Skin Graft Rejection Research Articles

CD8 T Cells Target Antigen Cross-Presented by Bone Marrow Derived Cells to Induce Bystander Rejection of Grafts Lacking the Cognate Peptide-MHC

CD8 T cells play a key role in cancer immunotherapy and allograft rejection. However, it is not clear how they kill cells and tissues that do not have the agonist peptide-major histocompatibility complex (MHC) on their surface, as in the settings of MHC class I deficient tumors and indirect rejection of MHC-mismatched transplants. CD8 T cells might respond to agonist antigen cross-presented on hematopoietic cells, leading to a “bystander” rejection. Alternatively, they may recognize agonist antigen cross-presented on recipient endothelial cells and kill the tissue’s vital blood supply. The latter mechanism predicts that all non-vascularized grafts, grafts dependent on in-growth of recipient blood vessels, will be susceptible to CD8 T cell mediated indirect rejection. In contrast, we show here that non-vascularized transplants, bearing the same agonist antigen, are not universally susceptible to this rejection pathway. Non-vascularized skin, but not islet or heart tissue transplants were indirectly rejected by CD8 T cells. Furthermore, CD8 T cells were able to indirectly reject skin grafts when recipient MHC class I expression was restricted to bone marrow derived cells but not when it was restricted to radioresistant cells (e.g. endothelial cells). These findings argue against a major role for endothelial cell cross-presentation in killing of tissue that does not present the agonist peptide-MHC class I. Instead, the data suggests that cross-presentation by recipient hematopoietic cells underlies the CD8 T cell mediated killing of tissue that is unable to directly present the target peptide-MHC class I.

M−CSF and prostratin induced Mregs promote immune tolerance in transplanted mice through Arg-1 pathway

ObjectiveRegulatory macrophages (Mregs) are a group of heterogeneous macrophages. These cells could induce immunosuppressive effects through the expression of immune regulatory molecules and cytokines. MethodsThe differentiation of Mregs was induced by treating bone marrow cells with M−CSF and prostratin in vitro. The cell-phenotypes and immunosuppressive function were determined by flow cytometry. Rt-PCR was employed to assess the mechanisms of Mregs. Skin grafted mouse model was used for in vivo validation. ResultsMregs induced by M−CSF + prostratin had a strong inhibitory effect on T cell proliferation and cytokines production. The phenotype of induced bone marrow cells changed towards Mregs. These Mregs could induce the differentiation of Tregs in vivo. Arg-1 expression in these cells were significantly upregulated. Inhibition of arginase (Arg) or arginine supplement significantly reversed the immunosuppressive function. In mice skin-grafted models, adoptive transfer of these Mregs significantly prolonged allograft survival. In mice models, Arg-1 expression significantly elevated on skin grafts cells and Tregs increased in graft tissues. ConclusionsWe successfully developed a Mregs-inducing protocol with the combination of M−CSF and prostratin in vitro. M−CSF + prostratin induced Mregs prevented mice skin graft rejection through upregulating the expression Arg-1.

Inhibition of NLRC5 regulates cytokine expression in CD4+ T helper lymphocytes and prolongs murine islet and skin allograft survival

The purpose of this study was to study the effect of inhibiting NLRC5 expression and function on CD4 + T cells, and islet and skin transplantation in mice. A murine skin graft model and islet cell transplantation model were established, and the expression of NLRC5 was compared in rejection and immune tolerance groups. Mice spleen-derived CD4 + T cells were cultured, purified, and enriched in vitro, and transfected with the shRNA lentiviral vector NLRC5-RNAi-GFP. Changes in cytokine secretion were detected to understand changes in immunological function. Murine islet and skin transplantation models were injected with CD4 + T cells transfected with the lentivirus, and the survival time of the grafts and the levels of IFN-γ and IL-10 were compared between groups. The expression of NLRC5 mRNA in islet and skin grafts was significantly increased. In vitro experiments showed that the expression of IL-4 and IL-10 was up-regulated in CD4 + T cells, and T cells differentiation turned to Th2 after inhibition of NLRC5. In vivo experiments showed that inhibition of NLRC5 prolonged islet and skin graft survival. Pathological examination showed that the rejection of transplanted skin and islets in the NLRC5-RNAi group was mild, and there was a correlation between high expression of NLRC5 and rejection of mouse islet and skin grafts. In summary, inhibition of NLRC5 can prolong islet and skin graft survival induce transplant immune tolerance through induction of the secretion of Th2 cytokines by CD4 + T cells.

Cyclic Helix B Peptide Prolongs Skin Allograft Survival via Inhibition of B Cell Immune Responses in a Murine Model.

Antibody-mediated rejection (AMR) represents a major cause of allograft dysfunction and results in allograft failure in solid organ transplantation. Cyclic helix B peptide (CHBP) is a novel erythropoietin-derived peptide that ameliorated renal allograft rejection in a renal transplantation model. However, its effect on AMR remains unknown. This study aimed to investigate the effect of CHBP on AMR using a secondary allogeneic skin transplantation model, which was created by transplanting skin from BALB/c mice to C57BL/6 mice with or without CHBP treatment. A secondary syngeneic skin transplantation model, involving transplantation from C57BL/6 mice to C57BL/6 mice, was also created to act as a control. Skin graft rejection, CD19+ B cell infiltration in the skin allograft, the percentages of splenic plasma cells, germinal center (GC) B cells, and Tfh cells, the serum levels of donor specific antibodies (DSAs), and NF-κB signaling in splenocytes were analyzed. Skin allograft survival was significantly prolonged in the CHBP group compared to the allogeneic group. CHBP treatment also significantly reduced the CD19+ B cell infiltration in the skin allograft, decreased the percentages of splenic plasma cells, GC B cells, and Tfh cells, and ameliorated the increase in the serum DSA level. At a molecular level, CHBP downregulated P100, RelB, and P52 in splenocytes. CHBP prolonged skin allograft survival by inhibiting AMR, which may be mediated by inhibition of NF-κB signaling to suppress B cell immune responses, thereby decreasing the DSA level.

DNA-PKcs Inhibition Extends Allogeneic Skin Graft Survival

Abstract Background: Organ transplantation is life-saving and continued investigations into immunological mechanisms that drive organ rejection are needed to improve immunosuppression therapies and prevent graft failure. DNA-dependent protein kinase catalytic subunit, DNA-PKcs, is a critical component of both the cellular and humoral immune responses. In this study, we investigate the contribution of DNA-PKcs to allogeneic skin graft rejection to potentially highlight a novel strategy for inhibiting transplant rejection. Methods: Fully MHC mismatched murine allogeneic skin graft studies were performed by transplanting skin from BalbC mice to C57bl6 mice and treating with either vehicle or the DNA-PKcs inhibitor NU7441. Graft rejection, cytokine production, immune cell infiltration, and donor-specific antibody (DSA) formation were analyzed. Results: DNA-PKcs inhibition significantly reduced necrosis and extended graft survival compared to controls (mean survival 14 days vs 9 days respectively). Inhibition reduced the production of the cytokines Interleukin (IL)2, IL4, IL6, IL10, TNFα, and IFNγ and the infiltration of CD3+ lymphocytes into grafts. Furthermore, DNA-PKcs inhibition reduced the number of CD19+ B cells and CD19+ CD138+ plasma cells coinciding with a significant reduction in DSAs. At a molecular level, we determined that the immunosuppressive effects of DNA-PKcs inhibition were mediated, in part, via inhibition of NFκB signaling through reduced expression of the p65 subunit. Conclusion: Our data confirm that DNA-PKcs contributes to allogeneic graft rejection and highlight a novel immunological function for DNA-PKcs in the regulation of NFκB and concomitant cytokine production.

DNA-PKcs Inhibition Extends Allogeneic Skin Graft Survival.

Organ transplantation is life-saving and continued investigations into immunologic mechanisms that drive organ rejection are needed to improve immunosuppression therapies and prevent graft failure. DNA-dependent protein kinase catalytic subunit, DNA dependent-protein kinase catalytic subunit (DNA-PKcs), is a critical component of both the cellular and humoral immune responses. In this study, we investigate the contribution of DNA-PKcs to allogeneic skin graft rejection to potentially highlight a novel strategy for inhibiting transplant rejection. Fully MHC mismatched murine allogeneic skin graft studies were performed by transplanting skin from BalbC mice to C57bl6 mice and treating with either vehicle or the DNA-PKcs inhibitor NU7441. Graft rejection, cytokine production, immune cell infiltration, and donor-specific antibody formation were analyzed. DNA-PKcs inhibition significantly reduced necrosis and extended graft survival compared with controls (mean survival 14 d versus 9 d, respectively). Inhibition reduced the production of the cytokines interleukin (IL)-2, IL-4, IL-6, IL-10, TNF-α, and IFN-γ and the infiltration of CD3+ lymphocytes into grafts. Furthermore, DNA-PKcs inhibition reduced the number of CD19+ B cells and CD19+ CD138+ plasma cells coinciding with a significant reduction in donor-specific antibodies. At a molecular level, we determined that the immunosuppressive effects of DNA-PKcs inhibition were mediated, in part, via inhibition of nuclear factor kappa-light-chain-enhancer of activated B cells signaling through reduced expression of the p65 subunit. Our data confirm that DNA-PKcs contributes to allogeneic graft rejection and highlight a novel immunologic function for DNA-PKcs in the regulation of nuclear factor kappa-light-chain-enhancer of activated B cells and concomitant cytokine production.

CTLA4-Ig prolongs graft survival specifically in young but not old mice.

Elderly organ transplant recipients have remained underrepresented in clinical trials, despite representing a rapidly growing population. Here, we assessed age-specific effects of CTLA4-Ig (cytotoxic T-lymphocyte antigen 4-Ig), a fusion protein blocking costimulatory signaling between antigen-presenting cells and T cells through CD28. Cardiac allografts in young mice (2-3months) treated with CTLA4-Ig survived indefinitely, whereas 80% of old recipients (18months) had lost their graft after 100days. CTLA4-Ig was also significantly less effective in older recipients of skin transplants. CTLA4-Ig reduced CD4+ central memory and effector memory T cells and diminished systemic interferon-gamma levels only in young recipients. These differences corresponded to a reduced expression of CD28 on antigen-experienced CD4+ T cells in old mice. In support, adoptive transfer of old CD4+ T cells that were transfected with a lentiviral vector inducing constant expression of CD28 accelerated the rejection of allogeneic skin grafts in young RAG2-/- recipient mice. Regulatory T cells (Tregs), in contrast, demonstrated an increased expression of CD28 with aging and CTLA4-Ig treatment in old recipients resulted in reduced frequencies, compromised proliferation, and diminished suppressive capacity of Tregs. These findings may prove to have unique clinical consequences for immunosuppression in the growing population of elderly transplant recipients.

CTLA-4-IG PROLONGS GRAFT SURVIVAL SPECIFICALLY IN YOUNG BUT NOT IN OLD RECIPIENTS

Introduction: The proportion of older transplant recipients has increased dramatically. Age-specific effects of established immunosuppressants are poorly understood. Here, we assessed the impact of CTLA4-Ig, a fusion protein blocking costimulatory signaling between APCs and T cells through CD28. We hypothesized that the immunosuppressive capacity of CTLA4-Ig will depend on an age-specific expression of CD28 on alloreactive T-cells. Methods: Heart and skin grafts from young DBA2/J mice were transplanted into either young or old (2-3 and 18 mths, resp.) allogeneic C57BL/6 recipients treated with CTLA4-Ig or PBS; T-cell frequencies and subsets in addition to cytokine expression were assessed by flow cytometry and ELISA; expression of CD28 was assessed on young and old T-cell subsets. To delineate the age-specific immunosuppressive potential of CTL4-Ig, T-cells were transfected with a lentiviral vector inducing CD28 expression; transfected T-cells were subsequently transferred into young RAG2-/- mice receiving a fully mismatched skin graft. Results: Treatment with CTLA4-Ig prolonged skin graft survival only in young (p<0.01) but not in old recipients (p=0.33). Age-specific immunosuppressive effects of CTLA4-Ig were also confirmed in a SOT model: cardiac allografts in young mice treated with CTLA4-Ig survived indefinitely. In contrast, 80% of old recipients treated with CTLA4-Ig had lost their graft by 100 days. CTLA4-Ig reduced CD4+ central-memory and effector-memory T cells and diminished systemic IFN-γ levels only in young (p<0.05), but not old recipients (p=0.8). These differences correlated with a reduced expression of CD28 on antigen-experienced CD4+ T cells in old mice (p<0.001). Interestingly, Tregs displayed an increased expression of CD28 with age making them more prone to be targeted by CTLA4-Ig. Strikingly, adoptive transfer of old CD4+ T cells that were transfected with a lentiviral vector augmenting the expression of CD28 accelerated the rejection of allogeneic skin grafts in young RAG2-/- recipient mice (p<0.01 vs. controls animals that received adoptively transferred, non-transfected old T cells) demonstrating the cardinal role of CD28 expression on alloreactive CD4+ T cells. Conclusion: Immunosuppressive effects of CTLA4-Ig showed distinct age-dependent effects in both skin and cardiac transplantation linked to a reduced CD28 expression of alloreactive old T-cells in parallel to an augmented CD28 expression on old T-regs. Transfection experiments confirmed the critical role of CD28 in mounting robust alloimmune responses. These findings carry relevant clinical consequences.

SINOMENINE ENHANCES IMDC DERIVED FROM IPS CELL-DIRECTED DIFFERENTIATION TO INDUCE TRANSPLANT IMMUNE HYPORESPONSIVENESS IN MOUSE

Introduction: Induced pluripotent stem cells (iPS) have a wide source and is not restricted by ethics, so that it is expected to become a new source of immature dendritic cells (imDCs). The Chinese medicine monomer sinomenine (SN) can reduce the expression of co-stimulatory molecules on the surface of imDCs, thereby inhibiting the maturation of imDCs. Therefore, in this study, we intend to explore the process of SN acting on induced pluripotent stem (iPS) to differentiate into imDCs, and in order to obtain imDCs (SN-iPS-imDCs) that can remain immature for a long time. Methods: IPS cells were differentiated into imDCs (SN-iPS-imDCs and iPS-imDCs) with three-steps differentiation method with SN. A mouse skin transplantation model was established; SN-iPS-imDCs (1×106 cells) were infused into the mouse skin transplantation model, and 5 groups of controls were established; the skin rejection score, graft survival rate and body weight were observed in recipient mouse; the serum levels of cytokines, the proportion of lymphocyte subsets CD4+CD25+Foxp3+Tregs in the spleen, and the relative expression of Foxp3 mRNA were detected in the recipient mouse; unrelated third-party lymphocytes were added to the lymphocyte mixed culture, and the specificity of induced transplant immunoreactivity by SN-iPS-imDCs and iPS-imDCs were observed; the tissue destruction and inflammatory cell infiltration in the skin graft were detected by histopathology. Results: A mouse skin transplantation model was successfully established. The scores of skin rejection in the SN-iPS-imDCs group were significantly lower than those in the PBS, SN and iPS-imDCs groups at each time point after surgery; on day 28 of transplantation, the body weight of the SN-iPS-imDCs group was increased significantly compared with day 0 (P<0.05); survival analysis showed that the survival time of skin grafts in the SN-iPS-imDCs group was significantly longer than that in the SN, iPS-imDCs and PBS groups (P<0.05);from the 3rd day to the 7th day of the transplantation, the expression levels of IL-12, IL-2 and IFN-γ in the serum of each group were increased except the CsA group, and the elevation level in the SN-iPS-imDCs group was significantly lower than that in the SN, iPS-imDCs and PBS groups (P<0.05); the serum IL-10 levels in the SN-iPS-imDCs group were second only to the CsA group but significantly higher than those in the PBS, iPS-imDCs and SN groups (P<0.05); in the SN-iPS-imDCs group, the spleen CD4+CD25+Tregs and CD4+CD25+Foxp3+Tregs accounted for the highest proportion of CD4+T cells, and there were significant differences compared with other groups (P<0.05); the Foxp3 mRNA expression in SN-iPS-imDCs group was significantly higher than that in iPS-imDCs group (P <0.05); on day 7 of transplantation, spleen T cells in SN-iPS-imDCs group and iPS-imDCs group were significantly less reactive to donor lymphocytes than unrelated third-party C3H mouse. The SN-iPS-imDCs group had lower response to donor lymphocytes than the iPS-imDC group (P<0.05). HE staining of skin grafts showed that the inflammatory response of the grafts in the SN-iPS-imDCs group was significantly lower than that in the iPS-imDCs and PBS groups. Conclusions: Infusion of donor-derived SN-iPS-imDCs could induce donor-specific transplantation immunoreactivity, could reduce the incidence of skin graft rejection, and could prolong the survival time of transplanted skin grafts. National Nature Science Foundation of China (No. 81900686). National Nature Science Foundation of China (No. 81100179).

Distinct roles for major and minor antigen barriers in chimerism-based tolerance under irradiation-free conditions.

Eliminating cytoreductive conditioning from chimerism‐based tolerance protocols would facilitate clinical translation. Here we investigated the impact of major histocompatibility complex (MHC) and minor histocompatibility antigen (MiHA) barriers on mechanisms of tolerance and rejection in this setting. Transient depletion of natural killer (NK) cells at the time of bone marrow (BM) transplantation (BMT) (20 × 106 BALB/c BM cells → C57BL/6 recipients under costimulation blockade [CB] and rapamycin) prevented BM rejection. Despite persistent levels of mixed chimerism, BMT recipients gradually rejected skin grafts from the same donor strain. Extending NK cell depletion did not improve skin graft survival. However, F1 (C57BL/6×BALB/c) donors, which do not elicit NK cell‐mediated rejection, induced durable chimerism and tolerance. In contrast, if F1 donors with BALB/c background only were used (BALB/c×BALB.B), no tolerance was observed. In the absence of MiHA disparities (B10.D2 donors, MHC‐mismatch only), temporal NK cell depletion established stable chimerism and tolerance. Conversely, MHC identical BM (BALB.B donors, MiHA mismatch only) readily engrafted without NK cell depletion but no skin graft tolerance ensued. Therefore, we conclude that under CB and rapamycin, MHC disparities provoke NK cell‐mediated BM rejection in nonirradiated recipients whereas MiHA disparities do not prevent BM engraftment but impede skin graft tolerance in established mixed chimeras.

B lymphocytes contribute to indirect pathway T cell sensitization via acquisition of extracellular vesicles.

B cells have been implicated in transplant rejection via antibody-mediated mechanisms and more recently by presenting donor antigens to T cells. We have shown in patients with chronic antibody-mediated rejection that B cells control the indirect T cell alloresponses. To understand more about the role of B cells as antigen-presenting cells for CD4+ T cell with indirect allospecificity, B cells were depleted in C57BL/6 mice, using an anti-CD20 antibody, prior to receiving MHC class I-mismatched (Kd ) skin. The absence of B cells at the time of transplantation prolonged skin graft survival. To study the mechanisms behind this observation, T cells with indirect allospecificity were transferred in mice receiving a Kd skin transplant. T cell proliferation was markedly inhibited in the absence of recipient B cells, suggesting that B cells contribute to indirect pathway sensitization. Furthermore, we have shown that a possible way in which B cells present alloantigens is via acquisition of MHC-peptide complexes. Finally, we demonstrate that the addition of B cell depletion to the transfer of regulatory T cells (Tregs) with indirect alloresponse further prolonged skin graft survival. This study supports an important role for B cells in indirect T cell priming and further emphasizes the advantage of combination therapies in prolonging transplant survival.

Metabolic reprogramming augments potency of human pSTAT3-inhibited iTregs to suppress alloreactivity.

Immunosuppressive donor Tregs can prevent graft-versus-host disease (GVHD) or solid-organ allograft rejection. We previously demonstrated that inhibiting STAT3 phosphorylation (pSTAT3) augments FOXP3 expression, stabilizing induced Tregs (iTregs). Here we report that human pSTAT3-inhibited iTregs prevent human skin graft rejection and xenogeneic GVHD yet spare donor antileukemia immunity. pSTAT3-inhibited iTregs express increased levels of skin-homing cutaneous lymphocyte-associated antigen, immunosuppressive GARP and PD-1, and IL-9 that supports tolerizing mast cells. Further, pSTAT3-inhibited iTregs significantly reduced alloreactive conventional T cells, Th1, and Th17 cells implicated in GVHD and tissue rejection and impaired infiltration by pathogenic Th2 cells. Mechanistically, pSTAT3 inhibition of iTregs provoked a shift in metabolism from oxidative phosphorylation (OxPhos) to glycolysis and reduced electron transport chain activity. Strikingly, cotreatment with coenzyme Q10 restored OxPhos in pSTAT3-inhibited iTregs and augmented their suppressive potency. These findings support the rationale for clinically testing the safety and efficacy of metabolically tuned, human pSTAT3-inhibited iTregs to control alloreactive T cells.

Indirectly Activated Treg Allow Dominant Tolerance to Murine Skin-grafts Across an MHC Class I Mismatch After a Single Donor-specific Transfusion.

Tolerance induced in stringent animal transplant models using donor-specific transfusions (DST) has previously required additional immunological manipulation. Here, we demonstrate a dominant skin-allograft tolerance model induced by a single DST across an major histocompatibility class I mismatch in an unmanipulated B6 host. C57BL/6 (H-2) (B6) mice were injected intravenously with splenocytes from B6.C.H-2 (H-2k) (bm1) or F1 (B6 × bm1) mice before skin transplantation. Mice were transplanted 7 days postinjection with donor (bm1 or F1) and third-party B10.BR (H-2) skin grafts. B6 hosts acutely rejected skin grafts from B6.C.H-2 (bm1) and F1 (B6 × bm1) mice. A single transfusion of F1 splenocytes into B6 mice without any additional immune modulation led to permanent acceptance of F1 skin grafts. This graft acceptance was associated with persistence of donor cells long-term in vivo. The more rapid removal of DST bm1 cells than F1 cells was reduced by natural killer-cell depletion. Tolerant grafts survived an in vivo challenge with naive splenocytes. Both CD4CD25 and CD4CD25 T cells from F1 DST treated B6 mice suppressed alloproliferation in vitro. Tolerance was associated with expansion of peripheral Foxp3CD4CD25 regulatory T cells (Treg) and increased forkhead box P3 (Foxp3) expression in tolerant grafts. In tolerant mice, Foxp3 Treg arises from the proliferation of indirectly activated natural Foxp3 Treg (nTreg) and depletion of Foxp3 Treg abrogates skin-graft tolerance. This study demonstrates that the persistence of transfused semiallogeneic donor cells mismatched at major histocompatibility class I can enhance tolerance to subsequent skin allografts through indirectly expanded nTreg leading to dominant tolerance without additional immunological manipulation.

Human pSTAT3-Inhibited Itregs Prevent Gvhd, Maintain Anti-Leukemia Immunity, and Increase Their Potency after Metabolic Reprogramming

Introduction Immune suppressive donor regulatory T cells (Tregs) can be expanded to prevent or treat graft-versus-host disease (GVHD). In human induced Tregs (iTregs), we demonstrated that inhibiting STAT3 phosphorylation (pSTAT3) with S3I-201 increases demethylated Foxp3 and significantly improves their suppressive potency in vitro, mitigating phenotypically plastic iTreg de-differentiation. Objectives To investigate whether human pSTAT3-inhibited iTregs 1) prevent GVHD and 2) maintain donor immunity against leukemia. Methods Our human skin/NSG mouse xenograft model is relevant to GVHD and permits preclinical testing of human pSTAT3-inhibited iTregs in vivo. NSG mice were transplanted with a 1cm2 human skin graft, followed by 5 × 106 allogeneic peripheral blood mononuclear cells with or without 1 × 105 iTregs, dendritic cell-expanded for 5 days with S3I-201 or DMSO. Results We now show human pSTAT3-inhibited iTregs prevent skin graft rejection by alloreactive T cells and spare the anti-leukemia activity of donor cytotoxic T lymphocytes (CTL) (Figure 1A-C). Compared to DMSO-treated iTregs, pSTAT3-inhibited iTregs upregulate skin-homing CLA, as well as immune suppressive IL-9, GARP, and PD-1 (P Conclusion We demonstrate that human pSTAT3-inhibited iTregs can prevent GVHD-mediated tissue damage, preserve anti-leukemia CTL function, and that metabolic reprogramming with coQ10 significantly enhances their suppressive potency. Based upon these data, we will clinically test the safety and efficacy of human pSTAT3-inhibited iTregs in GVHD prevention.

Donor-Specific Regulatory T Cell-Mediated Immune Tolerance in an Intrahepatic Murine Allogeneic Islet Transplantation Model with Short-Term Anti-CD154 mAb Single Treatment

Anti-CD154 blockade-based regimens remain unequaled in prolonging graft survival in various organ transplantation models. Several studies have focused on transplantation tolerance with the anti-CD154 blockade, but none of these studies has investigated the mechanisms associated with its use as the sole treatment in animal models, delaying our understanding of anti-CD154 blockade-mediated immune tolerance. The purpose of this study was to investigate the mechanism underlying the anti-CD154 monoclonal antibody (mAb) blockade in inducing immune tolerance using an intrahepatic murine allogeneic islet transplantation model. Allogeneic BALB/c AnHsd (BALB/c) islets were infused into the liver of diabetic C57BL/6 (B6) mice via the cecal vein. Anti-CD154 mAb (MR1) was administered on −1, 0, 1, 3, 5, and 7 d posttransplantation at 0.5 mg per mouse. We showed that short-term MR1 monotherapy could prolong the allogeneic islet grafts to more than 250 d in the murine intrahepatic islet transplantation model. The second islet grafts transplanted under the kidney capsule of the recipients were protected from rejection. We also found that rejection of same-donor skin grafts transplanted to the tolerant mice was modestly delayed. Using a DEREG mouse model, FoxP3+ regulatory T (Treg) cells were shown to play important roles in transplantation tolerance. In mixed lymphocyte reactions, Treg cells from the tolerant mice showed more potency in suppressing BALB/c splenocyte-stimulated Teff cell proliferation than those from naïve mice. In this study, we demonstrated for the first time that a short-term anti-CD154 mAb single treatment could induce FoxP3+ Treg cell-mediated immune tolerance in the intrahepatic murine allogeneic islet transplantation model.

Treg-inducing microparticles promote donor-specific tolerance in experimental vascularized composite allotransplantation

For individuals who sustain devastating composite tissue loss, vascularized composite allotransplantation (VCA; e.g., hand and face transplantation) has the potential to restore appearance and function of the damaged tissues. As with solid organ transplantation, however, rejection must be controlled by multidrug systemic immunosuppression with substantial side effects. As an alternative therapeutic approach inspired by natural mechanisms the body uses to control inflammation, we developed a system to enrich regulatory T cells (Tregs) in an allograft. Microparticles were engineered to sustainably release TGF-β1, IL-2, and rapamycin, to induce Treg differentiation from naïve T cells. In a rat hindlimb VCA model, local administration of this Treg-inducing system, referred to as TRI-MP, prolonged allograft survival indefinitely without long-term systemic immunosuppression. TRI-MP treatment reduced expression of inflammatory mediators and enhanced expression of Treg-associated cytokines in allograft tissue. TRI-MP also enriched Treg and reduced inflammatory Th1 populations in allograft draining lymph nodes. This local immunotherapy imparted systemic donor-specific tolerance in otherwise immunocompetent rats, as evidenced by acceptance of secondary skin grafts from the hindlimb donor strain and rejection of skin grafts from a third-party donor strain. Ultimately, this therapeutic approach may reduce, or even eliminate, the need for systemic immunosuppression in VCA or solid organ transplantation.

Human CD8+ Tregs expressing a MHC-specific CAR display enhanced suppression of human skin rejection and GVHD in NSG mice

AbstractPolyclonal CD8+CD45RClow/− Tregs are potent regulatory cells able to control solid organ transplantation rejection and even induce tolerance. However, donor major histocompatibility complex (MHC)–specific Tregs are more potent than polyclonal Tregs in suppressing T-cell responses and preventing acute as well as chronic rejection in rodent models. The difficulty of identifying disease-relevant antigens able to stimulate Tregs has reduced the possibility of obtaining antigen-specific Tregs. To bypass this requirement and gain the advantage of antigen specificity, and thus improve the therapeutic potential of CD8+ Tregs, we stably introduced a chimeric antigen receptor (CAR) derived from a HLA-A*02 antigen-specific antibody (A2-CAR) in human CD8+ Tregs and developed a clinically compatible protocol of transduction and expansion. We demonstrated that A2-CAR CD8+ Tregs were not phenotypically altered by the process, were specifically activated, and did not exhibit cytotoxic activity toward HLA-A*02+ kidney endothelial cells (ECs). We showed that A2-CAR CD8+ Tregs were more potent suppressors of immune responses induced by HLA-A*02 mismatch than control-CAR CD8+ Tregs, both in vitro and in vivo, in models of human skin graft rejection and graft-versus-host disease (GVHD) in NOD.Cg-PrkdcscidIl2rgtm1Wjl/SzJ (NSG) mice. We showed that integrity of human skin graft was preserved with A2-CAR CD8+ Tregs at least 100 days in vivo after administration, and that interaction between the A2-CAR CD8+ Tregs and HLA-A*02+ kidney ECs resulted in a fine-tuned and protolerogenic activation of the ECs without cytotoxicity. Together, our results demonstrated the relevance of the CAR engineering approach to develop antigen-specific CAR-CD8+ Tregs for clinical trials in transplantation, and potentially in other diseases.

ECDI-fixed donor splenocytes prolong skin allograft survival by promoting M2 macrophage polarization and inducing regulatory T cells.

Rejection is a common complication of allogeneic tissue transplantation. Fixation of splenocytes (SP) with 1‐ethyl‐3‐(3'‐dimethylaminopropyl)‐carbodiimide (ECDI) induces immune tolerance in recipients post‐transplantation; however, the mechanism underlying this effect remains unclear. Here, we determined the mechanisms of ECDI‐fixed donor SP (ECDI‐SP) in inducing tolerance in skin allograft transplantation. C57BL/6‐recipient mice that received Balb/c full‐thickness skin transplants with two infusions of donor‐derived ECDI‐SP, along with rapamycin showed superior skin allograft survival and lower inflammatory cell infiltration than mice that received rapamycin‐only treatment. In ECDI‐SP‐treated mice, the levels of anti‐inflammatory cytokines such as interleukin (IL)‐10 in sera were markedly increased, whereas the expression of inflammatory cytokines was significantly suppressed. Splenic macrophages were significantly polarized to the alternative activated macrophage (M2) phenotype, with expansion of CD4+Foxp3+ regulatory T cells (Tregs) in the spleen and draining lymph nodes. Allostimulatory activity of ECDI‐SP in vitro and donor‐specific ex vivo hyporesponsiveness were observed. C57BL/6 macrophages engulfed allogeneic Balb/c‐derived ECDI‐SP, polarized to the M2 phenotype, with pronounced cAMP response element‐binding (CREB) protein phosphorylation. By facilitating increased IL‐10 expression, ECDI‐SP induced M2 polarization and Treg production, inhibiting effector T‐cell proliferation. Thus, ECDI‐SP modulates macrophage M2 polarization by increasing CREB phosphorylation and promoting Treg production to suppress allogeneic skin graft rejection.

Skin-restricted commensal colonization accelerates skin graft rejection.

Solid organ transplantation can treat end-stage organ failure, but the half-life of transplanted organs colonized with commensals is much shorter than that of sterile organs. Whether organ colonization plays a role in this shorter half-life is not known. We have previously shown that an intact whole-body microbiota can accelerate the kinetics of solid organ allograft rejection in untreated colonized mice when compared to germ-free (GF) or to antibiotic-pre-treated colonized mice, by enhancing the capacity of antigen presenting cells (APCs) to activate graft-reactive T cells. However, the contribution of intestinal versus skin microbiota to these effects was unknown. Here, we demonstrate that colonizing the skin of GF mice with a single commensal, Staphylococcus epidermidis (S. epi), while preventing intestinal colonization with oral vancomycin, was sufficient to accelerate skin graft rejection. Notably, unlike the mechanism by which whole-body microbiota accelerates skin graft rejection, cutaneous S. epi did not enhance the priming of alloreactive T cells in the skin-draining lymph nodes (LNs). Rather, cutaneous S. epi augmented the ability of skin APCs to drive the differentiation of alloreactive T cells. This study reveals that the extra-intestinal donor microbiota can affect transplant outcome and may contribute to the shorter half-life of colonized organs.

Expression of a core gene module of anergy governs maternal CD8+ T cell hypofunction after pregnancy

Abstract Maternal exposure to fetal antigen during pregnancy results in T cell alloimmunization that impacts immunologic responses later in postpartum life. To study the mechanisms of memory T cell differentiation during pregnancy, we transferred 1x106 CD45.2 OVA-specific OT-1 CD8 T cells into CD45.1 mice. Mice were either 1) mated with Act-mOVA males (pOVA), 2) received an OVA skin graft from an Act-mOVA donor (gOVA) or 3) had no antigen exposure (naïve). Sixty days after cell transfer (~30 days after delivery in pOVA mice and ~30 days after skin graft rejection in gOVA mice), OT-1 cells were recovered for functional, phenotypic, and transcriptional analysis. Whereas gOVA OT-1 T cells differentiated into PD-1intCD127+CD62L+ central memory cells with enhanced recall capacity, pOVA OT-1 T cells persisted as hypofunctional PD-1hi long-lived effectors (CD127-CD62L-). pOVA OT-1 cells were hypoproliferative during recall challenge [Fold expansion over naïve: 4.6 (gOVA) vs. 1.5 (pOVA); p&amp;lt;0.001] and demonstrated impaired cytotoxicity and cytokine production [%IFNγ+TNFα+ = 46±6% (gOVA), vs. 7±6% (pOVA); p&amp;lt;0.001]. Transcriptional profiling using RNA-seq revealed 400 differentially expressed genes (FDR&amp;lt;0.05) between gOVA and pOVA OT-1 T cells; these included anergy-inducing genes such as master regulators of T cell hypofunction (i.e. Tox), repressors of the IL-2 locus (i.e. Aiolos), modulators of calcium responses (i.e. CD38), and enzymes which mediate ubiquitination of signaling molecules of the MAP kinase pathway (i.e. Deltex1). Altogether, pregnancy alloimmunization primes a program of hypofunction in long-lived maternal CD8+ T cell that is shared with other models of anergy.