Delicate balance among three types of T cells in concurrent regulation of tumor immunity

摘要

The nature of the regulatory cell types that dominate in any given tumor is not understood at present. Here we addressed this question for Tregs and type II NKT cells in syngeneic models of colorectal and renal cancer. In mice with both type I and type II NKT cells, or in mice with neither type of NKT cell, Treg depletion was sufficient to protect against tumor outgrowth. Surprisingly, in mice lacking only type I NKT cells, Treg blockade was insufficient for protection. Thus, we hypothesized that type II NKT cells may be neutralized by type I NKT cells, leaving Treg cells as the primary suppressor, whereas in mice lacking type I NKT cells, unopposed type II NKT cells could suppress tumor immunity even when Tregs were blocked. We confirmed this hypothesis in three ways by reconstituting type I NKT cells as well as selectively blocking or activating type II NKT cells with antibody or the agonist sulfatide, respectively. In this manner, we demonstrated that blockade of both type II NKT cells and Tregs is necessary to abrogate suppression of tumor immunity, but a third cell, the type I NKT cell, determines the balance between these regulatory mechanisms. As cancer patients often have deficient type I NKT cell function, managing this delicate balance among three T cell subsets may be critical for the success of immunotherapy of human cancer.