Transplantectomy is associated with presensitization with donor-reactive T cells and graft failure after kidney retransplantation: a cohort study

Background

The number of kidney transplant recipients (KTRs) being waitlisted for a subsequent transplantation has disproportionately increased to almost 25%. Evidence for the optimal management of the failed allograft, however, remains inconsistent.

Methods

We studied 111 KTRs who underwent their second kidney transplantation from 1998 to 2015. In 51/111 KTRs (46%) the failed allograft was removed and in 60/111 (54%) the failed allograft was retained. KTRs with primary non-function and allograft loss <12  months of the first failed allograft were excluded from analysis. Samples were collected before transplantation and at  1  month posttransplantation and donor-reactive T cells were measured using an interferon-γ enzyme-linked immunosorbent spot assay.

Results

KTRs with the previous allograft removed showed significantly higher rates of acute cellular rejection compared with KTRs with the previous allograft retained [27/51 KTRs (53%) versus 18/60 KTRs (30%); P = 0.019]. KTRs with the previous allograft removed showed significantly inferior death-censored allograft survival compared with KTRs with the previous allograft retained (P = 0.022). Here, KTRs with the previous allograft removed showed significantly higher donor-reactive T cells pretransplantation compared with KTRs with the previous allograft retained (P = 0.012). Interestingly, no differences were observed for the presence of panel reactive antibodies and for the development of de novo donor-specific antibodies.

Conclusions

Our data suggest higher cellular presensitization among KTRs with the previous allograft removed, which is associated with higher rates of acute cellular rejection and inferior allograft survival. Immunological mechanisms that may account for these differences may include prolonged maintenance immunosuppression to save urine output in KTRs with the first kidney allograft retained and cellular presensitization after withdrawal of maintenance immunosuppression, which lead to allograft rejection and ultimately to allograft nephrectomy.

Biomarkers to assess donor-reactive T-cell responses in kidney transplant patients

Different to antibody-mediated rejection (ABMR), T-cell mediated rejection (TCMR) still unpredictably occurs after kidney transplantation in a great part because of a poor immunologic evaluation of the cellular allogeneic immune response. However, in the last years, important efforts have focused on the development of novel and more sensitive assays to monitor T-cell alloimmune responses at different biological levels that may improve the understanding of the functional status of the cellular immune compartment in patients undergoing organ transplantation. In this direction, immune assays evaluating T-cell proliferation, intracellular ATP release, multiparameter flow cytometry, profiling T-cell receptor repertoires and measurements of frequencies of cytokine-producing T-cells using an IFN-γ enzyme-linked immunospot assay (IFN-γ ELISPOT) have been reported showing interesting associations between the cellular alloimmune response and kidney transplant outcomes. In summary, an important progress has been made in the assessment of alloreactive T-cell responses in the context of organ transplantation using novel immune assays at different biological levels. However, there is an urgent need for prospective, randomized clinical studies to validate these encouraging preliminary data to ultimately introduce them in current clinical practice for refining current immune-risk stratification in kidney transplantation.

Activation-induced CD137 is a fast assay for identification and multi-parameter flow cytometric analysis of alloreactive T cells

Detection and isolation of viable alloreactive T cells at the single-cell level requires a cell surface marker induced specifically upon T cell receptor activation. In this study, a member of the tumour necrosis factor receptor (TNFR)-family, CD137 (4-1BB) was investigated for its potential to identify the total pool of circulating alloreactive T cells. Optimal conditions for sensitive and specific detection of allogeneic-induced CD137 expression on circulating T cells were established. Thereafter, CD137(+) alloreactive T cells were phenotypically and functionally characterized by multi-parameter flow cytometry. Alloantigen-induced CD137 expression identified both alloreactive CD8(+) T cells (mean ± standard error of the mean: 0·21 ± 0·07%) and alloreactive CD4(+) T cells (0·21 ± 0·05%). CD137(+) alloreactive T cells were detected in different T cell subsets, including naive T cells, but were found preferentially in CD28(+) T cells and not in the terminally differentiated T cell subset. Upon allogeneic (re-)stimulation, the cytokine-producing as well as proliferative capacity of T cells resided mainly within the CD137-expressing fraction. About 10% of the CD137(+) alloreactive T cells produced any combination of interferon (IFN)-γ, interleukin (IL)-2 and TNF-α. Polyfunctional alloreactive T cells, defined by multiple cytokine expression, were observed infrequently. In conclusion, activation-induced CD137 expression is a fast assay allowing for detection and functional analysis of the total alloreactive T cell compartment at the single-cell level by multi-parameter flow cytometry.

Monitoring tolerance and rejection in organ transplant recipients

To avoid toxic side effects caused by permanent immunosuppressive treatment, research in transplantation focuses on new treatment strategies inducing tolerance or allowing drug weaning. Implementing drug minimization into clinical routine can be only safely achieved when guided by biomarkers reflecting the individual immune reactivity. We review recently described biomarkers and assays allowing identification of patients suitable for drug weaning or at risk of rejection. However, the majority of described biomarkers and assays have not been validated in prospective clinical trials. Thus, collaborative efforts are needed to design and perform prospective multicenter trials to validate the identified biomarkers across different laboratories.

Pretransplant immune risk assessment

PURPOSE OF REVIEW

Despite the introduction of advanced immunosuppressive drug therapies, clinical and subclinical rejections still occur in many graft recipients with a negative impact on the long-term transplant outcome. The immunological status of the patients awaiting the transplantation is a key factor for these processes. Here we summarize the recent efforts to identify and develop biomarkers and functional assays that allow an individual pretransplant risk assessment.

RECENT FINDINGS

New sensitive techniques assessing T-cell memory and B-cell activation have been developed. Furthermore, the expression level of soluble and molecular markers reflecting the activation state of the immune system and donor graft intrinsic factors have been shown to influence graft outcome.

SUMMARY

A variety of parameters and assays that determine the pretransplant immune activation status has been developed. Some of these assays have already been used prospectively to define high-risk patients receiving advanced immunosuppressive induction therapy.However, the conflicting results obtained in different studies show that biomarker analysis and functional assays performance need to be further standardized and validated in large prospective trials before they can be routinely implemented into a pretransplant risk assessment. Subsequently, a combined effort to design pretransplant risk stratification algorithms should lead to personalized immunosuppressive treatment regimes and improved graft survival and long-term graft function.

Inhibition of polyomavirus BK-specific T-Cell responses by immunosuppressive drugs

BACKGROUND

Reducing immunosuppression is the treatment of choice for polyomavirus-associated nephropathy in kidney transplant (KT) patients, but strategies and targets are uncertain.

METHODS

Using interferon-gamma ELISpot assays, we investigated immunosuppressive drug levels and polyomavirus BK (BKV) large T-antigen-specific T-cell responses in KT patients in vivo and in healthy donors after titrating immunosuppression in vitro.

RESULTS

In KT patients, BKV-specific T-cell responses were inversely correlated with tacrolimus trough levels (R=0.28, P<0.002), but not with mycophenolate levels, prednisone, or overall immunosuppressive dosing. In vitro tacrolimus concentrations above 6 ng/mL inhibited BKV- and cytomegalovirus-specific T-cells more than 50%, whereas less than 30% inhibition was observed below 3 ng/mL. Inhibition by cyclosporine A was more than 50% at concentrations of 1920 ng/mL and less than 30% below 960 ng/mL, corresponding to clinical C0 trough levels of 200 and 100 ng/mL, respectively. However, mycophenolate up to 8 microg/mL, leflunomide 50 microg/mL, or sirolimus concentrations 64 ng/mL did not inhibit BKV-specific interferon-gamma production, but antigen-dependent T-cell expansion.

CONCLUSIONS

Calcineurin-inhibitor concentrations are critical for BKV-specific T-cell activation. Reducing calcineurin inhibitors should be considered as first step, whereas conversion to mTOR inhibitors may be an attractive alternative or second step that should be validated in clinical BKV intervention trials.

Identification of dialysis patients with panel-reactive memory T cells before kidney transplantation using an allogeneic cell bank

Donor-reactive cellular sensitization does not routinely suggest humoral sensitization and vice versa, but both predict poor kidney transplant outcome. Irrespective of donor reactivity, panel-reactive antibody (PRA) screening identifies patients who are at enhanced risk. Therefore, it was hypothesized that panel-reactive memory T cell reactivity (PRT) might be an additional risk assessment factor of dialysis patients who are on the transplant waiting list. IFN-gamma-enzyme-linked immunosorbent spot memory T cell frequencies were determined in 10 healthy volunteers and 41 hemodialysis patients using for stimulation an allogeneic cell bank (ACB) from 17 healthy individuals who represented the most frequent white HLA antigens. Positive responses to ACB were analogous to PRA defined as percentage of positive assays of the ACB sets. Hemodialysis patients expressed higher PRT levels compared with healthy volunteers. Five of 10 PRT++ patients were PRA negative, and only four of 10 PRA++ patients exhibited PRT reactivity, suggesting independence of humoral and cellular sensitization. Pretransplantation PRT testing of recipients might improve individual risk assessment to make individualized therapy decisions.

Comparison of proliferation and rapid cytokine induction assays for flow cytometric T-cell epitope mapping

BACKGROUND

T-cell epitope mapping by flow cytometry based on rapid ex vivo peptide-specific cytokine induction in T cells is very efficient and time saving compared with traditional assays. We investigated whether the same epitopes could be identified by proliferation studies.

METHODS

An assay based on rapid interferon-gamma induction in T cells (6 h of ex vivo stimulation) was run in parallel with a proliferation assay based on the incremental loss of carboxy-fluorescein diacetate succinimidyl ester staining in proliferating cells. The proliferation assay was chosen because it can be evaluated by high-resolution modern multiparameter flow cytometry. In both cases, T cells were stimulated with the same cytomegalovirus-derived peptides. The peptides identified by the rapid induction of interferon-gamma were compared with those inducing T-cell proliferation.

RESULTS

Most epitopes were identified by proliferation and rapid cytokine induction methods; however, each method also identified epitopes that the other one did not. In general, rapid cytokine induction was associated with considerably less background noise, making epitope identification easier, and, owing to the short stimulation time necessary, several identification steps could be carried out on material stored in the incubator.

CONCLUSIONS

Even though most epitopes were identified by both approaches, the rapid cytokine induction method had major logistic advantages. However, it may be best to use both assays, particularly in situations in which the identification of epitopes may depend on prior clonal T-cell expansion.

Cellular methods used to evaluate the immune response in transplantation

Cellular assays have been developed to test for various effector, cytotoxic, and regulatory functions of T cells and have been used throughout the history of clinical transplantation to assess the immune profile of solid organ and marrow recipients. One goal of these cellular studies has been to determine if posttransplant changes in the donor antigen-specific cellular response could predict good and poor graft outcome, thereby allowing for individualization of immunosuppression. This review outlines the use of established and newly developed cellular assays to assess the dynamic processes of the posttransplant immune response and to provide insights into the mechanisms involved and potential points for intervention.