Genetic risk factors for inhibitors in haemophilia A

Effectiveness of emicizumab in preventing bleeding events in severe and moderate hemophilia A: A single-center experience in Bangladesh

Emicizumab is a monoclonal antibody that bridges activated factor IX (FIX) and factor X (FX) to replace the function of missing activated factor VIII (FVIII) in hemophilia A patients irrespective of FVIII inhibitor status. This study assessed the effectiveness of emicizumab in preventing bleeding episodes in patients with hemophilia A. This observational study included patients with moderate to severe hemophilia A who were undergoing episodic FVIII replacement therapy. The primary endpoint was the difference in annualized bleeding rates (ABR) and the secondary endpoint was the difference in Hemophilia Joint Health Score (HJHS) before and after emicizumab prophylaxis. A total of 30 male hemophilia patients were included, the mean age was 16.7 (SD: ±8.1) years, and most of them had moderate hemophilia A [63.3%]. Before prophylaxis, the median ABR was 48 (interquartile range [IQR]: 35-60), and 93.3% of patients had ABR greater than eight, whereas after prophylaxis the median ABR decreased significantly (median [IQR]: 0 [0.0-0.4], p < 0.001), and 56.7% had zero bleeds. ABR was not significantly different in patient with and without FVIII inhibitors. The HJHS scores significantly improved after prophylaxis (10 vs. 2.5, p < 0.001). The bleeding events were reduced significantly (23 vs. 0.0, p < 0.001), and zero new target joints were reported after prophylaxis. Most of the patients [93.3%] did not face any serious adverse events after prophylaxis. Emicizumab prophylaxis was associated with a significantly lower rate of bleeding events among participants with hemophilia A, regardless of inhibitor status.

Spectrum of Causative Mutations in Patients with Hemophilia A in Russia

Hemophilia A (HA) is one of the most widespread, X-linked, inherited bleeding disorders, which results from defects in the F8 gene. Nowadays, more than 3500 different pathogenic variants leading to HA have been described. Mutation analysis in HA is essential for accurate genetic counseling of patients and their relatives. We analyzed patients from 273 unrelated families with different forms of HA. The analysis consisted of testing for intron inversion (inv22 and inv1), and then sequencing all functionally important F8 gene fragments. We identified 101 different pathogenic variants in 267 patients, among which 35 variants had never been previously reported in international databases. We found inv22 in 136 cases and inv1 in 12 patients. Large deletions (1-8 exons) were found in 5 patients, and we identified a large insertion in 1 patient. The remaining 113 patients carried point variants involving either single nucleotide or several consecutive nucleotides. We report herein the largest genetic analysis of HA patients issued in Russia.

Insights into the Molecular Genetic of Hemophilia A and Hemophilia B: The Relevance of Genetic Testing in Routine Clinical Practice

Hemophilia A and hemophilia B are rare congenital, recessive X-linked disorders caused by lack or deficiency of clotting factor VIII (FVIII) or IX (FIX), respectively. The severity of the disease depends on the reduction of coagulation FVIII or FIX activity levels, which is determined by the type of the pathogenic variants in the genes encoding the two factors (F8 and F9, respectively). Molecular genetic analysis is widely applied in inherited bleeding disorders. The outcome of genetic analysis allows genetic counseling of affected families and helps find a link between the genotype and the phenotype. Genetic analysis in hemophilia has tremendously improved in the last decades. Many new techniques and modifications as well as analysis softwares became available, which made the genetic analysis and interpretation of the data faster and more accurate. Advances in genetic variant detection strategies facilitate identification of the causal variants in up to 97% of patients. In this review, we discuss the milestones in genetic analysis of hemophilia and highlight the importance of identification of the causative genetic variants for genetic counseling and particularly for the interpretation of the clinical presentation of hemophilia patients.

Novel Coagulation Factor VIII Gene Therapy in a Mouse Model of Hemophilia A by Lipid-Coated Fe3O4 Nanoparticles

Hemophilia A is a bleeding disease caused by loss of coagulation factor VIII (FVIII) function. Although prophylactic FVIII infusion prevents abnormal bleeding, disability and joint damage in hemophilia patients are common. The cost of treatment is among the highest for a single disease, and the adverse effects of repeated infusion are still an issue that has not been addressed. In this study, we established a nonviral gene therapy strategy to treat FVIII knockout (FVIII KO) mice. A novel gene therapy approach was developed using dipalmitoylphosphatidylcholine formulated with iron oxide (DPPC-Fe₃O₄) to carry the B-domain-deleted (BDD)-FVIII plasmid, which was delivered into the FVIII KO mice via tail vein injection. Here, a liver-specific albumin promoter-driven BDD-FVIII plasmid was constructed, and the binding ability of circular DNA was confirmed to be more stable than that of linear DNA when combined with DPPC-Fe₃O₄ nanoparticles. The FVIII KO mice that received the DPPC-Fe₃O₄ plasmid complex were assessed by staining the ferric ion of DPPC-Fe₃O₄ nanoparticles with Prussian blue in liver tissue. The bleeding of the FVIII KO mice was improved in a few weeks, as shown by assessing the activated partial thromboplastin time (aPTT). Furthermore, no liver toxicity, thromboses, deaths, or persistent changes after nonviral gene therapy were found, as shown by serum liver indices and histopathology. The results suggest that this novel gene therapy can successfully improve hemostasis disorder in FVIII KO mice and might be a promising approach to treating hemophilia A patients in clinical settings.

In Silico Study of Correlation between Missense Variations of F8 Gene and Inhibitor Formation in Severe Hemophilia A

Objective:

Deleterious substitutions of the F8 gene are responsible for causing hemophilia A, which is an inherited bleeding disorder resulting from reduced or absent activity of the coagulant protein factor VIII (FVIII). The most important complication in treatment is inhibitor development toward therapeutic factor VIII. In this study, we aimed to analyze the effects of deleterious substitutions in the F8 gene upon protein structure and function.

Materials and Methods:

All tests were conducted by computational methods from the CHAMP (CDC Hemophilia A Mutation Project) database. We performed an in silico analysis of deleterious variations using five software programs, Sift, PolyPhen-2, Align-GVGD, KD4v, and MutationTaster, in order to analyze the correlation between variation and the disease. We also studied the correlation between these variations and inhibitor formation.

Results:

Our analysis showed that these in silico tools are coherent and that there are more variations in the A than the C domains. Moreover, we noticed that there are more deleterious variations than neutral variations in each of the A and C domains. We also found that 13.51% of the patients suffered from a severe form of hemophilia A and that carriers of missense variations developed inhibitors. Also, for the first time, we determined that variation nature is not associated with inhibitor formation. Furthermore, this analysis showed that the risk of developing inhibitors increases when the variation causes a change of amino acid class.

Conclusion:

This study will help to correctly associate variations with inhibitor development and aid in early characterization of novel variants.

octanate®: over 20 years of clinical experience in overcoming challenges in haemophilia A treatment

Treatment of haemophilia A with FVIII replacement has evolved over the past decades to adapt to the needs of patients. octanate®, a plasma-derived, double virus-inactivated, von Willebrand factor (VWF)-containing FVIII concentrate, has been used in clinics worldwide for over 20 years. First licensed in 1998 in Germany, octanate® is approved in over 80 countries for the prevention and treatment of bleeding and for surgical prophylaxis in patients with haemophilia A, and in over 40 countries for immune tolerance induction (ITI). The manufacturing process for octanate® was developed to ensure high viral safety and effectively eliminates both enveloped and nonenveloped viruses. Over the past 20 years, the excellent safety and efficacy of octanate® have been demonstrated in pivotal clinical trials in adult and paediatric previously treated patients (PTPs) for on-demand treatment, prophylaxis and as surgical cover. Importantly, octanate® has displayed low immunogenicity in previously untreated patients (PUPs), with only 9.8% of PUPs developing FVIII inhibitors. octanate® has also shown to be highly effective in inhibitor elimination when used as ITI therapy. In a population of patients with high risk of ITI failure, success was achieved in 79.2% of patients (70.8% complete success), even when using exceptionally stringent success criteria. No relapses were observed. Here we present an overview of the clinical data with octanate® that support its use in a range of patient populations and clinical indications.

Prevalence of inhibitors and clinical characteristics in patients with haemophilia in a middle-income Latin American country

INTRODUCTION

Development of inhibitors is the most serious complication in patients with haemophilia (PWH). The prevalence of inhibitors in patients with severe haemophilia A (HA) is approximately 25%-30%. Inhibitor prevalence differs among populations. Some studies report a prevalence of almost twice in Hispanic as compared to Caucasian patients. Most data available, on the prevalence of inhibitors and their predisposing factors, originate from centres in developed countries.

AIM

Establish the prevalence of inhibitors of FVIII and FIX in Mexico.

METHODS

This was an observational, cross-sectional and descriptive study. The records of all patients diagnosed with haemophilia A (HA) or B (HB), with and without inhibitors, were included. Clinical and demographical characteristics of patients with inhibitors were assessed. Statistical analysis was performed using IBM SPSS version 22. The Ethics Committees of the various participating institutions approved this study.

RESULTS

A total of 1455 patients from the 20 participating centres were recruited, from which 1208 (83.02%) had HA and 247 (16.97%) were diagnosed with HB. The presence of inhibitors in severe HA was reported in 93/777(11.96%), and 10/162 (6.17%) in severe HB. Of them, 91.7% exhibited high titres in HA and 100% in HB.

CONCLUSION

In Mexico, the general prevalence of inhibitors varies considerably among centres. This study established a basis of comparison for future development and advances in the treatment and follow-up of patients. These findings also augment our understanding of risk factors related to inhibitor development.

Sedimentation Velocity Analytical Ultracentrifugation of Oxidized Recombinant Full-Length Factor VIII

Anti-drug antibodies to coagulation factor VIII (fVIII), often termed inhibitors, present the greatest economical and treatment related obstacle in the management of hemophilia A. Although several genetic and environmental risk factors associated with inhibitor development have been identified, the precise mechanisms responsible for the immune response to exogenous fVIII therapies remain undefined. Clinical trials suggest there is an increased immunogenic potential of recombinant fVIII compared to plasma-derived products. Additional biochemical and immunological studies have demonstrated that changes in recombinant fVIII production and formulation can alter fVIII structure and immunogenicity. Recently, one study demonstrated increased immunogenicity of the recombinant fVIII product Helixate in hemophilia A mice following oxidation with hypochlorite (ClO⁻). It is widely reported that protein aggregates within drug products can induce adverse immune reactions in patients. Several studies have therefore investigated the prevalence of molecular aggregates in commercial recombinant products with and without use-relevant stress and agitation. To investigate the potential link between oxidation-induced immunogenicity and molecular aggregation, we analyzed the recombinant fVIII product, Helixate, via sedimentation velocity analytical ultracentrifugation following oxidation with ClO⁻. At 80 μM ClO⁻, a concentration that reduced the specific-activity by 67%, no detectable increase in large molecular aggregates (s > 12 S) was observed when compared to non-oxidized fVIII. This lack of aggregates was demonstrated both in commercial excipient as well as a HEPES buffered saline formulation. These data suggest that oxidation induced immunogenicity is independent of aggregate-mediated immune response. Therefore, our data support multiple, independent mechanisms underlying fVIII immunogenicity.

Hemophilia - Impact of Recent Advances on Management

There have been numerous advances in the field of hemophilia management in the past decade, including long acting factor products, non-factor products, and potentially curative interventions such as gene therapy. Each of these interventions introduces exciting treatment modalities to patients with both hemophilia A and B, however they also pose a daunting array of possible management options. Adverse reactions to novel agents are being reported as more patients are treated and long-term sustainability of interventions such as gene therapy is yet to be determined. The practicing hematologist should be aware of the intricacies involved in customizing care for their individual patients and be aware of the monitoring strategies for each interventional strategy to avoid adverse events. Upfront cost vs. long term benefit should be considered as choices of treatment strategies are made, especially in resource poor countries. The goal of the newer agents is to decrease annualized bleed rates and avoid debilitating arthropathy. This article looks at current treatment models for prophylaxis and management of inhibitors, reviews the recent advances in the field (with bioengineered factor products, non-factor products and gene therapy) and summarizes the incorporation of these new interventions in the treatment plan for patients with hemophilia.

Safety and efficacy of turoctocog alfa in the prevention and treatment of bleeds in previously untreated paediatric patients with severe haemophilia A: Results from the guardian 4 multinational clinical trial

Introduction

Turoctocog alfa is a recombinant, B domain‐truncated factor VIII (FVIII) approved for patients with haemophilia A.

Aim

To evaluate the safety and efficacy of turoctocog alfa in previously untreated patients (PUPs) with severe haemophilia A.

Methods

Guardian 4 was a multicentre, multinational, non‐randomized, open‐label phase 3 trial comprising a main and extension phase. The former concluded once ≥ 50 patients had received treatment for ≥ 50 exposure days (EDs) or developed inhibitors. Patients received turoctocog alfa intravenously for prevention and treatment of bleeds. The primary endpoint was the incidence rate of FVIII inhibitors (≥0.6 Bethesda Units) reported during the first 50 EDs.

Results

Of the 58 patients who completed the main phase, 25 (43.1%) patients developed inhibitors (detected within 6‐24 [mean: 14.2] EDs from treatment start). High‐risk mutations were identified in 60% of patients who developed inhibitors in the main phase and were a significant predictor of inhibitor development (P = .003). Of the 21 patients who started immune tolerance induction therapy, 85.7% completed treatment with a negative inhibitor test (note that data on the last 3 patients completing ITI are based on information collated from sites prior to the final database lock). Haemostatic response (including missing values as failure) was rated as ‘excellent’ or ‘good’ for 86.1% of bleeds occurring during prophylaxis. The estimated mean annualized bleeding rate for patients on prophylaxis was 4.26 bleeds/patient/year (95% CI: 3.34 − 5.44).

Conclusions

Turoctocog alfa was effective at preventing and stopping bleeds and was well tolerated. Inhibitor development was within the expected range for this PUP population.

HLA-DRB1*01:01, but not HLA-DRB1:1503 or HLA-DRB1*11, is associated with decreased inhibitor risk in Iranian hemophilia A patients

BACKGROUND/OBJECTIVE

Hemophilia A is a genetic disorder through which patients suffer from recurrent bleeding. This can be caused by a defect in human plasma coagulation factor VIII. High incidence of FVIII inhibitors in some severe hemophilia A patients after FVIII therapy is a considerable complication. Determination of good predictive factors can improve the safety of this treatment. HLA-II have been shown as a predictive element for inhibitor development. The goal of this study is to determine the association between HLA-DRB1*15:03, HLA-DRB1*11 and HLA-DRB1*01:01 alleles and FVIII inhibitors in severe hemophilia A patients in Iran.

MATERIALS/METHODS

HLA-DRB1 genotyping was performed using Multiplex sequences Specific Primers (PCR-SSP) in two groups of severe hemophilia A patients comprising 51 and 50 individuals with and without FVIII inhibitors respectively. The levels of inhibitor were determined through Nijmegen-modified Bethesda assay. HLA-DRB1 allele frequencies were compared between groups by using multiple logistic regression models.

RESULTS

HLA-DRB1*01:01 allele frequency was significantly higher in patients without inhibitor OR_adj: 2.7 (95%CI: 1.08, 6.97; P = 0.034). There wasn't any statistically significant difference in HLA-DRB1*11 allele frequency between groups OR_adj: 0.7 (95%CI: 0.27, 1.82; P = 0.47). There was no connection between HLA-DRB1*15:03 and inhibitor development OR_adj: 0.94 (95%CI: 0.38, 2.35; P = 0.94).

CONCLUSION

An association between HLA-DRB1*01:01 and paucity of FVIII inhibitor showed that this allele has probably a protective effect in severe hemophilia A patients in Iran. Determination of the predictive and protective alleles are beneficial in pre-treatment activities and decrease the risk of unsuccessful therapy with FVIII in each population.

A study to determine the prevalence, clinical profile and incidence of formation of inhibitors in patients of hemophilia in North Eastern part of India

Introduction:

Deficiency of factor VIII (Hemophilia A), factor IX (Hemophilia B) and Von Willebrand's factor are the most frequent coagulation defects. The incidence of inhibitors in patients of factor VIII deficiency is varies in different regions of India.

Aim:

To determine the prevalence, clinical profile and incidence of formation of inhibitors in patients of Hemophilia in north eastern part of India.

Methods:

Selected patients were under went for complete Blood Count (CBC), General Blood Picture (GBP), Prothrombin time (PT), Activated partial thromboplastin time (APTT), Thrombin time, Correction experiment to know the specific factor deficiency or inhibitors present by Normal Plasma, Normal aged serum, Al(OH)₃ adsorbed plasma.

Results:

92 patients diagnosed as suffering with Hemophilia A or B were included in study. The age of patients ranged from 2.5 month to 53 years. Out of 92, seventy nine (85.87%) were Haemophilia A and thirteen were (14.13%) Hemophilia B patients. 3.50% (2/55) cases of treated Hemophilia A patient develop inhibitor.

Conclusion:

The prevalence of hemophilia and incidence of inhibitors in these patients is varies in different regions of India. This variation may be due to the type of product used as treatment, intensity of treatment or the genetic characteristics of the patients.

Prevalence of FVIII inhibitors in severe haemophilia A patients: Effect of treatment and genetic factors in an Indian population

INTRODUCTION

Factor replacement therapy in treatment of haemophilia A is complicated by the production of neutralising antibodies known as inhibitors. The formation of inhibitors is multifactorial being associated with both genetic and environmental factors.

AIM

To document the prevalence of inhibitors in severe haemophilia in the community where most patients receive only infrequent episodic replacement therapy and evaluate the factors which could be contributing to it.

METHODS

Community based camps were conducted in different parts of the country. Patients were assessed through a structured questionnaire and blood samples were obtained for laboratory evaluation of inhibitors and defined immunological parameters.

RESULTS

Inhibitors were present in 87/447 (19.5%) of the evaluated patients. High-titre inhibitor (>5 Bethesda Units [BU]) was identified in 31 (35.6%) patients. HLA DRB1-13-positive cases (RR = 2.04; 95% CI 1.06-3.911; P = 0.033) had an increased risk of inhibitor formation which was retained in the high-titre subset. A decreased risk of inhibitor formation was noted with heterozygous IL4-590 C/T allele (RR = 0.22; 95% CI 0.108-0.442: P = 0.000). There were no significant correlations between any of the evaluated environmental factors and the development of inhibitors in this study.

CONCLUSION

The overall prevalence of inhibitors in patients with severe haemophilia A is similar to that reported among patients receiving regular replacement therapy. The data from this study, limited by its retrospective and cross-sectional study design, would suggest that genetic rather than environmental are more likely to impact the development of inhibitors.

Prediction of factor VIII inhibitor development in the SIPPET cohort by mutational analysis and factor VIII antigen measurement

Essentials A residual factor VIII synthesis is likely to be protective towards inhibitor (INH) development. Mutation type-inhibitor risk association was explored in 231 patients with severe hemophilia A. A 2-fold increase in INH development for in silico null vs. non-null mutations was found. A 3.5-fold increase in INH risk for antigen negative vs. antigen positive mutations was found.

SUMMARY

Background The type of F8 mutation is the main predictor of inhibitor development in patients with severe hemophilia A. Mutations expected to allow residual synthesis of factor VIII are likely to play a protective role against alloantibody development by inducing immune tolerance. According to the expected full or partial impairment of FVIII synthesis, F8 variants are commonly classified as null and non-null. Objectives To explore the mutation type-inhibitor risk association in a cohort of 231 patients with severe hemophilia A enrolled in the Survey of Inhibitors in Plasma-Product Exposed Toddlers (SIPPET) randomized trial. Methods The genetic defects in these patients, consisting of inversions of intron 22 (n = 110) and intron 1 (n = 6), large deletions (n = 16), and nonsense (n = 38), frameshift (n = 28), missense (n = 19) and splicing (n = 14) variants, of which 34 have been previously unreported, were reclassified according to two additional criteria: the functional effects of missense and splicing alterations as predicted by multiple in silico analyses, and the levels of FVIII antigen in patient plasma. Results A two-fold increase in inhibitor development for in silico null mutations as compared with in silico non-null mutations (hazard ratio [HR] 2.08, 95% confidence interval [CI] 0.84-5.17) and a 3.5-fold increase in inhibitor development for antigen-negative mutations as compared with antigen-positive mutations (HR 3.61, 95% CI 0.89-14.74] were found. Conclusions Our findings confirm an association between the synthesis of minute amounts of FVIII and inhibitor protection, and underline the importance of investigating the residual FVIII antigen levels associated with causative variants in order to understand their clinical relevance.

Long-term tolerability, immunogenicity and efficacy of Nuwiq® (human-cl rhFVIII) in children with severe haemophilia A

INTRODUCTION

Nuwiq^® (human-cl rhFVIII, simoctocog alfa) is a 4th generation recombinant human FVIII, without chemical modification or fusion with any other protein, produced in a human cell line.

AIM/METHODS

This study (GENA-13) was an extension of the GENA-03 study in which previously treated children aged 2-12 years with severe haemophilia A received Nuwiq^® prophylaxis for ≥6 months. GENA-13 examined long-term tolerability, immunogenicity and efficacy of Nuwiq^® prophylaxis in children.

RESULTS

Of 59 patients enrolled in GENA-03, 49 continued Nuwiq^® prophylaxis in GENA-13 for a median (range) of 30.0 (9.5-52.0) months. No patient withdrew due to drug-related adverse events or developed inhibitors. Only 2 of 20 518 infusions were associated with possibly related adverse events (dyspnoea, fever). The estimated annualized bleeding rate (ABR) was 0.67 (95% CI: 0.44, 1.02) for spontaneous and 2.88 (95% CI: 1.86, 4.46) for all bleeds. Younger children (2-5 years) had lower ABRs than children aged 6-12 years. Annualized bleeding rates were reduced in GENA-13 vs GENA-03, especially for spontaneous bleeds in younger children (71% reduction; ABR ratio 0.29 [95% CI: 0.11, 0.74]). Nuwiq^® efficacy was rated as excellent/good in the treatment of 83.0% of 305 evaluated breakthrough bleeds. Surgical prophylaxis with Nuwiq^® was rated as excellent for all 17 assessed procedures.

CONCLUSION

Long-term treatment with Nuwiq^® for the prevention of bleeds in children with severe haemophilia A was well tolerated, effective and reduced spontaneous bleeding by up to 70% compared with GENA-03.

Identification of aggregates in therapeutic formulations of recombinant full-length factor VIII products by sedimentation velocity analytical ultracentrifugation

Essentials Factor VIII inhibitors are the most serious complication in patients with hemophilia A. Aggregates in biopharmaceutical products are an immunogenic risk factor. Aggregates were identified in recombinant full-length factor VIII products. Aggregates in recombinant factor VIII products are identified by analytical ultracentrifugation.

SUMMARY

Background The development of inhibitory anti-factor VIII antibodies is the most serious complication in the management of patients with hemophilia A. Studies have suggested that recombinant full-length FVIII is more immunogenic than plasma-derived FVIII, and that, among recombinant FVIII products, Kogenate is more immunogenic than Advate. Aggregates in biopharmaceutical products are considered a risk factor for the development of anti-drug antibodies. Objective To evaluate recombinant full-length FVIII products for the presence of aggregates. Methods Advate, Helixate and Kogenate were reconstituted to their therapeutic formulations, and subjected to sedimentation velocity (SV) analytical ultracentrifugation (AUC). Additionally, Advate and Kogenate were concentrated and subjected to buffer exchange by ultrafiltration to remove viscous cosolvents for the purpose of measuring s20,w values and molecular weights. Results The major component of all three products was a population of ~7.5 S heterodimers with a weight-average molecular weight of ~230 kDa. Helixate and Kogenate contained aggregates ranging from 12 S to at least 100 S, representing ≈ 20% of the protein mass. Aggregates greater than 12 S represented < 3% of the protein mass in Advate. An approximately 10.5 S aggregate, possibly representing a dimer of heterodimers, was identified in buffer-exchanged Advate and Kogenate. SV AUC analysis of a plasma-derived FVIII product was confounded by the presence of von Willebrand factor in molar excess over FVIII. Conclusions Aggregate formation has been identified in recombinant full-length FVIII products, and is more extensive in Helixate and Kogenate than in Advate. SV AUC is an important method for characterizing FVIII products.

Application of a molecular diagnostic algorithm for haemophilia A and B using next-generation sequencing of entire F8, F9 and VWF genes

Currently, molecular diagnosis of haemophilia A and B (HA and HB) highlights the excess risk-inhibitor development associated with specific mutations, and enables carrier testing of female relatives and prenatal or preimplantation genetic diagnosis. Molecular testing for HA also helps distinguish it from von Willebrand disease (VWD). Next-generation sequencing (NGS) allows simultaneous investigation of several complete genes, even though they may span very extensive regions. This study aimed to evaluate the usefulness of a molecular algorithm employing an NGS approach for sequencing the complete F8, F9 and VWF genes. The proposed algorithm includes the detection of inversions of introns 1 and 22, an NGS custom panel (the entire F8, F9 and VWF genes), and multiplex ligation-dependent probe amplification (MLPA) analysis. A total of 102 samples (97 FVIII- and FIX-deficient patients, and five female carriers) were studied. IVS-22 screening identified 11 out of 20 severe HA patients and one female carrier. IVS-1 analysis did not reveal any alterations. The NGS approach gave positive results in 88 cases, allowing the differential diagnosis of mild/moderate HA and VWD in eight cases. MLPA confirmed one large exon deletion. Only one case did have no pathogenic variants. The proposed algorithm had an overall success rate of 99 %. In conclusion, our evaluation demonstrates that this algorithm can reliably identify pathogenic variants and diagnose patients with HA, HB or VWD.

Supplementary Material to this article is available online at www.thrombosis-online.com.

Hemophilia Care in the Pediatric Age

Hemophilia is the most common of the severe bleeding disorders and if not properly managed since early infancy can lead to chronic disease and lifelong disabilities. However, it enjoys the most efficacious and safe treatment among the most prevalent monogenic disorders. Hemophilia should be considered in the neonatal period in the case of unusual bleeding or in the case of positive family history. Later, hemophilia should be suspected mainly in males because of abnormal bruising/bleeding or unusual bleeding following invasive procedures-for example, tonsillectomy or circumcision. Prophylactic treatment that is started early with clotting-factor concentrates has been shown to prevent hemophilic arthropathy and is, therefore, the gold standard of care for hemophilia A and B in most countries with adequate resources. Central venous access catheters and arterovenous fistulas play an important role in the management of hemophilia children requiring repeated and/or urgent administration of coagulation factor concentrates. During childhood and adolescence, personalized treatment strategies that suit the patient and his lifestyle are essential to ensure optimal outcomes. Physical activity is important and can contribute to better coordination, endurance, flexibility and strength. The present article focuses also on questions frequently posed to pediatric hematologists like vaccinations, day-care/school access and dental care.

Reversal of direct oral anticoagulants in hemophilia treatment: ASH meeting 2015

During the 57^th annual meeting of the American Society of Hematology 2015 in Orlando, Florida, various aspects in the field of hemostaseology were presented. The Choosing Wisely® campaign pointed out the importance of the critical use of diagnostic tools to rule out pulmonary embolism and questioned the relevance of thrombophilia testing in women undergoing routine infertility evaluation. Furthermore, the approval of idarucizumab, a specific antidote for the reversal of the anticoagulant effects of the direct thrombin inhibitor dabigatran, was highlighted. Finally, hemophilia specialists awaited the results of the SIPPET Trial, which were presented for the first time during the plenary session. Replacement therapy of previously untreated hemophilia A patients with plasma-derived factor VIII containing von Willebrand factor resulted in a lower incidence of inhibitors compared with patients treated with recombinant factor VIII.

Inhibitor development in previously untreated patients with severe haemophilia A: a nationwide multicentre study in Finland

INTRODUCTION

Currently the most serious treatment complication of haemophilia is the inhibitor development (ID), i.e. neutralizing antibody development.

AIM

This nationwide multicentre study in Finland evaluated the incidence and risk factors of ID in previously untreated patients (PUPs) with severe haemophilia A (FVIII:C < 0.01 IU mL(-1) ).

METHODS

We enrolled all PUPs (N = 62) born between June 1994 and May 2013 with at least 75 exposure days (EDs) to screen ID during follow-up extending to September 2013.

RESULTS

Thirteen ID (21% of 62) occurred; 10 (16% of 62) with high titre. Fifty-one patients (82%) were on primary prophylaxis (regular prophylaxis before the age of 2 and before the first joint bleed) from the median age of 11.4 months, 90% via a central venous access device. The initial product was rFVIII in 63% and pd-FVIII in 37%, moreover in 24% pd-FVIII was switched to rFVIII concentrate during the 75 EDs. Non-transient inhibitors developed in 9/51 (17.6%; 13.7% high titre) children with primary and in 4/11 (36.4%; 27.3% high titre) patients with secondary prophylaxis (P = 0.24). Overall, 74% had a high-risk genotype similarly distributed among the prophylaxis groups. The history of a major bleed enhanced ID (aHR, 4.0; 95% CI, 1.2-13.7), whereas FVIII treatment intensity or source and early implantation of ports did not increase ID risk.

CONCLUSION

The cumulative incidence of ID was low notwithstanding prevalent high-risk mutations. Despite patient-related risk factors, our management involving early intensive primary prophylaxis via ports helps to prevent bleeds and lower the incidence of inhibitors.

Whole-exome sequencing to identify genetic risk variants underlying inhibitor development in severe hemophilia A patients

The development of neutralizing antibodies (inhibitors) against coagulation factor VIII (FVIII) is the most problematic and costly complication of FVIII replacement therapy that affects up to 30% of previously untreated patients with severe hemophilia A. The development of inhibitors is a multifactorial complication involving environmental and genetic factors. Among the latter, F8 gene mutations, ethnicity, family history of inhibitors, and polymorphisms affecting genes involved in the immune response have been previously investigated. To identify novel genetic elements underling the risk of inhibitor development in patients with severe hemophilia A, we applied whole-exome sequencing (WES) and data analysis in a selected group of 26 Italian patients with (n = 17) and without (n = 9) inhibitors. WES revealed several rare, damaging variants in immunoregulatory genes as novel candidate mutations. A case-control association analysis using Cochran-Armitage and Fisher's exact statistical tests identified 1364 statistically significant variants. Hierarchical clustering of these genetic variants showed 2 distinct patterns of homozygous variants with a protective or harmful role in inhibitor development. When looking solely at coding variants, a total of 28 nonsynonymous variants were identified and replicated in 53 inhibitor-positive and 174 inhibitor-negative Italian severe hemophilia A patients using a TaqMan genotyping assay. The genotyping results revealed 10 variants showing estimated odds ratios in the same direction as in the discovery phase and confirmed the association of the rs3754689 missense variant (OR 0.58; 95% CI 0.36-0.94; P = .028) in a highly conserved haplotype region surrounding the LCT locus on chromosome 2q21 with inhibitor development.

Recombinant factor VIII Fc (rFVIIIFc) fusion protein reduces immunogenicity and induces tolerance in hemophilia A mice

Anti-factor VIII (FVIII) antibodies is a major complication of FVIII replacement therapy for hemophilia A. We investigated the immune response to recombinant human factor VIII Fc (rFVIIIFc) in comparison to BDD-rFVIII and full-length rFVIII (FL-rFVIII) in hemophilia A mice. Repeated administration of therapeutically relevant doses of rFVIIIFc in these mice resulted in significantly lower antibody responses to rFVIII compared to BDD-rFVIII and FL-rFVIII and reduced antibody production upon subsequent challenge with high doses of rFVIIIFc. The induction of a tolerogenic response by rFVIIIFc was associated with higher percentage of regulatory T-cells, a lower percentage of pro-inflammatory splenic T-cells, and up-regulation of tolerogenic cytokines and markers. Disruption of Fc interactions with either FcRn or Fcγ receptors diminished tolerance induction, suggesting the involvement of these pathways. These results indicate that rFVIIIFc reduces immunogenicity and imparts tolerance to rFVIII demonstrating that recombinant therapeutic proteins may be modified to influence immunogenicity and facilitate tolerance.

Engineering less immunogenic and antigenic FVIII proteins

The development of neutralizing antibodies against blood coagulation factor VIII (FVIII), referred to clinically as "inhibitors", is the most challenging and deleterious adverse event to occur following intravenous infusions of FVIII to treat hemophilia A. Inhibitors occlude FVIII surfaces that must bind to activated phospholipid membranes, the serine proteinase factor IXa, and other components of the 'intrinsic tenase complex' in order to carry out its important role in accelerating blood coagulation. Inhibitors develop in up to one of every three patients, yet remarkably, a substantial majority of severe hemophilia A patients, who circulate no detectable FVIII antigen or activity, acquire immune tolerance to FVIII during initial infusions or else after intensive FVIII therapy to overcome their inhibitor. The design of less immunogenic FVIII proteins through identification and modification ("de-immunization") of immunodominant T-cell epitopes is an important goal. For patients who develop persistent inhibitors, modification of B-cell epitopes through substitution of surface-exposed amino acid side chains and/or attachment of bulky moieties to interfere with FVIII attachment to antibodies and memory B cells is a promising approach. Both experimental and computational methods are being employed to achieve these goals. Future therapies for hemophilia A, as well as other monogenic deficiency diseases, are likely to involve administration of less immunogenic proteins in conjunction with other novel immunotherapies to promote a regulatory cellular environment promoting durable immune tolerance.

Donor antigen-primed regulatory T cells permit liver regeneration and phenotype correction in hemophilia A mouse by allogeneic bone marrow stem cells

INTRODUCTION

Cell replacement therapy may be considered as an alternate approach to provide therapeutic dose of plasma factor VIII (FVIII) in patients with hemophilia A (HA). However, immune rejection limits the use of allogeneic cells in this mode of therapy. Here, we have examined the role of donor major histocompatibility complex (MHC)-stimulated host CD4(+)CD25(+) regulatory T (Treg) cells in suppressing immune responses against allogeneic uncommitted (Lin(-)) bone marrow cells (BMCs) for correction of bleeding disorder in HA mice.

METHODS

Allogeneic donor Lin(-) BMCs were co-transplanted with allo-antigen sensitized Treg cells in HA mice having acetaminophen-induced acute liver injury. Plasma FVIII activity was determined by in vitro functional assay, and correction of bleeding phenotype was assessed on the basis of capillary blood clotting time and tail-clip challenge. The immunosuppression potential of the sensitized Treg cells on CD4(+) T cells was studied both in vitro and in vivo. Suppression of inflammatory reactions in the liver against the homed donor cells by sensitized Treg cells was analysed by histopathological scoring. Allo-specificity of sensitized Treg cells and long-term retention of immunosuppression were examined against a third-party donor and by secondary challenge of allogeneic donor cells, respectively. The engraftment and phenotype change of donor BMCs in the liver and their role in synthesis of FVIII and liver regeneration were also determined.

RESULTS

Co-transplantation of allogeneic Lin(-) BMCs with sensitized Treg cells led to systemic immune modulation and suppression of inflammatory reactions in the liver, allowing better engraftment of allogeneic cells in the liver. Allo-antigen priming led to allo-specific immune suppression even after 1 year of transplantation. Donor-derived endothelial cells expressed FVIII in HA mice, leading to the correction of bleeding phenotype. Donor-derived hepatocyte-like cells, which constitute the major fraction of engrafted cells, supported regeneration of the liver after acute injury.

CONCLUSIONS

A highly proficient FVIII secreting core system can be created in regenerating liver by transplanting allogeneic Lin(-) BMCs in HA mice where transplantation tolerance against donor antigens can be induced by in vitro allo-antigen primed Treg cells. This strategy can be beneficial in treatment of genetic liver disorders for achieving prophylactic levels of the missing proteins.