INEFFECTIVE IMMUNE ENHANCEMENT BY IL-12 IN TUMOR-BEARING MICE WHOSE IMMUNE DEPRESSION IS MEDIATED BY SUPPRESSIVE GRANULOCYTE-MACROPHAGE PROGENITOR CELLS

Lewis lung carcinoma (LLC-LN7) tumors stimulate myelopoiesis and induc e immunosuppressive granulocyte-macrophage (GM)-progenitor cells. Trea ting mice having palpable turners with IL-12 enhanced the frequency of GM-progenitors and did not diminish GM-suppressor activity. Prolifera tion of splenic T-cells of tumor-bearers to Con-A or to anti-CD3 plus IL-2 was suppressed; this was not enhanced by IL-12 treatment. Also no t stimulated was T-cell secretion of IL-2 in response to autologous tu mor, or the intratumoral T-cell content. IL-12 slightly increased sple nic IFN-gamma secretion, and increased cytotoxicity of lymph node (but not spleen) cells toward autologous tumor. In these tumor-bearing mic e that were immune depressed as a result of GM-suppressor cells, immun e modulatory effects of IL-12 were marginal and did not affect tumor s ize or metastasis.