Mahesh Yadav

Neuropilin-1 distinguishes natural and inducible regulatory T cells among regulatory T cell subsets in vivo

Neuropilin-1 is identified as a surface marker to distinguish different Foxp3+ T reg cell subsets under homeostatic conditions.

Peripherally Induced Tregs – Role in Immune Homeostasis and Autoimmunity

Thymically derived Foxp3+ regulatory T cells (tTregs) constitute a unique T cell lineage that is essential for maintaining immune tolerance to self and immune homeostasis. However, Foxp3 can also be turned on in conventional T cells as a consequence of antigen exposure in the periphery, under both non-inflammatory and inflammatory conditions. These so-called peripheral Tregs (pTregs) participate in the control of immunity at sites of inflammation, especially at the mucosal surfaces. Although numerous studies have assessed in vitro generated Tregs (termed induced or iTregs), these cells most often do not recapitulate the functional or phenotypic characteristics of in vivo generated pTregs. Thus, there are still many unanswered questions regarding the T cell receptor (TCR) repertoire and function of pTregs as well as conditions under which they are generated in vivo, and the degree to which these characteristics identify specialized features of pTregs versus features that are shared with tTregs. In this review, we summarize the current state of our understanding of pTregs and their relationship to the tTreg subset. We describe the recent discovery of unique cell surface markers and transcription factors (including Neuropilin-1 and Helios) that can be used to distinguish tTreg and pTreg subsets in vivo. Additionally, we discuss how the improved ability to distinguish these subsets provided new insights into the biology of tTregs versus pTregs and suggested differences in their function and TCR repertoire, consistent with a unique role of pTregs in certain inflammatory settings. Finally, these recent advances will be used to speculate on the role of individual Treg subsets in both tolerance and autoimmunity.

Tolerance induction and reversal of diabetes in mice transplanted with human embryonic stem cell-derived pancreatic endoderm.

Type 1 diabetes (T1D) is an autoimmune disease caused by T cell-mediated destruction of insulin-producing β cells in the islets of Langerhans. In most cases, reversal of disease would require strategies combining islet cell replacement with immunotherapy that are currently available only for the most severely affected patients. Here, we demonstrate that immunotherapies that target T cell costimulatory pathways block the rejection of xenogeneic human embryonic-stem-cell-derived pancreatic endoderm (hESC-PE) in mice. The therapy allowed for long-term development of hESC-PE into islet-like structures capable of producing human insulin and maintaining normoglycemia. Moreover, short-term costimulation blockade led to robust immune tolerance that could be transferred independently of regulatory T cells. Importantly, costimulation blockade prevented the rejection of allogeneic hESC-PE by human PBMCs in a humanized model in vivo. These results support the clinical development of hESC-derived therapy, combined with tolerogenic treatments, as a sustainable alternative strategy for patients with T1D.

Divergent Phenotypes of Human Regulatory T Cells Expressing the Receptors TIGIT and CD226

Regulatory T cells (Tregs) play a central role in counteracting inflammation and autoimmunity. A more complete understanding of cellular heterogeneity and the potential for lineage plasticity in human Treg subsets may identify markers of disease pathogenesis and facilitate the development of optimized cellular therapeutics. To better elucidate human Treg subsets, we conducted direct transcriptional profiling of CD4+FOXP3+Helios+ thymic-derived Tregs and CD4+FOXP3+Helios− T cells, followed by comparison with CD4+FOXP3−Helios− T conventional cells. These analyses revealed that the coinhibitory receptor T cell Ig and ITIM domain (TIGIT) was highly expressed on thymic-derived Tregs. TIGIT and the costimulatory factor CD226 bind the common ligand CD155. Thus, we analyzed the cellular distribution and suppressive activity of isolated subsets of CD4+CD25+CD127lo/− T cells expressing CD226 and/or TIGIT. We observed TIGIT is highly expressed and upregulated on Tregs after activation and in vitro expansion, and is associated with lineage stability and suppressive capacity. Conversely, the CD226+TIGIT− population was associated with reduced Treg purity and suppressive capacity after expansion, along with a marked increase in IL-10 and effector cytokine production. These studies provide additional markers to delineate functionally distinct Treg subsets that may help direct cellular therapies and provide important phenotypic markers for assessing the role of Tregs in health and disease.

Cutting Edge: Vasoactive Intestinal Peptide (VIP) Induces Differentiation of Th17 Cells with a Distinctive Cytokine Profile

Immune cellular effects of vasoactive intestinal peptide (VIP) are transduced by VIP G protein-coupled receptors type 1 (VPAC1) and type 2 (VPAC2). We now show that VIP with TGFβ stimulates the transformation of CD4 T cells to a distinctive type of Th17 cell that generates IL-17 but not IL-6 or IL-21. VIP induction of Th17 cells was higher in VPAC2 knockout mice than wild-type mice, suggesting that VPAC1 is the principal transducer. Compared with Th17 cells elicited by IL-6, those evoked by VIP were similar in the secretion of IL-17 and IL-22, but lacked IL-21 secretion. Suppression of VIP induction of Th17 cells by protein kinase A inhibitors and enhancement by pharmacologically increased cAMP supports a role for this signal. The ability of VIP-VPAC1 axis signals to evoke development of a novel type of Th17 cells demonstrates the unique specificity of neuroregulatory mechanisms in the immunological environment.

VPAC1 (vasoactive intestinal peptide (VIP) receptor type 1) G protein-coupled receptor mediation of VIP enhancement of murine experimental colitis

Distinct roles of the two T cell G protein-coupled receptors for vasoactive intestinal peptide (VIP), termed VPAC1 and VPAC2, in VIP regulation of autoimmune diseases were investigated in the dextran sodium sulfate (DSS)-induced murine acute colitis model for human inflammatory bowel diseases. In mice lacking VPAC2 (VPAC2-KO), DSS-induced colitis appeared more rapidly with greater weight loss and severe histopathology than in wild-type mice. In contrast, DSS-induced colitis in VPAC1-KO mice was milder than in wild-type mice and VPAC2-KO mice. Tissues affected by colitis showed significantly higher levels of myeloperoxidase, IL-6, IL-1β and MMP-9 in VPAC2-KO mice than wild-type mice, but there were no differences for IL-17, IFN-γ, IL-4, or CCR6. Suppression of VPAC1 signals in VPAC2-KO mice by PKA inhibitors reduced the clinical and histological severity of DSS-induced colitis, as well as tissue levels of IL-6, IL-1β and MMP-9. Thus VIP enhancement of the severity of DSS-induced colitis is mediated solely by VPAC1 receptors.

Vasoactive Intestinal Peptide–Mediated Th17 Differentiation

Interactions between neural and immune effector pathways serve a vital role in mammalian defenses against foreign pathogens and toxins. The immune system initiates processes leading to the release of diverse mediators and cytokines that recruit neural and endocrine involvement in immunity. Inversely, transmitters released from nerves innervating immune organs regulate the development and functions of the immune cells. Vasoactive intestinal peptide (VIP) is the quantitatively and functionally most prominent immunoregulatory neuropeptide that participates in local tissue immune responses by potently affecting T cell and macrophage migration, proliferation, and cytokine production. T cells, macrophages, and mast cells express the VIP G protein–coupled receptors (GPCR) VPAC1 and VPAC2 that transduce the effects of VIP on immunity. The VIP–VPAC axes also are coupled to abnormal T cell functions in different autoimmune conditions. Recently, it has been shown that VIP also enhances the differentiation of distinctive type of proinflammatory Th17 cells by a VPAC1‐dependent mechanism. This unique VIP–VPAC1 signaling in Th17 cell differentiation expands our understanding of VIP immune functions, provides new insights into the immune roles of individual VPAC receptors, and offers meaningful possibilities for improving therapeutic potential of VIP in immune disorders.

Interleukin-1 receptor mediates the interplay between CD4+ T cells and ocular resident cells to promote keratinizing squamous metaplasia in Sjögren’s syndrome

Keratinizing squamous metaplasia (SQM) of the ocular mucosal epithelium is a blinding corneal disease characterized by the loss of conjunctival goblet cells (GCs), pathological ocular surface keratinization and tissue recruitment of immune cells. Using the autoimmune regulator (Aire)-deficient mouse as a model for Sjögrens syndrome (SS)-associated SQM, we identified CD4+ T lymphocytes as the main immune effectors driving SQM and uncovered a pathogenic role for interleukin-1 (IL-1). IL-1, a pleiotropic cytokine family enriched in ocular epithelia, governs tissue homeostasis and mucosal immunity. Here, we used adoptive transfer of autoreactive CD4+ T cells to dissect the mechanism whereby IL-1 promotes SQM. CD4+ T cells adoptively transferred from both Aire knockout (KO) and Aire/IL-1 receptor type 1 (IL-1R1) double KO donors conferred SQM to severe-combined immunodeficiency (scid) recipients with functional IL-1R1, but not scid recipients lacking IL-1R1. In the lacrimal gland, IL-1R1 was primarily immunolocalized to ductal epithelium surrounded by CD4+ T cells. In the eye, IL-1R1 was expressed on local mucosal epithelial and stromal cells, but not on resident antigen-presenting cells or infiltrating immune cells. In both tissues, autoreactive CD4+ T-cell infiltration was only observed in the presence of IL-1R1-postive resident cells. Moreover, persistent activation of IL-1R1 signaling led to chronic immune-mediated inflammation by retaining CD4+ T cells in the local microenvironment. Following IL-1R1-dependent infiltration of CD4+ T cells, we observed SQM hallmarks in local tissues—corneal keratinization, conjunctival GC mucin acidification and epithelial cell hyperplasia throughout the ocular surface mucosa. Proinflammatory IL-1 expression in ocular epithelial cells significantly correlated with reduced tear secretion, while CD4+ T-cell infiltration of the lacrimal gland predicted the development of ocular SQM. Collectively, data in this study indicated a central role for IL-1 in orchestrating a functional interplay between immune cells and resident cells of SS-targeted tissues in the pathogenesis of SQM.

Diverse Mechanisms and Consequences of Immunoadoption of Neuromediator Systems

Modern investigations of the mechanisms of both neuroregulation of immunity and neural effects of immune reactions have focused on identification of the mediators, their receptors, and signal transduction pathways in both systems. Less attention has been directed to delineation of the tissue context of neuroregulation of immunity that determines the principal sources of neuromediators, the physiological consequences of integration of neural and immune activities, and possible approaches to pharmacological manipulation. To illustrate these points, we describe here the corticotropin‐releasing hormone (CRH) and vasoactive intestinal peptide (VIP) axes. When generated by the hypothalamus in response to inflammation or other stresses, CRH is immunosuppressive through its ability to increase levels of glucocorticoids and catecholamines. In contrast, CRH from peripheral nerves and immune accessory cells is immunostimulatory in tissue immune responses through direct effects on macrophages and lymphocytes. VIP released from several sets of nerves is immunosuppressive as a result of actions on macrophages and T cells in lymphoid organs, whereas VIP from immune cells in local tissue responses to antigen enhances development of some types of memory T cells and effector Th17 cells. Better understanding of how tissue context establishes the nature of neuroregulation of immunity will improve neuropharmacological and other neurotherapeutic approaches to immune diseases.

Immunosuppressive human anti-lymphocyte autoantibodies specific for the type 1 sphingosine 1-phosphate receptor

Anti‐lymphocyte antibodies (Abs) that suppress T‐cell chemotactic and other responses to sphingosine 1‐phosphate (S1P), but not to chemokines, were found in a lymphopenic patient with recurrent infections. Lymphocyte type 1 S1P receptor (S1P1) that transduces S1P chemotactic stimulation was recognized by patient Abs in Western blots of T cells, S1P1 transfectants, and S1P1‐hemagglutinin purified by monoclonal anti‐hemagglutinin Ab absorption. The amino terminus of S1P1, but not any extracellular loop, preventedanti‐S1P1 Ab suppression of S1P1 signaling and T‐cell chemotaxis to S1P. Human purifiedanti‐S1P1 Abs decreased mouse blood lymphocyte levels by a mean of 72%, suppressed mouse T‐cell chemotaxis to S1P in vivo, and significantly reduced the severity of dextran sodium sulfate‐induced colitis in mice. Human Abs to the amino terminus of S1P1 suppress T‐cell trafficking sufficiently to impair host defense and provide therapeutic immunosuppression.—Liao, J.‐J., Huang, M.‐C., Fast, K., Gundling, K., Yadav, M., Van Brocklyn, J.R., Wabl, M.R., Goetzl, E.J. Immunosuppressive human anti‐lymphocyte autoantibodies specific for the type 1 sphingosine 1‐phosphate receptor. FASEB J. 23, 1786–1796 (2009)