IL-12 Enhances Immune Response by Modulation of Myeloid Derived Suppressor Cells in Tumor Microenvironment

Abstract

Myeloid derived suppressor cells (MDSCs) are a heterogenous population of immature cells that play a critical role in tumor associated immune suppression. In tumor conditions, the population of MDSCs increases. The main feature of these cells is their ability to suppress the T cell response in antigen specific or nonspecific manners depending on the condition of T cell activation. IL-12 can modulate MDSC in preliminary reports, so we investigated how IL-12 can affect MDSC in a tumor microenvironment. After implanting tumor based cells on syngeneic host, 4T-1/BALB/c or EL4/C57BL6 mice, MDSCs (Gr1+CD11b+) were isolated from splenocytes. Isolated MDSCs were treated with GM-CSF with or without IL-12 and analyzed based on their phenotypes and functions. Treatment of MDSC with IL-12 increased co-stimulatory molecules of CD80, CD86, OX-40L, enhancing the DC phenotype (CD11c) and maturation markers such as p-NF-κB and p-GSK3β. In addition to a change of surface markers, T-cell suppressive function of MDSC after IL-12 treatment was significantly improved compared with the control MDSC. In addition, PD-L1+F4/80+ macrophages, which show aninhibitory effect in phagocytosis, were decreased after IL-12 treatment. The changes of cell surface expression of CD80, CD86, MHC class II were also shown in vivo. Our results showed that the IL-12 can modulate MDSC into APC and recover the macrophage function. These results suggested that IL-12 plays a role in improving the tumor immune microenvironment through MDSC modulation.

Keywords: Interleukin-12; Myeloid-Derived Suppressor Cells; Tumor Microenvironment.

FIG. 1. Surface phenotypes of splenic MDSCs from tumor bearing mouse with IL-12 treatment. (A) Co-stimulatory molecules of spleen-derive MDSCs from 4T1/BALB/c tumor mouse model. Splenic MDSCs were cultured with IL-12 (10 ng/mL) and GM-CSF (10 ng/mL) for 1 day. (B) Fold changes of co-stimulatory molecules phenotype.

FIG. 2. IL-12 treated MDSCs stimulate CD8+ T cell proliferation.

FIG. 3. Modulation of MDSCs into dendritic cells after IL-12 treatment. (A) CD11c fraction in tumor bearing splenocyte was increased after IL-12 treatment. (B) Fold changes of CD11c fraction in normal and tumoral splenocytes. (C) IL-12 decrease Ly6C expression in CD11b+MDSC. (D) Dendritic cell maturation markers are increased in splenic MDSC from tumor bearing mouse after IL-12 treatment.

FIG. 4. Effect of IL-12 on the differentiation of macrophage. (A) Cytokine analysis in MDSC after IL-12 treatment. (B) Phenotypic changes of macrophage after IL-12 treatment.

FIG. 5. In vivo characteristics of surface antigen molecules after adenoviral IL-12 injection.