STAT3 and cancer: In addition, our study further demonstrated that the population of CD8+ cytotoxic T cells was significantly expended after CPA-7 treatment, in support of the recent studies that STAT3 inhibitors abrogate immunosuppressive effects in PC patient-derived MDSCs on CD8+ T cells and increase the ratio of tumor-infiltrating CD8+ T cells to regulatory T cells, resulting in CD8+ T cell dependent regression of cancer [9, 38].