Tumor regulatory T cells potently abrogate antitumor immunity.

Regulatory T cell (Treg) from mice bearing a breast tumor were elevated (tumor Treg). In vitro, whereas tumor Treg ability to inhibit tumor-primed CD4(+) T cell activity is comparable to Treg from naive mice (naive Treg), only tumor Treg suppress naive CD8(+) T cell activation and DC function. Neither tumor Treg nor naive Treg can suppress antitumor immunity at the effector phase of the immune response induced by adoptively transferred tumor-primed CD4(+) T cells. This is consistent with the observation that, in this model, neither tumor Treg nor naive Treg can inhibit effectors in vitro or in vivo. However, tumor Treg abrogate tumor-specific CD8(+) T cell responses in tumor-draining lymph nodes and antitumor immunity at the early stage of the immune response induced by adoptively transferred tumor-primed CD4(+) T cells. These data indicate that, in this model, tumor Treg potently abrogate tumor-specific CD8(+) T cell responses in tumor-draining lymph nodes, thereby suppressing antitumor immunity at the early stage of the immune response induced by adoptively transferred tumor-primed CD4(+) T cells.