Comparison of Utilization and Clinical Outcomes for Belatacept- and Tacrolimus-Based Immunosuppression in Renal Transplant Recipients

Use of a Belatacept-based Immunosuppression for Kidney Transplantation From Donors After Circulatory Death: A Paired Kidney Analysis

Background

Efficacy and safety of belatacept have not been specifically reported for kidney transplantations from donors after circulatory death.

Methods

In this retrospective multicenter paired kidney study, we compared the outcome of kidney transplantations with a belatacept-based to a calcineurin inhibitor (CNI)-based immunosuppression. We included all kidney transplant recipients from donors after uncontrolled or controlled circulatory death performed in our center between February 2015 and October 2020 and treated with belatacept (n = 31). The control group included the recipients of the contralateral kidney that were treated with CNI in 8 other centers (tacrolimus n = 29, cyclosporine n = 2).

Results

There was no difference in the rate of delayed graft function. A higher incidence of biopsy-proven rejections was noted in the belatacept group (24 versus 6 episodes). Estimated glomerular filtration rate (eGFR) was significantly higher in the belatacept group at 3-, 12-, and 36-mo posttransplant, but the slope of eGFR was similar in the 2 groups. During a mean follow-up of 4.1 y, 12 patients discontinued belatacept and 2 patients were switched from CNI to belatacept. For patients who remained on belatacept, eGFR mean value and slope were significantly higher during the whole follow-up. At 5 y, eGFR was 80.7 ± 18.5 with belatacept versus 56.3 ± 22.0 mL/min/1.73 m2 with CNI (P = 0.003). No significant difference in graft and patient survival was observed.

Conclusions

The use of belatacept for kidney transplants from either uncontrolled or controlled donors after circulatory death resulted in a better medium-term renal function for patients remaining on belatacept despite similar rates of delayed graft function and higher rates of cellular rejection.

The Impact of ABCC2 -24C>T Gene Polymorphism on Graft Survival in Kidney Transplant Recipients

Personalized medicine in kidney transplantation has the potential to improve outcomes and reduce complications. The aim of this study was to investigate the influence of single nucleotide polymorphisms in genes encoding metabolizing enzymes (CYP3A5) and transporters (ABCC2) on clinical outcomes (acute graft failure and/or acute tubular necrosis (ATN)) in kidney transplant recipients (KTR). This was a multicenter, retrospective cohort study where adult KTR who had undergone kidney transplantation between 2020 and 2021 and received tacrolimus-mycophenolate treatment were enrolled in the study. DNA was extracted from collected blood samples using a commercially available kit. CYP3A5*3, ABCC2 -24C>T and ABCC2 3972C>T SNP were determined by polymerase chain reaction. Of the total 39 patients included, nine (23.1%) KTR had an incidence of acute graft failure and/or ATN. A multiple logistic regression showed wildtype ABCC2 -24C>T C allele had a higher risk of developing acute graft rejection and/or ATN compared to the variant allele carriers (adjusted Odd Ratios [aOR]: 27.675, p = 0.038). Recipients who had delayed graft function (aOR: 49.214, p = 0.012) and a history of CMV infection (aOR: 18.097, p = 0.009) were at 49.2 and 18.1-times increased risk for acute graft failure and/or ATN, respectively. The large aOR was inevitable due to the small sample size and required cautious interpretation. This is the first study to determine the effect of the ABCC2 -24C>T genetic polymorphism on clinical outcomes in Malaysian KTR and forms the basis for further work on ABCC2 -24C>T effects in long-term KTR.

Conversion from calcineurin inhibitors to belatacept-based immunosuppressive therapy skews terminal proliferation of non-classical monocytes and lowers lymphocyte counts

Belatacept, a modified form of CTLA-Ig that blocks CD28-mediated co-stimulation of T cells, is an immune-suppressant that can be used as an alternative to calcineurin inhibitors (CNIs). In kidney transplant recipients, belatacept has been associated with improved renal function and reduced cardiovascular toxicity. Monocytes as well as T-lymphocytes play causal roles in the pathophysiology of atherosclerotic disease. We hypothesized that the beneficial impact of the use of belatacept over CNIs on cardiovascular risk could be partly explained by the impact of belatacept therapy on these circulating leukocytes. Hence, we phenotyped circulating leukocytes in transplanted patients with a stable renal function that were randomized between either continuation of CNI or conversion to belatacept in two international studies in which we participated. In 41 patients, we found that belatacept-treated patients consistently showed lower numbers of B-lymphocytes, T-lymphocytes as well as CD14-negative monocytes (CD14NM), especially in non-diabetic patients. Our observation that this decrease was associated to plasma concentrations of TNFα is consistent with a model where CD14NM-production of TNFα is diminished by belatacept-treatment, due to effects on the antigen-presenting cell compartment.

Early conversion to belatacept-based immunosuppression regimen promotes improved long-term renal graft function in kidney transplant recipients

BACKGROUND

Belatacept has been demonstrated as an effective alternative immunosuppressant in kidney transplant recipients. This study focuses on outcomes of early and late conversion to Belatacept-based immunosuppression after kidney transplant.

MATERIALS AND METHODS

This retrospective analysis of a prospectively collected database included all adult kidney transplants patients at SUNY Upstate Medical Hospital from 1 January 2014 to 30 December 2022. Early conversion was defined as all conversions done at <6 months after kidney transplantation, and late conversion to belatacept was defined as conversion at >6 months after kidney transplantation.

RESULTS

Out of 61 patients included in this study, 33 patients (54%) were in the early conversion group, and 28 patients (46%) were in the late conversion group. The mean eGFR in the early conversion group was 26.73 ± 16.26 ml/min/1.73 m2 before conversion to belatacept, which improved to 45.3 ± 21.01 ml/min/1.73 m2 at one-year post-conversion (p = 0.0006). Furthermore, eGFR changes in the late conversion group were insignificant, with 46.30 ± 15.65 ml/min/1.73 m2 before conversion to belatacept, and 44.76 ± 22.91 ml/min/1.73 m2 after one year of follow-up (p = 0.72). All four biopsy-proven allograft rejections in the early conversion group were acute T-cell-mediated rejections (ATMR). In the late conversion group, out of three biopsy-proven rejections, one was chronic antibody-mediated rejection (CAMR), one was ATMR, and one was mixed ATMR/CAMR. All four patients with ATMR rejection received mycophenolic acid (MPA) as part of their immunosuppressive regimen, and none received tacrolimus. The one-year post-conversion allograft survival rate in early and late conversion groups was 100%. However, the one-year post-conversion patient survival rate was 90.9% in the early conversion group and 100% in the late conversion group (P = 0.11).

CONCLUSIONS

Early post-transplant conversion to belatacept can improve the eGFR more meaningful when compared to late conversion. Patients who receive belatacept and MPA rather than tacrolimus may have increased rates of T-cell-mediated rejection.

TNX-1500, a crystallizable fragment-modified anti-CD154 antibody, prolongs nonhuman primate renal allograft survival

The blockade of the CD154-CD40 pathway with anti-CD154 monoclonal antibody has been a promising immunomodulatory approach to prevent allograft rejection. However, clinical trials of immunoglobulin G1 antibodies targeting this pathway revealed thrombogenic properties, which were subsequently shown to be mediated by crystallizable fragment (Fc)-gamma receptor IIa-dependent platelet activation. To prevent thromboembolic complications, an immunoglobulin G4 anti-CD154 monoclonal antibody, TNX-1500, which retains the fragment antigen binding region of ruplizumab (humanized 5c8, BG9588), was modified by protein engineering to decrease Fc binding to Fc-gamma receptor IIa while retaining certain other effector functions and pharmacokinetics comparable with natural antibodies. Here, we report that TNX-1500 treatment is not associated with platelet activation in vitro and consistently inhibits kidney allograft rejection in vivo without clinical or histologic evidence of prothrombotic phenomena. We conclude that TNX-1500 retains efficacy similar to that of 5c8 to prevent kidney allograft rejection while avoiding previously identified pathway-associated thromboembolic complications.

Interventions Against Posttransplantation Diabetes: A Scientific Rationale for Treatment Hierarchy Based on Literature Review

Posttransplant diabetes (PTD) is a common medical complication after solid organ transplantation. Because of adverse outcomes associated with its development and detrimental impact on long-term survival, strategies to prevent or manage PTD are critically important but remain underresearched. Treatment hierarchies of antidiabetic therapies in the general population are currently being revolutionized based on cardiovascular outcome trials, providing evidence-based rationale for optimization of medical management. However, opportunities for improving medical management of PTD are challenged by 2 important considerations: (1) translating clinical evidence data from the general population to underresearched solid organ transplant cohorts and (2) targeting treatment based on primary underlying PTD pathophysiology. In this article, the aim is to provide an overview of PTD treatment options from a new angle. Rationalized by a consideration of underlying PTD pathophysiological defects, which are heterogeneous among diverse transplant patient cohorts, a critical appraisal of the published literature and summary of current research in progress will be reviewed. The aim is to update transplant professionals regarding medical management of PTD from a new perspective tailored therapeutic intervention based on individualized characteristics. As the gap in clinical evidence between management of PTD versus type 2 diabetes widens, it is imperative for the transplant community to bridge this gap with targeted clinical trials to ensure we optimize outcomes for solid organ transplant recipients who are at risk or develop PTD. This necessary clinical research should help efforts to improve long-term outcomes for solid transplant patients from both a patient and graft survival perspective.

Belatacept in Kidney Transplantation: What Are the True Benefits? A Systematic Review

The current gold standard to prevent allograft rejection for maintenance immunosuppression in kidney transplantation currently consists in glucocorticoids, an antiproliferative agent and a calcineurin inhibitor (CNI), with better outcome for tacrolimus than cyclosporin. Although, CNI drastically improved early graft survival, so far, CNI have failed to significantly improve long-term survival mainly because of nephrotoxicity. In addition, CNI carry several other side effects such as an increased risk for cardiovascular events and for diabetes mellitus. Therefore, seeking alternatives to CNI remains of paramount importance in kidney transplantation. Belatacept is a fusion protein composed of the human IgG1 Fc fragment linked to the modified extracellular domain of cytotoxic T lymphocyte–associated antigen 4. In kidney transplant recipients, pivotal phase III randomized studies suggested clinical benefits of belatacept as an initial maintenance regimen, as compared with cyclosporine, mainly on kidney function. Recently, a randomized study also suggested a clinical benefit on renal function of a conversion from a CNI-based to a belatacept-based maintenance regimen in patients. However, conversion from CNIs to belatacept is probably associated with an increased risk of biopsy-proven acute rejection and should prompt close clinical surveillance. On the other hand, other studies suggest a decrease in de novo humoral transplant immunization. Belatacept is probably associated with an increase in both risk and severity of some infectious diseases, including EBV-linked post-transplantation lymphoproliferative disorders, and with a decreased response to vaccines. Most studies on belatacept are observational, retrospective, and non-comparative. Consequently, high-quality data about the safety and efficacy profile of belatacept, as compared with the current gold standard for maintenance regimens (tacrolimus-based), is uncertain. Our review will therefore focus on the most recent published data aiming at evaluating the evidence-based or the “true” benefits and risks of belatacept-based regimens in kidney transplantation.

Post-Transplant Cardiovascular Disease

Cardiovascular disease remains a leading cause of death and morbidity in kidney transplant recipients and a common reason for post-transplant hospitalization. Several traditional and nontraditional cardiovascular risk factors exist, and many of them present pretransplant and worsened, in part, due to the addition of immunosuppression post-transplant. We discuss optimal strategies for identification and treatment of these risk factors, including the emerging role of sodium-glucose cotransporter 2 inhibitors in post-transplant diabetes and cardiovascular disease. We present common types of cardiovascular disease observed after kidney transplant, including coronary artery disease, heart failure, pulmonary hypertension, arrhythmia, and valvular disease. We also discuss screening, treatment, and prevention of post-transplant cardiac disease. We highlight areas of future research, including the need for goals and best medications for risk factors, the role of biomarkers, and the role of screening and intervention.

Post-Transplant Diabetes Mellitus and Prediabetes in Renal Transplant Recipients: An Update

Post-transplant diabetes mellitus (PTDM) is a frequent and relevant complication after renal transplantation: it affects 20-30% of renal transplant recipients and increases the risk for cardiovascular and infectious events. Thus, understanding pathogenesis of PTDM would help limiting its consequences. In this review, we analyse novel aspects of PTDM, based on studies of the last decade, such as the clinical evolution of PTDM, early and late, the reversibility rate, diagnostic criteria, risk factors, including pre-transplant metabolic syndrome and insulin resistance (IR) and the interaction between these factors and immunosuppressive medications. Also, we discuss novel pathogenic factors, in particular the role of β-cell function in an environment of IR and common pathways between pre-existing cell damage and tacrolimus-induced toxicity. The relevant role of prediabetes in the pathogenesis of PTDM and cardiovascular disease is also addressed. Finally, current evidence on PTDM treatment is discussed.

Improved ability to achieve target trough levels with liquid versus capsule tacrolimus in kidney transplant patients with HIV on protease inhibitor- or cobicistat-based regimens

HIV + patients are commonly accepted for kidney transplantation. However, patients on protease inhibitor (PI)- or cobicistat (cobi)-based regimens have trouble achieving optimal tacrolimus (Tac) levels. Our study compared the ability to achieve target levels using liquid versus immediate-release capsule Tac in kidney transplant patients with HIV on PI- or cobi-based regimens. The study included four kidney transplant patients who were converted to liquid Tac due to inability to achieve acceptable drug levels on the capsule formulation. Tac trough levels were analyzed retrospectively to compare target levels before and after conversion. The individual patient time in the therapeutic range (TTR) was calculated using Rosendaal's linear interpolation method, and the difference between before and after conversion TTR was determined. In combined data, 44.63% of all Tac trough levels were within the target range after conversion to liquid Tac compared to 22.07% prior to conversion (P < .001). Furthermore, 3.31% and 7.44% of Tac trough levels were lower than 3 ng/mL or higher than 12 ng/mL, respectively, after conversion compared to 11.72% (P = .0564) and 24.14% (P < .0001) prior to conversion. The overall mean TTR was 45.1% after conversion to liquid Tac compared to 16.2% prior to conversion (P = .097). Finally, the coefficient of variation for Tac trough levels was 42.6 after conversion compared to 56.4 prior to conversion. A significantly improved ability to achieve target trough Tac levels was achieved with liquid Tac extemporaneous versus capsule formulation in kidney transplant patients with HIV taking a PI- or cobi-based regimen.

Prevention of acute rejection after rescue with Belatacept by association of low-dose Tacrolimus maintenance in medically complex kidney transplant recipients with early or late graft dysfunction

Background

Increased acute rejection risk in rescue protocols with Belatacept may limit its use particularly in medically complex patients where preexisting increased risk of rejection couples with CNI toxicity.

Methods

Retrospective analysis was performed in 19 KTs shifted to a Belatacept-based immunosuppression with low-dose Tacrolimus (2–3 ng/mL) after evidence of allograft disfunction, including patients with primary non-function (PNF), chronic-active antibody-mediated rejection (cAMR), history of previous KTs and/or other concomitant transplants (liver, pancreas). Evaluation of CD28⁺ CD4⁺ effector memory T cell (T_EM) before conversion was performed in 10/19.

Results

Kidney function significantly improved (median eGFR 16.5 ml/min/1.73m² before vs 25 ml/min after; p = 0.001) at a median time after conversion of 12.5 months (9.1–17.8). Overall graft and patient survival were 89.5% and 100% respectively. Definitive weaning from dialysis in 5/5 KTs with PNF was observed, whereas 7/8 patients lost their graft within first year in a control group. eGFR significantly ameliorated in re-trasplants (p = 0.001) and stabilized in KTs with other organ transplants or cAMR. No acute rejection episodes occurred, despite the significant risk suggested by high frequency of CD28⁺ CD4⁺ T_EM in most patients. Opportunistic infections were limited and most common in early vs late-converted.

Conclusions

Rescue association of Belatacept with low-dose Tacrolimus in medically complex KTs is a feasible option that allows prevention of acute rejection and amelioration of graft function.

Memory T cell-mediated rejection is mitigated by FcγRIIB expression on CD8+ T cells

Donor-reactive memory T cells generated via heterologous immunity represent a potent barrier to long-term graft survival following transplantation because of their increased precursor frequency, rapid effector function, altered trafficking patterns, and reduced reliance on costimulation signals for activation. Thus, the identification of pathways that control memory T cell survival and secondary recall potential may provide new opportunities for therapeutic intervention. Here, we discovered that donor-specific effector/memory CD8⁺ T cell populations generated via exposure to acute vs latent vs chronic infections contain differential frequencies of CD8⁺ T cells expressing the inhibitory Fc receptor FcγRIIB. Results indicated that frequencies of FcγRIIB-expressing CD8⁺ donor-reactive memory T cells inversely correlated with allograft rejection. Furthermore, adoptive T cell transfer of Fcgr2b^-/- CD8⁺ T cells resulted in an accumulation of donor-specific CD8⁺ memory T cells and enhanced recall responses, indicating that FcγRIIB functions intrinsically to limit T cell CD8⁺ survival in vivo. Lastly, we show that deletion of FcγRIIB on donor-specific CD8⁺ memory T cells precipitated costimulation blockade-resistant rejection. These data therefore identify a novel cell-intrinsic inhibitory pathway that functions to limit the risk of memory T cell-mediated rejection following transplantation and suggest that therapeutic manipulation of this pathway could improve outcomes in sensitized patients.

T Cell Repertoire Maturation Induced by Persistent and Latent Viral Infection Is Insufficient to Induce Costimulation Blockade Resistant Organ Allograft Rejection in Mice

CD28:CD80/86 pathway costimulation blockade (CoB) with the CD80/86-specific fusion protein CTLA4-Ig prevents T cell-mediated allograft rejection in mice. However, in humans, transplantation with CoB has been hampered by CoB-resistant rejection (CoBRR). CoBRR has been attributed in part to pathogen-driven T cell repertoire maturation and resultant heterologous alloreactive memory. This has been demonstrated experimentally in mice. However, prior murine models have used viral pathogens, CoB regimens, graft types, and/or antigen systems atypically encountered clinically. We therefore sought to explore whether CoBRR would emerge in a model of virus-induced memory differentiation designed to more closely mimic clinical conditions. Specifically, we examined mouse homologs of clinically prevalent viruses including murine polyomavirus, cytomegalovirus, and gammaherpesvirus 68 in the presence of clinically relevant maintenance CoB regimens using a fully MHC-mismatched, vascularized allograft model. Infected mice developed a significant, sustained increase in effector memory T cells consistent with that seen in humans, but neither developed heterologous alloreactivity nor rejected primarily vascularized heterotopic heart transplants at an increased rate compared with uninfected mice. These results indicate that memory acquisition alone is insufficient to provoke CoBRR and suggest that knowledge of prior latent or persistent viral infection may have limited utility in anticipating heterologous CoB-resistant alloimmunity.

Belatacept Combined With Transient Calcineurin Inhibitor Therapy Prevents Rejection and Promotes Improved Long-Term Renal Allograft Function

Belatacept, a T cell costimulation blocker, demonstrated superior renal function, lower cardiovascular risk, and improved graft and patient survival in renal transplant recipients. Despite the potential benefits, adoption of belatacept has been limited in part due to concerns regarding higher rates and grades of acute rejection in clinical trials. Since July 2011, we have utilized belatacept-based immunosuppression regimens in clinical practice. In this retrospective analysis of 745 patients undergoing renal transplantation at our center, we compared patients treated with belatacept (n = 535) with a historical cohort receiving a tacrolimus-based protocol (n = 205). Patient and graft survival were equivalent for all groups. An increased rate of acute rejection was observed in an initial cohort treated with a protocol similar to the low-intensity regimen from the BENEFIT trial versus the historical tacrolimus group (50.5% vs. 20.5%). The addition of a transient course of tacrolimus reduced rejection rates to acceptable levels (16%). Treatment with belatacept was associated with superior estimated GFR (belatacept 63.8 mL/min vs. tacrolimus 46.2 mL/min at 4 years, p < 0.0001). There were no differences in serious infections including rates of cytomegalovirus or BK viremia. We describe the development of a costimulatory blockade-based strategy that ultimately allows renal transplant recipients to achieve calcineurin inhibitor-free immunosuppression.

A Randomized Controlled Clinical Trial Comparing Belatacept With Tacrolimus After De Novo Kidney Transplantation

BACKGROUND

Belatacept, an inhibitor of the CD28-CD80/86 costimulatory pathway, allows for calcineurin-inhibitor free immunosuppressive therapy in kidney transplantation but is associated with a higher acute rejection risk than ciclosporin. Thus far, no biomarker for belatacept-resistant rejection has been validated. In this randomized-controlled trial, acute rejection rate was compared between belatacept- and tacrolimus-treated patients and immunological biomarkers for acute rejection were investigated.

METHODS

Forty kidney transplant recipients were 1:1 randomized to belatacept or tacrolimus combined with basiliximab, mycophenolate mofetil, and prednisolone. The 1-year incidence of biopsy-proven acute rejection was monitored. Potential biomarkers, namely, CD8CD28, CD4CD57PD1, and CD8CD28 end-stage terminally differentiated memory T cells were measured pretransplantation and posttransplantation and correlated to rejection. Pharmacodynamic monitoring of belatacept was performed by measuring free CD86 on monocytes.

RESULTS

The rejection incidence was higher in belatacept-treated than tacrolimus-treated patients: 55% versus 10% (P = 0.006). All 3 graft losses, due to rejection, occurred in the belatacept group. Although 4 of 5 belatacept-treated patients with greater than 35 cells CD8CD28 end-stage terminally differentiated memory T cells/μL rejected, median pretransplant values of the biomarkers did not differ between belatacept-treated rejectors and nonrejectors. In univariable Cox regressions, the studied cell subsets were not associated with rejection-risk. CD86 molecules on circulating monocytes in belatacept-treated patients were saturated at all timepoints.

CONCLUSIONS

Belatacept-based immunosuppressive therapy resulted in higher and more severe acute rejection compared with tacrolimus-based therapy. This trial did not identify cellular biomarkers predictive of rejection. In addition, the CD28-CD80/86 costimulatory pathway appeared to be sufficiently blocked by belatacept and did not predict rejection.

Belatacept Compared With Tacrolimus for Kidney Transplantation: A Propensity Score Matched Cohort Study

BACKGROUND

Although tacrolimus is the basis of most maintenance immunosuppression regimens for kidney transplantation, concerns about toxicity have made alternative agents, such as belatacept, attractive to clinicians. However, limited data exist to directly compare outcomes with belatacept-based regimens to tacrolimus.

METHODS

We performed a propensity score matched cohort study of adult kidney transplant recipients transplanted between May 1, 2001, and December 31, 2015, using national transplant registry data to compare patient and allograft survival in patients discharged from their index hospitalization on belatacept-based versus tacrolimus-based regimens.

RESULTS

In the primary analysis, we found that belatacept was not associated with a statistically significant difference in risk of patient death (hazard ratio, 0.84; 95% confidence interval [CI], 0.61-1.15, P = 0.28) or allograft loss (hazard ratio, 0.83; 95% CI, 0.62-1.11; P = 0.20) despite an increased risk of acute rejection in the first year posttransplant (odds ratio, 3.12; 95% CI, 2.13-4.57; P < 0.001). These findings were confirmed in additional sensitivity analyses that accounted for use of belatacept in combination with tacrolimus, transplant center effects, and differing approaches to matching.

CONCLUSIONS

Belatacept appears to have similar longitudinal risk of mortality and allograft failure compared with tacrolimus-based regimens. These data are encouraging but require confirmation in prospective randomized controlled trials.

Successful Treatment of T Cell-Mediated Acute Rejection with Delayed CTLA4-Ig in Mice

Clinical observations that kidney transplant recipients receiving belatacept who experienced T cell-mediated acute rejection can be successfully treated and subsequently maintained on belatacept-based immunosuppression suggest that belatacept is able to control memory T cells. We recently reported that treatment with CTLA4-Ig from day 6 posttransplantation successfully rescues allografts from acute rejection in a BALB/c to C57BL/6 heart transplant model, in part, by abolishing B cell germinal centers and reducing alloantibody titers. Here, we show that CTLA4-Ig is additionally able to inhibit established T cell responses independently of B cells. CTLA4-Ig inhibited the in vivo cytolytic activity of donor-specific CD8⁺ T cells, and the production of IFNγ by graft-infiltrating T cells. Delayed CTLA4-Ig treatment did not reduce the numbers of graft-infiltrating T cells nor prevented the accumulation of antigen-experienced donor-specific memory T cells in the spleen. Nevertheless, delayed CTLA4-Ig treatment successfully maintained long-term graft acceptance in the majority of recipients that had experienced a rejection crisis, and enabled the acceptance of secondary BALB/c heart grafts transplanted 30 days after the first transplantation. In summary, we conclude that delayed CTLA4-Ig treatment is able to partially halt ongoing T cell-mediated acute rejection. These findings extend the functional efficacy of CTLA4-Ig therapy to effector T cells and provide an explanation for why CTLA4-Ig-based immunosuppression in the clinic successfully maintains long-term graft survival after T cell-mediated rejection.

CTLA4-Ig in combination with FTY720 promotes allograft survival in sensitized recipients

Despite recent evidence of improved graft outcomes and safety, the high incidence of early acute cellular rejection with belatacept, a high-affinity CTLA4-Ig, has limited its use in clinical transplantation. Here we define how the incomplete control of endogenous donor-reactive memory T cells results in belatacept-resistant rejection in an experimental model of BALB/c.2W-OVA donor heart transplantation into C57BL/6 recipients presensitized to donor splenocytes. These sensitized mice harbored modestly elevated numbers of endogenous donor-specific memory T cells and alloantibodies compared with naive recipients. Continuous CTLA4-Ig treatment was unexpectedly efficacious at inhibiting endogenous graft-reactive T cell expansion but was unable to inhibit late CD4+ and CD8+ T cell infiltration into the allografts, and rejection was observed in 50% of recipients by day 35 after transplantation. When CTLA4-Ig was combined with the sphingosine 1-phosphate receptor-1 (S1PR1) functional antagonist FTY720, alloantibody production was inhibited and donor-specific IFN-γ-producing T cells were reduced to levels approaching nonsensitized tolerant recipients. Late T cell recruitment into the graft was also restrained, and graft survival improved with this combination therapy. These observations suggest that a rational strategy consisting of inhibiting memory T cell expansion and trafficking into the allograft with CTLA4-Ig and FTY720 can promote allograft survival in allosensitized recipients.

Two Decades of Tacrolimus in Renal Transplant: Basic Science and Clinical Evidences

Tacrolimus, a calcineurin inhibitor, has been the cornerstone of immunosuppressive regimens in renal transplant over 2 decades. This has significantly improved the outcomes of renal transplant, including reduction of acute rejection episodes, improvement of renal function and graft survival, and reduction of some of the adverse effects associated with cyclosporine. However, use of tacrolimus is associated with a number of undesirable effects, such as nephrotoxicity, posttransplant diabetes mellitus, neurotoxicity, and cosmetic and electrolyte disturbances. To alleviate these effects, several strategies have been adopted to minimize or eliminate tacrolimus from maintenance regimens of immunosuppression, with some success. This review focuses on advancements in the understanding of the basic science related to tacrolimus and the clinical evidences that have examined the efficacy and safety of tacrolimus in renal transplant over the past 2 decades and highlights the future directions.