Maha Othman

Standardization of thromboelastography: A report from the TEG-ROTEM working group

Summary.  Laboratory evaluation of bleeding disorders has been performed with the standard clotting assays such as the PT and PTT for several decades. Our improved understanding of the process of blood coagulation has now revealed the important role played by the cellular elements such as platelets, monocytes and red blood cells. The need for a test that can assess clotting in a more ‘global’ manner, beyond the initiation of clot formation, has led to greater interest in assays such as thrombin generation and thromboelastography. Even though there are several publications using thromboelastography it remains a research tool as the methodology is not standardized. In an attempt to show reproducibility and consistency using thromboelastography, a group of investigators from different countries joined hands to form the TEG‐ROTEM Working Group. Two studies were performed using PRP and FVIII deficient plasma and an intrinsic pathway activator. This article summarizes the results of the first international effort at standardization of thromboelastography. Both of the instruments using this technology (TEG® and ROTEM®) were used. Nine laboratories from countries around the globe participated in this effort. The results showed a significant inter‐laboratory variance with CV’s greater than 10%. Although these results were not satisfactory, this has been the first effort to standardize this methodology and significant work remains to be done to improve reliability and reproducibility. These studies were performed on PRP and the results may be more reliable when preformed on whole blood samples. We believe that it is important to continue this work so that we may investigate the usefulness and potential applications of thromboelastography in the evaluation of bleeding and thrombosis.

Spontaneous Pregnancy Loss Mediated by Abnormal Maternal Inflammation in Rats Is Linked to Deficient Uteroplacental Perfusion

Abnormal maternal inflammation during pregnancy is associated with spontaneous pregnancy loss and intrauterine fetal growth restriction. However, the mechanisms responsible for these pregnancy outcomes are not well understood. In this study, we used a rat model to demonstrate that pregnancy loss resulting from aberrant maternal inflammation is closely linked to deficient placental perfusion. Administration of LPS to pregnant Wistar rats on gestational day 14.5, to induce maternal inflammation, caused fetal loss in a dose-dependent manner 3–4 h later, and surviving fetuses were significantly growth restricted. Pregnancy loss was associated with coagulopathy, structural abnormalities in the uteroplacental vasculature, decreased placental blood flow, and placental and fetal hypoxia within 3 h of LPS administration. This impairment in uteroplacental hemodynamics in LPS-treated rats was linked to increased uterine artery resistance and reduced spiral arteriole flow velocity. Pregnancy loss induced by LPS was prevented by maternal administration of the immunoregulatory cytokine IL-10 or by blocking TNF-α activity after treatment with etanercept (Enbrel). These results indicate that alterations in placental perfusion are responsible for fetal morbidities associated with aberrant maternal inflammation and support a rationale for investigating a potential use of immunomodulatory agents in the prevention of spontaneous pregnancy loss.

A high-throughput sequencing test for diagnosing inherited bleeding, thrombotic, and platelet disorders

Inherited bleeding, thrombotic, and platelet disorders (BPDs) are diseases that affect ∼300 individuals per million births. With the exception of hemophilia and von Willebrand disease patients, a molecular analysis for patients with a BPD is often unavailable. Many specialized tests are usually required to reach a putative diagnosis and they are typically performed in a step-wise manner to control costs. This approach causes delays and a conclusive molecular diagnosis is often never reached, which can compromise treatment and impede rapid identification of affected relatives. To address this unmet diagnostic need, we designed a high-throughput sequencing platform targeting 63 genes relevant for BPDs. The platform can call single nucleotide variants, short insertions/deletions, and large copy number variants (though not inversions) which are subjected to automated filtering for diagnostic prioritization, resulting in an average of 5.34 candidate variants per individual. We sequenced 159 and 137 samples, respectively, from cases with and without previously known causal variants. Among the latter group, 61 cases had clinical and laboratory phenotypes indicative of a particular molecular etiology, whereas the remainder had an a priori highly uncertain etiology. All previously detected variants were recapitulated and, when the etiology was suspected but unknown or uncertain, a molecular diagnosis was reached in 56 of 61 and only 8 of 76 cases, respectively. The latter category highlights the need for further research into novel causes of BPDs. The ThromboGenomics platform thus provides an affordable DNA-based test to diagnose patients suspected of having a known inherited BPD.

Recombinant and plasma-derived factor VIII products induce distinct splenic cytokine microenvironments in hemophilia A mice

The use of plasma-derived factor VIII (pdFVIII) concentrates in hemophilia A has been reported to result in reduced anti-FVIII antibody formation. In this study, we have investigated whether the cytokine microenvironment induced by pdFVIII has an influence on reducing anti-FVIII antibody titers in hemophilic mice. Microarray and confirmatory quantitative reverse transcription polymerase chain reaction (RT-PCR) experiments show that pdFVIII infusion causes a different transcriptional profile in dendritic cells than recombinant FVIII (rFVIII). Both treatments caused up-regulation of proinflammatory gene expression, but rFVIII and pdFVIII treatments promote expression of genes that induce Th1 and Th2 responses, respectively. Moreover, administration of rFVIII or pdFVIII concentrates resulted in distinct T-cell splenic cytokine microenvironments. rFVIII induced the release of Th1 cytokines and IL-10, whereas pdFVIII induced the release of Th2 cytokines and transforming growth factor-beta. We have also observed high titers of anti-human von Willebrand factor (VWF) antibodies in the pdFVIII-treated mice and propose that this results from antigenic competition. We further investigated the role of this phenomenon using infusions of FVIII and increasing concentrations of recombinant human factor IX (FIX). These studies show an inverse relationship between increasing concentrations of FIX and the production of anti-FVIII antibodies. In summary, these studies report new mechanisms that contribute to reduced anti-FVIII antibody development in hemophilia A after pdFVIII infusions.

Frequency of Platelet type versus Type 2B von Willebrand Disease: An international registry-based study

Less than 50 patients are reported with platelet type von Willebrand disease (PT-VWD) worldwide. Several reports have discussed the diagnostic challenge of this disease versus the closely similar disorder type 2B VWD. However, no systematic study has evaluated this dilemma globally. Over three years, a total of 110 samples/data from eight countries were analysed. A molecular approach was utilised, analysing exon 28 of the von Willebrand factor (VWF) gene, and in mutation negative cases the platelet GP1BA gene. Our results show that 48 cases initially diagnosed as putative type 2B/PT-VWD carried exon 28 mutations consistent with type 2B VWD, 17 carried GP1BA mutations consistent with a PT-VWD diagnosis, three had other VWD types (2A and 2M) and five expressed three non-previously published exon 28 mutations. Excluding 10 unaffected family members and one acquired VWD, 26 cases did not have mutations in either genes. Based on our study, the percentage of type 2B VWD diagnosis is 44% while the percentage of misdiagnosis of PT-VWD is 15%. This is the first large international study to investigate the occurrence of PT-VWD and type 2B VWD worldwide and to evaluate DNA analysis as a diagnostic tool for a large cohort of patients. The study highlights the diagnostic limitations due to unavailability/poor application of RIPA and related tests in some centres and proposes genetic analysis as a suitable tool for the discrimination of the two disorders worldwide. Cases that are negative for both VWF and GP1BA gene mutations require further evaluation for alternative diagnoses.

Reduction of the immune response to factor VIII mediated through tolerogenic factor VIII presentation by immature dendritic cells

Summary.  Background: The development of neutralizing antibodies to factor FVIII (FVIII) represents the most serious complication in the treatment of hemophilia A. Objective: We have explored the potential of using immature dendritic cells (iDCs) to present FVIII in a tolerogenic manner to T cells. Methods: The iDCs were isolated from hemophilic murine bone marrow and pulsed with canine cFVIII (cFVIII‐iDCs) in the presence or absence of the NFκB pathway blocking compound Andrographolide (Andro‐cFVIII‐iDCs). Three weekly intravenous infusions of one million cFVIII pulsed‐iDCs were administered to a group of five hemophilic Balb/c mice. Anti‐FVIII antibody levels were monitored by functional Bethesda assay after four weekly intravenous challenges with 2 IU of cFVIII. Results: We have shown that cFVIII in the presence or absence of Andro is efficiently taken up by iDCs and that this process does not result in the maturation of DCs or the activation of co‐cultured T cells. Following repeated infusion of the cFVIII‐iDCs and Andro‐cFVIII‐iDCs into hemophilic mice, which were subsequently challenged with cFVIII, long‐term reductions of FVIII inhibitors of 25% and 40%, respectively, were documented. Studies of cytokine release and T‐cell phenotypes indicate that the mechanisms responsible for reducing immunologic responsiveness to cFVIII appear to involve an expansion of Foxp3 T regulatory cells in the case of cFVIII‐iDC infusion and the elaboration of the immunosuppressive cytokines IL‐10 and TGF‐β following andrographolide‐treated cFVIII‐iDCs. Conclusions: This study shows that tolerogenic presentation of cFVIII to the immune system can significantly reduce immunogenicity of the protein.

Platelet-type von Willebrand disease: new insights into the molecular pathophysiology of a unique platelet defect.

Compared with coagulation factor defects, little attention is given to defects of platelet function as causes of rare bleeding disorders. Platelet-type von Willebrand disease (PT-VWD) is an autosomal dominant bleeding disorder and is unique among platelet disorders because it is characterized by platelet hyperresponsiveness rather than decreased function. The disease is caused by gain-of-function mutations in the platelet GP1BA gene, which codes for the platelet von Willebrand factor (VWF) receptor, GPIbα. Only five mutations (four missense and one deletion) have so far been reported. Affected patients suffer from mild to moderate mucocutaneous bleeding, low VWF activity compared with antigen, decreased high-molecular-weight VWF multimers, variable degree of thrombocytopenia and typically platelet aggregation in response to low concentrations of ristocetin. All reported PT-VWD missense mutations occur within the R-loop of GPIbα and it was speculated that the introduction of short branched chain mutations such as Val in PT-VWD stabilized the extended β-hairpin. Examination of this theory by surveying all the available GPIbα structures showed that a distinct conformation predominates for the R-loop when GPIbα is not bound to VWF-A1 and this provides the framework of a new hypothesis for the molecular basis of PT-VWD. Worldwide efforts to improve diagnosis of PT-VWD continue, and international systematic studies are required to further our understanding of the phenotype and the influence of the hyperresponsive GPIbα beyond hemostasis.

Platelet-type Von Willebrand disease: Three decades in the life of a rare bleeding disorder

Almost thirty years has passed since the description of platelet-type von Willebrand disease. Named initially pseudo-von Willebrand disease, this mild mucocutaneous bleeding disorder has an intrinsic defect in platelets rather than VWF. Due to its unique features and its similarity to the more common type 2B VWD, many investigators were intrigued by its nature, pathophysiology and molecular genetics aspects. The challenges to diagnose this disorder have created debate in literature about the best method of discrimination from type 2B VWD. The recent development of the PT-VWD mouse model carries huge potential for further understanding of the disease as well as the platelet defect and its influence on other biological processes. This review provides a basic as well as updated knowledge about the PT-VWD including history, clinical and laboratory features and treatment in addition to the diagnostic challenges with a focus on molecular genetics aspects and PT-VWD research.

Immunoglobulin isotypes and functional anti-FVIII antibodies in response to FVIII treatment in Balb/c and C57BL/6 haemophilia A mice

Summary.  Previous studies have demonstrated that genetic factors play an important role in determining the likelihood of formation of anti‐factor VIII (FVIII) antibodies in haemophilia A patients. We were interested in characterizing the spectrum of FVIII antibody formation and the primary and secondary immune responses after FVIII administration in two different exon 16‐disrupted haemophilia A mouse strains, Balb/c and C57BL/6. Balb/c and C57BL/6 E16 haemophilia A mice were used in all experiments. Total FVIII antibodies and FVIII inhibitors were measured using ELISA and Bethesda assays respectively. T‐ and B‐cell cytokines were quantified using ELISA and flow cytometry. FVIII antibodies, but not functional inhibitors were detectable 1 week after the first FVIII treatment in both strains. These antibodies mainly belonged to the IgM and IgA isotypes. After the fourth FVIII treatment, neutralizing anti‐FVIII antibodies were detected in both mouse strains: Balb/c (mean inhibitory titer 58 BU) and C57BL/6 (mean inhibitory titer 82 BU). IgG1 levels were similar in both strains but the IgG2A and IgG2B subclasses were higher in C57BL/6 mice. The results of intracellular cytokine staining of T cells indicated that the FVIII‐treated C57BL/6 mice produced more IL10 and Th1 cytokines than the FVIII‐treated Balb/c mice. These studies show that C57BL/6 mice develop a stronger immune response towards FVIII than Balb/c mice. We propose that the enhanced Th1 and IL10 cytokine micro‐environment induced in C57BL/6 mice is responsible for this difference. Therefore, genetic strain‐dependent differences must be considered when evaluating immunological outcomes in mouse models of haemophilia A.

Genetics of type 2B von Willebrand disease: "true 2B," "tricky 2B," or "not 2B." What are the modifiers of the phenotype?

Type 2B von Willebrand disease (VWD) is a qualitative type of VWD with a unique feature among VWD types, resulting from an increased binding of von Willebrand factor (VWF) to its platelet receptor glycoprotein 1b-alpha (GP1BA). This heightened responsiveness takes place in vivo without endothelial injury or shear stress induction, typically resulting in loss of the hemostatically most active high-molecular-weight VWF multimers and leading to a bleeding diathesis. This process also typically leads to clearance of platelets and thus usually mild thrombocytopenia. At least this describes the classic representation of type 2B VWD (i.e., the typical picture we have come to know since the description/classification of this disorder in the early 1990s). Over more recent years, several reports have described individual cases, groups of patients, and families diagnosed with type 2B VWD where this picture was not typical in one or more aspects. This review discusses type 2B-like disorders and sheds light on potential phenotypic modifiers that might be responsible for the variation encountered with the classic picture of type 2B VWD as well as the impact on the diagnostic certainty of type 2B VWD.