Modulation of renal carcinoma cells in vitro:: Comparison after transduction with retroviral vector containing a human IFN-γ gene versus incubation with soluble IFN-γ

Transduction of renal cell carcinoma (RCC) cells in vitro with a gene for human interferon-gamma (IFN-gamma) results in enhanced expression of key molecules needed for immune recognition, In this study, we investigated the ability of soluble IFN-gamma protein to enhance expression of these key molecules. RCC cells were incubated with and without IFN-gamma, then analyzed by flow cytometry for the percent positive and mean intensity fluorescence (MIF), a measurement of mean antigen density, of HLA-I, HLA-II, ICAM-1, and tumor antigens (URO-2, URO-3, and URO-4), Results were compared to those seen for RCC cells transduced by IFN-gamma, The ability of cytotoxic T lymphocytes (CTL) to lyse RCC targets was measured using a standard [Cr-51]lytic assay. Control cells were 99% (MIF 751) and 98% (MIF 315) positive for HLA-I and ICAM-1, respectively, with 2% (MIF 8) positive for HLA-II, Incubation with IFN-gamma protein resulted in 98% positive HLA-I (MIF 2288), 98% positive ICAM-1 (MIF 1132), and 95% positive HLA-II (MIF 287), The results for the cells incubated with IFN-gamma protein were similar to those for the transduced line. Importantly, the enhanced expression was maintained for several days after irradiation and cryopreservation, Expression of the URO tumor markers was not affected. Protein-treated RCC targets showed superior CTL lysis compared with untreated cells. Our results show that IFN-gamma protein incubation in vitro enhances expression of important immune recognition molecules to levels expressed by transduced cells. Increased expression may enhance tumor recognition by the host's immune system, as in the case of tumor cell vaccines. There may be no advantage to IFN-gamma transduction over in vitro incubation with IFN-gamma protein.