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

Alloreactive T cells to assess acute rejection risk in kidney transplant recipients

Background.Memory T cells are important mediators of transplant rejection but are not routinely measured before or after kidney transplantation. The aims of this study were as follows: (1) validate whether pretransplant donor-reactive memory T cells are reliable predictors of acute rejection (AR) (2) determine whether donor-reactive memory T cells can distinguish AR from other causes of transplant dysfunction. Methods.Samples from 103 consecutive kidney transplant recipients (2018-2019) were obtained pretransplantation and at time of for-cause biopsy sampling within 6 mo of transplantation. The number of donor-reactive interferon gamma (IFN-gamma) and interleukin (IL)-21-producing memory T cells was analyzed by enzyme-linked immunosorbent spot (ELISPOT) assay. Results.Of the 63 patients who underwent a biopsy, 25 had a biopsy-proven acute rejection (BPAR; 22 aTCMR and 3 aAMR), 19 had a presumed rejection, and 19 had no rejection. Receiver operating characteristic analysis showed that the pretransplant IFN-gamma ELISPOT assay distinguished between patients who later developed BPAR and patients who remained rejection-free (area under the curve [AUC] 0.73; sensitivity 96% and specificity 41%). Both the IFN-gamma and IL-21 assays were able to discriminate BPAR from other causes of transplant dysfunction (AUC 0.81; sensitivity 87% and specificity 76% and AUC 0.81; sensitivity 93% and specificity 68%, respectively). Conclusions.This study validates that a high number of donor-reactive memory T cells before transplantation is associated with the development of AR after transplantation. Furthermore, it demonstrates that the IFN-gamma and IL-21 ELISPOT assays are able to discriminate between patients with AR and patients without AR at the time of biopsy sampling.Personalised Therapeutic

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

High Tacrolimus Intrapatient Variability and Subtherapeutic Immunosuppression are Associated With Adverse Kidney Transplant Outcomes

Background: Kidney transplant recipients with high intrapatient variability (IPV) in tacrolimus (Tac) exposure experience more rejection and reduced graft survival. To understand the underlying pathophysiology of this association, the authors investigated whether patients with high tacrolimus IPV have a more activated immune system than patients with low IPV. In addition, exposure to tacrolimus and mycophenolic acid (MPA) was studied in relation to rejection and graft survival. Methods: At the time of patient inclusion (5-7 years post-transplantation), the frequency of donor-reactive cells was determined by enzyme-linked immunosorbent assay, and the development of donor-specific anti-Human Leukocyte Antigen antibodies (DSA) was measured by Luminex Single Antigen assay. Tacrolimus IPV was retrospectively calculated between 6 and 12 months and the exposure to tacrolimus and MPA was determined between 1 and 5 years post-transplantation. Results: A total of 371 kidney transplant recipients were included in this study, of whom 56 developed a rejection episode after 12 months and 60 experienced graft failure after 5-7 years. No correlations were found between tacrolimus IPV or immunosuppression exposure and the number of donor-reactive cells after 5 years of transplantation. DSA were detected more often in patients with low exposure to both tacrolimus and MMF [4/21 (19%) versus 17/350 (4.9%), P = 0.04]. In this cohort, neither tacrolimus IPV nor low overall immunosuppression exposure was associated with a higher incidence of rejection. However, regression analysis showed that a higher tacrolimus IPV was associated with an increased incidence of graft failure (odds ratio = 1.03, P = 0.02). Conclusions: This study verifies the relationship between high tacrolimus IPV and impaired kidney allograft survival in long-term follow-up. DSA was also found to be more prevalent in patients with subtherapeutic concentrations of tacrolimus and MPA. An increased prevalence of donor-specific alloreactivity is yet to be demonstrated in patients with high IPV.Personalised Therapeutic

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