Regulatory T cells suppress tumor-specific CD8 T cell cytotoxicity through TGF-β signals in vivo

Cancer patients can harbor significant numbers of CD8 and CD4 T cells with specificities to tumor antigens (Ags). Yet, in most cases, such T cells fail to eradicate the tumor in vivo. Here, we investigated the interference of Ag-specific CD4 + CD25 + regulatory T cells (Treg) with the tumor-specific CD8 T cell immune response in vivo , by monitoring the homing, expansion, and effector function of both subsets in draining and nondraining lymph nodes. The results show that CD8 cells expand to the same extent and produce similar levels of IFN-γ in the presence or absence of Ag-specific Treg. Nevertheless, these Treg abrogate CD8 T cell-mediated tumor rejection by specifically suppressing the cytotoxicity of…