Comparative Evaluation of αCD40 (2C10R4) and αCD154 (5C8H1 and IDEC-131) in a Nonhuman Primate Cardiac Allotransplant Model

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

Blockade of the CD40/CD154 T cell costimulation pathway is a promising approach to supplement or replace current clinical immunosuppression in solid organ transplantation. We evaluated the tolerability and activity of a novel humanized anti-CD154 monoclonal antibody, TNX-1500 (TNX), in a nonhuman primate heterotopic cardiac allogeneic (allo) transplant model. TNX-1500 contains a rupluzimab fragment antigen-binding region and an immunoglobin G4 crystallizable fragment region engineered to reduce binding to the crystallizable fragment gamma receptor IIa and associated risks of thrombosis. Recipients were treated for 6 months with standard-dose TNX (sTNX) monotherapy, low-dose TNX monotherapy (loTNX), or loTNX with mycophenolate mofetil (MMF) (loTNX + MMF). Results were compared with historical data using chimeric humanized 5c8 monotherapy dosed as for loTNX but discontinued at 3 months. Median survival time was similar for humanized 5c8 and both loTNX groups, but significantly longer with sTNX (>265 days) than with loTNX (99 days) or loTNX + MMF (88 days) (P < 0.05 for both comparisons against sTNX). Standard-dose TNX prevented antidonor alloantibody elaboration, inhibited chronic rejection, and was associated with a significantly reduced effector T cells/regulatory T cells ratio relative to loTNX with MMF. No thrombotic complications were observed. This study demonstrated that TNX was well tolerated, prolongs allograft survival, and prevents alloantibody production and cardiac allograft vasculopathy in a stringent preclinical nonhuman primate heart allotransplant model.

CD40-CD40L Blockade: Update on Novel Investigational Therapeutics for Transplantation

Effective immune responses require antigen presentation by major histocompatibility complexes with cognate T-cell receptor and antigen-independent costimulatory signaling for T-cell activation, proliferation, and differentiation. Among several costimulatory signals, CD40-CD40L is of special interest to the transplantation community because it plays a vital role in controlling or regulating humoral and cellular immunity. Blockade of this pathway has demonstrated inhibition of donor-reactive T-cell responses and prolonged the survival of transplanted organs. Several anti-CD154 and anti-CD40 antibodies have been used in the transplantation model and demonstrated the potential of extending allograft and xenograft rejection-free survival. The wide use of anti-CD154 antibodies was hampered because of thromboembolic complications in transplant recipients. These antibodies have been modified to overcome the thromboembolic complications by altering the antibody binding fragment (Fab) and Fc (fragment, crystallizable) receptor region for therapeutic purposes. Here, we review recent preclinical advances to target the CD40-CD40L pair in transplantation.

Pathways to Clinical Cardiac Xenotransplantation

Heart transplantation is the only long-lasting lifesaving option for patients with terminal cardiac failure. The number of available human organs is however far below the actual need, resulting in substantial mortality of patients while waiting for a human heart. Mechanical assist devices are used to support cardiac function but are associated with a high risk of severe complications and poor quality of life for the patients. Consistent success in orthotopic transplantation of genetically modified pig hearts into baboons indicates that cardiac xenotransplantation may become a clinically applicable option for heart failure patients who cannot get a human heart transplant. In this overview, we project potential paths to clinical cardiac xenotransplantation, including the choice of genetically modified source pigs; associated requirements of microbiological, including virological, safety; optimized matching of source pig and recipient; and specific treatments of the donor heart after explantation and of the recipients. Moreover, selection of patients and the regulatory framework will be discussed.

Translational impact of NIH-funded nonhuman primate research in transplantation

The National Institutes of Health (NIH) has long supported using nonhuman primate (NHP) models for research on kidney, pancreatic islet, heart, and lung transplantation. The primary purpose of this research has been to develop new treatments for down-modulating or preventing deleterious immune responses after transplantation in human patients. Here, we discuss NIH-funded NHP studies of immune cell depletion, costimulation blockade, regulatory cell therapy, desensitization, and mixed hematopoietic chimerism that either preceded clinical trials or prevented the human application of therapies that were toxic or ineffective.

An update on potentials and promises of T cell co-signaling molecules in transplantation

The promising outcomes of immune-checkpoint based immunotherapies in cancer have provided a proportional perspective ahead of exploiting similar approaches in allotransplantation. Belatacept (CTLA-4-Ig) is an example of costimulation blockers successfully exploited in renal transplantation. Due to the wide range of regulatory molecules characterized in the past decades, some of these molecules might be candidates as immunomodulators in the case of tolerance induction in transplantation. Although there are numerous attempts on the apprehension of the effects of co-signaling molecules on immune response, the necessity for a better understanding is evident. By increasing the knowledge on the biology of co-signaling pathways, some pitfalls are recognized and improved approaches are proposed. The blockage of CD80/CD28 axis is an instance of evolution toward more efficacy. It is now evident that anti-CD28 antibodies are more effective than CD80 blockers in animal models of transplantation. Other co-signaling axes such as PD-1/PD-L1, CD40/CD154, 2B4/CD48, and others discussed in the present review are examples of critical immunomodulatory molecules in allogeneic transplantation. We review here the outcomes of recent experiences with co-signaling molecules in preclinical studies of solid organ transplantation.

Impact of infection on transplantation tolerance

Allograft tolerance is the ultimate goal of organ transplantation. Current strategies for tolerance induction mainly focus on inhibiting alloreactive T cells while promoting regulatory immune cells. Pathogenic infections may have direct impact on both effector and regulatory cell populations, therefore can alter host susceptibility to transplantation tolerance induction as well as impair the quality and stability of tolerance once induced. In this review, we will discuss existing data demonstrating the effect of infections on transplantation tolerance, with particular emphasis on the role of the stage of infection (acute, chronic, or latent) and the stage of tolerance (induction or maintenance) in this infection-tolerance interaction. While the deleterious effect of acute infection on tolerance is mainly driven by proinflammatory cytokines induced shortly after the infection, chronic infection may generate exhausted T cells that could in fact facilitate transplantation tolerance. In addition to pathogenic infections, commensal intestinal microbiota also has numerous significant immunomodulatory effects that can shape the host alloimmunity following transplantation. A comprehensive understanding of these mechanisms is crucial for the development of therapeutic strategies for robustly inducing and stably maintaining transplantation tolerance while preserving host anti-pathogen immunity in clinically relevant scenarios.

Transplant research in nonhuman primates to evaluate clinically relevant immune strategies in organ transplantation

Research in transplant immunology using non-human primate (NHP) species to evaluate immunologic strategies to prevent rejection and prolong allograft survival has yielded results that have translated successfully into human organ transplant patient management. Other therapies have not proceeded to human translation due to failure in NHP testing, arguably sparing humans the futility and risk of such testing. The NHP transplant models are ethically necessary for drug development in this field and provide the closest analogue to human transplant patients available. The refinement of this resource with respect to colony MHC typing, reagent and assay development, and availability to the research community has greatly enhanced knowledge about transplant immunology and drug development.

Long-term Nonhuman Primate Renal Allograft Survival Without Ongoing Immunosuppression in Recipients of Delayed Donor Bone Marrow Transplantation

BACKGROUND

We have previously reported successful induction of renal allograft tolerance in nonhuman primates (NHP) after an initial posttransplant period of conventional immunosuppression (delayed tolerance) using a nonmyeloablative conditioning regimen consisting of anti-CD154 and anti-CD8 mAbs plus equine antithymocyte globulin (Atgam) and donor bone marrow transplantation (DBMT). Because these reagents are not currently clinically available, the protocol was revised to be applicable to human recipients of deceased donor allografts.

METHOD

Four cynomolgus monkeys received major histocompatibility complex-mismatched kidney allografts with conventional immunosuppression for 4 months. The recipients were then treated with a nonmyeloablative conditioning regimen consisting of thymoglobulin, belatacept, and DBMT. The results were compared with recipients treated with conditioning regimen consisting of Atgam and anti-CD154 mAb, with and without anti-CD8 mAb.

RESULTS

In 4 consecutive NHP recipients treated with the modified conditioning regimen, homeostatic recovery of CD8 TEM was delayed until after day 20 and multilineage chimerism was successfully induced. Three of the 4 recipients achieved long-term allograft survival (>728, >540, >449 days) without ongoing maintenance immunosuppression. Posttransplant MLR showed loss of antidonor CD8 T cell and CD4 IFNγ responses with expansion of CD4FOXP3 regulatory T cells. However, the late development of donor-specific antibody in NHP recipients confirms the need for additional anti-B-cell depletion with agents, such as rituximab, as has been shown in our clinical trials.

CONCLUSIONS

This study provides proof of principle that induction of mixed chimerism and long-term renal allograft survival without immunosuppression after delayed DBMT is possible with clinically available reagents.

Selective CD28 Inhibition Modulates Alloimmunity and Cardiac Allograft Vasculopathy in Anti-CD154-Treated Monkeys

BACKGROUND

Selective CD28 inhibition is actively pursued as an alternative to B7 blockade using cytotoxic T lymphocyte antigen 4 Ig based on the hypothesis that the checkpoint immune regulators cytotoxic T lymphocyte antigen 4 and programmed death ligand 1 will induce tolerogenic immune signals. We previously showed that blocking CD28 using a monovalent nonactivating reagent (single-chain anti-CD28 Fv fragment linked to alpha-1 antitrypsin [sc28AT]) synergizes with calcineurin inhibitors in nonhuman primate (NHP) kidney and heart transplantation. Here, we explored the efficacy of combining a 3-week "induction" sc28AT treatment with prolonged CD154 blockade.

METHODS

Cynomolgus monkey heterotopic cardiac allograft recipients received sc28AT (10 mg/kg, d0-20, n = 3), hu5C8 (10-30 mg/kg, d0-84, n = 4), or combination (n = 6). Graft survival was monitored by telemetry. Protocol biopsies and graft explants were analyzed for International Society of Heart and Lung Transplantation acute rejection grade and cardiac allograft vasculopathy score. Alloantibody, T-cell phenotype and regulatory T cells were analyzed by flow cytometry. Immunochemistry and gene expression (NanoString) characterized intra-graft cellular infiltration.

RESULTS

Relative to modest prolongation of median graft survival time with sc28AT alone (34 days), hu5C8 (133 days), and sc28AT + hu5C8 (141 days) prolonged survival to a similar extent. CD28 blockade at induction, added to hu5C8, significantly attenuated the severity of acute rejection and cardiac allograft vasculopathy during the first 3 months after transplantation relative to hu5C8 alone. These findings were associated with decreased proportions of circulating CD8 and CD3CD28 T cells, and modulation of inflammatory gene expression within allografts.

CONCLUSIONS

Induction with sc28AT promotes early cardiac allograft protection in hu5C8-treated NHPs. These results support further investigation of prolonged selective CD28 inhibition with CD40/CD154 blockade in NHP transplants.

Pilot Study of Delayed ICOS/ICOS-L Blockade With αCD40 to Modulate Pathogenic Alloimmunity in a Primate Cardiac Allograft Model

Supplemental digital content is available in the text.

Background

Inducible costimulator (ICOS) is rapidly upregulated with T-cell stimulation and may represent an escape pathway for T-cell costimulation in the setting of CD40/CD154 costimulation blockade. Induction treatment exhibited no efficacy in a primate renal allograft model, but rodent transplant models suggest that the addition of delayed ICOS/ICOS-L blockade may prolong allograft survival and prevent chronic rejection. Here, we ask whether ICOS-Ig treatment, timed to anticipate ICOS upregulation, prolongs NHP cardiac allograft survival or attenuates pathogenic alloimmunity.

Methods

Cynomolgus monkey heterotopic cardiac allograft recipients were treated with αCD40 (2C10R4, d0-90) either alone or with the addition of delayed ICOS-Ig (d63-110).

Results

Median allograft survival was similar between ICOS-Ig + αCD40 (120 days, 120-125 days) and αCD40 (124 days, 89-178 days) treated animals, and delayed ICOS-Ig treatment did not prevent allograft rejection in animals with complete CD40 receptor coverage. Although CD4⁺ T_EM cells were decreased in peripheral blood (115 ± 24) and mLNs (49 ± 1.9%) during ICOS-Ig treatment compared with monotherapy (214 ± 27%, P = 0.01; 72 ± 9.9%, P = 0.01, respectively), acute and chronic rejection scores and kinetics of alloAb elaboration were similar between groups.

Conclusions

Delayed ICOS-Ig treatment with the reagent tested is probably ineffective in modulating pathogenic primate alloimmunity in this model.