Activated NKT cells and NK cells render T cells resistant to myeloid-derived suppressor cells and result in an effective adoptive cellular therapy against breast cancer in the FVBN202 transgenic mouse.

Attempts to cure breast cancer by adoptive cellular therapy (ACT) have not been successful. This is primarily due to the presence of tumor-induced immune-suppressive mechanisms as well as the failure of tumor-reactive T cells to provide long-term memory responses in vivo. To address these clinically important challenges, we developed an ex vivo protocol for the expansion of tumor-reactive immune cells obtained from tumor-bearing animals prior to or after local radiation therapy. We used an Ag-free protocol that included bryostatin 1/ionomycin and sequential common γ-chain cytokines (IL-7/IL-15 + IL-2). The proposed protocol expanded tumor-reactive T cells as well as activated non-T cells, including NKT cells, NK cells, and IFN-γ-producing killer dendritic cells. Antitumor efficacy of T cells depended on the presence of non-T cells. The effector non-T cells also rendered T cells resistant to myeloid-derived suppressor cells. Radiation therapy altered phenotypic distribution and differentiation of T cells as well as their ability to generate central memory T cells. ACT by means of the expanded cells protected animals from tumor challenge and generated long-term memory responses against the tumor, provided that leukocytes were derived from tumor-bearing animals prior to radiation therapy. The ex vivo protocol was also able to expand HER-2/neu-specific T cells derived from the PBMC of a single patient with breast carcinoma. These data suggest that the proposed ACT protocol should be studied further in breast cancer patients.