Depletion of CD4(+)CD25(high) regulatory T cells from tumor infiltrating lymphocytes predominantly induces Th1 type immune response in vivo which inhibits tumor growth in adoptive immunotherapy

Adoptive cell transfer (ACT) immunotherapy administered with prior host immunosuppression significantly improved the anti-tumor efficacy in a murine model. However, bulk transfer of lymphocytes containing suppressor lymphocyte subsets, including regulatory T cells to mice bearing late-stage tumors impaired this anti-tumor effect. In this study, we investigated the enhanced antitumor efficacy by adoptive transfer of Treg-depleted autologous tumor infiltrating lymphocytes in advanced murine breast cancer. We found that, compared to bulk cell transfer, Treg-depleted cell transfer enhanced the activation and proliferation of both CD4(+) and CD8(+) T cells. Most importantly, the immune response deviated towards the Th1 response reflected by increased IFN gamma and reduced IL-4 secretion in both CD4(+) and CD8+ T cells and an enhanced granzyme B release of CTL. Furthermore, the elicited Th1 response subsequently resulted in delayed tumor growth and prolonged mice survival as well as reduced lung metastasis in tumor-bearing nude mice. These results strongly indicated that Treg-depleted autologous cell transfer greatly enhanced Th1 type immune response, consequently leading to delayed tumor growth and reduced tumor burden. Therefore, ACT immunotherapy based on ex vivo selection of tumor-reactive lymphocytes resulted in enhanced anti-tumor immunity and provides important implications for further human studies.