Costimulatory blockade with belatacept in clinical and experimental transplantation – a review

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.

Belatacept As an Alternative to Calcineurin Inhibitors in Patients with Solid Organ Transplants

The goal of immunosuppression in transplantation has shifted to improving long-term outcomes, reducing drug-induced toxicities while preserving the already excellent short-term outcomes. Long-term gains in solid organ transplantation have been limited at least partly due to the nephrotoxicity and metabolic side effects of calcineurin inhibitors (CNIs). The alloimmune response requires activation of the costimulatory pathway for T cell proliferation and amplification. Belatacept is a molecule that selectively blocks T cell costimulation. In June 2011, the U.S. Food and Drug Administration approved it for maintenance immunosuppression in kidney transplantation based on two open-label, randomized, phase III trials. Since its introduction, belatacept has shown promise in both short- and long-term renal transplant outcomes in several other trials. It exhibits a superior side effect profile compared to CNIs with a comparable efficacy. Across all solid organ transplants, the burden of chronic kidney disease, its associated cardiovascular morbidity, mortality, and inferior patient/allograft survival is a well-documented problem. In this review, we aim to discuss the evidence behind the use of belatacept in solid organ transplants as an effective alternative to CNIs for renal rescue in patients with acute and/or chronic kidney injury.

Fcγ1 fragment of IgG1 as a powerful affinity tag in recombinant Fc-fusion proteins: immunological, biochemical and therapeutic properties

Affinity tags are vital tools for the production of high-throughput recombinant proteins. Several affinity tags, such as the hexahistidine tag, maltose-binding protein, streptavidin-binding peptide tag, calmodulin-binding peptide, c-Myc tag, glutathione S-transferase and FLAG tag, have been introduced for recombinant protein production. The fragment crystallizable (Fc) domain of the IgG1 antibody is one of the useful affinity tags that can facilitate detection, purification and localization of proteins and can improve the immunogenicity, modulatory effects, physicochemical and pharmaceutical properties of proteins. Fcγ recombinant forms a group of recombinant proteins called Fc-fusion proteins (FFPs). FFPs are widely used in drug discovery, drug delivery, vaccine design and experimental research on receptor-ligand interactions. These fusion proteins have become successful alternatives to monoclonal antibodies for drug developments. In this review, the physicochemical, biochemical, immunological, pharmaceutical and therapeutic properties of recombinant FFPs were discussed as a new generation of bioengineering strategies.

Immunosuppressive properties of mitomycin C-incubated human myeloid blood cells (MIC) in vitro

Previous animal studies showed that donor-derived blood cells treated with mitomycin C (MMC) prolong allograft survival when injected into recipients. This model was effective with whole blood, peripheral blood mononuclear cells (PBMC) (monocytes being the active cell subpopulation) or dendritic cells. In view of a potential clinical application, we study now the immunosuppressive properties of human myeloid cells in vitro. Mature dendritic cells (generated from naïve monocytes) or monocytes treated with mitomycin C do not or only weakly inhibit allogeneic T cells in vitro, whereas cells in an early differentiation state between monocytes and DC exert suppressive activity when treated with MMC. In contrast, DC generated from MMC-treated monocytes show the morphology and phenotype of early immature DC (iDC) and suppress T-cell responses. It is known that untreated monocytes injected into a recipient encounter a cytokine milieu which differentiates them to stimulatory DC. In our in vitro experiment MMC-treated monocytes cultured in a DC-maturing milieu transform themselves into suppressive early iDC. This reproduces a process which takes place when administering MMC-monocytes to a recipient. In conclusion, human MMC-DC or MMC-monocytes are not or only weakly suppressive in vitro. When MMC-monocytes are differentiated to DC the resulting cells become suppressive.

Introduction to the use of belatacept: a fusion protein for the prevention of posttransplant kidney rejection

The development of new immunosuppressive drugs for kidney transplantation resulted both in better short-term outcomes and in decreased metabolic, cardiovascular, and nephrotoxicity risk. Belatacept belongs to a new class of immunosuppressive drugs that selectively inhibits T-cell activation by preventing CD28 activation and by binding its ligands B7-1 and B7-2. The result is an inactivation of costimulatory pathways. A comparative analysis of the BENEFIT and BENEFIT-EXT datasets showed belatacept regimens resulted in better cardiovascular and metabolic risk profiles than did cyclosporin A (CsA) regimens: belatacept likewise outperformed CsA in terms of lower blood pressure and serum lipids and less new onset diabetes after transplantation. About 20% of belatacept-treated patients developed adverse effects which included anemia, pyrexia, neutropenia, diarrhea, urinary tract infection, headache, and peripheral edema. At present, belatacept does not seem to predispose patients to a higher rate of infection than CsA maintenance immunosuppression. The risk of posttransplant lymphoproliferative diseases was higher in Epstein-Barr virus (EBV)-seronegative patients than in EBV-seropositive patients, but the risk may be reduced by use of a less intensive regimen and avoidance of EBV-negative patients and of patients whose pretransplant EBV serology is unknown. Belatacept provides a new option for immunosuppressive therapy in kidney transplantation, but needs further evaluation in terms of the late effects that may derive from prolonged blockage of the costimulatory system and the induction of tolerance status.

Decreased frequency of peripheral CD4(+) CD161(+) Th(17) -precursor cells in kidney transplant recipients on long-term therapy with Belatacept

Clinical trials have pointed out the promising role of co-stimulation blocker Belatacept for improvement of graft function and avoidance of undesired side-effects associated with calcineurin-inhibitors (CNI). However, due to the worldwide limited availability of appropriate patients, almost no data exist to assess the effects of sustained application of this immunomodulator on the recipient's immune system. The aim of this study was to reveal specific alterations in the composition of immunologic subpopulations potentially involved in development of tolerance or chronic graft rejection following long-term Belatacept therapy. For this, peripheral lymphocyte subsets of kidney recipients treated with Belatacept (n=5; average 7.8years) were determined by flow-cytometry and compared with cells from matched patients on CNI (n=9) and healthy controls (n=10). T cells capable of producing IL-17 and serum levels of soluble CD30 were quantified. Patients on CNI showed a higher frequency of CD4(+) CD161(+) Th(17) -precursors and IL-17-producing CD4(+) T cells than Belatacept patients and controls. Significantly higher serum levels of soluble CD30 were observed in CNI patients, indicating a possible involvement of the CD30/CD30L-system in Th(17) -differentiation. No differences were found concerning CD4(+) CD25(+) CD127(low) FoxP3(+) regulatory T cells. In conclusion, patients on therapy with Belatacept did not show a comparable Th(17) -profile to that seen in individuals with chronic intake of CNI. The distinct effects of Belatacept on Th(17) -immunity might prove beneficial for the long-term outcome following kidney transplantation.

Pharmacology of immunosuppressive medications in solid organ transplantation

The multitude of immunosuppressants available for solid organ transplantation allows for many combinations of immunosuppressive therapies that can be tailored to a patient’s specific lifestyle and immunosuppression needs. Newer agents currently being studied offer even more possibilities for the future to further reduce the incidence of acute rejection and prolong graft and patient survival.

Molecular cloning, expression and characterization of the functional domain of CTLA4 from the rhesus monkey, Macaca mulatta

Cytotoxic T lymphocyte-associated antigen 4 (CTLA4) is a potent inhibitor of T cell activation. The genes encoding the membrane and soluble forms of Macaca mulatta CTLA4 (mmCTLA4) were isolated from peripheral blood mononuclear cells (PBMCs). The predicted mmCTLA4 protein is nearly identical to human CTLA4 (hCTLA4), with the exception of a serine instead of an asparagine residue at position 49 and a leucine instead of a methionine residue at position 141 of its extracellular domain. The fusion protein mmCTLA4Ig, containing the extracellular domain of mmCTLA4 and the constant region of the human IgG1 antibody, was expressed in Pichia pastoris. The mmCTLA4Ig produced by P. pastoris exhibited specific binding to human B7-positive Raji cells that could be inhibited by competitive binding of hCTLA4Ig. MmCTLA4Ig and hCTLA4Ig could comparably suppress the proliferation of lymphocytes derived from rhesus monkeys, humans, or mice that had been stimulated either by concanavalin A (Con A) or allogeneic cells. These results suggest that mmCTLA4 is a negative regulator of T cell activation and that mmCTLA4Ig may be useful for immunotherapy of immunologic diseases in the rhesus monkey.

Cell-autonomous and -non-autonomous roles of CTLA-4 in immune regulation

It is controversial how cytotoxic T lymphocyte antigen (CTLA)-4, a co-inhibitory molecule, contributes to immunological tolerance and negative control of immune responses. Its role as an inducer of cell-intrinsic negative signals to activated effector T cells is well documented. However, there is accumulating evidence that CTLA-4 is essential for the function of naturally occurring Foxp3(+) regulatory T (Treg) cells, which constitutively express the molecule. CTLA-4 deficiency in Foxp3(+) Treg cells indeed impairs their in vivo and in vitro suppressive function. Further, Treg cells can modulate the function of CD80- and CD86-expressing antigen-presenting cells via CTLA-4. Here we discuss how CTLA-4 expression by one T cell can influence the activation of another in a cell non-autonomous fashion and thus control immune responses.

RNA interference for improving the outcome of islet transplantation

Islet transplantation has the potential to cure type 1 diabetes. Despite recent therapeutic success, it is still not common because a large number of transplanted islets get damaged by multiple challenges including instant blood mediated inflammatory reaction, hypoxia/reperfusion injury, inflammatory cytokines, and immune rejection. RNA interference (RNAi) is a novel strategy to selectively degrade target mRNA. The use of RNAi technologies to downregulate the expression of harmful genes has the potential to improve the outcome of islet transplantation. The aim of this review is to gain a thorough understanding of biological obstacles to islet transplantation and discuss how to overcome these barriers using different RNAi technologies. This eventually will help improve islet survival and function post transplantation. Chemically synthesized small interferring RNA (siRNA), vector based short hairpin RNA (shRNA), and their critical design elements (such as sequences, promoters, and backbone) are discussed. The application of combinatorial RNAi in islet transplantation is also discussed. Last but not the least, several delivery strategies for enhanced gene silencing are discussed, including chemical modification of siRNA, complex formation, bioconjugation, and viral vectors.

Receptor-Fc fusion therapeutics, traps, and MIMETIBODY technology

Fc fusion proteins are molecules in which the immunoglobulin Fc is fused genetically to a protein of interest, such as an extracellular domain of a receptor, ligand, enzyme, or peptide. Fc fusion proteins have some antibody-like properties such as long serum half-life and easy expression and purification, making them an attractive platform for therapeutic drugs. Five Fc fusion based drugs are on the market presently, and many more are in different stages of clinical trials, demonstrating that Fc fusion proteins have become credible alternatives to monoclonal antibodies as therapeutics. This review summarizes the Fc fusion proteins that have been approved for use in the clinic and those that are currently in clinical trials, as well as the different approaches to design Fc fusion proteins.