Interleukin-10 (IL-10) exerts both immunosuppressive and immunostimulatory effects. While the immunosuppressive effects are widely known, it has only been recently reported that pegylated recombinant human IL-10 (PEG-rHuIL-10) elicits potent interferon-γ (IFN-γ) and CD8 T-cell-dependent antitumor effects in murine tumor models. In this study, we show that PEG-rHuIL-10 exerts immune inhibitory effects on human peripheral blood mononuclear cell (PBMC) bulk cultures and stimulatory effects in CD8 T cells within the same culture. Also, in isolated CD8 T cells, PEG-rHuIL-10 potentiates prototypic Tc1 cytokine IFN-γ expression and induces perforin and granzyme B secretion. IFN-γ and granzyme B secretion is dependent on T-cell receptor ligation and is therefore not indiscriminately released by PEG-rHuIL-10 treatment. STAT3, NF-κB, AP1, and MEK inhibition blocks IFN-γ potentiation, while perforin induction is impeded by AP1 inhibition, and granzyme B induction is blocked by both AP1 and MEK inhibition. These results extend previous pegylated IL-10 preclinical findings to human CD8 T cells and implicate a strong degree of translation for pegylated IL-10 use in cancer therapy.