The accumulation of myeloid suppressor cells (MSCs) is associated with immune suppression in tumor-bearing mice and in cancer patients. The suppressive activity of MSC correlates with the expression of the myeloid markers Gr-1, CD115 (macrophage colony-stimulating factor receptor), and F4/80. Gr-1 +CD115+ MSCs, in addition to being able to suppress T-cell proliferation in vitro, can induce the development of Foxp3+ T regulatory cells (Treg) in vivo, which are anergic and suppressive. Furthermore, the secretion of interleukin (IL)-10 and transforming growth factor-β by Gr-1+CD115+ MSCs was induced and enhanced, respectively, on IFN-γ stimulation. The development of Treg requires antigen-associated activation of tumor-specific T cells, depends on the presence of IFN-γ and IL-10, and is independent of the nitric oxide-mediated suppressive mechanism by MSC. Our data provide evidence that Gr-1+CD115+ MSC can mediate the development of Treg in tumor-bearing mice and show a novel immune suppressive mechanism by which MSCs can suppress antitumor responses.
ASJC Scopus subject areas
- Cancer Research