IL-2 comparable to that released by the transduced cells, were able to expand both nonspecific and melanoma-specific CTL precursors from autologous peripheral blood lymphocytes (PBL). In mixed lymphocytes-tumor cultures, IL-2 gene-transduced melanoma cells stimulated the expansion of major histocompatibility complex (MHC)-unrestricted effectors from autologous PBL, and of CD3+ CD8+ MHC-restricted CTL from tumor-invaded lymph nodes. These results indicate that IL-2 gene transduction does not alter significantly the expression of the immunologically relevant molecules of human melanoma lines while increasing their ability to stimulate both specific and nonspecific lymphocyte responses. These lines will be of value in the vaccination of melanoma patients.