Glioma-Infiltrating Myeloid Cells through Interleukin-4 Receptor-GM-CSF Promotes the Immunosuppressive Activity of

Malignant gliomas are lethal cancers in the brain and heavily infiltrated by myeloid cells. Interleukin-4 receptor-a (IL-4Ra) mediates the immunosuppressive functions of myeloid cells, and polymorphisms in the IL-4Ra gene are associated with altered glioma risk and prognosis. In this study, we sought to evaluate a hypothesized causal role for IL-4Ra and myeloid suppressor cells in glioma development. In both mouse de novo gliomas and human glioblastoma cases, IL-4Ra was upregulated on glioma-infiltrating myeloid cells but not in the periphery or in normal brain. Mice genetically deficient for IL-4Ra exhibited a slower growth of glioma associated with reduced production in the glioma microenvironment of arginase, a marker of myeloid suppressor cells, which is critical for their T-cell inhibitory function. Supporting this result, investigations using bone marrow-derived myeloid cells showed that IL-4Ra mediates IL-13–induced production of arginase. Furthermore, glioma-derived myeloid cells suppressed T-cell proliferation in an IL-4Ra–dependent manner, consistent with their identification as myeloid-derived suppressor cells (MDSC). Granulocyte macrophage colony-stimulating factor (GM-CSF) plays a central role for the induction of IL-4Ra expression on myeloid cells, and we found that GM-CSF is upregulated in both human and mouse glioma microenvironments compared with normal brain or peripheral blood samples. Together, our findings establish a GM-CSF–induced mechanism of immunosuppression in the glioma microenvironment via upregulation of IL-4Ra on MDSCs. Cancer Res; 73(21); 6413–23. 2013 AACR. Introduction Malignant gliomas represent approximately 80% of all malignant brain tumors accounting for as many as 26,000 U.S. and European deaths annually, making them a significant unmetmedical need (1). Prognosis for patients withmalignant glioma remains dismal with amedian survival of approximately 15 months for glioblastoma following surgery and chemo/ radiation therapy (2). Despite extensive research, treatment options for malignant gliomas remain limited. Although immunotherapeutic approaches have shown safety and promising preliminary activities (3), their effectiveness can be improved by overcoming the immunosuppressive mechanisms induced by these tumors (2). Myeloid cells are the most abundant hematopoietic cells in the human body and have diverse functions. Mounting evidence indicates that the tumor microenvironment alters myeloid cells, and the concept of myeloid-derived suppressor cells (MDSC) has emerged (4, 5). MDSCs represent a heterogenic population of immature myeloid cells (IMC) with an impaired ability to fully develop into macrophages, granulocytes, or dendritic cells and have highly pleiotropic abilities to suppress a variety of T-cell functions and promote tumor growth through effector molecules including arginase (4, 5). In mice, MDSCs are identified as cells that simultaneously express the two markers CD11b and Gr1 (6–8), and are subdivided into two different subsets based on their expression of the two molecules Ly6C and Ly6G (4). CD11bþLy-6G Ly6C cells have monocytic-like morphology and are termed monocytic-MDSCs (M-MDSC), whereas CD11bþLy6GþLy6Clow cells have granulocyte-like morphology and are termed granulocytic-MDSCs (G-MDSC). In patients with cancer, MDSCs are defined as cells that express the common myeloid marker CD33 but lack markers of mature myeloid cells, such as the human leukocyte antigen (HLA)-DR (9–13). Human MDSCs can be divided into at least two subsets that likely parallel those in the mouse model: the CD15þ G-MDSCs and the CD14þ MMDSCs. Interleukin-4 receptor-a (IL-4Ra) expression on Authors' Affiliations: Department of Infectious Diseases and Microbiology, University of Pittsburgh Graduate School of Public Health; Brain Tumor Program, University of Pittsburgh Cancer Institute, Hillman Cancer Center; Departments of Neurological Surgery, Surgery, and Immunology, University of PittsburghSchool ofMedicine, Pittsburgh, Pennsylvania; and Department of Pediatrics, University of Minnesota, Minneapolis, Minnesota Note: Supplementary data for this article are available at Cancer Research Online (http://cancerres.aacrjournals.org/). Corresponding Author: Hideho Okada, 1.19E Research Pavilion at Hillman Cancer Center, 5117 Centre Avenue, Pittsburgh, PA 15213. Phone: 412-623-1111; Fax: 412-623-1415; E-mail: okadah@upmc.edu doi: 10.1158/0008-5472.CAN-12-4124 2013 American Association for Cancer Research. Cancer Research www.aacrjournals. org 6413 on January 14, 2014. © 2013 American Association for Cancer Research. cancerres.aacrjournals. org Downloaded from Published OnlineFirst September 12, 2013; DOI: 10.1158/0008-5472.CAN-12-4124