CD4+Foxp3- type 1 regulatory T cells in glioblastoma multiforme suppress T cell responses through multiple pathways and are regulated by tumor-associated macrophages.

CD4+Foxp3- type 1 regulatory T (Tr1) cells are potent producers of interleukin 10 (IL-10) and transforming growth factor beta (TGF-β), through which they suppress pathogenic inflammation and autoimmune responses. The role of Tr1 response in glioblastoma multiforme (GBM) is still unclear. Here, we examined the frequency, phenotype, induction mechanism, and function of Tr1 cells in GBM patients. Compared to healthy controls, GBM patients presented significantly higher frequency of Tr1 cells in peripheral blood. The Tr1 frequency was further elevated in the tumor. By surface marker expression, the Tr1 cells were enriched in the antigen-experienced effector/memory cell compartment. A minority of Tr1 cells presented IL-10+TGF-β+ double expression. Interestingly, naive CD4+CD45RA+ T cells could differentiate into IL-10- and TGF-β-expressing cells, if incubated with tumor-associated macrophages (TAMs) or with macrophages conditioned with primary glioma cells, suggesting that tumor cells and TAMs had a role in inducing Tr1 cells in GBM patients. Coculture of Tr1 cells with proinflammatory CD4+ T cells resulted in TGF-β-dependent reduction of interferon gamma (IFN-γ) and IL-10-dependent reduction of tumor necrosis factor alpha (TNF-α), while coculture of Tr1 cells with CD8+ T cells resulted in lower tumor-specific cytotoxicity. Together, these results demonstrated an upregulation of Tr1 cells in GBM with anti-inflammatory functions.