The TYK2-P1104A Autoimmune Protective Variant Limits Coordinate Signals Required to Generate Specialized T Cell Subsets

TYK2 is a JAK family member that functions downstream of multiple cytokine receptors. Genome wide association studies have linked a SNP (rs34536443) within TYK2 encoding a Proline to Alanine substitution at amino acid 1104, to protection from multiple autoimmune diseases including systemic lupus erythematosus (SLE) and multiple sclerosis (MS). The protective role of this SNP in autoimmune pathogenesis, however, remains incompletely understood. Here we found that T follicular helper (Tfh) cells, switched memory B cells, and IFNAR signaling were decreased in healthy individuals that expressed the protective variant TYK2A1104 (TYK2P). To study this variant in vivo, we developed a knock-in murine model of this allele. Murine Tyk2P expressing T cells homozygous for the protective allele, but not cells heterozygous for this change, manifest decreased IL-12 receptor signaling, important for Tfh lineage commitment. Further, homozygous Tyk2P T cells exhibited diminished in vitro Th1 skewing. Surprisingly, despite these signaling changes, in vivo formation of Tfh and GC B cells was unaffected in two models of T cell dependent immune responses and in two alternative SLE models. TYK2 is also activated downstream of IL-23 receptor engagement. Here, we found that Tyk2P expressing T cells had reduced IL-23 dependent signaling as well as a diminished ability to skew toward Th17 in vitro. Consistent with these findings, homozygous, but not heterozygous, Tyk2P mice were fully protected in a murine model of MS. Homozygous Tyk2P mice had fewer infiltrating CD4+ T cells within the CNS. Most strikingly, homozygous mice had a decreased proportion of IL-17+/IFNγ+, double positive, pathogenic CD4+ T cells in both the draining lymph nodes (LN) and CNS. Thus, in an autoimmune model, such as EAE, impacted by both altered Th1 and Th17 signaling, the Tyk2P allele can effectively shield animals from disease. Taken together, our findings suggest that TYK2P diminishes IL-12, IL-23, and IFN I signaling and that its protective effect is most likely manifest in the setting of autoimmune triggers that concurrently dysregulate at least two of these important signaling cascades

An innate-like role of memory T cells in HSV-2 immunity

Thesis (Ph.D.)--University of Washington, 2022Mucosal infections pose a significant global health burden and remain a top cause of mortality worldwide. Herpes Simplex Virus type-2 (HSV-2) infection is one of the most prevalent sexually transmitted infections, yet no vaccine is currently available. An understanding of the cellular composition of tissue-resident immune cells at the primary site of infection is essential for effective vaccine design for targeted immune response. Antigen-specific tissue-resident memory T cells or TRMs are critical to maintaining barrier immunity. TRMs are non-circulating memory CD8 T cells which remain poised at the barrier sites and possess an increased cytotoxic potential to antigen-reencounter, can proliferate in-situ. We previously observed that systemic immunization with an HSV glycoprotein B (gB) epitope activates mucosal CD8 TRM and confers partial protection against HSV-2 challenge. However, recent studies reveal that the sensing and alarming function of CD8 TRMs is not restricted to cognate antigen interaction, but CD8 TRM can mediate protection against antigenically unrelated pathogens, termed “bystander activation.” Previous studies in the context of systemic infection suggest that memory CD8 T cells may also provide innate-like protection against antigenically unrelated pathogens independent of TCR engagement. Whether "bystander T cell activation" is also an important defense mechanism in the mucosa is poorly understood. In chapter 2, we investigated if innate-like memory CD8 T cells could protect against a model mucosal virus infection, genital HSV-2. We found that immunization with an irrelevant antigen delayed disease progression from a lethal HSV-2 challenge, suggesting that memory CD8 T cells may mediate protection despite the lack of antigen-specificity. Upon HSV-2 infection, we observed an early infiltration, rather than substantial local proliferation of antigen-non-specific CD8 T cells, which became bystander-activated upon entering the vaginal mucosa from circulation. Further, local cytokine cues within the tissue microenvironment after infection were sufficient for bystander activation of mucosal tissue memory CD8 T cells from mice and humans. Finally, we show that bystander-activated CD8 T cells are sufficient to delay disease progression and reduce viral burden after HSV-2 infection. Altogether, our findings suggest that local bystander activation of infiltrating CD8 memory T cells contributes a fast and effective innate-like response in mucosal tissue. Consistent antigen exposure in a systemic chronic infection such as LCMV leads to T cell exhaustion; however, whether episodic mucosal localized infection results in T cell exhaustion has not been well studied. Detailed analysis of HSV-infected human tissue reveals that TRMs limit the duration and severity of HSV-2 shedding episodes. Since CD8 TRMs are subjected to recurrent antigen exposure due to the episodic nature of HSV-2 infection, it is important to assess the cellular kinetics and functionality of the HSV-specific and non-specific population within the genital mucosa upon episodic infection. We investigated the T cell phenotype and function within HSV-2 lesion in HSV-2 positive patients and within the genital mucosa in HSV infected mice at the acute phase, effector phase and the lesion resolution phase in chapter 3. Our findings indicate that T cells maintain their functionality in response to recurrent antigen exposure rather than becoming functionally exhausted

DOCK8 regulates fitness and function of regulatory T cells through modulation of IL-2 signaling

Foxp3+ regulatory T (Treg) cells possess potent immunosuppressive activity, which is critical for maintaining immune homeostasis and self-tolerance. Defects in Treg cell development or function result in inadvertent immune activation and autoimmunity. Despite recent advances in Treg cell biology, we still do not completely understand the molecular and cellular mechanisms governing the development and suppressive function of these cells. Here, we have demonstrated an essential role of the Dedicator of cytokinesis 8 (DOCK8), guanine nucleotide exchange factors required for cytoskeleton rearrangement, cell migration and immune cell survival, in controlling Treg cell fitness and their function. Treg cell-specific DOCK8-deletion led to spontaneous multi-organ inflammation in mice due to uncontrolled T cell activation and production of pro-inflammatory cytokines. In addition, we show that DOCK8-deficient Treg cells are defective in competitive fitness and in vivo suppressive function. Furthermore, DOCK8 controls IL-2 signaling, crucial for maintenance and competitive fitness of Treg cells, via a STAT5-dependent manner. Our study provides novel insights into the essential function of DOCK8 in Treg cells and immune regulation, and explains the autoimmune manifestations associated with DOCK8-deficiency.</p

The TYK2-P1104A Autoimmune Protective Variant Limits Coordinate Signals Required to Generate Specialized T Cell Subsets

TYK2 is a JAK family member that functions downstream of multiple cytokine receptors. Genome wide association studies have linked a SNP (rs34536443) within TYK2 encoding a Proline to Alanine substitution at amino acid 1104, to protection from multiple autoimmune diseases including systemic lupus erythematosus (SLE) and multiple sclerosis (MS). The protective role of this SNP in autoimmune pathogenesis, however, remains incompletely understood. Here we found that T follicular helper (Tfh) cells, switched memory B cells, and IFNAR signaling were decreased in healthy individuals that expressed the protective variant TYK2(A1104) (TYK2(P)). To study this variant in vivo, we developed a knock-in murine model of this allele. Murine Tyk2(P) expressing T cells homozygous for the protective allele, but not cells heterozygous for this change, manifest decreased IL-12 receptor signaling, important for Tfh lineage commitment. Further, homozygous Tyk2(P) T cells exhibited diminished in vitro Th1 skewing. Surprisingly, despite these signaling changes, in vivo formation of Tfh and GC B cells was unaffected in two models of T cell dependent immune responses and in two alternative SLE models. TYK2 is also activated downstream of IL-23 receptor engagement. Here, we found that Tyk2(P) expressing T cells had reduced IL-23 dependent signaling as well as a diminished ability to skew toward Th17 in vitro. Consistent with these findings, homozygous, but not heterozygous, Tyk2(P) mice were fully protected in a murine model of MS. Homozygous Tyk2(P) mice had fewer in filtrating CD4(+) T cells within the CNS. Most strikingly, homozygous mice had a decreased proportion of IL-17(+)/IFN gamma(+), double positive, pathogenic CD4(+) T cells in both the draining lymph nodes (LN) and CNS. Thus, in an autoimmune model, such as EAE, impacted by both altered Th1 and Th17 signaling, the Tyk2(P) allele can effectively shield animals from disease. Taken together, our findings suggest that TYK2(P) diminishes IL-12, IL-23, and IFN I signaling and that its protective effect is most likely manifest in the setting of autoimmune triggers that concurrently dysregulate at least two of these important signaling cascades

The A946T variant of the RNA sensor IFIH1 mediates an interferon program that limits viral infection but increases the risk for autoimmunity

The single-nucleotide polymorphism rs1990760 in the gene encoding the cytosolic viral sensor IFIH1 results in an amino-acid change (A946T; IFIH1T946) that is associated with multiple autoimmune diseases. The effect of this polymorphism on both viral sensing and autoimmune pathogenesis remains poorly understood. Here we found that human peripheral blood mononuclear cells (PBMCs) and cell lines expressing the risk variant IFIH1T946 exhibited heightened basal and ligand-triggered production of type I interferons. Consistent with those findings, mice with a knock-in mutation encoding IFIH1T946 displayed enhanced basal expression of type I interferons, survived a lethal viral challenge and exhibited increased penetrance in autoimmune models, including a combinatorial effect with other risk variants. Furthermore, IFIH1T946 mice manifested an embryonic survival defect consistent with enhanced responsiveness to RNA self ligands. Together our data support a model wherein the production of type I interferons driven by an autoimmune risk variant and triggered by ligand functions to protect against viral challenge, which probably accounts for its selection within human populations but provides this advantage at the cost of modestly promoting the risk of autoimmunity