Clinical transplantation tolerance: The promise and challenges

Renal transplant immunology in the last 20 years: A revolution towards graft and patient survival improvement

To deride the hope of progress is the ultimate fatuity, the last word in poverty of spirit and meanness of mind. There is no need to be dismayed by the fact that we cannot yet envisage a definitive solution of our problems, a resting-place beyond which we need not try to go. -P.B. Medawar, 1969 * Thomas E. Starlz, also known as the Father of Clinical Transplantation, once said that organ transplantation was the supreme exception to the rule that most major advances in medicine spring from discoveries in basic science [Starzl T. The mystique of organ transplantation. J Am Coll Surg 2005 Aug;201(2):160-170]. In fact, the first successful identical-twin kidney transplantation performed by Murray's team in December 1954 (Murray J et al. Renal homotransplantations in identical twins. Surg Forum 1955;6:432-436) was the example of an upside down translation medicine: Human clinical transplantation began and researchers tried to understand the underlying immune response and how to control the powerful rejection pathways through experimental models. In the last 20 years, we have witnessed an amazing progress in the knowledge of immunological mechanisms regarding alloimmune response and an outstanding evolution on the identification and characterization of major and minor histocompatibility antigens. This review presents an historical and clinical perspective of those important advances in kidney transplantation immunology in the last 20 years, which contributed to the improvement in patients' quality of life and the survival of end-stage renal patients. In spite of these significant progresses, some areas still need substantial progress, such as the definition of non-invasive biomarkers for acute rejection; the continuous reduction of immunosuppression; the extension of graft survival, and finally the achievement of real graft tolerance extended to HLA mismatch donor: recipient pairs.

The SPLIT research agenda 2013

This review focuses on active clinical research in pediatric liver transplantation with special emphasis on areas that could benefit from studies utilizing the SPLIT infrastructure and data repository. Ideas were solicited by members of the SPLIT Research Committee and sections were drafted by members of the committee with expertise in those given areas. This review is intended to highlight priorities for clinical research that could successfully be conducted through the SPLIT collaborative and would have significant impact in pediatric liver transplantation.

Profiling the proteome in renal transplantation

Improved monitoring of transplanted solid organs is one of the next crucial steps leading to an increase in both patient and allograft survival. This can be facilitated through one or a set of surrogate biomarker molecules that accurately and precisely indicate the health status of the transplanted organ. Recent developments in the field of high throughput "omic" methods including genomics and proteomics have facilitated robust and comprehensive analysis of genes and proteins. This development has stimulated efforts in the identification of effective and clinically applicable gene and protein biomarkers in solid organ transplantation, including kidney transplantation. Some achievements have been made through proteomics in terms of profiling proteins and identification of potential biomarkers. However, the road to a successful biomarker discovery and its clinical implementation has proved to be challenging, requiring a number of key issues to be addressed. Such issues are: the lack of widely accepted protocols, difficulty in sample processing and transportation and a lack of collaborative efforts to achieve significant sample sizes in clinical studies. In this review using our area of expertise, we describe the current strategies used for proteomic-based biomarker discovery in renal transplantation, discuss inherent issues associated with these efforts and propose better strategies for successful biomarker discovery.

Toward a B-cell signature of tolerance?

Operational tolerance is a rare and still unexplained phenomenon in organ transplantation. Pallier et al. analyzed the peripheral B-cell compartment of 12 renal transplant patients with drug-free long-term graft function and found a peculiar blood B-cell phenotype, with an expansion of memory activated B cells and increased expression of inhibitory molecules, suggesting a role of B cells in maintaining graft tolerance.

The Toll-IL-1R member Tir8/SIGIRR negatively regulates adaptive immunity against kidney grafts

Members of the TLR/IL-1R superfamily mediate ischemia/reperfusion injury and initiate immune response in transplanted organs. In this study, we tested the hypothesis that Toll-IL-1R8 (TIR8), a negative regulator of TLR/IL-1R highly expressed in the kidney, modulates immune cell activation underlying kidney rejection. In a mouse model of fully mismatched kidney allotransplantation in which the graft is spontaneously accepted, intragraft Tir8 expression was enhanced compared with naive kidneys. Targeted deletion of Tir8 in the graft exerted a powerful antitolerogenic action leading to acute rejection. Similarly, in a mouse model of kidney graft acceptance induced by costimulation blockade, most Tir8(-/-) grafts were acutely rejected. Despite similar levels of TLR4, IL-1R, and their ligands, the posttransplant ischemia/reperfusion-induced inflammatory response was more severe in Tir8(-/-) than in Tir8(+/+) grafts and was followed by expansion and maturation of resident dendritic cell precursors. In vitro, Tir8(-/-) dendritic cell precursors acquired higher allostimulatory activity and released more IL-6 upon stimulation with a TLR4 ligand and TNF-alpha than Tir8(+/+) cells, which may explain the increased frequency of antidonor-reactive T cells and the block of regulatory T cell formation in recipients of a Tir8(-/-) kidney. Thus, TIR8 acts locally as a key regulator of allogeneic immune response in the kidney. Tir8 expression and/or signaling in donor tissue are envisaged as a novel target for control of innate immunity and amelioration of graft survival.

Immunosuppressive drug-free operational immune tolerance in human kidney transplant recipients: Part I. Blood gene expression statistical analysis

Survival of solid organ grafts depends on life-long immunosuppression, which results in increased rates of infection and malignancy. Induction of tolerance to allografts would represent the optimal solution for controlling both chronic rejection (CR) and side effects of immunosuppression. Although spontaneous "operational tolerance" can occur in human kidney transplantation, the lack of noninvasive peripheral blood biological markers of this rare phenomenon precludes the identification of potentially tolerant patients in whom immunosuppression could be tapered as well as the development of new tolerance inducing strategies. Here, the potential of high throughput microarray technology to decipher complex pathologies allowed us to study the peripheral blood specific gene expression profile and corresponding EASE molecular pathways associated to operational tolerance in a cohort of human kidney graft recipients. In comparison with patients with CR, tolerant patients displayed a set of 343 differentially expressed genes, mainly immune and defense genes, in their peripheral blood mononuclear cells (PBMC), of which 223 were also different from healthy volunteers. Using the expression pattern of these 343 genes, we were able to classify correctly >80% of the patients in a cross-validation experiment and classified correctly all of the samples over time. Collectively, this study identifies a unique PBMC gene signature associated with human operational tolerance in kidney transplantation by a classical statistical microarray analysis and, in the second part, by a nonstatistical analysis.

Short-term cyclosporine therapy and cotransplantation of donor splenocytes: effects on graft rejection and survival rates in pigs subjected to renal transplantation

BACKGROUND

Donor-specific allogeneic loading can prolong the survival of solid organ transplants by inducing a state known as acceptance. Several populations of cells are known to be involved in this process, but their exact roles have yet to be defined. The aim of this study was to assess the effects of portal-vein transfusion of donor-specific splenocytes (DST) after short-term cyclosporine A (CyA) therapy in pigs subjected to renal transplantation.

METHODS

Four groups of unrelated swine underwent renal transplantation with removal of the native kidneys. Antirejection protocols consisted in portal-vein DST (3 x 10(8) cells/kg) (Group 2, n = 7); intravenous CyA (9 mg/kg/d) on postoperative days 1-12 (Group 3, n = 14); and DST + CyA (as described above) (Group 4, n = 13). Results (through postoperative day 90) were compared with those obtained in untreated control recipients (Group 1, n = 7).

RESULTS

Compared with animals of Groups 1, 2, and 3, Group 4 recipients presented significantly longer survival (mean: 90 days, P < 0.01 in Kaplan-Meier analysis) and better renal function (P < 0.05). Graft histology revealed preserved parenchyma.

CONCLUSION

The role of spleen cells in the immune response has probably been underestimated. Cotransplantation of donor splenocytes seems to induce a certain degree of acceptance toward the renal allograft. The route of administration (portal-vein infusion in this study) may be crucial for developing favorable mechanisms of recognition.

???Prope??? Tolerance in a Noncompliant Living Related Small Bowel Transplant Recipient After Severe Rejection

Advances in immunosuppression and surgical technique have greatly improved patient outcomes after intestinal transplantation. However, the procedure remains one of the most challenging among solid organ transplantation as a result of the high rate of acute rejection, sepsis, and posttransplantation lymphoproliferative disorder. Recently, clinical trials to explore tolerance protocols in humans have been initiated, including small bowel transplant recipients, with results not always reproducible. The concept of operational tolerance is more meaningful in the clinical setting when physiological stability of graft function is achieved in the absence of maintenance immunosuppression. We report the intriguing case of a living related small bowel transplant recipient who developed clinical "prope" tolerance to the graft after treatment of severe acute rejection despite continuous noncompliance with immunosuppressive therapy.

Monitoring tolerance after human liver transplantation

The validation of reliable, non-invasive immunological assays evaluating anti-donor responsiveness in allograft recipients would provide a clinically relevant tool for the early detection of ongoing rejection process as well as for the identification of operational tolerance in the long term. A sequential approach towards immunological monitoring of allografts is proposed in this review: (i) investigations exploring the initial donor-recipient alloresponses, including the analysis of the cytokine network; (ii) investigations regarding graft acceptance and operational tolerance in long-term transplant patients, consisting in the analysis of regulatory T cells and of circulating precursors of dendritic cells, in the measurement of T cell alloreactivity as well as in the study of T cell receptor repertoires. Beside the conventional in vivo and in vitro immunological techniques, the potential applications of molecular imaging in transplantation also deserve further exploration, with particular respect to allograft immune monitoring. Enforced collaboration between transplant clinicians and immunologists will be required to develop the translational research protocols required for the development of immunological monitoring, within an international multicentric network.

Chipping into the human genome: novel insights for transplantation

High throughput, high density platforms for transcriptional, proteomic, and metabonomic analyses are opening new doors for improving our understanding of the complexity and redundancy of the immune system in the interplay of the innate and allo-immune responses in organ transplantation. New insights are being obtained into the possible discrepancies between the gold standard of tissue pathological diagnosis and clinical graft outcomes, as new transcriptional categories of transplant rejection evolve. The bystander effects of chronic immunosuppression underlying the complexities of graft dysfunction are beginning to be understood. Non-invasive mechanisms to monitor transplants, by following 'footprints' of biomarker sets that reflect the disease phenotype, are being pursued for their clinical application for direct patient care. Utilization of these same biomarker sets may also offer a unique means to titrate immunosuppression and predict specific graft dysfunction events prior to clinical decline, thus bringing in the potential to reduce patient morbidity from infection and malignancy, preserve graft integrity, and limit the progression of chronic graft injury. Bioinformatics support is integral to the unraveling of the mysteries of the human genome, proteome, and metabolome in disease and in health.

The immunological monitoring of alloreactive responses in liver transplant recipients: a review

The aim of this work is to review the current knowledge in the field of immunological monitoring of allogenic responsiveness in clinical liver transplantation. When compared to other solid-organ transplants, liver allografts are considered as immunologically privileged, and, accordingly, constitute a favorable setting to develop experimental as well as clinical strategies for minimization of immunosuppression and even induction of operational tolerance. The validation of simple, reliable, noninvasive assays exploring antidonor alloreactivity will constitute a crucial step toward implementing such approaches in the clinic. In contrast to research in rodents claiming the development of donor-specific tolerance in case of graft survivals of over 100 days without immunosuppression, it is impractical to confirm tolerance induction in this way in humans. Promising candidate assays include the detection of post-transplant immune deviation, of circulating precursors of dendritic cells subtypes, and of regulatory T cells. A conceptual framework for the development of tolerance assays in clinical liver transplantation is also proposed.

Optimal management of the post-intestinal transplant patient

The lack of controlled interventional studies limits the ability to assess optimal management of intestine transplant recipients. This report aims to examine factors that probably impact on the quality of patient care in the setting of intestine transplantation. The specific practice in the most experienced intestine transplant programs in the United States was surveyed with regard to immunosuppressive regimens, treatment of acute allograft rejection, feeding, and viral surveillance and treatment. The most striking finding was in the level of agreement between the centers, particularly with regard to use of tacrolimus for maintenance immunosuppression, methylprednisone boluses for treatment of acute rejection, early postoperative enteral feeding, and ganciclovir prophylaxis.

2005 immunosuppressive strategies in kidney transplantation: which role for the calcineurin inhibitors?

The calcineurin inhibitors (CNIs) cyclosporine and tacrolimus have been the cornerstones of immunosuppressive strategies in clinical transplantation. Currently, regimens that are most widely used for induction and maintenance therapy include CNIs. However, many clinical trials aiming at reducing or eliminating CNIs have been performed in recent years. Here, we review and discuss current and future immunosuppressive strategies with a special emphasis on the role of CNIs, in the light of recent studies in the field of kidney transplantation. In the current era, CNIs still play an important role.

Evidence-based investigations and treatments of recurrent pregnancy loss

OBJECTIVE

To give an overview of currently used investigations and treatments offered to women with recurrent pregnancy loss (RPL) and, from an evidence-based point of view, to evaluate the usefulness of these interventions.

DESIGN

Ten experts on epidemiologic, genetic, anatomic, endocrinologic, thrombophilic, immunologic, and immunogenetic aspects of RPL discussed methodologic problems threatening the validity of research in RPL during and after an international workshop on the evidence-based management of RPL.

CONCLUSION(S)

Most RPL patients have several risk factors for miscarriage, and an extensive investigation for all major factors should always be undertaken. There is an urgent need for agreement concerning the thresholds for detecting what is normal and abnormal, irrespective of whether laboratory tests or uterine abnormalities are concerned. A series of lifestyle factors should be reported in future studies of RPL because they might modify the effect of laboratory or anatomic risk factors. More and larger randomized controlled trials, including trials of surgical procedures, are urgently needed, and to achieve this objective multiple centers have to collaborate. Current meta-analyses evaluating the efficacy of treatments of RPL are generally pooling very heterogeneous patient populations and treatments. It is recommended that future meta-analyses look at subsets of patients and treatment protocols that are more combinable.