CAR Tregs mediate linked suppression and infectious tolerance in islet transplantation

Regulatory T cells (Tregs) have potential as a cell-based therapy to prevent or treat transplant rejection and autoimmunity. Using an HLA-A2-specific chimeric antigen receptor (A2-CAR), we previously showed that adoptive transfer of A2-CAR Tregs limited anti-HLA-A2 alloimmunity. However, it was unknown if A2-CAR Tregs could also limit immunity to autoantigens. Using a model of HLA-A2 + islet transplantation into immunodeficient non-obese diabetic mice, we investigated if A2-CAR Tregs could control diabetes induced by islet-autoreactive (BDC2.5) T cells. In mice transplanted with HLA-A2 + islets, A2-CAR Tregs reduced BDC2.5 T cell engraftment, proliferation and cytokine production, and protected mice from diabetes. Tolerance to islets was systemic, including protection of the HLA-A2 negative endogenous pancreas. In tolerant mice, a significant proportion of BDC2.5 T cells gained FOXP3 expression suggesting that long-term tolerance is maintained by de novo Treg generation. Thus, A2-CAR Tregs mediate linked suppression and infectious tolerance and have potential therapeutic use to simultaneously control both allo- and autoimmunity in islet transplantation.

One Sentence Summary

Alloreactive chimeric antigen receptor-engineered regulatory T cells limit diabetogenic T cell engraftment and function to prevent type 1 diabetes.

Tregs with an MHC class II peptide-specific chimeric antigen receptor prevent autoimmune diabetes in mice

Adoptive immunotherapy with Tregs is a promising approach for preventing or treating type 1 diabetes. Islet antigen-specific Tregs have more potent therapeutic effects than polyclonal cells, but their low frequency is a barrier for clinical application. To generate Tregs that recognize islet antigens, we engineered a chimeric antigen receptor (CAR) derived from a monoclonal antibody with specificity for the insulin B chain 10-23 peptide presented in the context of the IAg7 MHC class II allele present in NOD mice. Peptide specificity of the resulting InsB-g7 CAR was confirmed by tetramer staining and T cell proliferation in response to recombinant or islet-derived peptide. The InsB-g7 CAR redirected NOD Treg specificity such that insulin B 10-23-peptide stimulation enhanced suppressive function, measured via reduction of proliferation and IL-2 production by BDC2.5 T cells and CD80 and CD86 expression on dendritic cells. Cotransfer of InsB-g7 CAR Tregs prevented adoptive transfer diabetes by BDC2.5 T cells in immunodeficient NOD mice. In WT NOD mice, InsB-g7 CAR Tregs prevented spontaneous diabetes. These results show that engineering Treg specificity for islet antigens using a T cell receptor-like CAR is a promising therapeutic approach for the prevention of autoimmune diabetes.

Insulin B peptide-MHC class II-specific chimeric antigen receptor-Tregs prevent autoimmune diabetes

Adoptive immunotherapy with Tregs is a promising approach for prevention or treatment of type 1 diabetes. Islet antigen-specific Tregs have more potent therapeutic effects than polyclonal cells, but their low frequency is a barrier for clinical application. To generate Tregs that recognize islet antigens, we engineered a chimeric antigen receptor (CAR) derived from a monoclonal antibody with specificity for the insulin B-chain 10-23 peptide presented in the context of the IA g7 MHC class II allele present in NOD mice. Peptide specificity of the resulting InsB-g7 CAR was confirmed by tetramer staining and T cell proliferation in response to recombinant or islet-derived peptide. The InsB-g7 CAR re-directed NOD Treg specificity such that insulin B 10-23-peptide stimulation enhanced suppressive function, measured via reduction of proliferation and IL-2 production by BDC2.5 T cells and CD80 and CD86 expression on dendritic cells. Co-transfer of InsB-g7 CAR Tregs prevented adoptive transfer diabetes by BDC2.5 T cells in immunodeficient NOD mice. In wild type NOD mice, InsB-g7 CAR Tregs stably expressed Foxp3 and prevented spontaneous diabetes. These results show that engineering Treg specificity for islet antigens using a T cell receptor-like CAR is a promising new therapeutic approach for the prevention of autoimmune diabetes.

Brief Summary

Chimeric antigen receptor Tregs specific for an insulin B-chain peptide presented by MHC class II prevent autoimmune diabetes.

Evaluating the Immunopathogenesis of Diabetes After Acute Pancreatitis in the Diabetes RElated to Acute Pancreatitis and Its Mechanisms Study: From the Type 1 Diabetes in Acute Pancreatitis Consortium

ABSTRACT

The association between acute pancreatitis (AP) and diabetes mellitus (DM) has long been established, with the initial descriptions of AP patients presenting with DM after a bout of AP published in the 1940s and 50s. However, the potential mechanisms involved, particularly those components related to the immune system, have not been well defined. The Diabetes RElated to Acute pancreatitis and its Mechanisms (DREAM) study is a multicenter clinical study designed to understand the frequency and phenotype of DM developing after AP. This article describes one objective of the DREAM study: to determine the immunologic mechanisms of DM after AP, including the contribution of β-cell autoimmunity. This component of the study will assess the presence of islet autoimmunity, as well as the magnitude and kinetics of the innate and adaptive immune response at enrollment and during longitudinal follow-up after 1 or more episodes of AP. Finally, DREAM will evaluate the relationship between immune features, DM development, and pancreatitis etiology and severity.

Distinct myeloid antigen presenting cells dictate differential fates of tumor-specific CD8 T cells in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDA) contains numerous protumor myeloid cells at the expense of antitumor dendritic cells (cDC1s). We identify that tumor antigenicity is a major determinant of myeloid composition and functionality. Neoantigen-tumors contained pro-tumor macrophages and a paucity of cDC1s whereas neoantigen+ tumors accumulate cDC1s via Xcr1 signaling and macrophages exhibit a diminished role. Effective immunotherapies increased splenic cDC1s, which were required for endogenous T cell expansion following α-PD-L1 and transferred effector and memory T cells. Batf3−/− mice, which lack cDC1s, failed to spontaneously generate tumor-specific CD8 T cells and were resistant to T cell therapy and α-PD-L1. In contrast, agonistic α-CD40 exhibited partial benefit in Batf3−/− mice and expanded atypical tumor-specific CD8 T cells. Monocyte depletion abrogated atypical tumor-specific CD8 T cell priming yet enhanced α-CD40-mediated antitumor activity in Batf3−/− mice. In contrast, α-Gr1 abrogated the therapeutic benefit of CD40 agonist in Batf3−/− mice. In sum, our study supports that CD40 agonist promotes a cDC1-dependent antitumor immunity and a monocyte-dependent protumor arm of immune system. These results further underscore an essential antigen presenting role for cDC1s in the expansion and differentiation of naïve, effector, and memory T cells into Klrg1+ potent cytotoxic effector T cells capable of targeting pancreatic cancer.

M.R. is supported by National Institutes of Health (NIH) T32 AI 007313 E.J.S. is supported by NIH T35 AI118620 I.M.S. is supported by NIH R01 CA249393, R01 CA255039, Department of Defense #PA200286, an American Association for Cancer Research (AACR) Pancreatic Cancer Action Network Career Development Award (17-20-25-STRO), an AACR Pancreatic Cancer Action Network Catalyst Award (19-35-STRO), American Cancer Society Institutional Research Grant (124166-IRG-58-001-55-IRG65).

CD4+ T cells targeting a hybrid insulin:chromogranin A self-antigen are necessary and sufficient for autoimmune diabetes initiation

Autoimmune diabetes induction requires CD4+ T cell responses directed against pancreatic islet self-antigens, and recent evidence implicates insulin C-chain:chromogranin A (InsC-ChgA) hybrid peptides as critical targets. Despite suggested contributions of InsC-ChgA-specific CD4+ T cells to diabetes pathology, the mechanisms underlying antigen encounter and pathogenicity are not understood. Here, we demonstrate these cells are absent in pancreata of adult diabetes-resistant mice, yet undergo rapid activation and expansion in neonatal non-obese diabetic (NOD) mice. InsC-ChgA-specific cells were clonally restricted to a public TRBV15 CDR3 sequence paired with shared α-chains in multiple mice, and the expansion of these cells was dependent upon early interactions with XCR1+ type 1 conventional dendritic cells. We also demonstrate pathogenicity upon transfer of InsC-ChgA-specific cells into NOD.Rag1−/− mice and disease abrogation with therapeutic administration of an anti-InsC-ChgA:I-Ag7 monoclonal antibody. Most importantly, this antibody prevents spontaneous diabetes. Together, these data establish the pathogenicity of InsC-ChgA-specific cells, demonstrating sufficiency and necessity for autoimmune diabetes.

Supported by grants from NIH (R01 AI156276, P01 AI35296, 2T32 AI007313)

Distinct myeloid antigen-presenting cells dictate differential fates of tumor-specific CD8+ T cells in pancreatic cancer

We investigate how myeloid subsets differentially shape immunity to pancreatic ductal adenocarcinoma (PDA). We show that tumor antigenicity sculpts myeloid cell composition and functionality. Antigenicity promotes accumulation of type 1 dendritic cells (cDC1), which is driven by Xcr1 signaling, and overcomes macrophage-mediated suppression. The therapeutic activity of adoptive T cell therapy or programmed cell death ligand 1 blockade required cDC1s, which sustained splenic Klrg1+ cytotoxic antitumor T cells and functional intratumoral T cells. KLRG1 and cDC1 genes correlated in human tumors, and PDA patients with high intratumoral KLRG1 survived longer than patients with low intratumoral KLRG1. The immunotherapy CD40 agonist also required host cDC1s for maximal therapeutic benefit. However, CD40 agonist exhibited partial therapeutic benefit in cDC1-deficient hosts and resulted in priming of tumor-specific yet atypical CD8+ T cells with a regulatory phenotype and that failed to participate in tumor control. Monocyte/macrophage depletion using clodronate liposomes abrogated T cell priming yet enhanced the antitumor activity of CD40 agonist in cDC1-deficient hosts via engagement of innate immunity. In sum, our study supports that cDC1s are essential for sustaining effective antitumor T cells and supports differential roles for cDC1s and monocytes/macrophages in instructing T cell fate and immunotherapy response.

Enhanced CD4+ and CD8+ T cell infiltrate within convex hull defined pancreatic islet borders as autoimmune diabetes progresses

The notion that T cell insulitis increases as type 1 diabetes (T1D) develops is unsurprising, however, the quantitative analysis of CD4+ and CD8+ T cells within the islet mass is complex and limited with standard approaches. Optical microscopy is an important and widely used method to evaluate immune cell infiltration into pancreatic islets of Langerhans for the study of disease progression or therapeutic efficacy in murine T1D. However, the accuracy of this approach is often limited by subjective and potentially biased qualitative assessment of immune cell subsets. In addition, attempts at quantitative measurements require significant time for manual analysis and often involve sophisticated and expensive imaging software. In this study, we developed and illustrate here a streamlined analytical strategy for the rapid, automated and unbiased investigation of islet area and immune cell infiltration within (insulitis) and around (peri-insulitis) pancreatic islets. To this end, we demonstrate swift and accurate detection of islet borders by modeling cross-sectional islet areas with convex polygons (convex hulls) surrounding islet-associated insulin-producing β cell and glucagon-producing α cell fluorescent signals. To accomplish this, we used a macro produced with the freeware software ImageJ equipped with the Fiji Is Just ImageJ (FIJI) image processing package. Our image analysis procedure allows for direct quantification and statistical determination of islet area and infiltration in a reproducible manner, with location-specific data that more accurately reflect islet areas as insulitis proceeds throughout T1D. Using this approach, we quantified the islet area infiltrated with CD4+ and CD8+ T cells allowing statistical comparison between different age groups of non-obese diabetic (NOD) mice progressing towards T1D. We found significantly more CD4+ and CD8+ T cells infiltrating the convex hull-defined islet mass of 13-week-old non-diabetic and 17-week-old diabetic NOD mice compared to 4-week-old NOD mice. We also determined a significant and measurable loss of islet mass in mice that developed T1D. This approach will be helpful for the location-dependent quantitative calculation of islet mass and cellular infiltration during T1D pathogenesis and can be combined with other markers of inflammation or activation in future studies.

The Role of Programmed Death-1 in Type 1 Diabetes

PURPOSE OF REVIEW

Programmed death-1 (PD-1) is an inhibitory receptor that controls T and B cell proliferation and function through interacting with its ligand PD-L1 or PD-L2. PD-1/PD-L1 blockade reboots anti-tumor immunity and is currently used to treat > 15 different types of cancer. However, the response rate is not at 100% and some patients relapse. Importantly, up to 37% of patients treated with PD-1/PD-L1 blocking antibodies develop immune-related adverse events, including overt autoimmunity, such as type 1 diabetes (T1D). Herein, we discuss the role of PD-1, PD-L1, and PD-L2 signaling in pre-clinical models of T1D, including recent work from our laboratory.

RECENT FINDINGS

We highlight ongoing efforts to harness PD-1/PD-L1 signaling and treat autoimmunity. We also evaluate studies aimed at defining biomarkers that could reliably predict the development of immune-related adverse events after clinical PD-1/PD-L1 blockade. With increasing use of PD-1 blockade in the clinic, onset of autoimmunity is a growing health concern. In this review, we discuss what is known about the role of PD-1 pathway signaling in T1D and comment on ongoing efforts to identify patients at risk of T1D development after PD-1 pathway blockade.

Repeated dermal application of the common preservative methylisothiazolinone triggers local inflammation, T cell influx, and prolonged mast cell-dependent tactile sensitivity in mice

Occupational exposure to toxic chemicals increases the risk of developing localized provoked vulvodynia—a prevalent, yet poorly understood, chronic condition characterized by sensitivity to touch and pressure, and accumulation of mast cells in painful tissues. Here, we topically sensitized female ND4 Swiss mice to the common household and industrial preservative methylisothiazolinone (MI) and subsequently challenged them daily with MI or acetone and olive oil vehicle on the labiar skin. MI-challenged mice developed significant, persistent tactile sensitivity and long-lasting local accumulation of mast cells alongside early, transient increases in CD4⁺ and CD8⁺ T cells, eosinophils, neutrophils, and increases in pro-inflammatory cytokines. Therapeutic administration of imatinib, a c-Kit inhibitor known to inhibit mast cell survival, led to reduced mast cell accumulation and alleviated tactile genital pain. We provide the first pre-clinical evidence of dermal MI-induced mast-cell dependent pain and lay the groundwork for detailed understanding of these intersections between MI-driven immunomodulation and chronic pain.

Limited proliferation capacity of aortic intima resident macrophages requires monocyte recruitment for atherosclerotic plaque progression

Early atherosclerosis depends upon responses by immune cells resident in the intimal aortic wall. Specifically, the healthy intima is thought to be populated by vascular dendritic cells (DCs) that, during hypercholesterolemia, initiate atherosclerosis by being the first to accumulate cholesterol. Whether these cells remain key players in later stages of disease is unknown. Using murine lineage-tracing models and gene expression profiling, we reveal that myeloid cells present in the intima of the aortic arch are not DCs but instead specialized aortic intima resident macrophages (Mac^AIR) that depend upon colony-stimulating factor 1 and are sustained by local proliferation. Although Mac^AIR comprise the earliest foam cells in plaques, their proliferation during plaque progression is limited. After months of hypercholesterolemia, their presence in plaques is overtaken by recruited monocytes, which induce Mac^AIR-defining genes. These data redefine the lineage of intimal phagocytes and suggest that proliferation is insufficient to sustain generations of macrophages during plaque progression.

Adoptive T Cell Therapy with IL-12-Preconditioned Low-Avidity T Cells Prevents Exhaustion and Results in Enhanced T Cell Activation, Enhanced Tumor Clearance, and Decreased Risk for Autoimmunity

Optimal ex vivo expansion protocols of tumor-specific T cells followed by adoptive cell therapy must yield T cells able to home to tumors and effectively kill them. Our previous study demonstrated ex vivo activation in the presence of IL-12-induced optimal CD8⁺ T cell expansion and melanoma regression; however, adverse side effects, including autoimmunity, can occur. This may be due to transfer of high-avidity self-specific T cells. In this study, we compared mouse low- and high-avidity T cells targeting the tumor Ag tyrosinase-related protein 2 (TRP2). Not surprisingly, high-avidity T cells provide superior tumor control, yet low-avidity T cells can promote tumor regression. The addition of IL-12 during in vitro expansion boosts low-avidity T cell responsiveness, tumor regression, and prevents T cell exhaustion. In this study, we demonstrate that IL-12-primed T cells are resistant to PD-1/PD-L1-mediated suppression and retain effector function. Importantly, IL-12 preconditioning prevented exhaustion as LAG-3, PD-1, and TOX were decreased while simultaneously increasing KLRG1. Using intravital imaging, we also determined that high-avidity T cells have sustained contacts with intratumoral dendritic cells and tumor targets compared with low-avidity T cells. However, with Ag overexpression, this defect is overcome, and low-avidity T cells control tumor growth. Taken together, these data illustrate that low-avidity T cells can be therapeutically beneficial if cocultured with IL-12 cytokine during in vitro expansion and highly effective in vivo if Ag is not limiting. Clinically, low-avidity T cells provide a safer alternative to high-avidity, TCR-engineered T cells, as IL-12-primed, low-avidity T cells cause less autoimmune vitiligo.

Development of canine PD-1/PD-L1 specific monoclonal antibodies and amplification of canine T cell function

Interruption of the programmed death 1 (PD-1) / programmed death ligand 1 (PD-L1) pathway is an established and effective therapeutic strategy in human oncology and holds promise for veterinary oncology. We report the generation and characterization of monoclonal antibodies specific for canine PD-1 and PD-L1. Antibodies were initially assessed for their capacity to block the binding of recombinant canine PD-1 to recombinant canine PD-L1 and then ranked based on efficiency of binding as judged by flow cytometry. Selected antibodies were capable of detecting PD-1 and PD-L1 on canine tissues by flow cytometry and Western blot. Anti-PD-L1 worked for immunocytochemistry and anti-PD-1 worked for immunohistochemistry on formalin-fixed paraffin embedded canine tissues, suggesting the usage of this antibody with archived tissues. Additionally, anti-PD-L1 (JC071) revealed significantly increased PD-L1 expression on canine monocytes after stimulation with peptidoglycan or lipopolysaccharide. Together, these antibodies display specificity for the natural canine ligand using a variety of potential diagnostic applications. Importantly, multiple PD-L1-specific antibodies amplified IFN-γ production in a canine peripheral blood mononuclear cells (PBMC) concanavlin A (Con A) stimulation assay, demonstrating functional activity.

CD8 T cell immunosurveillance and elimination of HIV target cells in the female reproductive tract

HIV infection is thought to establish in a single founder CD4 T cell in the genital mucosa, however, an effective CD8 T cell-based vaccine must enable timely surveillance of all mucosal CD4 T cells within the first few days after HIV exposure. The HVTN 502 (STEP) vaccine trial employed a CD8 T cell based vaccine that while promising in animal studies, did not protect human vaccinees from mucosal HIV acquisition. We hypothesize that the quantity of mucosal HIV-specific CD8 T cells is a critical determinant of tissue immunosurveillance and was insufficient to adequately survey and eliminate HIV target cells in the STEP trial. To test our hypothesis, we applied intravital mucosal imaging to visualize how efficiently CD8 T cells survey CD4 T cells in the murine uterus. Based on CD8-CD4 T cell contact rates, a density of 4 (0.8%) HIV-specific mucosal CD8 T cells/mm2 would be required to survey all mucosal CD4 T cells within 2 days. However, vaccinees in the STEP trial had ELISPOT readings of ≥55 spot-forming units/106 blood leucocytes or approximately 0.09% mucosal HIV-specific CD8 T cells, which is 10 fold lower than the required density. Surveillance efficiency was directly correlated with the number of CD8 T cells and was independent of target cell numbers. Upon antigen recognition in the context of MHC-I on CD4 T cells, CD8 T cells formed kinapses with CD4 T cells in an LFA-1/ICAM-1 dependent manner, facilitating tethering and prolonged tracking. Direct killing of CD4 T cells by single or multiple CD8 T cells occurred by 3h after antigen presentation. We conclude that CD8 T cells are capable of rapid tissue surveillance and killing of CD4 T cell targets, and that sub-optimal numbers of HIV-specific CD8 T cells may have contributed to the failure of the STEP trial.

Interstitial Migration of CD8αβ T Cells in the Small Intestine Is Dynamic and Is Dictated by Environmental Cues

The migratory capacity of adaptive CD8αβ T cells dictates their ability to locate target cells and exert cytotoxicity, which is the basis of immune surveillance for the containment of microbes and disease. The small intestine (SI) is the largest mucosal surface and is a primary site of pathogen entrance. Using two-photon laser scanning microscopy, we found that motility of antigen (Ag)-specific CD8αβ T cells in the SI is dynamic and varies with the environmental milieu. Pathogen-specific CD8αβ T cell movement differed throughout infection, becoming locally confined at memory. Motility was not dependent on CD103 but was influenced by micro-anatomical locations within the SI and by inflammation. CD8 T cells responding to self-protein were initially affected by the presence of self-Ag, but this was altered after complete tolerance induction. These studies identify multiple factors that affect CD8αβ T cell movement in the intestinal mucosa and show the adaptability of CD8αβ T cell motility.

Type 1 diabetes pathogenesis and the role of inhibitory receptors in islet tolerance

Type 1 diabetes (T1D) affects over a million Americans, and disease incidence is on the rise. Despite decades of research, there is still no cure for this disease. Exciting beta cell replacement strategies are being developed, but in order for such approaches to work, targeted immunotherapies must be designed. To selectively halt the autoimmune response, researchers must first understand how this response is regulated and which tolerance checkpoints fail during T1D development. Herein, we discuss the current understanding of T1D pathogenesis in humans, genetic and environmental risk factors, presumed roles of CD4+ and CD8+ T cells as well as B cells, and implicated autoantigens. We also highlight studies in non-obese diabetic mice that have demonstrated the requirement for CD4+ and CD8+ T cells and B cells in driving T1D pathology. We present an overview of central and peripheral tolerance mechanisms and comment on existing controversies in the field regarding central tolerance. Finally, we discuss T cell- and B cell-intrinsic tolerance mechanisms, with an emphasis on the roles of inhibitory receptors in maintaining islet tolerance in humans and in diabetes-prone mice, and strategies employed to date to harness inhibitory receptor signaling to prevent or reverse T1D.

Long-term surviving influenza infected cells evade CD8+ T cell mediated clearance

Influenza A virus (IAV) is a seasonal pathogen with the potential to cause devastating pandemics. IAV infects multiple epithelial cell subsets in the respiratory tract, eliciting damage to the lungs. Clearance of IAV is primarily dependent on CD8+ T cells, which must balance control of the infection with immunopathology. Using a virus expressing Cre recombinase to permanently label infected cells in a Cre-inducible reporter mouse, we previously discovered infected club cells that survive both lytic virus replication and CD8+ T cell-mediated clearance. In this study, we demonstrate that ciliated epithelial cells, type I and type II alveolar cells can also become survivor cells. Survivor cells are stable in the lung long-term and demonstrate enhanced proliferation compared to uninfected cells. When we investigated how survivor cells evade CD8+ T cell killing we observed that survivor cells upregulated the inhibitory ligand PD-L1, but survivor cells did not use PD-L1 to evade CD8+ T cell killing. Instead our data suggest that survivor cells are not inherently resistant to CD8+ T cell killing, but instead no longer present IAV antigen and cannot be detected by CD8+ T cells. Finally, we evaluate the failure of CD8+ T cells to kill these previously infected cells. This work demonstrates that additional cell types can survive IAV infection and that these cells robustly proliferate and are stable long term. By sparing previously infected cells, the adaptive immune system may be minimizing pathology associated with IAV infection.

Programmed Death-1 Restrains the Germinal Center in Type 1 Diabetes

Programmed death-1 (PD-1) inhibits T and B cell function upon ligand binding. PD-1 blockade revolutionized cancer treatment, and although numerous patients respond, some develop autoimmune-like symptoms or overt autoimmunity characterized by autoantibody production. PD-1 inhibition accelerates autoimmunity in mice, but its role in regulating germinal centers (GC) is controversial. To address the role of PD-1 in the GC reaction in type 1 diabetes, we used tetramers to phenotype insulin-specific CD4⁺ T and B cells in NOD mice. PD-1 or PD-L1 deficiency, and PD-1 but not PD-L2 blockade, unleashed insulin-specific T follicular helper CD4⁺ T cells and enhanced their survival. This was concomitant with an increase in GC B cells and augmented insulin autoantibody production. The effect of PD-1 blockade on the GC was reduced when mice were treated with a mAb targeting the insulin peptide:MHC class II complex. This work provides an explanation for autoimmune side effects following PD-1 pathway inhibition and suggests that targeting the self-peptide:MHC class II complex might limit autoimmunity arising from checkpoint blockade.

Tetrahydrocannabinol Reduces Hapten-Driven Mast Cell Accumulation and Persistent Tactile Sensitivity in Mouse Model of Allergen-Provoked Localized Vulvodynia

Vulvodynia is a remarkably prevalent chronic pain condition of unknown etiology. An increase in numbers of vulvar mast cells often accompanies a clinical diagnosis of vulvodynia and a history of allergies amplifies the risk of developing this condition. We previously showed that repeated exposures to oxazolone dissolved in ethanol on the labiar skin of mice led to persistent genital sensitivity to pressure and a sustained increase in labiar mast cells. Here we sensitized female mice to the hapten dinitrofluorobenzene (DNFB) dissolved in saline on their flanks, and subsequently challenged them with the same hapten or saline vehicle alone for ten consecutive days either on labiar skin or in the vaginal canal. We evaluated tactile ano-genital sensitivity, and tissue inflammation at serial timepoints. DNFB-challenged mice developed significant, persistent tactile sensitivity. Allergic sites showed mast cell accumulation, infiltration of resident memory CD8⁺CD103⁺ T cells, early, localized increases in eosinophils and neutrophils, and sustained elevation of serum Immunoglobulin E (IgE). Therapeutic intra-vaginal administration of Δ⁹-tetrahydrocannabinol (THC) reduced mast cell accumulation and tactile sensitivity. Mast cell-targeted therapeutic strategies may therefore provide new ways to manage and treat vulvar pain potentially instigated by repeated allergenic exposures.

Increased β-cell proliferation before immune cell invasion prevents progression of type 1 diabetes

Type 1 diabetes (T1D) is characterized by pancreatic islet infiltration by autoreactive immune cells and a near-total loss of β-cells¹. Restoration of insulin-producing β-cells coupled with immunomodulation to suppress the autoimmune attack has emerged as a potential approach to counter T1D^2-4. Here we report that enhancing β-cell mass early in life, in two models of female NOD mice, results in immunomodulation of T-cells, reduced islet infiltration and lower β-cell apoptosis, that together protect them from developing T1D. The animals displayed altered β-cell antigens, and islet transplantation studies showed prolonged graft survival in the NOD-LIRKO model. Adoptive transfer of splenocytes from the NOD-LIRKOs prevented development of diabetes in pre-diabetic NOD mice. A significant increase in the splenic CD4⁺CD25⁺FoxP3⁺ regulatory T-cell (Treg) population was observed to underlie the protected phenotype since Treg depletion rendered NOD-LIRKO mice diabetic. The increase in Tregs coupled with activation of TGF-β/SMAD3 signaling pathway in pathogenic T-cells favored reduced ability to kill β-cells. These data support a previously unidentified observation that initiating β-cell proliferation, alone, prior to islet infiltration by immune cells alters the identity of β-cells, decreases pathologic self-reactivity of effector cells and increases Tregs to prevent progression of T1D.

TCR Affinity Biases Th Cell Differentiation by Regulating CD25, Eef1e1, and Gbp2

Naive CD4⁺ T lymphocytes differentiate into various Th cell subsets following TCR binding to microbial peptide:MHC class II (p:MHCII) complexes on dendritic cells (DCs). The affinity of the TCR interaction with p:MHCII plays a role in Th differentiation by mechanisms that are not completely understood. We found that low-affinity TCRs biased mouse naive T cells to become T follicular helper (Tfh) cells, whereas higher-affinity TCRs promoted the formation of Th1 or Th17 cells. We explored the basis for this phenomenon by focusing on IL-2R signaling, which is known to promote Th1 and suppress Tfh cell differentiation. SIRP⍺⁺ DCs produce abundant p:MHCII complexes and consume IL-2, whereas XCR1⁺ DCs weakly produce p:MHCII but do not consume IL-2. We found no evidence, however, of preferential interactions between Th1 cell-prone, high-affinity T cells and XCR1⁺ DCs or Tfh cell-prone, low-affinity T cells and SIRP⍺⁺ DCs postinfection with bacteria expressing the peptide of interest. Rather, high-affinity T cells sustained IL-2R expression longer and expressed two novel Th cell differentiation regulators, Eef1e1 and Gbp2, to a higher level than low-affinity T cells. These results suggest that TCR affinity does not influence Th cell differentiation by biasing T cell interactions with IL-2-consuming DCs, but instead, directly regulates genes in naive T cells that control the differentiation process.

The vimentin intermediate filament network restrains regulatory T cell suppression of graft-versus-host disease

Regulatory T cells (Tregs) are critical for maintaining immune homeostasis. However, current Treg immunotherapies do not optimally treat inflammatory diseases in patients. Understanding the cellular processes that control Treg function may allow for the augmentation of therapeutic efficacy. In contrast to activated conventional T cells, in which protein kinase C-θ (PKC-θ) localizes to the contact point between T cells and antigen-presenting cells, in human and mouse Tregs, PKC-θ localizes to the opposite end of the cell in the distal pole complex (DPC). Here, using a phosphoproteomic screen, we identified the intermediate filament vimentin as a PKC-θ phospho target and show that vimentin forms a DPC superstructure on which PKC-θ accumulates. Treatment of mouse Tregs with either a clinically relevant PKC-θ inhibitor or vimentin siRNA disrupted vimentin and enhanced Treg metabolic and suppressive activity. Moreover, vimentin-disrupted mouse Tregs were significantly better than controls at suppressing alloreactive T cell priming in graft-versus-host disease (GVHD) and GVHD lethality, using a complete MHC-mismatch mouse model of acute GVHD (C57BL/6 donor into BALB/c host). Interestingly, vimentin disruption augmented the suppressor function of PKC-θ-deficient mouse Tregs. This suggests that enhanced Treg activity after PKC-θ inhibition is secondary to effects on vimentin, not just PKC-θ kinase activity inhibition. Our data demonstrate that vimentin is a key metabolic and functional controller of Treg activity and provide proof of principle that disruption of vimentin is a feasible, translationally relevant method to enhance Treg potency.

Interferon-gamma drives programmed death-ligand 1 expression on islet β cells to limit T cell function during autoimmune diabetes

Type 1 diabetes is caused by autoreactive T cell-mediated β cell destruction. Even though co-inhibitory receptor programmed death-1 (PD-1) restrains autoimmunity, the expression and regulation of its cognate ligands on β cell remains unknown. Here, we interrogated β cell-intrinsic programmed death ligand-1 (PD-L1) expression in mouse and human islets. We measured a significant increase in the level of PD-L1 surface expression and the frequency of PD-L1+ β cells as non-obese diabetic (NOD) mice aged and developed diabetes. Increased β cell PD-L1 expression was dependent on T cell infiltration, as β cells from Rag1-deficient mice lacked PD-L1. Using Rag1-deficient NOD mouse islets, we determined that IFN-γ promotes β cell PD-L1 expression. We performed analogous experiments using human samples, and found a significant increase in β cell PD-L1 expression in type 1 diabetic samples compared to type 2 diabetic, autoantibody positive, and non-diabetic samples. Among type 1 diabetic samples, β cell PD-L1 expression correlated with insulitis. In vitro experiments with human islets from non-diabetic individuals showed that IFN-γ promoted β cell PD-L1 expression. These results suggest that insulin-producing β cells respond to pancreatic inflammation and IFN-γ production by upregulating PD-L1 expression to limit self-reactive T cells.

Programmed death-1 restrains the germinal center reaction in type 1 diabetes

Programmed death-1 (PD-1) is a T cell inhibitory receptor important for tolerance maintenance. PD-1 deficiency or blockade accelerates autoimmune diabetes in non-obese diabetic (NOD) mice, but the mechanism remains unclear. Autoantibody production is a hallmark of autoimmunity, and has also been reported in patients treated with PD-1 blockade, suggesting that PD-1 might regulate this process. Autoantibody production results from B cell:CD4 T cell interactions in the germinal center of the lymph node. The dynamics and regulation of the germinal center response in spontaneous autoimmunity and in the face of PD-1 deprivation are not well understood, primarily due to an inability to track self-specific lymphocytes. To bridge this knowledge gap, we used tetramers to phenotype islet-specific CD4 T cells and B cells in mice. PD-1-deficient mice, and NOD mice treated with anti-PD-1, had increased insulin autoantibodies, as well as increased insulin-specific germinal center T follicular helper CD4 T cells and germinal center B cells compared to controls. This work provides a mechanistic explanation for autoantibody onset following PD-1 blockade in the clinic, and has important implications for cancer immunotherapy and autoimmunity.

TCR affinity influences helper T cell differentiation by biasing dendritic cell interactions

Naïve CD4+ T lymphocytes differentiate into various subsets when their TCRs detect microbial peptide-MHCII complexes presented by dendritic cells. However, the mechanism by which TCR signaling influences differentiation is unknown. We found that low affinity TCRs biased naïve T cells to become B cell helpers while high affinity TCRs promoted the phagocyte helper fate. We created software for high-throughput, multicolor, quantitative imaging called Chrysalis to determine if differentiation was influenced by the type of dendritic cell that the naïve T cell interacted with. Our results show that T cells with high affinity TCRs had prolonged interactions with XCR1+ dendritic cells and tended to become phagocyte helpers, while T cells with lower affinity TCRs preferentially interacted with SIRPα+ dendritic cells and tended to become B cell helpers. Thus, TCR affinity influences T cell differentiation by dictating interactions with distinct dendritic cell types.

ST8Sia6 attenuates diabetes progression and severity

Nearly 1.25 million Americans suffer from type 1 diabetes, an autoimmune disease which destroys insulin-producing beta cells of the pancreatic islets. Although insulin therapy is a lifesaving treatment, it is not a cure and secondary complications remain a significant concern. Experimental islet transplantation as a curative measure has yet to overcome the barrier of immune-mediated destruction, as patients eventually revert back to insulin-dependency. Immunotherapies to date have focused on targeting the adaptive immune response, largely ignoring the innate immune system, and have had limited success. Siglec-E is an inhibitory receptor expressed on innate immune cells such as macrophages and dendritic cells; it is known to dampen inflammation through several mechanisms. Here, we demonstrate that the sialic acid transferase ST8Sia6, which catalyzes addition of a2,8-linked disialic acids to glycoproteins, produces cell surface ligands for Siglec-E. We selectively expressed ST8Sia6 in pancreatic beta cells, hypothesizing this would have a beneficial effect in delaying disease in the murine multiple low-dose streptozocin model of diabetes. We observe that when diabetes is induced, mice that express ST8Sia6 in beta cells have delayed onset of diabetes and less severe hyperglycemia as compared to littermate controls. Notably, expression of ST8Sia6 in beta cells does not interfere with normal glucose response. Therefore, ST8Sia6 expression in pancreatic beta cells is safe and attenuates diabetes progression and severity. Because cell surface glycans play a major role in recognition of self, this work has significance in islet-targeted gene therapy, transplantation, and graft survival.

T Cells in Nonlymphoid Tissues Give Rise to Lymph-Node-Resident Memory T Cells

Immunosurveillance of secondary lymphoid organs (SLO) is performed by central memory T cells that recirculate through blood. Resident memory T (Trm) cells remain parked in nonlymphoid tissues and often stably express CD69. We recently identified Trm cells within SLO, but the origin and phenotype of these cells remains unclear. Using parabiosis of "dirty" mice, we found that CD69 expression is insufficient to infer stable residence of SLO Trm cells. Restimulation of nonlymphoid memory CD8+ T cells within the skin or mucosa resulted in a substantial increase in bona fide Trm cells specifically within draining lymph nodes. SLO Trm cells derived from emigrants from nonlymphoid tissues and shared some transcriptional and phenotypic signatures associated with nonlymphoid Trm cells. These data indicate that nonlymphoid cells can give rise to SLO Trm cells and suggest vaccination strategies by which memory CD8+ T cell immunosurveillance can be regionalized to specific lymph nodes.

Intravital mucosal imaging of CD8+ resident memory T cells shows tissue-autonomous recall responses that amplify secondary memory

CD8⁺ T cell immunosurveillance dynamics influence the outcome of intracellular infections and cancer. Here we used two-photon intravital microscopy to visualize the responses of CD8⁺ resident memory T cells (T_RM cells) within the reproductive tracts of live female mice. We found that mucosal T_RM cells were highly motile, but paused and underwent in situ division after local antigen challenge. T_RM cell reactivation triggered the recruitment of recirculating memory T cells that underwent antigen-independent T_RM cell differentiation in situ. However, the proliferation of pre-existing T_RM cells dominated the local mucosal recall response and contributed most substantially to the boosted secondary T_RM cell population. We observed similar results in skin. Thus, T_RM cells can autonomously regulate the expansion of local immunosurveillance independently of central memory or proliferation in lymphoid tissue.

Cutting Edge: Allograft Rejection Is Associated with Weak T Cell Responses to Many Different Graft Leukocyte-Derived Peptides

Organ transplants are rapidly rejected because T cells in the recipient attack the foreign MHC molecules on the graft. The robustness of the T cell response to histoincompatible tissue is not understood. We found that mice have many small T cell populations with Ag receptors specific for a foreign MHC class II molecule type loaded with peptides from leukocytes from the graft. These T cells proliferated modestly after skin transplantation and underwent relatively weak functional differentiation compared with T cells stimulated by a vaccine. Thus, the potency of the T cell response to histoincompatible tissue is likely due to many small T cell populations responding weakly to hundreds of MHC-bound peptides from graft-derived leukocytes.

Increased Effector Memory Insulin-Specific CD4+ T Cells Correlate With Insulin Autoantibodies in Patients With Recent-Onset Type 1 Diabetes

Type 1 diabetes (T1D) results from T cell-mediated destruction of insulin-producing β-cells. Insulin represents a key self-antigen in disease pathogenesis, as recent studies identified proinsulin-responding T cells from inflamed pancreatic islets of organ donors with recent-onset T1D. These cells respond to an insulin B-chain (InsB) epitope presented by the HLA-DQ8 molecule associated with high T1D risk. Understanding insulin-specific T-cell frequency and phenotype in peripheral blood is now critical. We constructed fluorescent InsB_10-23:DQ8 tetramers, stained peripheral blood lymphocytes directly ex vivo, and show DQ8⁺ patients with T1D have increased tetramer⁺ CD4⁺ T cells compared with HLA-matched control subjects without diabetes. Patients with a shorter disease duration had higher frequencies of insulin-reactive CD4⁺ T cells, with most of these cells being antigen experienced. We also demonstrate that the number of insulin tetramer⁺ effector memory cells is directly correlated with insulin antibody titers, suggesting insulin-specific T- and B-cell interactions. Notably, one of four control subjects with tetramer⁺ cells was a first-degree relative who had insulin-specific cells with an effector memory phenotype, potentially representing an early marker of T-cell autoimmunity. Our results suggest that studying InsB_10-23:DQ8 reactive T-cell frequency and phenotype may provide a biomarker of disease activity in patients with T1D and those at risk.

Programmed Death-1 Culls Peripheral Accumulation of High-Affinity Autoreactive CD4 T Cells to Protect against Autoimmunity

Self-reactive CD4 T cells are incompletely deleted during thymic development, and their peripheral seeding highlights the need for additional safeguards to avert autoimmunity. Here, we show an essential role for the coinhibitory molecule programmed death-1 (PD-1) in silencing the activation of high-affinity autoreactive CD4 T cells. Each wave of self-reactive CD4 T cells that escapes thymic deletion autonomously upregulates PD-1 to maintain self-tolerance. By tracking the progeny derived from individual autoreactive CD4 T cell clones, we demonstrate that self-reactive cells with the greatest autoimmune threat and highest self-antigen affinity express the most PD-1. Reciprocally, PD-1 deprivation unleashes high-affinity self-reactive CD4 T cells in target tissues to exacerbate neuronal inflammation and autoimmune diabetes. Reliance on PD-1 to actively maintain self-tolerance may explain why exploiting this pathway by cancerous cells and invasive microbes efficiently subverts protective immunity, and why autoimmune side effects can develop after PD-1-neutralizing checkpoint therapies.

Landscape review of current HIV 'kick and kill' cure research - some kicking, not enough killing

BACKGROUND

Current antiretroviral therapy (ART) used to treat human immunodeficiency virus (HIV) patients is life-long because it only suppresses de novo infections. Recent efforts to eliminate HIV have tested the ability of a number of agents to reactivate ('Kick') the well-known latent reservoir. This approach is rooted in the assumption that once these cells are reactivated the host's immune system itself will eliminate ('Kill') the virus. While many agents have been shown to reactivate large quantities of the latent reservoir, the impact on the size of the latent reservoir has been negligible. This suggests that the immune system is not sufficient to eliminate reactivated reservoirs. Thus, there is a need for more emphasis on 'kill' strategies in HIV cure research, and how these might work in combination with current or future kick strategies.

METHODS

We conducted a landscape review of HIV 'cure' clinical trials using 'kick and kill' approaches. We identified and reviewed current available clinical trial results in human participants as well as ongoing and planned clinical trials. We dichotomized trials by whether they did not include or include a 'kill' agent. We extracted potential reasons why the 'kill' is missing from current 'kick and kill' strategies. We subsequently summarized and reviewed current 'kill' strategies have entered the phase of clinical trial testing in human participants and highlighted those with the greatest promise.

RESULTS

The identified 'kick' trials only showed promise on surrogate measures activating latent T-cells, but did not show any positive effects on clinical 'cure' measures. Of the 'kill' agents currently being tested in clinical trials, early results have shown small but meaningful proportions of participants remaining off ART for several months with broadly neutralizing antibodies, as well as agents for regulating immune cell responses. A similar result was also recently observed in a trial combining a conventional 'kick' with a vaccine immune booster ('kill').

CONCLUSION

While an understanding of the efficacy of each individual component is crucial, no single 'kick' or 'kill' agent is likely to be a fully effective cure. Rather, the solution is likely found in a combination of multiple 'kick and kill' interventions.

Cutting Edge: Dual TCRα Expression Poses an Autoimmune Hazard by Limiting Regulatory T Cell Generation

Despite accounting for 10-30% of the T cell population in mice and humans, the role of dual TCR-expressing T cells in immunity remains poorly understood. It has been hypothesized that dual TCR T cells pose an autoimmune hazard by allowing self-reactive TCRs to escape thymic selection. We revisited this hypothesis using the NOD murine model of type 1 diabetes. We bred NOD mice hemizygous at both TCRα and β (TCRα^+/- β^+/-) loci, rendering them incapable of producing dual TCR T cells. We found that the lack of dual TCRα expression skewed the insulin-specific thymocyte population toward greater regulatory T (T_reg) cell commitment, resulting in a more tolerogenic T_reg to conventional T cell ratio and protection from diabetes. These data support a novel hypothesis by which dual TCR expression can promote autoimmunity by limiting agonist selection of self-reactive thymocytes into the T_reg cell lineage.

T cell progenitor therapy-facilitated thymopoiesis depends upon thymic input and continued thymic microenvironment interaction

Infusion of in vitro-derived T cell progenitor (proT) therapy with hematopoietic stem cell transplant aids the recovery of the thymus damaged by total body irradiation. To understand the interaction between proTs and the thymic microenvironment, WT mice were lethally irradiated and given T cell-deficient (Rag1-/-) marrow with WT in vitro-generated proTs, limiting mature T cell development to infused proTs. ProTs within the host thymus led to a significant increase in thymic epithelial cells (TECs) by day 21 after transplant, increasing actively cycling TECs. Upon thymus egress (day 28), proT TEC effects were lost, suggesting that continued signaling from proTs is required to sustain TEC cycling and cellularity. Thymocytes increased significantly by day 21, followed by a significant improvement in mature T cell numbers in the periphery by day 35. This protective surge was temporary, receding by day 60. Double-negative 2 (DN2) proTs selectively increased thymocyte number, while DN3 proTs preferentially increased TECs and T cells in the spleen that persisted at day 60. These findings highlight the importance of the interaction between proTs and TECs in the proliferation and survival of TECs and that the maturation stage of proTs has unique effects on thymopoiesis and peripheral T cell recovery.

Visualizing antigen-specific CD8 T cell dynamics in the small intestine

The small intestine (SI) represents the largest mucosal barrier between the environment and the host. As such, the SI limits both normal and pathogenic microbe invasion and must balance immune tolerance and activation. CD8ab T cells constitute a dominant lymphocyte population in the SI and contribute to both of these processes but detailed investigation into their in situ behavior in response to various stimuli is lacking. We visualized Ag-specific CD8 T cell migration in the SI using two-photon microscopy to understand CD8 T cell immunosurveillance. We found that pathogen-specific CD8 T cells are initially slowed early after infection but regain motility directly after Ag clearance. At a memory time point, CD8 T cells exhibited slower migration concurrent with acquisition of a resident memory phenotype. Current studies are focused on determining what is required for CD8 T cell motility throughout the course of infection. Additionally, as tolerance reversal and expansion of self-specific CD8 T cells has recently become a focus of cancer therapy, we characterized in situ behavior of self-specific CD8 T cells. Using a mouse expressing a model Ag in the SI as a self-protein, we observed self-specific CD8 T cells before and after tolerance reversal. Tolerant CD8 T cells migrate significantly faster than pathogen-specific cells at acute time points after infection. Contrastingly, ex-tolerant CD8 T cells were comparable to pathogen-specific CD8 T cells indicating that indeed their in situ scanning behavior had been altered upon tolerance reversal. These observations have provided valuable insight into CD8 T cell motility within the SI and can inform targeted treatment options and vaccines to ensure effective immunosurveillance of this tissue.

The role of programmed death-1 in regulating islet-specific CD4 T cells

The inhibitory receptor programmed death (PD)-1 and its ligand PD-L1 negatively regulate T cell function. PD-1 blockade is used in the clinic to reinvigorate anti-tumor immunity. However, patients often experience autoimmune-like symptoms, or develop autoimmunity, including type 1 diabetes. We used peptide:MHC Class II tetramers to track islet-specific CD4 T cells in diabetes-prone (NOD) mice and ask how PD-1 regulated this population. We found that insulin-specific cells with the highest affinity for cognate antigen expressed the most PD-1. In turn, PD-1 blockade promoted the accumulation of high-affinity cells in the pancreas, and exacerbated diabetes. Given that 70% of insulin-specific cells are anergic, we investigated whether PD-1 was required for the maintenance of anergic state, using an adoptive cell transfer model. Anergic cells remained functionally blunted in comparison to effector cells after anti-PD-L1 treatment, suggesting that anergy maintenance depends on other signaling pathways. This work highlights how the differentiation status of a T cell may predetermine its susceptibility to PD-1 blockade, and has implications for cancer immunotherapy and autoimmunity.

Dual TCRα expression alters agonist selection, redirecting Treg-biased insulin-specific thymocytes into the conventional T cell lineage

Despite accounting for ~10% of the T cell population in mice and humans, the role of dual TCR-expressing T cells in immunity remains poorly understood. It has been hypothesized that dual TCR T cells pose an “autoimmune hazard” by allowing self-reactive TCRs to escape negative selection. We revisited this hypothesis using the non-obese diabetic (NOD) mouse model of type 1 diabetes (T1D). We bred NOD mice hemizygous at both TCRα and β (TCRα+/− β+/−) loci, rendering them incapable of producing dual TCR T cells. We found that NOD mice lacking dual TCRα expression were resistant to developing diabetes resulting from an increased insulin-specific Treg:Tconv ratio. Furthermore, early depletion of CD25-expressing cells was sufficient to induce diabetes in single TCR T cell NOD mice demonstrating that these mice are capable of developing diabetes and that Treg cells are responsible for their observed resistance to diabetes. Further investigation uncovered a previously-unrecognized impact of dual TCRα expression on agonist selection. Specifically, we found in single TCR T cell mice that single positive (SP) thymocytes had a higher Treg:CD4 ratio indicating increased Treg commitment, that insulin-specific thymocytes exhibited higher CD5 expression suggesting increased TCR signaling, and that deletion of SP thymocytes was reduced. Altogether these data demonstrate that dual TCRα expression perturbs agonist selection of the insulin-specific thymocyte subset, resulting in skewing of this population toward the diabetogenic conventional CD4+ T cell lineage and away from the regulatory T cell lineage. Thus, dual TCR expression can promote autoimmunity by reducing the ratio of protective Treg cells to pathogenic T cells.

Visualizing mucosal resident memory CD8 T cell reactivation dynamics reveals in situ division and bystander resident memory T cell development

CD8 T cells survey tissues for the presence of abnormal cells. The parameters of CD8 T cell search patterns and immunosurveillance determines outcome of infections and cancer (elimination, controlled persistence, or death). We established a two-photon intravital microscopy model to visualize resident memory CD8 T cell (TRM) behavior and recall responses within the female reproductive tract (FRT) mucosa of living mice. Unlike what has been described in skin epidermis, FRT TRM were highly motile (10 μm/min). Local antigen recognition induced pausing and initiation of in situ TRM division, and this appeared CD4 T cell and dendritic cell independent. Expansion by dividing TRM dominated the local recall response compared to recruitment of recirculating cells or progeny of reactivated central memory T cells. TRM reactivation also triggered recruitment of Ag-specific and bystander recirculating memory cells, and these underwent a de novo TRM differentiation program in situ. These results demonstrate that 1) T cell migration patterns and differentiation may be permanently altered by unrelated infectious experience, 2) that cognate antigen within the FRT is not required to induce local TRM differentiation, 3) TRM undergo in situ division upon recall that 4) may dominate the local secondary effector and memory response.

T Cell-Mediated Beta Cell Destruction: Autoimmunity and Alloimmunity in the Context of Type 1 Diabetes

Type 1 diabetes (T1D) results from destruction of pancreatic beta cells by T cells of the immune system. Despite improvements in insulin analogs and continuous blood glucose level monitoring, there is no cure for T1D, and some individuals develop life-threatening complications. Pancreas and islet transplantation have been attractive therapeutic approaches; however, transplants containing insulin-producing cells are vulnerable to both recurrent autoimmunity and conventional allograft rejection. Current immune suppression treatments subdue the immune system, but not without complications. Ideally a successful approach would target only the destructive immune cells and leave the remaining immune system intact to fight foreign pathogens. This review discusses the autoimmune diabetes disease process, diabetic complications that warrant a transplant, and alloimmunity. First, we describe the current understanding of autoimmune destruction of beta cells including the roles of CD4 and CD8 T cells and several possibilities for antigen-specific tolerance induction. Second, we outline diabetic complications necessitating beta cell replacement. Third, we discuss transplant recognition, potential sources for beta cell replacement, and tolerance-promoting therapies under development. We hypothesize that a better understanding of autoreactive T cell targets during disease pathogenesis and alloimmunity following transplant destruction could enhance attempts to re-establish tolerance to beta cells.

Programmed death ligand-1 expression on donor T cells drives graft-versus-host disease lethality

Programmed death ligand-1 (PD-L1) interaction with PD-1 induces T cell exhaustion and is a therapeutic target to enhance immune responses against cancer and chronic infections. In murine bone marrow transplant models, PD-L1 expression on host target tissues reduces the incidence of graft-versus-host disease (GVHD). PD-L1 is also expressed on T cells; however, it is unclear whether PD-L1 on this population influences immune function. Here, we examined the effects of PD-L1 modulation of T cell function in GVHD. In patients with severe GVHD, PD-L1 expression was increased on donor T cells. Compared with mice that received WT T cells, GVHD was reduced in animals that received T cells from Pdl1-/- donors. PD-L1-deficient T cells had reduced expression of gut homing receptors, diminished production of inflammatory cytokines, and enhanced rates of apoptosis. Moreover, multiple bioenergetic pathways, including aerobic glycolysis, oxidative phosphorylation, and fatty acid metabolism, were also reduced in T cells lacking PD-L1. Finally, the reduction of acute GVHD lethality in mice that received Pdl1-/- donor cells did not affect graft-versus-leukemia responses. These data demonstrate that PD-L1 selectively enhances T cell-mediated immune responses, suggesting a context-dependent function of the PD-1/PD-L1 axis, and suggest selective inhibition of PD-L1 on donor T cells as a potential strategy to prevent or ameliorate GVHD.

Efficient generation of monoclonal antibodies against peptide in the context of MHCII using magnetic enrichment

Monoclonal antibodies specific for foreign antigens, auto-antigens, allogeneic antigens and tumour neo-antigens in the context of major histocompatibility complex II (MHCII) are highly desirable as novel immunotherapeutics. However, there is no standard protocol for the efficient generation of monoclonal antibodies that recognize peptide in the context of MHCII, and only a limited number of such reagents exist. In this report, we describe an approach for the generation and screening of monoclonal antibodies specific for peptide bound to MHCII. This approach exploits the use of recombinant peptide:MHC monomers as immunogens, and subsequently relies on multimers to pre-screen and magnetically enrich the responding antigen-specific B cells before fusion and validation, thus saving significant time and reagents. Using this method, we have generated two antibodies enabling us to interrogate antigen presentation and T-cell activation. This methodology sets the standard to generate monoclonal antibodies against the peptide–MHCII complexes.

Generating antibodies specific for the peptide–MHCII complexes has been challenging, with only a handful made to date. Here, the authors develop a more efficient approach to generate these antibodies, and demonstrate their potential in research and therapeutic applications.

Absence of dual TCR T cells protects NOD mice from diabetes due to an increased insulin-specific Treg:Teff ratio

Due to allelic exclusion, most αβ T cells express only a single αβ TCR specificity. However, around 10% of human and mouse T cells express two different α chains with the potential for dual specificities. Dual β-expressing T cells also exist and account for ~1% of all T cells. Expression of two different TCR specificities by a single T cell is one hypothesized mechanism by which self-reactive TCRs escape central tolerance to initiate autoimmunity. While peripheral tolerance mechanisms typically control any self-reactive T cells in healthy animals, these mechanisms are hypo-functional in NOD mice. We hypothesized that eliminating dual TCR T cells would protect NOD mice from diabetes. To test this hypothesis we generated NOD mice hemizygous at both the TCRα and β loci (TCRα+/−β+/−). Indeed, we found that NOD mice incapable of generating dual TCR T cells were protected from diabetes with both lower diabetes incidence than wildtype (WT) NOD mice (0% versus 70% at 30 weeks of age) and also lower insulitis scores at 10 weeks of age. Examination of the insulin-specific T cell population in the pancreas-draining lymph node revealed a lower Treg:Teff ratio in WT NOD mice compared to single TCR T cell NOD mice. Anti-PD-1 treatment resulted in the rapid development of diabetes in 100% of WT NOD mice but in only 30% of single TCR T cell mice, suggesting that the diabetes resistance phenotype of single TCR T cell mice is not primarily due to increased anergy. These data support the hypothesis that the presence of dual TCR T cells increases the risk of diabetes in NOD mice by altering the insulin-specific Treg:Teff ratio.

Protein Kinase C-θ and vimentin modulate multiple facets of Regulatory T-cell function

Regulatory T-cells (Tregs) prevent autoimmune and alloimmune reactions. Augmenting Treg function may enhance Treg therapies for these diseases. Treg-specific inhibition of protein kinase C-theta (PKC-θ) enhances Treg function. However, it is unclear whether PKC-θ inhibition can boost Treg function in systemic inflammatory conditions.

In a mouse model of acute GVHD, we found that Tregs treated with the PKC-θ inhibitor AEB071 reduced GVHD mortality and severity significantly better than DMSO treated Tregs. Compared to DMSO, AEB071 treated Tregs significantly reduced conventional T-cells (Tcon) proliferation on D4 after transplant. Multi-photon microscopy showed that AEB071 treated Tregs significantly increased Tcon velocity and displacement compared to DMSO.

Mechanistically, AEB071 augments expression of Neuropilin-1 (Nrp1) and Lymphocyte activation gene 3 (Lag3). Antibody blockade of Nrp1 and Lag3 in transwell suppression assays reduced the effect of AEB071 on Treg function. PKC-θ inhibition also reduces phosphorylation of mTORC2 targets FoxO3a and Akt phospho-site S473, but not mTORC1 targets S6, 4E-BP1 or Akt phospho-site T308. Compared to DMSO, AEB071 treatment significantly increased fatty acid uptake and oxygen consumption rate (OCR).

Phosphoproteomic analysis identified a significant alteration in the interaction between PKC-θ and the intermediate filament vimentin after AEB071 treatment, which was confirmed by confocal. Vimentin siRNA treatment also significantly reduces PKC-θ/vimentin interaction, increases Treg function, Nrp1 expression and OCR.

In summary, PKC-θ and vimentin modulate multiple aspects of Treg function, and altering these molecules may enhance the efficacy of Treg therapeutics.

Specific patterns of self-antigen expression determine the mechanisms by which polyclonal self-reactive CD4+ T cells are tolerized

Understanding how self-tolerance is maintained requires the ability to track rare, self-reactive T cells of known specificity in normal individuals. However, due to technical limitations much of our knowledge has relied on the study of T cell receptor transgenic cells that recognize model antigens. While this work has identified numerous modes of tolerance, it is unclear which mechanisms operate in normally diverse repertoires and how this decision is made. We studied polyclonal CD4+ T cells specific for an epitope from green fluorescent protein (GFP) in fourteen different mouse strains that express GFP under the control of tissue-specific promoters. We found that clonal deletion was the key tolerance mechanism for self-antigens that were uniformly expressed by thymic antigen-presenting cells. In contrast, self-antigens that were absent from the thymus were ignored. A more complex form of tolerance regulated CD4+ T cells specific for self-antigens with limited expression by thymic antigen-presenting cells. These populations showed partial clonal deletion and impaired effector T cell potential but enhanced regulatory T cell potential of remaining cells. Furthermore, these tolerance mechanisms were also found to regulate CD4+ T cells specific for endogenously expressed self-antigens. Thus, self-antigen expression patterns dictate the tolerance mechanisms by which self-reactive polyclonal CD4+ T cells are regulated.

Phenotypic characterization of islet antigen-specific CD4 T cell subsets in mice of varying susceptibilities to Type 1 Diabetes

Type 1 diabetes (T1D) results from lymphocyte-mediated destruction of insulin-producing pancreatic beta cells. Islet-reactive CD4 T cells are critical mediators of disease. Here, we investigated the phenotype and regulation of insulin-specific and bulk CD4 T cells in diabetes-prone (NOD) and diabetes-resistant (NOR or B6.g7) mice. We utilized dual color tetramer staining with enriment techniques to enumerate and phenotype insulin-specific CD4 T cells in NOD, NOR and B6.g7 mice. To test whether there are inherent differences in the CD4 T cell compartment between the strains, we stimulated sorted CD4 T cells in vitro with αCD3/CD28 and performed transcriptional analysis of >40 targets. Additionally, we analyzed Th1/Th2/Th9/Th17/Th22/Treg cytokine production. Both insulin-specific CD4 T cells and bulk polyclonal CD4 T cells displayed a strong Th1 skewing in NOD and not in NOR or B6.g7 mice, indicating that different disease susceptibilities could be in part due to inherent differences in CD4 T cell activation. Experiments are underway to determine the transcriptional profile of insulin-specific CD4 T cells in these strains using an unbiased approach, and identify the peripheral tolerance mechanisms underlying diabetes resistance.

PD-1 pathway-mediated regulation of islet-specific CD4+ T cell subsets in autoimmune diabetes

Type 1 diabetes (T1D) is a CD4⁺ T cell-driven autoimmune disease resulting from the destruction of insulin-producing pancreatic beta cells. Clinical evidence and studies in non-obese diabetic (NOD) mice suggest that insulin is a major autoantigen. With this in mind, we developed insulin B_10-23:IA^g7 tetramer reagents to track insulin-specific CD4⁺ T cells in mice and interrogated the role of Programmed death-1 (PD-1) for peripheral tolerance. PD-1 is a T cell inhibitory receptor necessary to maintain tolerance and prevent T1D in NOD mice. PD-1 pathway inhibitors are increasingly used in the clinic for treating malignancies, and while many patients benefit, some develop adverse autoimmune events, including T1D. We therefore sought to understand the role of PD-1 in maintaining islet-specific tolerance in diabetes-resistant strains. B6.g7 mice express the same MHC Class II allele as NOD mice, have predominantly naïve insulin-specific CD4⁺ T cells in the periphery, and remain diabetes-free even after PD-1 pathway blockade. Here, we examined the trafficking potential of insulin-specific CD4⁺ T cells in NOD and B6.g7 mice with or without anti-PD-L1 treatment, and found that PD-L1 blockade preferentially increased the number of CD44^highCXCR3⁺ insulin-specific cells in NOD but not B6.g7 mice. Additionally, we investigated whether pancreatic islets in NOD and B6.g7 mice expressed CXCL10, a lymphocyte homing chemokine and ligand for CXCR3. Anti-PD-L1 treated and control NOD mice had detectable CXCL10 expression in the islets, while B6.g7 islets did not. These data suggest that islet tolerance may be in part attributed to the pancreatic environment and in the absence of pancreas inflammation, chemotactic cytokines may be missing. This, together with our previous data showing that PD-1 pathway blockade preferentially affects effector but not anergic self-specific T cells has implications for the use of checkpoint blockade in treating tumor patients. Our work suggests that determining tumor- and self-specific CD4⁺ T cell activation status (naïve, effector or anergic) prior to initiation of immunotherapy would likely help to stratify individuals who would benefit from this therapy versus those who might have adverse effects or incomplete tumor control.

Most microbe-specific naïve CD4⁺ T cells produce memory cells during infection

Infection elicits CD4(+) memory T lymphocytes that participate in protective immunity. Although memory cells are the progeny of naïve T cells, it is unclear that all naïve cells from a polyclonal repertoire have memory cell potential. Using a single-cell adoptive transfer and spleen biopsy method, we found that in mice, essentially all microbe-specific naïve cells produced memory cells during infection. Different clonal memory cell populations had different B cell or macrophage helper compositions that matched effector cell populations generated much earlier in the response. Thus, each microbe-specific naïve CD4(+) T cell produces a distinctive ratio of effector cell types early in the immune response that is maintained as some cells in the clonal population become memory cells.

CD4(+) T cell anergy prevents autoimmunity and generates regulatory T cell precursors

The role of anergy, an acquired state of T cell functional unresponsiveness, in natural peripheral tolerance remains unclear. In this study, we found that anergy was selectively induced in fetal antigen-specific maternal CD4(+) T cells during pregnancy. A naturally occurring subpopulation of anergic polyclonal CD4(+) T cells, enriched for self antigen-specific T cell antigen receptors, was also present in healthy hosts. Neuropilin-1 expression in anergic conventional CD4(+) T cells was associated with hypomethylation of genes related to thymic regulatory T cells (Treg cells), and this correlated with their ability to differentiate into Foxp3(+) Treg cells that suppressed immunopathology. Thus, our data suggest that not only is anergy induction important in preventing autoimmunity but also it generates the precursors for peripheral Treg cell differentiation.