Recently, many experiments have shown that the expression of the
costimulatory molecule B7-1 on
tumor cells can induce
tumor-specific immunity. These results suggest that
tumor cells modified to express costimulatory molecules can be used as a potential
tumor vaccine. For this purpose, we transduced B7-1 gene into
renal adenocarcinoma cells of spontaneous origin (Renca) in BALB/c mouse using the retroviral vector system. Our results indicated that approximately 60% of cells expressed B7-1 gene product using the retroviral vector system, and that B7-1 transduction did not affect the expression of MHC molecules on
tumor cells nor the in vitro growth rate of
tumor cells, but only in vivo tumorigenicity. As for the antitumor effect on the remote site, there were no significant differences among parental Renca, Renca lac Z and Renca B7-1 sublines, although
tumors grew a little more slowly in the mice injected with Renca B7-1 cells as a
vaccine. Even if the growth of
tumors was significantly delayed in the mice treated by Renca B7-1 as a
vaccine combined with the injection of BALB/c3T3
IL-12 near to the
tumor on the same or following day, no significant antitumor effects were observed when the Renca B7-1 cells were injected as a
vaccine compared with
cytokines near the
vaccine site. These results indicated that B7-1 gene transduction can decrease the tumorigenicity of murine
renal cell carcinoma cells, but fails to induce sufficient antitumor response when it is used as a
tumor vaccine. It is necessary to develop immunogenicity, by such means as irradiation or a combination of appropriate
cytokines, to stimulate effective
tumor immunity in a therapeutic setting.