Recombinant ADAMTS13 for Immune Thrombotic Thrombocytopenic Purpura.

In patients with immune thrombotic thrombocytopenic purpura (iTTP), autoantibodies against the metalloprotease ADAMTS13 lead to catastrophic microvascular thrombosis. However, the potential benefits of recombinant human ADAMTS13 (rADAMTS13) in patients with iTTP remain unknown. Here, we report the clinical use of rADAMTS13, which resulted in the rapid suppression of disease activity and complete recovery in a critically ill patient whose condition had proved to be refractory to all available treatments. We also show that rADAMTS13 causes immune complex formation, which saturates the autoantibody and may promote its clearance. Our data support the role of rADAMTS13 as a novel adjunctive therapy in patients with iTTP.

Computer vision quantitation of erythrocyte shape abnormalities provides diagnostic, prognostic, and mechanistic insight.

Examination of red blood cell (RBC) morphology in peripheral blood smears can help diagnose hematologic diseases, even in resource-limited settings, but this analysis remains subjective and semiquantitative with low throughput. Prior attempts to develop automated tools have been hampered by their poor reproducibility and limited clinical validation. Here, we present a novel, open-source machine-learning approach (denoted as RBC-diff) to quantify abnormal RBCs in peripheral smear images and generate an RBC morphology differential. RBC-diff cell counts showed high accuracy for single-cell classification (mean AUC, 0.93) and quantitation across smears (mean R2, 0.76 compared with experts, interexperts R2, 0.75). RBC-diff counts were concordant with the clinical morphology grading for 300 000+ images and recovered the expected pathophysiologic signals in diverse clinical cohorts. Criteria using RBC-diff counts distinguished thrombotic thrombocytopenic purpura and hemolytic uremic syndrome from other thrombotic microangiopathies, providing greater specificity than clinical morphology grading (72% vs 41%; P < .001) while maintaining high sensitivity (94% to 100%). Elevated RBC-diff schistocyte counts were associated with increased 6-month all-cause mortality in a cohort of 58 950 inpatients (9.5% mortality for schist. >1%, vs 4.7% for schist; <0.5%; P < .001) after controlling for comorbidities, demographics, clinical morphology grading, and blood count indices. RBC-diff also enabled the estimation of single-cell volume-morphology distributions, providing insight into the influence of morphology on routine blood count measures. Our codebase and expert-annotated images are included here to spur further advancement. These results illustrate that computer vision can enable rapid and accurate quantitation of RBC morphology, which may provide value in both clinical and research contexts.

Pathway-driven rare germline variants associated with transplant-associated thrombotic microangiopathy (TA-TMA).

The significance of rare germline mutations in transplant-associated thrombotic microangiopathy (TA-TMA) is not well studied. We performed a genetic association study in 100 adult TA-TMA patients vs. 98 post-transplant controls after matching by race, sex, and year. We focused on 5 pathways in complement, von Willebrand factor (VWF) function and related proteins, VWF clearance, ADAMTS13 function and related proteins, and endothelial activation (3641variants in 52 genes). In the primary analysis focused on 189 functional rare variants, no differential variant enrichment was observed in any of the pathways; specifically, 29 % TA-TMA and 33 % controls had at least 1 rare complement mutation. In the secondary analysis focused on 37 rare variants predicted to be pathogenic or likely pathogenic by ClinVar, Complement Database, or REVEL in-silico prediction tool, rare variants in the VWF clearance pathway were found to be significantly associated with TA-TMA (p = 0.008). On the gene level, LRP1 was the only one with significantly increased variants in TA-TMA in both analyses (p = 0.025 and 0.015). In conclusion, we did not find a significant association between rare variants in the complement pathway and TA-TMA; however, we discovered a new signal in the VWF clearance pathway driven by the gene LRP1 among likely pathogenic variants.

Emergency transfusion with whole blood versus packed red blood cells: A study of 1400 patients.

BACKGROUND: Low-titer group O whole blood (LTOWB) is increasingly used for emergency transfusion. We studied whether initial release of LTOWB compared with packed red blood cells (pRBCs) reduced overall blood requirements for patients needing emergency transfusion. Secondary outcomes examined included survival and non-lethal adverse clinical outcomes. STUDY DESIGN AND METHODS: A retrospective, single-center, before-versus-after study compared patients transfused with emergency-release, uncrossmatched pRBC followed by component therapy (2016-2019) versus patients transfused with emergency-release, uncrossmatched LTOWB followed by component therapy (2019-2022). RESULTS: Outcomes were available for 602 patients in the pRBC group versus 749 in the whole blood group. The two groups were similar for age, sex, race, estimated blood volume, ABO blood groups, and underlying diagnosis. Use of LTOWB was associated with increased blood product use at 24 h (4.0 (2.0-12.0) in pRBC group versus 6.5 (4.2-12.7) in LTOWB group, p < .0001) and at 7 days (5.5 (3.0-13.0) in pRBC group versus 7.3 (4.3-14.3) in LTOWB group, p < .0001). Initial use of LTOWB was not associated with improved 24 h or 30 day survival nor lower incidence of non-lethal adverse clinical outcomes compared with pRBC. DISCUSSION: Our study showed a statistically significant increase in total blood use and blood acquisition costs for patients receiving initial emergency transfusion with LTOWB compared with pRBC. The initial use of LTOWB offered no advantage over component therapy for 30 day survival or selected non-lethal adverse outcomes.

Retrospective analysis of outcomes in patients with acute hypertriglyceridemic pancreatitis treated without therapeutic plasma exchange.

BACKGROUND: Therapeutic plasma exchange (TPE) is often used to decrease serum triglyceride levels in hypertriglyceridemic pancreatitis (HTGP), although there is a lack of high-quality data directly attributing improved clinical outcomes to TPE. There are currently no large studies evaluating the treatment of HTGP without TPE. STUDY DESIGN AND METHODS: This study retrospectively analyzes clinical and laboratory outcomes of 115 encounters at Massachusetts General Hospital (MGH) wherein a HTGP patient was treated without TPE and compares these outcomes to those of HTGP patients in the literature treated with TPE. RESULTS: After management without TPE, the median reduction in serum triglycerides was 48% (IQR 29%-63%) on day one and 74% (IQR 60%-84%) on day two in 115 episodes of acute HTGP. The reductions were comparable to those reported in several large published case series after a course of TPE (65.8% to 81% reduction). In 25 episodes among 24 patients, treatment included admission to an intensive care unit. There was no significant difference in mortality or rates of local complication, mechanical ventilation, or use of vasoactive medication or renal replacement therapy between this ICU subset and published cohorts (all P > .05). CONCLUSIONS: HTGP patients who do not receive TPE do not experience inferior outcomes compared to patients in the literature treated with TPE. The added value of TPE in HTGP, if any exists, needs to be demonstrated in controlled trials.

Non-Alloimmune Mechanisms of Thrombocytopenia and Refractoriness to Platelet Transfusion.

Refractoriness to platelet transfusion is a common clinical problem encountered by the transfusion medicine specialist. It is well recognized that most causes of refractoriness to platelet transfusion are not a consequence of alloimmunization to human leukocyte, platelet-specific, or ABO antigens, but are a consequence of platelet sequestration and consumption. This review summarizes the clinical factors that result in platelet refractoriness and highlights recent data describing novel biological mechanisms that contribute to this clinical problem.

Deaths and complications associated with the management of acute immune thrombotic thrombocytopenic purpura.

BACKGROUND: The introduction of therapeutic plasma exchange (TPE) dramatically decreased mortality in patients with immune thrombotic thrombocytopenic purpura (iTTP). However, there are few modern descriptions of residual causes of death from iTTP and complications associated with TPE. STUDY DESIGN AND METHODS: This was a retrospective study in a multi-institutional cohort of 109 patients with iTTP between 2004 and 2017. Complications of TPE were analyzed in a subset of this cohort (74 patients representing 101 treatment courses). RESULTS: Death occurred in 8 of 109 patients (7.3%) and in 8 of 219 captured episodes of acute iTTP (mortality rate per episode: 3.7%). Neither the number of TPE treatments nor length of hospitalization predicted mortality. The majority of deaths (5/8) were associated with delay in the diagnosis of iTTP or initiation of TPE or presentation to the hospital in a moribund state. A subset of patients (N = 74) was analyzed for TPE-related complications. Most patients (56/74; 76%) had at least one minor or major complication of TPE. Seven of 101 (6.9%) discrete treatment courses were associated with one or more severe complications, including anaphylaxis and line-associated infections and thrombosis. Overall, the most frequent adverse events were mild allergic (urticarial) transfusion reactions, which affected 34 of 101 (34%) treatment courses. One patient died from a TPE-related complication, line-associated bacteremia. CONCLUSION: Early identification of patients with iTTP and the rapid initiation of TPE are paramount in preventing mortality. While TPE was associated with a high rate of adverse events, the vast majority were treatable and TPE-related mortality is low.

Management of hemostatic complications in acute leukemia: Guidance from the SSC of the ISTH.

Patients with acute leukemia frequently develop thrombocytopenia and hemostatic complications caused by coagulopathy. Coagulopathy complicates the management of these patients and can lead to significant morbidity and mortality. This guidance document aims to review and provide guidance on the management of hemostatic complications in adult patients with acute leukemia, addressing four main issues, including platelet transfusion, disseminated intravascular coagulation, L-asparaginase-related hypofibrinogenemia, and the use of antifibrinolytic agents.

Severe CD4+ T-cell lymphopenia is not observed in frequent plateletpheresis donors collected on the Fenwal Amicus.

BACKGROUND: In a recent study, we determined that 30% of frequent plateletpheresis donors collected using the Trima Accel Automated Blood Collection System (Terumo BCT) had a CD4+ T-cell count below 200 cells/µL. Whether CD4+ T-cell lymphopenia is associated with donation using other plateletpheresis instruments is unknown. STUDY DESIGN AND METHODS: We obtained blood samples from 30 current frequent Fenwal Amicus plateletpheresis donors. All participants had made 20 to 24 plateletpheresis donations in the most recent 365-day period, and all had previously donated over 50 times on the Fenwal Amicus instrument. Blood samples were analyzed to determine blood counts, including CD4+ and CD8+ counts. RESULTS: Of 30 study participants, none had a CD4+ count below 200 cells/µL. There was one participant with a CD4+ count between 200 and 300 cells/µL. This individual was over the age of 55 and had a history of more than 300 lifetime plateletpheresis sessions. One participant had a CD8+ count below the lower limit of normal (125 cells/µL) and a normal CD4+ count. CONCLUSION: We did not detect severe CD4+ lymphopenia in frequent platelet donors undergoing plateletpheresis with the Fenwal Amicus. Since the Fenwal Amicus does not incorporate a leukoreduction system chamber, this finding supports the hypothesis that such chambers-found in the Trima Accel instrument-contribute to CD4+ lymphopenia in frequent platelet donors.

Routine Solid Phase Multiplex Anti-HLA Antibody Tests Predict Platelet Refractoriness.

OBJECTIVES: No validated screening methods identify patients at risk for human leukocyte antigen (HLA) alloimmune-mediated platelet refractoriness (alloPR). We determined if bead-based HLA antibody tests could predict risk of developing HLA alloPR. METHODS: Hematopoietic progenitor cell transplant patients screened for HLA antibodies without prior refractoriness were identified. Phenotype bead screening results were compared between patients who later did and did not develop alloPR. RESULTS: Seven of 27 patients identified subsequently developed alloPR. The panel reactive antibody (PRA) and mean fluorescence intensity (MFI) of the 10 most reactive beads in the initial screen were significantly higher among patients who later developed alloPR (P < .001). Specifically, PRA of more than 30% and mean MFI of 1,500 or more in the most reactive beads identified at-risk patients. Administration of HLA-compatible platelets yielded significant posttransfusion count increments compared with routine platelets. CONCLUSIONS: HLA antibody screening by phenotype bead assay may prospectively identify at-risk patients for the development of alloPR. However, clinical trials are needed to validate these findings.

Predictors of relapse and efficacy of rituximab in immune thrombotic thrombocytopenic purpura.

Patients with immune-mediated thrombotic thrombocytopenic purpura (iTTP) often experience life-threatening relapses of the disease, and rituximab (RTX) can be used to mitigate relapse risk. However, the predictors of relapse in iTTP and the magnitude and duration of effect of RTX remain key unanswered questions. Using a multi-institutional cohort of consecutive adult patients with iTTP, we used survival analysis to compare relapse rates between patients who received RTX during the index presentation with acute iTTP and those who did not. Of 124 patients, 60 (48%) received RTX and 34 (27%) experienced relapse. Median time to relapse was 3.71 (interquartile range, 1.75-4.9) and 1.33 (interquartile range, 0.43-2.35) years for RTX-treated and untreated patients, respectively. RTX conferred protection from relapse at 1 year of follow-up (P = .01) but not at 5 years of follow-up. Extended Cox regression was then used to identify predictors of relapse and to estimate the protective effect of RTX. The following parameters were independently associated with increased risk for subsequent relapse: presenting in iTTP relapse (hazard ratio [HR], 2.97; 95% confidence interval [CI], 1.4-6.4), age younger than 25 years (HR, 2.94; 95% CI, 1.2-7.2), and non-O blood group (HR, 2.15; 95% CI, 1.06-4.39). RTX initially provided protection from relapse (HR, 0.16; 95% CI, 0.04-0.70), but this effect gradually diminished, returning to the baseline risk for untreated patients at approximately 2.6 years. Patients who are young, have non-O blood group, or present with relapsed iTTP are at increased risk for subsequent relapse. RTX appears to confer short-term protection from relapse.

Utilizing a PLASMIC score-based approach in the management of suspected immune thrombotic thrombocytopenic purpura: a cost minimization analysis within the Harvard TMA Research Collaborative.

The PLASMIC score is a recently described clinical scoring algorithm that rapidly assesses the probability of severe ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) deficiency among patients presenting with microangiopathic haemolytic anaemia. Using a large multi-institutional cohort, we explored whether an approach utilizing the PLASMIC score to risk-stratify patients with suspected immune thrombotic thrombocytopenic purpura (iTTP) could lead to significant cost savings. Our consortium consists of institutions with an unrestricted approach to ADAMTS13 testing (Group A) and those that require pre-approval by the transfusion medicine service (Group B). Institutions in Group A tested more patients than those in Group B (P < 0·001) but did not identify more cases of iTTP (P = 0·29) or have lower iTTP-related mortality (P = 0·84). Decision tree cost analysis showed that applying a PLASMIC score-based strategy to screen patients for ADAMTS13 testing in Group A would have reduced costs by approximately 27% over the 12-year period of our study compared to the current approach. Savings were primarily driven by a reduction in unnecessary therapeutic plasma exchanges, but lower utilization of ADAMTS13 testing and subspecialty consultations also contributed. Our data indicate that using the PLASMIC score to guide ADAMTS13 testing and the management of patients with suspected iTTP could be associated with significant cost savings.

Red blood cell alloantibodies are associated with increased alloimmunization against human leukocyte antigens.

BACKGROUND: Alloantibodies recognizing human leukocyte antigens (HLA) can cause immune-mediated refractoriness to platelet transfusion. An association between HLA alloimmunization and red blood cell (RBC) alloimmunization has been suggested but remains uncertain. STUDY DESIGN AND METHODS: We tested for HLA alloantibodies in 660 patients with and without RBC alloantibodies. Calculated panel reactive antibody (cPRA) values were determined for HLA alloimmunized patients. Current and historical diagnoses and blood product exposure were catalogued. Variables associated with high-level HLA alloimmunization (cPRA ≥ 90%) were evaluated. RESULTS: The cohort included 366 women and 294 men with median age of 66 years (interquartile range [IQR], 53-76). The number of patients with and without RBC alloantibodies was 447 and 213, respectively. Among patients with and without RBC alloantibodies, 20.6% and 8.5% had a cPRA ≥ 90%, respectively (p < 0.0001). In univariate analyses of men and nulliparous women and previously pregnant women, the median number of RBC alloantibodies was significantly higher in patients with a cPRA ≥ 90% (p < 0.0001). The number of RBC alloantibodies remained an independent predictor of a cPRA ≥ 90% in multivariate analysis (odds ratio [OR] 1.50, 95% confidence interval [CI] 1.22-1.85). Other independent predictors of a cPRA ≥ 90% were parity (OR 1.26, 95% CI 1.08-1.47), age (OR 0.98, 95% CI 0.97-1.00), history of renal disease (OR 1.88, 95% CI 1.02-3.48), and number of non-leukoreduced products transfused (OR 1.02, 95% CI 1.00-1.04). CONCLUSIONS: RBC alloimmunization was significantly associated with HLA alloimmunization with a cPRA ≥ 90%. RBC alloimmunization status combined with specific components of the clinical history may estimate the risk of high-level HLA alloimmunization.

Clinical features and outcomes in patients with thrombotic microangiopathy not associated with severe ADAMTS13 deficiency.

BACKGROUND: The a disintegrin and metalloprotease with thrombospondin type 1 motifs, member 13 (ADAMTS13) activity assay has become important in distinguishing autoimmune thrombotic thrombocytopenic purpura from other forms of thrombotic microangiopathy (TMA). Although the significance of severe deficiency in ADAMTS13 (activity levels 10% or less) has been well defined, little data are available on the clinical importance of mild to moderate deficiency (activity levels 11%-70%) among patients with TMA. STUDY DESIGN AND METHODS: We conducted a retrospective study using the Harvard TMA Research Collaborative Registry. Among 254 patients who met the inclusion criteria for TMA, 186 patients with ADAMTS13 activity levels greater than 10% were divided into moderate-deficiency (11%-40%), mild-deficiency (41%-70%), and no-deficiency (greater than 70%). RESULTS: Compared with mild or no deficiency, moderate ADAMTS13 deficiency correlated with older age; higher bilirubin and international normalized ratio; and increased frequency of sepsis, shock, or multiorgan failure. Platelet counts, lactate dehydrogenase levels, and the presence of renal or neurologic dysfunction did not vary across the three patient cohorts. While moderate ADAMTS13 deficiency was associated with increased 90-day mortality in univariate analysis, this association was no longer significant in multivariate analysis. Variables that independetly predicted 90-day mortality in this cohort of patients included Charlson comorbidity index, alanine aminotransferase level, platelet count, creatinine, and the presence of sepsis, shock, or multiorgan failure. CONCLUSION: Moderately deficient ADAMTS13 activity identifies a cohort of patients with TMA who are at increased risk for 90-day mortality. The ADAMTS13 activity level in this group is not an independent predictor of poor outcomes but instead appears to be a marker of disease acuity.

Derivation and external validation of the PLASMIC score for rapid assessment of adults with thrombotic microangiopathies: a cohort study.

BACKGROUND: Among the syndromes characterised by thrombotic microangiopathy, thrombotic thrombocytopenic purpura is distinguished by a severe deficiency in the ADAMTS13 enzyme. Patients with this disorder need urgent treatment with plasma exchange. Because ADAMTS13 activity testing typically requires prolonged turnaround times and might be unavailable in resource-poor settings, a method to rapidly assess the likelihood of severe ADAMTS13 deficiency is needed. METHODS: All consecutive adult patients presenting to three large academic medical centres in Boston, MA, USA, with thrombotic microangiopathy and a possible diagnosis of thrombotic thrombocytopenic purpura between Jan 8, 2004, and Dec 6, 2015, were included in an ongoing multi-institutional registry (the Harvard TMA Research Collaborative). Univariate analysis was used to identify covariates for a logistic regression model predictive of severe ADAMTS13 deficiency (≤10% activity). A clinical point score was generated, and its diagnostic performance was assessed using internal and external validation cohorts and compared to clinical assessment alone. FINDINGS: 214 patients with thrombotic microangiopathy were included in the derivation cohort. A seven-component clinical prediction tool, termed the PLASMIC score, was developed and found to reliably assess the pretest probability of severe ADAMTS13 deficiency (C statistic 0·96, 95% CI 0·92-0·98). Our diagnostic model was reproducibly accurate in both the internal (0·95, 0·91-0·98) and external (0·91, 0·85-0·95) validation cohorts. The scoring system also more consistently diagnosed thrombotic microangiopathy due to severe ADAMTS13 deficiency than did standard clinical assessment, as measured by C statistic (0·96, 95% CI 0·92-0·98 for PLASMIC vs 0·83, 0·77-0·88 for clinical assessment; p<0·0001) and mean Brier score (0·065 for PLASMIC vs 0·111 for clinical assessment; mean paired difference 0·05, 95% CI 0·01-0·08; p<0·0001). When utilised in addition to clinical assessment, the PLASMIC score contributed significant discriminatory power (integrated discrimination improvement 0·24, 95% CI 0·11-0·37). INTERPRETATION: We have developed and validated a clinical prediction tool-the PLASMIC score-to stratify patients with thrombotic microangiopathy according to their risk of having severe ADAMTS13 deficiency. We have shown that this scoring system is superior to standard clinical assessment in addressing the diagnostic challenge presented by thrombotic microangiopathy. Its use, together with clinical judgment, may facilitate treatment decisions in patients for whom timely results of ADAMTS13 activity testing are unavailable. FUNDING: The Luick Family Fund of Massachusetts General Hospital.

Treatment with or without plasma exchange for patients with acquired thrombotic microangiopathy not associated with severe ADAMTS13 deficiency: a propensity score-matched study.

BACKGROUND: Therapeutic plasma exchange (TPE) is a proven treatment for thrombotic thrombocytopenic purpura (TTP) characterized by severe ADAMTS13 deficiency, but the efficacy of TPE in suspected TTP with an ADAMTS13 activity level of more than 10% remains controversial. STUDY DESIGN AND METHODS: We conducted a propensity score (PS)-matched study of 186 adult patients included in the Harvard Thrombotic Microangiopathy (TMA) Research Collaborative registry who presented with TMA suggestive of TTP but an ADAMTS13 activity level of more than 10%. RESULTS: Before matching, patients treated with TPE (n = 71) differed from untreated patients (n = 115) by several clinical measures. PS matching was performed to address clinical disparities between the two groups and resulted in a well-balanced cohort of 59 TPE-treated patients paired with 59 untreated controls, all of whom had TMA. After matching, we observed no significant difference in the primary outcome of 90-day survival between the treated and untreated groups (hazard ratio, 0.88; 95% confidence interval [CI], 0.44-1.77; p = 0.72). In-hospital mortality (odds ratio [OR], 0.77; 95% CI, 0.34-1.75; p = 0.53) and the percentage of patients with platelet count recovery (OR, 1.58; 95% CI, 0.77-3.26; p = 0.21) also did not differ significantly between the two matched groups. CONCLUSION: Our data suggest that routine use of TPE in the diverse group of TMA patients without severe ADAMTS13 deficiency may not significantly improve outcomes.