In FY2018 we have made progress in the following areas: 1) 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 in the tumor microenvironment remains unclear. We recently demonstrated that IFN-alpha receptor (IFNAR) signaling promotes Treg function in autoimmunity. We have dissected the functional role of IFNAR-signaling in Tregs using Treg-specific IFNAR deficient (IFNARfl/flxFoxp3YFP-Cre) mice in acute LCMV Armstrong, chronic Clone-13 viral infection, and in tumor models. In both viral infection and tumor models, IFNARfl/flxFoxp3YFP-Cre mice Tregs expressed enhanced Treg associated activation antigens. LCMV-specific CD8+ T cells and tumor infiltrating lymphocytes from IFNARfl/flxFoxp3YFP-Cre mice produced less antiviral and antitumor IFN-gamma and TNF-alpha. In the chronic viral model, the numbers of antiviral effector and memory CD8+ T cells were decreased in IFNARfl/flxFoxp3YFP-Cre mice and the effector CD4+ and CD8+ T cells exhibited a phenotype compatible with enhanced exhaustion. IFNARfl/flxFoxp3YFP-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 IFNARfl/flxFoxp3YFP-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. 2. In collaboration with the group of Shoba Amarnath at Newcastle University, we have identified a unique role of the PD-1 co-inhibitory receptor in the induction of Tregs from differentiated Th1 IFN-gamma producing T cells. CD4+ T cell differentiation into multiple T helper (Th) cell lineages is critical for optimal adaptive immune responses. We have discovered an intrinsic mechanism by which programmed death-1 receptor (PD-1) signaling imparted regulatory phenotype to Foxp3+ Th1 cells (denoted as Tbet+iTregPDL1 cells) and inducible regulatory T (iTreg) cells. Tbet+iTregPDL1 cells prevented inflammation in murine models of experimental colitis and experimental graft versus host disease (GvHD). Programmed death ligand-1 (PDL-1) binding to PD-1 imparted regulatory function to Tbet+iTregPDL1 cells and iTreg cells by specifically downregulating endolysosomal protease asparaginyl endopeptidase (AEP). AEP regulated Foxp3 stability and blocking AEP imparted regulatory function in Tbet+iTreg cells. Also, Aep deficient iTreg cells significantly inhibited GvHD and maintained Foxp3 expression. PD-1- mediated Foxp3 maintenance in Tbet+ Th1 cells occurred both in tumor infiltrating lymphocytes (TILs) and during chronic viral infection. Collectively,these studies have identified an intrinsic function for PD-1 in maintaining Foxp3 through proteolytic pathways. 3. Multiple sclerosis is an inflammatory demyelinating autoimmune disorder affecting the central nervous system whose severity is reduced using immune suppressive drugs. Therapeutic intervention with interferon-beta reduces disease exacerbations and delays relapses. The receptor for type 1 interferon, IFNAR, is present on virtually all cell types making it difficult to dissect the mechanisms involved. We generated mice with a conditional deletion (cKO) of IFNAR in Treg cells (IFNARfl/flFoxp3cre). RNA seq analysis revealed little differences between steady state Treg cells from WT and cKO mice. Yet cKO mice developed severe EAE with an earlier onset than control mice. Although Treg cells from cKO mice appeared to be more activated, the activation status and effector cytokine production of CD4+ and CD8+ T cells in the draining lymph nodes (dLN) was similar in WT and cKO mice during the priming phase, but higher in cKO CD4 T cells in the effector phase. Interestingly, we noted a substantial reduction of myeloid derived suppressor cells (MDSCs) in the dLN of cKO mice, while generation of MDSCs in bone marrow and recruitment to spleen of WT and cKO mice was comparable. CD4+ T cells from cKO mice were found to be defective in chemokine secretion suggesting that IFNAR signaling on Treg cells modulates the capacity of CD4+ T cells to secrete MDSC recruiting chemokines during the priming phase. While modulation of Treg cell number and function by MDSCs has been documented, this study is one of the first to demonstrate that Treg cells may modulate MDSC homing and raises the possibility of a novel role for Treg cells in regulating the kinetics of MDSC recruitment during inflammatory conditions.
