Alloimmune Response Research Articles

The Impact of T-cell Aging on Alloimmunity and Inflammaging.

Aging affects immunity broadly through changes caused by immunosenescence, clinically resulting in augmented susceptibility to infections, autoimmunity, and cancer. The most striking alterations associated with immunosenescence have been observed in the T-cell compartment with a significant shift toward a terminally differentiated memory phenotype taking on features of innate immune cells. At the same time, cellular senescence impairs T-cell activation, proliferation, and effector functions, compromising the effectiveness of immunity. In clinical transplantation, T-cell immunosenescence has been the main driver of less frequent acute rejections in older transplant recipients. This patient population, at the same time, suffers more frequently from the side effects of immunosuppressive therapy including higher rates of infections, malignancies, and chronic allograft failure. T-cell senescence has also been identified as an instigator of age-specific organ dysfunction through a process that has been coined "inflammaging," accelerating organ injury and potentially contributing to the limited lifetime of organ transplants. Here, we provide a summary of the latest evidence on molecular characteristics of T-cell senescence affecting alloimmunity and organ quality while dissecting the consequences of unspecific organ injury and immunosuppression on T-cell senescence. Rather than conceptualizing immunosenescence as a broad and general "weaker" alloimmune response, it appears critical to understand both mechanisms and clinical effects in detail as a basis to refine treatment.

Targeting Cellular Senescence in Organ Transplantation.

Targeting Cellular Senescence in Organ Transplantation.

1729-P: Role of ß-Cell Senescence in Islet Transplantation

Islet transplantation (Tx) is an effective intervention to prevent severe hypoglycemia and provide insulin independence in type 1 diabetes (T1D). Previous studies have shown that islets from older donors are less effective in reversing blood glucose (BG) than those of younger ones. Cellular senescence leads to age-related β-cell dysfunction and drives alloimmune responses to organs from older donors, but can be targeted with senolysis. However, the mechanism of pancreatic β-cell senescence in transplant grafts and its pathological significance are unknown. Therefore, we performed two types of islet Tx to test the hypothesis that cellular senescence may play a role in loss of graft functionality/viability and that the use of senolysis may ameliorate it: 1) overnight cultured 600 IEQ islets from normoglycemic rats were transplanted into kidney capsule of streptozotocin-induced diabetic immunodeficient mice (Stz-Ms). After 2 weeks, the grafts were removed and compared with the cultured islets (control). In Stz-Ms, the nuclear exclusion rate of Hmgb1 and p21-positive cells tended to increase, and the mRNA levels of p16, Il-6, and β-cells related genes were significantly higher than in control islets indicating β-cell senescence after transplantation. To test if the elimination of p16 positive senescent β-cells from transplanted islets improved BG levels, 2) 440 IEQ islets from INK-ATTAC mice (p16Ink4a mediated apoptosis through targeted activation of caspase) were transplanted into Stz-Ms and treated intraperitoneally with BB Homodimerizer (BB) or vehicle for 2 terms of 3 consecutive days, of which 2 weeks of rest. With senolysis, there was a decrease in fed glucose levels and p16 mRNA expression while expression of hallmark β-cell genes increased by 74%, which correlates with improved response to high glucose. In conclusion, islet transplantation increases β-cell senescence in grafts and senolysis improves β-cell function. This has important implications in increasing graft function and survival in the treatment of T1D. Disclosure K.Iwasaki: None. P.Carapeto: None. C.Aguayo-mazzucato: None. Funding Manpei Suzuki Diabetes Foundation

Mesenchymal Stromal Cell Therapy in Lung Transplantation.

Lung transplantation is often the only viable treatment option for a patient with end-stage lung disease. Lung transplant results have improved substantially over time, but ischemia-reperfusion injury, primary graft dysfunction, acute rejection, and chronic lung allograft dysfunction (CLAD) continue to be significant problems. Mesenchymal stromal cells (MSC) are pluripotent cells that have anti-inflammatory and protective paracrine effects and may be beneficial in solid organ transplantation. Here, we review the experimental studies where MSCs have been used to protect the donor lung against ischemia-reperfusion injury and alloimmune responses, as well as the experimental and clinical studies using MSCs to prevent or treat CLAD. In addition, we outline ex vivo lung perfusion (EVLP) as an optimal platform for donor lung MSC delivery, as well as how the therapeutic potential of MSCs could be further leveraged with genetic engineering.

From support to therapy: rethinking the role of nutrition in acute graft-versus-host disease.

Allogeneic Hematopoietic stem cell transplantation (HSCT) offers a potential cure for patients with hematologic malignancies. Unfortunately, graft-versus-host disease (GVHD) remains a major obstacle to the greater success of this treatment. Despite intensive research efforts over the past several decades, GVHD is still a major cause of morbidity and mortality in patients receiving allogeneic HSCT. The genetic disparity between donor and recipient is the primary factor that dictates the extent of alloimmune response and the severity of acute GVHD (aGVHD). However, some nongenetic factors are also actively involved in GVHD pathogenesis. Thus, identifying host factors that can be readily modified to reduce GVHD risk is of important clinical significance. We are particularly interested in the potential role of nutrition, as a nongenetic factor, in the etiology and management of aGVHD. In this article, we summarize recent findings regarding how different routes of nutritional support and various dietary factors affect aGVHD. Since diet is one of the most important factors that shape gut microbiota, we also provide evidence for a potential link between certain nutrients and gut microbiota in recipients of allogeneic HSCT. We propose a shifting role of nutrition from support to therapy in GVHD by targeting gut microbiota.

Complement activation and kidney transplantation; a complex relationship

Although kidney transplantation is the best treatment for end stage kidney disease, the benefits are limited by factors such as the short fall in donor numbers, the burden of immunosuppression and graft failure. Although there have been improvements in one-year outcomes, the annual rate of graft loss beyond the first year has not significantly improved, despite better therapies to control the alloimmune response. There is therefore a need to develop alternative strategies to limit kidney injury at all stages along the transplant pathway and so improve graft survival. Complement is primarily part of the innate immune system, but is also known to enhance the adaptive immune response. There is increasing evidence that complement activation occurs at many stages during transplantation and can have deleterious effects on graft outcome. Complement activation begins in the donor and occurs again on reperfusion following a period of ischemia. Complement can contribute to the development of the alloimmune response and may directly contribute to graft injury during acute and chronic allograft rejection. The complexity of the relationship between complement activation and allograft outcome is further increased by the capacity of the allograft to synthesise complement proteins, the contribution complement makes to interstitial fibrosis and complement’s role in the development of recurrent disease. The better we understand the role played by complement in kidney transplant pathology the better placed we will be to intervene. This is particularly relevant with the rapid development of complement therapeutics which can now target different the different pathways of the complement system. Combining our basic understanding of complement biology with preclinical and observational data will allow the development and delivery of clinical trials which have best chance to identify any benefit of complement inhibition.

CTLA4-Ig alleviates the allogeneic immune responses against insulin-producing cells in a murine model of cell transplantation.

The adoptive transfer of insulin-producing cells (IPCs) is one of the promising treatments for insulin-dependent diabetes mellitus. While the use of allogeneic cell resources is inevitable in the case of a series of patients, alloimmune responses are a major barrier ahead of the successful implementation of allogeneic therapeutic cells. This study is aimed at evaluating the potential of CTLA4-Ig, as an approved immunomodulatory biologic, in protecting the IPCs against allogeneic immune responses. The C57BL/6 and BALB/c mice were used to establish a murine model of allogeneic cell transplantation. The mouse bone-marrow-derived mesenchymal stem cells were in vitro differentiated into IPCs, and the in vitro as well as the in vivo immune responses against IPCs were evaluated in the presence and absence of CTLA4-Ig. The allogeneic IPCs induced the in vitro activation of CD4+ T-cells, IFN-γ release, and the proliferation of lymphocytes, which all were controlled by CTLA4-Ig. Upon in vivo transfer of IPC into an allogeneic host, the splenic CD4+ and CD8+ T-cells exhibited a significant activation, and there was a significant donor-specific antibody response. Either of the mentioned cellular and humoral responses were modulated by a CTLA4-Ig regimen. This regimen also reduced the infiltration of CD3+ T-cells into the IPC injection site along with the improved overall survival of diabetic mice. CTLA4-Ig could be a complementary therapy for improving the efficacy of allogeneic IPC therapy through modulating the cellular and humoral responses that can lead to prolonged durability of IPCs within an allogeneic host.

Immediate major dynamic changes in the T- and NK-cell subset composition after cardiac transplantation.

Early kinetics of lymphocyte subsets involved in tolerance and rejection following heart transplantation (HTx) are barely defined. Here, we aimed to delineate the early alloimmune response immediately after HTx. Therefore, blood samples from 23 heart-transplanted patients were collected before (pre-), immediately (T0), 24 hours (T24), and 3 weeks (3wks) after HTx. Immunophenotyping was performed using flow cytometry. A significant increase was detected for terminally differentiated (TEMRA) CD4+ or CD8+ T cells and CD56dim CD16+ NK cells immediately after HTx linked to a decrease in naïve CD8+ and CM CD4+ T as well as CD56bright CD16- NK cells, returning to baseline levels at T24. More detailed analyses revealed increased CD69+ CD25- and diminished CD69- CD25- CD4+ or CD8+ T-cell proportions at T0 associated with decreasing S1PR1 expression. Passenger T and NK cells were found at low frequencies only in several patients at T0 and did not correlate with lymphocyte alterations. Collectively, these results suggest an immediate, transient shift toward memory T and NK cells following HTx. Opposite migratory properties of naïve versus memory T and NK cells occurring in the early phase after HTx could underlie these observations and may impinge on the development of allo-specific immune responses.

Assessment of donor compatibility in human solid organ transplantation and evaluation of allogeneic responses using a novel humanized mouse model.

Abstract The end result of solid organ transplantation is dictated by selection of a well-matched donor, leading to allograft survival. An allogeneic immune response is the main immunological barrier for successful organ transplantation. Donor and recipient human leukocyte antigen (HLA) mismatching results in poor graft acceptance, inflammation and rejection. The current evaluations for donor-recipient HLA incompatibility does not provide adequate information on the immunogenicity of individual HLA mismatches and impact of non-HLA-related alloantigens, especially in vivo. Here we demonstrate a novel method for analysis of alloimmune responsiveness between donor and recipient in vivoby introducing a humanized mouse model. Using molecular, cellular, and genomic analyses, we demonstrated that a recipient’s personalized humanized mouse provided the most sensitive assessment of allogeneic responsiveness to potential donors. In our study, HLA typing and mixed lymphocyte reaction (MLR) for assessment of allogeneic response was indistinguishable between 2 related donors of the recipient. Contrastingly in recipient’s humanized mouse model, the donor selected by HLA typing induced the strongest allogeneic response with increased infiltration of cytotoxic GzmB +CD8 +T cells. Moreover, the same donor induced upregulation of genes involved in the allograft rejection identified by transcriptomic analysis of graft infiltrating CD45 +cells. Humanized mouse model determined the lowest degree of recipient-donor alloimmune response, allowing for better selection of donor and minimized immunological risk of allograft rejection in transplantation. This approach can be used to evaluate alloresponses in cell based therapies as well. This study was supported by research funding from the Carlos and Marguerite Mason Trust, and by U.S. National Institutes of Health, National Cancer Institute Grant CA 172230

A new slow-releasing formulation of butyrate prolongs allograft survival

Abstract The microbiota consists of diverse microbes producing metabolites that can influence the immune system locally as well as systemically. These bioactive metabolites (postbiotics) have therapeutic potential and may prove useful to facilitate graft acceptance. Short-chain fatty acids (SCFA) promote intestinal homeostasis and have been linked to health and disease. The Hubbell-Nagler laboratories at the University of Chicago have developed a micelle-based platform that can deliver the SCFA butyrate systemically, with long-term retention and induction of tolerogenic responses. We hypothesized that the administration of this butyrate formulation will improve graft survival by suppressing the alloimmune response. Our preliminary data showed that only oral delivery of the butyrate formulation prolonged survival of a C57Bl/6 male to female minor-mismatched skin graft significantly, whereas sub-cutaneous and intra-peritoneal administration were ineffective. Improved graft survival was associated with diminished production of TNFα by splenic and skin-draining lymph node myeloid cells upon LPS stimulation, suggesting that butyrate modulates the myeloid compartment to reduce levels of pro-inflammatory cytokines. The postbiotic also enhanced survival of a BALB/c to C57Bl/6 major-mismatched skin graft, without the use of immunosuppressive drugs, and resulted in lower levels of donor-specific alloantibodies. Prolonging the administration of butyrate post-transplantation ameliorated graft survival even further, confirming the micelle-based platform has therapeutic potential. Current efforts focus on determining if the butyrate formulation drives myeloid cell polarization toward an anti-inflammatory phenotype. This project was supported by grant NIH/NIAID 2R01AI115716

Autoantibodies against DNA topoisomerase I promote renal allograft rejection by increasing alloreactive T cell responses

Antibodies reactive to self-antigens are an important component of posttransplant immune responses. The generation requirements and functions of autoantibodies, as well as the mechanisms of their influence on alloimmune responses, still remain to be determined. Our study investigated the contribution of autoimmunity during rejection of renal allografts. We have previously characterized a mouse model in which the acute rejection of a life-supporting kidney allograft is mediated by antibodies. At rejection, recipient sera screening against >4000 potential autoantigens revealed DNA topoisomerase I peptide 205-219 (TI-I205-219) as the most prominent epitope. Subsequent analysis showed TI-I205-219-reactive autoantibodies are induced in nonsensitized recipients of major histocompatibility complex–mismatched kidney allografts in a T cell–dependent manner. Immunization with TI-I205-219 broke self-tolerance, elicited TI-I205-219 immunoglobin G autoantibodies, and resulted in acute rejection of allogeneic but not syngeneic renal transplants. The graft loss was associated with increased priming of donor-reactive T cells but not with donor-specific alloantibodies elevation. Similarly, passive transfer of anti-TI-I205-219 sera following transplantation increased donor-reactive T cell activation with minimal effects on donor-specific alloantibody levels. The results identify DNA topoisomerase I as a novel self-antigen in transplant settings and demonstrate that autoantibodies enhance activation of donor-reactive T cells following renal transplantation.

Marginal zone B cells are responsible for the production of alloantibodies following platelet transfusion in mice.

Alloimmunization against platelets remains a potentially serious adverse transfusion event. Alloantibodies produced by the recipient, mainly directed against human leukocyte antigen class I donor antigens, can compromise the therapeutic efficacy of subsequent transfusions, and may lead to refractoriness. Because the mechanism of anti-HLA alloantibody formation is poorly understood, this study aimed to identify the cells involved in the platelet immune response by focusing on the spleen, the main organ that orchestrates this alloimmune response. In the spleen, transfused allogeneic platelets are located in the marginal zone and interact with marginal zone B (MZB) cells, a specialized B-cell population implicated in the capture and follicular delivery of blood-borne antigens. To study the involvement of MZB cells in alloantibody production, we used a murine model reproducing major histocompatibility complex incompatibility between a donor (H2b) and recipient (H2d) that occurs during platelet transfusion. Following weekly H2b platelet transfusions, recipient H2d mice produced anti-H2b immunoglobulin G, which induced a refractory state upon subsequent transfusions. Specific immunodepletion of MZB cells or their displacement from the marginal zone to the B-cell follicles by treatment with an S1P1 antagonist before each transfusion prevented significant alloantibody formation. Under these conditions, transfused platelets were still circulating after 24 hours, whereas they were rapidly removed from circulation in alloimmunized mice. The identification of MZB cells as key players in the plateletalloimmune response opens up new perspectives for minimizing plateletalloimmunization and avoiding the associated refractory state in frequently transfused patients.

Local Delivery of Adipose Stem Cells Promotes Allograft Survival in a Rat Hind-Limb Model of Vascularized Composite Allotransplantation.

Adipose stem cells (ASCs) are a promising cell-based immunotherapy because of their minimally invasive harvest, high yield, and immunomodulatory capacity. In this study, the authors investigated the effects of local versus systemic ASC delivery on vascularized composite allotransplant survival and alloimmune regulation. Lewis rats received hind-limb transplants from Brown Norway rats and were administered donor-derived ASCs (passage 3 or 4, 1 × 10 6 cells/rat) locally in the allograft, or contralateral limb, or systemically at postoperative day 1. Recipients were treated intraperitoneally with rabbit anti-rat lymphocyte serum on postoperative days 1 and 4 and daily tacrolimus for 21 days. Limb allografts were monitored for clinical signs of rejection. Donor cell chimerism, immune cell differentiation, and cytokine expression in recipient lymphoid organs were measured by flow cytometric analysis. The immunomodulation function of ASCs was tested by mixed lymphocyte reaction assay and ASC stimulation studies. Local-ASC-treated recipients achieved significant prolonged allograft survival (85.7% survived >130 days; n = 6) compared with systemic-ASC and contralateral-ASC groups. Secondary donor skin allografts transplanted to the local-ASC long-term surviving recipients accepted permanently without additional immunosuppression. The increases in donor cell chimerism and regulatory T-cells were evident in blood and draining lymph nodes of the local-ASC group. Moreover, mixed lymphocyte reaction showed that ASCs inhibited donor-specific T-cell proliferation independent of direct ASC-T-cell contact. ASCs up-regulated antiinflammatory molecules in response to cytokine stimulation in vitro. Local delivery of ASCs promoted long-term survival and modulated alloimmune responses in a full major histocompatibility complex-mismatched vascularized composite allotransplantation model and was more effective than systemic administration. ASCs are a readily available and abundant source of therapeutic cells that could decrease the amount of systemic immunosuppression required to maintain limb and face allografts.

Innate immune cellular therapeutics in transplantation.

Successful organ transplantation provides an opportunity to extend the lives of patients with end-stage organ failure. Selectively suppressing the donor-specific alloimmune response, however, remains challenging without the continuous use of non-specific immunosuppressive medications, which have multiple adverse effects including elevated risks of infection, chronic kidney injury, cardiovascular disease, and cancer. Efforts to promote allograft tolerance have focused on manipulating the adaptive immune response, but long-term allograft survival rates remain disappointing. In recent years, the innate immune system has become an attractive therapeutic target for the prevention and treatment of transplant organ rejection. Indeed, contemporary studies demonstrate that innate immune cells participate in both the initial alloimmune response and chronic allograft rejection and undergo non-permanent functional reprogramming in a phenomenon termed "trained immunity." Several types of innate immune cells are currently under investigation as potential therapeutics in transplantation, including myeloid-derived suppressor cells, dendritic cells, regulatory macrophages, natural killer cells, and innate lymphoid cells. In this review, we discuss the features and functions of these cell types, with a focus on their role in the alloimmune response. We examine their potential application as therapeutics to prevent or treat allograft rejection, as well as challenges in their clinical translation and future directions for investigation.

Uncovering a novel role of focal adhesion and interferon-gamma in cellular rejection of kidney allografts at single cell resolution.

Kidney transplant recipients are currently treated with nonspecific immunosuppressants that cause severe systemic side effects. Current immunosuppressants were developed based on their effect on T-cell activation rather than the underlying mechanisms driving alloimmune responses. Thus, understanding the role of the intragraft microenvironment will help us identify more directed therapies with lower side effects. To understand the role of the alloimmune response and the intragraft microenvironment in cellular rejection progression, we conducted a Single nucleus RNA sequencing (snRNA-seq) on one human non-rejecting kidney allograft sample, one borderline sample, and T-cell mediated rejection (TCMR) sample (Banff IIa). We studied the differential gene expression and enriched pathways in different conditions, in addition to ligand-receptor (L-R) interactions. Pathway analysis of T-cells in borderline sample showed enrichment for allograft rejection pathway, suggesting that the borderline sample reflects an early rejection. Hence, this allows for studying the early stages of cellular rejection. Moreover, we showed that focal adhesion (FA), IFNg pathways, and endomucin (EMCN) were significantly upregulated in endothelial cell clusters (ECs) of borderline compared to ECs TCMR. Furthermore, we found that pericytes in TCMR seem to favor endothelial permeability compared to borderline. Similarly, T-cells interaction with ECs in borderline differs from TCMR by involving DAMPS-TLRs interactions. Our data revealed novel roles of T-cells, ECs, and pericytes in cellular rejection progression, providing new clues on the pathophysiology of allograft rejection.

The evolving use of biomarkers in heart transplantation: Consensus of an expert panel

In heart transplantation, the use of biomarkers to detect the risk of rejection has been evolving. In this setting, it is becoming less clear as to what is the most reliable test or combination of tests to detect rejection and assess the state of the alloimmune response. Therefore, a virtual expert panel was organized in heart and kidney transplantation to evaluate emerging diagnostics and how they may be best utilized to monitor and manage transplant patients. This manuscript covers the heart content of the conference and is a work product of the American Society of Transplantation’s Thoracic and Critical Care Community of Practice. This paper reviews currently available and emerging diagnostic assays and defines the unmet needs for biomarkers in heart transplantation. Highlights of the in-depth discussions among conference participants that led to development of consensus statements are included. This conference should serve as a platform to further build consensus within the heart transplant community regarding the optimal framework to implement biomarkers into management protocols and to improve biomarker development, validation and clinical utility. Ultimately, these biomarkers and novel diagnostics should improve outcomes and optimize quality of life for our transplant patients.

Related donor platelet transfusion improves platelet transfusion refractoriness in hematological patients.

Transfusion of HLA-matched platelets can reduce the effect of alloimmune responses on platelet transfusion efficacy; however, finding HLA-matched platelets in the population is nearly impossible. Almost all HLA-matched platelets from related are half-matched, but the hemostatic efficacy of related donor platelets is unclear. Our goal was to compare the hemostatic effect of related donated platelets and unrelated donors platelets. In this retrospective cohort study, we included acute leukemia and myelodysplastic syndrome patients with thrombocytopenia after chemotherapy. These patients were all transfused with platelets. This study excluded patients younger than 16 years and older than 65 years, or patients with abnormal coagulation parameters during platelet transfusion. We compared the hemostatic effect of related donated platelets and unrelated donors platelet. The primary outcome was transfusion efficacy after platelet transfusion, and the number of platelet counts and corrected count increments at 24 h after platelet transfusion. We analyzed 31 patients who received platelet transfusions from related donors (Treatment group) and 35 patients who received platelet transfusions from unrelated donors (Comparator group). Except for the relatively small proportion of patients with myelodysplastic syndrome in the treatment group, baseline clinical and laboratory characteristics were similar between the two groups. Hemostasis and prevention of bleeding in the treatment group showed significant superiority; the number of platelets increased 24 h after platelet transfusion in the treatment group was significantly higher than that in the comparator group. After 24 h, the corrected count increments treatment group was also higher than the comparator group; in the treatment group, the transfusion effect was better when the three sites of HLA-A, B, and C were identical, and the different blood types of platelet donors and recipients did not affect the transfusion effect. Related donated platelets have better hemostasis and prevention effects, and no increase in adverse blood transfusion reactions. It may be a better transfusion strategy for platelet refractoriness patients in emergency situations.

Hubungan Usia Kehamilan, Riwayat Abortus Dan Paritas Terhadap Kejadian Preeklampsia Berat Di RSUD Abdoel Wahab Sjahranie Tahun 2022

Introduction : In 2021, Abdoel Wahab Sjahranie Hospital recorded a total of 55 pregnant mothers suffering from severe preeclampsia. Preeclampsia can be treated by controlling the risk factors it carries. This study examines the relationship between gestational age, prior miscarriage record, and parity which incited severe preeclampsia cases in Abdul Wahab Sjahranie Hospital.
 Method : This research is an observational analytical study with case control design. A total sample of 110 respondents was taken from medical record data in 2021. The PEB group sample was taken using total sampling and the control group was taken by quota sampling. The bivariate analysis was conducted with chi-square test.
 Results : From the test conducted, gestational age has Pvalue of 0.008 and odd ratio of 0.244 . In addition, prior miscarriage has Pvalue of 0.041 and odd ratio of 2.628. Lastly, parity has Pvalue of 0.038.
 Discussion : Growing and aging placenta with gestational age more than 34 weeks will limit intervillous perfusion which causes secondary syncytiotrophoblast stress and the release of placental factors into the maternal bloodstream, maternal alloimmune response to fetal trophoblasts resulting in miscarriage, and primiparous parity due to first-time exposure to chorionic villi, whereas the case in grandemultipara is associated with a decrease in the function of reproductive system and nutritional fulfillment which lead to preeclampsia.
 Conclusions : Early detection of preeclampsia requires a more complete diagnostic procedure and it is associated with maternal and neonatal morbidity.
 Keywords: Gestational Age, Prior Miscarriage, Parity, Preeclampsia

Inhibition of thrombin on endothelium enhances recruitment of regulatory T cells during IRI and when combined with adoptive Treg transfer, significantly protects against acute tissue injury and prolongs allograft survival.

Ischemia-reperfusion injury (IRI) amplifies T cell alloimmune responses after transplantation with thrombin playing a key pro-inflammatory role. To explore the influence of thrombin on regulatory T cell recruitment and efficacy we used a well-established model of IRI in the native murine kidney. Administration of the cytotopic thrombin inhibitor PTL060 inhibited IRI, and by skewing expression of chemokines (reducing CCL2 and CCL3 but increasing CCL17 and CCL22) increased the infiltration of M2 macrophages and Tregs. When PTL060 was combined with infusion of additional Tregs, these effects were further amplified. To test the benefits of thrombin inhibition in a transplant model, BALB/c hearts were transplanted into B6 mice with or without perfusion with PTL060 in combination with Tregs. Thrombin inhibition or Treg infusion alone led to small increments in allograft survival. However, the combined therapy led to modest graft prolongation by the same mechanisms as in renal IRI; graft survival was accompanied by increased numbers of Tregs and anti-inflammatory macrophages, and reduced expression of pro-inflammatory cytokines. While the grafts succumbed to rejection associated with the emergence of alloantibody, these data suggest that thrombin inhibition within the transplant vasculature enhances the efficacy of Treg infusion, a therapy that is currently entering the clinic to promote transplant tolerance.

Conventional type I migratory CD103+ dendritic cells are required for corneal allograft survival

Corneal transplant rejection primarily occurs because of the T helper 1 (Th1) effector cell-mediated immune response of the host towards allogeneic tissue. The evidence suggests that type 1 migratory conventional CD103+ dendritic cells (CD103+DC1) acquire an immunosuppressive phenotype in the tumor environment; however, the involvement of CD103+DC1 in allograft survival continues to be an elusive question of great clinical significance in tissue transplantation. In this study, we assess the role of CD103+DC1 in suppressing Th1 alloreactivity against transplanted corneal allografts. The immunosuppressive function of CD103+DC1 has been extensively studied in non-transplantation settings. We found that host CD103+DC1 infiltrates the corneal graft and migrates to the draining lymph nodes to suppress alloreactive CD4+ Th1 cells via the programmed death-ligand 1 axis. The systemic depletion of CD103+ DC1 in allograft recipients leads to amplified Th1 activation, impaired Treg function, and increased rate of allograft rejection. Although allograft recipient Rag1 null mice reconstituted with naïve CD4+CD25- T cells efficiently generated peripheral Treg cells (pTreg), the CD103+DC1-depleted mice failed to generate pTreg. Furthermore, adoptive transfer of pTreg failed to rescue allografts in CD103+DC1-depleted recipients from rejection. These data demonstrate the critical role of CD103+DC1 in regulating host alloimmune responses.