CD57(+) CD4 T Cells Underlie Belatacept-Resistant Allograft Rejection

Antibody-Suppressor CXCR5+CD8+ T Cells Are More Potent Regulators of Humoral Alloimmunity after Kidney Transplant in Mice Compared to CD4+ Regulatory T Cells

Adoptive cell therapy (ACT), especially with CD4+ regulatory T cells (CD4+ Tregs), is an emerging therapeutic strategy to minimize immunosuppression and promote long-term allograft acceptance, although much research remains to realize its potential. In this study, we investigated the potency of novel Ab-suppressor CXCR5+CD8+ T cells (CD8+ TAb-supp) in comparison with conventional CD25highFoxp3+CD4+ Tregs for suppression of humoral alloimmunity in a murine kidney transplant (KTx) model of Ab-mediated rejection (AMR). We examined quantity of peripheral blood, splenic and graft-infiltrating CD8+ TAb-supp, and CD4+ Tregs in KTx recipients and found that high alloantibody-producing CCR5 knockout KTx recipients have significantly fewer post-transplant peripheral blood and splenic CD8+ TAb-supp, as well as fewer splenic and graft-infiltrating CD4+ Tregs compared with wild-type KTx recipients. ACT with alloprimed CXCR5+CD8+ T cells reduced alloantibody titer, splenic alloprimed germinal center (GC) B cell quantity, and improved AMR histology in CCR5 knockout KTx recipients. ACT with alloprimed CD4+ Treg cells improved AMR histology without significantly inhibiting alloantibody production or the quantity of splenic alloprimed GC B cells. Studies with TCR transgenic mice confirmed Ag specificity of CD8+ TAb-supp-mediated effector function. In wild-type recipients, CD8 depletion significantly increased alloantibody titer, GC B cells, and severity of AMR pathology compared with isotype-treated controls. Anti-CD25 mAb treatment also resulted in increased but less pronounced effect on alloantibody titer, quantity of GC B cells, and AMR pathology than CD8 depletion. To our knowledge, this is the first report that CD8+ TAb-supp cells are more potent regulators of humoral alloimmunity than CD4+ Treg cells.

Cellular Immunobiology and Molecular Mechanisms in Alloimmunity-Pathways of Immunosuppression

Current maintenance immunosuppression commonly comprises a synergistic combination of tacrolimus as calcineurin inhibitor (CNI), mycophenolic acid, and glucocorticoids. Therapy is often individualized by steroid withdrawal or addition of belatacept or inhibitors of the mechanistic target of rapamycin. This review provides a comprehensive overview of their mode of action, focusing on the cellular immune system. The main pharmacological action of CNIs is suppression of the interleukin-2 pathway that leads to inhibition of T cell activation. Mycophenolic acid inhibits the purine pathway and subsequently diminishes T and B cell proliferation but also exerts a variety of effects on almost all immune cells, including inhibition of plasma cell activity. Glucocorticoids exert complex regulation via genomic and nongenomic mechanisms, acting mainly by downregulating proinflammatory cytokine signatures and cell signaling. Belatacept is potent in inhibiting B/T cell interaction, preventing formation of antibodies; however, it lacks the potency of CNIs in preventing T cell-mediated rejections. Mechanistic target of rapamycin inhibitors have strong antiproliferative activity on all cell types interfering with multiple metabolic pathways, partly explaining poor tolerability, whereas their superior effector T cell function might explain their benefits in the case of viral infections. Over the past decades, clinical and experimental studies provided a good overview on the underlying mechanisms of immunosuppressants. However, more data are needed to delineate the interaction between innate and adaptive immunity to better achieve tolerance and control of rejection. A better and more comprehensive understanding of the mechanistic reasons for failure of immunosuppressants, including individual risk/benefit assessments, may permit improved patient stratification.

The Entangled World of Memory T Cells and Implications in Transplantation

Memory T cells that are specific for alloantigen can arise from a variety of stimuli, ranging from direct allogeneic sensitization from prior transplantation, blood transfusion, or pregnancy to the elicitation of pathogen-specific T cells that are cross-reactive with alloantigen. Regardless of the mechanism by which they arise, alloreactive memory T cells possess key metabolic, phenotypic, and functional properties that render them distinct from naive T cells. These properties affect the immune response to transplantation in 2 important ways: first, they can alter the speed, location, and effector mechanisms with which alloreactive T cells mediate allograft rejection, and second, they can alter T-cell susceptibility to immunosuppression. In this review, we discuss recent developments in understanding these properties of memory T cells and their implications for transplantation.

Costimulatory Blockade and Solid Organ Transplantation: The Past, Present, and Future

Belatacept is the first costimulatory blockade agent clinically approved for transplant immunosuppression. Although more than 10 years of study have demonstrated that belatacept offers superior long-term renal allograft and patient survival compared to conventional calcineurin inhibitor (CNI)-based immunosuppression regimens, the clinical adoption of belatacept has continued to lag because of concerns of an early risk of acute cellular rejection (ACR) and various logistical barriers to its administration. In this review, the history of the clinical development of belatacept is examined, along with the findings of the seminal BENEFIT and BENEFIT-EXT trials culminating in the clinical approval of belatacept. Recent efforts to incorporate belatacept into novel CNI-free immunosuppression regimens are reviewed, as well as the experience of the Emory Transplant Center in using a tapered course of low-dose tacrolimus in belatacept-treated renal allograft patients to garner the long-term outcome benefits of belatacept without the short-term increased risks of ACR. Potential avenues to increase the clinical adoption of belatacept in the future are explored, including surmounting the logistical barriers of belatacept administration through subcutaneous administration or more infrequent belatacept dosing. In addition, belatacept conversion strategies and potential expanded clinical indications of belatacept are discussed for pediatric transplant recipients, extrarenal transplant recipients, treatment of antibody-mediated rejection (AMR), and in patients with failed renal allografts. Finally, we discuss the novel immunosuppressive drugs currently in the development pipeline that may aid in the expansion of costimulation blockade utilization.

Siplizumab combination therapy with belatacept or abatacept broadly inhibits human T cell alloreactivity in vitro

Combined antigen-specific T cell receptor stimulation and costimulation are needed for complete T cell activation. Belatacept and abatacept are nondepleting fusion proteins blocking CD28/B7 costimulation, whereas siplizumab is a depleting antiCD2 immunoglobulin G1 monoclonal antibody targeting CD2/CD58 costimulation. Herein, the effect of siplizumab combination therapy with abatacept or belatacept on T cell alloreactivity in mixed lymphocyte reactions was investigated. In contrast to monotherapy, the combination of siplizumab with belatacept or abatacept induced near-complete suppression of T cell proliferation and increased the potency of siplizumab-mediated T cell inhibition. Furthermore, dual targeting of CD2 and CD28 costimulation enhanced the selective depletion of memory T cells compared with monotherapy. Although siplizumab monotherapy leads to significant regulatory T cell enrichment, high doses of cytotoxic T-lymphocyte-associated antigen 4 and a human IgG1 Fc fragment in the combination therapy reduced this effect. These results support the clinical evaluation of dual costimulation blockade, combining siplizumab with abatacept or belatacept, for the prophylaxis of organ transplant rejection and improvement of long-term outcomes following transplantation. Ongoing investigative research will elucidate when other forms of siplizumab-based dual costimulatory blockade may be able to induce similarly strong inhibition of T cell activation although still allowing for enrichment of regulatory T cells.

Biomarkers of biological aging in recipients of solid organ transplantation and clinical outcomes: A scoping review

INTRODUCTION

Biological aging is the accumulation of cellular and molecular damage within an individual over time. The biological age of a donor organ is known to influence clinical outcomes of solid organ transplantation, including delayed graft function and frequency of rejection episodes. While much research has focused on the biological age of donor organs, the recipient's biological age may also influence transplantation outcomes. The aim of this scoping review was to identify and provide an overview of the existing evidence regarding biological aging in solid organ transplant recipients and the impact on patient outcomes post-transplant.

METHODS

Literature searches were carried out on PubMed, Web of Science, Google Scholar, Embase and TRIP using the phrases 'solid organ transplant', 'cell senescence', 'cell aging' and 'outcomes', using boolean 'and/or' phrases and MeSH terms. Duplicates were removed and abstracts were reviewed by two independent reviewers. Full papers were then screened for inclusion by two reviewers. Data extraction was carried out using a standardised proforma agreed on prior to starting.

RESULTS

32 studies, including data on a total of 7760 patients, were identified for inclusion in this review; 23 relating to kidney transplant recipients, three to liver transplant, five to lung transplant and one to heart transplantation. A wide range of biomarkers of biological aging have been assessed in kidney transplant recipients, whereas studies of liver, lung and heart transplant have predominantly assessed recipient telomere length. The most robust associations with clinical outcomes are observed in kidney transplant recipients, possibly influenced by the larger number of studies and the use of a wider range of biomarkers of biological aging. In kidney transplant recipients reduced thymic function and accumulation of terminally differentiated T cell populations was associated with reduced risk of acute rejection but increased risk of infection and mortality.

CONCLUSION

Studies to date on biological aging in transplant recipients have been heavily biased to kidney transplant recipients. The results from these studies suggest recipient biological age can influence clinical outcomes and future research is needed to prioritise robust biomarkers of biological aging in transplant recipients.

mTOR Inhibition Impairs the Activation and Function of Belatacept-Resistant CD4+CD57+ T Cells In Vivo and In Vitro

Calcineurin inhibitors have improved graft survival in solid-organ transplantation but their use is limited by toxicity, requiring a switch to another immunosuppressor in some cases. Belatacept is one option that has been shown to improve graft and patient survival despite being associated with a higher risk of acute cellular rejection. This risk of acute cellular rejection is correlated with the presence of belatacept-resistant T cells. We performed a transcriptomic analysis of in vitro-activated cells to identify pathways affected by belatacept in belatacept-sensitive cells (CD4⁺CD57^-) but not in belatacept-resistant CD4⁺CD57⁺ T cells. mTOR was significantly downregulated in belatacept-sensitive but not belatacept-resistant T cells. The inhibition of mTOR strongly decreases the activation and cytotoxicity of CD4⁺CD57⁺ cells. In humans, the use of a combination of mTOR inhibitor and belatacept prevents graft rejection and decreases the expression of activation markers on CD4 and CD8 T cells. mTOR inhibition decreases the functioning of belatacept-resistant CD4⁺CD57⁺ T cells in vitro and in vivo. It could potentially be used in association with belatacept to prevent acute cellular rejection in cases of calcineurin intolerance.

Systems prediction of chronic lung allograft dysfunction: Results and perspectives from the Cohort of Lung Transplantation and Systems prediction of Chronic Lung Allograft Dysfunction cohorts

Background

Chronic lung allograft dysfunction (CLAD) is the leading cause of poor long-term survival after lung transplantation (LT). Systems prediction of Chronic Lung Allograft Dysfunction (SysCLAD) aimed to predict CLAD.

Methods

To predict CLAD, we investigated the clinicome of patients with LT; the exposome through assessment of airway microbiota in bronchoalveolar lavage cells and air pollution studies; the immunome with works on activation of dendritic cells, the role of T cells to promote the secretion of matrix metalloproteinase-9, and subpopulations of T and B cells; genome polymorphisms; blood transcriptome; plasma proteome studies and assessment of MSK1 expression.

Results

Clinicome: the best multivariate logistic regression analysis model for early-onset CLAD in 422 LT eligible patients generated a ROC curve with an area under the curve of 0.77. Exposome: chronic exposure to air pollutants appears deleterious on lung function levels in LT recipients (LTRs), might be modified by macrolides, and increases mortality. Our findings established a link between the lung microbial ecosystem, human lung function, and clinical stability post-transplant. Immunome: a decreased expression of CLEC1A in human lung transplants is predictive of the development of chronic rejection and associated with a higher level of interleukin 17A; Immune cells support airway remodeling through the production of plasma MMP-9 levels, a potential predictive biomarker of CLAD. Blood CD9-expressing B cells appear to favor the maintenance of long-term stable graft function and are a potential new predictive biomarker of BOS-free survival. An early increase of blood CD4 + CD57 + ILT2+ T cells after LT may be associated with CLAD onset. Genome: Donor Club cell secretory protein G38A polymorphism is associated with a decreased risk of severe primary graft dysfunction after LT. Transcriptome: blood POU class 2 associating factor 1, T-cell leukemia/lymphoma domain, and B cell lymphocytes, were validated as predictive biomarkers of CLAD phenotypes more than 6 months before diagnosis. Proteome: blood A2MG is an independent predictor of CLAD, and MSK1 kinase overexpression is either a marker or a potential therapeutic target in CLAD.

Conclusion

Systems prediction of Chronic Lung Allograft Dysfunction generated multiple fingerprints that enabled the development of predictors of CLAD. These results open the way to the integration of these fingerprints into a predictive handprint.

TIGIT agonism alleviates costimulation blockade-resistant rejection in a regulatory T cell-dependent manner

Belatacept-based immunosuppression in kidney transplantation confers fewer off-target toxicities than calcineurin inhibitors but comes at a cost of increased incidence and severity of acute rejection, potentially due to its deleterious effect on both the number and function of Foxp3+ regulatory T cells (Tregs). TIGIT is a CD28 family coinhibitory receptor expressed on several subsets of immune cells including Tregs. We hypothesized that coinhibition through TIGIT signaling could function to ameliorate costimulation blockade-resistant rejection. The results demonstrate that treatment with an agonistic anti-TIGIT antibody, when combined with costimulation blockade by CTLA-4Ig, can prolong allograft survival in a murine skin graft model compared with CTLA-4Ig alone. Further, this prolongation of graft survival is accompanied by an increase in the frequency and number of graft-infiltrating Tregs and a concomitant reduction in the number of CD8+ T cells in the graft. Through the use of Treg-specific TIGIT conditional knockout animals, we demonstrated that the TIGIT-mediated reduction in the graft-infiltrating CD8+ T cell response is dependent on signaling of TIGIT on Foxp3+ Tregs. Our results highlight both the key functional role of TIGIT on Foxp3+ Tregs under conditions in which CTLA-4 is blocked and the therapeutic potential of TIGIT agonism to optimize costimulation blockade-based immunosuppression.

Treatment of De Novo Renal Transplant Recipients With Calcineurin Inhibitor-free, Belatacept Plus Everolimus-based Immunosuppression

Compared with calcineurin inhibitor-based immunosuppression, belatacept (BELA)-based treatment has been associated with better renal function but higher acute rejection rates. This phase 2 study (NCT02137239) compared the antirejection efficacy of BELA plus everolimus (EVL) with tacrolimus (TAC) plus mycophenolate mofetil (MMF), each following lymphocyte-depleting induction and rapid corticosteroid withdrawal.

Methods

Patients who were de novo renal transplant recipients seropositive for Epstein-Barr virus were randomized to receive BELA+EVL or TAC+MMF maintenance therapy after rabbit antithymocyte globulin induction and up to 7 d of corticosteroids. The primary endpoint was the rate of biopsy-proven acute rejection at month 6.

Results

Because of an unanticipated BELA supply constraint, enrollment was prematurely terminated at 68 patients, of whom 58 were randomized and transplanted (intention-to-treat [ITT] population: n = 26, BELA+EVL; n = 32, TAC+MMF). However, 25 patients received BELA+EVL' and 33 received TAC+MMF (modified ITT population). In the ITT population, the 6-mo biopsy-proven acute rejection rates were 7.7% versus 9.4% in the BELA+EVL versus TAC+MMF group. The corresponding 24-mo biopsy-proven acute rejection rates were 19.2% versus 12.5% in the ITT population and 16.0% versus 15.2% in the mITT population; all events were Banff severity grade ≤IIA and similar between groups. One patient in each group experienced graft loss unrelated to acute rejection. The 24-mo mean unadjusted estimated glomerular filtration rates were 71.8 versus 68.7 mL/min/1.73 m² in the BELA+EVL versus TAC+MMF groups. Posttransplant lymphoproliferative disorder was reported for 1 patient in each group. No deaths or unexpected adverse events were observed.

Conclusions

A steroid-free maintenance regimen of BELA+EVL may be associated with biopsy-proven acute rejection rates comparable to TAC+MMF.

Malnutrition and immune cell subsets in children undergoing kidney transplantation

BACKGROUND

Malnutrition, including obesity and undernutrition, among children is increasing in prevalence and is common among children on renal replacement therapy. The effect of malnutrition on the pre-transplant immune system and how the pediatric immune system responds to the insult of both immunosuppression and allotransplantation is unknown. We examined the relationship of nutritional status with post-transplant outcomes and characterized the peripheral immune cell phenotypes of children from the Immune Development of Pediatric Transplant (IMPACT) study.

METHODS

Ninety-eight patients from the IMPACT study were classified as having obesity, undernutrition, or normal nutrition-based pre-transplant measurements. Incidence of infectious and alloimmune outcomes at 1-year post-transplantation was compared between nutritional groups using Gray's test and Fine-Gray subdistribution hazards model. Event-free survival was estimated by Kaplan-Meier method and compared between groups. Differences in immune cell subsets between nutritional groups over time were determined using generalized estimating equations accounting for the correlation between repeated measurements.

RESULTS

We did not observe that nutritional status was associated with infectious or alloimmune events or event-free survival post-transplant. We demonstrated that children with obesity had distinct T-and B-cell signatures relative to those with undernutrition and normal nutrition, even when controlling for immunosuppression. Children with obesity had a lower frequency of CD8 Tnaive cells 9-month post-transplant (p < .001), a higher frequency of CD4 CD57 + PD1- T cells, and lower frequencies of CD57-PD1+ CD8 and CD57-PD1- CD8 T cells at 12-month transplant (p < .05 for all).

CONCLUSIONS

Children with obesity have distinct immunophenotypes that may influence the tailoring of immunosuppression.

Preservation of Antiviral Immunologic Efficacy Without Alloimmunity After Switch to Belatacept in Calcineurin Inhibitor-Intolerant Patients

Introduction

Belatacept has shown potential for prevention of rejection after kidney transplantation, given its demonstration of reduced nephrotoxicity in combination with absence of significant incidence of rejection. However, concerns have been raised regarding increased risk of viral infection.

Methods

We set out to explore the impact of the switch to belatacept on alloimmune and antiviral immunity through the study of patients switched from calcineurin inhibitor (CNI) to belatacept within 3 months of kidney transplantation compared with a matched cohort of control patients on a CNI-based regimen.

Results

After the switch to belatacept, immune phenotyping demonstrated a decrease in naive and an increase in terminally differentiated effector memory (TMRA) T cells, with no significant difference compared with control patients. Donor-specific immune response, measured by intracellular cytokine staining (ICS), did not change significantly either by single or double cytokine secretion, but it was associated with the appearance of donor-specific antibody (DSA) in the control but not the belatacept cohort (P = 0.039 for naive and P = 0.002 for TMRA subtypes). Increased incidence of de novo DSA development was observed in the control group (P = 0.035). Virus-specific immune response, as measured by ICS in response to cytomegalovirus (CMV) or Epstein-Barr virus (EBV), was similar in both groups and stable over time.

Conclusion

We found that belatacept use was associated with an absence of alloreactivity without impact on immune phenotype, while preserving the antiviral immune response, for patients switched from a CNI-based regimen. In parallel, the antiviral immune response against CMV and EBV was preserved after the belatacept switch (clinicaltrials.gov: NCT01953120).

Targeting inflammation and immune activation to improve CTLA4-Ig-based modulation of transplant rejection

For the last few decades, Calcineurin inhibitors (CNI)-based therapy has been the pillar of immunosuppression for prevention of organ transplant rejection. However, despite exerting effective control of acute rejection in the first year post-transplant, prolonged CNI use is associated with significant side effects and is not well suited for long term allograft survival. The implementation of Costimulation Blockade (CoB) therapies, based on the interruption of T cell costimulatory signals as strategy to control allo-responses, has proven potential for better management of transplant recipients compared to CNI-based therapies. The use of the biologic cytotoxic T-lymphocyte associated protein 4 (CTLA4)-Ig is the most successful approach to date in this arena. Following evaluation of the BENEFIT trials, Belatacept, a high-affinity version of CTLA4-Ig, has been FDA approved for use in kidney transplant recipients. Despite its benefits, the use of CTLA4-Ig as a monotherapy has proved to be insufficient to induce long-term allograft acceptance in several settings. Multiple studies have demonstrated that events that induce an acute inflammatory response with the consequent release of proinflammatory cytokines, and an abundance of allograft-reactive memory cells in the recipient, can prevent the induction of or break established immunomodulation induced with CoB regimens. This review highlights advances in our understanding of the factors and mechanisms that limit CoB regimens efficacy. We also discuss recent successes in experimentally designing complementary therapies that favor CTLA4-Ig effect, affording a better control of transplant rejection and supporting their clinical applicability.

Longitudinal evaluation of the impact of immunosuppressive regimen on immune responses to COVID-19 vaccination in kidney transplant recipients

Immunocompromised patients have a high risk of death from SARS-CoV-2 infection. Vaccination with an mRNA vaccine may protect these patients against severe COVID-19. Several studies have evaluated the impact of immune-suppressive drug regimens on cellular and humoral responses to SARS-CoV-2 variants of concern in this context. We performed a prospective longitudinal study assessing specific humoral (binding and neutralizing antibodies against spike (S) and T-lymphocyte (cytokine secretion and polyfunctionality) immune responses to anti-COVID-19 vaccination with at least two doses of BNT162b2 mRNA vaccine in stable kidney transplant recipients (KTR) on calcineurin inhibitor (CNI)- or belatacept-based treatment regimens. Fifty-two KTR−31 receiving CNI and 21 receiving belatacept—were enrolled in this study. After two doses of vaccine, 46.9% of patients developed anti-S IgG. Anti-spike IgG antibodies were produced in only 21.4% of the patients in the belatacept group, vs. 83.3% of those in the CNI group. The Beta and Delta variants and, more importantly, the Omicron variant, were less well neutralized than the Wuhan strain. T-cell functions were also much weaker in the belatacept group than in the CNI group. Renal transplant patients have an impaired humoral response to BNT162b2 vaccination. Belatacept-based regimens severely weaken both humoral and cellular vaccine responses. Clinically, careful evaluations of at least binding IgG responses, and prophylactic or post-exposure strategies are strongly recommended for transplant recipients on belatacept-based regimens.

Harnessing the B Cell Response in Kidney Transplantation - Current State and Future Directions

Despite dramatic improvement in kidney transplantation outcomes over the last decades due to advent of modern immunosuppressive agents, long-term outcomes remain poor. Antibody-mediated rejection (ABMR), a B cell driven process, accounts for the majority of chronic graft failures. There are currently no FDA-approved regimens for ABMR; however, several clinical trials are currently on-going. In this review, we present current mechanisms of B cell response in kidney transplantation, the clinical impact of sensitization and ABMR, the B cell response under current immunosuppressive regimens, and ongoing clinical trials for ABMR and desensitization treatment.

IFI16-STING-NF-κB signaling controls exogenous mitochondrion-induced endothelial activation

Mitochondria released from injured cells activate endothelial cells (ECs), fostering inflammatory processes, including allograft rejection. The stimulator of interferon genes (STING) senses endogenous mitochondrial DNA, triggering innate immune activation via NF-κB signaling. Here, we show that exogenous mitochondria exposure induces EC STING-NF-κB activation, promoting EC/effector memory T cell adhesion, which is abrogated by NF-κB and STING inhibitors. STING activation in mitochondrion-activated ECs is independent of canonical cGMP-AMP synthetase sensing/signaling, but rather is mediated by interferon gamma-inducible factor 16 (IFI16) and can be inhibited by IFI16 inhibition. Internalized mitochondria undergo mitofusion and STING-dependent mitophagy, leading to selective sequestration of internalized mitochondria. The exposure of donor hearts to exogenous mitochondria activates murine heart ECs in vivo. Collectively, our results suggest that IFI16-STING-NF-κB signaling regulates exogenous mitochondrion-induced EC activation and mitophagy, and exogenous mitochondria foster T cell-mediated CoBRR. These data suggest a novel, donor-directed, therapeutic approach toward mitigating perioperative allograft immunogenicity.

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.

Modulation of Xenogeneic T-cell Proliferation by B7 and mTOR Blockade of T Cells and Porcine Endothelial Cells

BACKGROUND

Activation of porcine endothelial cells (PECs) is the mechanistic centerpiece of xenograft rejection. This study sought to characterize the immuno-phenotype of human T cells in response to PECs and to explore the immuno-modulation of B7 and mammalian target of rapamycin blockade of T cells and/or PECs during xeno-responses.

METHODS

Rapid memory T-cell (TM) responses to PECs were assessed by an intracellular cytokine staining. T-cell proliferation to PEC with or without belatacept or rapamycin was evaluated by a mixed lymphocyte-endothelial cell reaction (MLER). Additionally, rapamycin-pretreated PECs were used in MLER. Cell phenotypes were analyzed by flow cytometry.

RESULTS

Tumor necrosis factor-α/interferon-γ producers were detected in CD8+ cells stimulated by human endothelium but not PECs. MLER showed proliferation of CD4+ and CD8+ cells with predominantly memory subsets. Purified memory and naive cells proliferated following PEC stimulation with an increased frequency of TM in PEC-stimulated naive cells. Proliferating cells upregulated programmed cell death-1 (PD-1) and CD2 expression. Belatacept partially inhibited T-cell proliferation with reduced CD2 expression and frequency of the CD8+CD2highCD28- subset. Rapamycin dramatically inhibited PEC-induced T-cell proliferation, and rapamycin-preconditioned PECs failed to induce T-cell proliferation. PD-1 blockade did not restore T-cell proliferation to rapamycin-preconditioned PECs.

CONCLUSIONS

Humans lack rapid TM-mediated responses to PECs but induce T-cell proliferative responses characterized largely as TM with increasing CD2 and PD-1 expression. B7-CD28 and mammalian target of rapamycin blockade of T cells exhibit dramatic inhibitory effects in altering xeno-proliferating cells. Rapamycin alters PEC xeno-immunogenicity leading to inhibition of xeno-specific T-cell proliferation independent of PD-1-PD ligand interaction.

The proliferation of belatacept-resistant T cells requires early IFNα pathway activation

Belatacept was developed to replace calcineurin inhibitors in kidney transplantation. Its use is associated with better kidney transplant function, a lower incidence of anti-donor antibodies and higher graft survival. However, it is also associated with a higher risk of cellular rejection. We studied the activation and proliferation mechanisms of belatacept-resistant T lymphocytes (TLs), to identify new pathways for control. We performed a transcriptomic analysis on CD4⁺ CD57⁺ PD1^- memory TLs, which are responsible for a higher incidence of graft rejection, after allogeneic stimulation with activated dendritic cells (aDCs) in the presence or absence of belatacept. After six hours of contact with aDCs, the (CD4⁺ CD57⁺ PD1^- ) (CD4⁺ CD57⁺ PD1⁺ ) and (CD4⁺ CD57^- ) lymphocytes had different transcriptional profiles with or without belatacept. In the CD4⁺ CD57⁺ PD1^- population, the IFNα-dependent activation pathway was positively overrepresented, and IRF7 transcript levels were high. IRF7 was associated with IFNα/β and IL-6 regulation. The inhibition of both these cytokines in a context of belatacept treatment inhibited the proliferation of CD4⁺ CD57⁺ PD1^- T cells. Our results show that IRF7 is rapidly upregulated in belatacept-resistant CD4⁺ CD57⁺ PD1^- TLs. The inhibition of type I IFN or IL-6 in association with belatacept treatment reduces the proliferation of belatacept-resistant TLs, paving the way for new treatments for use in organ transplantation.

Single-Cell-Based High-Throughput Ig and TCR Repertoire Sequencing Analysis in Rhesus Macaques

Recent advancements in microfluidics and high-throughput sequencing technologies have enabled recovery of paired H and L chains of Igs and VDJ and VJ chains of TCRs from thousands of single cells simultaneously in humans and mice. Despite rhesus macaques being one of the most well-studied model organisms for the human adaptive immune response, high-throughput single-cell immune repertoire sequencing assays are not yet available due to the complexity of these polyclonal receptors. We used custom primers that capture all known rhesus macaque Ig and TCR isotypes and chains that are fully compatible with a commercial solution for single-cell immune repertoire profiling. Using these rhesus-specific assays, we sequenced Ig and TCR repertoires in >60,000 cells from cryopreserved rhesus PBMCs, splenocytes, and FACS-sorted B and T cells. We were able to recover every Ig isotype and TCR chain, measure clonal expansion in proliferating T cells, and pair Ig and TCR repertoires with gene expression profiles of the same single cells. Our results establish the ability to perform high-throughput immune repertoire analysis in rhesus macaques at the single-cell level.

TIGIT regulates apoptosis of risky memory T cell subsets implicated in belatacept-resistant rejection

Belatacept confers increased patient and graft survival in renal transplant recipients relative to calcineurin inhibitors, but is associated with an increased rate of acute rejection. Recent immunophenotypic studies comparing pretransplant T cell phenotypes of patients who reject versus those who remain stable on belatacept identified three potential "risky" memory T cell subsets that potentially underlie belatacept-resistant rejection: CD4⁺ CD28⁺ T_EM , CD8⁺ CD28^null , and CD4⁺ CD57⁺ PD1^- subsets. Here, we compared key phenotypic and functional aspects of these human memory T cell subsets, with the goal of identifying additional potential targets to modulate them. Results demonstrate that TIGIT, an increasingly well-appreciated immune checkpoint receptor, was expressed on all three risky memory T cell subsets in vitro and in vivo in the presence of belatacept. Coculture of human memory CD4⁺ and CD8⁺ T cells with an agonistic anti-TIGIT mAb significantly increased apoptotic cell death of all three risky memory T cell subsets. Mechanistically, TIGIT-mediated apoptosis of risky memory T cells was dependent on FOXP3⁺ Treg, suggesting that agonism of the TIGIT pathway increases FOXP3⁺ Treg suppression of human memory T cell populations. Overall, these data suggest that TIGIT agonism could represent a new therapeutic target to inhibit belatacept-resistant rejection during transplantation.

Designing biomaterials for the modulation of allogeneic and autoimmune responses to cellular implants in Type 1 Diabetes

The effective suppression of adaptive immune responses is essential for the success of allogeneic cell therapies. In islet transplantation for Type 1 Diabetes, pre-existing autoimmunity provides an additional hurdle, as memory autoimmune T cells mediate both an autoantigen-specific attack on the donor beta cells and an alloantigen-specific attack on the donor graft cells. Immunosuppressive agents used for islet transplantation are generally successful in suppressing alloimmune responses, but dramatically hinder the widespread adoption of this therapeutic approach and fail to control memory T cell populations, which leaves the graft vulnerable to destruction. In this review, we highlight the capacity of biomaterials to provide local and nuanced instruction to suppress or alter immune pathways activated in response to an allogeneic islet transplant. Biomaterial immunoisolation is a common approach employed to block direct antigen recognition and downstream cell-mediated graft destruction; however, immunoisolation alone still permits shed donor antigens to escape into the host environment, resulting in indirect antigen recognition, immune cell activation, and the creation of a toxic graft site. Designing materials to decrease antigen escape, improve cell viability, and increase material compatibility are all approaches that can decrease the local release of antigen and danger signals into the implant microenvironment. Implant materials can be further enhanced through the local delivery of anti-inflammatory, suppressive, chemotactic, and/or tolerogenic agents, which serve to control both the innate and adaptive immune responses to the implant with a benefit of reduced systemic effects. Lessons learned from understanding how to manipulate allogeneic and autogenic immune responses to pancreatic islets can also be applied to other cell therapies to improve their efficacy and duration. STATEMENT OF SIGNIFICANCE: This review explores key immunologic concepts and critical pathways mediating graft rejection in Type 1 Diabetes, which can instruct the future purposeful design of immunomodulatory biomaterials for cell therapy. A summary of immunological pathways initiated following cellular implantation, as well as current systemic immunomodulatory agents used, is provided. We then outline the potential of biomaterials to modulate these responses. The capacity of polymeric encapsulation to block some powerful rejection pathways is covered. We also highlight the role of cellular health and biocompatibility in mitigating immune responses. Finally, we review the use of bioactive materials to proactively modulate local immune responses, focusing on key concepts of anti-inflammatory, suppressive, and tolerogenic agents.

Age-related effects on thymic output and homeostatic T cell expansion following depletional induction in renal transplant recipients

Thymic output and homeostatic mature cell proliferation both influence T cell repopulation following depletional induction, though the relative contribution of each and their association with recipient age have not been well studied. We investigated the repopulating T cell kinetics in kidney transplant recipients who underwent alemtuzumab induction followed by belatacept/rapamycin-based immunosuppression over 36-month posttransplantation. We focused specifically on the correlation between repopulating T cell subsets and the age of patients. Substantial homeostatic Ki67-expressing T cell proliferation was seen posttransplantation. A repertoire enriched for naïve T (T_Naïve ) cells emerged posttransplantation. Analysis by generalized estimating equation linear models revealed a strong negative linear association between reconstituting T_Naïve cells and advancing age. A relationship between age and persistence of effector memory cells was shown. We assessed thymic output and found an increase in the frequency of recent thymic emigrants (RTEs, CD4⁺ CD31⁺ ) at 12-month posttransplantation. Patients under 30 years of age showed significantly higher levels of CD4⁺ CD31⁺ cells than patients over 55 years of age pre- and posttransplantation. IL-7 and autologous mature dendritic cells (mDCs) induced CD57^- cell proliferation. In contrast, mDCs, but not IL-7, induced CD57⁺ cell proliferation. This study establishes the relationship between age and thymic output during T cell homeostatic repopulation after alemtuzumab induction. Trial Registration: ClinicalTrials.gov - NCT00565773.

Optimal Immunosuppression Strategy in the Sensitized Kidney Transplant Recipient

Patients with previous sensitization events against anti-human leukocyte antigens (HLA) often have circulating anti-HLA antibodies. Following organ transplantation, sensitized patients have higher rates of antibody-mediated rejection (AMR) compared to those who are non-sensitized. More stringent donor matching is required for these patients, which results in a reduced donor pool and increased time on the waitlist. Current approaches for sensitized patients focus on reducing preformed antibodies that preclude transplantation; however, this type of desensitization does not modulate the primed immune response in sensitized patients. Thus, an optimized maintenance immunosuppressive regimen is necessary for highly sensitized patients, which may be distinct from non-sensitized patients. In this review, we will discuss the currently available therapeutic options for induction, maintenance, and adjuvant immunosuppression for sensitized patients.

CD69+ resident memory T cells are associated with graft-versus-host disease in intestinal transplantation

Graft-versus-host disease (GvHD) is a common, morbid complication after intestinal transplantation (ITx) with poorly understood pathophysiology. Resident memory T cells (T_RM ) are a recently described CD69+ memory T cell subset localizing to peripheral tissue. We observed that T effector memory cells (T_EM ) in the blood increase during GvHD and hypothesized that they derive from donor graft CD69+T_RM migrating into host blood and tissue. To probe this hypothesis, graft and blood lymphocytes from 10 ITx patients with overt GvHD and 34 without were longitudinally analyzed using flow cytometry. As hypothesized, CD4+ and CD8+CD69+T_RM were significantly increased in blood and grafts of GvHD patients, alongside higher cytokine and activation marker expression. The majority of CD69+T_RM were donor derived as determined by multiplex immunostaining. Notably, CD8/PD-1 was significantly elevated in blood prior to transplantation in patients who later had GvHD, and percentages of HLA-DR, CD57, PD-1, and naïve T cells differed significantly between GvHD patients who died vs. those who survived. Overall, we demonstrate that (1) there were significant increases in T_EM at the time of GvHD, possibly of donor derivation; (2) donor T_RM in the graft are a possible source; and (3) potential biomarkers for the development and prognosis of GvHD exist.

Optimization of de novo belatacept-based immunosuppression administered to renal transplant recipients

Kidney transplant recipients administered belatacept-based maintenance immunosuppression present with a more favorable metabolic profile, reduced incidence of de novo donor-specific antibodies (DSAs), and improved renal function and long-term patient/graft survival relative to individuals receiving calcineurin inhibitor (CNI)-based immunosuppression. However, the rates and severity of acute rejection (AR) are greater with the approved belatacept-based regimen than with CNI-based immunosuppression. Although these early co-stimulation blockade-resistant rejections are typically steroid sensitive, the higher rate of cellular AR has led many transplant centers to adopt immunosuppressive regimens that differ from the approved label. This article summarizes the available data on these alternative de novo belatacept-based maintenance regimens. Steroid-sparing, belatacept-based immunosuppression (following T cell-depleting induction therapy) has been shown to yield AR rates comparable to those seen with CNI-based regimens. Concomitant treatment with belatacept plus a mammalian target of rapamycin inhibitor (mTORi; sirolimus or everolimus) has yielded AR rates ranging from 0 to 4%. Because the optimal induction agent and number of induction doses; blood levels of mTORi; and dose, duration, and use of corticosteroids have yet to be determined, larger prospective clinical trials are needed to establish the optimal alternative belatacept-based regimen for minimizing early cellular AR occurrence.

CMV Status Drives Distinct Trajectories of CD4+ T Cell Differentiation

Cytomegalovirus (CMV) is one of the most commonly recognized opportunistic pathogens and remains the most influential known parameter in shaping an individual's immune system. As such, T cells induced by CMV infection could have a long-term impact on subsequent immune responses. Accumulating evidence indicates that memory T cells developed during past bacterial and viral infection can cross-react with unrelated pathogens, including transplant antigens, and can alter responses to de novo infections, vaccines, cancers, or rejection. Therefore, careful examination of T cell responses elicited by CMV is warranted to understand their potentially beneficial or harmful roles in future major immune events. Our detailed exploration of the distribution, phenotype, TCR repertoire and transcriptome of CD4+ T cells within CMV seropositive healthy individuals using high-dimensional flow cytometry and single cell multi-omics sequencing reveals that CMV seropositivity has highly significant age-independent effects, leading to a reduction in CD4+ naïve T cells and an expansion of CD4+ effector memory T cells and CD45RA+ effector memory T cells. These induced CD4+ effector memory T cells undergo a specific differentiation trajectory resulting in a subpopulation of CD57+CD27-CD28-CD244+ CD4+ T cells with cytotoxic function and TCR oligoclonality for optimal controlled coexistence with cytomegalovirus. Through gene set enrichment analysis, we found that this subpopulation is similar to virus-specific CD8+ T cells and T cells that mediate acute rejection in patients using tacrolimus and belatacept, a selective costimulation blocker. Together, these data suggest that memory CD4+ T cells induced by cytomegalovirus are formed via a distinct differentiation program to acquire cytotoxic function and can be potentially detrimental to transplant patients adopting costimulation blockade immunosuppressive regimen.

Belatacept in renal transplantation in comparison to tacrolimus and molecular understanding of resistance pattern: Meta-analysis and systematic review

BACKGROUND

The T-cell costimulation blocking agent belatacept has been identified as a possible substitute for calcineurin inhibitors, however, no consensus has been established against its use over the standard care agent Tacrolimus.

AIM

To evaluate the effectiveness of belatacept based maintenance immuno-suppressive regimens in comparison to tacrolimus in renal transplantion.

METHODS

We did extensive search of all the available literature comparing the role of belatacept to tacrolimus in renal transplant recipients by searching the PubMed, Embase, Cochrane, Crossref, Scopus, clinical trials registry on October 5, 2020.

RESULTS

The literature search identified four randomized controlled trials (n = 173 participants) comparing belatacept with tacrolimus. There was no significant difference in estimated renal function at 12 mo [mean difference 4.12 mL/min/1.73 m², confidence interval (CI): -2.18 to 10.42, P = 0.20]. Further, belatacept group was associated with significant increase in biopsy proven acute rejection [relative risk (RR) = 3.27, CI: 0.88 to 12.11, P = 0.08] and worse 12 mo allograft survival (RR = 4.51, CI: 1.23 to 16.58, P = 0.02). However, incidence of new onset diabetes mellitus was lower with belatacept at 12 mo (RR = 0.26, CI: 0.07 to 0.99, P = 0.05).

CONCLUSION

The evidence reviewed in this meta-analysis suggested that belatacept-based maintenance immunosuppression regimens were associated with an increased risk allograft loss in renal transplant recipients with equivalent renal functioning against standard tacrolimus; however, observed significantly reduced new onset diabetes mellitus after transplantation incidence and lower serum low density lipid profile levels in belatacept group. In addition, the adaptation of belatacept in renal transplantation has been forestalled by increased rates of rejection and resistance owing to development of various effector memory T cells through, parallel differentiation and immunological plasticity.

Rejection of intestinal allotransplants is driven by memory T helper type 17 immunity and responds to infliximab

Intestinal transplantation (ITx) can be life-saving for patients with advanced intestinal failure experiencing complications of parenteral nutrition. New surgical techniques and conventional immunosuppression have enabled some success, but outcomes post-ITx remain disappointing. Refractory cellular immune responses, immunosuppression-linked infections, and posttransplant malignancies have precluded widespread ITx application. To shed light on the dynamics of ITx allograft rejection and treatment resistance, peripheral blood samples and intestinal allograft biopsies from 51 ITx patients with severe rejection, alongside 37 stable controls, were analyzed using immunohistochemistry, polychromatic flow cytometry, and reverse transcription-PCR. Our findings inform both immunomonitoring and treatment. In terms of immunomonitoring, we found that while ITx rejection is associated with proinflammatory and activated effector memory T cells in the blood, evidence of treatment efficacy can only be found in the allograft itself, meaning that blood-based monitoring may be insufficient. In terms of treatment, we found that the prominence of intra-graft memory TNF-α and IL-17 double-positive T helper type 17 (Th17) cells is a leading feature of refractory rejection. Anti-TNF-α therapies appear to provide novel and safer treatment strategies for refractory ITx rejection; with responses in 14 of 14 patients. Clinical protocols targeting TNF-α, IL-17, and Th17 warrant further testing.

Functional Characteristics and Phenotypic Plasticity of CD57+PD1- CD4 T Cells and Their Relationship with Transplant Immunosuppression

Costimulation blockade (CoB)-based immunosuppression offers the promise of improved transplantation outcomes with reduced drug toxicity. However, it is hampered by early acute rejections, mediated at least in part by differentiated, CoB-resistant T cells, such as CD57⁺PD1^- CD4 T cells. In this study, we characterize these cells pretransplant, determine their fate posttransplant, and examine their proliferative capacity in vitro in humans. Our studies show that CD57⁺PD1^- CD4 T cells are correlated with increasing age and CMV infection pretransplant, and persist for up to 1 y posttransplant. These cells are replication incompetent alone but proliferated in the presence of unsorted PBMCs in a contact-independent manner. When stimulated, cells sorted by CD57/PD1 status upregulate markers of activation with proliferation. Up to 85% of CD57⁺PD1^- cells change expression of CD57/PD1 with stimulation, typically, upregulating PD1 and downregulating CD57. PD1 upregulation is accentuated in the presence of rapamycin but prevented by tacrolimus. These data support a general theory of CoB-resistant cells as Ag-experienced, costimulation-independent cells and suggest a mechanism for the synergy of belatacept and rapamycin, with increased expression of the activation marker PD1 potentiating exhaustion of CoB-resistant cells.

Memory T Cells in Transplantation: Old Challenges Define New Directions

Immunologic memory is the ability of adaptive immune system to quickly and specifically recognize previously encountered antigens and initiate an effector response. Alloreactive memory cells can mount rapid and robust responses to the transplanted organ resulting in allograft injury. Thus preexisting humoral or cellular memory alloresponses are typically associated with poor graft outcomes in experimental and clinical transplantation. While both B and T lymphocytes exhibit memory responses, this review discusses recent updates on the biology of memory T cells and their relevance to the field of transplantation. Three major areas of focus are the emergence and characterization of tissue resident memory T cells, manipulation of T cell metabolic pathways, and the latest promising approaches to targeting detrimental T cell memory in the settings of organ transplantation.

Kidney transplantation using alemtuzumab, belatacept, and sirolimus: Five-year follow-up

Kidney transplant outcomes are limited by toxicities associated with calcineurin inhibitors and steroids. This trial was conducted to determine whether a costimulation blockade (CoB)-based regimen could achieve acceptable long-term outcomes and graft survival could be maintained solely with CoB. Forty patients underwent alemtuzumab induction followed by belatacept and sirolimus maintenance therapy. Patients were offered weaning to belatacept monotherapy after 1 year and followed for 5 years. Five-year patient and graft survival rates were 100% and 95%, respectively. Graft function remained stable with a mean estimated glomerular filtration rates of 67 ± 21 and 71 ± 19 at 36 and 60 months, respectively. There was no clinical rejection in the first year; subclinical rejection was detected by protocol biopsy in 4 patients. Twelve patients were successfully weaned to belatacept monotherapy. Cytomegalovirus and Epstein-Barr virus reactivations were well controlled, but 9 patients experienced transient BK viremia during the first year. Alemtuzumab produced profound lymphopenia followed by gradual T cell and more rapid B cell reconstitution to a repertoire deviated toward naïve cells with increased regulatory T cells. This regimen effectively prevents allograft rejection without using steroids or calcineurin inhibitors, enriches for naïve cells susceptible to control with CoB, and permits control of rejection with belatacept monotherapy in selected patients.

The impact of belatacept on the phenotypic heterogeneity of renal T cell-mediated alloimmune response: The critical role of maintenance treatment and inflammatory load

Belatacept offers superior long-term outcome relative to calcineurin inhibitor (CNI)-based immunosuppression. However, the higher frequency of early T cell-mediated rejection (TCMR) in belatacept-treated patients hampered the widespread adoption of costimulation blockade. Here, we applied gene expression analysis and whole-slide inflammatory cell quantification to assess the impact of belatacept on intragraft immune signature. We studied formalin-fixed, paraffin-embedded renal biopsies from 92 patients stratified by histopathologic diagnosis (TCMR, borderline changes, or normal) and immunosuppression regimen (belatacept, CNI). An interaction model was built to explore maintenance treatment-dependent expression level changes of immune response-related genes across diagnostic categories of normal, borderline changes, and TCMR. Ninety-one percent of genes overexpressed in TCMR showed significant correlation with whole section inflammatory load. There were 27 genes that had a positive association with belatacept treatment. These were mostly related to myeloid cells and innate immunity. Genes negatively associated with costimulation blockade (n = 14) could be linked to B-cell differentiation and proliferation. We concluded that expression levels of genes characteristic of TCMR are strongly interconnected with quantitative changes of the biopsy inflammatory load. Our results might suggest differential involvement of the innate immune system, and an altered B-cell engagement during TCMR in belatacept-treated patients relative to CNI-treated referents.

Sensitization in transplantation: Assessment of risk (STAR) 2019 Working Group Meeting Report

The purpose of the STAR 2019 Working Group was to build on findings from the initial STAR report to further clarify the expectations, limitations, perceptions, and utility of alloimmune assays that are currently in use or in development for risk assessment in the setting of organ transplantation. The goal was to determine the precision and clinical feasibility/utility of such assays in evaluating both memory and primary alloimmune risks. The process included a critical review of biologically driven, state-of-the-art, clinical diagnostics literature by experts in the field and an open public forum in a face-to-face meeting to promote broader engagement of the American Society of Transplantation and American Society of Histocompatibility and Immunogenetics membership. This report summarizes the literature review and the workshop discussions. Specifically, it highlights (1) available assays to evaluate the attributes of HLA antibodies and their utility both as clinical diagnostics and as research tools to evaluate the effector mechanisms driving rejection; (2) potential assays to assess the presence of alloimmune T and B cell memory; and (3) progress in the development of HLA molecular mismatch computational scores as a potential prognostic biomarker for primary alloimmunity and its application in research trial design.

Modulating the wayward T cell: New horizons with immune checkpoint inhibitor treatments in autoimmunity, transplant, and cancer

The T-cell response is regulated by the balance between costimulatory and coinhibitory signals. Immune checkpoints are essential for efficient T-cell activation, but also for maintaining self-tolerance and protecting tissues from damage caused by the immune system, and for providing protective immunity. Modulating immune checkpoints can serve diametric goals, such that blocking a coinhibitory molecule can unleash anti-cancer immunity whereas stimulating the same molecule can reduce an over-reaction in autoimmune disease. The purpose of this review is to examine the regulation of T-cell costimulation and coinhibition, which is central to the processes underpinning autoimmunity, transplant rejection and immune evasion in cancer. We will focus on the immunomodulation agents that regulate these unwanted over- and under-reactions. The use of such agents has led to control of symptoms and slowing of progression in patients with rheumatoid arthritis, reduced rejection rates in transplant patients, and prolonged survival in patients with cancer. The management of immune checkpoint inhibitor treatment in certain challenging patient populations, including patients with pre-existing autoimmune conditions or transplant patients who develop cancer, as well as the management of immune-related adverse events in patients receiving antitumor therapy, is examined. Finally, the future of immune checkpoint inhibitors, including examples of emerging targets that are currently in development, as well as recent insights gained using new molecular techniques, is discussed. T-cell costimulation and coinhibition play vital roles in these diverse therapeutic areas. Targeting immune checkpoints continues to be a powerful avenue for the development of agents suitable for treating autoimmune diseases and cancers and for improving transplant outcomes. Enhanced collaboration between therapy area specialists to share learnings across disciplines will improve our understanding of the opposing effects of treatments for autoimmune disease/transplant rejection versus cancer on immune checkpoints, which has the potential to lead to improved patient outcomes.

Costimulation Blockade in Vascularized Composite Allotransplantation

Vascular composite allotransplantation (VCA) is a field under research and has emerged as an alternative option for the repair of severe disfiguring defects that result from infections or traumatic amputation in a selected group of patients. VCA is performed in centers with appropriate expertise, experience and adequate resources to effectively manage the complexity and complications of this treatment. Lifelong immunosuppressive therapy, immunosuppression associated complications, and the effects of the host immune response in the graft are major concerns in VCA. VCA is considered a quality of life transplant and the risk-benefit ratio is dissimilar to life saving transplants. Belatacept seems a promising drug that prolongs patient and graft survival in kidney transplantation and it could also be an alternative approach to VCA immunosuppression. In this review, we are summarizing current literature about the role of costimulation blockade, with a focus on belatacept in VCA.

Efficacy and tolerance of immune checkpoint inhibitors in transplant patients with cancer: A systematic review

Solid organ transplant (SOT) is frequently complicated by cancers, which render immunosuppression challenging. Immune checkpoint inhibitors have emerged as treatments for many cancers. Data are lacking regarding efficacy and rejection risk in the SOT population. We conducted a systematic literature review and analyzed 83 cases of immune checkpoint inhibitor use for cancer in SOT. Two thirds of these patients received anti-programmed death ligand 1 therapy, 15.7% received anti-cytotoxic T lymphocyte-associated protein 4 therapy, and 10.8% received a combination. Allograft rejection occurred in 39.8% of patients, leading to end-stage organ failure in 71.0% of cases. Outcomes were similar across organs and immunotherapy regimens. The use of immunosuppressants other than steroids, time since transplant, and prior episodes of rejection were associated with the risk of rejection. The median overall survival of patients was 36 weeks. Most of the deaths were related to cancer progression. In nonkidney recipients, graft rejection was strongly associated with worse survival. At the end of the study, 19.3% of the patients were alive, free from rejection and tumor progression. This study highlights the difficult tradeoff facing oncologists and transplant specialists managing transplant recipients with cancer, and the need for prospective data and novel biomarkers for identifying the patients likely to benefit from immunotherapy in the SOT setting.

Costimulation Blockade in Kidney Transplant Recipients

Costimulation between T cells and antigen-presenting cells is essential for the regulation of an effective alloimmune response and is not targeted with the conventional immunosuppressive therapy after kidney transplantation. Costimulation blockade therapy with biologicals allows precise targeting of the immune response but without non-immune adverse events. Multiple costimulation blockade approaches have been developed that inhibit the alloimmune response in kidney transplant recipients with varying degrees of success. Belatacept, an immunosuppressive drug that selectively targets the CD28-CD80/CD86 pathway, is the only costimulation blockade therapy that is currently approved for kidney transplant recipients. In the last decade, belatacept therapy has been shown to be a promising therapy in subgroups of kidney transplant recipients; however, the widespread use of belatacept has been tempered by an increased risk of acute kidney transplant rejection. The purpose of this review is to provide an overview of the costimulation blockade therapies that are currently in use or being developed for kidney transplant indications.

Challenges of calcineurin inhibitor withdrawal following combined pancreas and kidney transplantation: Results of a prospective, randomized clinical trial

In a phase 2 multicenter open-label randomized trial sponsored by the National Institutes of Health, simultaneous pancreas-kidney (SPK) recipients were randomized to a calcineurin inhibitor (CNI)-based immunosuppressive regimen (tacrolimus) (n = 21), or an investigational arm using low-dose CNI plus costimulation blockade (belatacept) with intended CNI withdrawal (n = 22). Both arms included induction therapy with rabbit ATG, mycophenolate sodium, or mycophenolate mofetil and rapid withdrawal of steroids. Enrollment and CNI withdrawal were stopped after 43/60 planned subjects had been enrolled. At that time, the rate of biopsy-proven acute rejection (BPAR) of the pancreas was low in both groups until CNI was withdrawn, with four of the five pancreas rejections occurring during or after CNI withdrawal. The rate of BPAR of kidney allografts was low in both control (9.5%) and investigational (9.1%) arms. Pancreas graft survival at 52 weeks, defined by insulin independence, was 21 (100%) in the control group and 19 (86%) in the investigational arm. One subject in the investigational arm died with functioning pancreas and kidney grafts. Renal function at week 52 was similar in both arms. Costimulation blockade with belatacept did not provide sufficient immunosuppression to reliably prevent pancreas rejection in SPK transplants undergoing CNI withdrawal.

Th17 cell inhibition in a costimulation blockade-based regimen for vascularized composite allotransplantation using a nonhuman primate model

Vascularized composite allotransplantation (VCA) is challenged by the morbidity of immunosuppression required to prevent rejection. The use of highly specific biologics has not been well explored in VCA. Given that psoriasis is T-cell mediated, as is rejection of skin-containing VCAs, we sought to assess the role of ustekinumab and secukinumab, which are approved to treat psoriasis by inhibiting Th17 cells. We combined these agents with belatacept and steroids in a VCA nonhuman primate model. Group I consisted of belatacept and steroids, group II was belatacept, ustekinumab with steroid taper, and group III was belatacept, secukinumab with steroid taper. Three animals were transplanted in each group. In group I, the mean graft survival time until the first sign of rejection was 10 days whereas in group II and III it was 10.33 and 11 days, respectively. The immunohistochemistry analysis showed that the number of IL-17a⁺ cells and the intensity of IL-17a expression were significantly reduced in both dermis and hypodermis parts in groups II and III when compared to group I (P < 0.01). Ustekinumab and secukinumab led to less T-cell infiltration and IL-17a expression in the allograft but provided no benefit to belatacept and steroids in VCA survival.

mTOR Inhibitor Therapy Diminishes Circulating CD8+ CD28- Effector Memory T Cells and Improves Allograft Inflammation in Belatacept-refractory Renal Allograft Rejection

BACKGROUND

Renal allograft rejection is more frequent under belatacept-based, compared with tacrolimus-based, immunosuppression. We studied kidney transplant recipients experiencing rejection under belatacept-based early corticosteroid withdrawal following T-cell-depleting induction in a recent randomized trial (Belatacept-based Early Steroid Withdrawal Trial, clinicaltrials.gov NCT01729494) to determine mechanisms of rejection and treatment.

METHODS

Peripheral mononuclear cells, serum creatinine levels, and renal biopsies were collected from 8 patients undergoing belatacept-refractory rejection (BRR). We used flow cytometry, histology, and immunofluorescence to characterize CD8 effector memory T cell (TEM) populations in the periphery and graft before and after mammalian target of rapamycin (mTOR) inhibition.

RESULTS

Here, we found that patients with BRR did not respond to standard antirejection therapy and had a substantial increase in alloreactive CD8 T cells with a CD28/DR/CD38/CD45RO TEM. These cells had increased activation of the mTOR pathway, as assessed by phosphorylated ribosomal protein S6 expression. Notably, everolimus (an mTOR inhibitor) treatment of patients with BRR halted the in vivo proliferation of TEM cells and their ex vivo alloreactivity and resulted in their significant reduction in the peripheral blood. The frequency of circulating FoxP3 regulatory T cells was not altered. Importantly, everolimus led to rapid resolution of rejection as confirmed by histology.

CONCLUSIONS

Thus, while prior work has shown that concomitant belatacept + mTOR inhibitor therapy is effective for maintenance immunosuppression, our preliminary data suggest that everolimus may provide an available means for effecting "rescue" therapy for rejections occurring under belatacept that are refractory to traditional antirejection therapy with corticosteroids and polyclonal antilymphocyte globulin.

Differential effects of Belatacept on virus-specific memory versus de novo allo-specific T cell responses of kidney transplant recipients and healthy donors

Belatacept, Nulojix®, inhibits the interaction of CD28 on naïve T cells with B7.1/B7.2 (CD80/86) on antigen presenting cells, leading to T cell hyporesponsiveness and anergy and is approved as immunosuppressive drug in kidney transplantation. Due to its specificity for B7.1/2 molecules, side effects are reduced compared to other immunosuppressive drugs like calcineurin- and mTOR-inhibitors. Kidney transplant recipients under Belatacept-based immunosuppression presented with superior renal function and similar graft survival seven years after transplantation compared to cyclosporine treatment. However, de novo Belatacept-based immunosuppression was associated with increased risk of early rejections and viral (EBV) infections in clinical trials, especially in EBV-naïve patients. Since there is no vaccination against EBV infection available, EBV-derived virus like particles (EBV-VLPs) are currently developed as vaccine strategy. Here, we investigated the immunosuppressive effects of Belatacept compared to calcineurin- and mTOR inhibitors on allo- versus virus-specific T cells and the potency of EBV-VLPs to induce virus-specific T cell responses in vitro. Using PBMC of kidney recipients and healthy donors, we could demonstrate selective inhibition of allo-specific de novo T cell responses but not virus-specific memory T cell responses by Belatacept, as measured by IFN-γ production. In contrast, calcineurin inhibitors suppressed IFN-γ production of virus-specific memory CD8⁺ T cells completely. These results experimentally confirm the concept that Belatacept blocks CD28-mediated costimulation in newly primed naïve T cells but does not interfere with memory T cell responses being already independent from CD28-mediated costimulation. Additionally, we could show that EBV-VLPs induce a significant though weak IFN-γ-mediated T cell response in vitro in both kidney recipients and healthy donors. In summary, we demonstrated that immunosuppression of kidney recipients by Belatacept may primarily suppress de novo allo-specific T cell responses sparing virus-specific memory T cells. Moreover, EBV-VLPs could represent a novel strategy for vaccination of immunocompromised renal transplant recipients to prevent EBV reactivation especially under Belatacept-based immunosuppression.

B cell reconstitution following alemtuzumab induction under a belatacept-based maintenance regimen

Lymphocyte depletion has been shown to control costimulation blockade-resistant rejection but, in some settings, to exacerbate antibody-mediated rejection (AMR). We have used alemtuzumab, which depletes T and B cells, combined with belatacept and rapamycin and previously reported control of both costimulation blockade-resistant rejection and AMR. To evaluate this regimen's effect on B cell signatures, we investigated 40 patients undergoing this therapy. B cell counts and phenotypes were interrogated using flow cytometry, and serum was analyzed for total IgG, IgM, and donor-specific alloantibody (DSA). Alemtuzumab induction produced pan-lymphocyte depletion; B cells repopulated faster and more completely than T cells. Reconstituting B cells were predominantly naïve, and memory B cells were significantly reduced (P = .001) post repopulation. Two B cell populations with potential immunomodulatory effects-regulatory (CD38^hi CD24^hi IgM^hi CD20^hi ) and transitional B cells (CD19⁺ CD27^- IgD⁺ CD38^hi )-were enriched posttransplant (P = .001). Total serum IgG decreased from baseline (P = .016) while IgM levels remained stable. Five patients developed DSAs within 36 months posttransplant, but none developed AMR. Baseline IgG levels in these patients were significantly higher than those in patients without DSAs. These findings suggest that belatacept and rapamycin together limit homeostatic B cell activation following B cell depletion and may lessen the risk of AMR. This regimen warrants prospective, comparative study. ClinicalTrials.gov NCT00565773.

Belatacept-based immunosuppression: A calcineurin inhibitor-sparing regimen in heart transplant recipients

Belatacept (BTC) is indicated for prophylaxis of graft rejection in adults receiving a renal transplant (Tx). This retrospective observational study (three centers) included all heart transplant recipients receiving BTC between January 2014 and October 2018. Forty EBV+ patients mean GFR 35 ± 20 mL/min/m² were identified, among whom belatacept was initiated during the first 3 months after transplantation in 12 patients, and later in 28 patients. Several patients were multiorgan transplant recipients. Study outcomes were GFR, safety, and changes in immunosuppressive therapy. The main reason for switching to BTC was to preserve renal function, resulting in discontinuation of CNI and changes in immunosuppressive therapy in 76% of cases. At study closeout, 24/40 patients were still on BTC therapy. GFR was improved (+59%, P = .0002*) within 1 month, particularly in the early group. More episodes of rejection were observed among "late" patients (1 death). Sixteen treatment discontinuations were recorded: GFR recovery (n = 4), DSA no longer detectable (n = 1), compliance issues (n = 3), poor venous access (n = 2), multiple infections (n = 1), 1 death (fungal lung infection), and treatment failure (n = 4). Median follow-up was 24 months. Four patients developed de novo DSA (MFI<1500). BTC is an effective alternative immunosuppressive for postoperative transient kidney failure, stabilizing delayed renal function, with acceptable safety profile under careful monitoring.

T cell reconstitution after lymphocyte depletion features a different pattern of inhibitory receptor expression in ABO- versus HLA-incompatible kidney transplant recipients

Chronic antigen stimulation can lead to immune exhaustion (a state of T cell dysfunction). Several phenotypical signatures of T cell exhaustion have been described in various pathological situations, characterized by aberrant expression of multiple inhibitory receptors (IR). This signature has been barely studied in the context of allogenic organ transplantation. We undertook a cross-sectional analysis of the expression of IR [CD244, CD279, T cell immunoreceptor with immunoglobulin (Ig) and immunoreceptor tyrosine-based inhibition motif (ITIM) domains (TIGIT) and CD57] and their correlation with cytokine-producing functions in T cells reconstituting after lymphocyte depletion in patients transplanted from living donors, with preformed donor-specific antibodies. After ABO incompatible transplantation, T cells progressively acquired a phenotype similar to healthy donors and the expression of several IR marked cells with increased functions, with the exception of TIGIT, which was associated with decreased cytokine production. In stark contrast, T cell reconstitution in patients with anti-human leukocyte antigen (HLA) antibodies was characterized with an increased co-expression of IR by T cells, and specifically by an increased expression of TIGIT. Furthermore, expression of these receptors was no longer directly correlated to cytokine production. These results suggest that T cell alloreactivity in HLA-incompatible kidney transplantation drives an aberrant T cell reconstitution with respect to IR profile, which could have an impact on the transplantation outcome.

Costimulation Blockade in Transplantation

T cells play a pivotal role in orchestrating immune responses directed against a foreign (allogeneic) graft. For T cells to become fully activated, the T-cell receptor (TCR) must interact with the major histocompatibility complex (MHC) plus peptide complex on antigen-presenting cells (APCs), followed by a second "positive" costimulatory signal. In the absence of this second signal, T cells become anergic or undergo deletion. By blocking positive costimulatory signaling, T-cell allo-responses can be aborted, thus preventing graft rejection and promoting long-term allograft survival and possibly tolerance (Alegre ML, Najafian N, Curr Mol Med 6:843-857, 2006; Li XC, Rothstein DM, Sayegh MH, Immunol Rev 229:271-293, 2009). In addition, costimulatory molecules can provide negative "coinhibitory" signals that inhibit T-cell activation and terminate immune responses; strategies to promote these pathways can also lead to graft tolerance (Boenisch O, Sayegh MH, Najafian N, Curr Opin Organ Transplant 13:373-378, 2008). However, T-cell costimulation involves an incredibly complex array of interactions that may act simultaneously or at different times in the immune response and whose relative importance varies depending on the different T-cell subsets and activation status. In transplantation, the presence of foreign alloantigen incites not only destructive T effector cells but also protective regulatory T cells, the balance of which ultimately determines the fate of the allograft (Lechler RI, Garden OA, Turka LA, Nat Rev Immunol 3:147-158, 2003). Since the processes of alloantigen-specific rejection and regulation both require activation of T cells, costimulatory interactions may have opposing or synergistic roles depending on the cell being targeted. Such complexities present both challenges and opportunities in targeting T-cell costimulatory pathways for therapeutic purposes. In this chapter, we summarize our current knowledge of the various costimulatory pathways in transplantation and review the current state and challenges of harnessing these pathways to promote graft tolerance (summarized in Table 10.1).

Secondary lymphoid tissue and costimulation-blockade resistant rejection: A nonhuman primate renal transplant study

Naïve T cell activation requires antigen presentation combined with costimulation through CD28, both of which optimally occur in secondary lymphoid tissues such as lymph nodes and the spleen. Belatacept impairs CD28 costimulation by binding its ligands, CD80 and CD86, and in doing so, impairs de novo alloimmune responses. However, in most patients belatacept is ineffective in preventing allograft rejection when used as a monotherapy, and adjuvant therapy is required for control of costimulation-blockade resistant rejection (CoBRR). In rodent models, impaired access to secondary lymphoid tissues has been demonstrated to reduce alloimmune responses to vascularized allografts. Here we show that surgical maneuvers, lymphatic ligation, and splenectomy, designed to anatomically limit access to secondary lymphoid tissues, control CoBRR and facilitate belatacept monotherapy in a nonhuman primate model of kidney transplantation without adjuvant immunotherapy. We further demonstrate that animals sustained on belatacept monotherapy progressively develop an increasingly naïve T and B cell repertoire, an effect that is accelerated by splenectomy and lost at the time of belatacept withdrawal and rejection. These pilot data inform the role of secondary lymphoid tissues on the development of CoBRR and the use of costimulation molecule-focused therapies.