Type I interferon signaling attenuates regulatory T cell function in viral infection and in the tumor microenvironment.

Regulatory T cells (Tregs) play a cardinal role in the immune system by suppressing detrimental autoimmune responses, but their role in acute, chronic infectious diseases and tumor microenvironment remains unclear. We recently demonstrated that IFN-alpha/beta receptor (IFNAR) signaling promotes Treg function in autoimmunity. Here we dissected the functional role of IFNAR-signaling in Tregs using Treg-specific IFNAR deficient (IFNAR(fl/fl)xFoxp3(YFP-Cre)) mice in acute LCMV Armstrong, chronic Clone-13 viral infection, and in tumor models. In both viral infection and tumor models, IFNAR(fl/fl)xFoxp3(YFP-Cre) mice Tregs expressed enhanced Treg associated activation antigens. LCMV-specific CD8(+) T cells and tumor infiltrating lymphocytes from IFNAR(fl/fl)xFoxp3(YFP-Cre) mice produced less antiviral and antitumor IFN-gamma and TNF-alpha. In chronic viral model, the numbers of antiviral effector and memory CD8(+) T cells were decreased in IFNAR(fl/fl)xFoxp3(YFP-Cre) mice and the effector CD4(+) and CD8(+) T cells exhibited a phenotype compatible with enhanced exhaustion. IFNAR(fl/fl)xFoxp3(YFP-Cre) mice cleared Armstrong infection normally, but had higher viral titers in sera, kidneys and lungs during chronic infection, and higher tumor burden than the WT controls. The enhanced activated phenotype was evident through transcriptome analysis of IFNAR(fl/fl)xFoxp3(YFP-Cre) mice Tregs during infection demonstrated differential expression of a unique gene signature characterized by elevated levels of genes involved in suppression and decreased levels of genes mediating apoptosis. Thus, IFN signaling in Tregs is beneficial to host resulting in a more effective antiviral response and augmented antitumor immunity.