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.

How I diagnose and treat thrombocytopenia in geriatric patients.

ABSTRACT: Thrombocytopenia in older individuals is a common but diagnostically challenging condition that has variable clinical impact to those who are affected. Diagnostic approach requires evaluation of the preexisting clinical conditions, detailed review of medications, and assessment for disorders that warrant urgent treatment. In this article, we describe a systematic approach to diagnosis of thrombocytopenia and present a schematic review for management strategies. Three clinical scenarios are presented that are relevant for their prevalence and management challenges in an older adult population. The first scenario addresses primary immune thrombocytopenia (ITP) and reviews different treatment options. The second one addresses complications of thrombocytopenia in management of the myelodysplastic syndrome. The last one reviews diagnostic challenges of drug-induced ITP.

Immunotactoid hepatopathy: A novel entity with histologically proven recurrence post liver transplantation.

Immunotactoid deposition is a rare fibrillary deposition disease that is primarily seen in the kidney and is associated with paraproteinemia. Here, we report a case of hepatic immunotactoid deposition in a 67-year-old male with a history of smoldering myeloma and chronic kidney disease who underwent liver transplantation for metabolic dysfunction-related cirrhosis. Immunotactoid deposition was first identified in the explanted liver and recurred in the allograft within only 7 weeks following transplantation, presenting as ascites with normal liver function tests. The patient's posttransplant course was complicated by proteinuria and renal failure requiring dialysis. Histologic examination of both native and allograft livers demonstrated pink amorphous material occupying sinusoidal spaces that were Congo-red negative and immunoglobulin M Kappa-restricted. Electron microscopy revealed characteristic deposits of electron-dense bundles of hollow microtubules with a 40 nm diameter within the sinusoids and space of Disse, consistent with immunotactoids. Therapy of the patient's underlying plasma-cell dyscrasia utilizing a daratumumab-based regimen showed decreased serum paraproteins, resolution of ascites, and improved kidney function, no longer requiring dialysis, without inducing rejection. The patient continues to respond to treatment 10 months posttransplant.

Observational cohort study of long-term outcomes of liver transplantation in haemophilia.

INTRODUCTION: Gene therapy is now a reality for individuals with haemophilia, yet little is known regarding the quality-of-life impact of factor correction. As few data exist, and recognizing the analogy to liver transplantation (OLTX), we identified OLTX+ and OLTX- men in the ATHNdataset to compare post-OLTX factor VIII and IX on quality of life (QoL) by Haem-A-QoL and PROMIS-29. METHODS: OLTX- were matched to OLTX+ by age, race, and haemophilia type and severity. Deidentified demographic data, including post-transplant factor levels, genotype and target joint disease were analysed by descriptive statistics. Haem-A-Qol and PROMIS-29 were compared in OLTX+ and OLTX- by student's t-test and univariate regression models. RESULTS: Of 86 people with haemophilia A (HA) or haemophilia B (HB) cared for at 10 haemophilia treatment centers (HTCs), 21 (24.4%) OLTX+ and 65 (75.6%) OLTX- were identified. OLTX+ and OLTX- had a similar frequency of target joint disease (p = .806), HA genotypes, null versus non-null (p = .696), and HIV infection (p = .316). At a median 9.2 years post-OLTX, median FVIII, .63 IU/mL [IQR 0.52-0.97] and FIX, .91 IU/mL [IQR .63-1.32], Haem-A-QoL, PROMIS-29, and HOT scores were comparable. Severe HA/HB had lower post-OLTX 'dealing with haemophilia' scores (p = .022) and higher 'sports and leisure' (p = .010) and 'view of yourself' scores (p = .024) than OLTX+ non-severe participants. Non-caucasian OLTX+ had significantly lower scores in sports and leisure (p = .042), future expectations (p = .021) and total score (p = .010). CONCLUSION: Nine years after OLTX, QoL is comparable to OLTX-, but significantly better in OLTX+ with severe than non-severe disease and in caucasians than non-caucasians.

Redefining outcomes in immune TTP: an international working group consensus report.

Immune-mediated thrombotic thrombocytopenic purpura (iTTP) is a potentially fatal thrombotic microangiopathy caused by autoantibody-mediated severe deficiency of ADAMTS13. Standardized definitions of response, exacerbation, remission, and relapse were initially proposed in 2003 and modified by the International Working Group for TTP in 2017. These definitions, which have been widely used in clinical practice and research, are based primarily on the platelet count and are benchmarked against the timing of discontinuation of therapeutic plasma exchange (TPE). They do not incorporate ADAMTS13 activity or the temporizing effects on the platelet count of caplacizumab, a novel anti-von Willebrand factor (VWF) nanobody. In light of these limitations, the IWG aimed to develop revised consensus outcome definitions that incorporate ADAMTS13 activity and the effects of anti-VWF therapy, by using an estimate-talk-estimate approach. The updated definitions distinguish clinical remission and clinical relapse (defined primarily by platelet count) from ADAMTS13 remission and ADAMTS13 relapse (defined by ADAMTS13 activity). The revised definitions of exacerbation and remission are benchmarked against not only the timing of discontinuation of TPE but also that of anti-VWF therapy. Retrospective validation of the revised definitions is described, although they have yet to be prospectively validated. Clinical implications of the updated outcome definitions are also discussed and an example of their application to clinical practice is provided to highlight their clinical relevance.

Annual incidence and severity of acute episodes in hereditary thrombotic thrombocytopenic purpura.

Hereditary thrombotic thrombocytopenic purpura (hTTP) is a rare thrombotic microangiopathy characterized by severe congenital ADAMTS13 deficiency and recurring acute episodes causing morbidity and premature death. Information on the annual incidence and severity of acute episodes in patients with hTTP is largely lacking. This study reports prospective data on 87 patients from the Hereditary TTP Registry (clinicaltrials.gov #NCT01257269) for survival, frequency, and severity of acute episodes from enrollment until December 2019. The 87 patients, followed up for a median of 4.2 years (range, 0.01-15 years), had a median age at overt disease onset and at clinical diagnosis of 4.6 years and 18 years (range, 0.0-70 years for both), respectively. Forty-three patients received regular plasma prophylaxis, whereas 22 did not, and treatment changed over time or was unknown in the remaining 22. Forty-three patients experienced 131 acute episodes, of which 91 (69%) occurred in patients receiving regular prophylaxis. This resulted in an annual incidence of acute episodes of 0.36 (95% confidence interval [CI], 0.29-0.44) with regular plasma treatment and of 0.41 (95% CI, 0.30-0.56) without regular plasma treatment. More than one-third of acute episodes (n = 51) were documented in children <10 years of age at enrollment and were often triggered by infections. Their annual incidence of acute episodes was significantly higher than in patients aged >40 years (1.18 [95% CI, 0.88-1.55] vs 0.14 [95% CI, 0.08-0.23]). The prophylactic plasma infusion regimens used were insufficient to prevent acute episodes in many patients. Such regimens are burdensome, and caregivers, patients, and their guardians are reluctant to start regular plasma infusions, from which children particularly would benefit.

Durable remission of thrombotic thrombocytopenic purpura in the setting of pembrolizumab therapy.

BACKGROUND: There is a small but growing number of thrombotic thrombocytopenic purpura (TTP) cases attributed to immune checkpoint inhibitor therapy, with nivolumab and ipilimumab therapy being the most frequently described in the literature. STUDY DESIGN AND METHODS: This report evaluates the course of a patient with a history of metastatic adenocarcinoma of the lung who developed TTP following treatment with the PD-1 inhibitor Pembrolizumab. The patient was treated with six sessions of therapeutic plasma exchange and appeared to be in remission. Exacerbation occurred 4 days later, and seven more sessions of plasma exchange were performed along with four total doses of Rituximab, and a steroid taper with monitoring of platelet counts and ADAMTS13 activity. RESULTS: His platelet count recovered to a peak of 318,000 UL with an ADAMTS13 activity of 77% at the time of discharge. The patient has been following up regularly for outpatient testing with no TTP relapse as of the completion of this report. DISCUSSION: This is one of a few cases of Pembrolizumab-associated TTP reported in the literature with successful complete remission following treatment. Plasma exchange in this setting may be an especially beneficial therapeutic intervention because of the removal of both the anti-ADAMTS13 antibody as well as the immune system upregulating anti-PDL1 monoclonal antibody with replacement of ADAMTS13 from donor plasma. Longer duration of plasma exchange and monitoring for normalization of ADAMTS13 levels in addition to platelet count before cessation of treatment may improve durable remission rates in this entity.

Real-world safety and effectiveness of recombinant porcine sequence factor VIII in acquired haemophilia A: A non-interventional, post-authorization safety study.

INTRODUCTION: Recombinant porcine factor VIII (rpFVIII, susoctocog alfa) is indicated for the treatment of bleeding episodes in adults with acquired haemophilia A (AHA). AIM: To provide long-term real-world safety and effectiveness data for rpFVIII in the management of AHA bleeding episodes. METHODS: US PASS (NCT02610127) was a multicentre, uncontrolled, open-label, post-marketing safety surveillance study conducted in adults with AHA. Data were collected retrospectively or prospectively for 180 days after rpFVIII treatment. The primary outcome was the incidence of treatment-related serious adverse events (SAEs). Secondary outcomes included haemostatic effectiveness of rpFVIII and rpFVIII utilization. RESULTS: Fifty-three patients were enrolled from December 2015 to June 2019 (prospective, n = 30; retrospective, n = 23). Six patients experienced seven treatment-related SAEs (incidence 12.0%). The most common treatment-related SAE was FVIII inhibition (inhibiting antibodies to rpFVIII; incidence 8.0%, 95% CI: 2.2-19.2). Five patients reported seven thromboembolic events; one was an SAE and possibly related to rpFVIII. Of bleeding events treated with rpFVIII, 80.3% (57/71) of bleeds resolved with rpFVIII. The median (range) dose of rpFVIII per infusion was 50 (10-300) units/kg, with a median (range) of 6.0 (1-140) infusions and a median (range) time from bleed onset to bleed resolution of 14.0 (2.0-132.7) days. CONCLUSION: In this real-world study of rpFVIII for AHA, no new safety signals were identified compared with previous clinical trial findings. Eighty percent of bleeds resolved with rpFVIII treatment.

A microfluidic analysis of thrombus formation in reconstituted whole blood samples comparing spray-dried plasma versus fresh frozen plasma.

BACKGROUND: Prompt resuscitation with plasma and other blood products reduces trauma-related morbidity and mortality. Standard storage and preparation techniques for frozen plasma limit its utility in the pre-hospital setting. Plasma can be dehydrated using hot air (spray-dried plasma), stored at room temperature and rehydrated quickly for use. The spray-dry process decreases high-molecular-weight multimers of von Willebrand factor compared with conventional plasma. The objective of this study was to compare platelet adhesion and thrombus formation in a microfluidic perfusion assay facilitated by spray-dried compared with frozen plasma using a non-inferiority design. STUDY DESIGN AND METHODS: Whole blood was centrifuged to obtain red cell concentrate, and a platelet pellet that was suspended in either spray-dried or frozen plasma to create recombined whole blood. Platelets were fluorescently labelled, and samples were flowed through a collagen-coated microchannel. Surface area coverage by platelets and thrombi was analysed and compared between each spray-dried and frozen plasma pair. RESULTS: Compared with whole blood samples containing frozen plasma, samples with spray-dried plasma had similar surface area coverage of platelets and thrombi after 180 s of flow. Even when diluted with von Willebrand factor-free plasma, there was no reduction thrombus formation. CONCLUSION: Spray-dried plasma is not inferior in supporting haemostasis compared with fresh frozen plasma in a paired analysis. It offers advantages with respect to portability and ease of preparation over frozen plasma in the pre-hospital setting. This study supports development of clinical studies to evaluate the efficacy and safety of spray-dried plasma in trauma patients.

Turning a Corner in ME/CFS Research.

This collection of research papers addresses fundamental questions concerning the nature of myalgic encephalomyelitis/ chronic fatigue syndrome (ME/CFS), the problem of disbelief and lack of knowledge and understanding of the condition among many doctors and the origins of this problem, and its impact on patients and their families. We report briefly the growing knowledge of the underlying pathological processes in ME/CFS, and the development of new organizations, including Doctors with ME, the US ME/CFS Clinical Coalition and EUROMENE, to address aspects of the challenges posed by the illness. We discuss the implications of COVID-19, which has much in common with ME/CFS, with much overlap of symptoms, and propose a new taxonomic category, which we are terming post-active phase of infection syndromes (PAPIS) to include both. This collection of papers includes a number of papers reporting similar serious impacts on the quality of life of patients and their families in various European countries. The advice of EUROMENE experts on diagnosis and management is included in the collection. We report this in light of guidance from other parts of the world, including the USA and Australia, and in the context of current difficulties in the UK over the promulgation of a revised guideline from the National Institute for Health and Care Excellence (NICE). We also consider evidence on the cost-effectiveness of interventions for ME/CFS, and on the difficulties of determining the costs of care when a high proportion of people with ME/CFS are never diagnosed as such. The Special Issue includes a paper which is a reminder of the importance of a person-centred approach to care by reviewing mind-body interventions. Finally, another paper reviews the scope for prevention in minimizing the population burden of ME/CFS, and concludes that secondary prevention, through early detection and diagnosis, could be of value.

Our Evolving Understanding of ME/CFS.

The potential benefits of the scientific insights gleaned from years of treating ME/CFS for the emerging symptoms of COVID-19, and in particular Longhaul- or Longhauler-COVID-19 are discussed in this opinion article. Longhaul COVID-19 is the current name being given to the long-term sequelae (symptoms lasting beyond 6 weeks) of SARS-CoV-2 infection. Multiple case definitions for ME/CFS exist, but post-exertional malaise (PEM) is currently emerging as the 'hallmark' symptom. The inability to identify a unique trigger of ME/CFS, as well as the inability to identify a specific, diagnostic laboratory test, led many physicians to conclude that the illness was psychosomatic or non-existent. However, recent research in the US and the UK, championed by patient organizations and their use of the internet and social media, suggest underlying pathophysiologies, e.g., oxidative stress and mitochondrial dysfunction. The similarity and overlap of ME/CFS and Longhaul COVID-19 symptoms suggest to us similar pathological processes. We put forward a unifying hypothesis that explains the precipitating events such as viral triggers and other documented exposures: For their overlap in symptoms, ME/CFS and Longhaul COVID-19 should be described as Post Active Phase of Infection Syndromes (PAPIS). We further propose that the underlying biochemical pathways and pathophysiological processes of similar symptoms are similar regardless of the initiating trigger. Exploration of the biochemical pathways and pathophysiological processes should yield effective therapies for these conditions and others that may exhibit these symptoms. ME/CFS patients have suffered far too long. Longhaul COVD-19 patients should not be subject to a similar fate. We caution that failure to meet the now combined challenges of ME/CFS and Longhaul COVID-19 will impose serious socioeconomic as well as clinical consequences for patients, the families of patients, and society as a whole.

Radiomic Features of Primary Rectal Cancers on Baseline T2 -Weighted MRI Are Associated With Pathologic Complete Response to Neoadjuvant Chemoradiation: A Multisite Study.

BACKGROUND: Twenty-five percent of rectal adenocarcinoma patients achieve pathologic complete response (pCR) to neoadjuvant chemoradiation and could avoid proctectomy. However, pretreatment clinical or imaging markers are lacking in predicting response to chemoradiation. Radiomic texture features from MRI have recently been associated with therapeutic response in other cancers. PURPOSE: To construct a radiomics texture model based on pretreatment MRI for identifying patients who will achieve pCR to neoadjuvant chemoradiation in rectal cancer, including validation across multiple scanners and sites. STUDY TYPE: Retrospective. SUBJECTS: In all, 104 rectal cancer patients staged with MRI prior to long-course chemoradiation followed by proctectomy; curated from three institutions. FIELD STRENGTH/SEQUENCE: 1.5T-3.0T, axial higher resolution T2 -weighted turbo spin echo sequence. ASSESSMENT: Pathologic response was graded on postsurgical specimens. In total, 764 radiomic features were extracted from single-slice sections of rectal tumors on processed pretreatment T2 -weighted MRI. STATISTICAL TESTS: Three feature selection schemes were compared for identifying radiomic texture descriptors associated with pCR via a discovery cohort (one site, N = 60, cross-validation). The top-selected radiomic texture features were used to train and validate a random forest classifier model for pretreatment identification of pCR (two external sites, N = 44). Model performance was evaluated via area under the curve (AUC), accuracy, sensitivity, and specificity. RESULTS: Laws kernel responses and gradient organization features were most associated with pCR (P ≤ 0.01); as well as being commonly identified across all feature selection schemes. The radiomics model yielded a discovery AUC of 0.699 ± 0.076 and a hold-out validation AUC of 0.712 with 70.5% accuracy (70.0% sensitivity, 70.6% specificity) in identifying pCR. Radiomic texture features were resilient to variations in magnetic field strength as well as being consistent between two different expert annotations. Univariate analysis revealed no significant associations of baseline clinicopathologic or MRI findings with pCR (P = 0.07-0.96). DATA CONCLUSION: Radiomic texture features from pretreatment MRIs may enable early identification of potential pCR to neoadjuvant chemoradiation, as well as generalize across sites. LEVEL OF EVIDENCE: 3 TECHNICAL EFFICACY STAGE: 2.

Caplacizumab for treatment of thrombotic thrombocytopenic purpura in a patient with anaphylaxis to fresh-frozen plasma.

BACKGROUND: Plasma exchange with plasma replacement has been the mainstay for the treatment of thrombotic thrombocytopenic purpura (TTP) for several decades. Recently an anti-von Willebrand factor (VWF) medication, caplacizumab, has been approved for treatment of TTP when used with plasma exchange. We report a patient with immune-mediated TTP that had an anaphylactic reaction to plasma who was then given caplacizumab daily for 1 week without further plasma exchange therapy with a good clinical and laboratory response. CASE REPORT: A 63-year-old woman with acute confusion and multiple ecchymoses after tooth extraction developed TTP with a hemoglobin (Hb) of 6.3 g/dL, white blood cell count 15 × 109 /L, platelets (PLTs) 12 × 109 /L, lactate dehydrogenase (LDH) 1212 IU/mL, and creatinine 0.9 mg/dL. Her ADAMTS13 level was less than 5% and plasma exchange was started. During the first plasma exchange the patient developed anaphylaxis with hypotension, shortness of breath, angioedema, and urticaria. She recovered from this reaction with treatment and no further plasma exchanges were performed. Instead she was given methylprednisolone, caplacizumab, and later rituximab. The caplacizumab was given daily for 8 days during which her PLT counts and ADAMTS13 levels improved. Her Hb level also increased. She continued to receive oral prednisone and rituximab after discharge was doing well latest follow up (Day 114). CONCLUSION: Caplacizumab may be used safely and effectively without concomitant plasma exchange in a patient with anaphylaxis to plasma.

The International Hereditary Thrombotic Thrombocytopenic Purpura Registry: key findings at enrollment until 2017.

Congenital thrombotic thrombocytopenic purpura is an autosomal recessive inherited disease with a clinically heterogeneous course and an incompletely understood genotype-phenotype correlation. In 2006, the Hereditary TTP Registry started recruitment for a study which aimed to improve the understanding of this ultra-rare disease. The objective of this study is to present characteristics of the cohort until the end of 2017 and to explore the relationship between overt disease onset and ADAMTS13 activity with emphasis on the recurring ADAMTS13 c.4143_4144dupA mutation. Diagnosis of congenital thrombotic thrombocytopenic purpura was confirmed by severely deficient ADAMTS13 activity (≤10% of normal) in the absence of a functional inhibitor and the presence of ADAMTS13 mutations on both alleles. By the end of 2017, 123 confirmed patients had been enrolled from Europe (n=55), Asia (n=52, 90% from Japan), the Americas (n=14), and Africa (n=2). First recognized disease manifestation occurred from around birth up to the age of 70 years. Of the 98 different ADAMTS13 mutations detected, c.4143_4144dupA (exon 29; p.Glu1382Argfs*6) was the most frequent mutation, present on 60 of 246 alleles. We found a larger proportion of compound heterozygous than homozygous carriers of ADAMTS13 c.4143_4144dupA with overt disease onset at < 3 months of age (50% vs 37%), despite the fact that ADAMTS13 activity was <1% in 18 of 20 homozygous, but in only 8 of 14 compound heterozygous carriers. An evaluation of overt disease onset in all patients with an available sensitive ADAMTS13 activity assay (n=97) shows that residual ADAMTS13 activity is not the only determinant of age at first disease manifestation. Registered at clinicaltrials.gov identifier NCT01257269.

Clinical and laboratory variability in a cohort of patients diagnosed with type 1 VWD in the United States.

von Willebrand disease (VWD) is the most common inherited bleeding disorder, and type 1 VWD is the most common VWD variant. Despite its frequency, diagnosis of type 1 VWD remains the subject of debate. In order to study the spectrum of type 1 VWD in the United States, the Zimmerman Program enrolled 482 subjects with a previous diagnosis of type 1 VWD without stringent laboratory diagnostic criteria. von Willebrand factor (VWF) laboratory testing and full-length VWF gene sequencing was performed for all index cases and healthy control subjects in a central laboratory. Bleeding phenotype was characterized using the International Society on Thrombosis and Haemostasis bleeding assessment tool. At study entry, 64% of subjects had VWF antigen (VWF:Ag) or VWF ristocetin cofactor activity below the lower limit of normal, whereas 36% had normal VWF levels. VWF sequence variations were most frequent in subjects with VWF:Ag <30 IU/dL (82%), whereas subjects with type 1 VWD and VWF:Ag ≥30 IU/dL had an intermediate frequency of variants (44%). Subjects whose VWF testing was normal at study entry had a similar rate of sequence variations as the healthy controls (14%). All subjects with severe type 1 VWD and VWF:Ag ≤5 IU/dL had an abnormal bleeding score (BS), but otherwise BS did not correlate with VWF:Ag. Subjects with a historical diagnosis of type 1 VWD had similar rates of abnormal BS compared with subjects with low VWF levels at study entry. Type 1 VWD in the United States is highly variable, and bleeding symptoms are frequent in this population.

Fatty acid-binding protein 1 is preferentially lost in microsatellite instable colorectal carcinomas and is immune modulated via the interferon γ pathway.

Fatty acid-binding protein 1 (FABP1) is an intracellular protein responsible for the transportation of long chain fatty acids. Aside from its functions in lipid metabolism and cellular differentiation, FABP1 also plays a role in inflammation through its interaction with peroxisome proliferator-activated receptors (PPARs). Previously, we compared expression of colonic epithelium genes in a subset of microsatellite instable (MSI) colorectal carcinomas (medullary carcinomas) to normal colonic mucosa and found that FABP1 expression was markedly decreased in the tumors. Further analysis of RNA expression in the colorectal subtypes and The Cancer Genome Atlas data set found that FABP1 expression is decreased in the CMS1 subset of colorectal carcinomas, which is characterized by microsatellite instability. As MSI colorectal carcinomas are known for their robust immune response, we then aimed to link FABP1 to the immune microenvironment of MSI carcinomas. To confirm the gene expression results, we performed immunohistochemical analysis of a cohort of colorectal carcinomas. FABP1 was preferentially lost in MSI carcinomas (123/133, 93%) compared with microsatellite stable carcinomas (240/562, 43%, P<0.0001). In addition, higher numbers of tumor-infiltrating lymphocytes were present in tumors with loss of FABP1 (P<0.0001). Decreased expression of the fatty acid storage and glucose regulator, PPARγ, was associated with the loss of FABP1 (P<0.0001). Colorectal cancer cell lines treated with interferon γ exhibited decreased expression of FABP1. FABP1 expression was partially recovered with the treatment of the cell lines with rosiglitazone, a PPARγ agonist. This study demonstrated that the loss of FABP1 expression is associated with MSI carcinomas and that interferon γ stimulation plays a role in this process via its interaction with PPARγ.

Crucial role for the VWF A1 domain in binding to type IV collagen.

Von Willebrand factor (VWF) contains binding sites for platelets and for vascular collagens to facilitate clot formation at sites of injury. Although previous work has shown that VWF can bind type IV collagen (collagen 4), little characterization of this interaction has been performed. We examined the binding of VWF to collagen 4 in vitro and extended this characterization to a murine model of defective VWF-collagen 4 interactions. The interactions of VWF and collagen 4 were further studied using plasma samples from a large study of both healthy controls and subjects with different types of von Willebrand disease (VWD). Our results show that collagen 4 appears to bind VWF exclusively via the VWF A1 domain, and that specific sequence variations identified through VWF patient samples and through site-directed mutagenesis in the VWF A1 domain can decrease or abrogate this interaction. In addition, VWF-dependent platelet binding to collagen 4 under flow conditions requires an intact VWF A1 domain. We observed that decreased binding to collagen 4 was associated with select VWF A1 domain sequence variations in type 1 and type 2M VWD. This suggests an additional mechanism through which VWF variants may alter hemostasis.

Impact of treatment and outcomes for patients with posttransplant drug-associated thrombotic microangiopathy.

BACKGROUND: Drug-induced transplant-associated thrombotic microangiopathy (DTA-TMA) is a rare but serious complication that can occur after hematopoietic cell transplantation (HCT) or solid organ transplantation (SOT) without guidelines for optimal management of this condition. STUDY DESIGN AND METHODS: Given the ambiguity surrounding the treatment for DTA-TMA, we conducted a retrospective review to evaluate the impact of different treatment strategies in DTA-TMA patients. Our primary endpoint was to determine the overall response rate (ORR) for DTA-TMA based on the type of treatment modality chosen while secondary endpoints included the time to response, relapse rates, and overall survival for DTA-TMA cases. RESULTS: There were a total of 14 DTA-TMA patients of whom nine were post-HCT and five were post-SOT. Most of the DTA-TMA cases were due to tacrolimus (n = 11) with a minority related to sirolimus (n = 3). A total of nine of 14 patients demonstrated response and five had no response to therapy. The ORR among the DTA-TMA patients after HCT and SOT who received plasma exchange (PLEX) were 25 and 100%, respectively. The ORRs among the patients (includes HCT and SOT) who received rituximab (n = 3) and eculizumab (n = 5) were 67 and 60%, respectively. There were two relapses noted in our study and both were in the HCT group. CONCLUSION: While discontinuation of the offending agent may be sufficient for treatment of DTA-TMA after HCT, PLEX may be a reasonable option for DTA-TMA after SOT. Although the results are encouraging with rituximab and eculizumab in the treatment of DTA-TMA, larger prospective studies are needed to validate our findings.