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Tumor‐infiltrating mesenchymal stem cells: Drivers of the immunosuppressive tumor microenvironment in prostate cancer?
Author(s) -
Krueger Timothy E.,
Thorek Daniel L. J.,
Meeker Alan K.,
Isaacs John T.,
Brennen W. Nathaniel
Publication year - 2019
Publication title -
the prostate
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.295
H-Index - 123
eISSN - 1097-0045
pISSN - 0270-4137
DOI - 10.1002/pros.23738
Subject(s) - prostate cancer , mesenchymal stem cell , cancer research , tumor microenvironment , bone marrow , prostate , medicine , cancer , stromal cell , pathology , immunology , immune system
Background Prostate cancer is characterized by T‐cell exclusion, which is consistent with their poor responses to immunotherapy. In addition, T‐cells restricted to the adjacent stroma and benign areas are characterized by anergic and immunosuppressive phenotypes. In order for immunotherapies to produce robust anti‐tumor responses in prostate cancer, this exclusion barrier and immunosuppressive microenvironment must first be overcome. We have previously identified mesenchymal stem cells (MSCs) in primary and metastatic human prostate cancer tissue. Methods An Opal Multiplex immunofluorescence assay based on CD73, CD90, and CD105 staining was used to identify triple‐labeled MSCs in human prostate cancer tissue. T‐cell suppression assays and flow cytometry were used to demonstrate the immunosuppressive potential of primary MSCs expanded from human bone marrow and prostate cancer tissue from independent donors. Results Endogenous MSCs were confirmed to be present at sites of human prostate cancer. These prostate cancer‐infiltrating MSCs suppress T‐cell proliferation in a dose‐dependent manner similar to their bone marrow‐derived counterparts. Also similar to bone marrow‐derived MSCs, prostate cancer‐infiltrating MSCs upregulate expression of PD‐L1 and PD‐L2 on their cell surface in the presence of IFNγ and TNFα. Conclusion Prostate cancer‐infiltrating MSCs suppress T‐cell proliferation similar to canonical bone marrow‐derived MSCs, which have well‐documented immunosuppressive properties with numerous effects on both innate and adaptive immune system function. Thus, we hypothesize that selective depletion of MSCs infiltrating sites of prostate cancer should restore immunologic recognition and elimination of malignant cells via broad re‐activation of cytotoxic pro‐inflammatory pathways.