Microenvironment and Immunology miR-124 Inhibits STAT3 Signaling to Enhance T Cell– Mediated Immune Clearance of Glioma

miRNAs (miR) have been shown to modulate critical gene transcripts involved in tumorigenesis, but their role in tumor-mediated immunosuppression is largely unknown. On the basis of miRNA gene expression in gliomas using tissue microarrays, in situ hybridization, and molecular modeling, miR-124 was identified as a lead candidate for modulating STAT3 signaling, a key pathway mediating immunosuppression in the tumor microenvironment. miR-124 is absent in all grades and pathologic types of gliomas. Upon upregulating miR124 in glioma cancer stem cells (gCSC), the STAT3 pathway was inhibited, and miR-124 reversed gCSC-mediated immunosuppression of T-cell proliferation and induction of forkhead box P3 (Foxp3)þ regulatory T cells (Treg). Treatment of T cells from immunosuppressed glioblastoma patients with miR-124 induced marked effector response including upregulation of interleukin (IL)-2, IFN-g , andTNF-a. Both systemic administration ofmiR-124 or adoptivemiR-124–transfected T-cell transfers exerted potent anti-glioma therapeutic effects in clonotypic and genetically engineered murine models of glioblastoma and enhanced effector responses in the local tumor microenvironment. These therapeutic effects were ablated in both CD4þand CD8þ-depleted mice and nude mouse systems, indicating that the therapeutic effect of miR-124 depends on the presence of a T-cell–mediated antitumor immune response. Our findings highlight the potential application of miR-124 as a novel immunotherapeutic agent for neoplasms and serve as a model for identifying miRNAs that can be exploited as immunotherapeutics. Cancer Res; 73(13); 3913–26. 2013 AACR.