Reduced enrichment of short-chain fatty acid (SCFA)-producing pathways in the gut microbiome (GM) and SCFA levels are associated with increased risk of type 1 diabetes (T1D). Free fatty acid receptor 2 (FFA2), an SCFA receptor on pancreatic β-cells, mediates GM and β-cell crosstalk. Here, we examine its T1D-specific role in male mice, using a novel tamoxifen-inducible adult-onset β-cell FFA2 knockout (FFA2 βKO) mouse model and its controls (cre and flox), treated with multiple low-dose streptozotocin (MLDS). FFA2 βKO mice show significantly lower diabetes incidence compared to control mice (57% vs 100%). Early in the MLDS insult (7th day), FFA2 βKO mice show significantly lower β-cell apoptosis and higher β-cell mass, persisting up to 43 days. Mechanistically, we observed higher SOCS1/3 expression and reduced T1-IFN signaling in FFA2 βKO islets. Our data suggest that β-cell FFA2 modulates early islet apoptosis, likely via the T1-IFN-SOCS1/3 pathway and may be a pharmacological target for slowing T1D progression.

Colorectal cancer and liver metastases are a leading cause of cancer-related mortality. Overexpression of the immunostimulatory cytokine TNFSF14/LIGHT associates with improved survival and correlates with increased tumor-infiltrating lymphocytes in patients and a clinically relevant model of colorectal liver metastases. We demonstrate that LIGHT monotherapy activates T cells, but also induces T cell exhaustion and the recruitment of immunosuppressive elements. As colorectal liver metastases exhibit high levels of CTLA-4 expression, we combined LIGHT overexpression with anti-CTLA-4, leading to complete tumor control. The combination functions by homing tumor-infiltrating lymphocytes, inducing tumor antigen-specific T cells, and reversing T cell exhaustion. Whereas both LIGHT overexpression and anti-CTLA-4 increase tumor-promoting macrophages, the combination eliminates this population. The ability of LIGHT overexpression combined with CTLA-4 inhibition to reverse T cell exhaustion and myeloid cell suppression is supported by analysis of complementary patient cohorts and has strong clinical relevance, especially given that liver metastases contribute to immunotherapy resistance across various cancer types.

Abstract Disclosure: K. Xu: None. M. Priyadarshini: None. P. Kumar: None. H.M. Electricwala: None. B.S. Prabhakar: None. B.T. Layden: None. Gut microbiome is recently recognized environmental factor in pathogenesis of type 1 diabetes (T1D). Reduced short chain fatty acid (SCFA) producing gut bacteria and also SCFA levels correlate with T1D risk (TEDDY study). We have previously shown that FFA2 is one of the main SCFA receptors, which is expressed on the β cell and mediates gut microbiome-β cell crosstalk. Based on these data, we hypothesized that β cell FFA2 may play a role in T1D β cell pathology. To examine this, we followed our novel tamoxifen induced β cell FFA2 knockout mice (FFA2 fl/fl; MIP CreERT+, FFA2 BKO) and wildtype littermates (FFA2 fl/fl) after multiple low dose streptozotocin (MLDS) induced T1D. Comparing to wildtype littermates, FFA2 BKO were significantly protected from MLDS insult and exhibited normal glycemic control owing to higher β cell mass. To understand the mechanism of this protective effect, we mined islet transcriptome data from our FFA2 global knockout mice and identified markedly upregulated type 1 interferon pathway in FFA2 global knockout. Accordingly, wildtype islets treated with high dose IFNα (mimicking T1D like conditions) showed significant upregulation of IFNαtargets while FFA2 BKO islets were unresponsive. Using pharmacological inhibition in isolated islets, we identified FFA2 mediated inhibition of NF-κB activation as a critical event in FFA2 mediated regulation of IFNαsignaling. In vivo studies with IFNAR1 antibody showed partial rescue of wildtype mice in the early stages of MLDS induced T1D. Thus, we propose a key role of β cell FFA2 in preserving β cell mass from IFNα signaling mediated damage in T1D. Further studies are needed to test this model. Presentation: Saturday, June 17, 2023

Recurrent waves of SARS CoV2 infections remain a major global health concern. Emergence of highly infectious variants with reduced sensitivity to neutralization by vaccines and monoclonal antibodies (mAb) necessitates a deeper understanding of factors involved in SARS CoV2 infections and identification of drug candidates to halt infection. Here, we determined the primacy of endosomal protease cathepsin-L in mediating SARS CoV2 entry and screened a library of well-annotated bioactive compounds for potent cathepsin-L inhibitory activity. Whilst the potent cathepsin-L inhibitors were capable of inhibiting SARS CoV2 entry and cytopathic effect (CPE) in less susceptible cell lines such as human ACE2 expressing 293T cells, these drugs failed to inhibit SARS CoV2 in highly susceptible cell lines such as human TMPRSS2 or human-ACE2-TMPRSS2 overexpressing Vero E6 cells. Only drugs with dual inhibitory effect on both host cathepsin-L and virus 3CL-Protease enzymes such as Z-FA-FMK and GC-376 were capable of inhibiting prototypic (USA-WA1/2020, Lineage A) SARS CoV2 induced CPE in highly susceptible cell lines. Moreover, these drugs inhibited delta (Lineage-B.1.617.2) and omicron (Lineage-B.1.1.529) infection with equal potency showing that the newer mutations harbored in these variants did not affect the mechanism of action of these drugs such as cathepsin-L or 3CL-Pro inhibition. Moreover, our early evidence that 3CL-Pro inhibition can effectively inhibit omicron-induced CPE in highly susceptible cell lines suggests that the recently FDA-approved oral drug, a 3CL-Pro inhibitor which is a combination of nirmatrelvir/ritonavir (Paxlovid) could be effective against omicron variant which shows reduced sensitivity to vaccines and mAb. Importance We report that cathepsin-L and 3CL-Pro as major targets for designing antivirals against SARS CoV2. Dual inhibition of cathepsin-L and 3CL-Pro by GC-376 renders it effective in inhibiting SARS CoV2-induced cytopathic effect in highly susceptible cell lines. Moreover, this candidate drug is equally effective against prototypic SARS CoV2 lineage A and emerging variants such as delta and omicron which show reduced sensitivity to vaccines and monoclonal antibodies. Given the recent wave of SARS CoV2 omicron variant infection around the world, and 3CL-Pro inhibitor nirmatrelvir is one of the components of the FDA-approved Paxlovid, our findings are timely, important and should be of broad interest.

Escalated innate immunity plays a critical role in SARS-CoV-2 pathology; however, the molecular mechanism is incompletely understood. Thus, we aim to characterize the molecular mechanism by which SARS-CoV-2 Spike protein advances human macrophage (Mϴ) inflammatory and glycolytic phenotypes and uncover novel therapeutic strategies. We found that human Mϴs exposed to Spike protein activate IRAK4 phosphorylation. Blockade of IRAK4 in Spike protein-stimulated Mϴs nullifies signaling of IRAK4, AKT, and baseline p38 without affecting ERK and NF-κB activation. Intriguingly, IRAK4 inhibitor (IRAK4i) rescues the SARS-CoV-2-induced cytotoxic effect in ACE2+HEK 293 cells. Moreover, the inflammatory reprogramming of Mϴs by Spike protein was blunted by IRAK4i through IRF5 and IRF7, along with the reduction of monokines, IL-6, IL-8, TNFα, and CCL2. Notably, in Spike protein-stimulated Mϴs, suppression of the inflammatory markers by IRAK4i was coupled with the rebalancing of oxidative phosphorylation over metabolic activity. This metabolic adaptation promoted by IRAK4i in Spike protein-activated Mϴs was shown to be in part through constraining PFKBF3, HIF1α, cMYC, LDHA, lactate expression, and reversal of citrate and succinate buildup. IRAK4 knockdown could comparably impair Spike protein-enhanced inflammatory and metabolic imprints in human Mϴs as those treated with ACE2, TLR2, and TLR7 siRNA. Extending these results, in murine models, where human SARS-CoV-2 Spike protein was not recognized by mouse ACE2, TLRs were responsible for the inflammatory and glycolytic responses instigated by Spike protein and were dysregulated by IRAK4i therapy. In conclusion, IRAK4i may be a promising strategy for severe COVID-19 patients by counter-regulating ACE2 and TLR-mediated Mϴ hyperactivation. IRAK4i therapy counteracts Mϴ inflammatory and glycolytic reprogramming triggered by Spike protein. This study illustrates that SARS-CoV-2 Spike protein activates IRAK4 signaling via ACE2 as well as TLR2 and TLR7 sensing in human Mϴs. Remarkably, IRAK4i treatment can dysregulate both ACE-dependent and independent (via TLR sensing) SARS-CoV-2 Spike protein-activated inflammatory and metabolic imprints.

Recurrent waves of COVID19 remain a major global health concern. Repurposing either FDA-approved or clinically advanced drug candidates can save time and effort required for validating the safety profile and FDA approval. However, the selection of appropriate screening approaches is key to identifying novel candidate drugs with a higher probability of clinical success. Here, we report a rapid, stratified two-step screening approach using pseudovirus entry inhibition assay followed by an infectious prototypic SARS CoV2 cytotoxic effect inhibition assay in multiple cell lines. Using this approach, we screened a library of FDA-approved and clinical-stage drugs and identified four compounds, apilimod, berbamine, cepharanthine and (S)-crizotinib which potently inhibited SARS CoV2-induced cell death. Importantly, these drugs exerted similar inhibitory effect on the delta and omicron variants although they replicated less efficiently than the prototypic strain. Apilimod is currently under clinical trial (NCT04446377) for COVID19 supporting the validity and robustness of our screening approach.

Class-switched antinuclear autoantibodies produced by T follicular helper (TFH) cell-dependent germinal center (GC) B cell response play an essential pathogenic role in lupus nephritis (LN). The role of T follicular regulatory (TFR) cells, an effector subset of CD4(+)Foxp3(+) T regulatory cells (Tregs), which are specialized in suppressing TFH-GC response and Ab production, remains elusive in LN. Contrasting reports have shown increased/reduced circulating TFR cells in human lupus that might not accurately reflect their presence in the GCs of relevant lymphoid organs. In this study, we report a progressive reduction in TFR cells and decreased TFR/ TFH ratio despite increased Tregs in the renal lymph nodes of NZBWF1/j mice, which correlated with increased GC-B cells and proteinuria onset. Cotreatment with soluble OX40L and Jagged-1 (JAG1) proteins increased Tregs, TFR cells, and TFR/TFH ratio, with a concomitant reduction in TFH cells, GC B cells, and anti-dsDNA IgG Ab levels, and suppressed LN onset. Mechanistic studies showed attenuated TFH functions and diminished GC events such as somatic hypermutation and isotype class-switching in OX40LJAG1-treated mice. RNA sequencing studies revealed inhibition of hypoxia-inducible factor 1-alpha (HIF-1 alpha) and STAT3 signaling in T conventional cells from OX40L-JAG1-treated mice, which are critical for the glycolytic flux and differentiation into TFH cell lineage. Therefore, the increased TFR/TFH ratio seen in OX40L-JAG1-treated mice could involve both impaired differentiation of TFH cells from T conventional cells and expansion of TFR cells. We show a key role for GC-TFR/TFH imbalance in LN pathogenesis and how restoring homeostatic balance can suppress LN.

Antinuclear autoantibodies (Nabs) promote tissue inflammation involving multiple organs including the kidneys in Systemic Lupus Erythmatosus (SLE). T-follicular helper (TFH) cell-dependent B-cell response plays an essential role in lupus nephritis (LN). TFH and B-cells receive mutual help in the germinal centers (GCs) to enable high-affinity autoantibody production. T follicular regulatory cells (TFR) cells, a specialized subset of CD4+Foxp3+Tregs, suppress GC formation and TFH-dependent B-cell response. Previously, we have shown that the expansion of functional Tregs using soluble OX40L and JAG1 proteins suppressed experimental autoimmune diabetes and thyroiditis. However, unlike other autoimmune diseases, the role of Tregs in lupus remains unresolved. Here, we show that NZBWF1/j mice with severe proteinuria and higher anti-dsDNA IgG levels had increased GC-TFH, GC-B cells, and GC-TFH/GC-TFR ratio in their renal lymph nodes compared to mice with no proteinuria. While total Tregs were significantly higher in mice with proteinuria, GC-TFRs were significantly reduced. Intriguingly, OX40L-JAG1 treatment significantly increased Tregs, GC-TFRs, and reduced GC-TFH/GC-TFR ratio. Periodic OX40L-JAG1 treatment resulted in a significant reduction in GC-B-cells, anti-dsDNA IgG level, proteinuria and kidney pathology, and increased survival. Mechanistic studies showed increased PD1 expression in Tconv cells, Tregs, TFH, and TFR cells, and PD-L1 expression in GC-B-cells suggesting a key role for PD1 signaling in the observed protective effect. Our results show that OX40L-JAG1 treatment expanded TFRs which inhibited GC-B cell activation and NAb production, proteinuria and LN.

Background/Purpose: The global coronavirus disease 2019 (COVID-19) pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) resulted in significant mortality, social disorder and economic hardships. We set out to understand why certain individuals could resolve the disease successfully without serious complications by immune profiling of PBMCs from convalescent COVID-19 patients (n = 14) with mild disease trajectory. Methods: We designed 7 peptides targeting the receptor binding region (RBD) of the spike protein of SARS-CoV-2, that encompass broad HLA class I / II alleles, with the aid of the Immune Epitope Database and Analysis Resource (IEDB) website. The RBD site was chosen as it was shown to be protective when neutralising antibodies against this region could negate binding of viral spike protein to host cell ACE-2 receptor. Convalescent COVID-19 patients enrolled in this study were screened and selected for positive antibody titre against the RBD region. PBMCs from convalescent COVID-19 patients were stimulated with/without the peptides for 72hrs and immune profiled (n = 70 markers across two panels) with the high dimensional single cell mass cytometry platform (CyToF). Results: Convalescent COVID-19 patients elicited a robust recall memory T follicular helper response (CD3 + CD4 + CD45RO + CXCR5 + Tigit + ;∗∗∗∗ p < 0.0001) demonstrating peptide efficacy. Unsupervised clustering (FlowSOM) of the CD4 T cell immune landscape reaffirmed increase in memory T follicular subsets and additionally CD4 + CD45RO + CXCR5 -subsets. Further gating of antigen specific memory cells (CD45RO + CD69 + ) revealed an increase in Tbet + CXCR3 + T effectors in both CD4 and CD8 compartments. Strikingly we detected a parallel increase in CD4 + Treg (CD25 + FoxP3 + ) CXCR3 + Tbet + CD45RO + CD152 + Tigit + expression. Conclusions: COVID-19 patients that successfully resolve the viral infection not only mount a robust T effector and follicular response but also in tandem a similar T regulatory profile.

TNF receptor superfamily comprises many T-cell costimulatory receptors, including TNFRSF1, TNFRSF2, TNFRSF4 (OX40), TNFRSF9 (4-1BB), TNFRSF18 (GITR), and TNFRSF7 (CD27). Signaling through these costimulatory stimulatory receptors can promote conventional T-cell (Tconv) proliferation, and effector functions in an antigen-dependent manner. Thus, agonistic antibodies and ligands for OX40, 4-1BB, GITR, and CD27 have been tested for inducing T-cell-mediated antitumor responses in several cancers. However, recently emerging reports show critical role for TNFR signaling in regulatory T-cell (Treg) differentiation and expansion, which might suppress effector T-cell proliferation and functions. Here, we show preferential over expression of TNFR2, OX40, 4-1BB, and GITR in Treg cells over Tconv cells, and the ability of OX40L and GITRL to induce selective proliferation of Treg cells, but not Tconv cells, in an antigen-independent manner. We describe the standard protocols used for Affymetrix gene expression profiling, T-cell isolation, and Cell Trace Violet-based cell proliferation assay.

Regulatory T-cells (Tregs) can facilitate immune evasion by tumor cells by dampening anti-tumor immunity. Reduced Teff/Treg ratio and enhanced Treg functional activity have been observed in patients suffering from different types of cancers, and attenuated Treg numbers/functions can serve as prognostic indicators. Normally, Tregs play an essential role in the maintenance of immune tolerance and prevention of autoimmunity. The most common immune checkpoint blockers (ICB) targeting co-inhibitory receptors such as anti-CTLA4 (ipilimumab and tremelimumab) and anti-PD1 (pembrolizumab and nivolumab)/anti-PD-L1 (atezolizumab) have achieved unprecedented success in cancer treatment by facilitating an effective anti-tumor immune response, at least in part, by blocking Treg mediated immunosuppression. While ICBs have shown remarkable success in cancer immunotherapy, immune-related adverse events (IRAEs) arising from ICB have forced consideration of ways to maintain immune homeostasis post ICB treatment. Preclinical models of IRAEs have shown a negative correlation between Treg numbers and IRAEs. Therefore, understanding the “ying-yang” role of Tregs in the regulation of autoimmunity and anti-tumor immunity is critical to provoking an effective anti-tumor response while maintaining immune homeostasis. Studies aimed at developing effective approaches to minimize IRAEs without compromising anti-tumor immunity are underway. Herein, we discuss 1) the critical role of key co-inhibitory receptors on Treg homeostasis and tumor tolerance; 2) how co-receptor blockade by cancer immunotherapy can lead to autoimmune adverse events; and 3) recently emerging management strategies to minimize autoimmune adverse events arising from ICB.

Regulatory T-cells (Tregs) can facilitate immune evasion by tumor cells by dampening anti-tumor immunity. Reduced Teff/Treg ratio and enhanced Treg functional activity have been observed in patients suffering from different types of cancers, and attenuated Treg numbers/functions can serve as prognostic indicators. Normally, Tregs play an essential role in the maintenance of immune tolerance and prevention of autoimmunity. The most common immune checkpoint blockers (ICB) targeting co-inhibitory receptors such as anti-CTLA4 (ipilimumab and tremelimumab) and anti-PD1 (pembrolizumab and nivolumab)/anti-PD-L1 (atezolizumab) have achieved unprecedented success in cancer treatment by facilitating an effective anti-tumor immune response, at least in part, by blocking Treg mediated immunosuppression. While ICBs have shown remarkable success in cancer immunotherapy, immune-related adverse events (IRAEs) arising from ICB have forced consideration of ways to maintain immune homeostasis post ICB treatment. Preclinical models of IRAEs have shown a negative correlation between Treg numbers and IRAEs. Therefore, understanding the "ying-yang" role of Tregs in the regulation of autoimmunity and anti-tumor immunity is critical to provoking an effective anti-tumor response while maintaining immune homeostasis. Studies aimed at developing effective approaches to minimize IRAEs without compromising anti-tumor immunity are underway. Herein, we discuss 1) the critical role of key co-inhibitory receptors on Treg homeostasis and tumor tolerance; 2) how co-receptor blockade by cancer immunotherapy can lead to autoimmune adverse events; and 3) recently emerging management strategies to minimize autoimmune adverse events arising from ICB.

Type-1 Diabetes (T1D) is the major autoimmune disease affecting the juvenile population in which insulin-producing pancreatic β-cells are destroyed by self-reactive T-cells and B-cells. Emerging studies have identified the presence of autoantibodies and altered T-cell reactivity against several autoantigens in individuals who are at risk of developing T1D even before the clinical onset of diabetes. Whilst these findings could lead to the development of predictive biomarkers for early diagnosis, growing evidence on the generation of neoepitopes, epitope spreading and diverse antigen repertoire in T1D poses a major challenge for developing approaches to induce antigen-specific tolerance. Mechanisms of neoepitope generation include post-translational modifications of existing epitopes, aberrant translational products, peptide fusion, and differences in MHC binding registers. Here, we focus our discussion on how post-translational modifications can give rise to immunogenic neoepitopes in T1D and present our perspective on how it could affect the development of therapeutic approaches to induce antigen-specific tolerance.

Key Points OX40L-JAG1 induced Treg proliferation mediated via noncanonical NF-κB signaling. OX40L-JAG1 expanded epigenetically stable and suppressive Tregs to ameliorate EAT. OX40L-JAG1 induced TCR-independent selective proliferation of human thymic Tregs. Foxp3+T regulatory cells (Tregs) control autoimmune response by suppressing proliferation and effector functions of self-reactive Foxp3−CD4+/CD8+ T cells and thereby maintain the critical balance between self-tolerance and autoimmunity. Earlier, we had shown that OX40L-JAG1 cosignaling mediated through their cognate receptors OX40 and Notch3 preferentially expressed on murine Tregs can selectively induce their proliferation in the absence of TCR stimulation. However, the differential molecular mechanisms regulating TCR-independent versus TCR-dependent Treg proliferation and lineage stability of the expanded Tregs remained unknown. In this study, we show that OX40L-JAG1 treatment induced TCR-independent proliferation of Tregs in the thymus and periphery. The use of Src kinase inhibitor permitted us to demonstrate selective inhibition of TCR-dependent T cell proliferation with little to no effect on OX40L-JAG1–induced TCR-independent Treg expansion in vitro, which was critically dependent on noncanonical NF-κB signaling. OX40L-JAG1–expanded Tregs showed sustained lineage stability as indicated by stable demethylation marks in Treg signature genes such as Foxp3, Il2ra, Ctla4, Ikzf2, and Ikzf4. Furthermore, OX40L-JAG1 treatment significantly increased CTLA4+ and TIGIT+ Tregs and alleviated experimental autoimmune thyroiditis in mice. Relevance of our findings to humans became apparent when human OX40L and JAG1 induced TCR-independent selective expansion of human Tregs in thymocyte cultures and increased human Tregs in the liver tissue of humanized NSG mice. Our findings suggest that OX40L-JAG1–induced TCR-independent Treg proliferation is a conserved mechanism that can be used to expand lineage-stable Tregs to treat autoimmune diseases.

Anaplastic Thyroid Cancer (ATC) is an aggressive malignancy with limited therapeutic options and dismal patient survival. We have previously shown MADD to be differentially overexpressed in multiple cancer histologies and to contribute to tumor cell growth and survival. Therefore, we targeted MADD by gene silencing, explored its effect on cellular proliferation and metastases and examined its therapeutic potential in an orthotopic ATC model in athymic nude mice. When compared to untreated control and scramble siRNA, MADD siRNA treatment inhibited the proliferative capacity of 8505C, C643 and HTH7 cells in vitro and 8505C-derived-orthotopic tumor growth in vivo. MADD ablation caused a significant reduction in cellular migration and invasion potential; clonogenic capacity; as well as, mitochondrial length and potential in vitro. This MADD siRNA-induced anti-migratory/invasive effect corresponded with inhibition of epithelial–mesenchymal transition (EMT) and Wnt signaling. Mechanistically, MADD siRNA inhibited TNFα induced activation of pERK, pGSK3β and β-catenin, suggesting that MADD knockdown might exert its anti-migratory/invasive effects, by blocking TNFα/ERK/GSK3β axis. MADD siRNA can inhibit β-catenin nuclear translocation and consequently, the expression of its target genes in ATC cells. In in vivo experiments, along with tumor regression, MADD siRNA treatment also decreased evidence of lung metastases. Immunohistochemically, MADD siRNA-treated tumor tissues exhibited a reduction in Ki67 and N-Cadherin expression, and an increase in E-Cadherin expression. In conclusion, we show the crucial role of MADD in ATC tumorigenesis and metastasis and its potential implications as a molecular target for ATC therapy.

Regulatory T-cells (Tregs) play a pivotal role in immune-tolerance, and loss of their function can lead to autoimmunity. Natural Tregs generated in the thymus contribute substantially to the Treg pool in the periphery where they suppress self-reactive Teff responses. Recently, we showed that OX40L (TNFSF4) can drive selective proliferation of peripheral Tregs independent of canonical antigen presentation (CAP-independent) in the presence of low dose IL-2. Therefore, we reasoned that OX40 signaling might be integral to the TCR-independent phase of murine and human thymic Treg (tTreg) development. Thymic Treg development is a two-step process: Strong T-cell receptor (TCR) signals combined with co-signals from the TNF receptor Super Family (TNFRSF) members facilitate tTreg precursor selection, followed by a TCR-independent phase of tTreg development when their maturation is driven by IL-2. Therefore, we investigated whether OX40 signaling can also play a critical role in the TCR-independent phase of tTreg development. OX40−/− mice had significantly reduced numbers of CD25−Foxp3low tTreg precursors and CD25+Foxp3+ matured tTregs, while OX40L treatment of WT mice induced significant proliferation of these cell subsets. Relative to tTeffs cells, OX40 was expressed at higher levels in both murine and human tTreg precursors and matured tTregs. In ex vivo cultures, OX40L increased tTreg maturation and induced CAP-independent proliferation of both murine and human tTregs which was mediated through the activation of AKT-mTOR signaling. These novel findings show an evolutionarily conserved role for OX40 signaling in tTreg development.

We have previously shown GM-CSF derived bone-marrow dendritic cells (G-BMDCs) can induce the selective expansion of Tregs through the surface-bound molecule OX40L; however, the physiological role of this ex vivo derived DC subset remained to be elucidated. We determined GM-CSF administration to mice induced the generation of in vivo derived OX40L+ DCs, phenotypically similar to ex vivo OX40L+G-BMDCs, in the spleen, brachial lymph nodes and liver. The generation of OX40L+ DCs correlated with increased percentages of functionally suppressive Tregs in the spleen, brachial lymph nodes, and liver of GM-CSF treated mice. DCs from GM-CSF treated mice expanded Tregs in CD4+ T-cell co-cultures in an OX40L dependent manner, suggesting OX40L+ DCs may play a role in peripheral Treg homeostasis. Furthermore, comparing the transcriptome data of OX40L+ DCs to that of all immune cell types revealed OX40L+ DCs to be distinct from steady-state immune cells and, microarray analysis of OX40L+G-BMDCs and OX40L−G-BMDCs revealed higher expression of molecules that are associated with tolerogenic phenotype and could play important roles in the function of OX40L+ DCs. These findings suggest that OX40L+ DCs may represent a unique DC subset induced under inflammatory conditions that may play an essential role in maintaining Treg homeostasis.

A high-fat diet can induce inflammation and metabolic diseases such as diabetes and atherosclerosis. The receptor for advanced glycation endproducts (RAGE) plays a critical role in metabolic disease pathophysiology and the soluble form of the receptor (sRAGE) can mitigate these effects. However, little is known about RAGE in the postprandial condition and the effect of exercise in this context. Thus, we aimed to determine the effects of a single high-fat meal (HFM) with and without prior exercise on peripheral blood mononuclear cell (PBMC) RAGE biology. Healthy males (n=12) consumed a HFM on two occasions, one without prior exercise and one 16-18hours following acute aerobic exercise. Total soluble RAGE (sRAGE) and endogenous secretory RAGE (esRAGE) were determined via ELISA and cleaved RAGE (cRAGE) was calculated as the difference between the two. Isolated PBMCs were analyzed for RAGE, ADAM10, TLR4, and MyD88 protein expression and ADAM10 activity. The HFM significantly (P<0.01) attenuated sRAGE, esRAGE, and cRAGE by 9.7%, 6.9%, and 10.5%, respectively. Whereas, the HFM increased PBMC RAGE protein expression by 10.3% (P<0.01), there was no meal effect on PBMC TLR4, MYD88, or ADAM10 protein expression, nor ADAM10 activity. There was also no exercise effect on any experimental outcomes. These findings suggest that PBMC RAGE and soluble RAGE may be important in the postprandial response to a HFM, and that prior aerobic exercise does not alter these processes in young healthy adult males. The mechanisms by which a HFM induces RAGE expression and reduces circulating soluble RAGE isoforms requires further study.

Self-tolerance, the state of unresponsiveness to self-tissues/antigens, is maintained through central and peripheral tolerance mechanisms, and a breach of these mechanisms leads to autoimmune diseases. Foxp3 + T-regulatory cells (Tregs) play an essential role in suppressing autoimmune response directed against self-antigens and thereby regulate self-tolerance. Natural Tregs are differentiated in the thymus on the basis of their higher TCR-affinity to self-antigens and migrate to the periphery where they maintain peripheral tolerance. In addition, extra-thymic differentiation of induced Tregs can occur in the periphery which can control abrupt immune responses under inflammatory conditions. A defect in Treg cell numbers and/or function is found to be associated with the development of autoimmune disease in several experimental models and human autoimmune diseases. Moreover, augmentation of Tregs has been shown to be beneficial in treating autoimmunity in preclinical models, and Treg based cellular therapy has shown initial promise in clinical trials. However, emerging studies have identified an unstable subpopulation of Tregs which expresses pro-inflammatory cytokines under both homeostatic and autoimmune conditions, as well as in ex vivo cultures. In addition, clinical translation of Treg cellular therapy is impeded by limitations such as lack of easier methods for selective expansion of Tregs and higher cost associated with GMP-facilities required for cell sorting, ex vivo expansion and infusion of ex vivo expanded Tregs. Here, we discuss the recent advances in molecular mechanisms regulating Treg differentiation, Foxp3 expression and lineage stability, the role of Tregs in the prevention of various autoimmune diseases, and critically review their clinical utility for treating human autoimmune diseases.

The immune system ensures optimum T-effector (Teff) immune responses against invading microbes and tumor antigens while preventing inappropriate autoimmune responses against self-antigens with the help of T-regulatory (Treg) cells. Thus, Treg and Teff cells help maintain immune homeostasis through mutual regulation. While Tregs can contribute to tumor immune evasion by suppressing anti-tumor Teff response, loss of Treg function can result in Teff responses against self-antigens leading to autoimmune disease. Thus, loss of homeostatic balance between Teff/Treg cells is often associated with both cancer and autoimmunity. Co-stimulatory and co-inhibitory receptors, collectively known as co-signaling receptors, play an indispensable role in the regulation of Teff and Treg cell expansion and function and thus play critical roles in modulating autoimmune and anti-tumor immune responses. Over the past three decades, considerable efforts have been made to understand the biology of co-signaling receptors and their role in immune homeostasis. Mutations in co-inhibitory receptors such as CTLA4 and PD1 are associated with Treg dysfunction, and autoimmune diseases in mice and humans. On the other hand, growing tumors evade immune surveillance by exploiting co-inhibitory signaling through expression of CTLA4, PD1 and PDL-1. Immune checkpoint blockade (ICB) using anti-CTLA4 and anti-PD1 has drawn considerable attention towards co-signaling receptors in tumor immunology and created renewed interest in studying other co-signaling receptors, which until recently have not been as well studied. In addition to co-inhibitory receptors, co-stimulatory receptors like OX40, GITR and 4-1BB have also been widely implicated in immune homeostasis and T-cell stimulation, and use of agonistic antibodies against OX40, GITR and 4-1BB has been effective in causing tumor regression. Although ICB has seen unprecedented success in cancer treatment, autoimmune adverse events arising from ICB due to loss of Treg homeostasis poses a major obstacle. Herein, we comprehensively review the role of various co-stimulatory and co-inhibitory receptors in Treg biology and immune homeostasis, autoimmunity, and anti-tumor immunity. Furthermore, we discuss the autoimmune adverse events arising upon targeting these co-signaling receptors to augment anti-tumor immune responses.