Assessing relative risks of infection and rejection: a meta-analysis using an immune function assay

Biomarkers in Kidney Transplantation

Currently in the United States, there are more than 250,000 patients with a functioning kidney allograft and over 100,000 waitlisted patients awaiting kidney transplant, with a burgeoning number added to the kidney transplant wait list every year. Although early post-transplant care is delivered at the transplant center, the increasing number of kidney transplant recipients requires general nephrologists to actively participate in the long-term care of these patients. Serum creatinine and proteinuria are imperfect traditional biomarkers of allograft dysfunction and lag behind subclinical allograft injury. This manuscript reviews the various clinically available biomarkers in the field of kidney transplantation for a general nephrologist with a focus on the utility of donor-derived cell-free DNA, as a marker of early allograft injury. Blood gene expression profiling, initially studied in the context of early identification of subclinical rejection, awaits validation in larger multicentric trials. Urinary cellular messenger ribonucleic acid and chemokine CXCL10 hold promising potential for early diagnosis of both subclinical and acute rejection. Torque tenovirus, a ubiquitous DNA virus is emerging as a biomarker of immunosuppression exposure as peripheral blood torque tenovirus copy numbers might mirror the intensity of host immunosuppression. Although high-quality evidence is still being generated, evidence and recommendations are provided to aid the general nephrologist in implementation of novel biomarkers in their clinical practice.

Biomarkers in Kidney Transplantation: A Rapidly Evolving Landscape

The last decade has seen an explosion in clinical research focusing on the use of noninvasive biomarkers in kidney transplantation. Much of the published literature focuses on donor-derived cell-free DNA (dd-cfDNA). Although initially studied as a noninvasive means of identifying acute rejection, it is now clear that dd-cfDNA is more appropriately described as a marker of severe injury and irrespective of the etiology, elevated dd-cfDNA ≥0.5% portends worse graft outcomes. Blood gene expression profiling is also commercially available and has mostly been studied in the context of early identification of subclinical rejection, although additional data is needed to validate these findings. Torque teno virus, a ubiquitous DNA virus, has emerged as a biomarker of immunosuppression exposure as peripheral blood Torque teno virus copy numbers might mirror the intensity of host immunosuppression. Urinary chemokine tests including C-X-C motif chemokine ligand 9 and C-X-C motif chemokine ligand 10 have recently been assessed in large clinical trials and hold promising potential for early diagnosis of both subclinical and acute rejection, as well as, for long-term prognosis. Urinary cellular messenger RNA and exosome vesicular RNA based studies require additional validation. Although current data does not lend itself to conclusion, future studies on multimodality testing may reveal the utility of serial surveillance for individualization of immunosuppression and identify windows of opportunity to intervene early and before the irreversible allograft injury sets in.

Whole blood stimulation as a tool for studying the human immune system

The human immune system is best accessible via tissues and organs not requiring major surgical intervention, such as blood. In many circumstances, circulating immune cells correlate with an individual's health state and give insight into physiological and pathophysiological processes. Stimulating whole blood ex vivo is a powerful tool to investigate immune responses. In the context of clinical research, the applications of whole blood stimulation include host immunity, disease characterization, diagnosis, treatment, and drug development. Here, we summarize different setups and readouts of whole blood assays and discuss applications for preclinical research and clinical practice. Finally, we propose combining whole blood stimulation with high-throughput technologies, such as single-cell RNA-sequencing, to comprehensively analyze the human immune system for the identification of biomarkers, therapeutic interventions as well as companion diagnostics.

The Role of Vasculature and Angiogenic Strategies in Bone Regeneration

Bone regeneration is a complex process that involves various growth factors, cell types, and extracellular matrix components. A crucial aspect of this process is the formation of a vascular network, which provides essential nutrients and oxygen and promotes osteogenesis by interacting with bone tissue. This review provides a comprehensive discussion of the critical role of vasculature in bone regeneration and the applications of angiogenic strategies, from conventional to cutting-edge methodologies. Recent research has shifted towards innovative bone tissue engineering strategies that integrate vascularized bone complexes, recognizing the significant role of vasculature in bone regeneration. The article begins by examining the role of angiogenesis in bone regeneration. It then introduces various in vitro and in vivo applications that have achieved accelerated bone regeneration through angiogenesis to highlight recent advances in bone tissue engineering. This review also identifies remaining challenges and outlines future directions for research in vascularized bone regeneration.

Immune monitoring of allograft status in kidney transplant recipients

Kidney transplant patients require careful management of immunosuppression to avoid rejection while minimizing the risk of infection and malignancy for the best long-term outcome. The gold standard for monitoring allograft status and immunosuppression adequacy is a kidney biopsy, but this is invasive and costly. Conventional methods of allograft monitoring, such as serum creatinine level, are non-specific. Although they alert physicians to the need to evaluate graft dysfunction, by the time there is a clinical abnormality, allograft damage may have already occurred. The development of novel and non-invasive methods of evaluating allograft status are important to improving graft outcomes. This review summarizes the available conventional and novel methods for monitoring allograft status after kidney transplant. Novel and less invasive methods include gene expression, cell-free DNA, urinary biomarkers, and the use of artificial intelligence. The optimal method to manage patients after kidney transplant is still being investigated. The development of less invasive methods to assess allograft function has the potential to improve patient outcomes and allow for a more personalized approach to immunosuppression management.

Selection and Interpretation of Molecular Diagnostics in Heart Transplantation

The number of heart transplants performed annually in the United States and worldwide continues to increase, but there has been little change in graft longevity and patient survival over the past 2 decades. The reference standard for diagnosis of acute cellular and antibody-mediated rejection includes histologic and immunofluorescence evaluation of endomyocardial biopsy samples, despite invasiveness and high interrater variability for grading histologic rejection. Circulating biomarkers and molecular diagnostics have shown substantial predictive value in rejection monitoring, and emerging data support their use in diagnosing other posttransplant complications. The use of genomic (cell-free DNA), transcriptomic (mRNA and microRNA profiling), and proteomic (protein expression quantitation) methodologies in diagnosis of these posttransplant outcomes has been evaluated with varying levels of evidence. In parallel, growing knowledge about the genetically mediated immune response leading to rejection (immunogenetics) has enhanced understanding of antibody-mediated rejection, associated graft dysfunction, and death. Antibodies to donor human leukocyte antigens and the technology available to evaluate these antibodies continues to evolve. This review aims to provide an overview of biomarker and immunologic tests used to diagnose posttransplant complications. This includes a discussion of pediatric heart transplantation and the disparate rates of rejection and death experienced by Black patients receiving a heart transplant. This review describes diagnostic modalities that are available and used after transplant and the landscape of future investigations needed to enhance patient outcomes after heart transplantation.

Contemporary Biomarkers for Renal Transplantation: A Narrative Overview

Renal transplantation (RT) is the preferred treatment for end-stage renal disease. However, clinical challenges persist, i.e., early detection of graft dysfunction, timely identification of rejection episodes, personalization of immunosuppressive therapy, and prediction of long-term graft survival. Biomarkers have emerged as valuable tools to address these challenges and revolutionize RT patient care. Our review synthesizes the existing scientific literature to highlight promising biomarkers, their biological characteristics, and their potential roles in enhancing clinical decision-making and patient outcomes. Emerging non-invasive biomarkers seemingly provide valuable insights into the immunopathology of nephron injury and allograft rejection. Moreover, we analyzed biomarkers with intra-nephron specificities, i.e., glomerular vs. tubular (proximal vs. distal), which can localize an injury in different nephron areas. Additionally, this paper provides a comprehensive analysis of the potential clinical applications of biomarkers in the prediction, detection, differential diagnosis and assessment of post-RT non-surgical allograft complications. Lastly, we focus on the pursuit of immune tolerance biomarkers, which aims to reclassify transplant recipients based on immune risk thresholds, guide personalized immunosuppression strategies, and ultimately identify patients for whom immunosuppression may safely be reduced. Further research, validation, standardization, and prospective studies are necessary to fully harness the clinical utility of RT biomarkers and guide the development of targeted therapies.

The End of Endomyocardial Biopsy?: A Practical Guide for Noninvasive Heart Transplant Rejection Surveillance

Noninvasive heart transplant rejection surveillance using gene expression profiling (GEP) to monitor immune activation is widely used among heart transplant programs. With the new development of donor-derived cell-free DNA (dd-cfDNA) assays, more programs are transitioning to a predominantly noninvasive rejection surveillance protocol with a reduced frequency of endomyocardial biopsies. As a result, many practical questions arise that potentially delay implementation of these valuable new tools. The purpose of this review is to provide practical guidance for clinicians transitioning toward a less invasive acute rejection monitoring protocol after heart transplantation, and to answer 10 common questions about the GEP and dd-cfDNA assays. Evidence supporting GEP and dd-cfDNA testing is reviewed, as well as guidance on test interpretation and future directions.

Immune cell function assay and T lymphocyte counts lack association with rejection or infection in pediatric heart transplant recipients

INTRODUCTION

Immune cell function assay (ICFA) and CD3 lymphocyte counts have been considered to be useful in discerning the overall intensity of immunosuppression in pediatric orthotopic heart transplant (OHT) recipients.

METHODS

The aim of this retrospective analysis was to evaluate trends of ICFA and CD3 lymphocyte counts and their association with adverse outcomes post-OHT.

RESULTS

A total of 381 ICFA and 493 CD3 laboratory values obtained in 78 patients within six months post-OHT were analyzed. There were 14 patients treated for biopsy-proven acute rejection, four of whom had ISHLT grade 2R/3A rejection. In patients with rejection versus those without, CD3 and ICFA values were 122 (IQR 74.5-308) cells/mm² and 224.5 (IQR 132-343.5) ng/ml compared to 231.8 (IQR 68-421) cells/m² and 191 (IQR 81.5-333) ng/mL (p = NS for both). Twenty-six patients had at least one detectable cytomegalovirus or Epstein-Barr virus DNAemia within the study timeframe. In patients with viremia versus those without, CD3 and ICFA values were 278.5 (IQR 68-552) cells/mm² and 130 (IQR 48-284) ng/ml compared to 195 (IQR 74.5-402.5) cells/mm² and 212 (IQR 89-342) ng/ml (p = NS for both).

CONCLUSIONS

No association was found between these immune markers and adverse outcomes. In the absence of larger pediatric studies justifying the role of these tests in identifying elevated risk profiles post OHT, we do not recommend their routine use.

Integrated Immunologic Monitoring in Solid Organ Transplantation: The Road Toward Torque Teno Virus-guided Immunosuppression

Potent immunosuppressive drugs have been introduced into clinical care for solid organ transplant recipients. It is now time to guide these drugs on an individual level to optimize their efficacy. An ideal tool simultaneously detects overimmunosuppression and underimmunosuppression, is highly standardized, and is straightforward to implement into routine. Randomized controlled interventional trials are crucial to demonstrate clinical value. To date, proposed assays have mainly focused on the prediction of rejection and were based on the assessment of few immune compartments. Recently, novel tools have been introduced based on a more integrated approach to characterize the immune function and cover a broader spectrum of the immune system. In this respect, the quantification of the plasma load of a highly prevalent and apathogenic virus that might reflect the immune function of its host has been proposed: the torque teno virus (TTV). Although TTV control is driven by T cells, other major immune compartments might contribute to the hosts' response. A standardized in-house polymerase chain reaction and a conformité européenne-certified commercially available polymerase chain reaction are available for TTV quantification. TTV load is associated with rejection and infection in solid organ transplant recipients, and cutoff values for risk stratification of such events have been proposed for lung and kidney transplantation. Test performance of TTV load does not allow for the diagnosis of rejection and infection but is able to define at-risk patients. Hitherto TTV load has not been used in interventional settings, but two interventional randomized controlled trials are currently testing the safety and efficacy of TTV-guided immunosuppression.

Biomarker-Based Assessment for Infectious Risk Before and After Heart Transplantation

Purpose of Review

Survival outcomes for heart transplant recipients have improved in recent decades, but infection remains a significant cause of morbidity and mortality. In this review, we discuss several biological markers, or biomarkers, that may be used to monitor immunologic status in this patient population.

Recent Findings

While modest, data on the utility of immune biomarkers in heart transplant recipients suggest correlation between low level of immune response and increased infection risk. More novel assays, such as the detection of circulating levels of pathogen cell-free DNA in plasma and the use of Torque teno virus load as a surrogate for net state of immunosuppression, have potential to be additional important biomarkers.

Summary

Biomarker approaches to individualize immunosuppression therapy among heart transplant recipients is a promising area of medicine. However, additional studies are needed to inform the optimal protocol in which to incorporate these biomarkers into clinical practice.

Prediction of Liver Transplant Rejection With a Biologically Relevant Gene Expression Signature

BACKGROUND

Noninvasive biomarkers distinguishing early immune activation before acute rejection (AR) could more objectively inform immunosuppression management in liver transplant recipients (LTRs). We previously reported a genomic profile distinguishing LTR with AR versus stable graft function. This current study includes key phenotypes with other causes of graft dysfunction and uses a novel random forest approach to augment the specificity of predicting and diagnosing AR.

METHODS

Gene expression results in LTRs with AR versus non-AR (combination of other causes of graft dysfunction and normal function) were analyzed from single and multicenter cohorts. A 70:30 approach (61 ARs; 162 non-ARs) was used for training and testing sets. Microarray data were normalized using a LT-specific vector.

RESULTS

Random forest modeling on the training set generated a 59-probe classifier distinguishing AR versus non-AR (area under the curve 0.83; accuracy 0.78, sensitivity 0.70, specificity 0.81, positive predictive value 0.54, negative predictive value [NPV] 0.89; F-score 0.61). Using a locked threshold, the classifier performed well on the testing set (accuracy 0.72, sensitivity 0.67, specificity 0.73, positive predictive value 0.48, NPV 0.86; F-score 0.56). Probability scores increased in samples preceding AR versus non-AR, when liver function tests were normal, and decreased following AR treatment (P < 0.001). Ingenuity pathway analysis of the genes revealed a high percentage related to immune responses and liver injury.

CONCLUSIONS

We have developed a blood-based biologically relevant biomarker that can be detected before AR-associated graft injury distinct from LTR never developing AR. Given its high NPV ("rule out AR"), the biomarker has the potential to inform precision-guided immunosuppression minimization in LTRs.

Donor-derived cell-free DNA levels predict graft injury in liver transplant recipients

Donor-derived cell-free DNA (dd-cfDNA) has been evaluated as a rejection marker in organ transplantation. This study sought to assess the utility of dd-cfDNA to diagnose graft injury in liver transplant recipients (LTR) and as a predictive biomarker prior to different causes of graft dysfunction. Plasma from single and multicenter LTR cohorts was analyzed for dd-cfDNA. Phenotypes of treated biopsy-proven acute rejection (AR, N = 57), normal function (TX, N = 94), and acute dysfunction no rejection (ADNR; N = 68) were divided into training and test sets. In the training set, dd-cfDNA was significantly different between AR versus TX (AUC 0.95, 5.3% cutoff) and AR versus ADNR (AUC 0.71, 20.4% cutoff). Using these cutoffs in the test set, the accuracy and NPV were 87% and 100% (AR vs. TX) and 66.7% and 87.8% (AR vs. ADNR). Blood samples collected serially from LTR demonstrated incremental elevations in dd-cfDNA prior to the onset of graft dysfunction (AR > ADNR), but not in TX. Dd-cfDNA also decreased following treatment of rejection. In conclusion, the serial elevation of dd-cfDNA identifies pre-clinical graft injury in the context of normal liver function tests and is greatest in rejection. This biomarker may help detect early signs of graft injury and rejection to inform LTR management strategies.

Management of Pulmonary Mucormycosis After Orthotopic Heart Transplant: A Case Series

Invasive pulmonary mucormycosis is a potentially fatal infection that can occur in immunosuppressed patients such as those who have undergone orthotopic heart transplant (OHT). High-dose intravenous antifungal agents, including amphotericin B, are generally accepted as the first-line medical treatment, with prompt surgical resection of lesions if feasible. The body of evidence guiding treatment decisions, however, is sparse, particularly regarding adjustment of immunosuppression during acute infection and long-term recovery. We present 2 cases of patients with pulmonary mucormycosis occurring within the first 6 months after OHT, both of whom successfully recovered after appropriate medical and surgical treatment, and we highlight differences in immunosuppression management strategies for this life-threatening condition.

Predictive Value of Immune Cell Functional Assay for Non-Cytomegalovirus Infection in Lung Transplant Recipients: A Multicenter Prospective Observational Study

INTRODUCTION

Immune cell functional assay (ImmuKnow®) is a non-invasive method that measures the state of cellular immunity in immunosuppressed patients. We studied the prognostic value of the assay for predicting non-cytomegalovirus (CMV) infections in lung transplant recipients.

METHODS

A multicenter prospective observational study of 92 patients followed up from 6 to 12 months after transplantation was performed. Immune cell functional assay was carried out at 6, 8, 10, and 12 months.

RESULTS

Twenty-three patients (25%) developed 29 non-CMV infections between 6 and 12 months post-transplant. At 6 months, the immune response was moderate (ATP 225-525ng/mL) in 14 (15.2%) patients and low (ATP<225ng/mL) in 78 (84.8%); no patients had a strong response (ATP≥525ng/mL). Only 1 of 14 (7.1%) patients with a moderate response developed non-CMV infection in the following 6 months compared with 22 of 78 (28.2%) patients with low response, indicating sensitivity of 95.7%, specificity of 18.8%, positive predictive value (PPV) of 28.2%, and negative predictive value (NPV) of 92.9% (AUC 0.64; p=0.043). Similar acute rejection rates were recorded in patients with mean ATP≥225 vs. <225ng/mL during the study period (7.1% vs. 9.1%, p=0.81).

CONCLUSION

Although ImmuKnow® does not seem useful to predict non-CMV infection, it could identify patients with a very low risk and help us define a target for an optimal immunosuppression.

Lymphocyte function based on IFN-γ secretion assay may be a promising indicator for assessing different immune status in renal transplant recipients

BACKGROUND

Immunological monitoring plays a crucial role in organ recipients for allowing tailoring of immunosuppression. However, there is still a paucity of promising indicators for detecting immune status in recipients.

METHODS

We conducted a prospective study to characterize the immune status by detecting dynamically lymphocyte subsets and function (represented by the abilities to secrete IFN-γ) in the first 6 months posttransplant in renal recipients. Participants were classified into an immune stable group, infected group, and rejected group.

RESULTS

In the stable group, our study suggested that the counts and function of CD4+ T, CD8+ T, and NK lymphocytes decreased to their nadir at week 2, and thereafter these indicators were gradually restored. The counts exceeded pre-operative levels, whereas function did not reach the pre-transplant levels by 6 months. We demonstrated that function of lymphocytes was considerably decreased in infected recipients compared with the stable group when infection occurred. By contrast, the function of lymphocytes was obviously increased at the point of rejection. Receiver operating characteristic (ROC) analysis in the combination of subsets and function of lymphocytes presented a superior clinical value with an area under the curve (AUC) of 0.903 in the diagnosis of infected receivers, and IFN-γ+CD8+ T cells% is the highest indicator with the auROC curve of 0.862. Another ROC analysis confirmed that IFN-γ+CD4  T cells% presented a preferable diagnostic value with an area of 0.887 for rejected recipients.

CONCLUSIONS

In conclusion, the ability of lymphocyte subsets secreting IFN-γ may provide a promising assessment of immune status in recipients and allow timely modifying immunosuppression.

Serological Response in Lung Transplant Recipients after Two Doses of SARS-CoV-2 mRNA Vaccines

BACKGROUND

Lung-transplant (LT) recipients are at high risk for COVID-19 due to immunosuppression and respiratory tropism of SARS-CoV-2. The information on the effect of COVID-19 mRNA vaccines to elicit immunogenic responses after a two-dose (2D) regimen in LT recipients is sparse. Thus, we assessed the effect of Pfizer-BioNTech and Moderna mRNA vaccines' 2D regimen on anti-spike responses in immunocompromised LT recipients.

METHODS

We utilized serum samples from LT recipients vaccinated for SARS-CoV-2 with 2D of either the Pfizer-BioNTech or Moderna vaccines and 2D-vaccinated naïve (non-transplanted and non-exposed to COVID-19) group. Antibody responses were assessed using the FDA-approved SARS-CoV-2 anti-nucleocapsid protein IgG assay (IgGNC), the SARS-CoV-2 anti-spike protein IgM assay (IgMSP), and the SARS-CoV-2 anti-spike protein IgG II assay (IgGSP). CD4+ T-cell activity was assessed as a marker of immune competence using the ImmuKnow® assay.

RESULTS

About 25% (18/73) of SARS-CoV-2 uninfected-LT patients generated a positive spike-IgG response following 2D of vaccines, with 36% (9/25) in the Moderna cohort and only 19% (9/48) in the Pfizer cohort. 2D in LT patients elicited a significantly lesser median IgGSP response (1.7 AU/mL, 95% CI: 0.6-7.5 AU/mL) compared to non-transplanted, uninfected naïve subjects (14,209 AU/mL, 95% CI: 11,261-18,836 AU/mL; p < 0.0001). In LT patients, the Moderna-evoked seropositivity trend was higher than Pfizer.

CONCLUSION

2D COVID-19 vaccination elicits a dampened serological response in LT patients. Whether assessing other arms of host immunity combined with a higher vaccine dose can better capture and elicit improved immunogenicity in this immunocompromised population warrants investigation.

Predictive Value of Immune Cell Functional Assay for Non-Cytomegalovirus Infection in Lung Transplant Recipients: A Multicenter Prospective Observational Study

INTRODUCTION

Immune cell functional assay (ImmuKnow®) is a non-invasive method that measures the state of cellular immunity in immunosuppressed patients. We studied the prognostic value of the assay for predicting non-cytomegalovirus (CMV) infections in lung transplant recipients.

METHODS

A multicenter prospective observational study of 92 patients followed up from 6 to 12 months after transplantation was performed. Immune cell functional assay was carried out at 6, 8, 10, and 12 months.

RESULTS

Twenty-three patients (25%) developed 29 non-CMV infections between 6 and 12 months post-transplant. At 6 months, the immune response was moderate (ATP 225-525ng/mL) in 14 (15.2%) patients and low (ATP<225ng/mL) in 78 (84.8%); no patients had a strong response (ATP≥525ng/mL). Only 1 of 14 (7.1%) patients with a moderate response developed non-CMV infection in the following 6 months compared with 22 of 78 (28.2%) patients with low response, indicating sensitivity of 95.7%, specificity of 18.8%, positive predictive value (PPV) of 28.2%, and negative predictive value (NPV) of 92.9% (AUC 0.64; p=0.043). Similar acute rejection rates were recorded in patients with mean ATP≥225 vs. <225ng/mL during the study period (7.1% vs. 9.1%, p=0.81).

CONCLUSION

Although ImmuKnow® does not seem useful to predict non-CMV infection, it could identify patients with a very low risk and help us define a target for an optimal immunosuppression.

Grant monitoring after intestinal transplantation

PURPOSE OF REVIEW

The current review aims to describe in detail the most common practices utilized to monitor graft function in intestinal transplant (ITx) recipients. In addition, to discussing the role of endoscopy and stool studies it will examine the use of other potential biomarkers which have been utilized. Data will be discussed from contemporary publications in the field, the Intestinal Transplant Registry as well as detailed data from a large, ITx single-center.

RECENT FINDINGS

Significant improvements have been made in early outcomes following ITx, yet long-term survival remains challenged by infection and rejection, both of which can present with diarrhea. While endoscopy and stool studies are the gold-standard for graft monitoring, calprotectin, citrulline, measurements of immunoreactivity and donor-specific antibodies have been investigated in the field and are herein reviewed.

SUMMARY

Despite a number of tests which are currently available for monitoring ITx recipients, a strong need exists for improved noninvasive, timely and accurate biomarkers to help improve ITx graft and patient survival.

Evaluation of Quantiferon®-Monitor as a biomarker of immunosuppression and predictor of infection in lung transplant recipients

BACKGROUND

Optimizing immunosuppression in lung transplant recipients (LTR) is crucially important in minimizing the risk of infection and rejection. Quantiferon®-Monitor (QFM) is a candidate immune function biomarker which has not yet been rigorously evaluated in the lung transplant setting. The aim of this prospective cohort study was to explore relationships between QFM results, immunosuppression, and infection/rejection in LTR.

METHODS

QFM, which measures interferon-γ after stimulation with innate and adaptive immune antigens, was tested before and at 2, 6, 12, 24 and 52 weeks post-transplant. Immunosuppression relationships were assessed with linear mixed effects models. Clinical outcomes were analyzed based on the preceding QFM result.

RESULTS

Eighty LTR were included. Median pre-transplant QFM levels were 171 IU/mL (IQR 45-461), decreasing to 3 IU/mL (IQR 1-8) at 2 weeks post-transplant then progressively recovering toward baseline with time from transplant. Prednisolone was strongly inversely associated with QFM level (0.1 mg/kg dose increase correlating with 88 IU/mL QFM decrease, 95% CI 61-114, P < .001). Patients with QFM values <10 and <60 IU/mL were more likely to develop a serious opportunistic infection between 3 and 6 months (HR 6.38, 95% CI 1.37-29.66, P = .02) and 6-12 months (HR 3.25, 95% CI 1.11-9.49, P = .03) post-transplant, respectively.

CONCLUSIONS

QFM values declined significantly post-transplant, with patients recovering at different rates. Prednisolone dose significantly impacted QFM results. Low levels were associated with infection beyond 3 months post-transplant, suggesting that QFM may be able to identify overly immunosuppressed patients who could be targeted for dose reduction. Larger prospective studies are needed to further evaluate this promising assay.

Biomarker and surrogate development in vascularised composite allograft transplantation: Current progress and future challenges

Vascularised composite allograft (VCA) transplantation is now a feasible reconstructive option for patients who have suffered significant soft tissue injuries. However, despite numerous technical advances in the field over two decades, a number of challenges remain, not least the management of transplant rejection. Part of the difficulty faced by clinicians is the early recognition and prevention of acute rejection episodes. Whilst this is potentially easier in VCAs than solid organ transplants, due to their visible skin component, at present the only validated method for the diagnosis of acute rejection is histological examination of a tissue biopsy. The aim of this review article is to provide an evidence-based overview of progress in the field of VCA biomarker discovery, including immune cell subsets, immune cell effector pathways, and circulating markers of allograft damage, and to discuss future challenges in the field.

Torque teno virus in liver diseases and after liver transplantation

Torque teno virus (TTV) has been proposed as a surrogate biomarker for immune monitoring in different patient cohorts. Historically, TTV has been associated with different liver diseases such as post-transfusion hepatitis, hepatitis B, and hepatitis C, but the virus's pathogenicity is controversial. TTV is a ubiquitous DNA virus, highly prevalent and mostly indolent in the general population. Thus, TTV viral load is more relevant than prevalence to understand TTV infection. In the context of liver transplantation, TTV viral load is modulated by the immune, viral, and inflammatory status. After liver transplantation, the TTV viral load positively correlates with the intensity of immunosuppression (IS), and low TTV viral burden is a predictor of acute rejection episodes, making it an attractive marker for the efficacy of IS. However, the TTV role as a single or a panel biomarker needs to be evaluated in further independent prospective trails.

Immunosuppressive Agents and Infectious Risk in Transplantation: Managing the "Net State of Immunosuppression"

Successful solid organ transplantation reflects meticulous attention to the details of immunosuppression, balancing risks for graft rejection against risks for infection. The 'net state of immune suppression' is a conceptual framework of all factors contributing to infectious risk. Assays which measure immune function in the immunosuppressed transplant recipient relative to infectious risk and allograft function are lacking. The best measures of integrated immune function may be quantitative viral loads to assess the individual's ability to control latent viral infections. Few studies address adjustment of immunosuppression during active infections. Thus, confronted with infection in solid organ recipients, the management of immunosuppression is based largely on clinical experience. This review examines known measures of immune function and the immunologic effects of common immunosuppressive drugs and available studies reporting modification of drug regimens for specific infections. These data provide a conceptual framework for the management of immunosuppression during infection in organ recipients.

Discovery and validation of a novel blood-based molecular biomarker of rejection following liver transplantation

Noninvasive biomarker profiles of acute rejection (AR) could affect the management of liver transplant (LT) recipients. Peripheral blood was collected following LT for discovery (Northwestern University [NU]) and validation (National Institute of Allergy and Infectious Diseases Clinical Trials in Organ Transplantation [CTOT]-14 study). Blood gene profiling was paired with biopsies showing AR or ADNR (acute dysfunction no rejection) as well as stable graft function samples (Transplant eXcellent-TX). CTOT-14 subjects had serial collections prior to AR, ADNR, TX, and after AR treatment. NU cohort gene expression (46 AR, 45 TX) was analyzed using random forest models to generate a classifier training set (36 gene probe) distinguishing AR vs TX (area under the curve 0.92). The algorithm and threshold were locked and tested on the CTOT-14 validation cohort (14 AR, 50 TX), yielding an accuracy of 0.77, sensitivity 0.57, specificity 0.82, positive predictive value (PPV) 0.47, and negative predictive value (NPV) 0.87 for AR vs TX. The probability score line slopes were positive preceding AR, and negative preceding TX and non-AR (TX + ADNR) (P ≤ .001) and following AR treatment. In conclusion, we have developed a blood biomarker diagnostic for AR that can be detected prior to AR-associated graft injury as well a normal graft function (non-AR). Further studies are needed to evaluate its utility in precision-guided immunosuppression optimization following LT.

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.

[Functional immunoassays in the setting of infectious risk and immunosuppressive therapy of non-HIV immunocompromised patients]

The holistic approach of the human immune system is based on the study of its components collectively driving a functional response to an immunogenic stimulus. To appreciate a specific immune dysfunction, a condition is mimicked ex vivo and the immune response induced is assessed. The application field of such assays are broad and expanding, from the diagnosis of primary and secondary immunodeficiencies, immunotherapy for cancer to the management of patients at-risk for infections and vaccination. These assays are immune monitoring tools that may contribute to a personalised and precision medicine. The purpose of this review is to describe immune functional assays available in the setting of non-HIV acquired immune deficiency. First, we will address the use of theses assays in the diagnosis of opportunistic infections such as viral reactivation. Secondly, we will report the usefulness of these assays to assess vaccine efficacy and to manage immunosuppressive therapies.

Monitoring cell-mediated immunity during immunosuppression reduction in heart transplant recipients with severe systemic infections

BACKGROUND

Treatment for severe systemic infections in heart transplantation is reduction in immunosuppression while treating the infection. An assay that measures adenosine triphosphate production in activated lymphocytes (ImmuKnow^® ) objectively monitors cellular immunity of transplant recipients. In this study, we used ImmuKnow^® to adjust immunosuppression in heart transplant recipients with severe systemic infections.

METHODS

Heart transplant recipients were followed with ImmuKnow^® at the time of biopsy and diagnosis of systemic infection. Patients who developed an infection were monitored by ImmuKnow^® assay with adjustments in immunosuppression based upon the results of the assay. Maintenance immunosuppression was reinstituted when the ImmuKnow^® increased to >225 ng/mL of ATP.

RESULTS

Two or more ImmuKnow^® assays were performed in 80 patients. Thirteen patients developed severe systemic infections. ImmuKnow^® mean value at the time of diagnosis of infection was 109 ± 49.2 ng/mL. Reduction in immunosuppression and treatment of infection resulted in normalization of ImmuKnow^® level, resolution of infection, and no episodes of rebound rejection.

CONCLUSION

Heart transplant recipients with severe systemic infections presented with a decreased ImmuKnow^® , suggesting over immunosuppression. ImmuKnow^® can be used as an objective measurement in withdrawing immunosuppression in heart transplant recipients with severe systemic infections.

Reconstitution of T-Cell Subsets Following Thymoglobulin-Induced Depletion in High Immunologic Risk and Donation After Cardiac Death Renal Transplant Recipients

INTRODUCTION

Depletion therapy in high immunologic risk (HR) patients by antithymocyte globulin (rATG) induces lymphopenia and subsequent compartmental repopulation of T-cell subsets. rATG is also given to patients receiving kidneys from donations after cardiac death (DCDs) to mitigate innate immune activation associated with the DCD process.

METHODS

We compared the T-cell response with rATG in both HR and DCD kidney recipients. We examined the reconstitution of T-cell subsets after rATG treatment in HR and DCD recipients (n = 19 per group) by multicolor flow cytometry.

RESULTS

Following treatment, there was a rapid drop in the frequency of T cells in both groups, which persisted over 28 days. HR patients had an early surge in the frequency of CD4⁺ naïve, effector-memory, and regulatory T cells. Although we found a significant proliferation of the T cells in both groups, the DCD cohort had a blunted response as well as reduced CD4⁺ T-cell immune-reactivity compare with the HR group.

CONCLUSIONS

Our data suggest that there is a lack of significant homeostatic proliferative response in DCD recipients following rATG, and CD4⁺ T cells may be less reactive in the DCD group than previously thought, indicating that rATG treatment may not have to be considered a first-line induction therapy in DCD recipients.

Extracellular ATP activates P2X7R-NF-κB (p65) pathway to promote the maturation of bone marrow-derived dendritic cells of mice

The maturation state of dendritic cell (DC) plays an important role in immune activities. Previously we had found that NF-κB (p65) pathway could promote DC maturation and subsequent immune effects. But the upstream mechanism of this pathway was still unclear. Extracellular adenosine triphosphate (ATP) activating its receptor P2X7R has recently been considered as the fourth signal to activate T lymphocytes. Here we aimed to find out the connection between P2X7R and NF-κB (p65) pathway in DC maturation. Results showed that the expression of P2X7R and the intracellular ATP levels were increased along with the maturation of DC. P2X7R agonist stimulated the morphological changes of DCs into the appearance of mature DCs, and promoted the expression of NF-κB (p65), as well as the release of IFN-γ and IL-12. Whereas, P2X7R inhibitor had the opposite influences. Co-immunoprecipitation assay confirmed the binding of P2X7R and NF-κB (p65). Our study suggested that extracellular ATP could promote DC maturation and release of inflammatory cytokines through the binding of P2X7R and NF-κB (p65). This is the first study to show the P2X7R-NF-κB (p65) pathway in DC. Interference with this pathway may be able to regulate immune responses in areas like infectious diseases, inflammation, transplantation, tumor and autoimmune diseases. In addition, intracellular ATP level could be a new indicator of the maturation state of DC.

Biomarkers in Solid Organ Transplantation

After more than 6 decades of clinical practice, the transplant community continues to research noninvasive biomarkers of solid organ injury to help improve patient care. In this review, we discuss the clinical usefulness of selective biomarkers and how they are processed at the laboratory. In addition, we organize these biomarkers based on specific aims and introduce innovative markers currently under investigation.

T-cell exhaustion correlates with improved outcomes in kidney transplant recipients

Continuous antigen stimulation during chronic infection or malignancy can promote functional T cell silencing, a phenomenon called T cell exhaustion. The prevalence and impact of T cell exhaustion following organ transplantation, another immune stimulus with persistently high antigen load, are unknown. Here, we characterized serially collected peripheral blood mononuclear cells from 26 kidney transplant recipients using time-of-flight mass cytometry (CyTOF) to define distinct subsets of circulating exhausted T cells and their relationship to induction therapy and allograft function. We observed an increase in specific subsets of CD4⁺ and CD8⁺ exhausted T cells from pre-transplant to 6-months post-transplant, with greater increases in participants given anti-thymocyte globulin induction than in participants who received no induction or non-depleting induction. The percentages of exhausted T cells at 6 months correlated inversely with adenosine triphosphate (ATP) production (a surrogate of T cell function) and with allograft interstitial fibrosis. Guided by the CyTOF data, we delineated a PD-1⁺CD57^- phenotype for CD4⁺ and CD8⁺ exhausted T cells, and confirmed that these cells have limited capacity for cytokine secretion and ATP production. In an independent cohort of 50 kidney transplant recipients, we confirmed the predicted increase of PD-1⁺CD57^- exhausted T cells after lymphocyte-depleting induction therapy and its direct correlation with better allograft function. Our findings suggest that monitoring T cell exhaustion can be useful for post-transplant risk assessment and support the need to develop and test strategies aimed at augmenting T cell exhaustion following kidney transplantation.

Can immune biomarkers predict infections in solid organ transplant recipients? A review of current evidence

Despite improvements in graft survival, solid organ transplantation is still associated with considerable infection induced morbidity and mortality. If we were able to show that serious infection risk was associated with excessive suppression of immune capacity, we would be justified in "personalizing" the extent of immunosuppression by carefully monitored reduction to see if we can improve immune compromize without increasing the risk of rejection. Reliable biomarkers are needed to identify this patients at an increased risk of infection. This review focuses on the currently available evidence in solid organ transplant recipients for immune non-pathogen specific biomarkers to predict severe infections with the susceptibility to particular pathogens according to the component of the immune system that is suppressed. This review is categorized into immune biomarkers representative of the humoral, cellular, phagocytic, natural killer cell and complement system. Biomarkers humoral and cellular systems of the that have demonstrated an association with infections include immunoglobulins, lymphocyte number, lymphocyte subsets, intracellular concentrations of adenosine triphosphate in stimulated CD4⁺ cells and soluble CD30. Biomarkers of the innate immune system that have demonstrated an association with infections include natural killer cell numbers, complement and mannose binding lectin. Emerging evidence shows that quantification of viral nucleic acid (such as Epstein Barr Virus) can act as a biomarker to predict all-cause infections. Studies that show the most promise are those in which several immune biomarkers are assessed in combination. Ongoing research is required to validate non-pathogen specific immune biomarkers in multi-centre studies using standardized study designs.

Characteristic analysis of TCR β-chain CDR3 repertoire for pre- and post-liver transplantation

Liver cirrhosis of hepatitis B is an immune-related disease in which liver cells die during the body’s immune system activation to clear the virus, and the progress is closely related to T lymphocytes. T lymphocyte cells recognise antigens, specifically by major histocompatibility complex (MHC), through a membrane protein T cell receptor (TCR). Here, we used high throughput immune repertoire sequencing technique to study the characteristics and diversity of the TCR repertoire between patients who underwent liver transplantation and healthy controls (NC). We sequenced the TCR β-chain complementary-determining region 3 (CDR3) repertoire in peripheral blood mononuclear cells (PBMCs) from 6 liver transplantation patients before transplantation (Pre) and on the first (Post1) and seventh days (Post7) after transplantation along with 6 NC. We observed that the distributions of CDR3, VD indel, and DJ indel lengths were similar among the Pre, Post1, Post7 and NC groups. We found that the TCR repertoire diversity of transplantation groups was relatively lower compared to NC group. The Pre-group had more highly expanded T cell clones compared to Post1, Post7 and NC groups, and the diversity of the T cell repertoire of the Post7 group was significantly decreased compared to the Pre, Post1 and NC groups. In addition, we found our results also show that various TRBV expression increased and some public sequences at different time points after liver transplantation, and the expression levels of 3 TRBV segments and 2 TRBJ segments were also significantly different in Pre, Post1, Post7 and NC groups. Moreover, 1 aa sequence shared by all liver transplantation patients and 2 aa sequences shared by at least two groups, which may serve as biomarkers to monitor the immune status of liver transplant patients.

Monitoring cellular immune function of renal transplant recipients based on adenosine triphosphate (ATP) production by mitogen-induced CD4+ T helper cells

Maintaining the balance between over- and under-immunosuppression has a critical role for successful immunosuppressive therapy after renal transplantation. We studied the predictive value of our functional immune assay, which works based on adenosine triphosphate (ATP) levels, in determining risk of infection and rejection among renal transplant recipients (RTRs). A total of 65 RTRs with less than 1 month (RTRL1) and 48 RTRs with more than 6 months (RTRM6) of post-transplant time, and 56 healthy individuals were included. Upon lymphocyte activation by phytohemagglutinin (PHA), CD4+ T cells were separated using magnetic beads (Dynabeads), the intracellular ATP (iATP) concentrations were measured by luciferin-luciferase reaction, and compared within and between the groups. Activated CD4+ cells iATP production directly correlated with post-transplant time (r = 0.32, P = 0.011). The iATP levels were significantly lower in both RTRL1 and RTRM6 groups compared to control (P < 0.001), and in the RTRL1 group compared to the RTRM6 (P < 0.05). The iATP concentrations were significantly lower in patients who suffered from infection versus the RTRs with stable graft function (SGF). However, the iATP levels were higher in those with allograft rejection episode (ARE). Our optimization experiments showed that best iATP levels cutoffs were 472.5 and 572.5 ng/ml for predicting risk of ARE, and 218.5 and 300.5 ng/ml for predicting risk of developing infection in RTRL1 and RTRM6 patients, respectively. iATP levels measured by immune function assay might be a promising predictive tool for identifying RTRs who are at risk of developing infection or allograft rejection.

Immunosuppression for Lung Transplantation: Current and Future

Purpose of the review

The number of lung transplantations performed worldwide continues to increase. There is a growing need in these patients for more effective immunosuppressive medications with less toxicity.

Recent findings

This review article summarizes the recent studies and developments in lung transplant immunosuppression. Novel immunosuppressive medications and strategies used in other solid organ transplantations are being trialed in lung transplantation. This includes the use of co-stimulation blockers like belatacept and mTOR inhibitors like everolimus. Calcineurin sparing regimens have been described in an attempt to minimize nephrotoxicity. Assays to measure the bioactivity of immunosuppressive medications to determine the global immune competence, such as Immuknow assay and Gamma interferon response are gaining traction.

Summary

Immunosuppression in lung transplant is evolving with the development of newer drugs and promising strategies to optimize immunosuppression. Further studies with multicenter randomized trials are required to increase the strength of the evidence.

Complications of Cardiac Transplantation

PURPOSE OF REVIEW

Despite the improvement in medical therapy for heart failure and the advancements in mechanical circulatory support, heart transplantation (HT) still remains the best therapeutic option to improve survival and quality of life in patients with advanced heart failure. Nevertheless, HT recipients are exposed to the risk of several potential complications that may impair their outcomes. In this article, we aim to provide a practical and scholarly framework for clinicians approaching heart transplant medicine, as well as a concise update for the experienced readers on the most relevant post-HT complications.

RECENT FINDINGS

While recognizing that most of the treatments herein discussed are based more on experience than on solid scientific evidence, significant step forward has been made in particular in the recognition and management of primary graft dysfunction, antibody-mediated rejection, and renal dysfunction. Complications after HT may vary according to the time from surgery and can be related to graft function and pathology or to diseases and dysfunctions occurring in other organs or systems, mainly as side effects of immunosuppressive drugs and progression of pre-existing conditions. Future research needs to focus on improving precision diagnostics of causes of graft dysfunction and on reaching an optimal and customized balance between efficacy and toxicities of immunosuppressive strategies.

Biomarkers to detect rejection after kidney transplantation

Detecting acute rejection in kidney transplantation has been traditionally done using histological analysis of invasive allograft biopsies, but this method carries a risk and is not perfect. Transplant professionals have been working to develop more accurate or less invasive biomarkers that can predict acute rejection or subsequent worse allograft survival. These biomarkers can use tissue, blood or urine as a source. They can comprise individual molecules or panels, singly or in combination, across different components or pathways of the immune system. This review highlights the most recent evidence for biomarker efficacy, especially from multicenter trials.

Association between baseline serum hepcidin levels and infection in kidney transplant recipients: Potential role for iron overload

BACKGROUND

The liver-synthesized peptide hepcidin is a key regulator of iron metabolism and correlates with total iron stores. We analyzed the association between pre-transplant hepcidin-25 levels and infection after kidney transplantation (KT).

METHODS

Serum hepcidin-25 levels were measured at baseline by high-sensitivity ELISA in 91 patients undergoing KT at our institution between December 2011 and March 2013. The impact of this biomarker on the incidence of post-transplant infection (excluding lower urinary tract infection) during the first year was assessed by Cox regression.

RESULTS

Mean hepcidin-25 level was 82.3 ± 67.4 ng/mL and strongly correlated with serum ferritin (Spearman's rho = 0.703; P < .001). There were no significant differences in hepcidin-25 levels between patients with or without overall infection (96.4 ± 67.5 vs 72.6 ± 66.7 ng/mL; P = .101). Such difference was evident for opportunistic (128.9 ± 75.0 vs 73.0 ± 62.3 ng/mL; P = .003) and, to a lesser extent, surgical-site infection (107.5 ± 73.3 vs 76.5 ± 65.2 ng/mL; P = .087). Patients with hepcidin-25 levels ≥72.5 ng/mL had higher 12-month cumulative incidence of overall infection (51.2% vs 29.2%; P = .032). After multivariate adjustment, hepcidin-25 ≥72.5 ng/mL acted as an independent risk factor for overall (adjusted hazard ratio [aHR] 3.86; 95% confidence interval [CI] 1.49-9.96; P = .005) and opportunistic infection (aHR 4.32; 95% CI 1.18-15.75; P = .027).

CONCLUSION

Elevated baseline serum hepcidin-25 levels were associated with increased risk of infection after KT, suggesting a role for iron overload in the individual susceptibility to post-transplant infection.

An integrated view of immune monitoring in vascularized composite allotransplantation

PURPOSE OF REVIEW

Vascularized composite allotransplantation (VCA) has several immunological peculiarities that imply a specific immune monitoring. Here, we provide an integrated view of current procedures of immune monitoring in VCA and potential complementary approaches learned from organ transplantation.

RECENT FINDINGS

Because the skin is highly immunogenic and is the main target of the alloimmune response, immune monitoring in VCA essentially relies on visual inspection and pathological examination of for-causes and protocol skin biopsies. Light microscopical and immunohistochemical analyses enable us to identify skin lesions that are characteristic, but not specific, of allograft rejection. Complementary approaches of immunological assessment may assist in reinforcing the diagnosis of rejection and preventing over-immunosuppression or under-immunosuppression. Such approaches can inform either on the patient's global immune status or more specifically on the B-cell-mediated or T-cell-mediated immune responses against donor antigens.

SUMMARY

Strategies that integrate both the current 'gold standards' of monitoring in VCA and a complementary multilayer immunological assessment are likely to provide the highest precision for the personalized determination of the recipients' immunological status. The objective is a tailored adaptation of immunosuppressive treatment.

Monitoring of peripheral blood cluster of differentiation 4+ adenosine triphosphate activity and CYP3A5 genotype to determine the pharmacokinetics, clinical effects and complications of tacrolimus in patients with autoimmune diseases

A total of 25 patients with autoimmune diseases receiving tacrolimus were screened using a peripheral blood cluster of differentiation 4⁺ adenosine triphosphate (ATP) activity assay (IMK assay) between October 2013 and July 2014. The autoimmune diseases of patients were as follows: Rheumatoid arthritis (n=15), lupus nephritis (n=6), ulcerative colitis (n=2) and myasthenia gravis (n=2). Patients were divided into two groups based on CYP3A5 genotype [expression of *1 allele: Expressor (EX; n=6) and non-expressor (NEX; n=19)]. The tacrolimus concentration and concentration/dose ratio was significantly lower in the EX group compared with the NEX group (P=0.0108 and 0.0056, respectively). In addition, all enrolled patients that presented with adverse effects belonged to the NEX group. No significant associations were observed between IMK ATP levels and the concentration or dose of tacrolimus (P=0.1092 and 0.6999, respectively). However, the IMK ATP high-level group exhibited a significantly higher occurrence rate of insufficient effect when compared with the normal and low-level groups (P=0.0014). In conclusion, the clearance of tacrolimus in patients with autoimmune diseases was affected by the CYP3A5 genotype, as previously reported in organ transplant patients. The IMK ATP level may indicate the clinical response irrespective of tacrolimus concentration.

Intestinal transplantation: current improvements and perspectives

PURPOSE OF REVIEW

This review summarizes the most recent relevant knowledge in clinical practice in the field of intestinal transplantation.

RECENT FINDINGS

Three important factors that have allowed improving results during the last few years are reviewed here. The first relates to the development of a different approach to tackle the underlying cause of intestinal failure and to the patient's characteristics in terms of liver function, age, and body size. The second involves immune modulation and especially the immunosuppressive regimen at induction. The third refers to posttransplantation monitoring, in particular the diagnosis and treatment of intestinal graft rejection and lymphoproliferative disorders. Patient status and referral for intestinal transplantation remain debated. The Intestinal Transplant Registry and a report from an individual program have demonstrated the relationship between a patient's pretransplant status and outcome. Candidacy for intestinal transplantation was analysed in a European survey of home parenteral nutrition patients. Early referral and listing are important for successful outcomes after intestinal grafting.

SUMMARY

Patient management should include therapies adapted to each stage of intestinal failure based on a multidisciplinary approach in centers involving surgery, gastroenterology, parenteral nutrition expertise, home parenteral nutrition programs, and liver-intestinal transplantation experience. Timing for referral of patients in specialized centers remains a crucial issue.