Myeloid derived suppressor cells (MDSCs) are heterogeneous population of immature cells at various stages of differentiation, characterized by the presence of CD11b and Gr1 in mice. They are major contributors of the tumor-induced immune suppression against the tumors. So far, various strategies have been introduced to overcome the endogenous MDSCs. Most of these approaches rely on the elimination of MDSCs and it is not clear whether tumor-reactive T cells may be differentiated towards phenotypes that are refractory to MDSCc. Our laboratory has previously shown that high affinity T cells derived from tumor-sensitized wild-type FVB mice and expanded ex vivo with the alternating common gamma chain cytokine formulation (initiation of culture with IL-7 + IL-15 followed by one day pulse with IL-2 and continuation of culture with IL-7 + IL-15) can successfully induce tumor regression in FVBN202 transgenic mouse model of breast carcinoma upon adoptive immunotherapy (AIT), only when combined with the depletion of endogenous MDSCs. In this study we have introduced a novel formulation of the sequential common gamma chain cytokines (initiation of culture with IL-7 + IL-15 followed by the expansion with IL-2 until 6 days) for the ex vivo expansion of the autologous and tumor-sensitized low affinity T cells derived from FVBN202 mice and further used for AIT. This novel formulation induced differentiation of tumor-reactive CD8+ T cells mainly towards effector and effector/memory phenotypes that were refractory to MDSCs in vitro and in vivo. AIT by using these T cells induced rejection of primary neu positive tumors and generated long-term memory responses against the recall tumor challenge. Importantly, these T cells also resulted in the inhibition of neu antigen negative relapsed tumor cells. Our findings in the present study provide a platform for AIT of breast cancer patients. .

Metastatic breast cancer treatment has seen few advances in recent years, yet treatment resistance continues to rise, causing disease recurrence. A pilot study was performed to determine the efficacy of ex vivo expansion and reprogramming of tumor-reactive immune cells from experimental metastatic tumor-sensitized mice. Also, phenotypic changes in tumors due to metastasis or tumor microenvironment influences were characterized. Metastatic neu+ mouse mammary carcinoma (mMMC) and its distant relapsing neu-antigen-negative variant (mANV) were investigated in FVBN202 mice. Tumor-reactive central memory CD8+ T cells and activated NK/NKT cells were successfully reprogrammed and expanded during 6-day expansion from mMMC- and/or mANV-sensitized mice, resulting in tumor-specific cytotoxicity. mMMC exhibited a flexible neu-expression pattern and acquired stem-like, tumorigenic phenotype following metastasis while mANV remained stable except decreased tumorigenicity. Myeloid-derived suppressor cell (MDSC) levels were not increased. Adoptive cellular therapy (ACT) with reprogrammed tumor-reactive immune cells may prove effective prophylaxis against metastatic or recurrent breast cancer.