T-cell immune monitoring in organ transplantation

Impact of donor-specific antibody with low mean fluorescence intensity on allograft outcomes in kidney transplant

BACKGROUND

Immune-mediated rejection is the most common cause of allograft failure in kidney transplant (KT) patients. Exposure to alloantigen, including human leukocyte antigen (HLA), results in the production of donor-specific antibodies (DSA). There are limited data about low levels of mean fluorescence intensity (MFI) DSA, especially post-transplantation. This study evaluated allograft outcomes in KT patients with low MFI DSA.

METHODS

From January 2007 to December 2021, KT patients who were tested for post-transplant DSA at Ramathibodi Hospital, Bangkok, Thailand, with the DSA MFI ≤ 1000 were evaluated. These KT patients were categorized into two groups: very low DSA (VLL; MFI = 1-500) and low DSA (LL; MFI = 501-1000). All KT patients were evaluated for the primary outcomes, such as the incidence of acute rejection, serum creatinine levels at one and five years after transplantation as well as allograft and patient survivals.

RESULTS

Among 36 KT patients 25 were included as those with VLL and 11 as those with LL. The LL group had significantly higher T-cell mediated allograft rejection (TCMR) than the VLL group (45% vs. 12%, P = 0.04). In addition, 10 patients, 5 in the VLL group and 5 in the LL group developed antibody-mediated allograft rejection (ABMR). Both TCMR and ABMR were confirmed by biopsy results. There was a trend toward higher MFI in KT patients with ABMR than without ABMR (P = 0.22). At 5 post-transplant years, serum creatinine, allograft and patient survivals were comparable between these two groups. Furthermore, the univariate and multivariate analyzes revealed that the LL group was a high risk for rejection.

CONCLUSION

Low MFI DSA values after transplantation may be associated with a higher incidence of rejection, but this finding did not show differences in allograft and patient survival in this study's analysis.

ELISpot Assay for Gene Therapy in Large Animal Studies

Formation of neutralizing antibodies and cellular immune response with repeat adeno-associated virus (AAV) gene therapy dosing are critical concerns in translational, large animal studies. The enzyme-linked immunospot/immunosorbent spot (ELISpot) assay introduced a way to track B- and/or T-cell response to therapy over time at a protein level. We describe the protocol for this assay looking at relative interferon (IFN)-γ secretion in pre- and post-AAV injections in a pig model.

Cytomegalovirus (CMV) Cell-Mediated Immunity and CMV Infection After Allogeneic Hematopoietic Cell Transplantation: The REACT Study

BACKGROUND

Cytomegalovirus (CMV) infection remains an important cause of morbidity and mortality in allogeneic hematopoietic cell transplant (allo-HCT) recipients. CMV cell-mediated immunity (CMV-CMI) as determined by a peptide-based enzyme-linked immunospot (ELISPOT) CMV assay may identify patients at risk for clinically significant CMV infection (CS-CMVi).

METHODS

The CS-CMVi was defined as CMV viremia and/or disease necessitating antiviral therapy. CMV-CMI was characterized as high when the intermediate-early 1 (IE-1) antigen spot counts (SPCs) were >100 (cutoff 1) or when the IE-1 and phosphoprotein 65 antigen SPCs were both >100 SPCs per 250 000 cells (cutoff 2), and a low CMV-CMI when SPCs were below these thresholds. In this prospective multicenter study, we evaluated CMV-CMI every 2 weeks from the pretransplant period until 6 months posttransplantation in 241 allo-HCT recipients with positive CMV serostatus. The primary endpoint was CS-CMVi occurring within 2 weeks of the last measurement of CMV-CMI.

RESULTS

CS-CMVi occurred in 70 allo-HCT recipients (29%). CMV-CMI was low in patients who experienced CS-CMVi (94%), whereas those who had a high CMV-CMI were less likely to have CS-CMVi (P < .0001). Patients with CS-CMVi had higher all-cause mortality (P = .007), especially those with low CMV-CMI (P = .035). On multivariable analysis, CMV-CMI, sex, race, antithymocyte globulin, and steroid use were independent predictors of CS-CMVi, and the time from transplant to engraftment was the only predictor of mortality.

CONCLUSIONS

Measurement of CMV-CMI using a novel ELISPOT assay would be useful clinically to monitor allo-HCT recipients and distinguish between those at risk of developing CS-CMVi and requiring antiviral prophylaxis or therapy and those who are protected.

T regulatory cell mediated immunotherapy for solid organ transplantation: A clinical perspective

T regulatory cells (Tregs) play a vital role in suppressing heightened immune responses, and thereby promote a state of immunological tolerance. Tregs modulate both innate and adaptive immunity, which make them a potential candidate for cell-based immunotherapy to suppress uncontrolled activation of graft specific inflammatory cells and their toxic mediators. These grafts specific inflammatory cells (T effector cells) and other inflammatory mediators (Immunoglobulins, active complement mediators) are mainly responsible for graft vascular deterioration followed by acute/chronic rejection. Treg mediated immunotherapy is under investigation to induce allospecific tolerance in various ongoing clinical trials in organ transplant recipients. Treg immunotherapy is showing promising results but the key issues regarding Treg immunotherapy are not yet fully resolved including their mechanism of action, and specific Treg cell phenotype responsible for a state of tolerance. This review highlights the involvement of various subsets of Tregs during immune suppression, novelty of Tregs functions, effects on angiogenesis, emerging technologies for effective Treg expansion, plasticity and safety associated with clinical applications. Altogether this information will assist in designing single/combined Treg mediated therapies for successful clinical trials in solid organ transplantations.

Moving Biomarkers toward Clinical Implementation in Kidney Transplantation

Long-term kidney transplant outcomes remain suboptimal, delineating an unmet medical need. Although current immunosuppressive therapy in kidney transplant recipients is effective, dosing is conventionally adjusted empirically on the basis of time after transplant or altered in response to detection of kidney dysfunction, histologic evidence of allograft damage, or infection. Such strategies tend to detect allograft rejection after significant injury has already occurred, fail to detect chronic subclinical inflammation that can negatively affect graft survival, and ignore specific risks and immune mechanisms that differentially contribute to allograft damage among transplant recipients. Assays and biomarkers that reliably quantify and/or predict the risk of allograft injury have the potential to overcome these deficits and thereby, aid clinicians in optimizing immunosuppressive regimens. Herein, we review the data on candidate biomarkers that we contend have the highest potential to become clinically useful surrogates in kidney transplant recipients, including functional T cell assays, urinary gene and protein assays, peripheral blood cell gene expression profiles, and allograft gene expression profiles. We identify barriers to clinical biomarker adoption in the transplant field and suggest strategies for moving biomarker-based individualization of transplant care from a research hypothesis to clinical implementation.

Quantitative characterization of T-cell repertoire and biomarkers in kidney transplant rejection

BACKGROUND

T-cell-mediated rejection (TCMR) remains a major cause of kidney allograft failure. The characterization of T-cell repertoire in different immunological disorders has emerged recently as a novel tool with significant implications. We herein sought to characterize T-cell repertoire using next generation sequencing to diagnose TCMR.

METHODS

In this prospective study, we analyzed samples from 50 kidney transplant recipients. We collected blood and kidney transplant biopsy samples at sequential time points before and post transplant. We used next generation sequencing to characterize T-cell receptor (TCR) repertoire by using illumina miSeq on cDNA synthesized from RNA extracted from six patients' samples. We also measured RNA expression levels of FOXP3, CD8, CD4, granzyme and perforin in blood samples from all 50 patients.

RESULTS

Seven patients developed TCMR during the first three months of the study. Out of six patients who had complete sets of blood and biopsy samples two had TCMR. We found an expansion of the TCR repertoire in blood at time of rejection when compared to that at pre-transplant or one-month post transplant. Patients with TCMR (n = 7) had significantly higher RNA expression levels of FOXP3, Perforin, Granzyme, CD4 and CD8 in blood samples than those with no TCMR (n = 43) (P = 0.02, P = 0.003, P = 0.002, P = 0.017, and P = 0.01, respectively).

CONCLUSIONS

Our study provides a potential utilization of TCR clone kinetics analysis in the diagnosis of TCMR. This approach may allow for the identification of the expanded T-cell clones associated with the rejection and lead to potential noninvasive diagnosis and targeted therapies of TCMR.

Monitoring T cell alloreactivity

Currently, immunosuppressive therapy in kidney transplant recipients is center-specific, protocol-driven, and adjusted according to functional or histological evaluation of the allograft and/or signs of drug toxicity or infection. As a result, a large fraction of patients receive too much or too little immunosuppression, exposing them to higher rates of infection, malignancy and drug toxicity, or increased risk of acute and chronic graft injury from rejection, respectively. The individualization of immunosuppression requires the development of assays able to reliably quantify and/or predict the magnitude of the recipient's immune response toward the allograft. As alloreactive T cells are central mediators of allograft rejection, monitoring T cell alloreactivity has become a priority for the transplant community. Among available assays, flow cytometry based phenotyping, T cell proliferation, T cell cytokine secretion, and ATP release (ImmuKnow), have been the most thoroughly tested. While numerous cross-sectional studies have found associations between the results of these assays and the presence of clinically relevant post-transplantation outcomes, data from prospective studies are still scanty, thereby preventing widespread implementation in the clinic. Future studies are required to test the hypothesis that tailoring immunosuppression on the basis of results offered by these biomarkers leads to better outcomes than current standard clinical practice.

Immunologic monitoring in transplantation revisited

PURPOSE OF REVIEW

Tailoring immunosuppressive drugs to an individual's needs is crucial to improve long-term outcomes of organ transplant patients. The purpose of this review is to summarize the data on promising biomarkers able to detect the risk of acute or chronic rejection and to discuss the potential issues for their implementation in the clinic.

RECENT FINDINGS

Multiple publications have indicated that circulating antibodies targeting human leukocyte antigen (HLA) and non-HLA antigens as well as donor-specific memory T cells are associated with accelerated graft failure. Other studies published within the year show that specific genomic and proteomic signatures obtained from urine, blood, and graft tissue correlate with acute rejection in kidney and heart transplant patients.

SUMMARY

The development of reliable biomarkers is crucial for individualizing therapy aimed at extending allograft survival and improving patient health. Emerging data indicate that monitoring assays, likely used in panels, have the potential to be diagnostic and possibly predictive of long-term outcome. In addition to ongoing discovery efforts, progress in the field will require multicenter validation, assay standardization, and commercialization so as to efficiently deliver reliable testing strategies to the practicing clinician.

Potential of surface acoustic wave biosensors for early sepsis diagnosis

Early diagnosis of sepsis is a difficult problem for intensivists and new biomarkers for early diagnosis have been difficult to come by. Here we discuss the potential of adapting a technology from the electronics industry, surface acoustic wave (SAW) sensors, for diagnosis of multiple markers of sepsis in real time, using non-invasive assays of exhaled breath condensate. The principles and advantages of the SAW technology are reviewed as well as a proposed plan for adapting this flexible technology to early sepsis detection.

Clinical operational tolerance in liver transplantation: state-of-the-art perspective and future prospects

BACKGROUND

Liver transplantation is the definite treatment for end-stage liver diseases with satisfactory results. However, untoward effects of life-long immunosuppression prevent the development of alternative strategies to achieve better long-term outcome. Achieving clinical operational tolerance is the ultimate goal.

DATA SOURCES

A PubMed and Google Scholar search using terms: "immune tolerance", "liver transplantation", "clinical trial", "operational tolerance" and "immunosuppression withdrawal" was performed, and relevant articles published in English in the past decade were reviewed. Full-text publications relevant to the field were selected and relevant articles from reference lists were also included. Priority was given to those articles which are relevant to the review.

RESULTS

Because of the inherent tolerogenic property, around 20%-30% of liver transplantation recipients develop spontaneous operational tolerance after immunosuppression withdrawal, and the percentage may be even higher in pediatric living donor liver transplantation recipients. Several natural killer and gammadeltaT cell related markers have been identified to be associated with the tolerant state in liver transplantation patients. Despite the progress, clinical operational tolerance is still rare in liver transplantation. Reprogramming the recipient immune system by creating chimerism and regulatory cell therapies is among newer promising means to achieve clinical liver transplantation tolerance in the future.

CONCLUSION

Although clinical operational tolerance is still rare in liver transplantation recipients, ongoing basic research and collaborative clinical trials may help to decipher the mystery of transplantation tolerance and extend the potential benefits of drug withdrawal to an increasing number of patients in a more predictable fashion.

T-cell immune monitoring in organ transplantation

PURPOSE OF REVIEW

Chronic injury and late allograft loss remain major causes of morbidity in clinical transplantation. Biomarkers that can reliably assess the risk of posttransplant complications are required to direct and individualize therapy aimed at prolonging graft survival and improving patient health. The purpose of this review is to provide a framework for understanding how to use biomarkers in the context of clinical transplantation and to summarize current data on available noninvasive cellular-based immune monitoring methods to predict transplant outcome.

RECENT FINDINGS

New microarray and gene profiling data reveal peripheral blood cell gene expression patterns that identify operational tolerance, raising the possibility that the measurements can be used to direct immunosuppression withdrawal. Additional data support the use of selective urine gene products and soluble CD30 measurements in serum as reliable biomarkers of acute graft injury. Finally, recent studies demonstrate that measurement of T-cell alloimmunity by cytokine enzyme-linked immunospot is a promising, supplementary pretransplant risk assessment tool.

SUMMARY

Recently published studies in organ transplantation suggest that results derived from assays focused on markers of T-cell immunity can segregate transplant candidates or recipients into high and low-risk subgroups for posttransplant graft injury. Larger prospective studies are needed, however, before any proposed biomarker can be incorporated into the transplant physicians' armamentarium to guide individualized therapeutic decision-making.

Characteristics of alloreactive T cells measured before renal transplantation

Several assays to measure pre-existing allospecific T cell immunity in renal transplant candidates have been developed in the past years. In 46 patients, we used flow cytometry-based mixed lymphocyte culture to measure the precursor frequency and phenotype of alloreactive T cells before renal transplantation, using donor-specific or third-party cells for allostimulation. Allostimulation induced up-regulation of co-stimulatory molecules, chemokine receptors relevant for migration of T cells into the graft and effector proteins. Recipients prone for acute rejection had a higher precursor frequency of alloreactive CD8(+) T cells and a lower percentage of interleukin (IL)-7Rα expressing alloreactive CD8(+) T cells than non-rejectors. These data point to quantitative and qualitative differences between T cells of patients who will experience acute cellular rejection episodes from those who will not.

Assessing immunologic function through CD4 T-lymphocyte ahenosine triphosphate levels by ImmuKnow assay in Chinese patients following renal transplantation

OBJECTIVE

Balancing immunosuppression to prevent rejection while minimizing infection/drug toxicity risk is a challenge in organ transplantation. Drug monitoring alone or with functional monitoring is inadequate to measure the immune response after transplantation. The Food and Drug Administration (FDA)-approved immune monitoring assay, ImmuKnow, offers an noninvasive method to assess the immune status of transplanted patients by measuring adenosine triphosphate (ATP) released from CD4 T cells. Herein, we have evaluated ATP levels reflecting the immune responses of Chinese kidney transplant recipients as a monitoring parameter to guide treatment after transplantation.

METHODS

From October 2008 to March 2010, we recruited 259 kidney transplant patients who were divided into four groups: stable (n = 174), postoperative infection (n = 32), postoperative rejection (n = 16), and high-dose corticosteroid treatment (n = 33). The ImmuKnow assay was performed to measure CD4 T-cell ATP levels. No prisoners or organs from prisoners were used in the study.

RESULTS

Receiver operating characteristics measurements indicated an ATP predictive range of 238 to 497 ng/mL to monitor immune responses after transplantation and immunosuppressive therapy. To identify patients with infection, we used a cutoff ATP value of 238 ng/mL with 100% specificity and positive predictive value and 92.9% sensitivity. To identify patients with rejection, we used a value of 497 ng/mL with 91.5% sensitivity. Compared with the 225 to 525 ng/mL ATP levels recommended by the FDA, our target values showed similar or better diagnostic accuracy.

CONCLUSION

We provide additional data to monitor immunosupressant treatment of Chinese kidney transplant patients.

T-cell immune monitoring in organ transplantation

Chronic allograft injury remains the leading cause of graft loss despite improvements in immunosuppression, clinical risk stratification, and state-of-the-art antibody testing. Emerging results indicate that T-cell immune monitoring by cytokine enzyme-linked immunosorbent spot, as part of a comprehensive risk assessment platform, has the potential to guide decision making and improve outcomes after transplantation.

Contribution of naïve and memory T-cell populations to the human alloimmune response

T-cell alloimmunity plays a dominant role in allograft rejection. The precise contribution of naïve and memory T cells to this response however remains unclear. To address this question, we established an ex vivo flow-cytometric assay that simultaneously measures proliferation, precursor frequency and effector molecule (IFNgamma, granzyme B/perforin) production of alloreactive T cells. By applying this assay to peripheral blood mononuclear cells from healthy volunteers, we demonstrate that the CD4+ and CD8+ populations mount similar proliferative responses and contain comparable frequencies of alloreactive precursors. Effector molecule expression, however, was significantly higher among CD8+ T cells. Analysis of sorted naïve and memory T cells showed that alloreactive precursors were equally present in both populations. The CD8+ effector and terminally differentiated effector memory subsets contained the highest proportion of granzyme B/perforin after allostimulation, suggesting that these cells present a significant threat to transplanted organs. Finally, we demonstrate that virus-specific lymphocytes contribute significantly to the alloresponse in certain responder-stimulator HLA combinations, underscoring the importance of T-cell cross-reactivity in alloimmunity. These results provide a quantitative assessment of the roles of naïve and memory T-cell subsets in the normal human alloimmune response and establish a platform for measuring T-cell alloreactivity pre- and posttransplantation.

Translating transplantation tolerance in the clinic: where are we, where do we go?

Research networks dedicated to translation of immune tolerance in the clinic currently support pilot trials aiming at immunosuppression withdrawal in kidney or liver allograft recipients. Although results obtained so far indicate that significant hurdles still need to be overcome before organ transplant recipients can be weaned off drugs safely and routinely, recent advances suggest that immunosuppression minimization on the basis of validated biomarkers might become standard practice in a near future.