Anti-CD47 Treatment Stimulates Phagocytosis of Glioblastoma by M1 and M2 Polarized Macrophages and Promotes M1 Polarized Macrophages In Vivo.

Michael Zhang,Irving Weissman,Siddhartha S Mitra,Chelsea Y Xu,Pia Sommerkamp,Suzana A Kahn,Melissa N Mccracken,Sharareh Gholamin,Chase Richard,Gregor Hutter,Jie Liu,Matthew Kenneth Schoen,Samuel H Cheshier,Tej D Azad,Ravi Majeti,Achal S Achrol

doi:10.1371/journal.pone.0153550

Michael Zhang, Irving Weissman + Show 14 more

Open Access

https://doi.org/10.1371/journal.pone.0153550

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Journal: PloS one	Publication Date: Apr 19, 2016
Citations: 233	License type: CC BY 4.0

Affiliation: Stanford University, Lucile Packard Children's Hospital

Abstract

Tumor-associated macrophages (TAMs) represent an important cellular subset within the glioblastoma (WHO grade IV) microenvironment and are a potential therapeutic target. TAMs display a continuum of different polarization states between antitumorigenic M1 and protumorigenic M2 phenotypes, with a lower M1/M2 ratio correlating with worse prognosis. Here, we investigated the effect of macrophage polarization on anti-CD47 antibody-mediated phagocytosis of human glioblastoma cells in vitro, as well as the effect of anti-CD47 on the distribution of M1 versus M2 macrophages within human glioblastoma cells grown in mouse xenografts. Bone marrow-derived mouse macrophages and peripheral blood-derived human macrophages were polarized in vitro toward M1 or M2 phenotypes and verified by flow cytometry. Primary human glioblastoma cell lines were offered as targets to mouse and human M1 or M2 polarized macrophages in vitro. The addition of an anti-CD47 monoclonal antibody led to enhanced tumor-cell phagocytosis by mouse and human M1 and M2 macrophages. In both cases, the anti-CD47-induced phagocytosis by M1 was more prominent than that for M2. Dissected tumors from human glioblastoma xenografted within NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ mice and treated with anti-CD47 showed a significant increase of M1 macrophages within the tumor. These data show that anti-CD47 treatment leads to enhanced tumor cell phagocytosis by both M1 and M2 macrophage subtypes with a higher phagocytosis rate by M1 macrophages. Furthermore, these data demonstrate that anti-CD47 treatment alone can shift the phenotype of macrophages toward the M1 subtype in vivo.

Highlights

Glioblastoma (GBM, WHO grade IV) is the most aggressive and common malignant primary brain tumor in adults
We show that M1 macrophages display a larger phagocytic response towards GBM than M2 macrophages upon tumor cell opsonization and/or CD47-SIRPα disruption in vitro
This was observed using both mouse and human macrophages, the phagocytic response by both species after anti-CD47 treatment varied by the targeted tumor cell line and the individual macrophage batch used per experiment

Summary

Introduction

Glioblastoma (GBM, WHO grade IV) is the most aggressive and common malignant primary brain tumor in adults. Novel therapeutics remain elusive despite an improved understanding of the GBM microenvironment. Macrophages have demonstrated promising anti-tumor potential given their inherent ability to phagocytose damaged cells [4]. The human body’s natural immune response is thought to have the means to selectively and effectively target GBM, and the development of immunotherapies against GBM using dendritic cells, T cells, or natural killer cells are currently underway [5,6,7]. Macrophages and microglia (tumor-associated macrophages/microglia, TAMs), which can comprise up to 30% of the bulk of tumors, are the dominant immune cells within many malignancies [8]. TAMs are an intriguing immune cell target for treatment in malignant gliomas

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