INCREASING INFILTRATION AND ACTIVATION OF CD8-INFILTRATING LYMPHOCYTES AFTER ELIMINATING IMMUNE SUPPRESSIVE GRANULOCYTE-MACROPHAGE PROGENITOR CELLS WITH LOW-DOSES OF INTERFERON GAMMA-PLUS TUMOR-NECROSIS-FACTOR-ALPHA( TUMOR)

By secreting granulocyte/macrophage colony-stimulating factor (GM-CSF) , metastatic Lewis lung carcinoma (LLC-LN7) tumors induce the appearan ce of myelopoiesis-associated immune-suppressor cells that resemble gr anulocytic-macrophage (GM) progenitor cells. The presence of these GM- suppressor cells in mice bearing LLC-LN7 tumors was associated with a reduced capacity of splenic T cells to proliferate in response to inte rleukin-2 (IL-2). Administration of low doses of 100 U interferon gamm a (IFNgamma) plus 10 U tumor necrosis factor alpha (TNFalpha) to the t umor bearers, a combination treatment that we previously showed to dim inish the presence of GM-suppressor cells synergistically, restored pr oliferative responsiveness of the splenic T cells to IL-2. These LLC-L N7-bearing mice were also examined for whether cells that phenotypical ly resemble GM-progenitor cells (ER-MP12+ cells) infiltrate the tumor mass. ER-MP12+ cells composed approximately 10% of the cells isolated from dissociated tumors of mice that had been treated with placebo or with either IFNgamma or TNFalpha alone, but IFNgamma /TNFalpha therapy markedly reduced the number of tumor-infiltrating ER-MP12+ suppressor cells. The IFNgamma/TNFalpha treatment to eliminate GM-suppressor cel ls and restore T cell responsiveness to IL-2 was next coupled with low dose IL-2 therapy (100 U twice daily). Addition of IL-2 to the treatm ent regimen did not significantly influence the effectiveness of the I FNgamma/TNFalpha treatment in eliminating GM-suppressor cells from the LLC-LN7 tumor mass. However, inclusion of IL-2 with the IFNgamma/TNFa lpha treatment regimen enhanced the CD8+, but not the CD4+, cell conte nt within the tumor, and diminished the number of metastatic lung nodu les within the mice.When these tumors were excised, dissociated, and b ulk-cultured with a low dose of IL-2, an increased level of cytotoxic T lymphocyte (CTL) activity was generated in the TIL cultures from mic e that had received IFNgamma/TNFalpha plus IL-2 treatments. A lesser b ut detectable level of CTL activity was generated in TIL cultures from mice that were treated with only IFNgamma/TNFalpha, while no CTL acti vity was generated in tumor cultures from mice receiving only placebo or low-dose IL-2. These results suggest the effectiveness of IFNgamma plus TNFalpha therapy in restoring IL-2 responsiveness in mice bearing GM-suppressor cell-inducing tumors and at enhancing both the intratum oral CD8+ cell content and the generation of CTL activity in bulk cult ures of these tumors.