Induction of endogenous cytokine-mRNA in circulating peripheral blood mononuclear cells by IL-2 administration to cancer patients.

The lymphokine IL-2 plays a central role in immune regulation. Recent clinical trials have shown that when administered systemically either alone, or in combination with lymphokine-activated killer cells, IL-2 can cause regression of metastatic tumors in some patients with a variety of otherwise refractory cancers. To evaluate the mechanism of in vivo action of IL-2, as well as the toxicity associated with its administration, we have studied the in vivo cytokine-mRNA expression of circulating PBMC in cancer patients undergoing treatment with high dose IL-2. Before IL-2 administration, we found low level or no evidence of cytokine-mRNA expression in PBMC. After IL-2 infusion, circulating PBMC showed enhanced proliferative activity and contained significant levels of mRNA for TNF-alpha and IL-6 as well as mRNA for the p55 IL-2R, Tac, but no mRNA coding for granulocyte-monocyte-CSF and TNF-beta (lymphotoxin). IL-1 beta mRNA was expressed at very low levels in circulating PBMC after IL-2 infusion. Each of these cytokine -mRNA was, however, inducible in vitro by stimulation of PBMC with IL-2 alone. The results of these in vivo studies suggest that IL-2 may be a physiologic inducer of TNF and IL-6 which, because of their pleiotropic effects, may be important endogenous signals in the body's immune response and account for some of the physiologic changes seen in patients receiving high dose IL-2.