Rejection Pathways in Heart Transplant Recipients

Since the beginning of this century experimental heart transplantations in animal studies were performed.' These studies were started in Rotterdam in the seventies to compare heterotopic and orthotopic heart transplantations, and to study the process of chronic rejection. The history of the first human heart transplantation started in South-Africa and it was carried out by Barnard in 1967. Several cardiac surgeons around the world initiated new transplantation programmes. However, the problems with patient and donor organ selection as well as with immunosuppression, severe rejection and infection were common. This meant in 1968, only 22% of all transplants survived after the first year.6 Consequently, many centres stopped their programmes. Heart transplantation, as a routine treatment for organ failure, only became possible with the development in 1973 of the endomyocardial biopsy technique for monitoring acute rejection? and in 1975 by the further discovery of cyclosporin A. In the early eighties cyclosporin A was successfully introduced as an immunosuppressive medicine post clinical heart transplantation.' Cyclosporin A acts by binding to calmodulin and thereby inhibits the transcription of the IL-2 and IFN-y gene." With the development of these new processes, a 50% survival rate after 5 years was achieved in 1982

The role of follicular T helper cells in the humoral alloimmune response after clinical organ transplantation

Over the past decade, antibody-mediated or humoral rejection in combination with development of de novo donor-specific antibodies (DSA) has been recognized as a distinct and common cause of transplant dysfunction and is responsible for one-third of the failed allografts. Detailed knowledge of the mechanisms that initiate and maintain B-cell driven antidonor reactivity is required to prevent and better treat this antidonor response in organ transplant patients. Over the past few years, it became evident that this response largely depends on the actions of both T follicular helper (Tfh) cells and the controlling counterparts, the T follicular regulatory (Tfr) cells. In this overview paper, we review the latest insights on the functions of circulating (c)Tfh cells, their subsets Tfh1, Tfh2 and Tfh17 cells, IL-21 and Tfr cells in antibody mediated rejection (ABMR). This may offer new insights in the process to reduce de novo DSA secretion resulting in a decline in the incidence of ABMR. In addition, monitoring these cell populations could be helpful for the development of biomarkers identifying patients at risk for ABMR and provide novel therapeutic drug targets to treat ABMR

Peripheral monitoring of direct and indirect alloantigen presentation pathways in clinical heart transplant recipients

It has been reported that the response to alloantigens presented by the direct and indirect pathway may be of differential relevance after human kidney transplantation. Accordingly, we monitored these routes in peripheral blood mononuclear cells (PBMC) of heart transplant patients from before transplantation and up to 2 years thereafter in an attempt to find a correlation with the clinical status of the patients. Both before and after transplantation, comparable proportions of PBMC samples reacted in mixed lymphocyte culture to nondepleted donor spleen cells (direct route), but never to donor cells depleted for antigen-presenting cells (indirect route). In contrast, the latter route could easily be activated by a nominal antigen and persisted after transplantation, although the proportion of PBMC samples responding was significantly suppressed, irrespective of the occurrence of rejection. Consequently, complete removal of antigen-presenting cells from the stimulator population in a mixed lymphocyte culture with PBMC as responder is not a suitable tool for measuring indirect presentation of alloantigens, and therefore not relevant for monitoring the immunological status of heart transplant recipients

Immunosuppression Has Long-Lasting Effects on Circulating Follicular Regulatory T Cells in Kidney Transplant Recipients

Background: FoxP3+ follicular regulatory T cells (Tfr) have been identified as the cell population controlling T follicular helper (Tfh) cells and B cells which, are both involved in effector immune responses against transplanted tissue. Methods: To understand the biology of Tfr cells in kidney transplant patients treated with tacrolimus and mycophenolate mofetil (MMF) combination immunosuppression, we measured circulating (c)Tfh and cTfr cells in peripheral blood by flow cytometry in n = 211 kidney transplant recipients. At the time of measurement patients were 5–7 years after transplantation. Of this cohort of patients, 23.2% (49/211) had been previously treated for rejection. Median time after anti-rejection therapy was 4.9 years (range 0.4–7 years). Age and gender matched healthy individuals served as controls. Results: While the absolute numbers of cTfh cells were comparable between kidney transplant recipients and healthy controls, the numbers of cTfr cells were 46% lower in immunosuppressed recipients (p < 0.001). More importantly, in transplanted patients, the ratio of cTfr to cTfh was decreased (median; 0.10 vs. 0.06), indicating a disruption of the balance between

Donor-specific ELISPOT assay for predicting acute rejection and allograft function after kidney transplantation

Acute rejection remains an important problem after kidney transplantation. Enzyme-linked immunosorbent spot (ELISPOT) assay has been investigated extensively and has shown promising results as a predictor of allograft rejection. The objective of this study was to systematically review and analyze the predictive value of the donor-specific ELISPOT assay to identify recipients at risk for acute rejection. Electronic databases were searched for stud

Donor-reactive cytokine profiles after HLA-identical living-related kidney transplantation

Background. After HLA-identical living-related (LR) kidney transplantation, only non-HLA antigen mismatches between donor and recipient may exist. We questioned whether donor-reactive responses against non-HLA antigens could be found after HLA-identical LR kidney transplantation, and wondered whether donor reactivity in the HLA-identical setting was different from the HLA-mismatched setting during immunological quiescence. Healthy individuals served as controls. Methods. Elispot assays were performed to determine the number of alloreactive IFN-γ-producing cells (pc), IL-10 pc, granzyme B (GrB) pc and IL-13 pc from peripheral blood mononuclear cells (PBMC) of HLA-identical, HLA-mismatched LR kidney transplant recipients and healthy individuals. Results. The frequency of alloreactive IFN-γ pc, IL-13 pc and GrB pc was higher in healthy individuals compared to both transplant patient groups. In the HLA-identical group, significantly higher numbers of donor-reactive IL-10 pc were found compared to their autologous control. These frequencies were also higher compared to the HLA-mismatched and healthy control group. The number of donor-reactive GrB pc was higher in the HLA-mismatched group than in the HLA-identical group. Donor-reactive IFN-γ pc and IL-13 pc were comparable in both transplant groups. Conclusions. In recipients of HLA-identical LR kidney transplant, high donor-reactive IL-10 pc, in combination with low donor-reactive IFN-γ pc, IL-13 pc and GrB pc, suggests active downregulation of reactivity against non-HLA molecules

Mycophenolic acid plasma concentrations in kidney allograft recipients with or without cyclosporin: a cross-sectional study

BACKGROUND: Combining cyclosporin (CsA) and prednisone with mycophenolate mofetil (MMF) results in a significant reduction in the rate of biopsy-proven acute rejection after kidney transplantation. This is achieved with a standard daily MMF dosage of 2 or 3 g. Whether monitoring of the pharmacologically active metabolite mycophenolic acid (MPA) will lead to improved safety and efficacy is unclear. METHODS: We monitored MPA trough levels in 18 kidney transplant recipients treated with CsA, prednisone, and MMF (63 samples) and in 11 patients (31 samples) treated with prednisone and MMF only, in a cross-sectional study. All patients were at least 3 months after transplantation with stable graft function. All patients were treated with 2 g MMF for at least 3 months and 10 mg prednisone. RESULTS: The MPA trough levels in the CsA-treated patients were significantly lower (P<0.0001; Mann-Whitney) than those in patients on MMF and prednisone only (mean MPA levels 1.98+/-0.12 vs 4.38+/-0.40 mg/l respectively). CONCLUSIONS: Although all patients were treated with an identical MMF dose, a significant difference was found in the MPA trough levels between CsA- vs non-CsA-treated patients. This suggests that CsA influences the MPA trough level. The level at which CsA affects the MPA trough levels is unclear

A systematic review and meta-analysis of enzyme-linked immunosorbent spot (ELISPOT) assay for BK polyomavirus immune response monitoring after kidney transplantation

BK virus (BKV) infection after kidney transplantation can cause BKV nephropathy (BKVAN) resulting in graft dysfunction and allograft loss. The treatment for BKVAN is reduction of the immunosuppressive load which increases the risk of kidney transplant rejection. There is no biomarker to monitor BKV activity besides BK viral load. The valu

The direct and indirect allogeneic presentation pathway during acute rejection after human cardiac transplantation

Alloreactive T cells may be activated via a direct or an indirect antigen presentation pathway. We questioned whether the frequency of interferon (IFN)-γ producing cells determined by enzyme-linked immunospot (ELISPOT) assay is an effective tool to monitor the direct and/or indirect presentation pathway. Secondly, we wondered whether early and late acute rejection (AR) are associated with both pathways. Before (n = 15), during (n = 18) and after (n = 16) a period of AR, peripheral blood mononuclear cell (PBMC) samples were tested from 13 heart transplant recipients. The direct presentation pathway was always present. The number of IFN-γ producing cells reactive to this pathway increased significantly (P = 0.04) during AR and the number decreased (P = 0.005) after AR therapy. In contrast, the indirect allogeneic presentation pathway was present in only eight of 18 AR samples. When the indirect presentation pathway was detectable, it increased significantly during AR. Five of eight of these AR occurred more than 6 months after transplantation. The ELISPOT assay, enumerating alloreactive IFN-γ producing cells, is a valuable tool to determine the reactivity via both the direct and the indirect presentation pathway. The direct presentation pathway always plays a role in AR, while the indirect pathway contributes especially to late AR

Human mesenchymal stem cells are susceptible to lysis by CD8+ T cells and NK cells

There is growing interest in the use of mesenchymal stem cells (MSCs) to improve the outcome of organ transplantation. The immunogenicity of MSCs is, however, unclear and is important for the efficacy of MSC therapy and for potential sensitization against donor antigens. We investigated the susceptibility of autolo- gous and allogeneic MSCs for lysis by CD8+ T-lymphocytes and NK cells in a kidney transplant setting. MSCs were derived from adipose tissue of human kidney donors and were CD90+, CD105+, CD166+, and HLA class I+. They showed differentiation ability and immunosuppressive capacity. Lysis of MSCs by peripheral blood mononuclear cells (PBMCs), FACS-sorted CD8+ T cells, and NK cells was measured by europium release assay. Allogeneic MSCs were susceptible for lysis by cytotoxic CD8+ T cells and NK cells, while autologous MSCs were lysed by NK cells only. NK cell-mediated lysis was inversely correlated with the expression of HLA class I on MSCs. Lysis of autologous MSCs was not dependent on culturing of MSCs in FBS, and MSCs in suspension as well as adherent to plastic were lysed by NK cells. Pretransplant recipient PBMCs did not lyse donor MSCs, but PBMCs isolated 3, 6, and 12 months after transplantation showed increasing lysing ability. After 12 months, CD8+ T-cell-mediated lysis of donor MSCs persisted, indicating there was no evidence for desensitization against donor MSCs. Lysis of MSCs is important to take into account when MSCs are considered for clinical application. Our results suggest that the HLA background of MSCs and timing of MSC administration are important for the efficacy of MSC therapy