Interleukin-Gene-Transduced Human Melanoma Cells Efficiently Stimulate MHC-Unrestricted and MHC-Restricted Autologous Lymphocytes

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Abstract
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 105 cells per 24 hr over 3 and 2 months by the Mel4932/IL-2 and the MelB6/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. Interleukin-2 (IL-2) production by tumor cells may confer immunogenicity, and such cells can be used as vaccines in cancer patients. Therefore, retroviral-mediated gene transfer was utilized for transduction of the IL-2 gene in clonal and bulk human melanoma lines that express a melanoma antigen (Melan-A) recognized by T cells. No significant differences in the expression of molecules (e.g., HLA, ICAMl) that are involved in the immunogenicity of tumor cells, including the T cell-recognized antigen, were observed between transduced and nontransduced lines. However, IL-2 gene-transduced melanoma cells acquired an in vitro stimulatory activity of major histocompatibility complex (MHC)-restricted and -unrestricted autologous lymphocytes. These observations underline the potential of these IL-2-transduced cells in human gene therapy of melanoma patients.