Kassem Safa

Long-term outcomes of kidney transplantation across a positive complement-dependent cytotoxicity crossmatch.

Background More than 30% of potential kidney transplant recipients have pre-existing anti–human leukocyte antigen antibodies. This subgroup has significantly lower transplant rates and increased mortality. Desensitization has become an important tool to overcome this immunological barrier. However, limited data is available regarding long-term outcomes, in particular for the highest risk group with a positive complement-dependent cytotoxicity crossmatch (CDC XM) before desensitization. Methods Between 2002 and 2010, 39 patients underwent living-kidney transplantation across a positive CDC XM against their donors at our center. The desensitization protocol involved pretransplant immunosuppression, plasmapheresis, and low-dose intravenous immunoglobulin±rituximab. Measured outcomes included patient survival, graft survival, renal function, rates of rejection, infection, and malignancy. Results The mean and median follow-up was 5.2 years. Patient survival was 95% at 1 year, 95% at 3 years, and 86% at 5 years. Death-censored graft survival was 94% at 1 year, 88% at 3 years, and 84% at 5 years. Uncensored graft survival was 87% at 1 year, 79% at 3 years, and 72% at 5 years. Twenty-four subjects (61%) developed acute antibody-mediated rejection of the allograft and one patient lost her graft because of hyperacute rejection. Infectious complications included pneumonia (17%), BK nephropathy (10%), and CMV disease (5%). Skin cancer was the most prevalent malignancy in 10% of patients. There were no cases of lymphoproliferative disorder. Mean serum creatinine was 1.7±1 mg/dL in functioning grafts at 5 years after transplantation. Conclusion Despite high rates of early rejection, desensitization in living-kidney transplantation results in acceptable 5-year patient and graft survival rates.

Eculizumab for drug-induced de novo posttransplantation thrombotic microangiopathy: A case report.

De novo thrombotic microangiopathy (TMA) following renal transplantation is a severe complication associated with high rates of allograft failure. Several immunosuppressive agents are associated with TMA. Conventional approaches to managing this entity, such as withdrawal of the offending agent and/or plasmapheresis, often offer limited help, with high rates of treatment failure and graft loss. We herein report a case of drug induced de novo TMA successfully treated using the C5a inhibitor eculizumab in a renal transplant patient. This report highlights a potentially important role for eculizumab in settings where drug-induced de novo TMA is refractory to conventional therapies.

Salt Accelerates Allograft Rejection through Serum- and Glucocorticoid-Regulated Kinase-1–Dependent Inhibition of Regulatory T Cells

A high-salt diet (HSD) in humans is linked to a number of complications, including hypertension and cardiovascular events. Whether a HSD affects the immune response in transplantation is unknown. Using a murine transplantation model, we investigated the effect of NaCl on the alloimmune response in vitro and in vivo. Incremental NaCl concentrations in vitro augmented T cell proliferation in the settings of both polyclonal and allospecific stimulation. Feeding a HSD to C57BL/6 wild-type recipients of bm12 allografts led to accelerated cardiac allograft rejection, despite similar mean BP and serum sodium levels in HSD and normal salt diet (NSD) groups. The accelerated rejection was associated with a reduction in the proportion of CD4(+)Foxp3(+) regulatory T cells (Tregs) and a significant decrease in Treg proliferation, leading to an increased ratio of antigen-experienced CD4(+) T cells to Tregs in mice recipients of a HSD compared with mice recipients of a NSD. Because serum- and glucocorticoid-regulated kinase-1 (SGK1) has been proposed as a potential target of salt in immune cells, we fed a HSD to CD4(Cre)SGK1(fl/fl) B6-transplanted recipients and observed abrogation of the deleterious effect of a HSD in the absence of SGK1 on CD4(+) cells. In summary, we show that NaCl negatively affects the regulatory balance of T cells in transplantation and precipitates rejection in an SGK1-dependent manner.

Dendritic Cells in Kidney Transplant Biopsy Samples Are Associated with T Cell Infiltration and Poor Allograft Survival

Progress in long-term renal allograft survival continues to lag behind the progress in short-term transplant outcomes. Dendritic cells are the most efficient antigen-presenting cells, but surprisingly little attention has been paid to their presence in transplanted kidneys. We used dendritic cell-specific intercellular adhesion molecule-3-grabbing nonintegrin as a marker of dendritic cells in 105 allograft biopsy samples from 105 kidney transplant recipients. High dendritic cell density was associated with poor allograft survival independent of clinical variables. Moreover, high dendritic cell density correlated with greater T cell proliferation and poor outcomes in patients with high total inflammation scores, including inflammation in areas of tubular atrophy. We then explored the association between dendritic cells and histologic variables associated with poor prognosis. Multivariate analysis revealed an independent association between the densities of dendritic cells and T cells. In biopsy samples with high dendritic cell density, electron microscopy showed direct physical contact between infiltrating lymphocytes and cells that have the ultrastructural morphologic characteristics of dendritic cells. The origin of graft dendritic cells was sought in nine sex-mismatched recipients using XY fluorescence in situ hybridization. Whereas donor dendritic cells predominated initially, the majority of dendritic cells in late allograft biopsy samples were of recipient origin. Our data highlight the prognostic value of dendritic cell density in allograft biopsy samples, suggest a new role for these cells in shaping graft inflammation, and provide a rationale for targeting dendritic cell recruitment to promote long-term allograft survival.

Jagged2-signaling promotes IL-6-dependent transplant rejection

The Notch pathway is an important intercellular signaling pathway that plays a major role in controlling cell fate. Accumulating evidence indicates that Notch and its ligands present on antigen‐presenting cells might be important mediators of T helper cell differentiation. In this study, we investigated the role of Jagged2 in murine cardiac transplantation by using a signaling Jagged2 mAb (Jag2) that activates recombinant signal‐binding protein‐Jκ. While administration of Jag2 mAb had little effect on graft survival in the fully allogeneic mismatched model BALB/c→B6, it hastened rejection in CD28‐deficient recipients. Similarly, Jag2 precipitated rejection in the bm12→B6 model. In this MHC class II‐mismatched model, allografts spontaneously survive for >56 days due to the emergence of Treg cells that inhibit the expansion of alloreactive T cells. The accelerated rejection was associated with upregulation of Th2 cytokines and proinflammatory cytokine IL‐6, despite expansion of Treg cells. Incubation of Treg cells with recombinant IL‐6 abrogated their inhibitory effects in vitro. Furthermore, neutralization of IL‐6 in vivo protected Jag2‐treated recipients from rejection and Jagged2 signaling was unable to further accelerate rejection in the absence of Treg cells. Our findings therefore suggest that Jagged2 signaling can affect graft acceptance by upregulation of IL‐6 and consequent resistance to Treg‐cell suppression.

Beyond calcineurin inhibitors: emerging agents in kidney transplantation.

Purpose of reviewDespite their effectiveness, calcineurin inhibitors (CNIs) represent a major obstacle in the improvement of long-term graft survival in transplantation. The identification of new agents to implement CNI-free regimens is the focus of current transplant research. The purpose of this review is to summarize the novel immunosuppressive agents, including details about their mechanisms of action, stages of development, potential benefits and challenges. Recent findingsTargeting costimulation with belatacept is now an option for controlling the alloimmune response and has proved to be more effective in preserving long-term allograft function than CNIs despite an increased rate of acute rejection in some studies. mTOR inhibitors are also promising with their remarkable antineoplastic properties, though frequent side-effects may limit their broader use. Other agents under development include JAK inhibitors, CD40 blockade and leukocyte adhesion blockers, with unique potential benefits and side-effects in transplantation. SummaryNovel immunosuppressive agents are now available for use in CNI-free regimens in solid organ transplantation. Timing of initiation as well as long-term efficacy and safety are questions that remain to be answered in future clinical trials.

Serine Protease Inhibitor‐6 Differentially Affects the Survival of Effector and Memory Alloreactive CD8‐T Cells

The clonal expansion of effector T cells and subsequent generation of memory T cells are critical in determining the outcome of transplantation. While cytotoxic T lymphocytes induce direct cytolysis of target cells through secretion of Granzyme‐B (GrB), they also express cytoplasmic serine protease inhibitor‐6 (Spi6) to protect themselves from GrB that has leaked from granules. Here, we studied the role of GrB/Spi6 axis in determining clonal expansion of alloreactive CD8‐T cells and subsequent generation of memory CD8‐T cells in transplantation. CD8‐T cells from Spi6−/− mice underwent more GrB mediated apoptosis upon alloantigen stimulation in vitro and in vivo following adoptive transfer into an allogeneic host. Interestingly, while OT1.Spi6−/− CD8 T cells showed significantly lower clonal expansion following skin transplants from OVA mice, there was no difference in the size of the effector memory CD8‐T cells long after transplantation. Furthermore, lack of Spi6 resulted in a decrease of short‐lived‐effector‐CD8‐cells but did not impact the pool of memory‐precursor‐effector‐CD8‐cells. Similar results were found in heart transplant models. Our findings suggest that the final alloreactive CD8‐memory‐pool‐size is independent from the initial clonal‐proliferation as memory precursors express low levels of GrB and therefore are independent of Spi6 for survival. These data advance our understanding of memory T cells generation in transplantation and provide basis for Spi6 based strategies to target effector T cells.

Immunologic monitoring in kidney transplant recipients

Transplant biopsy has always been the gold standard for assessing the immune response to a kidney allograft (Chandraker A: Diagnostic techniques in the work-up of renal allograft dysfunction—an update. Curr Opin Nephrol Hypertens 8:723–728, 1999). A biopsy is not without risk and is unable to predict rejection and is only diagnostic once rejection has already occurred. However, in the past two decades, we have seen an expansion in assays that can potentially put an end to the “drug level” era, which until now has been one of the few tools available to clinicians for monitoring the immune response. A better understanding of the mechanisms of rejection and tolerance, and technological advances has led to the development of new noninvasive methods to monitor the immune response. In this article, we discuss these new methods and their potential uses in renal transplant recipients.

Pharmacologic Targeting of Regulatory T Cells for Solid Organ Transplantation: Current and Future Prospects

The last three decades have witnessed significant advances in the development of immunosuppressive medications used in kidney transplantation leading to a remarkable gain in short-term graft function and outcomes. Despite these major breakthroughs, improvements in long-term outcomes lag behind due to a stalemate between drug-related nephrotoxicity and chronic rejection typically due to donor-specific antibodies. Regulatory T cells (Tregs) have been shown to modulate the alloimmune response and can exert suppressive activity preventing allograft rejection in kidney transplantation. Currently available immunosuppressive agents impact Tregs in the alloimmune milieu with some of these interactions being deleterious to the allograft while others may be beneficial. Variable effects are seen with common antibody induction agents such that basiliximab, an IL-2 receptor blocker, decreases Tregs while lymphocyte depleting agents such as antithymocyte globulin increase Tregs. Calcineurin inhibitors, a mainstay of maintenance immunosuppression since the mid-1980s, seem to suppress Tregs while mammalian targets of rapamycin (less commonly used in maintenance regimens) expand Tregs. The purpose of this review is to provide an overview of Treg biology in transplantation, identify in more detail the interactions between commonly used immunosuppressive agents and Tregs in kidney transplantation and lastly describe future directions in the use of Tregs themselves as therapy for tolerance induction.

A critical review of biomarkers in kidney transplantation

Purpose of review Improved long-term kidney allograft survival remains a critical goal in transplantation; the achievement of this, however, is highly dependent on the identification of biomarkers that can either predict or allow advance detection of patients at risk of allograft injury. The present review outlines the commonly used biomarkers in kidney transplantation, while also highlighting those currently under investigation, discussing their advantages and limitations. Recent findings Most of the approved biomarkers currently used in kidney transplantation capture antigen recognition or alloantibody production. However, tremendous progress has recently been made in the development of markers of other signaling pathways pertinent to the alloimmune response. Microarray gene sets that predict rejection or poor prognostic phenotypes have been identified in kidney biopsies (the ‘molecular microscope diagnostic system’ and the ‘genomics of chronic allograft rejection’ scores), peripheral blood (the ‘kidney solid organ response test’), and urine (the ‘3-genes signature’). Strategies targeting serial measurements of urinary chemokines such as CXCL9 and CXCL10 also appear promising. Summary Although the range of biomarkers in current use is limited, there are many assays in the development and validation pipeline that appear promising but that have yet to reach mainstream clinical transplantation. The ‘ideal biomarker’ may eventually transpire to be the combination of several assays.