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Tumor Microenvironment as A “Game Changer” in Cancer Radiotherapy
Open AccessArticle

GARP as an Immune Regulatory Molecule in the Tumor Microenvironment of Glioblastoma Multiforme

Department of Dermatology, University Medical Center Mainz, 55131Mainz, Germany
Department of Neurosurgery, University Medical Center Mainz, 55131 Mainz, Germany
Translational Neurooncology Research Group, Johannes Gutenberg University, 55131 Mainz, Germany
Institute of Neuropathology, University Medical Center Mainz, 55131 Mainz, Germany
Department of Neurosurgery, SHG-Klinikum Idar-Oberstein, 55743 Idar-Oberstein, Germany
Author to whom correspondence should be addressed.
Int. J. Mol. Sci. 2019, 20(15), 3676;
Received: 9 July 2019 / Revised: 22 July 2019 / Accepted: 23 July 2019 / Published: 26 July 2019
(This article belongs to the Special Issue Tumor Microenvironment 2019)
Glycoprotein A repetition predominant (GARP), a specific surface molecule of activated regulatory T cells, has been demonstrated to significantly contribute to tolerance in humans by induction of peripheral Treg and regulatory M2-macrophages and by inhibition of (tumorantigen-specific) T effector cells. Previous work identified GARP on Treg, and also GARP on the surface of several malignant tumors, as well as in a soluble form being shedded from their surface, contributing to tumor immune escape. Preliminary results also showed GARP expression on brain metastases of malignant melanoma. On the basis of these findings, we investigated whether GARP is also expressed on primary brain tumors. We showed GARP expression on glioblastoma (GB) cell lines and primary GB tissue, as well as on low-grade glioma, suggesting an important influence on the tumor micromilieu and the regulation of immune responses also in primary cerebral tumors. This was supported by the finding that GB cells led to a reduced, in part GARP-dependent effector T cell function (reduced proliferation and reduced cytokine secretion) in coculture experiments. Interestingly, GARP was localized not only on the cell surface but also in the cytoplasmatic, as well as nuclear compartments in tumor cells. Our findings reveal that GARP, as an immunoregulatory molecule, is located on, as well as in, tumor cells of GB and low-grade glioma, inhibiting effector T cell function, and thus contributing to the immunosuppressive tumor microenvironment of primary brain tumors. As GARP is expressed on activated Treg, as well as on brain tumors, it may be an interesting target for new immunotherapeutic approaches using antibody-based strategies as this indication. View Full-Text
Keywords: glioblastoma; GARP; tumor microenvironment; immunotherapy; regulatory T cells glioblastoma; GARP; tumor microenvironment; immunotherapy; regulatory T cells
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Zimmer, N.; Kim, E.; Schupp, J.; Sprang, B.; Leukel, P.; Khafaji, F.; Ringel, F.; Sommer, C.; Tuettenberg, J.; Tuettenberg, A. GARP as an Immune Regulatory Molecule in the Tumor Microenvironment of Glioblastoma Multiforme. Int. J. Mol. Sci. 2019, 20, 3676.

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