Lymphocyte markers and prediction of long-term renal allograft acceptance:

The Identity Card of T Cells-Clinical Utility of T-cell Receptor Repertoire Analysis in Transplantation

There is a clear medical need to change the current strategy of "one-size-fits-all" immunosuppression for controlling transplant rejection to precision medicine and targeted immune intervention. As T cells play a key role in both undesired graft rejection and protection, a better understanding of the fate and function of both alloreactive graft-deteriorating T cells and those protecting to infections is required. The T-cell receptor (TCR) is the individual identity card of each T cell clone and can help to follow single specificities. In this context, tracking of lymphocytes with certain specificity in blood and tissue in clinical follow up is of especial importance. After overcoming technical limitations of the past, novel molecular technologies opened new avenues of diagnostics. Using advantages of next generation sequencing, a method was established for T-cell tracing by detection of variable TCR region as identifiers of individual lymphocyte clones. The current review describes principles of laboratory and computational methods of TCR repertoire analysis, and gives an overview on applications for the basic understanding of transplant biology and immune monitoring. The review also delineates methodological pitfalls and challenges. With the outlook on prediction of antigens in immune-mediated processes including those of unknown causative pathogens, monitoring the fate and function of individual T cell clones, and the adoptive transfer of protective effector or regulatory T cells, this review highlights the current and future capability of TCR repertoire analysis.

The TreaT-Assay: A Novel Urine-Derived Donor Kidney Cell-Based Assay for Prediction of Kidney Transplantation Outcome

Donor-reactive immunity plays a major role in rejection after kidney transplantation, but analysis of donor-reactive T-cells is not applied routinely. However, it has been shown that this could help to identify patients at risk of acute rejection. A major obstacle is the limited quantity or quality of the required allogenic stimulator cells, including a limited availability of donor-splenocytes or an insufficient HLA-matching with HLA-bank cells. To overcome these limitations, we developed a novel assay, termed the TreaT (Transplant reactive T-cells)-assay. We cultivated renal tubular epithelial cells from the urine of kidney transplant patients and used them as stimulators for donor-reactive T-cells, which we analyzed by flow cytometry. We could demonstrate that using the TreaT-assay the quantification and characterization of alloreactive T-cells is superior to other stimulators. In a pilot study, the number of pre-transplant alloreactive T-cells negatively correlated with the post-transplant eGFR. Frequencies of pre-transplant CD161⁺ alloreactive CD4⁺ T-cells and granzyme B producing alloreactive CD8⁺ T-cells were substantially higher in patients with early acute rejection compared to patients without complications. In conclusion, we established a novel assay for the assessment of donor-reactive memory T-cells based on kidney cells with the potential to predict early acute rejection and post-transplant eGFR.

BK viremia is not associated with adverse outcomes in the absence of BK nephropathy

There are limited data regarding the association of different levels of BK viremia and BK nephropathy (BKN), and graft outcomes. We studied the BK plasma PCR levels of all kidney transplant recipients (KTR) transplanted at our institution between 01/01/2006 and 06/30/2014. Patients were divided into groups based on their highest BK plasma PCR level within the first year following transplantation: undetectable, low (<1000 copies/mL), moderate (1000-10 000 copies/mL), high (>10 000-100 000 copies/mL), very high (>100 000 copies/mL), and those that had biopsy-proven BKN. There were a total of 1146 KTR during the study period: 813 with undetectable BK levels and 333 with any detectable BK level (87 with low, 79 with moderate, 88 with high, 34 with very high level BK, and 45 that had BKN). Compared to KTR with an undetectable BK level, incidence of mortality, graft failure, rejections,and infections were not significantly different for those with low, moderate, high, or very high BK level. Patients with BKN had a higher rate of infection and higher rates of total graft failure or death-censored graft failure compared to those with undetectable BK levels. BK viremia in the absence of BKN does not significantly increase the risk of rejection, infections, or graft failure compared to an undetectable BK level.

Immunologic monitoring in kidney transplant recipients

Transplant biopsy has always been the gold standard for assessing the immune response to a kidney allograft (Chandraker A: Diagnostic techniques in the work-up of renal allograft dysfunction-an update. Curr Opin Nephrol Hypertens 8:723-728, 1999). A biopsy is not without risk and is unable to predict rejection and is only diagnostic once rejection has already occurred. However, in the past two decades, we have seen an expansion in assays that can potentially put an end to the "drug level" era, which until now has been one of the few tools available to clinicians for monitoring the immune response. A better understanding of the mechanisms of rejection and tolerance, and technological advances has led to the development of new noninvasive methods to monitor the immune response. In this article, we discuss these new methods and their potential uses in renal transplant recipients.

Surface markers of lymphocyte activation and markers of cell proliferation

The individualization of immunosuppression is an approach for preventing rejection in the early phase after transplantation and for avoiding the long-term side effects of over immunosuppression. Pharmacodynamic markers, either specific or nonspecific, have been proposed as complementary tools to drug monitoring of immunosuppressive drugs. A key event in graft rejection is the activation and proliferation of the recipient's lymphocytes, particularly T cells. Activated T cells express surface receptors, such as CD25 (the IL-2 receptor) and CD71 (the transferrin receptor), or co-stimulatory molecules (CD26, CD27, CD28, CD30, CD154 or CD40L, and CD134). Both surface marker expression and cell proliferation are predominately assessed by flow cytometry. Protocols have been established and utilized for both in vitro and ex vivo investigations with either isolated lymphocytes or whole blood. This article reviews the current body of research regarding the use of lymphocyte proliferation and surface activation markers with an emphasis on T cells. Experimental and clinical results related to these markers, as well as methodological issues and open questions, are addressed.

Immunosuppression: does one regimen fit all?

There has been considerable interest in the individualization of immunosuppressive regimens in an attempt to avoid side effects and improve long-term outcomes. Most available studies have addressed steroid and calcineurin inhibitor minimization in an attempt to prevent the development of chronic allograft dysfunction and cardiovascular mortality. Herein, we evaluate the available evidence for incorporation of these novel strategies in standard clinical care of kidney transplant recipients. Protocol biopsies, pharmacogenetics, and other assays have been developed to guide tailoring of immunosuppression; however, although promising results have been obtained, trials showing their ability to improve long-term outcome are lacking and urgently needed.

Premature senescence of T cells in long-term survivors of renal transplantation

Prevention of graft rejection in renal transplant recipients depends on chronic treatment with immunosuppressive agents. However, impaired immune functions and immunosurveillance may cause infection, cancer and many other problems, which subsequently compromise quality of life and survival of patients. In the present study, we assessed potential premature immune-senescence in long-term survivors of kidney transplant patients receiving immunosuppressive agents. Peripheral blood lymphocytes derived from patients had significantly shorter telomeres than those from age- and sex-matched healthy individuals. Consistent with this, lower expression of telomerase reverse transcriptase (hTERT) and telomerase activity was observed in patients' lymphocytes. The level of p16(ink4A) expression was elevated in patients' cells. Moreover, the CD8(+)/CD28(-) fraction of late-stage differentiated T cells was significantly increased in the patients. In vitro studies further showed that cyclosporine A, a widely used immunosuppressive drug in transplant patients, attenuated induction of hTERT and telomerase activation in T cells treated with the mitogenic agent concanavalin A. Taken together, immunosuppressant-mediated premature senescence of T lymphocytes occurs in renal transplant recipients.