Studies of the Function of Naturally Occurring and Adaptive T Regulatory Cells

National Institute Of Allergy And Infectious Diseases

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Abstract

Four distinct areas were studied in this project in FY2021: 1. The transcription factor Helios is expressed in the majority of Foxp3+ Treg cells, where it is necessary for the maintenance of self-tolerance. Mice with a Foxp3-specific deficiency in Helios develop systemic immune activation with increased T follicular helper (Tfh) and T helper 1 (Th1) effector responses. Notably, mice with a CD4-specific deletion of Helios do not exhibit autoimmunity, pointing to an additional role for Helios in CD4+ T cells. In fact, Helios is expressed in a minor population of conventional CD4+ T cells and its expression is upregulated upon activation of CD4+ T cells, yet the role of Helios in these cells remains unknown. We generated TCR Tg mice with a CD4-specific Helios deletion and have shown that Helios deficient naive CD4+ T cells are fully able to differentiate into Th1, Th2 and Tfh effector cells in vivo. Helios deficient CD4+ T cells show no defect in expansion or the production of cytokines. However, Helios deficiency increased the propensity of naive T cells to differentiate into antigen-specific pTregs under inflammatory as well as tolerizing conditions and attenuated the induction of a memory response. To further characterize CD4+Foxp3Helios+ cells, Next-generation sequencing (NGS) analysis was performed. This analysis has yielded evidence for a heterogenous population that is comprised of Tfh, Tmem, iNKT and a population of cells that have Treg-like features. In vitro activation assays and qPCR have validated differentially expressed cytokines between Helios+ and Helios- CD4+ T cell populations, in agreement with the NGS data. Together, these findings suggest that Helios may play a role in stabilizing effector function. 2. Eos (lkzf4) is a member of the Ikaros family of transcription factors and is preferentially expressed in Treg cells. However, the role of Eos in Treg function is controversial. Deletion of Eos in Treg resulted in activation of CD4+Foxp3- and CD8+ T cells at the age of 3 months, cellular infiltration in non-lymphoid tissues, hyperglobulinemia, and anti-nuclear antibodies. While Tregs from Eos cKO mice displayed normal suppressive function in vitro, Eos cKO mice developed severe Experimental Autoimmune Encephalomyelitis (EAE) following immunization with myelin oligodendrocyte glycoprotein (MOG) and Eos cKO Treg were unable to suppress Inflammatory Bowel Disease (IBD). Eos cKO mice had decreased growth of the transplantable murine adenocarcinoma MC38 tumor accompanied by enhanced IFN-gamma/TNF-alpha production by CD8+ T cells in tumor draining lymph nodes. Mice with a global deficiency of Eos or a deficiency of Eos only in T cells developed autoimmunity at a much older age (12 months or 7- 8 months, respectively). Eos appears to play an essential role in multiple aspects of Treg suppressor function, but also plays an unknown role in the function of CD4+Foxp3- and CD8+ T cells and potentially in non-T cells. To facilitate the analysis of Eos function, we generated a mAb to Eos which readily detected Eos expression by intracellular staining and FACS analysis. Eos could easily be detected in 50% of freshly explanted Foxp3+ T cells. More importantly, while Eos could not be detected in resting conventional T cells, Eos was present in 100% of activated CD4+ and CD8+ T cells. This result is consistent with an important role of Eos not only in controlling Treg function, but also in controlling multiple aspects of the function of non-Treg cells. 3. While both Treg development in Helios Foxp3 cKO mice and their in vitro suppressor function are normal, the selective deletion of Helios in Tregs leads to slow, progressive systemic immune activation with a Th1 phenotype, hypergammaglobulinemia, and enhanced germinal center formation. Initially, we observed significant lymphocytic infiltrates only in the salivary gland and not in any other organs typically affected by Treg dysregulation. Strikingly, the mice developed lipodystrophy, hepatic steatosis, and insulin resistance. Further analysis revealed a significant lymphocytic infiltrate in both the inguinal and perigonadal adipose tissue, indicating autoimmune mediated destruction of the white adipose tissue (WAT). We have further shown that the lymphocytic infiltrate specific to WAT can be transferred from mice with lipodystrophy to immunodeficient mice, confirming the autoimmune nature of the lipodystrophy. Thus, Helios deficiency in Treg disrupts immune homeostasis in the adipose tissue, leading to the destruction of WAT and redirection of lipids to the liver, and ultimately causes metabolic dysfunction. This model represents the first description of an autoimmune lipodystrophy. 4. Natural Killer (NK) cells are innate lymphocytes involved in the first line of immune defense and T cell adaptive immunity against viral infection and cancer, including metastasis. While on patrol, NK cells contact other cells and recognize MHC-I Ags via stochastically expressed MHC-I specific inhibitory receptors (Ly49s in mice and KIRs in humans) that prevent NK cell activation via cytoplasmic ITIM. The binding site on MHC-Class-I for Ly49 inhibitory receptors is distinct from that for TCRs. The loss of MHC-I expression on tumor cells (missing self) abrogates inhibitory signals, resulting in NK activation. Global inhibition of the NK inhibitory receptor interactions in vivo by a pan-anti-MHC-I monoclonal antibody markedly activated IFN-gamma producing NK cells, independent of Fc receptors. NK cell-derived IFN-gamma, along with other cytokines (MCSF & FLT3L), primed APC to induce IL-12/-15/-18 cytokine cascades and enhanced levels of MHC-I and MHC-II expression that further drove the proliferation of NK cells and memory phenotype (MP) T cells. The global disruption of NK cell/MHC-I interactions significantly enhanced Th1 type signature transcription factors (Tbet & Eomes), cytokines (IFN-gamma and Granzyme B), and chemokine receptors (CXCR3) on NK and MP T cells. Administration of pan-anti-MHC-I to unmanipulated mice profoundly augmented innate and adaptive immunity against viral infection, PD1-resistant transplanted tumors, successfully restrained lung and liver metastasis, and protected the animals from tumor burden. Moreover, in vitro enhancement of human NK cell proliferation by a pan-anti-HLA Mab suggests that pan-anti-HLA could be a promising therapeutic strategy against chronic viral infection and cancer metastasis.