Biomarkers of immunoregulatory status in stable liver transplant recipients undergoing weaning of immunosuppressive therapy

European Society for Organ Transplantation Consensus Statement on Biomarkers in Liver Transplantation

Currently, one-year survival following liver transplantation (LT) exceeds 90% in large international registries, and LT is considered definitive treatment for patients with end-stage liver disease and liver cancer. Recurrence of disease, including hepatocellular carcinoma (HCC), significantly hampers post-LT outcomes. An optimal approach to immunosuppression (IS), including safe weaning, may benefit patients by mitigating the effect on recurrent diseases, as well as reducing adverse events associated with over-/under-IS, including chronic kidney disease (CKD). Prediction of these outcome measures-disease recurrence, CKD, and immune status-has long been based on relatively inaccurate clinical models. To address the utility of new biomarkers in predicting these outcomes in the post-LT setting, the European Society of Organ Transplantation (ESOT) and International Liver Transplant Society (ILTS) convened a working group of experts to review literature pertaining to primary disease recurrence, development of CKD, and safe weaning of IS. Summaries of evidence were presented to the group of panelists and juries to develop guidelines, which were discussed and voted in-person at the Consensus Conference in Prague November 2022. The consensus findings and recommendations of the Liver Working Group on new biomarkers in LT, clinical applicability, and future needs are presented in this article.

Diagnosing Acute Cellular Rejection after Paediatric Liver Transplantation-Is There Room for Interleukin Profiles?

BACKGROUND

The current gold standard to diagnose T-cell-mediated acute rejection (TCMR) requires liver histology. Using data from the ChilSFree study on immune response after paediatric liver transplantation (pLT), we aimed to assess whether soluble cytokines can serve as an alternative diagnostic tool in children suspected to have TCMR.

METHODS

A total of n = 53 blood samples obtained on the day of or up to 3 days before liver biopsy performed for suspected TCMR at median 18 days (range 7-427) after pLT in n = 50 children (38% female, age at pLT 1.8 (0.5-17.5) years) were analysed for circulating cytokine levels using Luminex-based Multiplex technology. Diagnostic accuracy of cytokine concentrations was assessed using a multivariable model based on elastic net regression and gradient boosting machine analysis.

RESULTS

TCMR was present in 68% of biopsies. There was strong evidence that patients with TCMR had increased levels of soluble CXCL8, CXCL9, CXCL10, IL-16, IL-18, HGF, CCL4, MIF, SCGF-β, and HGF before biopsy. There was some evidence for increased levels of sCD25, ICAM-1, IL-6, IL-3, and CCL11. Diagnostic value of both single cytokine levels and a combination of cytokines and clinical markers was poor, with AUROCs not exceeding 0.7.

CONCLUSION

Patients with TCMR showed raised levels of cytokines and chemokines reflective of T-cell activation and chemotaxis. Despite giving insight into the mechanisms of TCMR, the diagnostic value of soluble cytokines for the confirmation of TCMR in a clinical scenario of suspected TCMR is poor.

Clinical parameters and biomarkers predicting spontaneous operational tolerance after liver transplantation: A scoping review

Indefinite allograft acceptance after immunosuppression withdrawal (ISW), also known as operational tolerance (OT), can occur spontaneously after liver transplantation (LT), but reliable and reproducible prognosis of OT versus non-OT outcomes remains elusive. To prime this, systematic extraction of OT-predictive factors from the literature is crucial. We provide the first comprehensive identification and synthesis of clinical parameters and biomarkers predicting spontaneous OT in non-autoimmune/non-replicative viral LT recipients selected for ISW. We searched Embase, Medline, the Cochrane Central Register of Controlled Trials, clinicaltrials.gov, and the World Health Organization International Clinical Trials Registry Platform for articles, conference abstracts, and ongoing trials. We contacted principal investigators of stand-alone abstracts and ongoing trials for unpublished data and screened citations and references of eligible articles. Twenty-three articles reporting on 11 completed ISW studies, 13 abstracts, and five trial registry entries were included. Longer time between LT and ISW was the only clinical parameter that may increase the incidence of OT. Prognostic biomarkers conspicuously differed between pediatric and adult ISW candidates. These included allograft gene expression patterns and peripheral blood immune exhaustion markers for adults, and histological allograft scores for children. Our results will foster cross-validation efforts to facilitate safe and harmonized candidate selection for successful ISW.

Identification of peripheral CD154+ T cells and HLA-DRB1 as biomarkers of acute cellular rejection in adult liver transplant recipients

Decreasing graft rejection and increasing graft and patient survival are great challenges facing liver transplantation (LT). Different T cell subsets participate in the acute cellular rejection (ACR) of the allograft. Cell-mediated immunity markers of the recipient could help to understand the mechanisms underlying acute rejection. This study aimed to analyse different surface antigens on T cells in a cohort of adult liver patients undergoing LT to determine the influence on ACR using multi-parametric flow cytometry functional assay. Thirty patients were monitored at baseline and during 1 year post-transplant. Two groups were established, with (ACR) and without (NACR) acute cellular rejection. Leukocyte, total lymphocyte, percentages of CD4+ CD154+ and CD8+ CD154+ T cells, human leukocyte antigen (HLA) mismatch between recipient-donor and their relation with ACR as well as the acute rejection frequencies were analysed. T cells were stimulated with concanavalin A (Con-A) and surface antigens were analysed by fluorescence activated cell sorter (FACS) analysis. A high percentage of CD4+ CD154+ T cells (P = 0·001) and a low percentage of CD8+ CD154+ T cells (P = 0·002) at baseline were statistically significant in ACR. A receiver operating characteristic analysis determined the cut-off values capable to stratify patients at high risk of ACR with high sensitivity and specificity for CD4+ CD154+ (P = 0·001) and CD8+ CD154+ T cells (P = 0·002). In logistic regression analysis, CD4+ CD154+ , CD8+ CD154+ and HLA mismatch were confirmed as independent risk factors to ACR. Post-transplant percentages of both T cell subsets were significantly higher in ACR, despite variations compared to pretransplant. These findings support the selection of candidates for LT based on the pretransplant percentages of CD4+ CD154+ and CD8+ CD154+ T cells in parallel with other transplant factors.

Maintenance Immunosuppression in Solid Organ Transplantation: Integrating Novel Pharmacodynamic Biomarkers to Inform Calcineurin Inhibitor Dose Selection

Calcineurin inhibitors, the primary immunosuppressive therapy used to prevent alloreactivity of transplanted organs, have a narrow therapeutic index. Currently, treatment is individualized based on clinical assessment of the risk of rejection or toxicity guided by trough concentration monitoring. Advances in immune monitoring have identified potential markers that may have value in understanding calcineurin inhibitor pharmacodynamics. Integration of these markers has the potential to complement therapeutic drug monitoring. Existing pharmacokinetic-pharmacodynamic (PK-PD) data is largely limited to correlation between the biomarker and trough concentrations at single time points. Immune related gene expression currently has the most evidence supporting PK-PD integration. Novel biomarker-based approaches to pharmacodynamic monitoring including development of enhanced PK-PD models are proposed to realize the full clinical benefit.

[Summary of the recommendations of the International Association of Therapeutic Drug Monitoring and Clinical Toxicology (IATDMCT) on the therapeutic drug monitoring of tacrolimus]

Recently, the International Association of Therapeutic Drug Monitoring (IATDMCT), that is the learning society for biological pharmacology and toxicology, issued recommendations on the therapeutic drug monitoring (TDM) of tacrolimus. This is the second consensus after the one issued in 2009. In this document, the role of tacrolimus TDM for the four principal transplanted organs is discussed. The analytical aspects, pharmacogenetics, TDM alternative approaches and the positioning of biomarkers are also presented. Stronger recommendations are about trough concentration targets in kidney and liver transplantation and for other indication of tacrolimus use. For the first time, an area under the curve of tacrolimus concentrations target is recommended for recipients management. Eventually, another set of recommendations are proposed for pharmacodynamic biomarkers used in patients' follow-up.

Immune monitoring after pediatric liver transplantation - the prospective ChilSFree cohort study

Background

Although trough levels of immunosuppressive drugs are largely used to monitor immunosuppressive therapy after solid organ transplantation, there is still no established tool that allows for a validated assessment of functional degree of immunosuppression or the identification of clinically relevant over- or under-immunosuppression, depending on graft homeostasis. Reliable non-invasive markers to predict biopsy proven acute rejection (BPAR) do not exist. Literature data suggest that longitudinal measurements of immune markers might be predictive of BPAR, but data in children are scarce. We therefore propose an observational prospective cohort study focusing on immune monitoring in children after liver transplantation. We aim to describe immune function in a cohort of children before and during the first year after liver transplantation and plan to investigate how the immune function profile is associated with clinical and laboratory findings.

Methods

In an international multicenter prospective approach, children with end-stage liver disease who undergo liver transplantation are enrolled to the study and receive extensive immune monitoring before and at 1, 2, 3, 4 weeks and 3, 6, 12 months after transplantation, and whenever a clinically indicated liver biopsy is scheduled. Blood samples are analyzed for immune cell numbers and circulating levels of cytokines, chemokines and factors of angiogenesis reflecting immune cell activation. Statistical analysis will focus on the identification of trajectorial patterns of immune reactivity predictive for systemic non-inflammatory states, infectious complications or BPAR using joint modelling approaches.

Discussion

The ChilSFree study will help to understand the immune response after pLTx in different states of infection or rejection. It may provide insight into response mechanisms eventually facilitating immune tolerance towards the graft. Our analysis may yield an applicable immune panel for non-invasive early detection of acute cellular rejection, with the prospect of individually tailoring immunosuppressive therapy. The international collaborative set-up of this study allows for an appropriate sample size which is otherwise difficult to achieve in the field of pediatric liver transplantation.

Active immunization in patients transplanted for hepatitis B virus related liver diseases: A prospective study

Introduction

Prophylactic administration of hepatitis B immunoglobulin (HBIG) and nucleos(t)ide analogues (NAs) is the standard treatment for controlling hepatitis B virus (HBV) recurrence after liver transplantation (LT). Since lifelong use of HBIG is expensive and inconvenient and the antibodies level in anti-hepatitis B surface (HBs) is not sustainable and stable, an alternative strategy is to produce anti-HBs antibodies by active immunization. Our present study aimed to prospectively investigate the efficacy and safety of procedural HBV vaccination in transplanted patients.

Methods

Recipients who had undergone LT for hepatitis B related liver diseases more than one year before, with no evidence of HBV recurrence or rejection and normal liver function were enrolled. All subjects received the hepatitis B vaccine (40 μg) by intramuscular injection at months 0, 1, 2, 6 and 12 after enrollment with continuous administration of NAs. The liver function and anti-HBs titers were measured before each vaccination and HBIG (400U) was administrated intramuscularly when anti-HBs titer was lower than 30 IU/L during the course. The results of routine blood tests, liver function, concentration of immunosuppressant, and HBV-DNA copies were monitored during the research. After completion of the vaccination procedure, recipients were regarded as responders if their anti-HBs greater than 30 IU/L were maintained for up to six months without using HBIG and vaccine.

Results

Twenty-seven patients were enrolled in this study and the average anti-HBs titer before vaccination was 19.86±14.80 IU/L. The average anti-HBs titer of the nine responders at the end of the follow-up was 57.14±22.75 IU/L, giving an overall response rate of 33.3% (9/27). There were no reports of reactivation of HBV, rejection, severe anaphylaxis or other adverse events. Responders and non-responders showed their significant difference in anti-HBs titers after the fourth vaccination (P<0.01). Moreover, the majority of non-responders (11/18, 63.64%) had high LY/EO rates (lymphocyte number/eosinophil number>15) while most responders (8/9, 88.89%) had low LY/EO rates at the beginning of vaccination (P = 0.019).

Conclusions

Active immunization is an effective, cost-saving, and safe method for the prevention of HBV reactivation in patients transplanted for hepatitis B virus related liver diseases. The LY/EO rate may be a valuable indicator in selecting potential recipients for vaccination.

The Effects of Tacrolimus on T-Cell Proliferation Are Short-Lived: A Pilot Analysis of Immune Function Testing

BACKGROUND

Optimal immunosuppression after organ transplant should balance the risks of rejection, infection, and malignancy while minimizing barriers to adherence including frequent or time-sensitive dosing. There is currently no reliable immune function assay to directly measure the degree of immunosuppression after transplantation.

METHODS

We developed an immune function assay to mea//sure T-cell proliferation after exposure to immunosuppression in vivo. We tested the assay in mice, and then piloted the approach using single time point samples, 11 pediatric kidney transplant recipients prescribed tacrolimus, mycophenolate, and prednisone 6 months to 5 years posttransplant, with no history of rejection, opportunistic infection, or cancer. Twelve healthy adults were controls.

RESULTS

We demonstrated that our assay can quantify suppression of murine T-cell proliferation after tacrolimus treatment in vivo. In humans, we found a mean 25% reduction in CD4 and CD8 T-cell proliferation in pediatric renal transplant recipients on triple immunosuppression compared with adult healthy controls, but the pilot results were not statistically significant nor correlated with serum tacrolimus levels. We observed that cell processing and washing reduced the effects of tacrolimus on T-cell proliferation, as did discontinuation of tacrolimus treatment shortly before sampling.

CONCLUSIONS

T-cell proliferation is currently not suitable to measure immunosuppression because sample processing diminishes observable effects. Future immune function testing should focus on fresh samples with minimal washing steps. Our results also emphasize the importance of adherence to immunosuppressive treatment, because T-cell proliferation recovered substantially after even brief discontinuation of tacrolimus.

Barcelona Consensus on Biomarker-Based Immunosuppressive Drugs Management in Solid Organ Transplantation

With current treatment regimens, a relatively high proportion of transplant recipients experience underimmunosuppression or overimmunosuppression. Recently, several promising biomarkers have been identified for determining patient alloreactivity, which help in assessing the risk of rejection and personal response to the drug; others correlate with graft dysfunction and clinical outcome, offering a realistic opportunity for personalized immunosuppression. This consensus document aims to help tailor immunosuppression to the needs of the individual patient. It examines current knowledge on biomarkers associated with patient risk stratification and immunosuppression requirements that have been generally accepted as promising. It is based on a comprehensive review of the literature and the expert opinion of the Biomarker Working Group of the International Association of Therapeutic Drug Monitoring and Clinical Toxicology. The quality of evidence was systematically weighted, and the strength of recommendations was rated according to the GRADE system. Three types of biomarkers are discussed: (1) those associated with the risk of rejection (alloreactivity/tolerance), (2) those reflecting individual response to immunosuppressants, and (3) those associated with graft dysfunction. Analytical aspects of biomarker measurement and novel pharmacokinetic-pharmacodynamic models accessible to the transplant community are also addressed. Conventional pharmacokinetic biomarkers may be used in combination with those discussed in this article to achieve better outcomes and improve long-term graft survival. Our group of experts has made recommendations for the most appropriate analysis of a proposed panel of preliminary biomarkers, most of which are currently under clinical evaluation in ongoing multicentre clinical trials. A section of Next Steps was also included, in which the Expert Committee is committed to sharing this knowledge with the Transplant Community in the form of triennial updates.

T-Cell Cytokines as Predictive Markers of the Risk of Allograft Rejection

Over the last decade, several biomarkers and surrogate markers have surfaced as promising predictive markers of risk of rejection in solid organ transplantation. The monitoring of these markers can help to improve graft and recipient care by personalizing immunomodulatory therapies. The complex immune system response against an implanted graft can change during long-term follow-up, and the dynamic balance between effector and regulatory T-cell populations is a crucial factor in antidonor response, risk of rejection, and immunosuppression requirements. Therefore, at any time before and after transplantation, T-effector activity, which is associated with increased production and release of proinflammatory cytokines, can be a surrogate marker of the risk of rejection and need for immunosuppression. In addition, immunosuppressive drugs may have a different effect in each individual patient. The pharmacokinetics and pharmacodynamics of these drugs show high interpatient variability, and pharmacodynamic markers, strongly associated with the specific mechanism of action, can potentially be used to measure individual susceptibility to a specific immunosuppressive agent. The monitoring of a panel of valid biomarkers can improve patient stratification and the selection of immunosuppressive drugs. After transplantation, therapy can be adjusted based on the prediction of rejection episodes (maintained alloreactivity), the prognosis of allograft damage, and the individual's response to the drugs. This review will focus on current data indicating that changes in the T-cell production of the intracellular cytokines interferon-γ and interleukin-2 could be used to predict the risk of rejection and to guide immunosuppressive therapy in transplant recipients.

Analytical Aspects of the Implementation of Biomarkers in Clinical Transplantation

In response to the urgent need for new reliable biomarkers to complement the guidance of the immunosuppressive therapy, a huge number of biomarker candidates to be implemented in clinical practice have been introduced to the transplant community. This includes a diverse range of molecules with very different molecular weights, chemical and physical properties, ex vivo stabilities, in vivo kinetic behaviors, and levels of similarity to other molecules, etc. In addition, a large body of different analytical techniques and assay protocols can be used to measure biomarkers. Sometimes, a complex software-based data evaluation is a prerequisite for appropriate interpretation of the results and for their reporting. Although some analytical procedures are of great value for research purposes, they may be too complex for implementation in a clinical setting. Whereas the proof of "fitness for purpose" is appropriate for validation of biomarker assays used in exploratory drug development studies, a higher level of analytical validation must be achieved and eventually advanced analytical performance might be necessary before diagnostic application in transplantation medicine. A high level of consistency of results between laboratories and between methods (if applicable) should be obtained and maintained to make biomarkers effective instruments in support of therapeutic decisions. This overview focuses on preanalytical and analytical aspects to be considered for the implementation of new biomarkers for adjusting immunosuppression in a clinical setting and highlights critical points to be addressed on the way to make them suitable as diagnostic tools. These include but are not limited to appropriate method validation, standardization, education, automation, and commercialization.

Pharmacodynamics of T cell function for monitoring pharmacologic immunosuppression after allogeneic hematopoietic stem cell transplantation

Information on pharmacodynamic monitoring after allogeneic hematopoietic cell transplantation (allo-SCT) to evaluate individual responses to immunosuppressive drugs is scarce. We studied the relationship between a panel of pharmacodynamic markers monitored during the first 3 months after transplant and the occurrence of graft-versus-host disease (GVHD). Lymphocyte activation assessed by intracellular ATP concentration in CD4⁺ T cells, a high percentage of CD8⁺ effector T cells, and a low percentage of CD4⁺ regulatory T (Treg) cells correlated significantly with GVHD. A cutoff value of 0.5 for the CD8⁺ effector T/Treg ratio provided the most accurate diagnosis of GVHD (sensitivity 58.8%, specificity 91%). These pharmacodynamic markers may provide an efficient complement to standard pharmacokinetic monitoring of immunosuppressive drugs after allo-SCT.

Tacrolimus Pharmacodynamics and Pharmacogenetics along the Calcineurin Pathway in Human Lymphocytes

BACKGROUND

Although therapeutic drug monitoring has improved the clinical use of immunosuppressive drugs, there is still interpatient variability in efficacy and toxicity that pharmacodynamic monitoring may help to reduce. To select the best biomarkers of tacrolimus pharmacodynamics, we explored the strength and variability of signal transduction and the influence of polymorphisms along the calcineurin pathway.

METHODS

Peripheral blood mononuclear cells from 35 healthy volunteers were incubated with tacrolimus (0.1–50 ng/mL) and stimulated ex vivo. Inhibition of NFAT1 (nuclear factor of activated T cells 1) translocation to the nucleus and intracellular expression of interleukin-2 in CD4+ and CD8+ T cells and the surface activation marker CD25 in CD3+ cells were measured by flow cytometry. We sequenced the promoter regions of immunophilins and calcineurin subunits and characterized selected single nucleotide polymorphisms in the genes of the calcineurin pathway with allelic discrimination assays.

RESULTS

All responses closely fitted an I/Imax sigmoid model. Large interindividual variability (n = 30) in I0 and IC50 was found for all biomarkers. Moreover, strong and statistically significant associations were found between tacrolimus pharmacodynamic parameters and polymorphisms in the genes coding cyclophilin A, the calcineurin catalytic subunit α isoenzyme, and CD25.

CONCLUSIONS

This study demonstrates the consistency and large interindividual variability of signal transduction along the calcineurin pathway, as well as the strong influence of pharmacogenetic polymorphisms in the calcineurin cascade on both the physiological activity of this route and tacrolimus pharmacodynamics.

Peripheral blood biomarkers for the characterization of alloimmune reactivity after pediatric liver transplantation

Individualization of immunosuppressive medications is an important objective in transplantation medicine. Reliable biomarkers to distinguish between patients dependent from intensive immunosuppressive therapy and those where therapy can be minimized among pediatric transplant recipients receiving immunosuppressive medications are still not established. We evaluated the potential of cross-sectional quantification of regulatory T cells, lymphocyte subsets, and cytokine concentrations as biomarkers in 60 pediatric liver transplant recipients with AR, CR, or normal graft function and in 11 non-transplanted patients. Transplant recipients presenting with AR had significantly higher CD8+ T-cell counts, significantly higher concentrations of IL-2, and increased levels of IFN-γ compared with asymptomatic patients or controls. Regulatory T-cell numbers did not differ between children with rejection and children with good graft function. A tendency toward increased concentrations of IL-4 and TGF-β was detected in transplant recipients with good graft function. Cross-sectional parameters of peripheral regulatory T cells in pediatric liver transplant recipients do not seem to be valuable biomarkers for individualizing immunosuppressive therapy prior to the weaning process. Lymphocyte subsets, IL-2, IFN-γ, IL-4, and TGF-β serum concentrations may be helpful to identify children in whom immunosuppression can be reduced or discontinued.

Differential expression of proteins in naïve and IL-2 stimulated primary human NK cells identified by global proteomic analysis

Natural killer (NK) cells efficiently cytolyse tumors and virally infected cells. Despite the important role that interleukin (IL)-2 plays in stimulating the proliferation of NK cells and increasing NK cell activity, little is known about the alterations in the global NK cell proteome following IL-2 activation. To compare the proteomes of naïve and IL-2-activated primary NK cells and identify key cellular pathways involved in IL-2 signaling, we isolated proteins from naïve and IL-2-activated NK cells from healthy donors, the proteins were trypsinized and the resulting peptides were analyzed by 2D LC ESI-MS/MS followed by label-free quantification. In total, more than 2000 proteins were identified from naïve and IL-2-activated NK cells where 383 proteins were found to be differentially expressed following IL-2 activation. Functional annotation of IL-2 regulated proteins revealed potential targets for future investigation of IL-2 signaling in human primary NK cells. A pathway analysis was performed and revealed several pathways that were not previously known to be involved in IL-2 response, including ubiquitin proteasome pathway, integrin signaling pathway, platelet derived growth factor (PDGF) signaling pathway, epidermal growth factor receptor (EGFR) signaling pathway and Wnt signaling pathway.

BIOLOGICAL SIGNIFICANCE

The development and functional activity of natural killer (NK) cells is regulated by interleukin (IL)-2 which stimulates the proliferation of NK cells and increases NK cell activity. With the development of IL-2-based immunotherapeutic strategies that rely on the IL-2-mediated activation of NK cells to target human cancers, it is important to understand the global molecular events triggered by IL-2 in human NK cells. The differentially expressed proteins in human primary NK cells following IL-2 activation identified in this study confirmed the activation of JAK-STAT signaling pathway and cell proliferation by IL-2 as expected, but also led to the discovery and identification of other factors that are potentially important in IL-2 signaling. These new factors warrant further investigation on their potential roles in modulating NK cell biology. The results from this study suggest that the activation of NK cells by IL-2 is a dynamic process through which proteins with various functions are regulated. Such findings will be important for the elucidation of molecular pathways involved in IL-2 signaling in NK cells and provide new targets for future studies in NK cell biology.

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.

Intracellular IFN-γ and IL-2 expression monitoring as surrogate markers of the risk of acute rejection and personal drug response in de novo liver transplant recipients

Biomarker monitoring is needed in transplantation to reflect individual response to immunosuppressive drugs and graft outcome. We evaluated intracellular expression and soluble production of interferon-(IFN)-γ and interleukin-(IL)-2 as predictive biomarkers of acute rejection (AR) and personal drug response. Pharmacokinetic-pharmacodynamic profiles were determined in 47 de novo liver recipients treated with tacrolimus, mycophenolate mofetil and prednisone. Of the 47 patients, AR occurred in nine. There were no differences in drug concentrations between rejectors and non-rejectors. A pre-transplantation cut-off value of 55.80% for %CD8(+)-IFN-γ(+) identified patients at high risk of AR with a sensitivity of 75% and a specificity of 82%. In the first week post-transplantation, patients with a % inhibition for soluble IFN-γ, %CD8(+)-IFN-γ(+) and %CD8(+)-IL2(+) lower than 40% developed AR, showing low susceptibility to immunosuppressive drugs. Therefore, effector-T-cell response monitoring may help physicians to identify personal response to treatment and patients at high risk of AR.

Effect of CD200 and CD200R1 expression within tissue grafts on increased graft survival in allogeneic recipients

In transgenic mice over-expressing CD200 (CD200(tg)) graft survival is associated with increased intra-graft expression of mRNAs for genes associated with altered T cell subset differentiation (Foxp3; TGFβ; IL-10). Grafts are rejected in recipients lacking the inhibitory receptor for CD200, CD200R1. We compared grafts of C57BL/6 skin taken from control, CD200KO, CD200(tg), CD200R1KO or CD200(tg).CD200R1KO C57BL/6 donor mice transplanted to control or CD200(tg) BALB/c recipients. Animals received either low-dose rapamycin (0.5mg/kg), which only enhanced survival in CD200(tg) mice, or high dose rapamycin (1.5mg/kg) which increased graft survival in all recipients. Recipient draining lymph nodes (DLNs) were analyzed at 14days post grafting in mixed leukocyte cultures (MLCs) with irradiated BL/6 or C3H/HeJ stimulator cells, assaying antigen-specific CTL at day 5. MLC responses were correlated with changes in mRNA gene expression in skin tissue harvested from the same recipients, focusing on genes altered in "graft-accepting" CD200(tg) recipients. Tissue histology was used to assess graft infiltrating Foxp3(+) Tregs, mast cells (MCs) and their degranulation. CD200(tg) grafts were accepted in control but not CD200KO/CD200R1KO recipients, along with decreased degranulation in graft MCs, diminished DLN MLC responses, and augmented intragraft Foxp3, TGFβ, IL-10 and mast cell gene expression. Skin grafts from either CD200KO or CD200R1KO donors to control mice were rejected, with no change in DLN MLC responses, no altered graft gene expression from that seen using control skin grafts, and pronounced graft MC degranulation. Our data highlight a role for both graft and host CD200/CD200R expression in increased allograft survival.

The association between cytokine gene polymorphisms and graft rejection in liver transplantation: a systematic review and meta-analysis

We investigated the contribution of polymorphisms in cytokine genes (TNFa-308, IL10-1082 and -592, TGFb1-c10 and c25, and IFNg+874) on the risk of graft rejection in liver transplantation. We performed a systematic review by identifying relevant studies and applied meta-analysis to pool gene effects. In total, 12 studies were eligible and included in the study. Data extraction and assessments for risk of bias were independently performed by two reviewers. Data for allele frequencies, allelic, and genotypic effects were pooled. Heterogeneity and publication bias were assessed. Pooled minor allele frequencies for TNFa-308, IL10-1082, TGFb1-c10, TGFb1-c25, IFNg+874, and IL10-592 were 0.140 (95% CI: 0.083, 0.198), 0.432 (95% CI: 0.392, 0.472), 0.387 (95% CI: 0.307, 0.467), 0.090 (95% CI: 0.056, 0.123), 0.460 (95% CI: 0.392, 0.528), and 0.224 (95% CI: 0.178, 0.269), respectively. OnlyTNFa-308 and IL10-1082 polymorphisms were significantly associated with graft rejection. Patients who carried minor homozygous genotypes for these two polymorphisms were at 3.5 and 1.69 times higher risk of graft rejections than patients who carried major homozygous genotypes. The estimated lambdas were 0.41 and 0.47, suggesting an additive mode of effect was most likely. However, we could not detect the associations of TGFb1at c10 and c25, INFg+874, and IL10-592 polymorphisms and graft rejection. In summary, our systematic review has demonstrated that TNFa-308 and IL10-1082 are potential risk factors of poor outcomes in liver transplantation. Future updated meta-analysis studies to confirm the power of these genotypes in association with allograft rejection are needed.

Flow cytometry: a flexible tool for biomarker research

Flow cytometry is increasingly recognized as an invaluable technology in biomarker research. Owing to its multiparametric nature it can provide highly detailed information on any single cell in a heterogeneous population. Its versatility means it can be conducted in both the preclinical and clinical setting, generating biomarker data that can drive decisions pertaining to dose selection in clinical trials, treatment options for cancer sufferers and even suitability of patients to receive transplants. Most tissue types can be utilized by the flow cytometrist, allowing the technology to be applied to many fields of research, yet consensus still needs to be reached on standardization, regulation and validation of multiparametric flow cytometry assays. In parallel, continual innovation in analysis software to manage the huge datasets that can be generated is also needed. Nevertheless, the flexibility of flow cytometry means that it remains at the forefront of both routine and exploratory biomarker studies.

Persistence of gene expression profile in CD200 transgenic skin allografts is associated with graft survival on retransplantation to normal recipients

BACKGROUND

Expression of CD200 increases allograft survival by suppressing inflammation and acquired immunity. Increased allograft survival in transgenic mice overexpressing CD200 (CD200) occurs in association with increased intragraft expression of messenger RNAs (mRNAs) for genes associated with altered T-cell differentiation.

METHODS

We investigated whether donor CD200 BL/6 skin grafts taken from primary control or CD200 recipient BALB/c mice persisted after retransplantation at 14 days to control (nontransgenic) secondary BALB/c recipients, with or without transfer of splenocytes from autologous primary recipients. Splenocytes from primary and secondary recipients were analyzed 14 days after grafting, using in vitro mixed leukocyte cultures (MLCs) incubated with irradiated BL/6 (or third-party C3H/HeJ) stimulator cells and assayed for antigen-specific cytotoxic T lymphocyte. Cytotoxic T lymphocyte responses were correlated with changes in the mRNA gene expression profile observed in the skin tissue harvested from primary or secondary recipients on day 14 after grafting, using real-time polymerase chain reaction to compare quantitative mRNA expression in the graft tissue of primary/secondary recipients.

RESULTS AND CONCLUSIONS

Adoptive transfer of tolerance in MLC to BL/6 grafts was most evident when both skin and splenocytes were transferred from primary BALB/c recipients, although there was an attenuation of MLC responses after graft transfer alone. Adoptive transfer of tolerance occurred concomitant with persistent overexpression of genes encoding Foxp3, transforming growth factor β, interleukin 10, and PD-1 (and PD-L1/PD-L2) in tolerant skin grafts and increased expression of mRNAs for indoleamine 2,3-dioxygenase and the subunits encoding interleukin 35. Infusion of anti-CD4 or anti-transforming growth factor β to secondary recipients on retransplantation abolished increased graft survival, suggesting the importance of each to the final outcome.

Identification of a novel biomarker gene set with sensitivity and specificity for distinguishing between allograft rejection and tolerance

Here we examined whether the expression of a novel immunoregulatory gene set could be used to predict outcomes in murine models of rapamycin-induced cardiac tolerance, spontaneous hepatic tolerance, and cardiac rejection. The expression of the immunoregulatory gene set was assessed with the GeXP multiplex reverse-transcription polymerase chain reaction (RT-PCR) analysis system, and it was correlated to the pathological and biochemical parameters of the allografts. In rejecting cardiac grafts, the increased expression of an inflammatory set of genes, which included CD45, CD4, CD25, suppressor of cytokine signaling 2, cytotoxic T lymphocyte-associated protein 4 (CTLA4), selectin lymphocyte, interferon-γ (IFN-γ), programmed cell death 1 (Pdcd1), and granzyme B (Gzmb), was seen 8 days after transplantation along with histological evidence of severe allograft rejection. In tolerant cardiac allografts, the expression of fibrinogen-like protein 2 (Fgl2), Pdcd1, killer cell lectin-like receptor G1 (Klrg1), CTLA4, and lymphocyte-activation gene 3 was associated with tolerance. In a model of liver allograft tolerance, the increased expression of lectin galactose-binding soluble 1, Fgl2, CD39, phosphodiesterase 3B, Klrg1, forkhead box P3 (Foxp3), and transforming growth factor β as well as the inflammatory set of genes was observed 8 to 14 days after transplantation (ie, when there was severe inflammatory injury). At a later time when the liver allografts had been fully accepted and were histologically normal, the expression of the inflammatory set of genes returned to the baseline, but the expression of the tolerogenic set of genes was still increased. Genes that were expressed in tolerant cardiac and liver allografts included Fgl2, Klrg1, and Foxp3, whereas genes associated with rejection included CD25, Gzmb, and IFN-γ. Our data indicate that monitoring the graft expression of a novel biomarker gene set with the GeXP multiplex RT-PCR analysis system may allow differentiation between rejection and tolerance.

Recent advances in biomarker discovery in solid organ transplant by proteomics

The identification and clinical use of more sensitive and specific biomarkers in the field of solid organ transplantation is an urgent need in medicine. Solid organ transplantation has seen improvements in the short-term survival of transplanted organs due to recent advancements in immunosuppressive therapy. However, the currently available methods of allograft monitoring are not optimal. Recent advancements in assaying methods for biomolecules such as genes, mRNA and proteins have helped to identify surrogate biomarkers that can be used to monitor the transplanted organ. These high-throughput 'omic' methods can help researchers to significantly speed up the identification and the validation steps, which are crucial factors for biomarker discovery efforts. Still, the progress towards identifying more sensitive and specific biomarkers remains a great deal slower than expected. In this article, we have evaluated the current status of biomarker discovery using proteomics tools in different solid organ transplants in recent years. This article summarizes recent reports and current status, along with the hurdles in efficient biomarker discovery of protein biomarkers using proteomics approaches. Finally, we will touch upon personalized medicine as a future direction for better management of transplanted organs, and provide what we think could be a recipe for success in this field.

Matchmaking the B-cell signature of tolerance to regulatory B cells

Confirmation of clinical tolerance requires the cessation of immunosuppressive drugs, which evoke immune reactivation and allograft rejection in all but the rare individuals who successfully transition into a state of operational transplantation tolerance. Therefore, the safe conduct of trials in transplantation tolerance requires two conditions: a sensitive and reliable means to identify individuals still being maintained on immunosuppression who are most likely to exhibit tolerance after immunosuppression is withdrawn and a noninvasive means that assesses the quality or robustness of the tolerant (TOL) state. Two recent studies attempting to identify a gene signature in peripheral blood of spontaneously TOL kidney transplant recipients made the unexpected observation that TOL, but not immune-suppressed transplant recipients, exhibited enriched B cells and B-cell transcripts in their blood. In concert with the emerging appreciation of a specialized subset of regulatory B cells (Bregs) that possess immune-modulatory function, these observations raise the possibility that Bregs play a critical role in the maintenance of tolerance to renal allografts in transplant patients. This review summarizes these recent findings and speculates on the relationship of Bregs to the maintenance of transplantation tolerance.

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.

Clinical transplantation tolerance

Transplantation is the treatment of choice for many if not most causes of end-stage organ failure. Over 20,000 organ transplant procedures were performed in the USA in 2009 to treat patients with failed or failing kidneys, livers, hearts, lungs, and intestines, and there remain 85,000 individuals waiting on the transplant list. Currently, in the USA, there are over 170,000 individuals living with a transplanted organ. Virtually, all of these individuals receive maintenance immunosuppression in an attempt to maximize the function and survival of the transplanted organ. However, it is clear that the long-term use of immunosuppressive agents is associated with an extensive list of undesirable side effects that have the potential to limit the survival of the patient and transplanted organ as well as to compromise quality of life. Although the ability to induce reproducibly a state of robust, stable tolerance would address this problem, tolerance remains an infrequent event in clinical transplantation that is largely a consequence of chance. Factors limiting the broader investigation of clinical transplantation tolerance include the lack of therapeutic regimens known to favor tolerance in humans, the lack of validated assays or biomarkers predictive of tolerance, and concerns about the safety and ethics of complete withdrawal of immunosuppression given the very good results achievable with current immunosuppression. Despite these barriers, a number of investigators have continued to conduct well-designed and carefully supervised studies with the long-term goal of making clinical transplantation tolerance more feasible. The aim of this review is to summarize the status of these studies.