Additional value of interleukin-6 level to predict histopathological features of hepatocellular carcinoma before liver transplantation.

BACKGROUND & AIMS: Inflammatory biomarkers are increasingly used as outcome predictors in the field of oncology and liver transplantation for HCC, but no study has shown the prognostic value of IL6 after LT. The goal of this study was to evaluate the predictive value of IL-6 on histopathological features of HCC on explant, its predictive value on recurrence risk and its additional value to other scores and inflammatory markers at the time of transplantation. METHODS: From 2009 to 2019, all adults transplanted with a first liver graft and diagnosed with HCC on the explant analysis were retrospectively included (n = 229). Only patients who had a pre-LT IL6 level determination were analysed in this study (n = 204). RESULTS: High IL-6 level at transplantation was associated with a significantly higher risk of vascular invasion (15% vs 6%; p = 0.023), microsatellitosis (11% vs 3%; p = 0.013), lower rate of histological response both in terms of complete response (2% vs 14%, p = 0.004) and of necrosis (p = 0.010). Patients with pre-LT IL-6 level > 15 ng/ml had a lower overall and cancer-specific survival (p = 0.013). Recurrence-free survival was lower in patients with IL-6 > 15 ng/ml with a 3-year recurrence-free survival of 88% versus 78% (p = 0.034). IL6 levels were significantly higher in patients with early recurrence compared to patients without (p = 0.002) or with late recurrence (p = 0.044). CONCLUSIONS: IL6 level at transplantation is an independent predictor of pejorative histological features of HCC and is associated to the risk of recurrence.

Location and allocation: Inequity of access to liver transplantation for patients with severe acute-on-chronic liver failure in Europe.

There is growing evidence that liver transplantation (LT) is the most effective treatment for acute-on-chronic liver failure grade-3 (ACLF-3). This study examines whether and how this evidence translates into practice by analyzing the variability in intensive care unit (ICU) admissions, listing strategies, and LT activity for patients with ACLF-3 across transplantation centers in Europe. Consecutive patients who were admitted to the ICU with ACLF-3, whether or not they were listed and/or transplanted with ACLF-3, between 2018 and 2019 were included across 20 transplantation centers. A total of 351 patients with ACLF-3 were included: 33 had been listed prior to developing ACLF-3 and 318 had not been listed at the time of admission to the ICU. There was no correlation between the number of unlisted patients with ACLF-3 admitted to the ICU and the number listed or transplanted while in ACLF-3 across centers. By contrast, there was a correlation between the number of patients listed and the number transplanted while in ACLF-3. About 21% of patients who were listed while in ACLF-3 died on the waiting list or were delisted. The percentage of LT for patients with ACLF-3 varied from 0% to 29% for those transplanted with decompensated cirrhosis across centers (average = 8%), with an I2 index of 68% (95% confidence interval, 49%-80%), showing substantial heterogeneity among centers. The 1-year survival for all patients with ACLF-3 was significantly higher in centers that listed and transplanted more patients with ACLF-3 (>10 patients) than in centers that listed and transplanted fewer: 36% versus 20%, respectively (p = 0.012). Patients with ACLF-3 face inequity of access to LT across Europe. Waitlisting strategies for patients with ACLF-3 influence their access to LT and, ultimately, their survival.

Immunosuppression in patients with grade 3 acute-on-chronic liver failure at transplantation: A practice analysis study.

Transplantation for patients with acute-on-chronic liver failure grade 3 (ACLF3) has encouraging results with 1-year-survival of 80-90%. These patients with multiple organ failure meet the conditions for serious alterations of drug metabolism and increased toxicity. The goal of this study was to identify immunosuppression-dependent factors that affect survival. This retrospective monocentric study was conducted in patients with ACLF3 consecutively transplanted between 2007 and 2019. The primary endpoint was 1-year survival. Secondary endpoints were overall survival, treated rejection, and surgical complications. Immunosuppression was evaluated as to type of immunosuppression, post-transplant introduction timing, trough levels, and trough level intra-patient variability (IPV). One hundred patients were included. Tacrolimus IPV < 40% (P = .019), absence of early tacrolimus overdose (P = .033), use of anti-IL2-receptor antibodies (P = .034), and early mycophenolic acid introduction (P = .038) predicted 1-year survival. Treated rejection was an independent predictor of survival (P = .001; HR 4.2 (CI 95%: 1.13-15.6)). Early everolimus introduction was neither associated with higher rejection rates nor with more surgical complications. Management of immunosuppression in ACLF3 critically ill patients undergoing liver transplantation is challenging. Occurrence and treatment of rejection impacts on survival. Early introduction of mTOR inhibitor seems safe and efficient in this situation.

Pretransplant Intensive Care Unit Management and Selection of Grade 3 Acute-on-Chronic Liver Failure Transplant Candidates.

The aim of this study is to report on the liver transplantation (LT) activity and posttransplant outcome, over time, of patients with grade 3 acute-on-chronic liver failure (ACLF-3) in a single transplant center performing a large number of LTs for patients with ACLF-3. It aims at showing how pre-LT intensive care unit (ICU) management impacts post-LT outcomes, in particular through monitoring the transplantation for ACLF-3 model (TAM) score. A total of 100 patients who had ACLF-3 at the time of LT between 2007 and 2019 were included retrospectively. The cohort was divided in 2 periods, with 50 patients in each period. There was an increase in the number of patients with ACLF-3 who received an LT during the course of the study period and significantly higher 1-year post-LT survival rates in the second period compared with the first period (86% versus 66%, respectively; P = 0.02). Interestingly, patients during both periods had similar severity profiles and scores apart from a significantly lower number of patients with TAM scores >2 at the time of LT in the second period compared with the first period (1 [2%] versus 11 [22%], respectively; P ≤ 0.01). In addition, patients whose clinical condition improved in the ICU (with a TAM score downstaged between admission and LT) had significantly higher post-LT survival rates than those whose TAM score stayed the same or increased: 88% versus 70%, respectively (P = 0.04). This study shows a learning curve in LT for patients with ACLF-3, with optimized ICU management and patient selection leading to increased numbers of LTs for patients with ACLF-3 and improved post-LT outcomes. It also delineates how the TAM score can be used to identify the optimal transplantability window for patients with ACLF-3.

Pre-operative CT scan helps predict outcome after liver transplantation for acute-on-chronic grade 3 liver failure.

OBJECTIVES: The aim of this study was to identify the prognostic value of pre-operative imaging to predict post-transplantation survival in critically ill cirrhotic patients with severe acute-on-chronic liver failure (ACLF). METHODS: Patients with grade 3 ACLF who underwent liver transplantation between January 2010 and January 2020 and with available contrast-enhanced abdominal computed tomography (CT) performed less than 3 months before LT were retrospectively included (n = 82). Primary endpoint was 1-year mortality. Imaging parameters (sarcopenia, liver morphology and volumetry, and signs of portal hypertension) were screened and tested to build a prognostic score. RESULTS: In the multivariate analysis, three independent CT-derived prognostic factors were found: splenomegaly (p = 0.021; HR = 5.6 (1.29-24.1)), liver atrophy (p = 0.05; HR = 2.93 (1.01-10.64)), and vena cava diameter ratio (p < 0.0001; HR = 12.7 (3.4-92)). A simple prognostic score was proposed, based on the presence of splenomegaly (5 points), liver atrophy (5 points), and vena cava diameter ratio < 0.2 (12 points). A cutoff at 10 points distinguished a high-risk group (score > 10) from a low-risk group (score ≤ 10) with 1-year survival of 27% vs. 67% respectively (p < 0.001). It was found to be an independent predictive factor in association with the Transplantation for ACLF3 Model (TAM) score. CONCLUSION: Pre-transplantation contrast-enhanced abdominal CT has a significant impact on selection of patients in ACLF3 in order to predict 1-year survival after LT. KEY POINTS: • Splenomegaly, liver atrophy, and vena cava diameter ratio are independent CT-derived prognostic factors after transplantation for severe acute-on-chronic liver failure. • A simple CT-based prognostic score is an independent predictive factor, complementary to clinical and biological parameters. • The use of the CT-derived score allows stratification based on 1-year mortality for patients with otherwise uncertain prognosis with clinical and biological parameters alone.

Liver transplantation for critically ill cirrhotic patients: Results from the French transplant registry.

This study describes the population of cirrhotic patients who were transplanted from the ICU in France, identifying pre-transplant risk factors of post-transplant mortality and describing geographic variations in ICU transplant activity. Cirrhotic patients transplanted between 2008 and 2018 were included through the national transplant registry. The demographic, clinical and biological characteristics of the patients transplanted from the ICU were compared to cirrhotic patients who were transplanted from home or from the hospital. Risk factors of post-transplant one-year mortality were identified in uni- and multivariable analysis within the population transplanted from the ICU. Funnel plots were used to illustrate center-specific differences in ICU transplant activity. 1,047 cirrhotic patients were transplanted from the ICU during the study period. While the national rate of transplants performed from the ICU was 14.3% the absolute number and the rate of cirrhotic patients transplanted from the ICU varied significantly from one center to another, ranging from 6.6% to 22.8% (p < 0.05). Three recipient-associated independent risk factors one-year post-LT mortality were identified in the population transplanted from the ICU: age > 50 years (HR 1.65, 95%CI 1.16-2.36), p = 0.005), diabetes (HR 1.46, 95%CI 1.07-1.98, p = 0.02) and intubation (HR2.12, 95%CI 1.62-2.78), p < 0.001). Donor age was also independently associated with mortality (HR 1.01, 95%CI 1.01-1.02, p < 0.001). Funnel plots showed significant differences in the proportion of patients transplanted from the ICU and the distribution of risk factors across French transplant centers, especially the inclination to transplant intubated patients. This study underlines the increased post-transplant mortality among cirrhotic patients transplanted from the ICU. It identifies four clinically pertinent independent risk factors associated with post-transplant mortality in this specific sub-group of transplant candidates. Finally, it illustrates how diverse the landscape of liver transplantation for critically ill cirrhotic patients is across a single country, despite a unified allocation algorithm.

Liver transplantation for patients with acute-on-chronic liver failure (ACLF) in Europe: Results of the ELITA/EF-CLIF collaborative study (ECLIS).

BACKGROUND & AIMS: Liver transplantation (LT) has been proposed as an effective salvage therapy even for the sickest patients with acute-on-chronic liver failure (ACLF). This large collaborative study was designed to assess the current clinical practice and outcomes of patients with ACLF who are wait-listed for LT in Europe. METHODS: This was a retrospective study including 308 consecutive patients with ACLF, listed in 20 centres across 8 European countries, from January 2018 to June 2019. RESULTS: A total of 2,677 patients received a LT: 1,216 (45.4%) for decompensated cirrhosis. Of these, 234 (19.2%) had ACLF at LT: 58 (4.8%) had ACLF-1, 78 (6.4%) had ACLF-2, and 98 (8.1%) had ACLF-3. Wide variations were observed amongst countries: France and Germany had high rates of ACLF-2/3 (27-41%); Italy, Switzerland, Poland and the Netherlands had medium rates (9-15%); and the United Kingdom and Spain had low rates (3-5%) (p <0.0001). The 1-year probability of survival after LT for patients with ACLF was 81% (95% CI 74-87). Pre-LT arterial lactate levels >4 mmol/L (hazard ratio [HR] 3.14; 95% CI 1.37-7.19), recent infection from multidrug resistant organisms (HR 3.67; 95% CI 1.63-8.28), and renal replacement therapy (HR 2.74; 95% CI 1.37-5.51) were independent predictors of post-LT mortality. During the same period, 74 patients with ACLF died on the waiting list. In an intention-to-treat analysis, 1-year survival of patients with ACLF on the LT waiting list was 73% for ACLF-1 or -2 and 50% for ACLF-3. CONCLUSION: The results reveal wide variations in the listing of patients with ACLF in Europe despite favourable post-LT survival. Risk factors for mortality were identified, enabling a more precise prognostic assessment of patients with ACLF. LAY SUMMARY: Acute-on-chronic liver failure (ACLF) is a severe clinical condition for which liver transplantation is an effective therapeutic option. This study has demonstrated that in Europe, referral and access to liver transplantation (LT) for patients with ACLF needs to be harmonised to avoid inequities. Post-LT survival for patients with ACLF was >80% after 1 year and some factors have been identified to help select patients with favourable outcomes.

Organ allocation in the age of the algorithm: avoiding futile transplantation - utility in allocation.

PURPOSE OF REVIEW: This review describes and questions the evolution of allocation systems from local team decisions in the 20th century to patient-oriented allocation using complex algorithm predicting transplant benefit. RECENT FINDINGS: The opening years of the 2000s have seen the implementation of prioritization scores aiming at increasing transparency and reducing waitlist mortality. The 2010s have underlined the necessity of drawing the upper limits of how sick a patient can be while still ensuring acceptable survival. More complex algorithms evaluating transplant benefit have been implemented in allocation systems to take this issue into account. SUMMARY: Allocation algorithms are becoming more and more complex, integrating numerous parameters from both donor and recipient to achieve optimal matching. The limitations of implementing these complex algorithms are represented by the evermoving waiting list demography, geographic disparities between recipients and donors, team policy adaptation to rule changes, and implicit biases within the transplant community. Survival as the only metric by which to define benefit may be seen as restrictive; quality of life may be a fruitful measure for better defining benefit in organ transplantation in the future.

Liver transplantation for critically ill cirrhotic patients: Stratifying utility based on pretransplant factors.

The aim of this study was to produce a prognostic model to help predict posttransplant survival in patients transplanted with grade-3 acute-on-chronic liver failure (ACLF-3). Patients with ACLF-3 who underwent liver transplantation (LT) between 2007 and 2017 in 5 transplant centers were included (n = 152). Predictors of 1-year mortality were retrospectively screened and tested on a single center training cohort and subsequently tested on an independent multicenter cohort composed of the 4 other centers. Four independent pretransplant risk factors were associated with 1-year mortality after transplantation in the training cohort: age ≥53 years (P = .044), pre-LT arterial lactate level ≥4 mml/L (P = .013), mechanical ventilation with PaO2 /FiO2  ≤ 200 mm Hg (P = .026), and pre-LT leukocyte count ≤10 G/L (P = .004). A simplified version of the model was derived by assigning 1 point to each risk factor: the transplantation for Aclf-3 model (TAM) score. A cut-off at 2 points distinguished a high-risk group (score >2) from a low-risk group (score ≤2) with 1-year survival of 8.3% vs 83.9% respectively (P < .001). This model was subsequently validated in the independent multicenter cohort. The TAM score can help stratify posttransplant survival and identify an optimal transplantation window for patients with ACLF-3.

Impact of early remote organ dysfunction on long-term survival after liver transplantation.

BACKGROUND: Attention is focused on graft function although extrahepatic organ dysfunction often occurs. Renal failure, cardiovascular events and sepsis have individually shown a significant impact on short- and long-term outcomes. The aim of the study was to identify how extrahepatic organ dysfunction (EROD) and allograft dysfunction (EAD) may be associated and their relative impact on long-term survival. METHODS: A retrospective study was conducted in a unicentric cohort of 294 patients transplanted between 2009 and 2014. The composite endpoint EROD was defined as requirement during the hospitalization of de novo renal replacement therapy, reintubation/ventilation > 7 days or cardiovascular event. Donor and recipient characteristics were evaluated as predictive of EROD in uni- and multivariate analysis. Main endpoint was overall survival evaluated by Kaplan-Meier method. RESULTS: EROD occurred in 91 patients (31%) among whom 42 also experienced EAD (46%). Predicting factors associated with EROD were IL6 level (P = 0.002) and lab-MELD (P < 0.001). Only patients experiencing both EAD and EROD had a worse survival (P = 0.001). In patients without EAD, time to normalization of bilirubin and INR were longer in patients with EROD compared to those without EROD (P = 0.002 and P = 0.008 respectively). CONCLUSIONS: The composite endpoint described as early remote organ dysfunction could be used as a predictive factor after transplantation and should be included in future studies together with early allograft dysfunction. Identifying patients in whom EROD and EAD occur together or one after the other could help to better predict long-term outcomes.

Intensive care for patients with gastric cancers: outcome and survival prognostic factors.

BACKGROUND: Admission and management of patients with solid malignancies in intensive care unit (ICU) is a controversial topic. To this day, there is no data published concerning patients with gastric cancers hospitalized in ICU. This single center retrospective study reports the characteristics, outcome and prognostic factors of patients hospitalized in ICU for medical reasons over a period of 10 years. METHODS: We performed a single center retrospective study which reports the characteristics, outcome and prognostic factors of patients hospitalized in ICU for medical reasons over a period of 10 years. RESULTS: Thirty-seven patients were included, among whom 24 (64.9%) had metastatic cancer. The most frequent diagnosis on admission was septic shock (48.6%) and 24 patients (64.9%) required intubation. Ten patients (27.0%) were alive 3 months after their admission in ICU. Metastatic cancer and intubation were independently associated with a higher risk of dying within 3 months of admission in multivariate analysis: odds ratio (OR) =13.7; 95% confidence interval (CI), 1.7-108 (P<0.01). Seventeen patients (45.9%) died during their ICU stay. Metastatic cancer: OR =89; 95% CI, 2.7-6,588, therapeutic intensification: OR =1,471; 95% CI, 9.8-811,973 and the logistic organ dysfunction score (LODS) on admission: OR =1.4; 95% CI, 1.1-2.3 were independently associated with mortality within the ICU in multivariate analysis (P<0.01). CONCLUSIONS: This is the first study that examines the outcome and prognostic factors of patients with gastric cancers who require life-sustaining therapy in ICU. The identification of 3 months and ICU mortality prognostic factors could contribute to guiding clinicians in the management of these patients and assist health professionals in their discussions with these patients and their families.

Passive mesenterico-saphenous shunt: An alternative to portocaval anastomosis for tailored portal decompression during liver transplantation.

BACKGROUND: Temporary portocaval shunt has a positive impact on short-term outcomes after liver transplantation. An alternative to temporary portocaval shunt is a distal passive decompression through mesenterico-saphenous shunt. The purpose of this study was to compare outcomes of these two types of surgical portosystemic shunt and discuss their respective place during the anhepatic phase. METHODS: Patients transplanted with portal decompression during a 4-year period were included. Patients were compared according to two types of surgical decompression techniques: temporary portocaval shunt (n = 44) and mesenterico-saphenous shunt (n = 77). Spontaneous >5-mm portosystemic shunts were described as absent, nonpersistent, distal, or proximal. Intraoperative portal pressure variations and inhospital course were compared between the two groups, with special attention on the impact of competing spontaneous and surgical shunts. RESULTS: Mesenterico-saphenous shunt and temporary portocaval shunt showed a comparable hemodynamic efficiency, with no significant difference in terms of portal pressure variations. We found no significant difference in terms of reperfusion syndrome (P = .956), transfusion rate (P = .575), renal failure (P = .239) nor early allograft dysfunction (P = .976). There was a significantly higher risk of early allograft dysfunction when competing surgical and spontaneous shunts were used (P = .002) with a lesser hemodynamic efficiency (analysis of variance test; P = .04). CONCLUSION: Portacaval or mesenterico-saphenous shunts offer similar hemodynamic efficiency without impacting the outcomes after liver transplantation. Their respective place and the place of portal decompression should be discussed regarding the presence of portal thrombosis and pre-existing portosystemic shunts. Evaluation of the anatomy and the efficiency of these shunts may guide tailored portal decompression.

Liver transplantation for critically ill cirrhotic patients: Overview and pragmatic proposals.

Liver transplantation for critically ill cirrhotic patients with acute deterioration of liver function associated with extrahepatic organ failures is controversial. While transplantation has been shown to be beneficial on an individual basis, the potentially poorer post-transplant outcome of these patients taken as a group can be held as an argument against allocating livers to them. Although this issue concerns only a minority of liver transplants, it calls into question the very heart of the allocation paradigms in place. Indeed, most allocation algorithms have been centered on prioritizing the sickest patients by using the model for end-stage liver disease score. This has led to allocating increasing numbers of livers to increasingly critically ill patients without setting objective or consensual limits on how sick patients can be when they receive an organ. Today, finding robust criteria to deem certain cirrhotic patients too sick to be transplanted seems urgent in order to ensure the fairness of our organ allocation protocols. This review starts by fleshing out the argument that finding such criteria is essential. It examines five types of difficulties that have hindered the progress of recent literature on this issue and identifies various strategies that could be followed to move forward on this topic, taking into account the recent discussion on acute on chronic liver failure. We move on to review the literature along four axes that could guide clinicians in their decision-making process regarding transplantation of critically ill cirrhotic patients.

Critically ill elderly patients (≥ 90 years): Clinical characteristics, outcome and financial implications.

BACKGROUND: Patients aged over 90 are being admitted to intensive care units (ICUs) with increasing frequency. The appropriateness of such decisions still remains controversial due to questionable outcome, limited resources and costs. Our objective was to determine the clinical characteristics and outcome in elderly patients (≥ 90 years) admitted in a medical ICU, with an additional focus on medico-economic implications. METHODS: We reviewed the charts of all patients (≥ 90 years) admitted to our ICU. We compared them with all other ICU patients (< 90 years), sought to identify ICU mortality predictors and also performed a long-term survival follow-up. RESULTS: In the study group of 317 stays: median age was 92 years (IQR: 91-94 years); most patients were female (71.3%.). Acute respiratory failure (52.4%) was the main admission diagnosis; mean SAPS II was 55.6±21.3; half the stays (49.2%) required mechanical ventilation (duration: 7.2±8.8 days); withholding and withdrawing decisions were made for 33.4% of all stays. ICU and hospital mortality rates were 35.7% and 42.6% respectively. Mechanical ventilation (OR = 4.83, CI95%: 1.59-15.82) was an independent predictor of ICU mortality whereas age was not (OR = 0.88, CI95%: 0.72-1.08). Social security reimbursement was significantly lower in the study group compared with all other ICU stays, both per stay (13,160 vs 22,092 Euros, p< 0.01) and per day of stay (p = 0.03). CONCLUSION: Among critically ill elderly patients (≥ 90 years), chronological age was not an independent factor of ICU mortality. ICU care-related costs in this population should not be considered as a limiting factor for ICU admission.

Liver transplantation in critically ill patients: Preoperative predictive factors of post-transplant mortality to avoid futility.

BACKGROUND: The allocation of liver transplants to patients with acute liver failure (ALF) and acute-on-chronic liver failure (ACLF) with multi-organ failure who are admitted in ICU remains controversial due to their high post-transplant mortality rate and the absence of identified mortality risk factors. METHODS: We performed a single-center retrospective cohort study to determine the post-transplant mortality rate of patients with ALF and ACLF requiring ICU care prior to liver transplant (LT) and identified pretransplant factors of post-transplant mortality. RESULTS: Eighty-four patients (29 with ALF and 55 with ACLF) received a liver transplant while they were hospitalized at the ICU. Their mean model for end-stage liver disease (MELD) score was 41, and their mean sequential organ failure assessment (SOFA) was 15 the day before transplant. The overall 1-year survival rate was 66%. In multivariate analysis, pretransplant lactate level and acute respiratory distress syndrome (ARDS) were the only two independent factors associated with post-transplant mortality. The absence of ARDS and a pretransplant lactate level< 5 mmol/L led to the identification of a subgroup of ICU patients with a good 1-year post-transplant survival (>80%). CONCLUSIONS: Low lactatemia lactate level and the absence of ARDS could be useful criteria in selecting those patients in ICU who could be eligible for liver transplant.

The ADAMTS131239-1253 peptide is a dominant HLA-DR1-restricted CD4+ T-cell epitope.

Acquired thrombotic thrombocytopenic purpura is a rare and severe disease characterized by auto-antibodies directed against "A Disintegrin And Metalloproteinase with Thrombospondin type 1 repeats, 13th member" (ADAMTS13), a plasma protein involved in hemostasis. Involvement of CD4+ T cells in the pathogenesis of the disease is suggested by the IgG isotype of the antibodies. However, the nature of the CD4+ T-cell epitopes remains poorly characterized. Here, we determined the HLA-DR-restricted CD4+ T-cell epitopes of ADAMTS13. Candidate T-cell epitopes were predicted in silico and binding affinities were confirmed in competitive enzyme-linked immunosorbent assays. ADAMTS13-reactive CD4+ T-cell hybridomas were generated following immunization of HLA-DR1 transgenic mice (Sure-L1 strain) and used to screen the candidate epitopes. We identified the ADAMTS131239-1253 peptide as the single immunodominant HLA-DR1-restricted CD4+ T-cell epitope. This peptide is located in the CUB2 domain of ADAMTS13. It was processed by dendritic cells, stimulated CD4+ T cells from Sure-L1 mice and was recognized by CD4+ T cells from an HLA-DR1-positive patient with acute thrombotic thrombocytopenic purpura. Interestingly, the ADAMTS131239-1253 peptide demonstrated promiscuity towards HLA-DR11 and HLA-DR15. Our work paves the way towards the characterization of the ADAMTS13-specific CD4+ T-cell response in patients with thrombotic thrombocytopenic purpura using ADAMTS131239-1253-loaded HLA-DR tetramers.