Therapeutic Drug Monitoring of Belatacept in Kidney Transplantation

The potential for therapeutic drug monitoring of belatacept and other biologicals in solid organ transplantation

In solid organ transplantation (SOT), biologicals such as recombinant therapeutic proteins, monoclonal antibodies, fusion proteins and conjugates are increasingly used for immunosuppression, desensitization, ABO (blood group) incompatibility, antibody-mediated rejections and atypical haemolytic uremic syndrome. In this paper, we review the medical evidence available for biologicals used in SOT and the potential for improvement by the application of therapeutic drug monitoring (TDM) and model-informed precision dosing. Biologicals are used for off-label indications within the field of SOT, building on the experience from their use on labelled indications. Dosing is currently mostly standard, and experience vs. effect and toxicity is limited. Pharmacokinetic characteristics of these large, partly also immunogenic molecules differ from those of traditional small molecules. Individualization by concentration measurements and modelling has mostly been proof-of-concept or feasibility studies that lack the power to provide evidence for improvement in clinical outcome. For some drugs such as alemtuzumab, eculizumab, rituximab, tocilizumab and belatacept, studies have demonstrated significant interindividual variability in pharmacokinetics. Variability in absorption from subcutaneous administration may increase interindividual variability. There is also an economic aspect of appropriate dosing that needs to be pursued. Available assays and models to refine interpretation are in place, but trials of adequate size to document the usefulness of TDM and MIPD are scarce. Collaboration within the TDM community seems mandatory to establish studies of sufficient strength to provide evidence for the use of biologicals that are currently used off-label in SOT and furthermore to identify the settings where TDM may be beneficial.

Quantification of belatacept by liquid chromatography-tandem mass spectrometry in human plasma: Application to a pharmacokinetic study in renal transplant recipients

Therapeutic drug monitoring is the cornerstone of immunosuppressive treatment in transplantation. The immunosuppressive drugs used in kidney transplant patients are mostly comprised of biologics, including therapeutic monoclonal antibodies (mAbs) and fusion proteins. Therefore, a specific and sensitive analytical technique that can universally quantify mAbs, as well as fusion proteins, is essential for clinical pharmacokinetics studies. In this short communication, we describe the validation of a liquid chromatography tandem mass-spectrometry (LC-MS/MS) method for quantification of the fusion protein belatacept in the plasma of kidney-transplant patients. Sample preparation was based on our previously published and implementable electrospray ionization LC-MS/MS method that allows the simultaneous quantification of seven mAbs. Immunocapture was made possible by the Fc domain of belatacept and identification/quantification by the choice of MRM transitions of peptides. The temporal evolution of the belatacept concentration after intravenous infusion and inter-individual variability of trough concentrations were assessed in 17 human plasma samples. The belatacept calibration curves were linear from 1 to 200 mg.L^-1 and within-day and between-day accuracy and precision fulfilled Food and Drug Administration validation criteria. Residual belatacept concentrations (n = 8) ranged from 5.1 to 15.0 mg.L^-1, with a median of 8.9 mg.L^-1 and an inter-individual CV of 33.0%. Our generic LC-MS/MS method allows the quantification of fusion proteins, such as belatacept, and could be used for therapeutic drug monitoring. This method provides a useful tool to study the intra-patient variability of belatacept and the association between belatacept exposure and its therapeutic effects.

CD86 occupancy in belatacept-treated kidney transplant patients is not associated with clinical and infectious outcomes

The CD86 occupancy assay has been developed to measure the number of CD86 molecules unbound to belatacept, but its association with clinical outcomes has not been assessed yet. All kidney transplant patients switched to belatacept in our center between 2016 and 2018 were included. Blood samples were collected before each infusion for 1 year to assess CD86 occupancy by CD86 antibody cytometry staining on the surface of CD14⁺ monocytes. Results were expressed as the median fluorescence intensity (MFI) value of CD86 staining. At each infusion, the MFI_{Day of infusion} /MFI_{Day 0} ratio was calculated. Forty-one patients were consecutively included. After every 2-week infusion period, CD86 MFI ratio dropped from 1.00 to 0.73 [0.57-0.98], p = .07. However, this ratio progressively increased to 0.78 [0.53-1.13] at 1 year, which was not statistically different from pre-switch ratio, p = .4. Over the first year, the MFI ratio coefficient of variation was 31.58% [23.75-38.31]. MFI ratio was not different between patients with or without opportunistic infections: 0.73 [0.60-0.88] versus 0.80 [0.71-1.00], p = .2, or between patients with or without EBV DNAemia, p = .2. Despite previous in vitro results, the CD86 occupancy assay suffers from a high intra-individual variability and does not appear to be relevant to clinical outcomes.

Model-informed precision dosing to optimise immunosuppressive therapy in renal transplantation

Immunosuppressive therapy is pivotal for sustained allograft and patient survival after renal transplantation. However, optimally balanced immunosuppressive therapy is challenged by between-patient and within-patient pharmacokinetic (PK) variability. This could warrant the application of personalised dosing strategies to optimise individual patient outcomes. Pharmacometrics, the science that investigates the xenobiotic-biotic interplay using computer-aided mathematical modelling, provides options to describe and quantify this PK variability and enables identification of patient characteristics affecting immunosuppressant PK and treatment outcomes. Here, we review and critically appraise the available pharmacometric model-informed dosing solutions for the typical immunosuppressants in modern renal transplantation, to guide their initial and subsequent dosing.

Role of donor macrophages after heart and lung transplantation

Since the 1960s, heart and lung transplantation has remained the optimal therapy for patients with end-stage disease, extending and improving quality of life for thousands of individuals annually. Expanding donor organ availability and immunologic compatibility is a priority to help meet the clinical demand for organ transplant. While effective, current immunosuppression is imperfect as it lacks specificity and imposes unintended adverse effects such as opportunistic infections and malignancy that limit the health and longevity of transplant recipients. In this review, we focus on donor macrophages as a new target to achieve allograft tolerance. Donor organ-directed therapies have the potential to improve allograft survival while minimizing patient harm related to global suppression of recipient immune responses. Topics highlighted include the role of ontogenically distinct donor macrophage populations in ischemia-reperfusion injury and rejection, including their interaction with allograft-infiltrating recipient immune cells and potential therapeutic approaches. Ultimately, a better understanding of how donor intrinsic immunity influences allograft acceptance and survival will provide new opportunities to improve the outcomes of transplant recipients.

Targeted Proteomic Analysis Detects Acute T Cell-Mediated Kidney Allograft Rejection in Belatacept-Treated Patients

BACKGROUND

There is an unmet need for reliable minimally invasive diagnostic biomarkers for immunological allograft monitoring and for the detection of acute kidney transplant rejection. Here, targeted proteomic analysis was applied to compare 92 proteins in sera of belatacept-treated patients who had biopsy-proven, acute T-cell-mediated rejection (aTCMR) with patients without aTCMR.

METHODS

Proximity extension immunoassay was used to measure 92 inflammation-related protein concentrations in the prerejection and rejection sera of 11 patients with aTCMR and 9 patients without aTCMR. This assay uses 2 matched oligonucleotide-labeled antibody probes for each protein and polymerase chain reaction to measure normalized protein expression values.

RESULTS

Five proteins (CD5, CD8A, NCR1, TNFRSF4, and TNFRSF9) were expressed significantly higher in samples with aTCMR compared with samples without aTCMR (adjusted P-value < 0.014) and had a good predictive capacity for aTCMR [area under the curve in a receiver-operator curve ranged from 0.83 to 0.91 (P < 0.014)]. These proteins are associated with CD8 cytotoxic T-cell and NK cell functions. Nonhierarchical clustering analysis showed distinct clustering of samples with aTCMR and samples without aTCMR. This clustering was not found in prerejection samples (1 month after transplantation). In prerejection samples, IFN-γ was expressed at a significantly lower level (normalized protein expression value median -0.15, interquartile range: -0.27 to 0.04) than in samples of patients without rejection (median 0.13, interquartile range: -0.07 to 0.15, adjusted P-value = 0.00367).

CONCLUSIONS

Targeted proteomic analysis with proximity extension immunoassay is a promising minimally invasive technique to diagnose aTCMR in kidney transplant recipients.

Belatacept in renal transplant recipient with mild immunologic risk factor: A pilot prospective study (BELACOR)

The benefit of belatacept on antibody-mediated rejection (ABMR) incidence after kidney transplant with preformed donor-specific antibodies (DSAs) has never been assessed. Between 2014 and 2016, we conducted a multicenter prospective clinical trial with 49 patients to determine kidney allograft outcome in recipients with preformed DSAs (maximal mean fluorescence intensity 500 to 3000) treated with belatacept (BELACOR trial). Immunosuppressive strategy included antithymocyte globulin, belatacept, mycophenolate mofetil, and steroids. An ancillary control group was designed retrospectively, including patients fulfilling the same inclusion criteria treated with calcineurin inhibitors. In BELACOR group, no patient exhibited acute ABMR, patient and allograft survival at 1 year was 100% and 95.4%, respectively, and the estimated glomerular filtration rate was 53.2 mL/min/1.73 m² . However, the 12-month incidence of acute T cell-mediated rejection was 25.4% (14.5% to 42.4%). Comparison with the control group showed significantly higher T cell-mediated rejection incidence only in the BELACOR group (P = .003). Considering the DSAs, the outcome was similar in the 2 groups except a significantly higher number of patients displayed a complete disappearance of class II DSAs in the BELACOR group (P = .001). Belatacept was not associated with an acute ABMR increased risk and may be considered as immunosuppressive strategy in transplant recipients with preformed DSAs (maximal mean fluorescence intensity 500 to 3000). Prospective randomized trials are needed to confirm these results.

Immunomics of Renal Allograft Acute T Cell-Mediated Rejection Biopsies of Tacrolimus- and Belatacept-Treated Patients

Supplemental digital content is available in the text.

Background

Belatacept-based therapy in kidney transplant recipient has been shown to increase long-term renal allograft and patient survival compared with calcineurin inhibitor–based therapy, however, with an increased risk of acute T cell-mediated rejection (aTCMR). An improved understanding of costimulation blockade-resistant rejections could lead to a more personalized approach to belatacept therapy. Here, immunomic profiles of aTCMR biopsies of patients treated with either tacrolimus or belatacept were compared.

Methods

Formalin-fixed paraffin-embedded renal transplant biopsies were used for immunohistochemistry and gene expression analysis using the innovative NanoString technique. To validate NanoString, transcriptomic profiles of patients with and without biopsy-proven aTCMR were compared. Biopsies from 31 patients were studied: 14 tacrolimus-treated patients with aTCMR, 11 belatacept-treated patients with aTCMR, and 6 controls without rejection.

Results

A distinct pattern was seen in biopsies with aTCMR compared to negative controls: 78 genes had a higher expression in the aTCMR group (false discovery rate P value <.05 to 1.42e–05). The most significant were T cell-associated genes (CD3, CD8, and CD4; P < 1.98e-04), γ-interferon-inducible genes (CCL5, CXCL9, CXCL11, CXCL10, TBX21; P < 1.33e-04) plus effector genes (GNLY, GZMB, ITGAX; P < 2.82e-03). Immunophenotypical analysis of the classic immune markers of the innate and adaptive immune system was comparable between patients treated with either tacrolimus or belatacept. In addition, the transcriptome of both groups was not significantly different.

Conclusions

In this small pilot study, no difference was found in immunomics of aTCMR biopsies of tacrolimus- and belatacept-treated patients. This suggests that clinically diagnosed aTCMR reflects a final common pathway of allorecognition which is unaffected by the type of immunosuppressive therapy.

Co-inhibitory profile and cytotoxicity of CD57+ PD-1- T cells in end-stage renal disease patients

Blockade of the CD80/86-CD28 pathway by belatacept after kidney transplantation is associated with an increased risk of rejection compared with standard, calcineurin inhibitor (CNI)-based therapy. CD28^- T cells, which express CD57, are not susceptible to belatacept treatment. High numbers of CD4⁺ CD57⁺ programmed death 1 (PD-1)^- T cells pretransplantation have been associated with a higher chance of rejection, although conflicting data have been reported. To investigate the working mechanism behind this possible higher chance of rejection, we studied the expression of co-inhibitory molecules (CD223, CD244 and PD-1), proliferative capacity and cytotoxic potential of fluorescence activated cell sorted (FACS) CD4⁺ CD57⁺ PD-1^- and CD8⁺ CD57⁺ PD-1^- T cells, and their CD57^- control populations, after alloantigen stimulation. The effect of belatacept on the cytotoxic capacity of pretransplantation peripheral blood mononuclear cells from 20 patients who received belatacept post-transplantation was also tested. Expression of co-inhibitory molecule CD223 increased by approximately 10-fold after allogeneic stimulation in all four T cell subsets. Proliferation and up-regulation of CD244 and PD-1 was observed for CD4⁺ CD57^- PD-1^- T cells after allogeneic stimulation, but no up-regulation of these markers occurred on CD8⁺ T cells or CD4⁺ CD57⁺ PD-1^- T cells. However, CD4⁺ CD57⁺ PD-1^- T cells and, to a lesser extent, CD8⁺ CD57⁺ PD-1^- T cells displayed higher cytotoxicity as indicated by granzyme B expression. Belatacept inhibited the cytotoxic potential of CD4⁺ CD57⁺ PD-1^- T cells (median of inhibition 31%, P < 0·01) and CD8⁺ CD57⁺ PD-1^- T cells (median of inhibition 10%, P < 0·05). In conclusion, alloantigen-activated CD4⁺ CD57⁺ PD-1^- T cells exhibited a less proliferative but more cytotoxic profile than their CD57^- counterparts. Their cytotoxic capacity can be inhibited partly by belatacept and was not associated with development of rejection after kidney transplantation.

Improved Glucose Tolerance in a Kidney Transplant Recipient With Type 2 Diabetes Mellitus After Switching From Tacrolimus To Belatacept: A Case Report and Review of Potential Mechanisms

Supplemental digital content is available in the text.

The introduction of immunosuppressant belatacept, an inhibitor of the CD28-80/86 pathway, has improved 1-year outcomes in kidney transplant recipients with preexistent diabetes mellitus and has also reduced the risk of posttransplant diabetes mellitus. So far, no studies have compared a tacrolimus-based with a belatacept-based immunosuppressive regimen with regard to improving glucose tolerance after kidney transplantation. Here, we present the case of a 54-year-old man with type 2 diabetes mellitus who was converted from belatacept to tacrolimus 1 year after a successful kidney transplantation. Thereafter, he quickly developed severe hyperglycemia, and administration of insulin was needed to improve metabolic control. Six months after this episode, he was converted back to belatacept because of nausea, diarrhea, and hyperglycemia. After switching back to belatacept and within 4 days after stopping tacrolimus glucose tolerance improved and insulin therapy could be discontinued. Although belatacept is considered less diabetogenic than tacrolimus, the rapid improvement of glucose tolerance after switching to belatacept is remarkable. In this article, the potential mechanisms of this observation are discussed.

Differential T Cell Signaling Pathway Activation by Tacrolimus and Belatacept after Kidney Transplantation: Post Hoc Analysis of a Randomised-Controlled Trial

Pharmacokinetic immunosuppressive drug monitoring poorly correlates with clinical outcomes after solid organ transplantation. A promising method for pharmacodynamic monitoring of tacrolimus (TAC) in T cell subsets of transplant recipients might be the measurement of (phosphorylated) p38MAPK, ERK1/2 and Akt (activated downstream of the T cell receptor) by phospho-specific flow cytometry. Here, blood samples from n = 40 kidney transplant recipients (treated with either TAC-based or belatacept (BELA)-based immunosuppressive drug therapy) were monitored before and throughout the first year after transplantation. After transplantation and in unstimulated samples, p-p38MAPK and p-Akt were inhibited in CD8⁺ T cells and p-ERK in CD4⁺ T cells but only in patients who received TAC-based therapy. After activation with PMA/ionomycin, p-p38MAPK and p-AKT were significantly inhibited in CD4⁺ and CD8⁺ T cells when TAC was given, compared to pre-transplantation. Eleven BELA-treated patients had a biopsy-proven acute rejection, which was associated with higher p-ERK levels in both CD4⁺ and CD8⁺ T cells compared to patients without rejection. In conclusion, phospho-specific flow cytometry is a promising tool to pharmacodynamically monitor TAC-based therapy. In contrast to TAC-based therapy, BELA-based immunosuppression does not inhibit key T cell activation pathways which may contribute to the high rejection incidence among BELA-treated transplant recipients.

Pharmacokinetic considerations related to therapeutic drug monitoring of tacrolimus in kidney transplant patients

INTRODUCTION

Tacrolimus (Tac) is the cornerstone of immunosuppressive therapy after solid organ transplantation and will probably remain so. Excluding belatacept, no new immunosuppressive drugs were registered for the prevention of acute rejection during the last decade. For several immunosuppressive drugs, clinical development halted because they weren't sufficiently effective or more toxic. Areas covered: Current methods of monitoring Tac treatment, focusing on traditional therapeutic drug monitoring (TDM), controversies surrounding TDM, novel matrices, pharmacogenetic and pharmacodynamic monitoring are discussed. Expert opinion: Due to a narrow therapeutic index and large interpatient pharmacokinetic variability, TDM has been implemented for individualization of Tac dose to maintain drug efficacy and minimize the consequences of overexposure. The relationship between predose concentrations and the occurrence of rejection or toxicity is controversial. Acute cellular rejection also occurs when the Tac concentration is within the target range, suggesting that Tac whole blood concentrations don't necessarily correlate with pharmacological effect. Intracellular Tac, the unbound fraction of Tac or pharmacodynamic monitoring could be better biomarkers/tools for adequate Tac exposure - research into this has been promising. Traditional TDM, perhaps following pre-emptive genotyping for Tac-metabolizing enzymes, must suffice for a few years before these strategies can be implemented in clinical practice.

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.

Targeting the Monocyte-Macrophage Lineage in Solid Organ Transplantation

There is an unmet clinical need for immunotherapeutic strategies that specifically target the active immune cells participating in the process of rejection after solid organ transplantation. The monocyte–macrophage cell lineage is increasingly recognized as a major player in acute and chronic allograft immunopathology. The dominant presence of cells of this lineage in rejecting allograft tissue is associated with worse graft function and survival. Monocytes and macrophages contribute to alloimmunity via diverse pathways: antigen processing and presentation, costimulation, pro-inflammatory cytokine production, and tissue repair. Cross talk with other recipient immune competent cells and donor endothelial cells leads to amplification of inflammation and a cytolytic response in the graft. Surprisingly, little is known about therapeutic manipulation of the function of cells of the monocyte–macrophage lineage in transplantation by immunosuppressive agents. Although not primarily designed to target monocyte–macrophage lineage cells, multiple categories of currently prescribed immunosuppressive drugs, such as mycophenolate mofetil, mammalian target of rapamycin inhibitors, and calcineurin inhibitors, do have limited inhibitory effects. These effects include diminishing the degree of cytokine production, thereby blocking costimulation and inhibiting the migration of monocytes to the site of rejection. Outside the field of transplantation, some clinical studies have shown that the monoclonal antibodies canakinumab, tocilizumab, and infliximab are effective in inhibiting monocyte functions. Indirect effects have also been shown for simvastatin, a lipid lowering drug, and bromodomain and extra-terminal motif inhibitors that reduce the cytokine production by monocytes–macrophages in patients with diabetes mellitus and rheumatoid arthritis. To date, detailed knowledge concerning the origin, the developmental requirements, and functions of diverse specialized monocyte–macrophage subsets justifies research for therapeutic manipulation. Here, we will discuss the effects of currently prescribed immunosuppressive drugs on monocyte/macrophage features and the future challenges.

Pharmacogenetic aspects of the use of tacrolimus in renal transplantation: recent developments and ethnic considerations

INTRODUCTION

Tacrolimus (Tac) is effective in preventing acute rejection but has considerable toxicity and inter-individual variability in pharmacokinetics and pharmacodynamics. Part of this is explained by polymorphisms in genes encoding Tac-metabolizing enzymes and transporters. A better understanding of Tac pharmacokinetics and pharmacodynamics may help to minimize different outcomes amongst transplant recipients by personalizing immunosuppression.

AREAS COVERED

The pharmacogenetic contribution of Tac metabolism will be examined, with a focus on recent discoveries, new developments and ethnic considerations.

EXPERT OPINION

The strongest and most consistent association in pharmacogenetics is between the CYP3A5 genotype and Tac dose requirement, with CYP3A5 expressers having a ~ 40-50% higher dose requirement compared to non-expressers. Two recent randomized-controlled clinical trials using CYP3A5 genotype, however, did not show a decrease in acute rejections nor reduced toxicity. CYP3A4*22, CYP3A4*26, and POR*28 are also associated with Tac dose requirements and may be included to provide the expected improvement of Tac therapy. Studies focusing on the intracellular drug concentrations and on calcineurin inhibitor-induced nephrotoxicity also seem promising. For all studies, however, the ethnic prevalence of genotypes should be taken into account, as this may significantly impact the effect of pre-emptive genotyping.

Down-Regulation of Surface CD28 under Belatacept Treatment: An Escape Mechanism for Antigen-Reactive T-Cells

Background

The co-stimulatory inhibitor of the CD28-CD80/86-pathway, belatacept, allows calcineurin-inhibitor-free immunosuppression in kidney transplantation. However, aggressive T-cell mediated allogeneic responses have been observed in belatacept-treated patients, which could be explained by effector-memory T-cells that lack membrane expression of CD28, i.e. CD28-negative (CD28^NULL) T-cells. CD28-positive (CD28^POS) T-cells that down regulate their surface CD28 after allogeneic stimulation could also pose a threat against the renal graft. The aim of this study was to investigate this potential escape mechanism for CD28^POS T-cells under belatacept treatment.

Materials & Methods

PBMCs, isolated T-cell memory subsets and isolated CD28^POS T-cells were obtained from end-stage renal disease (ESRD) patients and co-cultured with allo-antigen in the presence of belatacept to mimic allogeneic reactions in kidney-transplant patients under belatacept treatment. As a control, IgG was used in the absence of belatacept.

Results

Despite high in vitro belatacept concentrations, a residual T-cell growth of ±30% was observed compared to the IgG control after allogeneic stimulation. Of the alloreactive T-cells, the majority expressed an effector-memory phenotype. This predominance for effector-memory T-cells within the proliferated cells was even larger when a higher dose of belatacept was added. Contrary to isolated naïve and central-memory T cells, isolated effector-memory T cells could not be inhibited by belatacept in differentiation or allogeneic IFNγ production. The proportion of CD28-positive T cells was lower within the proliferated T cell population, but was still substantial. A fair number of the isolated initially CD28^POS T-cells differentiated into CD28^NULL T-cells, which made them not targetable by belatacept. These induced CD28^NULL T-cells were not anergic as they produced high amounts of IFNγ upon allogeneic stimulation. The majority of the proliferated isolated originally CD28^POS T-cells, however, still expressed CD28 and also expressed IFNγ.

Conclusion

This study provides evidence that, apart from CD28^NULL T-cells, also CD28^POS, mostly effector-memory T-cells can mediate allogeneic responses despite belatacept treatment.