Murine Skin Allograft Research Articles

Electrostimulation suppresses allograft rejection via promoting lymphatic regulatory T cell migration mediated by lymphotoxin - lymphotoxin receptor β signaling

Conventional immunosuppressants that suppress allograft rejection cause various side effects. Although regulatory T cells (Tregs) are essential for allograft survival, the limited efficacy of Treg therapy demands improvement. Thus, it is imperative to seek new approaches to enhancing Treg suppression. Low-intensity electrostimulation (ES) has been shown to exert antiinflammatory effects without causing major adverse reactions. However, it remains unknown whether and how ES regulates alloimmunity. Here, we found that regional ES delayed murine skin allograft rejection and promoted long-term allograft survival induced by an mTOR inhibitor, rapamycin. ES also extended islet allograft survival. Mechanistically, ES enhanced the expression of lymphotoxin α (LTα) on Tregs after transplantation. Blockade of lymphotoxin β receptor–mediated nonclassical NFκB signaling suppressed lymphatic Treg migration and largely reversed the effects of ES on allograft survival. Moreover, ES failed to extend allograft survival when recipients lacked LTα/lymph nodes or if transferred Tregs lacked LTα. Therefore, ES promoted the lymphatic migration of CD4+Foxp3+ Tregs by upregulating their surface expression of LTα. Finally, ES augmented expression of LTα on murine or human Tregs, but not conventional T cells, while promoting their calcium influx in vitro. This ES-mediated upregulation of LTα relied on calcium influx. Thus, our findings have unveiled novel mechanisms underlying ES-mediated immunoregulation.

Memory T follicular helper cells drive donor-specific antibodies independent of memory B cells and primary germinal center and alloantibody formation

Human leukocyte antigen antibodies are important immunologic mediators of renal allograft loss and are difficult to control. The inability to permanently eliminate donor-specific antibodies (DSA) is partly due to an incomplete understanding of the cellular mechanisms driving alloantibody formation, recurrence, and maintenance. Memory T follicular helper (mTfh) cells rapidly interact with memory B cells upon antigen re-exposure for anamnestic humoral responses, but little is known about Tfh memory in transplantation. We hypothesized that alloreactive mTfh cells form after transplantation and play a critical role in DSA formation following alloantigen re-encounter. To test this hypothesis, we utilized murine skin allograft models to identify and characterize Tfh memory and interrogate its ability to mediate alloantibody responses. We identified alloreactive Tfh memory as a mediator of accelerated humoral alloresponses independent of memory B cells and primary germinal center, or DSA, formation. Furthermore, we demonstrate that mTfh-driven alloantibody formation is susceptible to CD28 costimulation blockade. These findings provide novel insight into a pathologic role for memory Tfh in alloantibody responses and strongly support shifting therapeutic focus from the singular targeting of B cell lineage cells and alloantibodies themselves to multimodal strategies that include inhibition of mTfh cells to treat DSA.

Inhibition of DAI refrains dendritic cells from maturation and prolongs murine islet and skin allograft survival.

Central to allograft rejection is the T cell-mediated adaptive immune response initiated by activated dendritic cells (DCs). Previous studies have shown that the DNA-dependent activator of IFN regulatory factors (DAI) is involved in the maturation and activation of DCs. Therefore, we hypothesized that inhibition of DAI could prevent DCs from maturation and prolong murine allograft survival. Donor mouse bone marrow-derived dendritic cells (BMDCs) were transduced with the recombinant adenovirus vector (AdV-DAI-RNAi-GFP) to inhibit DAI expression (DC-DAI-RNAi), and the immune cell phenotype and function of DC-DAI-RNAi upon lipopolysaccharide (LPS) stimulation were evaluated. Then DC-DAI-RNAi was injected into recipient mice before islet transplantation and skin transplantation. The survival times of islet and skin allograft were recorded and the proportions of T cell subsets in spleen and secretion levels of cytokines in serum were measured. We identified that DC-DAI-RNAi inhibited the expression of main co-stimulatory molecules and MHC-II, exhibited strong phagocytic ability, and secreted high levels of immunosuppressive cytokines and low levels of immunostimulating cytokines. Recipient mice treated with DC-DAI-RNAi had longer islet and skin allograft survival times. In the murine islet transplantation model, we observed an increase in Treg cells proportion, a reduction in Th1 and Th17 cells proportions in spleen, and similar trends in their secreted cytokines in serum in the DC-DAI-RNAi group. Inhibition of DAI by adenovirus transduction inhibits the maturation and activation of DCs, affects the differentiation of T cell subsets as well as their secreted cytokines, and prolongs allograft survival.

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.

CHBP induces stronger immunosuppressive CD127+ M-MDSC via erythropoietin receptor

Erythropoietin (EPO) is not only an erythropoiesis hormone but also an immune-regulatory cytokine. The receptors of EPO (EPOR)2 and tissue-protective receptor (TPR), mediate EPO’s immune regulation. Our group firstly reported a non-erythropoietic peptide derivant of EPO, cyclic helix B peptide (CHBP), which could inhibit macrophages inflammation and dendritic cells (DCs) maturation. As a kind of innate immune regulatory cell, myeloid-derived suppressor cells (MDSCs) share a common myeloid progenitor with macrophages and DCs. In this study, we investigated the effects on MDSCs differentiation and immunosuppressive function via CHBP induction. CHBP promoted MDSCs differentiate toward M-MDSCs with enhanced immunosuppressive capability. Infusion of CHBP-induced M-MDSCs significantly prolonged murine skin allograft survival compared to its counterpart without CHBP stimulation. In addition, we found CHBP increased the proportion of CD11b+Ly6G−Ly6Chigh CD127+ M-MDSCs, which exerted a stronger immunosuppressive function compared to CD11b+Ly6G−Ly6Chigh CD127− M-MDSCs. In CHBP induced M-MDSCs, we found that EPOR downstream signal proteins Jak2 and STAT3 were upregulated, which had a strong relationship with MDSC function. In addition, CHBP upregulated GATA-binding protein 3 (GATA-3) protein translation level, which was an upstream signal of CD127 and regulator of STAT3. These effects of CHBP could be reversed if Epor was deficient. Our novel findings identified a new subset of M-MDSCs with better immunosuppressive capability, which was induced by the EPOR-mediated Jak2/GATA3/STAT3 pathway. These results are beneficial for CHBP clinical translation and MDSC cell therapy in the future.

A Novel Immunosuppressant, Luteolin, Modulates Alloimmunity and Suppresses Murine Allograft Rejection.

An allograft is rejected in the absence of any immunosuppressive treatment because of vigorous alloimmunity and thus requires extensive immunosuppression for its survival. Although there are many conventional immunosuppressants for clinical use, it is necessary to seek alternatives to existing drugs, especially in case of transplant patients with complicated conditions. Luteolin, a natural ingredient, exists in many plants. It exhibits multiple biological and pharmacological effects, including anti-inflammatory properties. In particular, luteolin has been shown to upregulate CD4+CD25+ regulatory T cells (Tregs) in the context of airway inflammation. However, it remains unknown whether luteolin regulates alloimmune responses. In this study, we demonstrated that luteolin significantly prolonged murine skin allograft survival, ameliorated cellular infiltration, and downregulated proinflammatory cytokine gene expression in skin allografts. Furthermore, luteolin increased the percentage of CD4+Foxp3+ Tregs while reducing frequency of mature dendritic cells and CD44highCD62Llow effector CD4+/CD8+ T cells posttransplantation. It also suppressed the proliferation of T cells and their production of cytokines IFN-γ and IL-17A in vitro while increasing IL-10 level in the supernatant. Moreover, luteolin promoted CD4+Foxp3+ Treg generation from CD4+CD25- T cells in vitro. Depleting Tregs largely, although not totally, reversed luteolin-mediated extension of allograft survival. More importantly, luteolin inhibited AKT/mTOR signaling in T cells. Thus, for the first time, to our knowledge, we found that luteolin is an emerging immunosuppressant as an mTOR inhibitor in allotransplantation. This finding could be important for the suppression of human allograft rejection, although it remains to be determined whether luteolin has an advantage over other conventional immunosuppressants in suppression of allograft rejection.

Mechanisms of Graft-versus-Host Disease Prevention by Post-transplantation Cyclophosphamide: An Evolving Understanding.

Post-transplantation cyclophosphamide (PTCy) has been highly successful at preventing severe acute and chronic graft-versus-host disease (GVHD) after allogeneic hematopoietic cell transplantation (HCT). The clinical application of this approach was based on extensive studies in major histocompatibility complex (MHC)-matched murine skin allografting models, in which cyclophosphamide was believed to act via three main mechanisms: (1) selective elimination of alloreactive T cells; (2) intrathymic clonal deletion of alloreactive T-cell precursors; and (3) induction of suppressor T cells. In these models, cyclophosphamide was only effective in very specific contexts, requiring particular cell dose, cell source, PTCy dose, and recipient age. Achievement of transient mixed chimerism also was required. Furthermore, these studies showed differences in the impact of cyclophosphamide on transplanted cells (tumor) versus tissue (skin grafts), including the ability of cyclophosphamide to prevent rejection of the former but not the latter after MHC-mismatched transplants. Yet, clinically PTCy has demonstrated efficacy in MHC-matched or partially-MHC-mismatched HCT across a wide array of patients and HCT platforms. Importantly, clinically significant acute GVHD occurs frequently after PTCy, inconsistent with alloreactive T-cell elimination, whereas PTCy is most active against severe acute GVHD and chronic GVHD. These differences between murine skin allografting and clinical HCT suggest that the above-mentioned mechanisms may not be responsible for GVHD prevention by PTCy. Indeed, recent work by our group in murine HCT has shown that PTCy does not eliminate alloreactive T cells nor is the thymus necessary for PTCy's efficacy. Instead, other mechanisms appear to be playing important roles, including: (1) reduction of alloreactive CD4+ effector T-cell proliferation; (2) induced functional impairment of surviving alloreactive CD4+ and CD8+ effector T cells; and (3) preferential recovery of CD4+ regulatory T cells. Herein, we review the history of cyclophosphamide's use in preventing murine skin allograft rejection and our evolving new understanding of the mechanisms underlying its efficacy in preventing GVHD after HCT. Efforts are ongoing to more fully refine and elaborate this proposed new working model. The completion of this effort will provide critical insight relevant for the rational design of novel approaches to improve outcomes for PTCy-treated patients and for the induction of tolerance in other clinical contexts.

Inhibition of DNA-PK(cs) Prevents Graft Rejection in a Murine Allograft Skin Graft Study

Abstract While the number of patients needing solid organ transplants has steadily increased over the years, the development of safer, more effective transplant drugs has stagnated. Current therapy has been largely successful at thwarting acute cellular rejection; however, antibody-mediated rejection (AMR) remains difficult to treat in the clinic making it the primary cause of graft loss. In this study, we provide proof of principle experiments that DNA-dependent protein kinase catalytic subunit DNA-PK(cs) is a worthwhile target for transplant immunosuppression. In our previous studies, we confirmed that DNA-PK(cs) controls NFAT-induced IL-2 expression, in part, through a mechanism that promotes calcineurin activity by preventing expression of the endogenous calcineurin inhibitor Cabin1. Here, we show that treatment with DNA-PK(cs) inhibitors prevents rejection in a murine skin allograft model by decreasing the production of cytokines including IL2 and IL6 and the infiltration of lymphocytes into the graft. Most importantly, our studies showed that DNA-PK(cs) inhibitors prevented the development of donor-specific antibodies, a driving force behind AMR. These results highlight novel functions for DNA-PK(cs) in the immune system and the potential use of DNA-PK(cs) inhibitors to prevent organ rejection there-bye warranting further investigation.

Importance of Hematopoietic Mixed Chimerism for Induction of Renal Allograft Tolerance in Nonhuman Primates.

Although induction of durable mixed chimerism is required for murine skin allograft tolerance (TOL), renal allograft TOL has been achieved after induction of only transient mixed chimerism in nonhuman primates (NHPs) and humans. To better define the level/duration of chimerism required for stable renal allograft TOL, we retrospectively analyzed these parameters and compared them with transplant outcomes in NHP combined kidney and bone marrow transplant recipients. Peripheral blood levels and duration of myeloid or lymphoid chimerism were retrospectively analyzed in 34 NHP combined kidney and bone marrow transplantation recipients which were divided into 3 groups: TOL, n = 10; chronic antibody-mediated rejection (CAMR), n = 12; and T cell-mediated rejection (TCMR), n = 12. All 4 of the recipients that failed to develop any chimerism lost their allografts due to TCMR after discontinuation of immunosuppression (56 ± 3 d). Among 30 recipients who successfully developed multilineage chimerism, 10 achieved long-term immunosuppression-free survival without rejection (1258 ± 388 d), 12 eventually developed CAMR (932 ± 155 d), and 8 developed TCMR (82 ± 10 d). The maximum level but not duration of lymphoid chimerism was significantly higher in TOL recipients compared with both CAMR (P = 0.0159) and TCMR (P = 0.0074). On the other hand, the maximum myeloid chimerism was significantly higher in TOL than in TCMR (P = 0.0469), but not in CAMR. Receiver operating characteristic analyses revealed that lymphoid chimerism levels of 3.1% or greater could reliably predict long-term immunosuppression-free renal allograft survival (P < 0.0001). This retrospective study confirmed that induction of chimerism is essential for long-term immunosuppression-free survival, which best correlates with lymphoid chimerism levels higher than 3.1%.

Herbal Components of a Novel Formula PSORI-CM02 Interdependently Suppress Allograft Rejection and Induce CD8+CD122+PD-1+ Regulatory T Cells.

A recipient usually rejects a transplanted organ and thus needs immunosuppressive treatments to prevent rejection. Achieving long-term allograft survival without continuous global immunosuppression is highly desirable in transplantation as long-term immunosuppression causes various side effects. Therefore, it is necessary to search for medicine with potentially less side effects. Traditional Chinese medicine PSORI-CM01 (Yin Xie Ling), a formula with seven natural herbs, has been used to treat patients with psoriasis. Here, we investigated a “sharpened” formula, PSORI-CM02 consisting of only five herbs from PSORI-CM01: Curcumae rhizoma, Radix paeoniae rubra, Rhizoma smilacis glabrae, Mume fructus, and Sarcandrae herba. We examined whether or not PSORI-CM02 would suppress alloimmunity and found that PSORI-CM02 significantly inhibited murine skin allograft rejection and reduced graft-infiltration of CD3+ T cells. Interestingly, omitting any single herbal component rendered the whole formula ineffective in suppression, indicating that these herbal components exert their effects cooperatively as a whole. Moreover, PSORI-CM02 increased CD8+CD122+PD-1+ Treg frequency with CD4+FoxP3+ Tregs remaining unchanged in recipient mice, whereas CsA reduced CD4+FoxP3+ Treg frequency. PSORI-CM02 also hindered CD11c+ DC maturation posttransplantation. Importantly, PSORI-CM02-induced CD8+CD122+PD-1+ Tregs were more potent in suppression of allograft rejection in Rag-/- mice than control Tregs. On the other hand, PSORI-CM02 suppressed T cell proliferation in vitro and reduced their phosphorylation of P70S6K and P50/P65, suggesting that it inhibits both mTOR and NFκB signaling pathways. It also increased IL-10 production while reducing IFNγ level in the supernatant of activated T cells co-cultured with CD8+CD122+PD-1+ Tregs. Furthermore, HPLC fingerprinting ruled out that PSORI-CM02 contained CsA or rapamycin. PSORI-CM02 also did not cause any illness and toxic injury in recipient mice. Thus, we demonstrate that PSORI-CM02 formula suppresses allograft rejection without toxicity.

The ligands of translocator protein inhibit human Th1 responses and the rejection of murine skin allografts.

The translocator protein (TSPO) ligands affected inflammatory and immune responses. However, the exact effects of TSPO ligands on Th1 responses invitro and invivo are still unclear. In the present study, we found that TSPO ligands, FGIN1-27 and Ro5-4864, suppressed the cytokine production in a dose-dependent manner by purified human CD4+ T-cells from peripheral blood mononuclear cells (PBMCs) after stimulation. TSPO ligands inhibited the production of interferon γ (IFN-γ) by memory CD4+ T-cells and the differentiation of naïve CD4+ T-cells into Th1 cells via suppressing the activity of the corresponding transcription factors as indicated by reduced expression of T-bet and down-regulation of STAT1, STAT4 and STAT5 phosphorylation. TSPO ligands suppressed cell proliferation and activation of CD4+ T-cells by the inhibition of TCR signal transduction including membrane proteins: Zap, Lck, Src; cytoplasm proteins: Plcγ1, Slp-76, ERK, JNK and the nucleoproteins: c-Jun and c-Fos. In addition, FGIN1-27 inhibited mixed lymphocyte reactions by human or murine cells. After the transplantation of allogeneic murine skin, injection of FGIN1-27 into mice prevented graft rejection by inhibition of cell infiltration and IFN-γ production. Taken together, our data suggest that TSPO ligands inhibit Th1 cell responses and might be novel therapeutic medicine for the treatment of autoimmune diseases and prevention of transplant rejection.

Selective CD28 Blockade Exhibits Superior Suppression of Donor-Specific Antibody Relative to CTLA4Ig.

Costimulation blockade in the form of CTLA4Ig is known to attenuate donor-specific antibody responses. However, CTLA4Ig indiscriminately blocks both the CD28 costimulatory and CTLA4 co-inhibitory pathways. While follicular helper T (TFH) cell development and germinal center (GC) formation are CD28-dependent, CTLA4 has been shown to play a critical role in suppressing the provision of T cell help for GC B cell function and immunoglobulin production. Thus, selective CD28 blockade has potential to inhibit GC development while garnering the inhibitory effects of intact CTLA4 signaling on T cell-dependent antibody responses. To test this possibility, we used a T cell receptor transgenic murine skin allograft model to compare a novel CD28-specific domain antibody (dAb) to CTLA4Ig. The selective CD28 dAb resulted in superior skin allograft survival in comparison to CTLA4Ig (MST >100d vs. 34d). Importantly, animals treated with the anti-CD28 dAb experienced a greater reduction in donor-specific IgG as compared to those treated with CTLA4Ig. Flow cytometric analysis of donor-reactive CD4+Thy1.1+ T cells from draining lymph nodes revealed increased expression of CTLA4 on TFH cells (CXCR5+GL7+/-) compared to naïve and non-TFH cells (CXCR5-GL7-), with the greatest level of CTLA4 expression on maximally polarized GC TFH cells (CXCR5+GL7+). Analysis of donor-specific CD4+Thy1.1+ T cells also revealed a greater reduction in the frequency and absolute number of TFH cells (CXCR5+GL7+/-) with selective CD28 blockade as compared to CTLA4Ig. Additionally, we observed a reciprocal increase in the frequency and absolute number of naïve and non-TFH cells (CXCR5-GL7-) that was greatest with CD28 dAb treatment. These findings suggest that selective CD28 blockade in the presence of intact CTLA4 signaling has a greater inhibitory effect on T cell dependent antibody responses than CTLA4Ig. DISCLOSURE:Suchard, S.: Employee, Bristol-Myers Squibb. Nadler, S.: Employee, Bristol-Myers Squibb.

Blocking of Interleukin 6 Receptor By Nonviral Minicircle DNA Producing Antibody in Skin Allograft Rejection.

Blocking of proinflammatory cytokine, interleukin-6 (IL-6) is effective in decreasing resistance to allogenic tolerance. In this study, we investigated whether anti-IL-6 receptor producing nonviral minicircle (MC)-DNA, is competent to inhibit alloresponse-induced IL-6 in highly immunogenic murine skin allograft model. We designed MC-DNA producing IL-6R antibody and verified in vitro system. One day before skin allograft modeling, systemic MC-DNA exposed via hydrodynamic delivery of MC-DNA in vivo (50ug of DNA, tail vein, single injection). Using GFP tagging MC-DNA, we confirmed its organ distribution. At day 5, we measured the amount of IL-6 and IL-6R antibody in serum. As functional examinations, we evaluated survival rate, morphological changes of graft, immune cell infiltration, and population of T helper 17 cells (Th17, FACS marker: CD4+/RoRγt) and regulatory T cells (Treg, FACS marker: CD4+Foxp3+). We compared its alloimmunity and graft survival efficiency with the cyclosporine A (CsA)-treated group (50 mg/kg, daily administration via oral gavage). Hydrodynamic delivery of MC-DNA was mainly localized in hepatocytes. Serum IL-6 and IL-6R antibody detected in anti-IL-6R MC-DNA treated mice. At day 8.5, untreated mice completely rejected the graft confirming by daily observation of loss of skin graft and erosion. However, mice received either anti-IL-6R MC-DNA or CsA presented prolonged acceptance of graft until day 15 or 15.6, respectively. Results from morphological changes and immune cell infiltration in the graft were also consistent with survival rate. FACS results showed that anti-IL-6R MC-DNA treatment markedly suppressed Th17 population compared with the untreated mice. However, there was no effect on Treg population. On the other hand, administration of CsA showed the increased Th17 and decreased Treg population compared with untreated group. We found that single injection of nonviral minicircle DNA targeting IL-6R is effective in both acute allograft acceptance and allogenic tolerance. This suggests that simple and effective gene therapy method using antibody producing minicircle DNA may represent a powerful tool for the transplantation.

Effect of Blocking with Minicircle DNA of Interleukin-6 on Skin Allograft Rejection

Blocking of proinflammatory cytokine, interleukin-6 (IL-6) is effective in decreasing resistance to allogenic tolerance. In this study, we investigated whether anti-IL-6 receptor producing nonviral minicircle (MC)-DNA, is competent to inhibit alloresponse-induced IL-6 in highly immunogenic murine skin allograft model. We designed MC-DNA producing IL-6R antibody and verified in vitro system. One day before skin allograft modeling, systemic MC-DNA exposed via hydrodynamic delivery of MC-DNA in vivo (50 ug of DNA, tail vein, single injection). Using GFP tagging MC-DNA, we confirmed its organ distribution. At day 5, we measured the amount of IL-6 and IL-6R antibody in serum. As functional examinations, we evaluated survival rate, morphological changes of graft, immune cell infiltration, and population of T helper 17 cells (Th17, FACS marker: CD4+/RoRγt) and regulatory T cells (Treg, FACS marker: CD4+ Foxp3+). We compared its alloimmunity and graft survival efficiency with the cyclosporine A (CsA)-treated group (50 mg/kg, daily administration via oral gavage). Hydrodynamic delivery of MC-DNA was mainly localized in hepatocytes. Serum IL-6 and IL-6R antibody detected in anti-IL-6R MC-DNA treated mice. At day 8.5, untreated mice completely rejected the graft confirming by daily observation of loss of skin graft and erosion. However, mice received either anti-IL-6R MC-DNA or CsA presented prolonged acceptance of graft until day 15 or 15.6, respectively. Results from morphological changes and immune cell infiltration in the graft were also consistent with survival rate. FACS results showed that anti-IL-6R MC-DNA treatment markedly suppressed Th17 population compared with the untreated mice. However, there was no effect on Treg population. On the other hand, administration of CsA showed the increased Th17 and decreased Treg population compared with untreated group. We found that single injection of nonviral minicircle DNA targeting IL-6R is effective in both acute allograft acceptance and allogenic tolerance. This suggests that simple and effective gene therapy method using antibody producing minicircle DNA may represent a powerful tool for the transplantation.

An Effective Immune-Monitoring Protocol Based on Gene Expression Profiles in the Peripheral T-Cell Fraction Reactive to Graft Antigens

The ability to induce tolerance, or at least minimize the need for immunosuppressive therapy, is a high priority in organ transplantation. Accomplishing this goal requires a novel method for determining when a patient has become tolerant to or is rejecting their graft. Here, we sought to develop an efficient monitoring protocol based on gene expression profiles of recipient T cells in murine skin and islet allograft models. Unlike previous studies, here, gene expression analysis was focused on donor antigen-reactive T cells, which were prepared by collecting CD69(+) T cells from cocultures of recipient peripheral T cells and donor antigen-presenting cells. Candidate tolerance and rejection biomarker genes were selected from a CD69(+) T-cell microarray analysis, and their expression levels were measured in the recipient CD69(+) T-cell fraction using quantitative reverse transcription polymerase chain reaction. Our new monitoring protocol was capable of precisely detecting the immune status of recipients relative to their graft regardless of the organ received, whether they were taking immunosuppressive drugs, or different strains of origin. Gene expression analysis focusing on recipient CD69(+) T cells as the donor antigen-reactive T-cell population could be used as an effective and sensitive method for monitoring transplant patients.

Characterization of mesenchymal stem cells from human normal and hyperplastic gingiva

Human gingiva plays an important role in the maintenance of oral health and shows unique fetal-like scarless healing process after wounding. Here we isolate and characterize mesenchymal stem cells from human normal and hyperplastic gingival tissues (N-GMSC and H-GMSC, respectively). Immunocytochemical staining indicated that gingival lamina propria contained Stro-1 and SSEA-4 positive cells, implying existence of putative gingival MSC. Under attachment-based isolating and culturing condition, gingival MSC displayed highly clonogenic and long-term proliferative capability. By using single colony isolation and expansion approaches, we found both N-GMSC and H-GMSC possessed self-renewal and multipotent differentiation properties. N-GMSC and H-GMSC showed distinct immunoregulatory functions in a murine skin allograft setting via up-regulation of putative systemic regulatory T cells (Tregs). N-GMSC and H-GMSC were capable of regenerating collagenous tissue following in vivo transplantation, in which H-GMSC exhibited more robust regenerative capability. These findings suggest that gingival tissue contains tissue-specific mesenchymal stem cell population and is an ideal resource for immunoregulatory therapy due to its substantial availability and accessibility. In addition, gingival MSC over-activation may contribute to gingival hyperplastic phenotype.

Indoleamine 2,3-dioxygenase and regulatory dendritic cells contribute to the allograft protection induced by infusion of donor-specific splenic stromal cells

It has been reported that splenic stromal cells (SSCs) are capable of directly supporting the development of CD11c(lo)CD45RB(+ )IL-10-producing dendritic cells (DCs) from lineage-negative c-kit(+) progenitor cells in the absence of exogenous cytokines. In vitro, DCs that differentiate on stromal cells suppress mixed leukocyte reaction responses and induce primary alloreactive CD4(+) T cells to differentiate into IL-10-producing Tr1 cells. However, the precise mechanisms by which these SSCs exert their regulatory functions in vivo remain undefined. Furthermore, their possible contribution to the development of allograft transplantation tolerance has yet to be examined. Here, we have used both murine skin and cardiac allograft transplantation models to explore whether in vivo alloresponses can be regulated by infusion with donor-derived SSCs and to investigate the possible mechanisms by which SSCs exert regulatory effects to prevent allograft rejection. We show that intravenous SSC infusion prolonged murine skin allograft survival. The prolonged graft survival is associated with augmentation of the generation of regulatory DC subsets and CD4(+)CD25(+)Foxp3(+) regulatory T cells (Tregs), as well as upregulation of the production of suppressive cytokines IL-10 and transforming growth factor (TGF)-β. Moreover, we found that indoleamine 2,3-dioxygenase and SSC-derived regulatory DCs contribute to allograft protection by infusion of donor-specific SSCs. Our data suggest that donor-derived SSCs could be used as a therapeutic target to promote transplantation tolerance.

Interleukin-17 Promotes Early Allograft Inflammation

Acute cellular rejection of organ transplants is executed by donor-reactive T cells, which are dominated by interferon-gamma-producing cells. As interferon-gamma is dispensable for graft destruction, we evaluated the contribution of interleukin-17A (IL-17) to intragraft inflammation in major histocompatibility complex-mismatched heart transplants. A/J (H-2(a)) cardiac allografts placed into wild-type BALB/c (H-2(d)) mice induced intragraft IL-17 production on day 2 after transplant. Allografts placed into BALB/c IL-17(-/-) recipients demonstrated diminished production of the chemokines CXCL1 and CXCL2 and delayed neutrophil and T cell recruitment. However, by day 7 after transplant, allografts from IL-17(-/-) and wild-type recipients had comparable levels of cellular infiltration. The priming of donor-specific T cells was not affected by the absence of IL-17, and the kinetics of cardiac allograft rejection were similar in wild-type and IL-17(-/-) recipients. In contrast, IL-17(-/-) mice depleted of CD8 T cells rejected A/J allografts in a delayed fashion compared with CD8-depleted wild-type recipients. Although donor-reactive CD4 T cells were efficiently activated in both groups, the infiltration of effector T cells into allografts was impaired in IL-17(-/-) recipients. Our data indicate that locally produced IL-17 amplifies intragraft inflammation early after transplantation and promotes tissue injury by facilitating T cell recruitment into the graft. Targeting the IL-17 signaling network in conjunction with other graft-prolonging therapies may decrease this injury and improve the survival of transplanted organs.

A Novel Clinically Relevant Approach to Tip the Balance Toward Regulation in Stringent Transplant Model

Regulatory T cells (Tregs) actively regulate alloimmune responses and promote transplantation tolerance. Thymoglobulin, a rabbit polyclonal antithymocyte globulin (ATG), is a widely used induction therapy in clinical organ transplantation that depletes peripheral T cells. However, resistance to tolerance induction is seen with certain T-cell depleting strategies and is attributed to alterations in the balance of naive, memory and Tregs. The exact mechanism of action of ATG and its effects on the homeostasis and balance between Tregs and T-effector-memory cells (Tem) are unknown. A novel antibody reagent, rabbit polyclonal anti-murine thymocyte globulin (mATG), generated by the same process used to manufacture thymoglobulin, was used alone or in combination with CTLA4Ig or sirolimus (SRL) in a stringent fully major histocompatibility complex-mismatched murine skin allograft model to study graft survival and mechanisms involved. mATG depletes T cells but preferentially spares CD25+ natural Tregs which limit skewing of T-cell repertoire toward Tem phenotype among the recovering T cells. T-cell depletion with mATG combined with CTLA4Ig and SRL synergize to prolong graft survival by tipping the Treg/Tem balance further in favor of Tregs by preserving Tregs, facilitating generation of new Tregs by a conversion mechanism and limiting Tem expansion in response to alloantigen and homeostatic proliferation. Simultaneous T-cell depletion with ATG and costimulatory blockade, combined with SRL, synergizes to promote regulation and prolong allograft survival in a stringent transplant model. These results provide the rationale for translating such novel combination therapy to promote regulation in primate and human organ transplantation.

IL-6 and TNF-α Synergistically Inhibit Allograft Acceptance

Previous studies suggested that activation of the innate immune system impairs the induction of transplantation tolerance, but the responsible inflammatory mediators have not been identified. In this study, we examined whether IL-6 and TNF-alpha promote resistance to transplantation tolerance. Using a highly immunogenic murine skin allograft model, we found that the absence of both IL-6 and TNF-alpha in the graft recipient synergized with co-stimulatory blockade to induce tolerance. Furthermore, IL-6 and TNF-alpha acted together to promote T cell alloimmune responses both in vitro and in vivo and to impair the ability of regulatory T cells to suppress effector T cell alloimmunity. In addition, deficiency of recipient IRAK-M, a negative regulator of certain innate immune pathways, augmented cellular IL-6 and TNF-alpha responses and impaired the ability of co-stimulatory blockade to extend allograft survival. In summary, IL-6 and TNF-alpha synergistically impair the efficacy of therapies that promote allograft acceptance.