Blocking immunosuppression
The antitumor effects of CD8+ T cells can be blocked in the tumor microenvironment, including through the suppressive function of regulatory T cells (Tregs). Standard in vitro systems fail to recapitulate the conditions that immune cells are exposed to in vivo. Budhu et al. used a three-dimensional, collagen-fibrin gel system to investigate the effects of CD8+ T cells on cocultured melanoma cells excised from mouse tumors. The antitumor activity of the CD8+ T cells was inhibited by the presence of tumor-derived Tregs, which depended on cell-cell contact or close proximity, required the cytokine TGF-β on the Treg cell surface, and resulted in the increased cell surface expression of the immune checkpoint receptor PD-1 on the CD8+ T cells. A blocking antibody against TGF-β prevented immunosuppression, suggesting a therapeutic strategy to inhibit Treg activity in tumors.
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