Belatacept-Based Maintenance Immunosuppression Controls the Post-Transplant Humoral Immune Response in Highly Sensitized Nonhuman Primates

CD154 blockade effectively controls antibody-mediated rejection in highly sensitized nonhuman primate kidney transplant recipients

Current desensitization and maintenance immunosuppression regimens for kidney transplantation in sensitized individuals show limited ability to control the posttransplant humoral response, resulting in high rates of antibody-mediated rejection (ABMR) and graft failure. Here, we showed that anti-CD154 monoclonal antibody (mAb)-based immunosuppression more effectively controlled allograft rejection and humoral rebound in a highly sensitized nonhuman primate kidney transplantation model compared with tacrolimus-based standard-of-care (SOC) immunosuppression. Desensitization with an anti-CD154 mAb (5C8) and a proteasome inhibitor led to decreased donor-specific antibodies (DSAs) and disruption of lymph node germinal centers with reduction of proliferating, memory, and class-switched B cells as well as T follicular helper cells. After transplant, the nonhuman primates maintained on 5C8-based immunosuppression had significantly better survival compared with those maintained on SOC immunosuppression (135.2 days versus 32.8 days, P = 0.013). The 5C8-treated group demonstrated better suppression of DSAs after transplant, more robust suppression of B cell populations, and better induction of regulatory T cells. Fewer infectious and welfare complications, including viral reactivation and weight loss, were also observed with 5C8-based immunosuppression compared with SOC immunosuppression. Therefore, anti-CD154 mAbs may improve kidney transplant outcomes through better control of posttransplant immune responses. The superior efficacy of anti-CD154 mAb-based immunosuppression over tacrolimus-based SOC seen in this highly sensitized NHP transplant model suggests that anti-CD154 mAbs could potentially be used to desensitize and treat highly sensitized patients receiving kidney transplantation.

Rethinking Immune Check Point Inhibitors Use in Liver Transplantation: Implications and Resistance

Immune checkpoint inhibitors (ICIs) have revolutionized cancer therapy, including the two most common liver tumors, hepatocellular carcinoma and cholangiocarcinoma, but their use in the peri-transplantation period is controversial. ICI therapy aims to heighten cytotoxic T lymphocytes response against tumors. However, tumor recurrence is common owing to tumor immune response escape involving ablation of CTL response by interfering with antigen presentation, triggering CLT apoptosis and inducing epigenetic changes that promote ICI therapy resistance. ICI can also affect tissue resident memory T cell population, impact tolerance in the post-transplant period, and induce acute inflammation risking graft survival post-transplant. Their interaction with immunosuppression may be key in reducing tumor burden and may thus, require multimodal therapy to treat these tumors. This review summarizes ICI use in the liver transplantation period, their impact on tolerance and resistance, and new potential therapies for combination or sequential treatments for liver tumors.

Prolonged xenokidney graft survival in sensitized NHP recipients by expression of multiple human transgenes in a triple knockout pig

Genetic modification of porcine donors, combined with optimized immunosuppression, has been shown to improve outcomes of experimental xenotransplant. However, little is known about outcomes in sensitized recipients, a population that could potentially benefit the most from the clinical implementation of xenotransplantation. Here, five highly allosensitized rhesus macaques received a porcine kidney from GGTA1 (α1,3-galactosyltransferase) knockout pigs expressing the human CD55 transgene (1KO.1TG) and were maintained on an anti-CD154 monoclonal antibody (mAb)-based immunosuppressive regimen. These recipients developed de novo xenoreactive antibodies and experienced xenograft rejection with evidence of thrombotic microangiopathy and antibody-mediated rejection (AMR). In comparison, three highly allosensitized rhesus macaques receiving a kidney from GGTA1, CMAH (cytidine monophospho-N-acetylneuraminic acid hydroxylase), and b4GNT2/b4GALNT2 (β-1,4-N-acetyl-galactosaminyltransferase 2) knockout pigs expressing seven human transgenes including human CD46, CD55, CD47, THBD (thrombomodulin), PROCR (protein C receptor), TNFAIP3 (tumor necrosis factor-α-induced protein 3), and HMOX1 (heme oxygenase 1) (3KO.7TG) experienced significantly prolonged graft survival and reduced AMR, associated with dampened post-transplant humoral responses, early monocyte and neutrophil activation, and T cell repopulation. After withdrawal of all immunosuppression, recipients who received kidneys from 3KO.7TG pigs rejected the xenografts via AMR. These data suggest that allosensitized recipients may be suitable candidates for xenografts from genetically modified porcine donors and could benefit from an optimized immunosuppression regimen designed to target the post-transplant humoral response, thereby avoiding AMR.

Early allogeneic immune modulation after establishment of donor hematopoietic cell-induced mixed chimerism in a nonhuman primate kidney transplant model

Background

Mixed lymphohematopoietic chimerism is a proven strategy for achieving operational transplant tolerance, though the underlying immunologic mechanisms are incompletely understood.

Methods

A post-transplant, non-myeloablative, tomotherapy-based total lymphoid (TLI) irradiation protocol combined with anti-thymocyte globulin and T cell co-stimulatory blockade (belatacept) induction was applied to a 3-5 MHC antigen mismatched rhesus macaque kidney and hematopoietic cell transplant model. Mechanistic investigations of early (60 days post-transplant) allogeneic immune modulation induced by mixed chimerism were conducted.

Results

Chimeric animals demonstrated expansion of circulating and graft-infiltrating CD4+CD25+Foxp3+ regulatory T cells (Tregs), as well as increased differentiation of allo-protective CD8+ T cell phenotypes compared to naïve and non-chimeric animals. In vitro mixed lymphocyte reaction (MLR) responses and donor-specific antibody production were suppressed in animals with mixed chimerism. PD-1 upregulation was observed among CD8+ T effector memory (CD28-CD95+) subsets in chimeric hosts only. PD-1 blockade in donor-specific functional assays augmented MLR and cytotoxic responses and was associated with increased intracellular granzyme B and extracellular IFN-γ production.

Conclusions

These studies demonstrated that donor immune cell engraftment was associated with early immunomodulation via mechanisms of homeostatic expansion of Tregs and early PD-1 upregulation among CD8+ T effector memory cells. These responses may contribute to TLI-based mixed chimerism-induced allogenic tolerance.

Belatacept and carfilzomib-based treatment for antibody-mediated rejection in a sensitized nonhuman primate kidney transplantation model

Introduction

One-third of HLA-incompatible kidney transplant recipients experience antibody mediated rejection (AMR) with limited treatment options. This study describes a novel treatment strategy for AMR consisting of proteasome inhibition and costimulation blockade with or without complement inhibition in a nonhuman primate model of kidney transplantation.

Methods

All rhesus macaques in the present study were sensitized to maximally MHC-mismatched donors by two sequential skin transplants prior to kidney transplant from the same donor. All primates received induction therapy with rhesus-specific ATG (rhATG) and were maintained on various immunosuppressive regimens. Primates were monitored postoperatively for signs of acute AMR, which was defined as worsening kidney function resistant to high dose steroid rescue therapy, and a rise in serum donor-specific antibody (DSA) levels. Kidney biopsies were performed to confirm AMR using Banff criteria. AMR treatment consisted of carfilzomib and belatacept for a maximum of four weeks with or without complement inhibitor.

Results

Treatment with carfilzomib and belatacept was well tolerated and no treatment-specific side effects were observed. After initiation of treatment, we observed a reduction of class I and class II DSA in all primates. Most importantly, primates had improved kidney function evident by reduced serum creatinine and BUN as well as increased urine output. A four-week treatment was able to extend graft survival by up to two months.

Discussion

In summary, combined carfilzomib and belatacept effectively treated AMR in our highly sensitized nonhuman primate model, resulting in normalization of renal function and prolonged allograft survival. This regimen may translate into clinical practice to improve outcomes of patients experiencing AMR.

Desensitization and belatacept-based maintenance therapy in pregnancy-sensitized monkeys receiving a kidney transplant

Among sensitized patients awaiting a transplant, females are disproportionately represented, partly because of pregnancy-induced sensitization. Using female NHPs sensitized by pregnancy alone, we examined the efficacy of costimulation blockade and proteasome inhibition for desensitization. Three animals received no desensitization (control), and seven animals received weekly carfilzomib (27 mg/m2) and belatacept (20 mg/kg) before kidney transplantation. All animals received renal allografts from crossmatch-positive/maximally MHC-mismatched donors. Controls and three desensitized animals received tacrolimus-based immunosuppression. Four desensitized animals received additional belatacept with tacrolimus-based immunosuppression. Multiparous females had less circulating donor-specific antibody when compared to skin-sensitized males before transplantation. While females receiving desensitization showed only a marginal survival benefit over control females (MST = 11 days versus 63 days), additional belatacept to posttransplant maintenance significantly prolonged graft survival (MST > 164 days) and suppressed posttransplant DSA and circulating follicular helper T-like cells. This combination of therapies demonstrates great potential to reduce antibody-mediated rejection in sensitized recipients.

Translation of therapeutic strategies to modulate B cell reponses from non-human primate models to human kidney transplantation

Using novel drugs targeting lymphocyte costimulation, cytokines, antibody, complement, and plasma cells, we have developed strategies in a non-human primate model to modulate the B cell response to incompatible kidney transplants. After more than two decades of research supported by mechanistic studies, this has resulted in clinically relevant approaches that are currently enrolling in clinical trials or preparing for such. In this manner, we aim to address the problems of HLA sensitization for very highly sensitized patients awaiting transplantation and the unmet need of effective treatment for antibody-mediated rejection.