Allogeneic Graft Rejection Research Articles

Potentials of bone marrow cells-derived from naïve or diabetic mice in autoimmune type 1 diabetes: immunomodulatory, anti-inflammatory, anti hyperglycemic, and antioxidative.

The scarcity of transplanted human islet tissue and the requirement for immunosuppressive drugs to prevent the rejection of allogeneic grafts have hindered the treatment of autoimmune type 1 diabetes mellitus (T1DM) through islet transplantation. However, there is hope in adoptively transferred bone marrow cells (BMCs) therapy, which has emerged as a propitious pathway for forthcoming medications. BMCs have the potential to significantly impact both replacement and regenerative therapies for a range of disorders, including diabetes mellitus, and have demonstrated anti-diabetic effects. The main goal of this study is to evaluate the effectiveness of adoptively transferred bone marrow cells derived from either naïve mice (nBMCs) or diabetic mice (dBMCs) in treating a T1DM mice model. Male Swiss albino mice were starved for 16 h and then injected with streptozotocin (STZ) at a dose of 40 mg/kg body weight for 5 consecutive days to induce T1DM. After 14 days, the diabetic mice were distributed into four groups. The first group served as a diabetic control treated with sodium citrate buffer, while the other three groups were treated for two weeks, respectively, with insulin (subcutaneously at a dose of 8 U/kg/day), nBMCs (intravenously at a dose of 1 × 106 cells/mouse/once), and dBMCs (intravenously at a dose of 1 × 106 cells/mouse/once). It is worth noting that administering adoptively transferred nBMCs or adoptively transferred dBMCs to STZ-induced T1DM mice resulted in a significant amelioration in glycemic condition, accompanied by a considerable reduction in the level of blood glucose and glycosylated hemoglobin % (HbA1C %), ultimately restoring serum insulin levels to their initial state in control mice. Administering nBMCs or dBMCs to STZ-induced T1DM mice led to a remarkable decrease in levels of inflammatory cytokine markers in the serum, including interferon-γ (INF-γ), tumor necrosis factor- α (TNF-α), tumor growth factor-β (TGF-β), interleukin-1 β (L-1β), interlekin-4 (IL-4), interleukin-6 (IL-6), and interleukin-10 (IL-10). Additionally, STZ-induced T1DM mice, when treated with nBMCs or dBMCs, experienced a notable rise in total immunoglobulin (Ig) level. Furthermore, there was a significant reduction in the levels of islet cell autoantibodies (ICA) and insulin autoantibodies (IAA). Furthermore, the serum of STZ-induced T1DM mice showed a significant increase in Zinc transporter 8 antigen protein (ZnT8), islet antigen 2 protein (IA-2), and glutamic acid decarboxylase antigen protein (GAD) levels. Interestingly, the administration of nBMCs or dBMCs resulted in a heightened expression of IA-2 protein in STZ-induced T1DM mice treated with nBMCs or dBMCs. Furthermore, the level of malondialdehyde (MDA) was increased, while the levels of catalase (CAT) and superoxide dismutase (SOD) were decreased in non-treated STZ-induced T1DM mice. However, when nBMCs or dBMCs were administered to STZ-induced T1DM mice, it had a significant impact on reducing oxidative stress. This was accomplished by reducing the levels of MDA in the serum and enhancing the activities of enzymatic antioxidants like CAT and SOD. STZ-induced T1DM mice displayed a significant elevation in the levels of liver enzymes ALT and AST, as well as heightened levels of creatinine and urea. Considering the crucial roles of the liver and kidney in metabolism and excretion, this research further examined the effects of administering nBMCs or dBMCs to STZ-induced T1DM mice. Notably, the administration of these cells alleviated the observed effects. The present study suggests that utilizing adoptively transferred nBMCs or adoptively transferred dBMCs in the treatment of T1DM led to noteworthy decreases in blood glucose levels, possibly attributed to their capacity to enhance insulin secretion and improve the performance of pancreatic islets. Additionally, BMCs may exert their beneficial effects on the pancreatic islets of diabetic mice through their immunomodulatory, antioxidant, anti-inflammatory, and anti-oxidative stress properties.

RapaLink-1 outperforms rapamycin in alleviating allogeneic graft rejection by inhibiting the mTORC1-4E-BP1 pathway in mice

Inhibition of mammalian target of rapamycin (mTOR), which is a component of both mTORC1 and mTORC2, leads to clinical benefits for organ transplant recipients. Pathways to inhibit mTOR include strengthening the association of FKBP12-mTOR or competing with ATP at the active site of mTOR, which have been applied to the design of first- and second-generation mTOR inhibitors, respectively. However, the clinical efficacy of these mTOR inhibitors may be limited by side effects, compensatory activation of kinases and attenuation of feedback inhibition of receptor expression. A new generation of mTOR inhibitors possess a core structure similar to rapamycin and covalently link to mTOR kinase inhibitors, resulting in moderate selectivity and potent inhibition of mTORC1. Since the immunosuppressive potential of this class of compounds remains unknown, our goal is to examine the therapeutic efficacy of a third-generation mTOR inhibitor in organ transplantation. In this study, RapaLink-1 outperformed rapamycin in inhibiting T-cell proliferation and significantly prolonged graft survival time. Mechanistically, the ameliorated rejection induced by RapaLink-1 is associated with a reduction in p-4E-BP1 in T cells, resulting in an elevation in Treg cells alongside a decline in Th1 and Th17 cells. For the first time, these studies demonstrate the effectiveness of third-generation mTOR inhibitors in inhibiting allograft rejection, highlighting the potential of this novel class of mTOR inhibitors for further investigation.

Efficiency of Bone Marrow-Derived Mesenchymal Stem Cells and Hesperetin in the Treatment of Streptozotocin-Induced Type 1 Diabetes in Wistar Rats.

Type 1 diabetes mellitus (T1DM) was established to be ameliorated by islet transplantation, but the shortage of the transplanted human islet tissue and the use of immunosuppressive drugs to inhibit the rejection of allogeneic grafts make this type of therapy is limited. Nowadays, therapy with stem cells is one of the most promising future treatments. This kind of therapy could have a profound impact on both replacement, as well as regenerative therapies, to improve or even cure various disorders, including diabetes mellitus. Flavonoids have also been shown to possess anti-diabetic effects. Thus, this study aims to evaluate the effectiveness of the bone marrow-derived mesenchymal stem cells (BM-MSCs) and hesperetin in the treatment of a T1DM rat model. T1DM was induced in male Wistar rats that had been starved for 16 h via intraperitoneal injection of STZ at a dose of 40 mg/kg body weight (b.wt.). After 10 days of STZ injection, the diabetic rats were allocated into four groups. The first diabetic animal group was considered a diabetic control, while the other three diabetic animal groups were treated for six weeks, respectively, with hesperetin (given orally at a dose of 20 mg/kg b.wt.), BM-MSCs (injected intravenously at a dose of 1 × 106 cells/rat/week), and their combination (hesperetin and BM-MSCs). The use of hesperetin and BM-MSCs in the treatment of STZ-induced diabetic animals significantly improved the glycemic state, serum fructosamine, insulin and C-peptide levels, liver glycogen content, glycogen phosphorylase, glucose-6-phosphatase activities, hepatic oxidative stress, and mRNA expressions of NF-κB, IL-1β, IL-10, P53, and Bcl-2 in pancreatic tissue. The study suggested the therapy with both hesperetin and BM-MSCs produced marked antihyperglycemic effects, which may be mediated via their potencies to ameliorate pancreatic islet architecture and insulin secretory response, as well as to decrease hepatic glucose output in diabetic animals. The improvement effects of hesperetin and BM-MSCs on the pancreatic islets of diabetic rats may be mediated via their antioxidant, anti-inflammatory, and antiapoptotic actions.

Local delivery of FK506 to a nerve allograft is comparable to systemic delivery at suppressing allogeneic graft rejection.

The objective of this study was to determine if locally delivered FK506 could prevent allogeneic nerve graft rejection long enough to allow axon regeneration to pass through the nerve graft. An 8mm mouse sciatic nerve gap injury repaired with a nerve allograft was used to assess the effectiveness of local FK506 immunosuppressive therapy. FK506-loaded poly(lactide-co-caprolactone) nerve conduits were used to provide sustained local FK506 delivery to nerve allografts. Continuous and temporary systemic FK506 therapy to nerve allografts, and autograft repair were used as control groups. Serial assessment of inflammatory cell and CD4+ cell infiltration into the nerve graft tissue was performed to characterize the immune response over time. Nerve regeneration and functional recovery was serially assessed by nerve histomorphometry, gastrocnemius muscle mass recovery, and the ladder rung skilled locomotion assay. At the end of the study, week 16, all the groups had similar levels of inflammatory cell infiltration. The local FK506 and continuous systemic FK506 groups had similar levels of CD4+ cell infiltration, however, it was significantly greater than the autograft control. In terms of nerve histmorphometry, the local FK506 and continunous systemic FK506 groups had similar amounts of myelinated axons, although they were significantly lower than the autograft and temporary systemic FK506 group. The autograft had significantly greater muscle mass recovery than all the other groups. In the ladder rung assay, the autograft, local FK506, and continuous systemic FK506 had similar levels of skilled locomotion performance, whereas the temporary systemic FK506 group had significanty better performance than all the other groups. The results of this study suggest that local delivery of FK506 can provide comparable immunosuppression and nerve regeneration outcomes as systemically delivered FK506.

Electroactive Hydroxyapatite/Carbon Nanofiber Scaffolds for Osteogenic Differentiation of Human Adipose-Derived Stem Cells.

Traditional bone defect treatments are limited by an insufficient supply of autologous bone, the immune rejection of allogeneic bone grafts, and high medical costs. To address this medical need, bone tissue engineering has emerged as a promising option. Among the existing tissue engineering materials, the use of electroactive scaffolds has become a common strategy in bone repair. However, single-function electroactive scaffolds are not sufficient for scientific research or clinical application. On the other hand, multifunctional electroactive scaffolds are often complicated and expensive to prepare. Therefore, we propose a new tissue engineering strategy that optimizes the electrical properties and biocompatibility of carbon-based materials. Here, a hydroxyapatite/carbon nanofiber (HAp/CNF) scaffold with optimal electrical activity was prepared by electrospinning HAp nanoparticle-incorporated polyvinylidene fluoride (PVDF) and then carbonizing the fibers. Biochemical assessments of the markers of osteogenesis in human adipose-derived stem cells (h-ADSCs) cultured on HAp/CNF scaffolds demonstrate that the material promoted the osteogenic differentiation of h-ADSCs in the absence of an osteogenic factor. The results of this study show that electroactive carbon materials with a fibrous structure can promote the osteogenic differentiation of h-ADSCs, providing a new strategy for the preparation and application of carbon-based materials in bone tissue engineering.

Nanoparticle dose and antigen loading attenuate antigen-specific T-cell responses.

Immune-mediated hypersensitivities such as autoimmunity, allergy, and allogeneic graft rejection are treated with therapeutics that suppress the immune system, and the lack of specificity is associated with significant side effects. The delivery of disease-relevant antigens (Ags) by carrier systems such as poly(lactide-co-glycolide) nanoparticles (PLG-Ag) and carbodiimide (ECDI)-fixed splenocytes (SP-Ag) has demonstrated Ag-specific tolerance induction in model systems of these diseases. Despite therapeutic outcomes by both platforms, tolerance is conferred with different efficacy. This investigation evaluated Ag loading and total particle dose of PLG-Ag on Ag presentation in a coculture system of dendritic cells (DCs) and Ag-restricted T cells, with SP-Ag employed as a control. CD25 expression was observed in nearly all T cells even at low concentrations of PLG-Ag, indicating efficient presentation of Ag by dendritic cells. However, the secretion of IL-2, Th1, and Th2 cytokines (IFNγ and IL-4, respectively) varied depending on PLG-Ag concentration and Ag loading. Concentration escalation of soluble Ag resulted in an increase in IL-2 and IFNγ and a decrease in IL-4. Treatment with PLG-Ag followed a similar trend but with lower levels of IL-2 and IFNγ secreted. Transcriptional Activity CEll ARrays (TRACER) were employed to measure the real-time transcription factor (TF) activity in Ag-presenting DCs. The kinetics and magnitude of TF activity was dependent on the Ag delivery method, concentration, and Ag loading. Ag positively regulated IRF1 activity and, as carriers, NPs and ECDI-treated SP negatively regulated this signaling. The effect of Ag loading and dose on tolerance induction were corroborated in vivo using the delayed-type hypersensitivity (DTH) and experimental autoimmune encephalomyelitis (EAE) mouse models where a threshold of 8 μg/mg Ag loading and 0.5 mg PLG-Ag dose were required for tolerance. Together, the effect of Ag loading and dosing on in vitro and in vivo immune regulation provide useful insights for translating Ag-carrier systems for the clinical treatment of immune disorders.

The Dual Regulatory Roles of Macrophages in Acute Allogeneic Organ Graft Rejection

Innate immune cells are critical for transplant response. As an important cellular component of innate immune cells, macrophages are the predominate infiltrated cells in allografts, and macrophage accumulation in allografts is negatively associated with the short- and long-term outcomes of organ transplantation. Macrophages are functionally heterogeneous and plastic. They participate in organ graft rejection through multiple pathways, including antigen presentation, the expression of costimulatory molecules and cytokines, and direct cytotoxicity and injury ability to allografts. However, some macrophage subpopulations, such as regulatory macrophages, can protect allografts from immune rejection and promote transplant immune tolerance with their immune regulatory properties. Although researchers recognize the potential roles macrophages play in allograft injury, they pay insufficient attention to the diverse roles of macrophages in allograft rejection. We herein briefly summarize the distinctive roles of macrophages in acute transplant immune response and the effect of immunosuppressive drugs on macrophages. Greater attention should be paid to the complex and critical function of macrophages in allograft rejection, and more effort should be put into developing immunosuppressive drugs that specifically target macrophages, which would ultimately improve the long-term survival of organ grafts in patients.

Local Dexamethasone Administration Delays Allogeneic Islet Graft Rejection in the Anterior Chamber of the Eye of Non-Human Primates

Pancreatic islet transplantation into the anterior chamber of the eye (ACE) has been shown to improve glycemic control and metabolic parameters of diabetes in both murine and primate models. This novel transplantation site also allows the delivery of therapeutic agents, such as immunosuppressive drugs, locally to prevent islet graft rejection and circumvent unwanted systemic side effects. Local intravitreal administration of micronized dexamethasone implant was performed prior to allogeneic islet transplantation into the ACEs of non-human primates. Two study groups were observed namely allogeneic graft without immunosuppression (n = 4 eyes) and allogeneic graft with local immunosuppression (n = 8 eyes). Survival of islet grafts and dexamethasone concentration in the ACE were assessed in parallel for 24 weeks. Allogeneic islet grafts with local dexamethasone treatment showed significantly better survival than those with no immunosuppression (median survival time- 15 weeks vs 3 weeks, log-rank test p<0.0001). Around 73% of the grafts still survived at week 10 with a single local dexamethasone implant, where the control group showed no graft survival. Dexamethasone treated islet grafts revealed a good functional response to high glucose stimulation despite there was a transient suppression of insulin secretion from week 8 to 12. Our findings show a significant improvement of allografts survival in the ACE with local dexamethasone treatment. These results highlight the feasibility of local administration of pharmacological compounds in the ACE to improve islet graft survival and function. By eliminating the need for systemic immunosuppression, these findings may impact clinical islet transplantation in the treatment of diabetes, and the ACE may serve as a novel therapeutic islet transplantation site with high potential for local pharmacological intervention.

Advances in Pancreatic Islet Transplantation Sites for the Treatment of Diabetes.

Diabetes is a complex disease that affects over 400 million people worldwide. The life-long insulin injections and continuous blood glucose monitoring required in type 1 diabetes (T1D) represent a tremendous clinical and economic burdens that urges the need for a medical solution. Pancreatic islet transplantation holds great promise in the treatment of T1D; however, the difficulty in regulating post-transplantation immune reactions to avoid both allogenic and autoimmune graft rejection represent a bottleneck in the field of islet transplantation. Cell replacement strategies have been performed in hepatic, intramuscular, omentum, and subcutaneous sites, and have been performed in both animal models and human patients. However more optimal transplantation sites and methods of improving islet graft survival are needed to successfully translate these studies to a clinical relevant therapy. In this review, we summarize the current progress in the field as well as methods and sites of islet transplantation, including stem cell-derived functional human islets. We also discuss the contribution of immune cells, vessel formation, extracellular matrix, and nutritional supply on islet graft survival. Developing new transplantation sites with emerging technologies to improve islet graft survival and simplify immune regulation will greatly benefit the future success of islet cell therapy in the treatment of diabetes.

Integrated Metabolomics and Proteomics Analyses in the Local Milieu of Islet Allografts in Rejection versus Tolerance.

An understanding of the immune mechanisms that lead to rejection versus tolerance of allogeneic pancreatic islet grafts is of paramount importance, as it facilitates the development of innovative methods to improve the transplant outcome. Here, we used our established intraocular islet transplant model to gain novel insight into changes in the local metabolome and proteome within the islet allograft’s immediate microenvironment in association with immune-mediated rejection or tolerance. We performed integrated metabolomics and proteomics analyses in aqueous humor samples representative of the graft’s microenvironment under each transplant outcome. The results showed that several free amino acids, small primary amines, and soluble proteins related to the Warburg effect were upregulated or downregulated in association with either outcome. In general, the observed shifts in the local metabolite and protein profiles in association with rejection were consistent with established pro-inflammatory metabolic pathways and those observed in association with tolerance were immune regulatory. Taken together, the current findings further support the potential of metabolic reprogramming of immune cells towards immune regulation through targeted pharmacological and dietary interventions against specific metabolic pathways that promote the Warburg effect to prevent the rejection of transplanted islets and promote their immune tolerance.

Overexpression of miR-223 Promotes Tolerogenic Properties of Dendritic Cells Involved in Heart Transplantation Tolerance by Targeting Irak1.

Dendritic cells (DCs) are key mediators of transplant rejection. Numerous factors have been identified that regulate transplant immunopathology by modulating the function of DCs. Among these, microRNAs (miRNAs), small non-coding RNA molecules, have received much attention. The miRNA miR-223 is very highly expressed and tightly regulated in hematopoietic cells. It plays an important role in modulating the immune response by regulating neutrophils and macrophages, and its dysregulation contributes to multiple types of immune diseases. However, the role of miR-223 in immune rejection is unclear. Here, we observed expression of miR-223 in patients and mice who had undergone heart transplantation and found that it increased in the serum of both, and also in DCs from the spleens of recipient mice, although it was unchanged in splenic T cells. We also found that miR-223 expression decreased in lipopolysaccharide-stimulated DCs. Increasing the level of miR-223 in DCs promoted polarization of DCs toward a tolerogenic phenotype, which indicates that miR-223 can attenuate activation and maturation of DCs. MiR-223 effectively induced regulatory T cells (Tregs) by inhibiting the function of antigen-presenting DCs. In addition, we identified Irak1 as a miR-223 target gene and an essential regulator of DC maturation. In mouse allogeneic heterotopic heart transplantation models, grafts survived longer and suffered less immune cell infiltration in mice with miR-223-overexpressing immature (im)DCs. In the miR-223-overexpressing imDC recipients, T cells from spleen differentiated into Tregs, and the level of IL-10 in heart grafts was markedly higher than that in the control group. In conclusion, miR-223 regulates the function of DCs via Irak1, differentiation of T cells into Tregs, and secretion of IL-10, thereby suppressing allogeneic heart graft rejection.

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.

10399 DNA-PK(cs) Regulates Stability of Egr1 During T Cell Activation

ABSTRACT IMPACT: This work provides supporting evidence for the development of a novel immunosuppression therapy for transplant patients. OBJECTIVES/GOALS: Our laboratory reported that inhibition of the kinase DNA-PK(cs) in mice delays allogeneic graft rejection in part by mitigating the induction of certain cytokines. We hypothesized that this was due to an inhibition of intracellular signaling programs in T cells and designed studies to identify the mechanism(s) by which this occurs. METHODS/STUDY POPULATION: The immortalized Jurkat T cell line was used to evaluate the effect of the DNA-PK(cs) inhibitor NU7441 on T cell activation by PMA/Ionomycin or PMA/PHA. Mouse primary splenocytes also were used to demonstrate the universality and reproducibility of our observations. Initially, protein mass spectrometry of lysates from untreated and NU7441-treated Jurkat cells identified proteins of interest regulated by DNA-PK(cs) that play a role in T cell activation and cytokine production. CRISPR genome editing was used to validate a potential downstream target of DNA-PK(cs). Western blot, ELISA, and flow cytometry were used to document changes in protein levels with respect to treatments. RESULTS/ANTICIPATED RESULTS: We observed that expression of the transcription factor Egr1 was highly induced after activation but attenuated after treatment with NU7441 in both Jurkat T cells and mouse splenocytes. Phosphorylated serine 301 of Egr1 was identified by mass spectrometry in stimulated cells and fits the kinase consensus sequence for DNA-PK(cs). Both an endogenous CRISPR-generated serine 301 to alanine mutant and expression of a plasmid-based S301A mutant resulted in an unstable form of Egr1 that was barely detectable. In contrast, expression of either a S301 to D or E phospho-mimetic mutant resulted in a stable form of the protein detectable by Western blot. Further evaluation of these mutants and Egr1 phosphorylation is underway to determine the mechanism by which DNA-PK(cs) kinase regulates protein stability. DISCUSSION/SIGNIFICANCE OF FINDINGS: We previously reported a role for DNA-PK(cs) in immunomodulation. We now have evidence that this occurs in part through stabilization of Egr1. We believe this novel finding will lead to uncovering a broader role for DNA-PK(cs) as a mediator of protein stability in T cells and provide support for targeting DNA-PK(cs) in immunosuppression therapy.

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.

1685-P: Islet Encapsulation with Tannic Acid Delays Allogeneic Islet Graft Rejection

Type 1 diabetes (T1D) is defined by the destruction of insulin-producing cells. Islet transplantation can restore glucose homeostasis and prevent serious hypoglycemic events; however, long-term graft survival is low. Oxidative stress can mediate islet transplantation rejection and suppressing oxidative stress with nanothin islet encapsulation materials comprised of alternating layers of tannic acid (TA), an immunomodulatory antioxidant, and poly(N-vinylpyrrolidone) (PVPON), a scaffold polymer, may allow for improved graft survival without systemic immunosuppression. We hypothesize that (PVPON/TA)-encapsulation of islets will prolong graft function following allotransplantation into immunocompetent recipients without utilizing systemic immunosuppression. Allogeneic transplantation of encapsulated C57BL/6 islets into diabetic non-obese diabetic (NOD) mice (n=12) significantly delayed graft failure by more than 90 days compared to controls and significantly reduced free radical-adduct formation produced by neutrophils and macrophages at the graft site. Gene expression displayed a 5- and 20-fold increase of anti-inflammatory genes Retnla and Arg1, respectively, and 3-fold reductions in Ccl5, Cxcl10, Prf1, and Grzmb mRNA accumulation in (PVPON/TA) versus control grafts. Flow cytometry analysis of encapsulated grafts contained fewer numbers of infiltrating dendritic cells and CD8 T cells and reduced frequencies of CCL5+, CXCR3+, MHC-II+ macrophages and perforin+ CD8 T cells by 3-fold compared to controls. Encapsulated grafts also reduced the frequencies of TNF+ and MHC-II+ dendritic cells by 2-fold. Additionally, encapsulation increased the frequency of arginase-1+ and CD206+ alternatively-activated macrophages 4-fold, suggesting that (PVPON/TA)-encapsulation may be a promising technique to prolong clinical islet graft function by skewing macrophage phenotypes and suppressing cytotoxic T cell effector responses in the absence of systemic immunosuppression. Disclosure J. Barra: None. V. Kozlovskaya: None. E. Kharlampieva: None. H.M. Tse: None. Funding National Institute of Diabetes and Digestive and Kidney Diseases (R01DK099550); JDRF (SRA-2016-270-S-B, JDRF 2-SRA-2019-692-S-B); National Science Foundation (NSF-DMR 1608728); National Institute of General Medical Sciences (T32GM008111)

IL-27Rα: A Novel Molecular Imaging Marker for Allograft Rejection.

Non-invasively monitoring allogeneic graft rejection with a specific marker is of great importance for prognosis of patients. Recently, data revealed that IL-27Rα was up-regulated in alloreactive CD4+ T cells and participated in inflammatory diseases. Here, we evaluated whether IL-27Rα could be used in monitoring allogeneic graft rejection both in vitro and in vivo. Allogeneic (C57BL/6 donor to BALB/c recipient) and syngeneic (BALB/c both as donor and recipient) skin grafted mouse models were established. The expression of IL-27Rα in grafts was detected. The radio-probe, 125I-anti-IL-27Rα mAb, was prepared. Dynamic whole-body phosphor-autoradiography, ex vivo biodistribution and immunofluorescence staining were performed. The results showed that the highest expression of IL-27Rα was detected in allogeneic grafts on day 10 post transplantation (top period of allorejection). 125I-anti-IL-27Rα mAb was successfully prepared with higher specificity and affinity. Whole-body phosphor-autoradiography showed higher radioactivity accumulation in allogeneic grafts than syngeneic grafts on day 10. The uptake of 125I-anti-IL-27Rα mAb in allogeneic grafts could be almost totally blocked by pre-injection with excess unlabeled anti-IL-27Rα mAb. Interestingly, we found that 125I-anti-IL-27Rα mAb accumulated in allogeneic grafts, along with weaker inflammation earlier on day 6. The high uptake of 125I-anti-IL-27Rα mAb was correlated with the higher infiltrated IL-27Rα positive cells (CD3+/CD68+) in allogeneic grafts. In conclusion, IL-27Rα may be a novel molecular imaging marker to predict allorejection.

Characterization of Clinical and Histological Rejection of Male Genital Tissues Using a Novel Microsurgical Rat Penile Transplantation Model.

Penis transplantation represents an exciting new avenue for restoration of male urogenitalia. However, little is known about the specific immunological features of penile transplants, limiting their application in complex urogenital reconstruction. To properly study this emerging form of transplantation, adequate preclinical models are a necessity. The purpose of this study is to establish a clinical and histological rejection classification of urogenital tissue transplants using a new rat heterotopic penile transplant model that includes preputial skin. Syngeneic and allogeneic heterotopic penile transplantations were performed on Lewis and Brown Norway rats using a new model designed by our group. Grafts were clinically and histologically monitored at postoperative days (POD) 3-30. Six syngeneic and 25 allogeneic transplants were performed. All syngeneic and tacrolimus-treated grafts survived until endpoint. Allogeneic graft rejection is shown to follow a 4-stage clinical progression with all untreated allografts developing epidermal sloughing at POD7 and full rejecting between POD14 and POD16. Histological samples were used to develop a specific 4-grade rejection classification analogous to the 2007 Banff Criteria for skin-containing allografts. Graft skin and urethral lining tissue are first rejection targets followed by tunica albuginea and corpora cavernosa in a distal to proximal pattern. We established a robust and reproducible murine model to study the immunobiology of male genital tissue in the context of transplantation and developed a novel 4-grade clinical and histological rejection scale based on graft skin and urethral lining as the main targets of rejection.

Recipient natural killer cells alter the course of rejection of allogeneic heart grafts in rats.

Rejection of solid organ grafts is regarded to be dependent on T cell responses. Nonetheless, numerous studies have focused on the contribution of NK cells in this process, resulting in contradictory theories. While some conclude that there is no participation of NK cells, others found an inflammatory or regulative role of NK cells. However, the experimental settings are rarely comparable with regard to challenged species, strain combinations or the nature of the graft. Thus, clear definition of NK cell contribution might be impeded by these circumstances. In this study we performed heterotopic heart transplantation (HTx) in rats, choosing one donor-recipient-combination leading to a fast and a second leading to a prolonged course of graft rejection. We intervened in the rejection process, by depletion of recipient NK cells on the one hand and by injection of activated NK cells syngeneic to the recipients on the other. The fast course of rejection could not be influenced by any of the NK cell manipulative treatments. However, the more prolonged course of rejection was highly susceptible to depletion of NK cells, resulting in significant acceleration of rejection, while injection of NK cells induced acceptance of the grafts. We suggest that, depending on the specific setting, NK cells can attenuate the first trigger of immune response, which allows establishing the regulatory activity leading to tolerance of the graft.

Inhibition of allogeneic islet graft rejection by VISTA-conjugated liposome

The Ig superfamily member V-domain Ig-containing suppressor of T-cell activation (VISTA) is a negative regulator with broad-spectrum activities and has reported that blockade of VISTA or combination with other negative checkpoint receptors sufficiently break tumor tolerance. However, it remains unclear whether VISTA could induce allogeneic T-cell hyporesponsiveness and inhibit allograft rejection. Here we found VISTA treatment significantly inhibited lymphocyte proliferation and activation in allogeneic MLR assay through impairing SYK-VAV pathway. Interestingly, though neither VISTA protein nor VISTA-Fc fusion protein administration exerted satisfactory immunosuppressive effect on allograft survival due to their short half-life in circulation, this problem was solved by conjugating VISTA protein on liposome by biotin-streptavidin system, which markedly prolonged its circulating half-life to 60 h. With islet transplant model, administration of VISTA-conjugated liposome could markedly prolong allograft survival by inhibition of SYK-VAV pathway, thus maintained the normal blood glucose level of recipients during treatment period. The results indicate VISTA is a promising therapeutic target to treat allograft rejection of islet transplantation.

Human Double-Negative Regulatory T Cells Modulate Effector Functions of Conventional T Cells By Selectively Blocking mTOR Signaling

Regulatory T cells play an important role in the maintenance of immune tolerance to self-antigens and are involved in modulating immune responses to promote resolution of inflammation. The population of TCRαβ+ CD4-/CD8- (double-negative, DN) T cells has attracted growing attention as a result of their potent immune regulatory function. In murine models, DN T cells were able to prevent rejection of allogeneic and xenogeneic organ grafts by effectively suppressing reactive T cells. In addition, DN T cells possess the capacity to resolve various inflammatory conditions, including graft-versus-host disease (GvHD) after allogeneic hematopoietic stem cell transplantation. Notably, first clinical studies in patients after stem cell transplantation demonstrated an inverse correlation between the frequency of circulating DN T cells and the severity of acute GvHD, suggesting a therapeutic potential of human DN T cells. To gain a better understanding of the molecular mechanism of suppression, we investigated whether human DN T cells modulate distinct signaling processes in conventional T cells. We found that DN T cells selectively block mTOR signaling but not activation of mitogen-activated protein kinases. Enforced activation of the mTOR pathway by a chemical activator rendered conventional T cells unsusceptible to DN T cell-mediated suppression, confirming the critical function of mTOR signaling. Given that mTOR is a major regulator of cellular metabolism, we further determined the impact of DN T cells on the metabolic framework of conventional T cells. Of interest, DN T cells diminished upregulation of the glycolytic machinery and glucose uptake in conventional T cells, whereas fatty acid uptake was not modified. Next, we investigated the fate and function of effector cells after DN T cell co-culture. Of importance, DN T cells suppressed proliferation but also altered expression of differentiation markers, transcription factors and homing receptors. Further analyses demonstrated that CD4+ T cells failed to produce effector cytokines IL-17 and IFN-γ after coculture with DN T cells, whereas IL-2 secretion was amplified. The selective modification was induced by a direct cell-cell contact dependent mechanism between CD4 and DN T cells and not as a consequence of competition for nutrients or growth factors. Together, our findings expand the understanding of DN T cell functionality and support that human DN T cells represent an interesting opportunity to limit and modulate T-cell reactivity. DisclosuresNo relevant conflicts of interest to declare.