Allorecognition by T Lymphocytes and Allograft Rejection

The MEK Inhibitor Trametinib Suppresses Major Histocompatibility Antigen-mismatched Rejection Following Pancreatic Islet Transplantation

Background.

Potential adverse effects, such as functional impairment of islets, render conventional immunosuppressive drugs unsuitable for use in islet transplantation. In addition, as a single therapy, they cannot prolong islet allograft survival. Here, we investigated the utility of the mitogen-activated protein kinase inhibitor trametinib and asked whether it ameliorates acute rejection of transplanted islets without the need for conventional immunosuppressants.

Methods.

Islets from fully major histocompatibility complex-mismatched BALB/c mice were transplanted into streptozotocin-induced diabetic C57BL/6 mice via the portal vein. These mice received trametinib or vehicle (orally) for 28 days. Isolated islets from BALB/c mice were incubated in vitro with different concentrations of trametinib to determine viability and function.

Results.

Trametinib (0.1 and 0.3 mg/kg) prolonged graft survival significantly (P = 0.0007 and P = 0.005, respectively) when compared with vehicle. Histologic analyses revealed that cellular infiltration of the graft by lymphocytes was inhibited significantly on day 7 (P < 0.05). In addition, trametinib suppressed functional differentiation of naive CD4⁺ T cells in recipients. Expression of mRNA encoding inflammatory cytokines interleukin (IL)-2, tumor necrosis factor α, and interferon γ in recipients treated with trametinib was also inhibited (P < 0.001, P < 0.05, and P < 0.01, respectively). Trametinib also increased production of IL-4 and IL-10 (P < 0.05 and P = 0.20, respectively). In vitro, islets incubated with different concentrations of trametinib exhibited no harmful effects with respect to viability and function.

Conclusions.

Trametinib delayed islet graft rejection by inhibiting functional differentiation of naive CD4⁺ T cells and regulating inflammatory cytokines. Trametinib might be a promising candidate for maintenance immunosuppressive therapy after allogeneic islet transplantation.

Lymph node fibroblastic reticular cells deposit fibrosis-associated collagen following organ transplantation

Although the immune response within draining lymph nodes (DLNs) has been studied for decades, how their stromal compartment contributes to this process remains to be fully explored. Here, we show that donor mast cells were prominent activators of collagen I deposition by fibroblastic reticular cells (FRCs) in DLNs shortly following transplantation. Serial analysis of the DLN indicated that the LN stroma did not return to its baseline microarchitecture following organ rejection and that the DLN contained significant fibrosis following repetitive organ transplants. Using several FRC conditional-knockout mice, we show that induction of senescence in the FRCs of the DLN resulted in massive production of collagen I and a proinflammatory milieu within the DLN. Stimulation of herpes virus entry mediator (HVEM) on FRCs by its ligand LIGHT contributed chiefly to the induction of senescence in FRCs and overproduction of collagen I. Systemic administration of ex vivo-expanded FRCs to mice decreased DLN fibrosis and strengthened the effect of anti-CD40L in prolonging heart allograft survival. These data demonstrate that the transformation of FRCs into proinflammatory myofibroblasts is critically important for the maintenance of a proinflammatory milieu within a fibrotic DLN.

The TNF/TNFR2 signaling pathway is a key regulatory factor in endothelial progenitor cell immunosuppressive effect

Background

Endothelial progenitor cells (EPCs) are non-differentiated endothelial cells (ECs) present in blood circulation that are involved in neo-vascularization and correction of damaged endothelial sites. Since EPCs from patients with vascular disorders are impaired and inefficient, allogenic sources from adult or cord blood are considered as good alternatives. However, due to the reaction of immune system against allogenic cells which usually lead to their elimination, we focused on the exact role of EPCs on immune cells, particularly, T cells which are the most important cells applied in immune rejection. TNFα is one of the main activators of EPCs that recognizes two distinct receptors. TNFR1 is expressed ubiquitously and its interaction with TNFα leads to differentiation and apoptosis, whereas, TNFR2 is expressed predominantly on ECs, immune cells and neural cells and is involved in cell survival and proliferation. Interestingly, it has been shown that different immunosuppressive cells express TNFR2 and this is directly related to their immunosuppressive efficiency. However, little is known about immunological profile and function of TNFR2 in EPCs.

Methods

Using different in-vitro combinations, we performed co-cultures of ECs and T cells to investigate the immunological effect of EPCs on T cells. We interrupted in the TNFα/TNFR2 axis either by blocking the receptor using TNFR2 antagonist or blocking the ligand using T cells derived from TNFα KO mice.

Results

We demonstrated that EPCs are able to suppress T cell proliferation and modulate them towards less pro-inflammatory and active phenotypes. Moreover, we showed that TNFα/TNFR2 immune-checkpoint pathway is critical in EPC immunomodulatory effect.

Conclusions

Our results reveal for the first time a mechanism that EPCs use to suppress immune cells, therefore, enabling them to form new immunosuppressive vessels. Furthermore, we have shown the importance of TNFα/TNFR2 axis in EPCs as an immune checkpoint pathway. We believe that targeting TNFR2 is especially crucial in cancer immune therapy since it controls two crucial aspects of tumor microenvironment: 1) Immunosuppression and 2) Angiogenesis.

Induction of immunological tolerance to myelinogenic glial-restricted progenitor allografts

The immunological barrier currently precludes the clinical utilization of allogeneic stem cells. Although glial-restricted progenitors have become attractive candidates to treat a wide variety of neurological diseases, their survival in immunocompetent recipients is limited. In this study, we adopted a short-term, systemically applicable co-stimulation blockade-based strategy using CTLA4-Ig and anti-CD154 antibodies to modulate T-cell activation in the context of allogeneic glial-restricted progenitor transplantation. We found that co-stimulation blockade successfully prevented rejection of allogeneic glial-restricted progenitors from immunocompetent mouse brains. The long-term engrafted glial-restricted progenitors myelinated dysmyelinated adult mouse brains within one month. Furthermore, we identified a set of plasma miRNAs whose levels specifically correlated to the dynamic changes of immunoreactivity and as such could serve as biomarkers for graft rejection or tolerance. We put forward a successful strategy to induce alloantigen-specific hyporesponsiveness towards stem cells in the CNS, which will foster effective therapeutic application of allogeneic stem cells.

Allo-priming as a universal anti-viral vaccine: protecting elderly from current COVID-19 and any future unknown viral outbreak

BACKGROUND

We present the rationale for a novel allo-priming approach to serve the elderly as a universal anti-virus vaccine, as well serving to remodel the aging immune system in order to reverse immunosenescence and inflammaging. This approach has the potential to protect the most vulnerable from disease and provide society an incalculable economic benefit. Allo-priming healthy elderly adults is proposed to provide universal protection from progression of any type of viral infection, including protection against progression of the current outbreak of COVID-19 infection, and any future variants of the causative SARS-CoV-2 virus or the next 'Disease X'. Allo-priming is an alternative approach for the COVID-19 pandemic that provides a back-up in case vaccination strategies to elicit neutralizing antibody protection fails or fails to protect the vulnerable elderly population. The allo-priming is performed using activated, intentionally mismatched, ex vivo differentiated and expanded living Th1-like cells (AlloStim^®) derived from healthy donors currently in clinical use as an experimental cancer vaccine. Multiple intradermal injections of AlloStim^® creates a dominate titer of allo-specific Th1/CTL memory cells in circulation, replacing the dominance of exhausted memory cells of the aged immune system. Upon viral encounter, by-stander activation of the allo-specific memory cells causes an immediate release of IFN-ϒ, leading to development of an "anti-viral state", by-stander activation of innate cellular effector cells and activation of cross-reactive allo-specific CTL. In this manner, the non-specific activation of allo-specific Th1/CTL initiates a cascade of spatial and temporal immune events which act to limit the early viral titer. The release of endogenous heat shock proteins (HSP) and DAMP from lysed viral-infected cells, in the context of IFN-ϒ, creates of conditions for in situ vaccination leading to viral-specific Th1/CTL immunity. These viral-specific Th1/CTL provide sterilizing immunity and memory for protection from disease recurrence, while increasing the pool of Th1/CTL in circulation capable of responding to the next viral encounter.

CONCLUSION

Allo-priming has potential to provide universal protection from viral disease and is a strategy to reverse immunosenescence and counter-regulate chronic inflammation (inflammaging). Allo-priming can be used as an adjuvant for anti-viral vaccines and as a counter-measure for unknown biological threats and bio-economic terrorism.

Genetic Ablation of HLA Class I, Class II, and the T-cell Receptor Enables Allogeneic T Cells to Be Used for Adoptive T-cell Therapy

Adoptive immunotherapy can induce sustained therapeutic effects in some cancers. Antitumor T-cell grafts are often individually prepared in vitro from autologous T cells, which requires an intensive workload and increased costs. The quality of the generated T cells can also be variable, which affects the therapy's antitumor efficacy and toxicity. Standardized production of antitumor T-cell grafts from third-party donors will enable widespread use of this modality if allogeneic T-cell responses are effectively controlled. Here, we generated HLA class I, HLA class II, and T-cell receptor (TCR) triple-knockout (tKO) T cells by simultaneous knockout of the B2M, CIITA, and TRAC genes through Cas9/sgRNA ribonucleoprotein electroporation. Although HLA-deficient T cells were targeted by natural killer cells, they persisted better than HLA-sufficient T cells in the presence of allogeneic peripheral blood mononuclear cells (PBMC) in immunodeficient mice. When transduced with a CD19 chimeric antigen receptor (CAR) and stimulated by tumor cells, tKO CAR-T cells persisted better when cultured with allogeneic PBMCs compared with TRAC and B2M double-knockout T cells. The CD19 tKO CAR-T cells did not induce graft-versus-host disease but retained antitumor responses. These results demonstrated the benefit of HLA class I, HLA class II, and TCR deletion in enabling allogeneic-sourced T cells to be used for off-the-shelf adoptive immunotherapy.

Trametinib Attenuates Delayed Rejection and Preserves Thymic Function in Rat Lung Transplantation

Delayed immunological rejection after human lung transplantation causes chronic lung allograft dysfunction, which is associated with high mortality. Delayed rejection may be attributable to indirect alloantigen presentation by host antigen-presenting cells; however, its pathophysiology is not fully understood. The mitogen-activated protein kinase pathway is activated in T cells upon stimulation, and we previously showed that the MEK inhibitor, trametinib, suppresses graft-versus-host disease after murine bone marrow transplantation. We investigated whether trametinib suppresses graft rejection after two types of rat lung transplantation and analyzed its immunological mode of action. Major histocompatibility complex-mismatched transplantation from brown Norway rats into Lewis rats and minor histocompatibility antigen-mismatched transplantation from Fischer 344 rats into Lewis rats were performed. Cyclosporine (CsA) and/or trametinib were administered alone or consecutively. Acute and delayed rejection, lymphocyte infiltration, and pulmonary function were evaluated. Administration of trametinib after CsA suppressed delayed rejection, reduced inflammatory cell infiltration and fibrosis within the graft, and preserved pulmonary functions at Day 28. Trametinib suppressed functional differentiation of T and B cells in the periphery but preserved thymic T cell differentiation. Donor B cells within the graft disappeared by Day 14, indicating that delayed graft rejection at Day 28 was mainly due to indirect presentation by host antigen-presenting cells. Finally, trametinib administration without CsA preconditioning suppressed rejection after minor histocompatibility antigen-mismatched transplantation. Trametinib attenuates delayed rejection upon major histocompatibility complex-mismatched transplantation by suppressing indirect presentation and is a promising candidate to treat chronic lung allograft dysfunction in humans.

Primed macrophages directly and specifically reject allografts

Monocytes and macrophages have long been associated with acute and chronic allograft rejection; this is mediated by their abilities to promote inflammation, kill target cells via antibody-dependent cytotoxicity and modulate adaptive immunity. Our present study showed that allogeneic antigen-primed macrophages acutely rejected skin grafts with specificity after adoptive transfer into MHC-matched immunodeficient mice. The ability of primed macrophages to reject allografts essentially requires the help of CD4+ T cells and does not require the help of CD8+ T cells. Moreover, the primed, perforin-deficient macrophages rejected the skin grafts in a significantly delayed pattern compared with WT macrophages, indicating that the perforin pathway of the primed macrophages is likely involved in the rejection process. Thus, primed macrophages are endowed with adaptive immunity-like features, such as specificity, with the help of CD4+ T cells during the immune response to allografts. The present study challenges our traditional views of macrophage functions and highlights the biological functions of macrophages beyond innate immunity in mammals.

T-Cell Immunotherapies Targeting Histocompatibility and Tumor Antigens in Hematological Malignancies

Over the last decades, T-cell immunotherapy has revealed itself as a powerful, and often curative, strategy to treat blood cancers. In hematopoietic cell transplantation, most of the so-called graft-vs.-leukemia (GVL) effect hinges on the recognition of histocompatibility antigens that reflect immunologically relevant genetic variants between donors and recipients. Whether other variants acquired during the neoplastic transformation, or the aberrant expression of gene products can yield antigenic targets of similar relevance as the minor histocompatibility antigens is actively being pursued. Modern genomics and proteomics have enabled the high throughput identification of candidate antigens for immunotherapy in both autologous and allogeneic settings. As such, these major histocompatibility complex-associated tumor-specific (TSA) and tumor-associated antigens (TAA) can allow for the targeting of multiple blood neoplasms, which is a limitation for other immunotherapeutic approaches, such as chimeric antigen receptor (CAR)-modified T cells. We review the current strategies taken to translate these discoveries into T-cell therapies and propose how these could be introduced in clinical practice. Specifically, we discuss the criteria that are used to select the antigens with the greatest therapeutic value and we review the various T-cell manufacturing approaches in place to either expand antigen-specific T cells from the native repertoire or genetically engineer T cells with minor histocompatibility antigen or TSA/TAA-specific recombinant T-cell receptors. Finally, we elaborate on the current and future incorporation of these therapeutic T-cell products into the treatment of hematological malignancies.

The Evolving Clinical Presentation of Acute Rejection in Facial Transplantation

Importance

Acute rejection is one of the most frequent complications in facial transplantation, with potentially severe consequences for the recipient if overlooked. Clinical signs, such as erythema or edema, are helpful to diagnose acute rejection in the early follow-up stage; however, it is not well known whether these clinical signs remain reliable markers of acute rejection beyond the second posttransplant year.

Objective

To determine the diagnostic value of clinical signs of acute rejection after facial transplantation over time.

Design, Setting, and Participants

A retrospective, single-center cohort study was conducted of patients who underwent facial transplantation at Brigham and Women's Hospital between April 2009 and October 2014, with up to an 8-year follow-up. Medical records were reviewed until September 30, 2017. The medical records from 104 encounters with 7 patients who underwent partial or full facial transplantation were analyzed for symptoms of rejection, immunosuppressive therapy, and histopathologic findings.

Main Outcomes and Measures

The occurrence of 5 clinical signs of acute rejection were evaluated: erythema, edema, exanthema, suture line erythema, and mucosal lesions. Odds ratios (ORs) were calculated to determine the statistically significant association of these signs with the histopathologic diagnosis of rejection. In addition, tacrolimus blood levels, as a surrogate marker of immunosuppressive therapy, were evaluated.

Results

Of the 7 patients included in the study, 5 were men. The mean follow-up was 66 months (range, 35-101). Of 104 clinical encounters, 46 encounters (44.2%) represented rejection episodes and 58 encounters (55.8%) represented no-rejection episodes. Beyond 2 years posttransplantation, only erythema (OR, 6.53; 95% CI, 1.84-20.11; P = .004) and exanthema (OR, ∞; 95% CI, 2.2-∞; P = .004) were demonstrated to be reliable clinical signs of acute rejection in facial transplantation. There was also a statistically significant association of subtherapeutic tacrolimus levels with late rejection episodes (OR, 3.79; 95% CI, 1.25-12.88; P = .03). In addition, the occurrence of subclinical rejection was more frequent during later follow-up times (7 [24.1%] late rejections vs 1 [5.9%] early rejection). Five of 8 subclinical rejections (62.5%) were associated with subtherapeutic tacrolimus levels.

Conclusions and Relevance

Clinical signs of acute rejection in facial transplantation appear to be of limited diagnostic value, particularly after the second postoperative year. Until alternative biomarkers for rejection are identified, protocol skin biopsies will remain necessary for guiding assessments of allograft rejection.

Level of Evidence

3.

Extracellular vesicles in allograft rejection and tolerance

Extracellular vesicles (EVs), including exosomes, ectosomes and apoptotic vesicles, play an essential role in communication between cells of the innate and adaptive immune systems. Recent studies showed that EVs released after transplantation of allogeneic tissues and organs are involved in the immune recognition and response leading to rejection or tolerance in mice. After skin, pancreatic islet, and solid organ transplantation, donor-derived EVs were shown to initiate direct inflammatory alloresponses by T cells leading to acute rejection. This occurred through presentation of intact allogeneic MHC molecules on recipient antigen presenting cells (MHC cross-dressing) and subsequent activation of T cells via semi-direct allorecognition. On the other hand, some studies have documented the role of EVs in maternal tolerance of fetal alloantigens during pregnancy and immune privilege associated with spontaneous tolerance of liver allografts in laboratory rodents. The precise nature of the EVs, which are involved in rejection or tolerance, and the cells which produce them, is still unclear. Nevertheless, several reports showed that EVs released in the blood and urine by allografts can be used as biomarkers of rejection. This article reviews current knowledge on the contribution of EVs in allorecognition by T cells and discusses some mechanisms underlying their influence on T cell alloimmunity in allograft rejection or tolerance.

Pretransplant Donor-Specific Anti-HLA Antibodies and the Risk for Rejection-Related Graft Failure of Kidney Allografts

Background

The presence of donor-specific antibodies (DSAs) against HLA before kidney transplantation has been variably associated with decreased long-term graft survival. Data on the relation of pretransplant DSA with rejection and cause of graft failure in recipients of donor kidneys are scarce.

Methods

Patients transplanted between 1995 and 2005 were included and followed until 2016. Donor-specific antibodies before transplantation were determined retrospectively. For cause, renal transplant biopsies were reviewed.

Results

Pretransplant DSAs were found in 160 cases on a total of 734 transplantations (21.8%). In 80.5% of graft failures, a diagnostic renal biopsy was performed. The presence of pretransplant DSA (DSApos) increased the risk of graft failure within the first 3 months after transplantation (5.2% vs. 9.4%) because of rejection with intragraft thrombosis (p < 0.01). One year after transplantation, DSApos recipients had an increased hazard for antibody-mediated rejection at 10 years (9% DSAneg vs. 15% DSApos, p < 0.01). One year after transplantation, DSApos recipients had an increased hazard for antibody-mediated rejection at 10 years (9% DSAneg vs. 15% DSApos, p < 0.01). One year after transplantation, DSApos recipients had an increased hazard for antibody-mediated rejection at 10 years (9% DSAneg vs. 15% DSApos.

Conclusions

Pretransplant DSAs are a risk factor for early graft loss and increase the incidence for humoral rejection and graft loss but do not affect the risk for T cell-mediated rejection.

Tumor necrosis factor-driven cell death in donor organ as a barrier to immunological tolerance

PURPOSE OF REVIEW

Regulated cell death (RCD) is likely to play a role in organ rejection but it is unclear how it may be invoked. A well-known trigger of regulated cell death is tumor necrosis factor-alpha (TNF), which activates both caspase-dependent apoptosis and caspase-independent necroptosis. TNF is best known as a pro-inflammatory cytokine because it activates NFκB and MAPK signaling to induce expression of pro-inflammatory genes.

RECENT FINDINGS

Emerging data from animal models now suggest that TNF-induced cell death can also be inflammatory. Therefore, the role of cellular demise in regulating immunity should be considered. In transplantation, TNF could have a role in cellular injury or death from ischemia reperfusion (IR) injury and this may dictate organ survival. The default response to TNF in most cells is survival, rather than death, because of the presence of cell death checkpoints. However, cells succumb to TNF-driven death when these checkpoints are disrupted, and sensitivity to death likely reflects a reduction in molecules that fortify these checkpoints. We propose that a cell's propensity to die in response to TNF may underlie allograft rejection.

SUMMARY

Genetic, epigenetic, and posttranslational control of death checkpoint regulators in donor tissues may determine graft survival. Therapeutically, drugs that prevent donor cell demise could be useful in preventing organ rejection.

Missing self triggers NK cell-mediated chronic vascular rejection of solid organ transplants

Current doctrine is that microvascular inflammation (MVI) triggered by a transplant -recipient antibody response against alloantigens (antibody-mediated rejection) is the main cause of graft failure. Here, we show that histological lesions are not mediated by antibodies in approximately half the participants in a cohort of 129 renal recipients with MVI on graft biopsy. Genetic analysis of these patients shows a higher prevalence of mismatches between donor HLA I and recipient inhibitory killer cell immunoglobulin-like receptors (KIRs). Human in vitro models and transplantation of β2-microglobulin-deficient hearts into wild-type mice demonstrates that the inability of graft endothelial cells to provide HLA I-mediated inhibitory signals to recipient circulating NK cells triggers their activation, which in turn promotes endothelial damage. Missing self-induced NK cell activation is mTORC1-dependent and the mTOR inhibitor rapamycin can prevent the development of this type of chronic vascular rejection.

‘Missing self’ is a mode of natural killer (NK) cell activation aimed to detect the lack of HLA-I molecules on infected or neoplastic cells. Here, the authors show that mismatch between donor HLA-I and cognate receptors on recipient NK cells mediates microvascular inflammation-associated graft rejection, a pathology that is preventable by mTOR inhibition.

PIRCHE-II: an algorithm to predict indirectly recognizable HLA epitopes in solid organ transplantation

Human leukocyte antigen (HLA) mismatches between donors and recipients may lead to alloreactivity after solid organ transplantation. Over the last few decades, our knowledge of the complexity of the HLA system has dramatically increased, as numerous new HLA alleles have been identified. As a result, the likelihood of alloreactive responses towards HLA mismatches after solid organ transplantation cannot easily be assessed. Algorithms are promising solutions to estimate the risk for alloreactivity after solid organ transplantation. In this review, we show that the recently developed PIRCHE-II (Predicted Indirectly ReCognizable HLA Epitopes) algorithm can be used to minimize alloreactivity towards HLA mismatches. Together with the use of other algorithms and simulation approaches, the PIRCHE-II algorithm aims for a better estimated alloreactive risk for individual patients and eventually an improved graft survival after solid organ transplantation.

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 CD44^highCD62L^low 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.

Recent advances of exosomes in immune-mediated eye diseases

Exosomes, nanosized extracellular vesicles of 30-150 nm, are shed by almost all cell types. Bearing proteins, lipids, RNAs, and DNAs, exosomes have emerged as vital biological mediators in cell-to-cell communication, affecting a plethora of physiological and pathological processes. Particularly, mounting evidence indicates that immunologically active exosomes can regulate both innate and adaptive immune responses. Herein, we review recent advances in the research of exosomes in several immune-mediated eye diseases, including Sjögren's syndrome (SS) dry eye, corneal allograft rejection, autoimmune uveitis, and age-related macular degeneration (AMD). Additionally, we discuss the potential of exosomes as novel biomarkers and drug delivery vesicles for the diagnosis and treatment of eye diseases.

Long-term tolerance of islet allografts in nonhuman primates induced by apoptotic donor leukocytes

Immune tolerance to allografts has been pursued for decades as an important goal in transplantation. Administration of apoptotic donor splenocytes effectively induces antigen-specific tolerance to allografts in murine studies. Here we show that two peritransplant infusions of apoptotic donor leukocytes under short-term immunotherapy with antagonistic anti-CD40 antibody 2C10R4, rapamycin, soluble tumor necrosis factor receptor and anti-interleukin 6 receptor antibody induce long-term (≥1 year) tolerance to islet allografts in 5 of 5 nonsensitized, MHC class I-disparate, and one MHC class II DRB allele-matched rhesus macaques. Tolerance in our preclinical model is associated with a regulatory network, involving antigen-specific Tr1 cells exhibiting a distinct transcriptome and indirect specificity for matched MHC class II and mismatched class I peptides. Apoptotic donor leukocyte infusions warrant continued investigation as a cellular, nonchimeric and translatable method for inducing antigen-specific tolerance in transplantation.

Injection of donor apoptotic cells induces graft tolerance in mice. Here the authors combine this approach with short immunosuppressive therapy to achieve long-term tolerance to allogeneic islets and restoration of normoglycemia in diabetic nonhuman primates, and delineate cellular and molecular correlates of tolerance induction.

Standardisation of flow cytometry for whole blood immunophenotyping of islet transplant and transplant clinical trial recipients

Understanding the immunological phenotype of transplant recipients is important to improve outcomes and develop new therapies. Immunophenotyping of whole peripheral blood (WPB) by flow cytometry is a rapid method to obtain large amounts of data relating to the outcomes of different transplant treatments with limited patient impact. Healthy individuals and patients with type 1 diabetes (T1D) enrolled in islet transplantation were recruited and WPB was collected. 46 fluorochrome-conjugated mouse-anti-human antibodies were used (43 of 46 antibodies were titrated). BD cytometer setup and tracking beads were used to characterize and adjust for cytometer performance. Antibody cocktails were pre-mixed <60 minutes before staining. Multicolour panels were designed based on fluorochrome brightness, antigen density, co-expression, and fluorochrome spillover into non-primary detectors in each panel on a 5 laser flow cytometer. WPB sample staining used 50–300 μl WPB for each panel and was performed within 2 hours of blood sample collection. Samples were acquired on a BD-LSRFortessa. The operating procedures, including specimen collection, antibody cocktails, staining protocol, flow-cytometer setup and data analysis, were standardized. The staining index of 43 antibodies and the spillover spreading matrix for each panel was calculated. The final concentrations for the 46 antibodies used was determined for staining of WPB samples. Absolute cell-count and 7 leukocyte profiling panels consisting of subsets and/or status of granulocytes, monocytes, dendritic, B, NK, and T cells including regulatory T cells (Tregs) and NKT were designed and established on a 5 laser BD-LSR Fortessa. 13 T1D patients, including 4 islet transplant recipients and 8 healthy controls, were evaluated. The ability to reproducibly measure immune subsets and immune-profiles of islet transplant patients up to 18 months post transplantation has been established as a tool to measure immune cell reconstitution after transplantation.

State of the Art: Role of the Dendritic Cell in Induction of Allograft Tolerance

Despite decades of research, the induction and maintenance of long-term allograft tolerance without immunosuppression remains an elusive goal in the field of solid organ and cell transplantation. Immunosuppressive medications frequently prevent or minimize acute cellular rejection but have failed to halt antidonor antibody production and chronic organ rejection. Past efforts aimed at promoting lasting allograft tolerance have focused primarily on peripheral T-cell depletion, augmentation of regulatory T cells, or induction via simultaneous hematopoietic stem cell transplantation and facilitation of donor chimerism. So far, none of these methods have led to consistently safe, feasible and long lasting donor organ acceptance. Over the course of the past 4 decades, the study of a unique population of antigen-presenting cells known as dendritic cells has shown promise for breaking new ground in achieving indefinite allograft survival without immunosuppression and its associated adverse effects. In this review, we discuss the discovery and early investigations of dendritic cells and chronicle some of the key studies demonstrating their role in transplantation, particularly in indirect allorecognition, the immunologic pathway thought to drive chronic rejection and perhaps tolerance induction.

Emerging role of exosomes in allorecognition and allograft rejection

PURPOSE OF REVIEW

This article reviews recent literature on the nature of extracellular vesicles released by allogeneic transplants and examine their role in T-cell alloimmunity involved in rejection and tolerance of these grafts.

RECENT FINDINGS

Donor cells release extracellular vesicles, including exosomes, after transplantation of allogeneic organs and tissues. Consequently, recipient APCs take up these exosomes and present donor MHC antigens on their surface (allo-MHC cross-dressing) thus, activating some alloreactive T cells via a mechanism called semi-direct pathway of allorecognition. In addition, one study shows that exosomes carrying noninherited maternal antigens are associated with maternal microchimerism and tolerance in offspring. Finally, a few studies describe potential utilization of exosomes as modulators of alloimmunity and biomarkers of rejection in allotransplantation.

SUMMARY

Extracellular vesicles, including exosomes, released by allografts contribute to recognition of donor antigens by T cells after allotransplantation. This occurs through cross-dressing of recipient APCs with donor MHC antigens and subsequent activation of T cells, a process called semi-direct alloreactivity. The relevance of this phenomenon in rejection and tolerance of allografts and the potential utilization of exosomes as biomarkers in transplantation are discussed.

Evaluation of the host immune response and functional recovery in peripheral nerve autografts and allografts

Allogeneic peripheral nerve (PN) transplants are an effective bridge for stimulating regeneration of segmental PN defects, but there are currently no detailed studies about the timeline and scope of the immunological response for PN allografting. In this study, the cellular immune response in PN allografts and autograft was studied during the acute and chronic phases of a 1.0 cm critical size defect in the rat sciatic nerve at 3, 7, 14, 28 and 98 days after grafting autologous or allogeneic nerves without any immunosuppressive treatment. The assessment was based on functional, histomorphometrical and immunohistochemical criteria. Results showed modestly better functional outcomes for autografts with coordinate and adaptive immune response represented by the presence of CD11c, CD3, CD4, NKp46 and CD8 cells at 3 days, CD45R positive cells and CD25 positive cells at seven and CD45R positive cells at 14 days which seems an adaptive immune response. In contrast, allograft in the early time points showed innate immune response instead of adaptive immune response until day 14, when there was some increase in cell-mediated immunity. In conclusion, in PN autografts the immune system is synchronic initiating with a more robust early innate response that more rapidly transitions to adaptive while for PN allografts the infiltration of immune cells is slower and more gradually progresses to a moderate adaptive response.

Cellular allorecognition and its roles in Dictyostelium development and social evolution

The social amoeba Dictyostelium discoideum is a tractable model organism to study cellular allorecognition, which is the ability of a cell to distinguish itself and its genetically similar relatives from more distantly related organisms. Cellular allorecognition is ubiquitous across the tree of life and affects many biological processes. Depending on the biological context, these versatile systems operate both within and between individual organisms, and both promote and constrain functional heterogeneity. Some of the most notable allorecognition systems mediate neural self-avoidance in flies and adaptive immunity in vertebrates. D. discoideum's allorecognition system shares several structures and functions with other allorecognition systems. Structurally, its key regulators reside at a single genomic locus that encodes two highly polymorphic proteins, a transmembrane ligand called TgrC1 and its receptor TgrB1. These proteins exhibit isoform-specific, heterophilic binding across cells. Functionally, this interaction determines the extent to which co-developing D. discoideum strains co-aggregate or segregate during the aggregation phase of multicellular development. The allorecognition system thus affects both development and social evolution, as available evidence suggests that the threat of developmental cheating represents a primary selective force acting on it. Other significant characteristics that may inform the study of allorecognition in general include that D. discoideum's allorecognition system is a continuous and inclusive trait, it is pleiotropic, and it is temporally regulated.

Glucocorticoids induce corneal allograft tolerance through expansion of monocytic myeloid-derived suppressor cells

Glucocorticoids (GCs) are the most widely used drugs to prevent transplant rejection; however, it is not yet clear how GCs induce immune tolerance in transplantation. Here, we demonstrate that GCs induce tolerance to corneal allografts in mice through expansion of MHC class II^- CD11b⁺ Ly6C⁺ monocytes in the bone marrow and mobilization of the cells to spleen, draining lymph nodes, and graft site. The GC-induced CD11b⁺ Ly6C⁺ monocytes inhibited T cell proliferation in vitro, and adoptive transfer of the cells improved the survival of corneal allografts. Depletion of CD11b⁺ Ly6C⁺ cells in mice during GC treatment abrogated the effects of GCs in prevention of immune rejection. Together, the results identify monocytic myeloid-derived suppressor cells as crucial mediators of the GC-induced tolerance in transplantation.

The impact of immune response on endochondral bone regeneration

Tissue engineered cartilage substitutes, which induce the process of endochondral ossification, represent a regenerative strategy for bone defect healing. Such constructs typically consist of multipotent mesenchymal stromal cells (MSCs) forming a cartilage template in vitro, which can be implanted to stimulate bone formation in vivo. The use of MSCs of allogeneic origin could potentially improve the clinical utility of the tissue engineered cartilage constructs in three ways. First, ready-to-use construct availability can speed up the treatment process. Second, MSCs derived and expanded from a single donor could be applied to treat several patients and thus the costs of the medical interventions would decrease. Finally, it would allow more control over the quality of the MSC chondrogenic differentiation. However, even though the envisaged clinical use of allogeneic cell sources for bone regeneration is advantageous, their immunogenicity poses a significant obstacle to their clinical application. The aim of this review is to increase the awareness of the role played by immune cells during endochondral ossification, and in particular during regenerative strategies when the immune response is altered by the presence of implanted biomaterials and/or cells. More specifically, we focus on how this balance between immune response and bone regeneration is affected by the implantation of a cartilaginous tissue engineered construct of allogeneic origin.

Galectin-1-induced tolerogenic dendritic cells combined with apoptotic lymphocytes prolong liver allograft survival

Donor-derived tolerogenic dendritic cells (DCs) and apoptotic lymphocytes (ALs) are practical tools for controlling rejection after transplantation by targeting direct and indirect allorecognition pathways, respectively. To date, few studies have investigated the combination of donor-derived tolerogenic DCs and ALs infusion in organ transplantation protection. In the present study, we generated galectin-1-induced tolerogenic DCs (DC_gal-1s) and ultraviolet irradiation-induced ALs with stable immune characteristics in vitro and potential immune regulatory activity in vivo. A rat model of acute liver transplant rejection was established, and the intrinsic tolerogenic profiles associated with the short-term alleviation of rejection and the long-term maintenance of tolerance in the absence of immunosuppressive drugs were evaluated. The DC_gal-1-AL treatment prolonged allograft survival more significantly than a transfusion of DC_gal-1s or ALs alone. This benefit was associated with CD4⁺ Treg cell expansion and decreased interferon (IFN)-γ⁺ T cell levels. Moreover, DC_gal-1-AL treatment led to different cytokine/chemokine changes in the allograft and peripheral blood, that indicated an alleviation of local and systemic inflammation on day 7 post-transplantation. TGF-β1 and TGF-β2 were significantly increased in the long-term surviving allografts after DC_gal-1-AL treatment. Our results indicate that the combination of DC_gal-1s with ALs effectively prolongs liver allograft survival and represents a novel therapeutic strategy for liver transplant rejection.

Comparison of Rejection-Specific Genes in Peripheral Blood and Allograft Biopsy From Kidney Transplant

BACKGROUND

Although improved understanding and assessment of organ rejection significantly contribute to long-term allograft survival after kidney transplantation, reliable and predictive biomarkers that enable diagnoses of rejection state are lacking. Patient rejection of a kidney graft displays a specific blood and biopsy transcriptional pattern, raising the question of whether transcript biomarkers in blood could reflect events within the allograft.

METHODS

Differential expression genes were screened on large-scale transcriptomic data from blood and allograft biopsies, which included recipients undergoing rejection and recipients with stable renal function.

RESULTS

We found that the number of rejection-related genes in biopsy samples was much greater than in blood. We observed only one overlapping gene, HIST1H4A, consistently expressed in biopsy samples and blood. Functional association of the identified genes in biopsies implicated a strong involvement of inflammatory-immune pathways. Rejection-related genes in the mammalian target of rapamycin-signaling pathway were down-regulated, and genes related to allograft rejection and graft-versus-host disease were up-regulated in allograft biopsy samples. We also recognized the core signaling elements (PIK3R2 and EGFR) in inflammatory-immune pathways based on biopsy samples.

CONCLUSIONS

We have expanded our understanding of rejection-specific gene expression pattern in allograft biopsy and peripheral blood, and provided a candidate set of overlapping genes for screening of rejection in kidney transplant recipients.

Cyclosporine a drug-delivery system for high-risk penetrating keratoplasty: Stabilizing the intraocular immune microenvironment

Cyclosporine A (CsA) is an essential medication used to prevent corneal allograft rejection. Our preliminary studies revealed that CsA drug-delivery system (DDS) was more effective in preventing high-risk corneal allograft rejection than topical CsA application. However, the impacts of CsA DDS on the intraocular immune microenvironment were not fully elucidated. In the present study, we investigated the effect of CsA DDS on the cornea allograft, aqueous humor, and iris-ciliary body using a rabbit model of high-risk penetrating keratoplasty. New Zealand white rabbits were divided into four groups: a normal control group, an untreated group, a CsA eye drop group and a CsA DDS group. Graft survival was monitored for 12 weeks, and the therapeutic effects of CsA DDS were evaluated at 3 and 12 weeks after high-risk keratoplasty. In the CsA DDS group, the mean graft survival time was significantly prolonged when compared with the untreated and CsA eye drop groups. At all time-points, Langerhans cell density, inflammatory cell density, and central corneal thickness in the CsA DDS group were much lower(all p < 0.01) than the untreated and CsA eye drop groups, in which their parameters were significantly higher than the normal control group (all p < 0.01). Compared with the untreated and CsA eye drop groups, an implanted CsA DDS markedly decreased the CD11b+ and CD8+ T cell infiltration in the corneal grafts. CsA DDS treatment also greatly reduced the CD4+ T cell density and the expression of interferon-gamma, interleukin-2 (IL-2), IL-6, CD80, and CD86 mRNA both in the corneal graft and iris-ciliary body (all p < 0.01). Moreover, CsA DDS significantly reduced the IL-2 level in aqueous humor (p < 0.01). Taken together, our results suggest that CsA DDS implanted into the anterior chamber create a relative immunosuppressive microenvironment in the corneal graft, iris-ciliary body, and aqueous humor. Stabilizing the intraocular immune microenvironment could partially elucidate the mechanism of CsA DDS in suppressing corneal graft rejection.

PIRCHE-II Is Related to Graft Failure after Kidney Transplantation

Individual HLA mismatches may differentially impact graft survival after kidney transplantation. Therefore, there is a need for a reliable tool to define permissible HLA mismatches in kidney transplantation. We previously demonstrated that donor-derived Predicted Indirectly ReCognizable HLA Epitopes presented by recipient HLA class II (PIRCHE-II) play a role in de novo donor-specific HLA antibodies formation after kidney transplantation. In the present Dutch multi-center study, we evaluated the possible association between PIRCHE-II and kidney graft failure in 2,918 donor–recipient couples that were transplanted between 1995 and 2005. For these donors–recipients couples, PIRCHE-II numbers were related to graft survival in univariate and multivariable analyses. Adjusted for confounders, the natural logarithm of PIRCHE-II was associated with a higher risk for graft failure [hazard ratio (HR): 1.13, 95% CI: 1.04–1.23, p = 0.003]. When analyzing a subgroup of patients who had their first transplantation, the HR of graft failure for ln(PIRCHE-II) was higher compared with the overall cohort (HR: 1.22, 95% CI: 1.10–1.34, p < 0.001). PIRCHE-II demonstrated both early and late effects on graft failure in this subgroup. These data suggest that the PIRCHE-II may impact graft survival after kidney transplantation. Inclusion of PIRCHE-II in donor-selection criteria may eventually lead to an improved kidney graft survival.

In Utero Exposure to Exosomal and B-Cell Alloantigens Lessens Alloreactivity of Recipients' Lymphocytes Rather than Confers Allograft Tolerance

According to actively acquired tolerance, antigen exposure before full immune development in fetal or early neonatal life will cause tolerance to this specific antigen. In this study, we aimed to examine whether allogeneic tolerance could be elicited by in utero exposure to surface MHC antigens of allogenic cells or soluble form of MHC exosomes. Gestational day 14 FVB/N fetuses were subjected to intraperitoneal injection of allogeneic major histocompatibility complex (MHC) exosomes or highly enriched B-cells. Postnatally, the recipients were examined for the immune responses to donor alloantigens by lymphocyte proliferative reactions and skin transplantation. In utero exposure to allogeneic MHC exosomes abolished the alloreactivity of recipients’ lymphocytes to the alloantigens, but could not confer skin allograft tolerance. In utero transplantation of highly enriched allogeneic B-cells generated low-level B-cell chimerism in the recipients. However, it only extended the survivals of skin allograft by a few days despite the lack of donor-specific alloreactivity of recipients’ lymphocyte. Thus, an early in utero contact with exosomal or B-cell alloantigens did not lead to full skin tolerance but rather, at best, only to delayed skin rejection in the presence of microchimerism made by B-cell inocula. These results argued against the theory of actively acquired tolerance, and implicated that in utero exposure to marrow cells in previous studies was a unique model of allo-tolerance induction that involved the establishment of significant hematopoietic chimerism. Taken together with the discovery of in utero sensitization to ovalbumin in our previous studies, the immunological consequences of fetal exposure to foreign antigens might vary according to the type or nature of antigens introduced.

Anti-Inflammatory and Immune Regulatory Actions of Naja naja atra Venom

Naja naja atra venom (NNAV) is composed of various proteins, peptides, and enzymes with different biological and pharmacological functions. A number of previous studies have reported that NNAV exerts potent analgesic effects on various animal models of pain. The clinical studies using whole venom or active components have confirmed that NNAV is an effective and safe medicine for treatment of chronic pain. Furthermore, recent studies have demonstrated that NNAV has anti-inflammatory and immune regulatory actions in vitro and in vivo. In this review article, we summarize recent studies of NNAV and its components on inflammation and immunity. The main new findings in NNAV research show that it may enhance innate and humoral immune responses while suppressing T lymphocytes-mediated cellular immunity, thus suggesting that NNAV and its active components may have therapeutic values in the treatment of inflammatory and autoimmune diseases.

Matching donor and recipient based on predicted indirectly recognizable human leucocyte antigen epitopes

The predicted indirectly recognizable human leucocyte antigen (HLA) epitopes (PIRCHE) algorithm is a novel in silico algorithm to determine donor-recipient compatibility. The PIRCHE algorithm determines donor-recipient compatibility by counting the number of mismatched HLA-derived epitopes that are involved in indirect T-cell alloimmune responses; these epitopes are designated as PIRCHE. Over the last few years, the PIRCHE algorithm has been investigated in both hematopoietic stem cell transplantation and solid organ transplantation. This review describes the theory of the algorithm, its application in transplantation, and highlights the future perspectives on the clinical application of the PIRCHE algorithm.

Adipose-derived cellular therapies in solid organ and vascularized-composite allotransplantation

PURPOSE OF REVIEW

Controlling acute allograft rejection following vascularized composite allotransplantation requires strict adherence to courses of systemic immunosuppression. Discovering new methods to modulate the alloreactive immune response is essential for widespread application of vascularized composite allotransplantation. Here, we discuss how adipose-derived cellular therapies represent novel treatment options for immune modulation and tolerance induction in vascularized composite allotransplantation.

RECENT FINDINGS

Adipose-derived mesenchymal stromal cells are cultured from autologous or allogeneic adipose tissue and possess immunomodulatory qualities capable of prolonging allograft survival in animal models of vascularized composite allotransplantation. Similar immunosuppressive and immunomodulatory effects have been observed with noncultured adipose stromal-vascular-fraction-derived therapies, albeit publication of in-vivo stromal vascular fraction cell modulation in transplantation models is lacking. However, both stromal vascular fraction and adipose derived mesenchymal stem cell therapies have the potential to effectively modulate acute allograft rejection via recruitment and induction of regulatory immune cells.

SUMMARY

To date, most reports focus on adipose derived mesenchymal stem cells for immune modulation in transplantation despite their phenotypic plasticity and reliance upon culture expansion. Along with the capacity for immune modulation, the supplemental wound healing and vasculogenic properties of stromal vascular fraction, which are not shared by adipose derived mesenchymal stem cells, hint at the profound therapeutic impact stromal vascular fraction-derived treatments could have on controlling acute allograft rejection and tolerance induction in vascularized composite allotransplantation. Ongoing projects in the next few years will help design the best applications of these well tolerated and effective treatments that should reduce the risk/benefit ratio and allow more patients access to vascularized composite allotransplantation therapy.

T cells upon activation promote endothelin 1 production in monocytes via IFN-γ and TNF-α

Endothelin 1 (ET-1), mainly produced from vascular endothelial cells, induces vasoconstriction in physiological conditions. The endothelin receptor antagonist is among the most effective agents for pulmonary hypertension. However, little is known about the production source of ET-1 in inflammation and immunity. Here, we studied whether T cell-mediated ET-1 production system exists and operates independent of the production system in vascular endothelial cells. ET-1 production was readily detectable in the culture supernatant of human PBMCs and murine spleen cells stimulated with anti-CD3 antibody. Immunocytostaining showed that ET-1-producing cells emerged only in PBMCs stimulated with anti-CD3 antibody. Using the Transwell system, both murine and human monocytes sorted with magnetic beads in the inner chamber produced ET-1 when T cells were activated with antigen or anti-CD3 antibody in the outer chamber. This ET-1 production was inhibited by anti-IFN-γ and/or TNF-α antibody. Furthermore, monocytes purified from ET^flox/flox;Tie2-Cre( + ) mice, which conditionally lack ET-1 in hematopoietic stem cells and vascular endothelial cells, did not produce ET-1 even when stimulated by antigen-specific T cell activation. This study demonstrates the existence of an immune-mediated ET-1 production induced by T cells upon activation through IFN-γ and TNF-α.

Differential inflammatory networks distinguish responses to bone marrow-derived versus adipose-derived mesenchymal stem cell therapies in vascularized composite allotransplantation

BACKGROUND

Vascularized composite allotransplantation (VCA) is aimed at enabling injured individuals to return to their previous lifestyles. Unfortunately, VCA induces an immune/inflammatory response, which mandates lifelong, systemic immunosuppression, with attendant detrimental effects. Mesenchymal stem cells (MSC)-both adipose-derived (AD-MSC) and bone marrow-derived (BM-MSC)-can reprogram inflammation and have been suggested as an alternative to immunosuppression, but their mechanism of action is as yet not fully elucidated. We sought to gain insights into these mechanisms using a systems biology approach.

METHODS

PKH26 (red) dye-labeled AD-MSC or BM-MSC were administered intravenously to Lewis rat recipients of mismatched Brown-Norway hindlimb transplants. Short course tacrolimus (FK-506) monotherapy was withdrawn at postoperative day 21. Sera were collected at 4 weeks, 6 weeks, and 18 weeks; assayed for 29 inflammatory/immune mediators; and the resultant data were analyzed using Dynamic Network Analysis (DyNA), Dynamic Bayesian Network (DyBN) inference, and Principal Component Analysis.

RESULTS

DyNA network complexity decreased with time in AD-MSC rats, but increased in BM-MSC rats. DyBN and Principal Component Analysis suggested mostly different central nodes and principal characteristics, respectively, in AD-MSC versus BM-MSC rats.

CONCLUSION

AD-MSC and BM-MSC are associated with both overlapping and distinct dynamic networks and principal characteristics of inflammatory/immune mediators in VCA grafts with short-course tacrolimus induction therapy. The decreasing inflammatory complexity of dynamic networks in the presence of AD-MSC supports the previously suggested role for T regulatory cells induced by AD-MSC. The finding of some overlapping and some distinct central nodes and principal characteristics suggests the role of key mediators in the response to VCA in general, as well as potentially differential roles for other mediators ascribed to the actions of the different MSC populations. Thus, combined in vivo/in silico strategies may yield novel means of optimizing MSC therapy for VCA.

Pre-transplant infusion of donor-derived dendritic cells maintained at the immature stage by sinomenine increases splenic Foxp3+ Tregs in recipient rats after renal allotransplantation

OBJECTIVE

The immunosuppressive mechanism of sinomenine in organ allotransplantation was investigated, especially its effect of blocking dendritic cell (DC) maturation, which might influence the frequency of regulatory T cells (Tregs).

METHODS

Bone marrow cells from male donor Wistar rats were induced to differentiate into DCs in vitro in the presence or absence of sinomenine, and characterized by flow cytometry. These two groups of DCs were respectively injected into male recipient Sprague-Dawley rats via the tail vein, at both high and low doses. Sprague-Dawley rats receiving saline injection were used as controls. Seven days later, renal transplantation was performed from donor Wistar rats to the recipient Sprague-Dawley rats. Seven days after transplantation, spleens were collected from the recipients. The proportions of Tregs and Foxp3⁺ Tregs to CD4⁺ T cells were determined using flow cytometry.

RESULTS

With sinomenine treatment, the frequency of mature DCs was reduced, as indicated by lower expression of the surface markers CD80, CD86, and RT1B. In recipient Sprague-Dawley rats that received sinomenine-treated DCs before renal allotransplantation, the proportions of splenic Tregs and Foxp3⁺ Tregs were significantly higher than in control recipients receiving saline or DCs without sinomenine treatment (all p<0.05). A high dose of sinomenine-treated DCs (10⁶ cells) had a more obvious effect in increasing Tregs than the low dose (10⁵ cells) (p<0.05).

CONCLUSION

Pre-transplant infusion of donor-derived sinomenine-induced maturation arrested DCs could result in the increase of Foxp3⁺ Tregs in the spleens of recipients after renal allotransplantation.

Allostimulatory capacity of conditionally immortalized proximal tubule cell lines for bioartificial kidney application

Novel renal replacement therapies, such as a bioartificial kidney (BAK), are needed to improve current hemodialysis treatment of end-stage renal disease (ESRD) patients. As BAK applications may reveal safety concerns, we assessed the alloimmunization and related safety aspects of readily available conditionally immortalized human proximal tubule epithelial cell (ciPTEC) lines to be used in BAK. Two ciPTEC lines, originally derived from urine and kidney tissue, were characterized for the expression and secretion of relevant molecules involved in alloimmunization and inflammatory responses, such as HLA class-I, HLA-DR, CD40, CD80, CD86, as wells as soluble HLA class I and proinflammatory cytokines (IL-6, IL-8 and TNF-α). A lack of direct immunogenic effect of ciPTEC was shown in co-culture experiments with peripheral blood mononuclear cells (PBMC), after appropriate stimulation of ciPTEC. Tight epithelial cell monolayer formation on polyethersulfone flat membranes was confirmed by zonula occludens-1 (ZO-1) expression in the ciPTEC tight junctions, and by restricted inulin-FITC diffusion. Co-culture with (activated) PBMC did not jeopardize the transepithelial barrier function of ciPTEC. In conclusion, the absence of allostimulatory effects and the stability of ciPTEC monolayers show that these unique cells could represent a safe option for BAK engineering application.

The mechanisms of rejection in solid organ transplantation

Organ transplantation represents the preferred treatment option for many patients in terminal organ failure. The half-life of transplanted organs, however, is still far from being satisfactory with the vast majority of the organs failing within the first two decades following transplantation. At this stage, it has become apparent that rejection (prevalently mediated by humoral events) remains the primary cause of graft loss after the first year. In this light, studies are underway to better comprehend the immune events underlying graft rejection and novel immunosuppressive strategies are being explored. In this context, therapeutic apheresis techniques, that include therapeutic plasma exchange (TPE), immunoadsorption (IA) and extracorporeal photochemotherapy (ECP), represent an important adjunct in the current immunosuppressive armamentarium. This article briefly reviews our current understanding of the immune process underlying rejection of a solid organ transplant and describes the principal areas of application of therapeutic apheresis techniques in transplantation.

Blood biomarkers of kidney transplant rejection, an endless search?

INTRODUCTION

The tailoring of immunosuppressive treatment is recognized as a promising strategy to improve long-term kidney graft outcome. To guide the standard care of transplant recipients, physicians need objective biomarkers that can identify an ongoing pathology with the graft or low intensity signals that will be later evolved to accelerated transplant rejection. The early identification of 'high-risk /low-risk' patients enables the adjustment of standard of caring, including managing the frequency of clinical visits and the immunosuppression dosing. Given their ease of availability and the compatibility with a large technical array, blood-based biomarkers have been widely scrutinized for use as potential predictive and diagnostic biomarkers. Areas covered: Here, the authors report on non-invasive biomarkers, such as modification of immune cell subsets and mRNA and miRNA profiles, identified in the blood of kidney transplant recipients collected before or after transplantation. Expert commentary: Combined with functional tests, the identification of biomarkers will improve our understanding of pathological processes and will contribute to a global improvement in clinical management.

The Immunogenicity and Immune Tolerance of Pluripotent Stem Cell Derivatives

Human embryonic stem cells (hESCs) can undergo unlimited self-renewal and differentiate into all cell types in human body, and therefore hold great potential for cell therapy of currently incurable diseases including neural degenerative diseases, heart failure, and macular degeneration. This potential is further underscored by the promising safety and efficacy data from the ongoing clinical trials of hESC-based therapy of macular degeneration. However, one main challenge for the clinical application of hESC-based therapy is the allogeneic immune rejection of hESC-derived cells by the recipient. The breakthrough of the technology to generate autologous-induced pluripotent stem cells (iPSCs) by nuclear reprogramming of patient’s somatic cells raised the possibility that autologous iPSC-derived cells can be transplanted into the patients without the concern of immune rejection. However, accumulating data indicate that certain iPSC-derived cells can be immunogenic. In addition, the genomic instability associated with iPSCs raises additional safety concern to use iPSC-derived cells in human cell therapy. In this review, we will discuss the mechanism underlying the immunogenicity of the pluripotent stem cells and recent progress in developing immune tolerance strategies of human pluripotent stem cell (hPSC)-derived allografts. The successful development of safe and effective immune tolerance strategy will greatly facilitate the clinical development of hPSC-based cell therapy.

Meat and Nicotinamide: A Causal Role in Human Evolution, History, and Demographics

Hunting for meat was a critical step in all animal and human evolution. A key brain-trophic element in meat is vitamin B3 / nicotinamide. The supply of meat and nicotinamide steadily increased from the Cambrian origin of animal predators ratcheting ever larger brains. This culminated in the 3-million-year evolution of Homo sapiens and our overall demographic success. We view human evolution, recent history, and agricultural and demographic transitions in the light of meat and nicotinamide intake. A biochemical and immunological switch is highlighted that affects fertility in the 'de novo' tryptophan-to-kynurenine-nicotinamide 'immune tolerance' pathway. Longevity relates to nicotinamide adenine dinucleotide consumer pathways. High meat intake correlates with moderate fertility, high intelligence, good health, and longevity with consequent population stability, whereas low meat/high cereal intake (short of starvation) correlates with high fertility, disease, and population booms and busts. Too high a meat intake and fertility falls below replacement levels. Reducing variances in meat consumption might help stabilise population growth and improve human capital.