Down-regulation of surface CD28 under belatacept treatment: An escape mechanism for antigen-reactive T-cells

Background The co-stimulatory inhibitor of the CD28-CD80/86-pathway, belatacept, allows calcineurininhibitor-free immunosuppression in kidney transplantation. However, aggressive T-cell mediated allogeneic responses have been observed in belatacept-treated patients, which could be explained by effector-memory T-cells that lack membrane expression of CD28, i.e. CD28-negative (CD28NULL) T-cells. CD28-positive (CD28POS) T-cells that down regulate their surface CD28 after allogeneic stimulation could also pose a threat against the renal graft. The aim of this study was to investigate this potential escape mechanism for CD28POS T-cells under belatacept treatment. Materials & Methods PBMCs, isolated T-cell memory subsets and isolated CD28POS T-cells were obtained from end-stage renal disease (ESRD) patients and co-cultured with allo-antigen in the presence of belatacept to mimic allogeneic reactions in kidney-transplant patients under belatacept treatment. As a control, IgG was used in the absence of belatacept. Results Despite high in vitro belatacept concentrations, a residual T-cell growth of ±30% was observed compared to the IgG control after allogeneic stimulation. Of the alloreactive Tcells, the majority expressed an effector-memory phenotype. This predominance for effector-memory T-cells within the proliferated cells was even larger when a higher dose of belatacept was added. Contrary to isolated naïve and central-memory T cells, isolated effectormemory T cells could not be inhibited by belatacept in differentiation or allogeneic IFNγ production. The proportion of CD28-positive T cells was lower within the proliferated T cell population, but was still substantial. A fair number of the isolated initially CD28POS T-cells differentiated into CD28NULL T-cells, which made them not targetable by belatacept. These induced CD28NULL T-cells were not anergic as they produced high amounts of IFNγ upon allogeneic stimulat

Belatacept does not inhibit follicular T cell-dependent B-cell differentiation in kidney transplantation

Humoral alloreactivity has been recognized as a common cause of kidney transplant dysfunction. B-cell activation, differentiation, and antibody production are dependent on IL-21+CXCR5+ follicular T-helper (Tfh) cells. Here, we studied whether belatacept, an inhibitor of the costimulatory CD28-CD80/86-pathway, interrupts the crosstalk between Tfh- and B-cells more efficiently than the calcineurin inhibitor tacrolimus. The suppressive effects of belatacept and tacrolimus on donor antigen-driven Tfh-B-cell interaction were functionally studied in peripheral blood mononuclear cells from 40 kidney transplant patients randomized to a belatacept- or tacrolimus-based immunosuppressive regimen. No significant differences in uncultured cells or donor antigen-stimulated cells were found between belatacept- and tacrolimus-treated patients in the CXCR5+Tfh cell generation and activation (upregulation of PD-1). Belatacept and tacrolimus in vitro minimally inhibited Tfh-cell generation (by ~6-7%) and partially prevented Tfh-cell activation (by ~30-50%). The proportion of IL-21+-activated Tfh-cells was partially decreased by in vitro addition of belatacept or tacrolimus (by ~60%). Baseline expressions and proportions of activated CD86+ B-cells, plasmablasts, and transitional B-cells after donor antigen stimulation did not differ between belatacept- and tacrolimus-treated patients. Donor antigen-drive

A Randomized Controlled Clinical Trial Comparing Belatacept With Tacrolimus After De Novo Kidney Transplantation

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Cytotoxicity and T-B Cell Crosstalk in Belatacept-Treated Kidney Transplant Patients

In this dissertation, we aimed to learn more about the immune mechanisms involved in alloreactivity in patients treated with belatacept or tacrolimus after kidney transplantation. In particular, we sought to explain the higher acute rejection rate in belatacept-treated patients by studying cytotoxic cell populations which are potentially less susceptible to co-stimulatory inhibition, and to explain the lower incidence of DSA in previous trials by studying the effects of belatacept on Tfh-B cell interaction. We found that next to CD28- T cells also a part of CD28+ T cells are not susceptible to inhibition by belatacept. These cells could still divide and produce cytokines in the presence of belatacept. In addition, belatacept was not as effective as tacrolimus in preventing Tfh-B cell interaction and the subsequent formation of plasmablasts. Additionally, we tried to characterize belatacept-resistant rejection clinically and immunologically, and to find a biomarker to distinguish between patients who will reject under belatacept-treatment and those who will not. We found that belatacept-treated patients had a higher acute rejection risk compared to tacrolimus-treated patients (55% versus 10%), and that these rejections could not be predicted by cellular biomarkers before transplantation, i.e., CD8+CD28- T cells, CD4+CD57+PD-1- T cells and CD8+CD28++ EMRA T cells. Baseline characteristics did not differ between (future) rejectors and non-rejectors in belatacept-treated patients. Mostly effector-memory T cells, both CD28+ and CD28-, infiltrated a rejected kidney graft during belatacept-treatment. These cells produced large amounts of IFN-gamma and granzyme B. For now, belatacept does not meet the requirements to be the new corner stone in immunosuppression after kidney transplantation, because short-term outcomes are inferior to tacrolimus. However, belatacept-treatment could be beneficial and increase quality of life for a selected group of patients. The search for an immunosuppressive drug or combination of immunosuppressants, possibly including belatacept, to further improve kidney transplant patients’ outcomes continues

Targeting the Monocyte–Macrophage Lineage in Solid Organ Transplantation

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