Benefit of immune monitoring in heart transplant patients using ATP production in activated lymphocytes

A gentler approach to monitor for heart transplant rejection

Despite developments in circulating biomarker and imaging technology in the assessment of cardiovascular disease, the surveillance and diagnosis of heart transplant rejection has continued to rely on histopathologic interpretation of the endomyocardial biopsy. Increasing evidence shows the utility of molecular evaluations, such as donor-specific antibodies and donor-derived cell-free DNA, as well as advanced imaging techniques, such as cardiac magnetic resonance imaging, in the assessment of rejection, resulting in the elimination of many surveillance endomyocardial biopsies. As non-invasive technologies in heart transplant rejection continue to evolve and are incorporated into practice, they may supplant endomyocardial biopsy even when rejection is suspected, allowing for more precise and expeditious rejection therapy. This review describes the current and near-future states for the evaluation of heart transplant rejection, both in the settings of rejection surveillance and rejection diagnosis. As biomarkers of rejection continue to evolve, rejection risk prediction may allow for a more personalized approach to immunosuppression.

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.

The evolving use of biomarkers in heart transplantation: consensus of an expert panel

In heart transplantation, the use of biomarkers to detect the risk of rejection has been evolving. In this setting, it is becoming less clear as to what is the most reliable test or combination of tests to detect rejection and assess the state of the alloimmune response. Therefore, a virtual expert panel was organized in heart and kidney transplantation to evaluate emerging diagnostics and how they may be best utilized to monitor and manage transplant patients. This manuscript covers the heart content of the conference and is a work product of the American Society of Transplantation's Thoracic and Critical Care Community of Practice. This paper reviews currently available and emerging diagnostic assays and defines the unmet needs for biomarkers in heart transplantation. Highlights of the in-depth discussions among conference participants that led to development of consensus statements are included. This conference should serve as a platform to further build consensus within the heart transplant community regarding the optimal framework to implement biomarkers into management protocols and to improve biomarker development, validation and clinical utility. Ultimately, these biomarkers and novel diagnostics should improve outcomes and optimize quality of life for our transplant patients.

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.

Circulating microRNAs in cellular and antibody-mediated heart transplant rejection

BACKGROUND

Noninvasive monitoring of heart allograft health is important to improve clinical outcomes. MicroRNAs (miRs) are promising biomarkers of cardiovascular disease and limited studies suggest they can be used to noninvasively diagnose acute heart transplant rejection.

METHODS

The Genomic Research Alliance for Transplantation (GRAfT) is a multicenter prospective cohort study that phenotyped heart transplant patients from 5 mid-Atlantic centers. Patients who had no history of rejection after transplant were compared to patients with acute cellular rejection (ACR) or antibody-mediated rejection (AMR). Small RNA sequencing was performed on plasma samples collected at the time of an endomyocardial biopsy. Differential miR expression was performed with adjustment for clinical covariates. Regression was used to develop miR panels with high diagnostic accuracy for ACR and AMR. These panels were then validated in independent samples from GRAfT and Stanford University. Receiver operating characteristic curves were generated and area under the curve (AUC) statistics calculated. Distinct ACR and AMR clinical scores were developed to translate miR expression data for clinical use.

RESULTS

The GRAfT cohort had a median age of 52 years, with 35% females and 45% Black patients. Between GRAfT and Stanford, we included 157 heart transplant patients: 108 controls and 49 with rejection (50 ACR and 38 AMR episodes). After differential miR expression and regression analysis, we identified 12 miRs that accurately discriminate ACR and 17 miRs in AMR. Independent validation of the miR panels within GRAfT led to an ACR AUC 0.92 (95% confidence interval [CI]: 0.86-0.98) and AMR AUC 0.82 (95% CI: 0.74-0.90). The externally validated ACR AUC was 0.72 (95% CI: 0.59-0.82). We developed distinct ACR and AMR miR clinical scores (range 0-100), a score ≥ 65, identified ACR with 86% sensitivity, 76% specificity, and 98% negative predictive value, for AMR score performance was 82%, 84% and 97%, respectively.

CONCLUSIONS

We identified novel miRs that had excellent performance to noninvasively diagnose acute rejection after heart transplantation. Once rigorously validated, the unique clinical ACR and AMR scores usher in an era whereby genomic biomarkers can be used to screen and diagnose the subtype of rejection. These novel biomarkers may potentially alleviate the need for an endomyocardial biopsy while facilitating the initiation of targeted therapy based on the noninvasive diagnosis of ACR or AMR.

Pre-transplant immune cell function assay as a predictor of early cardiac allograft rejection

INTRODUCTION

ImmuKnow, an immune cell function assay that quantifies overall immune system activity can assist in post-transplant immunosuppression adjustment. However, the utility of pre-transplant ImmuKnow results representing a patient's baseline immune system activity is unknown. This study sought to assess if pre-transplant ImmuKnow results are predictive of rejection at the time of first biopsy in our cardiac transplant population.

METHODS

This is a single center, retrospective observational study of consecutive patients from January 1, 2018 to October 1, 2020 who underwent orthotopic cardiac transplantation at NYU Langone Health. Patients were excluded if a pre-transplant ImmuKnow assay was not performed. ImmuKnow results were categorized according to clinical interpretation ranges (low, moderate, and high activity), and patients were divided into two groups: a low activity group versus a combined moderate-high activity group. Pre-transplant clinical characteristics, induction immunosuppression use, early postoperative tacrolimus levels, and first endomyocardial biopsy results were collected for all patients. Rates of clinically significant early rejection (defined as rejection ≥ 1R/1B) were compared between pre-transplant ImmuKnow groups.

RESULTS

Of 110 patients who underwent cardiac transplant, 81 had pre-transplant ImmuKnow results. The low ImmuKnow activity group was comprised of 15 patients, and 66 patients were in the combined moderate-high group. Baseline characteristics were similar between groups. Early rejection occurred in 0 (0%) patients with low pre-transplant ImmuKnow levels. Among the moderate- high pre-transplant ImmuKnow group, 16 (24.2%) patients experienced early rejection (P = .033). The mean ImmuKnow level in the non-rejection group was the 364.9 ng/ml of ATP compared to 499.3 ng/ml of ATP for those with rejection (P = .020).

CONCLUSION

Patients with low pre-transplant ImmuKnow levels had lower risk of early rejection when compared with patients with moderate or high levels. Our study suggests a possible utility in performing pre-transplant ImmuKnow to identify patients at-risk for early rejection who may benefit from intensified upfront immunosuppression as well as to recognize those where slower calcineurin inhibitor initiation may be appropriate.

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.

Extracorporeal Photopheresis With Low-Dose Immunosuppression in High-Risk Heart Transplant Patients-A Pilot Study

In severely ill patients undergoing urgent heart transplant (HTX), immunosuppression carries high risks of infection, malignancy, and death. Low-dose immunosuppressive protocols have higher rejection rates. We combined extracorporeal photopheresis (ECP), an established therapy for acute rejection, with reduced-intensity immunosuppression. Twenty-eight high-risk patients (13 with high risk of infection due to infection at the time of transplant, 7 bridging to transplant via extracorporeal membrane oxygenation, 8 with high risk of malignancy) were treated, without induction therapy. Prophylactic ECP for 6 months (24 procedures) was initiated immediately postoperatively. Immunosuppression consisted of low-dose tacrolimus (8–10 ng/ml, months 1–6; 5–8 ng/ml, >6 months) with delayed start; mycophenolate mofetil (MMF); and low maintenance steroid with delayed start (POD 7) and tapering in the first year. One-year survival was 88.5%. Three patients died from infection (POD 12, 51, 351), and one from recurrence of cancer (POD 400). Incidence of severe infection was 17.9% (n = 5, respiratory tract). Within the first year, antibody-mediated rejection was detected in one patient (3.6%) and acute cellular rejection in four (14.3%). ECP with reduced-intensity immunosuppression is safe and effective in avoiding allograft rejection in HTX recipients with risk of severe infection or cancer recurrence.

Burkitt Lymphoma After Cardiac Transplantation: Therapeutic Considerations

Postsolid organ transplant Burkitt lymphoma (PSOT-BL) is rare but more aggressive than other post-transplant lymphoproliferative disorders (PTLD). Little is known about optimal treatment and outcome of postcardiac transplant Burkitt lymphoma (BL). We report an 8-year-old boy with a history of heart transplant who developed Epstein-Barr virus positive, late-onset PSOT-BL. He was successfully treated with BL specific chemoimmunotherapy and cessation of baseline immunosuppression. In this pediatric case of PSOT-BL, the use of standard intensive pediatric based chemoimmunotherapy regimen without modifications was feasible, well tolerated and resulted in complete remission. Long-term toxicities need further study.

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.

Non-invasive cardiac allograft rejection surveillance: reliability and clinical value for prevention of heart failure

Allograft rejection-related acute and chronic heart failure (HF) is a major cause of death in heart transplant recipients. Given the deleterious impact of late recognized acute rejection (AR) or non-recognized asymptomatic antibody-mediated rejection on short- and long-term allograft function improvement of AR surveillance and optimization of action strategies for confirmed AR can prevent AR-related allograft failure and delay the development of cardiac allograft vasculopathy, which is the major cause for HF after the first posttransplant year. Routine non-invasive monitoring of cardiac function can improve both detection and functional severity grading of AR. It can also be helpful in guiding the anti-AR therapy and timing of routine surveillance endomyocardial biopsies (EMBs). The combined use of EMBs with non-invasive technologies and methods, which allow detection of subclinical alterations in myocardial function (e.g., tissue Doppler imaging and speckle-tracking echocardiography), reveal alloimmune activation (e.g., screening of complement-activating donor-specific antibodies and circulating donor-derived cell-free DNA) and help in predicting the imminent risk of immune-mediated injury (e.g., gene expression profiling, screening of non-HLA antibodies, and circulating donor-derived cell-free DNA), can ensure the best possible surveillance and management of AR. This article gives an overview of the current knowledge about the reliability and clinical value of non-invasive cardiac allograft AR surveillance. Particular attention is focused on the potential usefulness of non-invasive tools and techniques for detection and functional grading of early and late ARs in asymptomatic patients. Overall, the review aimed to provide a theoretical and practical basis for those engaged in this particularly demanding up-to-date topic.

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.

Clinical relevance of a CD4+ T cell immune function assay in the diagnosis of infection in pediatric living-donor liver transplantation

The aim of the present study was to investigate the potential of the Immuknow immune cell function assay for the diagnosis of infection after pediatric living-donor liver transplantation (LDLT). Based on clinical data obtained following liver transplantation, 66 patients were divided into infection (n=28) and non-infection (n=38) groups. The following factors were considered in the present analysis: Primary disease, lymphocyte count, tacrolimus plasma concentration/dose (C0/D) ratio, CD4+ T lymphocyte ATP levels, at pre-transplant stage and at weeks 1-4, and 2 and 3 months post-transplant. The CD4+ T lymphocyte ATP values were plotted in a receiver operating characteristic (ROC) curve. The CD4+ T lymphocyte ATP value of the infection group was significantly lower compared with that of the non-infection group (188.6±93.5 vs. 424.4±198.1 ng/ml, respectively; P<0.05). No correlation was observed between the ATP value and tacrolimus plasma C0/D ratio (R2=0.0001484); however, a correlation was reported between the ATP value and lymphocyte count (R2=0.2149). Analysis of the ROC curve indicated that the ATP levels of CD4+ T cells were significantly associated with the diagnostic value of infection (area under the curve=0.866). These findings suggest that low CD4+ T lymphocyte ATP levels may be an independent risk factor for infection following pediatric LDLT, and that the Immuknow assay may be used as a tool to evaluate T lymphocyte function in such patients to predict the risk of infection.

Update on heart failure management and future directions

Heart failure (HF) is an important cardiovascular disease because of its increasing prevalence, significant morbidity, high mortality, and rapidly expanding health care cost. The number of HF patients is increasing worldwide, and Korea is no exception. There have been marked advances in definition, diagnostic modalities, and treatment of HF over the past four decades. There is continuing effort to improve risk stratification of HF using biomarkers, imaging and genetic testing. Newly developed medications and devices for HF have been widely adopted in clinical practice. Furthermore, definitive treatment for end-stage heart failure including left ventricular assist device and heart transplantation are rapidly evolving as well. This review summarizes the current state-of-the-art management for HF and the emerging diagnostic and therapeutic modalities to improve the outcome of HF patients.

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.

The Past, Present and Future of Heart Transplantation

Heart transplantation (HTx) has become standard treatment for selected patients with end-stage heart failure. Improvements in immunosuppressant, donor procurement, surgical techniques, and post-HTx care have resulted in a substantial decrease in acute allograft rejection, which had previously significantly limited survival of HTx recipients. However, limitations to long-term allograft survival exist, including rejection, infection, coronary allograft vasculopathy, and malignancy. Careful balance of immunosuppressive therapy and vigilant surveillance for complications can further improve long-term outcomes of HTx recipients.

Evaluation of the Infection Risk in Dialysis and Chronic Kidney Disease Patients Using an ATP Monitoring Assay

The ATP monitoring assay is a useful biomarker for risk monitoring to detect infection and rejection episodes in transplant recipients. Hemodialysis patients have a higher rate of infectious mortality. Infections in hemodialysis patients are mainly caused by venous catheters, uremia, malnutrition and inflammation. However, the risk of infection episodes has not been evaluated using a lymphocyte ATP monitoring assay in hemodialysis and chronic kidney disease (CKD) patients. We measured the ATP amounts in the peripheral CD4+ cells of CKD (N = 85) and dialysis patients (N = 17) using an "Immuknow" assay kit. These CKD patients were divided, according to kidney disease stage, into G3a, G3b, G4, and G5 groups. The ATP amounts in CD4+ cells of the dialysis patients and each of the CKD groups were compared with healthy subjects. In both the dialysis and CKD patients, the ATP amounts in CD4+ cells were lower than in healthy subjects. Furthermore, there were significant differences in the ATP amounts between healthy subjects and each of the CKD-G3a, CKD-G3b, and CKD-G4 groups (P < 0.05). Patients with CKD-G3a, CKD-G3b and CKD-G4 were evaluated as being at high risk for infection according to the lymphocyte ATP monitoring assay. However, the ATP amounts in the dialysis and CKD-G5 patients did not differ from those in healthy subjects to a statistically significant extent. These results suggest that the ATP amount in the CD4+ cells of these patients with serve renal failure are influenced by dialysis treatment, uremia and/or oxidative stress.

Usefulness of cell-mediated immune function in risk stratification for patients with advanced heart failure

Although heightened inflammation and autoimmune responses have been well described in patients with heart failure, the role of cell-mediated immune function in the pathogenesis and progression of heart failure is unclear. The aim of our study is to evaluate the prognostic role of cell-mediated immune function in patients with advanced heart failure.

METHODS

We studied patients with advanced heart failure referred for evaluation of candidacy for advanced heart failure therapies between 2007 and 2010. Cell-mediated immune response was categorized into 3 groups-low or poor immune response (≤225 ng/mL), moderate or normal immune response (226-524 ng/mL), and strong immune response (≥525 ng/mL)-using a phytohemagglutinin-stimulated T-cell response assay.

RESULTS

Out of 368 patients, 41 patients (11.1%) had poor immune function, 258 patients (70.1%) had normal immune function, and 69 patients (18.7%) had strong immune function. The primary outcome of all-cause mortality or cardiac transplantation occurred in 63.4%, 45.3%, and 34.8% in the poor immunity, normal immunity, and strong immune function groups, respectively. In univariate analysis, cell-mediated immune function was strongly associated with the primary outcome (P=.014). Poor immune function portended worse prognosis (hazard ratio=2.18, 95% CI 1.01-4.70, P=.047), and strong immune function was associated with better survival (hazard ratio=0.67, 95% CI 0.43-1.04). However, when adjusted for multiple variables in multivariate analysis, immune function status lost its overall significance to predict primary outcome (P=.11), but the direction to an increased risk of primary outcome was maintained in the poor immune function group.

CONCLUSIONS

Poor cell-mediated immune function measured by a clinically available assay could be associated with more adverse long-term prognosis in patients with advanced heart failure.

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.

Immune function monitoring in lung transplantation using adenosine triphosphate production: time trends and relationship to postoperative infection

PURPOSE

The ImmuKnow (IK) assay is a comprehensive immune function test that involves measuring adenosine triphosphate produced by the cluster of differentiation 4+ T lymphocytes in peripheral blood. The aim of this study was to analyze the time trends of IK values and assess the relationship between IK values and infections in lung transplants.

METHODS

We prospectively collected 178 blood samples from 22 deceased-donor lung transplant (DDLT) recipients and 17 living-donor lobar lung transplant (LDLLT) recipients. A surveillance IK assay was performed postoperatively, then after 1 week and 1, 3, 6, and 12 months.

RESULTS

Time trends of IK values in stable recipients peaked 1 week after DDLT (477 ± 247 ATP ng/ml), and 1 month after LDLLT (433 ± 134 ng/ml), followed by a gradual decline over 1 year. The mean IK values in infections were significantly lower than those in the stable state (119 vs 312 ATP ng/ml, p = 0.0002).

CONCLUSIONS

IK values increased sharply after lung transplantation and then decreased gradually over time in the first year, suggesting a natural history of immune function. IK values were also significantly reduced during infections. These results may provide new insights into the utility of immune monitoring after lung transplantation.

Evaluation of humoral immunity profiles to identify heart recipients at risk for development of severe infections: A multicenter prospective study

BACKGROUND

New biomarkers are necessary to improve detection of the risk of infection in heart transplantation. We performed a multicenter study to evaluate humoral immunity profiles that could better enable us to identify heart recipients at risk of severe infections.

METHODS

We prospectively analyzed 170 adult heart recipients at 8 centers in Spain. Study points were before transplantation and 7 and 30 days after transplantation. Immune parameters included IgG, IgM, IgA and complement factors C3 and C4, and titers of specific antibody to pneumococcal polysaccharide antigens (anti-PPS) and to cytomegalovirus (CMV). To evaluate potential immunologic mechanisms leading to IgG hypogammaglobulinemia, before heart transplantation we assessed serum B-cell activating factor (BAFF) levels using enzyme-linked immunoassay. The clinical follow-up period lasted 6 months. Clinical outcome was need for intravenous anti-microbials for therapy of infection.

RESULTS

During follow-up, 53 patients (31.2%) developed at least 1 severe infection. We confirmed that IgG hypogammaglobulinemia at Day 7 (defined as IgG <600 mg/dl) is a risk factor for infection in general, bacterial infections in particular, and CMV disease. At Day 7 after transplantation, the combination of IgG <600 mg/dl + C3 <80 mg/dl was more strongly associated with the outcome (adjusted odds ratio 7.40; 95% confidence interval 1.48 to 37.03; p = 0.014). We found that quantification of anti-CMV antibody titers and lower anti-PPS antibody concentrations were independent predictors of CMV disease and bacterial infections, respectively. Higher pre-transplant BAFF levels were a risk factor of acute cellular rejection.

CONCLUSION

Early immunologic monitoring of humoral immunity profiles proved useful for the identification of heart recipients who are at risk of severe infection.

An optimized protocol for adenosine triphosphate quantification in T lymphocytes of lymphopenic patients

In several clinical contexts, the measurement of ATP concentration in T lymphocytes has been proposed as a biomarker of immune status, predictive of secondary infections. However, the use of such biomarker in lymphopenic patients requires some adaptations in the ATP dosage protocol. We used blood from healthy volunteers to determine the optimal experimental settings. We investigated technical aspects such as the type of anticoagulant for blood sampling, the effect of freeze and thaw cycles, the reagent and sample mixing sequence, and the optimal dilution buffer. We also shortened the incubation time to 8h, and even showed that a 30min incubation may be sufficient. To evaluate the ATP rise upon lymphocyte activation, the optimal dose of stimulant was defined to be 4μg/mL of phytohaemagglutinin. Lastly, we determined that the number of T cells needed for this measurement was as low as 50,000, which is compatible with the existing lymphopenia in clinical settings. This optimized protocol appears ready to be assessed in lymphopenic patients to further investigate the interconnection between T lymphocyte metabolism and impaired phenotype and functions.

Elevated immune monitoring as measured by increased adenosine triphosphate production in activated lymphocytes is associated with accelerated development of cardiac allograft vasculopathy after cardiac transplantation

BACKGROUND

Elevated immune monitoring (IM), as measured by adenosine triphosphate (ATP) release from activated lymphocytes, has been suggested to represent an under-immunosuppressed state. Its association with the development of angiographic cardiac allograft vasculopathy (CAV) is unknown.

METHODS

Patients transplanted between January 2007 and December 2011 with annual angiograms and at least 1 IM assay were included in the analysis. Peak IM scores were determined for each patient. Patients with peak IM in the highest quartile (Group 2) were compared with those with scores in the lower quartiles (Group 1). Mild disease was scored as Grade 1 (CAV1) and moderate or severe disease was scored as Grades 2 or 3 (CAV2/3).

RESULTS

Two hundred forty patients were included. The mean age at transplant was 54.2 ± 12.1 years. Time to peak IM assay was 105.9 ± 44.1 days and average number of assays obtained per patient was 3.1 ± 1.8. Patients in the highest quartile (Group 2) had peak IM ≥446 ng ATP/ml. Mean clinical follow-up was 4.6 ± 1.7 years. CAV1 was observed in 86 of 180 (47.8%) patients in Group 1 and 39 of 60 (65.0%) in Group 2. Freedom from CAV1 was significantly lower in patients in Group 2 (log rank, p = 0.012). CAV2/3 occurred in 7 of 180 (3.7%) patients in Group 1 and 9 of 60 (15.0%) patients in Group 2. Freedom from CAV2/3 was significantly lower in patients in Group 2 (p = 0.003). In multivariate analysis elevated peak IM assay was still found to be associated with angiographic CAV (hazard ratio 1.647, confidence interval 1.020 to 2.661, p = 0.041).

CONCLUSION

Elevated peak IM, as measured by increased ATP production, in activated lymphocytes is associated with decreased freedom from angiographic CAV.

Successful Orthotopic Heart Transplantation and Immunosuppressive Management in 2 Human Immunodeficiency Virus-Seropositive Patients

Few orthotopic heart transplantations have been performed in patients infected with the human immunodeficiency virus since the first such case was reported in 2001. Since that time, advances in highly active antiretroviral therapy have resulted in potent and durable suppression of the causative human immunodeficiency virus-accompanied by robust immune reconstitution, reversal of previous immunodeficiency, a marked decrease in opportunistic and other infections, and near-normal long-term survival. Although human immunodeficiency virus infection is not an absolute contraindication, few centers in the United States and Canada have performed heart transplantations in this patient population; these patients have been de facto excluded from this procedure in North America. Re-evaluation of the reasons for excluding these patients from cardiac transplantation is warranted in light of such significant advances in antiretroviral therapy. This case report documents successful orthotopic heart transplantation in 2 patients infected with human immunodeficiency virus, and we describe their antiretroviral therapy and immunosuppressive management challenges. Both patients were doing well without sequelae 43 and 38 months after transplantation.

Immunosuppression Modifications Based on an Immune Response Assay: Results of a Randomized, Controlled Trial

BACKGROUND

An immune function assay shows promise for identifying solid organ recipients at risk for infection or rejection. The following randomized prospective study was designed to assess the clinical benefits of adjusting immunosuppressive therapy in liver recipients based on immune function assay results.

METHODS

Adult liver recipients were randomized to standard practice (control group; n = 102) or serial immune function testing (interventional group; n = 100) performed with a commercially available in vitro diagnostic assay (ImmuKnow; Viracor-IBT Laboratories, Lee's Summit, MO) before transplantation, immediately after surgery and at day 1, weeks 1 to 4, 6, and 8, and months 3 to 6, 9, and 12. The assay was repeated within 7 days of suspected/confirmed rejection/infection and within 1 week after event resolution.

RESULTS

Based on immune function values, tacrolimus doses were reduced 25% when values were less than 130 ng/mL adenosine triphosphate (low immune cell response) and increased 25% when values were greater than 450 ng/mL adenosine triphosphate (strong immune cell response). The 1-year patient survival was significantly higher in the interventional arm (95% vs 82%; P < 0.01) and the incidence of infections longer than 14 days after transplantation was significantly lower among patients in the interventional arm (42.0% vs. 54.9%, P < 0.05). The difference in infection rates was because of lower bacterial (32% vs 46%; P < 0.05) and fungal infection (2% vs 11%; P < 0.05). Among recipients without adverse events, the study group had lower tacrolimus dosages and blood levels.

CONCLUSIONS

Immune function testing provided additional data which helped optimize immunosuppression and improve patient outcomes.

The role of immunological biomarkers in cardiac rejection

PURPOSE OF REVIEW

To summarize the promises and limitations of candidate noninvasive immunological biomarkers in cardiac rejection, with a special focus on the chemokine CXCL10, as a pretransplant predictive marker of early heart acute rejection. Potential issues for transfer from research to the clinic are addressed.

RECENT FINDINGS

Early changes of immune biomolecules in peripheral blood, reflecting graft or heart recipient's immune status, are candidate biomarkers able to diagnose or predict cardiac rejection, ideally giving an opportunity to intervene before heart failure occurs. The support of robust analytical methodologies is necessary for the transition from biomarker discovery to clinical implementation.

SUMMARY

Cardiac rejection represents the main problem after heart transplantation. Endomyocardial biopsy, although invasive and not risk free, is the gold-standard procedure for rejection monitoring. Noninvasive heart damage biomarkers manifest substantially after rejection occurrence. The goal is to detect graft injury at the earliest possible stage in disease initiation. Some biomolecules associated with the early immune response to cardiac allograft retain the power to be diagnostic and, even better, predictive of acute rejection, as in the case of pretransplant CXCL10 serum level. Multicenter studies for assay validation and standardization, integrated analysis of multiple biomarkers, and cost-effectiveness evaluation are mandatory efforts.

Evaluation of the immune function assay in pediatric living donor liver transplantation

The immune function (ImmuKnow) assay is a measure of cell-mediated immunity based on the peripheral CD4+ T cell ATP activity. The efficacy of ImmuKnow in pediatric LDLT is not well documented. The aim of this study was to assess the correlations between the ImmuKnow and the clinical status in pediatric LDLT recipients. A total of 716 blood samples were obtained from 60 pediatric LDLT recipients (one month to 16 yr of age). The recipient's status was classified as follows: stable, infection, or rejection. The ImmuKnow values in the pediatric LDLT recipients with a clinically stable status had a lower immune response (IQR 85-297 ATP ng/mL) than that previously reported in adults. Meanwhile, the ImmuKnow values of the stable patients were not correlated with age. Furthermore, a significant difference was found in the ImmuKnow values between the bacterial or fungal infection and stable groups, but not between the CMV or EBV infection and stable groups. The ImmuKnow levels in the pediatric LDLT were lower than those observed in the adult LDLT. The proposed reference value is between 85 and 297 ATP ng/mL in pediatric LDLT recipients. We conclude that the ImmuKnow assay could be helpful for monitoring pediatric LDLT recipients with bacterial or fungal infections.

Monitoring T cell alloreactivity

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

Immunosuppression following heart transplantation: prospects and challenges

Immunosuppression after heart transplantation has significantly reduced the incidence of cellular rejection and improved patient outcomes with the routine use of calcineurin inhibitors. Antimetabolites and proliferation signal inhibitors add to the improvement in patient outcomes, particularly with respect to the reduced burden of cardiac allograft vasculopathy. Patients with antibody sensitization are potentially at higher risk of postoperative complications. Sensitized patients are undergoing heart transplantation with increased frequency, in part due to the emergence of ventricular assist device use as a bridge to heart transplantation. Despite improvements in immunosuppressive therapies, many challenges face physicians and patients, which will further refine and improve care of the post-heart transplant patient.

Immune cell function assay in pediatric heart transplant recipients

The ImmuKnow ICFA reports ex vivo CD4 lymphocyte activation to quantify immunosuppression. Limited organ and age-specific data exist for pediatric heart transplant recipients. We sought to examine their normative values and ICFA's association with rejection/infection. A total of 380 ICFAs from 58 heart transplant recipients (6.5/recipient) were studied retrospectively. The median age at the time of their first ICFA was 5.3 yr (IQR 2.4-12.1 yr). ICFA levels during immunologic stability (n = 311) were a median of 305 (IQR: 172-483) and mean of 353 (s.d. ± 224) ng ATP/mL. ICFA levels trended lower with advancing age. ICFA levels during immunologic stability increased over time from transplant after the first six months but were not correlated with calcineurin inhibitor levels or the type used. There is no association between ICFA values during stability and rejection (median 368 ATP ng/mL; IQR 153-527) or infection (median 293 ATP ng/mL; IQR 198-432). In contrast to the manufacturer's suggested ranges, the immunologic stable ranges in pediatric cardiac recipients were very different. ICFA values during immunologic stability are related to time from transplant in pediatric heart recipients. ICFA's ability to discriminate rejection or infection from immunologic stability was not demonstrated.

Current insights: use of Immuknow in heart transplant recipients

Despite the advances in medical management of congenital and acquired cardiac disease, heart transplant remains the only curative option for certain patients. Transplant physicians aim to maintain a fine balance between too much and too little immunosuppression, so as to prevent complications such as infections, malignant growths, and toxic effects of drugs on one hand and acute or chronic rejection of the graft on the other hand. The ImmuKnow assay (by Cylex, recently acquired by Viracor-IBT Laboratories, Inc) was first introduced in 2002 by the Food and Drug Administration for detecting cell-mediated global immunity, thus providing an additional tool to help identify patients at risk for infection and rejection. All studies done to date are reviewed to examine the use of ImmuKnow in heart transplant recipients, both adults and children. Advantages and disadvantages are described, as well as areas in need of further investigation and improvement.

Preoperative Cylex assay predicts rejection risk in patients with kidney transplant

INTRODUCTION AND OBJECTIVES

The ImmuKnow assay measures cell-mediated immunity by quantifying ATP release from CD4+ T-cells in peripheral blood. Herein, we hypothesized that this assay could predict complications associated with over-/under-immunosuppression in patients with kidney transplant (KT).

METHODS

Sixty-seven patients undergoing KT were recruited prospectively and had ATP levels measured preoperatively, and at specified intervals over two months. Clinicians were blinded to ATP levels. Clinical events including rejection and infection/cancer were documented with a median follow-up of 21 months. Parameters including absolute ATP levels and changes in ATP patterns (slopes, delta) were analyzed. Association between ATP parameters and clinical outcomes was compared using the likelihood-ratio test and Kaplan-Meier curves.

RESULTS

Absolute ATP values postoperatively had poor predictive value with regard to rejection or infection/malignancy. As well, changes in ATP values were poorly associated with complications. Importantly, patients with pre-transplant ATP values <300 ng/mL had significantly less rejection episodes vs. those with ATP values >300 ng/mL (p < 0.0001).

CONCLUSIONS

For the first time, we have evidence that a preoperative ImmuKnow level can stratify patients with KT into low/high risk groups for rejection. Future studies used to assess the utility of this assay to design individualized immunosuppressive regimens are required.

Clinical immune-monitoring strategies for predicting infection risk in solid organ transplantation

Infectious complications remain a leading cause of morbidity and mortality after solid organ transplantation (SOT), and largely depend on the net state of immunosuppression achieved with current regimens. Cytomegalovirus (CMV) is a major opportunistic viral pathogen in this setting. The application of strategies of immunological monitoring in SOT recipients would allow tailoring of immunosuppression and prophylaxis practices according to the individual's actual risk of infection. Immune monitoring may be pathogen-specific or nonspecific. Nonspecific immune monitoring may rely on either the quantification of peripheral blood biomarkers that reflect the status of a given arm of the immune response (serum immunoglobulins and complement factors, lymphocyte sub-populations, soluble form of CD30), or on the functional assessment of T-cell responsiveness (release of intracellular adenosine triphosphate following a mitogenic stimulus). In addition, various methods are currently available for monitoring pathogen-specific responses, such as CMV-specific T-cell-mediated immune response, based on interferon-γ release assays, intracellular cytokine staining or main histocompatibility complex-tetramer technology. This review summarizes the clinical evidence to date supporting the use of these approaches to the post-transplant immune status, as well as their potential limitations. Intervention studies based on validated strategies for immune monitoring still need to be performed.

Issues in solid-organ transplantation in children: translational research from bench to bedside

In this review, we identify important challenges facing physicians responsible for renal and cardiac transplantation in children based on a review of the contemporary medical literature. Regarding pediatric renal transplantation, we discuss the challenge of antibody-mediated rejection, focusing on both acute and chronic antibody-mediated rejection. We review new diagnostic approaches to antibody-mediated rejection, such as panel-reactive antibodies, donor-specific cross-matching, antibody assays, risk assessment and diagnosis of antibody-mediated rejection, the pathology of antibody-mediated rejection, the issue of ABO incompatibility in renal transplantation, new therapies for antibody-mediated rejection, inhibiting of residual antibodies, the suppression or depletion of B-cells, genetic approaches to treating acute antibody-mediated rejection, and identifying future translational research directions in kidney transplantation in children. Regarding pediatric cardiac transplantation, we discuss the mechanisms of cardiac transplant rejection, including the role of endomyocardial biopsy in detecting graft rejection and the role of biomarkers in detecting cardiac graft rejection, including biomarkers of inflammation, cardiomyocyte injury, or stress. We review cardiac allograft vasculopathy. We also address the role of genetic analyses, including genome-wide association studies, gene expression profiling using entities such as AlloMap®, and adenosine triphosphate release as a measure of immune function using the Cylex® ImmuKnow™ cell function assay. Finally, we identify future translational research directions in heart transplantation in children.

Handling and interpretation of heart transplant biopsies

The biopsy material that is available for evaluation of the transplant heart is retrieved from an invasive biopsy procedure that is often small or suboptimal for evaluation. It is essential that the tissue is handled optimally from the time it is removed from the body to the time it is placed on the microscope stage to facilitate the best opportunity for an adequate diagnosis and to prevent the necessity for repeat costly and invasive procedures. Furthermore, the diagnostic information may be time sensitive for the treating clinician and mishandling the tissue or requiring a repeat biopsy will delay the start of treatment if the biopsy discloses actionable information. Herein we describe an optimized protocol for handling and interpreting heart transplant biopsies.

Trends in immune cell function assay and donor-specific HLA antibodies in kidney transplantation: A 3-year prospective study

The immune cell function assay (ICFA) and de novo anti-donor-specific HLA antibodies (DSA) have been proposed as assays for immune monitoring in renal transplantation, but longitudinal studies examining the modification of both parameters over time and their relation with clinical events are lacking. We prospectively measured longitudinal changes in ICFA and DSA levels in 55 kidney transplant recipients over 3-year follow-up (534 visits) and analyzed their relation with the risk of developing acute rejections or infections. Seven patients (12.7%) developed biopsy-proven acute rejection, and 20 (36.4%) developed viral infections. At 3 years posttransplant, 28% of the patients had developed de novo DSA. ICFA levels peaked at 1-2 months posttransplant (p = 0.005) and leveled off thereafter. They were not associated with the risk of acute rejections, viral infections or development of de novo DSA. Instead, the incidence of de novo DSA was higher in patients who previously had viral infections (adjusted-odds ratio of de novo DSA associated with prior infections: 6.03 [95% CI, 1.64-22.06; p = 0.007]). Our prospective, longitudinal study does not support using ICFA to quantify the immune risk in kidney transplantation. Further studies are needed to confirm the relationship between viral infections and the subsequent development of de novo DSA.

Immunologic monitoring in transplantation revisited

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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