Interleukin-27 Exerts Its Antitumor Effects By Promoting Differentiation Of Hematopoietic Stem Cells To M1 Macrophages

The interleukin IL27 promotes expansion and differentiation of hematopoietic stem cells into myeloid progenitor cells. Many tumor-infiltrating myeloid cells exert immunosuppressive effects, but we hypothesized that the myeloid cells induced by IL27 would have antitumor activity. In this study, we corroborated this hypothesis as investigated in two distinct mouse transplantable tumor models. Malignant mouse cells engineered to express IL27 exhibited reduced tumor growth in vivo. Correlated with this effect was a significant increase in the number of tumor-infiltrating CD11b(+) myeloid cells exhibiting a reduced immunosuppressive activity. Notably, these CD11b(+) cells were characterized by an activated M1 macrophage phenotype, on the basis of increased expression of inducible nitric oxide synthase and other M1 biomarkers. In vivo depletion of these cells by administering anti-Gr-1 eradicated the antitumor effects of IL27. When admixed with parental tumors, CD11b(+) cells inhibited tumor growth and directly killed the tumor in a nitric oxide-dependentmanner. Mechanistically, IL27 expanded Lineage(-) Sca-1(+) c-Kit(+) cells in bone marrow. Transplant experiments in Ly5.1/5.2 congenic mice revealed that IL27 directly acted on these cells and promoted their differentiation into M1 macrophages, which mobilized into tumors. Overall, our results illustrated how IL27 exerts antitumor activity by enhancing the generation of myeloid progenitor cells that can differentiate into anti-tumorigenic M1 macrophages. (C) 2017 AACR.