We and others have previously demonstrated that IL-4-dependent Tc2 are inferior to Tc1 effector CD8+ T cells in regulating tumor progression in vivo. This functional disparity relates, in part, to the comparatively poor ability of Tc2 to migrate into diseased tissues. We now show that IL-4 treatment of committed Tc1 cells promotes the selective loss in expression of Very-Late Antigen (VLA)-4, without impacting the Tc1 cytokine production profile, cytotoxic activity, or expression of alternate cell surface markers. Down-regulation of VLA-4 expression on Tc1 cells was unique to treatment with IL-4 (i.e. Tc1IL-4), and did not occur in the presence of the Type 2 cytokine IL-13 or the regulatory cytokines IL-10 or TGF-β. Notably, the inhibitory effects of IL-4 on Tc1 expression of VLA-4 could be blocked by the presence of IL-12, but not IFN-γ. Predictably, Tc1IL-4 (but not Tc1 control) cells adhere poorly to plate-bound VCAM-1-Fc fusion protein and fail to be co-stimulated by VCAM-1 in vitro. They were also markedly impaired in their ability to traffic into intracranial melanoma lesions after adoptive transfer, yielding inferior therapeutic benefit to tumor-bearing mice. These results suggest a novel suppressive mechanism for IL-4 that limits Tc1 efficacy via preventing their recruitment into tumors. (200 words)
