Prevalent inhibitors in haemophilia B subjects enrolled in the Universal Data Collection database

Pleiotropic effects of different exonic nucleotide changes at the same position contribute to hemophilia B phenotypic variation

BACKGROUND

The disease-causing effects of genetic variations often depend on their location within a gene. Exonic changes generally lead to alterations in protein production, secretion, activity, or clearance. However, owing to the overlap between proteins and splicing codes, missense variants can also affect messenger RNA splicing, thus adding a layer of complexity and influencing disease phenotypes.

OBJECTIVES

To extensively characterize a panel of 13 exonic variants in the F9 gene occurring at 6 different factor IX positions and associated with varying severities of hemophilia B (HB).

METHODS

Computational predictions, splicing analysis, and recombinant factor IX assays were exploited to characterize F9 variants.

RESULTS

We demonstrated that 5 (38%) of 13 selected F9 exonic variants have pleiotropic effects. Although bioinformatic approaches accurately classified effects, extensive experimental assays were required to elucidate and deepen the molecular mechanisms underlying the pleiotropic effects. Importantly, their characterization was instrumental in developing tailored RNA therapeutics based on engineered U7 small nuclear RNA to mask cryptic splice sites and compensatory U1 small nuclear RNA to enhance exon definition.

CONCLUSION

Overall, albeit a multitool bioinformatic approach suggested the molecular effects of multiple HB variants, the deep investigation of molecular mechanisms revealed insights into the HB phenotype-genotype relationship, enabling accurate classification of HB variants. Importantly, knowledge of molecular mechanisms allowed the development of tailored RNA therapeutics, which can also be translated to other genetic diseases.

Haemophilia in the era of novel therapies: Where do inhibitors feature in the new landscape?

INTRODUCTION

The advent of therapeutic recombinant factor VIII (FVIII) and factor IX (FIX) protein infusions revolutionized the care of persons with haemophilia in the 1990s. It kicked off an era with the increasing use of prophylactic factor infusions for patients and transformed conversations around the ideal trough activity levels as well as the ultimate goals in tailored, individualized care. Our knowledge surrounding the immunologic basis of inhibitor development and treatment derives from a time when patients were receiving frequent factor infusions and focused on immune tolerance induction following inhibitor development.

DISCUSSION

More recently, care was revolutionized again in haemophilia A with the approval of emicizumab, a bispecific antibody mimicking activated FVIII function, to prevent bleeding. The use of emicizumab prophylaxis has resulted in a significantly slower accumulation of factor exposure days and continued effective prophylaxis in the case of inhibitor development. While emicizumab is effective at reducing the frequency of bleeding events in patients with haemophilia A, management of breakthrough bleeds, trauma, and surgeries still requires additional treatment. Ensuring that FVIII is a therapeutic option, particularly for life-threatening bleeding events and major surgeries is critical to optimizing the care of persons with haemophilia A. Other novel non-factor concentrate therapies, including rebalancing agents, will dramatically change the landscape for persons with haemophilia B with inhibitors.

CONCLUSION

This review discusses the changing landscape regarding the timing of inhibitor development and management strategies after inhibitor development, stressing the importance of education across the community to continue to vigilantly monitor for inhibitors and be prepared to treat persons with inhibitors.

Factor IX inhibitors in haemophilia B: A report of National Haemophilia Registry in China

INTRODUCTION

The development of inhibitors against factor FIX (FIX) is the most serious complication of FIX replacement therapy in haemophilia B (HB) patients. Currently, only few cohorts of HB inhibitor patients have been reported worldwide.

AIM

This Chinese nationwide study of HB inhibitor patients explored their risk factors for FIX inhibitor development and experience on their management.

METHODS

We retrospectively analysed patient characteristics, F9 genotypes, treatment strategies and outcomes of HB inhibitor patients registered to the Chinese National Registry and Patient Organization Registry.

RESULTS

Forty-four unique HB inhibitor patients were identified in 4485 unique HB patients registered by year 2021 to the two Registries. Inhibitor diagnosis were usually delayed and the low prevalence (.98%) may suggest some inhibitor patients were not identified. Their median age at inhibitor diagnosis was 7.5 (IQR, 3.0-14.8) years. Most patients (95.5%) had high-titre inhibitors. Allergic/Anaphylactic reactions occurred in 59.1% patients. Large deletions and nonsense mutations were the most common F9 mutation types in our FIX inhibitor patients. Patients with large F9 gene deletions were more likely to develop inhibitors (p = .0002), while those with missense mutations had a low risk (p < .0001). Thirteen (29.5%) patients received immune tolerance induction (ITI) therapy using low-dose prothrombin complex concentrate regimens. Twelve completed ITI with three (25.0%) achieving success. Nephrotic syndrome developed in two (16.7%) patients during ITI.

CONCLUSION

This study reports the largest Chinese cohort of HB inhibitor patients. Large deletions were most significantly associated with inhibitor development. Low-dose ITI might be feasible for FIX inhibitor eradication.

Updates on Novel Non-Replacement Drugs for Hemophilia

Over the last decade, the world of hemophilia has experienced an unprecedented therapeutic advance, thanks to the progress in bioengineering technologies, leading to the introduction of drugs with novel mechanisms of action based on restoring thrombin generation or coagulation factor VIII mimicking. Apart from the bispecific monoclonal antibody emicizumab, already approved for patients with severe hemophilia A with and without inhibitors, novel non-replacement drugs designed to reduce the treatment burden of patients with hemophilia A or B with or without inhibitors are undergoing evaluation in clinical trials. Thanks to their innovative mechanism of action and subcutaneous administration, these drugs promise to provide effective bleeding protection together with improved adherence and improve health-related quality of life for patients with hemophilia. On the other hand, rare thromboembolic events have been reported with some of these drugs and warrant continuous post-marketing surveillance and investigation of predisposing factors, although the overall safety profile of most of these drugs is good. Finally, new challenges need to be faced in the clinical and laboratory monitoring of the hemostatic status in patients treated with these innovative therapies. In this review, we provide an update on the available data on novel non-replacement drugs currently undergoing evaluation in clinical trials for patients with hemophilia.

Results of genetic analysis of 11 341 participants enrolled in the My Life, Our Future hemophilia genotyping initiative in the United States

BACKGROUND

Hemophilia A (HA) and hemophilia B (HB) are rare inherited bleeding disorders. Although causative genetic variants are clinically relevant, in 2012 only 20% of US patients had been genotyped.

OBJECTIVES

My Life, Our Future (MLOF) was a multisector cross-sectional US initiative to improve our understanding of hemophilia through widespread genotyping.

METHODS

Subjects and potential genetic carriers were enrolled at US hemophilia treatment centers (HTCs). Bloodworks performed genotyping and returned results to providers. Clinical data were abstracted from the American Thrombosis and Hemostasis Network dataset. Community education was provided by the National Hemophilia Foundation.

RESULTS

From 2013 to 2017, 107 HTCs enrolled 11 341 subjects (68.8% male, 31.2% female) for testing for HA (n = 8976), HB (n = 2358), HA/HB (n = 3), and hemophilia not otherwise specified (n = 4). Variants were detected in most male patients (98.2%% HA, 98.1% HB). 1914 unique variants were found (1482 F8, 431 F9); 744 were novel (610 F8, 134 F9). Inhibitor data were available for 6986 subjects (5583 HA; 1403 HB). In severe HA, genotypes with the highest inhibitor rates were large deletions (77/80), complex intron 22 inversions (9/17), and no variant found (7/14). In severe HB, the highest rates were large deletions (24/42). Inhibitors were reported in 27.3% of Black versus 16.2% of White patients.

CONCLUSIONS

The findings of MLOF are reported, the largest hemophilia genotyping project performed to date. The results support the need for comprehensive genetic approaches in hemophilia. This effort has contributed significantly towards better understanding variation in the F8 and F9 genes in hemophilia and risks of inhibitor formation.

Activated partial thromboplastin time-based clot waveform analysis enables measurement of very low levels of factor IX activity in patients with severe hemophilia B

The precise measurement of very low levels of factor IX activity (FIX:C < 1 IU/dL) is essential for understanding clinical severity and risk of inhibitor development in patients with severe hemophilia B (Pw-SHB). However, such measurement sensitivity has not yet been achieved. We aimed to establish a measurement method using clot waveform analysis (CWA). Residual FIX:C by adding anti-FIX monoclonal antibody, FIX:C by adding recombinant (r)FIX to the commercial Pw-SHB plasmas, and FIX:C in our Pw-SHB were determined by CS-2000i^™/CS-2400^™, followed by analysis of CWA parameters. The presence of anti-FIX antibody in the commercial Pw-SHB plasmas significantly decreased coagulation potential compared to its absence. The addition of rFIX to these innate plasma samples produced significant changes in three parameters upon adding FIX:C at 0.1-1 IU/dL, supporting the presence of trace FIX:C in Pw-SHB. Therefore, appropriate FIX-depleted plasma containing minimum residual FIX:C was chosen from reference curves of FIX:C (0.01-1 IU/dL). Among patients with untreated Pw-SHB, two had FIX:C 0.6-0.7 IU/dL and two had lower than detectable levels using FIX-depleted plasma. One of the latter had detectable trough levels post-rFIX administration. In conclusion, CWA enabled measurement of very low levels of FIX:C using appropriate FIX-deficient plasma.

Clinical conditions and risk factors for inhibitor-development in patients with haemophilia: A decade-long prospective cohort study in Japan, J-HIS2 (Japan Hemophilia Inhibitor Study 2)

BACKGROUND

Inhibitor-development is a serious complication in patients with haemophilia (PwH). Previous studies reported that therapeutic and genetic factors could be associated with these alloantibodies. Relevant clinical features such as genetic-background and different treatment regimens in Japan remain unclear, however.

AIMS

To analyse a nation-wide Japanese registry for PwH, and to examine risk factors for inhibitor-development.

METHODS AND RESULTS

Newly diagnosed patients with haemophilia A (PwHA) or haemophilia B (PwHB) without inhibitors after 2007, and with treatment records traceable from 0 to 75 exposure days (ED), were enrolled in the Japan Hemophilia Inhibitor Study 2 (J-HIS2) initiated in 2008. Of 417 patients (340 PwHA, 77 PwHB) from 46 facilities, 83 (76 PwHA, 7 PwHB) were recorded with inhibitors by July 2020. Inhibitors were observed in 31.0% of severe PwHA, 8.0% moderate and 1.6% mild and in 17.1% of severe PwHB. The majority of inhibitors (89.7% in severe PwHA and 71.4% in severe PwHB) were detected on or before 25ED (median 12ED in PwHA and 19ED in PwHB). Genotyping in these severe patients identified an association between inhibitor-development and null variants of F8 (P < .01) or F9 (P < .05). A lower incidence of inhibitors was recorded in severe PwHA treated with prophylaxis than in those treated on-demand (P < .01). A past-history of intracranial-haemorrhage appeared to be associated with inhibitor-development, while FVIII-concentrates infusion and routine vaccination on the same day was not related to inhibitor-development.

CONCLUSION

The J-HIS2 study has identified significant clinical variables associated with inhibitor-development in Japanese PwH, consistent with other global studies.

Eradication of FIX inhibitor in haemophilia B children using low-dose immune tolerance induction with rituximab-based immunosuppressive agent(s) in China

INTRODUCTION

Development of haemophilia B inhibitors (HBI) results in the ineffectiveness of FIX replacement therapy. Inhibitor eradication by immune tolerance induction (ITI) is therefore necessary. In HBI, ITI even at high FIX dose is less effective and has a higher risk of severe complications.

AIM

To characterize clinical features and outcome of ITI on HBI.

METHODS

This retrospective study was conducted in Haemophilia Paediatric Comprehensive Care Centre of China. We used low-dose ITI (25-50 FIX IU/kg/three-times-weekly to every-other-day) with domestic prothrombin complex concentrate (PCC), combined with two successive immunosuppressive (IS) regimens.

RESULTS

Sixteen HBI children, representing 5.7% of all and 14.4% of our severe registered HB patients, were enroled. Seven cases reported allergic reactions (ARs) proximal to inhibitor development. The historic peak inhibitor titre was median 54.2 (range 4.7-512) BU, and 15 (93.8%) had high-titre inhibitors. Twelve patients adherent to ITI were analysable. Of the nine ITI patients who received rituximab/prednisone (IS Regimen-1), four achieved tolerization in 1.4-43.3 months. Two subsequently relapsed but re-tolerized after a second course of IS Regimen-1. During ITI, the median treated bleed was .39/month (82.7% reduction from before ITI), and the incidence of AR and nephrotic syndrome (NS) complications was each at 22% (2/9). Three ITI patients received modified 'Beutel' protocol (IS Regimen-2) using multiple-IS-drugs, and two had rapid tolerization (.8 and 1.8 months).

CONCLUSIONS

Inhibitor eradication could be achieved by low-dose ITI protocol using PCC combined with IS. Larger studies are needed to confirm if ITI with IS Regimen-2 is more effective with less complications.

International consensus recommendations on the management of people with haemophilia B

Haemophilia B is a rare X-linked genetic deficiency of coagulation factor IX (FIX) that, if untreated, can cause recurrent and disabling bleeding, potentially leading to severe arthropathy and/or life-threatening haemorrhage. Recent decades have brought significant improvements in haemophilia B management, including the advent of recombinant FIX and extended half-life FIX. This therapeutic landscape continues to evolve with several non-factor replacement therapies and gene therapies under investigation. Given the rarity of haemophilia B, the evidence base and clinical experience on which to establish clinical guidelines are relatively sparse and are further challenged by features that are distinct from haemophilia A, precluding extrapolation of existing haemophilia A guidelines. Due to the paucity of formal haemophilia B-specific clinical guidance, an international Author Group was convened to develop a clinical practice framework. The group comprised 15 haematology specialists from Europe, Australia, Japan, Latin America and North America, covering adult and paediatric haematology, laboratory medicine and biomedical science. A hybrid approach combining a systematic review of haemophilia B literature with discussion of clinical experience utilized a modified Delphi format to develop a comprehensive set of clinical recommendations. This approach resulted in 29 recommendations for the clinical management of haemophilia B across five topics, including product treatment choice, therapeutic agent laboratory monitoring, pharmacokinetics considerations, inhibitor management and preparing for gene therapy. It is anticipated that this clinical practice framework will complement existing guidelines in the management of people with haemophilia B in routine clinical practice and could be adapted and applied across different regions and countries.

Long-term efficacy and safety of subcutaneous concizumab prophylaxis in hemophilia A and hemophilia A/B with inhibitors

Despite current treatments, there remains an unmet need for patients with hemophilia. The main parts of two phase 2 trials established clinical proof-of-concept for once-daily, subcutaneous concizumab prophylaxis in patients with hemophilia A/B with inhibitors (HAwI/HBwI; explorer4) and severe hemophilia A without inhibitors (HA; explorer5,). Here, we present results from extension parts of these trials, included to evaluate longer-term safety and efficacy. Both trials included main (≥24 weeks) and extension parts (52-102 weeks), with patients receiving 0.15 mg/kg concizumab with potential dose escalation to 0.20 or 0.25 mg/kg if they experienced ≥3 treated spontaneous bleeds within 12 weeks. Endpoints included annualized bleeding rate (ABR), adverse events (AEs), and anti-drug antibody (ADA) occurrence. Thromboembolic events were AEs of special interest. Thirty-six patients with HA, 15 with HAwI and 10 with HBwI were exposed to concizumab. Estimated ABRs during the main+extension parts at last dose level were 4.8 (95% confidence interval [CI]: 3.2-7.2) and 6.4 (95% CI: 4.1-9.9) in explorer4 and explorer5, respectively (spontaneous ABRs were 1.8 [95% CI: 1.2-2.6] and 2.1 [95% CI: 1.3-3.3]). Most AEs were mild, with no deaths, events leading to withdrawal or thromboembolic events. ADAs developed in 25% of patients and were low titer and transient with no observed clinical effect in most cases. Results of the main+extension parts of these trials were consistent with the main parts. Ongoing phase 3 trials will further evaluate concizumab as a once-daily, subcutaneous treatment across hemophilia subtypes. Trials registered at www.clinicaltrials.gov (NCT03196284; NCT03196297).

The Clinical Genetics of Hemophilia B (Factor IX Deficiency)

Hemophilia B (HB) is a bleeding disorder caused by deficiency of or defect in blood coagulation factor IX (FIX) inherited in an X-linked manner. It results from one of over 1000 known pathogenic variants in the FIX gene, F9; missense and frameshift changes predominate. Although primarily males are affected with HB, heterozygous females may have excessive bleeding due to random or non-random X chromosome inactivation; in addition, homozygous, compound heterozygous, and hemizygous females have been reported. Somatic and germinal mosaicism for F9 variants has been observed. Development of antibodies to FIX treatment products (inhibitors) is rare and related to the type of causative variant present. Treatment is with products produced by recombinant DNA technology, and gene therapy is in clinical trials. Genetic counseling with up-to-date information is warranted for heterozygotes, potential heterozygotes, and men and women affected with HB.

Hemophilia Gene Therapy Value Assessment: Methodological Challenges and Recommendations

Gene therapy for hemophilia is designed to produce health gains for patients over many years. Rewarding that value creation on the basis of a one-time treatment implies a large upfront cost. This cost can only be justified by long-term health benefits and being cost-effective compared with conventional treatments. Yet, uncertainties about the long-term benefits make it challenging to assess clinical and economic value of gene therapies at launch. We identify and discuss key methodological challenges in assessing the value of gene therapy for hemophilia, including the immaturity of evidence on the durability of benefits, lack of definition and valuation of cure for chronic diseases, absence of randomized controlled trials, limitations of traditional quality of life measures in hemophilia, approach for qualifying cost-savings compared with current treatments, and choice of perspective. The Institute for Clinical and Economic Review has developed a framework for assessing single or short-term therapies (ICER-SST) and has applied it in hemophilia. After reviewing this framework and its application, we recommend the following when assessing the value of hemophilia gene therapies: (1) leveraging expert clinical opinion to justify assumptions on the durability of benefits; (2) using external synthetic controls and lead-in, self-controlled trials to assess comparative effectiveness; (3) addressing limitations of traditional quality of life measures through the use of modified utility collection approaches; (4) adjusting cost offsets from gene therapies with caution; (5) considering outcome-based contracting to address uncertainties about prices and long-term outcomes; and (6) presenting societal and healthcare system perspectives in parallel.

Preclinical development of plant-based oral immune modulatory therapy for haemophilia B

Anti-drug antibody (ADA) formation is a major complication in treatment of the X-linked bleeding disorder haemophilia B (deficiency in coagulation factor IX, FIX). Current clinical immune tolerance protocols are often not effective due to complications such as anaphylactic reactions against FIX. Plant-based oral tolerance induction may address this problem, as illustrated by the recent first regulatory approval of orally delivered plant cells to treat peanut allergy. Our previous studies showed that oral delivery of plant cells expressing FIX fused to the transmucosal carrier CTB (cholera toxin subunit B) in chloroplasts suppressed ADA in animals with haemophilia B. We report here creation of the first lettuce transplastomic lines expressing a coagulation factor, in the absence of antibiotic resistance gene. Stable integration of the CTB-FIX gene and homoplasmy (transformation of ˜10 000 copies in each cell) were maintained in both T1 and T2 generation marker-free plants. CTB-FIX expression in lyophilized leaves of T1 and T2 marker-free plants was 1.0-1.5 mg/g dry weight, confirming that the marker excision did not affect antigen levels. Oral administration of CTB-FIX to Sprague Dawley rats at 0.25, 1 or 2.5 mg/kg did not produce overt adverse effects or toxicity. The no-observed-adverse-effect level (NOAEL) is at least 2.5 mg/kg for a single oral administration in rats. Oral administration of CTB-FIX at 0.3 or 1.47 mg/kg either mixed in food or as an oral suspension to Beagle dogs did not produce any observable toxicity. These toxicology studies should facilitate filing of regulatory approval documents and evaluation in haemophilia B patients.

Haemophilia: factoring in new therapies

Haemophilia is an inherited bleeding disorder in which the haemostatic defect results from deficiency of coagulation factor VIII (FVIII) in haemophilia A or factor IX (FIX) in haemophilia B. Traditional treatments for haemophilia have largely worked by directly replacing the missing coagulation factor, but face challenges due to the short half-life of FVIII and FIX, the need for frequent intravenous access and development of neutralising antibodies to coagulation factors (inhibitors). Recent advances in haemophilia therapy have worked to eliminate these challenges. Half-life extension of factor concentrates has lengthened the time needed between infusions, enhancing quality of life. Subcutaneous administration of therapeutics utilising alternative mechanisms to overcome inhibitors have expanded the options to prevent bleeding. Finally, initial successes with gene therapy offer a cautious hope for durable cure. In the present review, we will discuss currently available treatments, as well as highlight therapeutics in various stages of clinical development for the treatment of haemophilia A and B. In this review, we present therapies that are currently clinically available and highlight therapeutics that are in various stages of clinical development for the treatment of haemophilia A and B.

Inhibitor incidence in an unselected cohort of previously untreated patients with severe haemophilia B: a PedNet study

The incidence of factor IX (FIX) inhibitors in severe hemophilia B (SHB) is not well defined. Frequencies of 3-5% have been reported but most studies to date have been small, including patients with different severities, and without prospective follow up for inhibitor incidence. The study objective was to investigate the inhibitor incidence in patients with SHB followed up for to 500 exposure days (ED), the frequency of allergic reactions, and the relationship with genotypes. Consecutive previously untreated patients (PUP) with SHB enrolled into the PedNet cohort were included. Detailed data was collected for the first 50 ED, followed by the annual collection of the inhibitor status and allergic re-actions. The presence of inhibitors was defined by at least two consecutive positive samples. Additionally, data on FIX gene mutation was collected. One hundred and fifty-four PUP with SHB were included; 75% were followed up until 75 ED, and 43% until 500 ED. Inhibitors developed in 14 patients (seven high-titer). The median number of ED at inhibitor manifestation was 11 (interquartile range [IQR]: 6.5-36.5). The cumulative inhibitor incidence was 9.3% (95% Confidence Interval [CI]: 4.4-14.1) at 75 ED, and 10.2% (95% CI: 5.1-15.3) at 500 ED. Allergic reactions occurred in four (28.6%) inhibitor patients. Missense mutations were most frequent (46.8%) overall but not associated with inhibitors. Nonsense mutations and deletions with large structural changes comprised all mutations among inhibitor patients and were associated with an inhibitor risk of 26.9% and 33.3%, respectively. In an unselected, well-defined cohort of PUP with SHB, the cumulative inhibitor incidence was 10.2% at 500 ED. Nonsense mutations and large deletions were strongly associated with the risk of inhibitor development. The ‘PedNet Registry’ is registered at clinicaltrials.gov; identifier: NCT02979119.

Safety and effectiveness of Rixubis in patients with hemophilia B: a real-world, prospective, postmarketing surveillance study in South Korea

Background

Rixubis (recombinant factor IX, nonacog gamma) is indicated for the control and prevention of bleeding episodes, perioperative management, and routine prophylaxis in hemophilia B patients. This real-world, postmarketing surveillance study aimed to evaluate the safety and effectiveness of Rixubis in adult and pediatric hemophilia B patients in South Korea.

Methods

This prospective, observational, multicenter study (clinicaltrials.gov identifier NCT029 22231) was conducted in hemophilia B patients between April 2015 and April 2019, who were observed for up to 6 months after the initiation of Rixubis treatment. Safety was evaluated based on the number and severity of adverse events (AEs) and serious AEs (SAEs). Hemostatic effectiveness was assessed by physicians and patients by using a four-point scale and rated as excellent, good, fair, or no response based on treatment type.

Results

In all, 58 patients were enrolled from four centers by seven physicians during the study period. The safety and effectiveness analysis sets included 57 and 54 patients, respectively. Overall, 11 AEs were reported in eight patients (14.0%), of which three were SAEs and occurred in three patients (5.3%). All 11 AEs were reported as unexpected and mild in severity, with no anaphylactic reaction, and 10 AEs (90.9%) resolved. The majority of AEs (10) were unrelated to Rixubis. Of the 142 hemostatic effectiveness assessments, 123 (86.6%) were reported as good or excellent.

Conclusion

Rixubis demonstrated an acceptable safety and effectiveness profile in the treatment of bleeding, perioperative management, and prophylaxis in hemophilia B patients in a real-world setting in South Korea.

Nonacog beta pegol (N9-GP) in hemophilia B: First report on safety and efficacy in previously untreated and minimally treated patients

BACKGROUND/OBJECTIVE

We report the first analysis of an extended half-life recombinant factor IX, nonacog beta pegol (N9-GP), in previously untreated patients (PUPs) and minimally treated patients with hemophilia B.

METHODS

Paradigm 6 (Safety and Efficacy of Nonacog Beta Pegol [N9-GP] in Previously Untreated Patients With Haemophilia B) is a multicenter, open-label, single-arm, phase 3 trial. Main inclusion criteria were males aged < 6 years, with hemophilia B with factor IX (FIX) activity ≤ 2%, who were previously untreated or with ≤ 3 exposure days (EDs) to FIX-containing products. Patients received N9-GP 40 IU/kg once weekly (prophylaxis) or individualized dosing (preprophylaxis). Bleeds were treated with N9-GP 40 IU/kg (80 IU/kg if severe). The primary end point was incidence of anti-FIX inhibitory antibodies (inhibitors). Secondary end points included safety outcomes and annualized bleeding rate (ABR).

RESULTS

At data cutoff (August 31, 2018), 38 patients had been screened, and 37 had received N9-GP (median age, 1.0 years [range, 0-4]). Total in-trial EDs amounted to 2833, representing ~ 65 patient-years. Two (6.1%) of 33 "at-risk" patients (patients with ≥ 10 EDs plus patients who developed inhibitors) developed high-titer inhibitors and were withdrawn. No other safety concerns, including thromboembolic events, were identified. In the prophylaxis group (n = 28), 67.9% were bleed free; all bleeds (n = 15) were treated with one N9-GP injection; and overall, spontaneous, and traumatic ABRs were low (median ABRs of 0.0, 0.0, and 0.0, respectively; modeled mean ABRs of 0.31, 0.08, and 0.23, respectively). Estimated mean FIX trough activity was 15.0%.

CONCLUSION

We report an inhibitor incidence of 6.1%, which is within the expected range for PUPs with hemophilia B. No other safety concerns were identified; moreover, N9-GP provided effective hemostatic coverage.

Postmarketing safety and effectiveness of recombinant factor IX (nonacog alfa) in Japanese patients with haemophilia B

INTRODUCTION

In 2010, nonacog alfa became the first recombinant factor IX (rFIX) available in Japan for patients with haemophilia B.

AIM

To determine real-world safety (adverse events, incidence of inhibitors) and effectiveness of nonacog alfa in Japan.

METHODS

This multicentre, prospective, observational, postmarketing surveillance study enrolled previously treated and untreated patients (PTPs and PUPs, respectively) who were observed for 1 and 2 years, respectively, after initiating nonacog alfa therapy. Safety and effectiveness were assessed for each treatment type. Annualized bleeding rate (ABR) and incremental recovery of rFIX were also evaluated.

RESULTS

Overall, 312 of 314 patients enrolled from 173 sites were eligible for the safety analysis set (PTPs, 281; PUPs, 28; other, 3). Mean age was 25.4 (PTPs) and 14.8 (PUPs) years. Haemophilic severity ranged from mild to severe, and 133 (42.6%) patients had haemophilic arthropathy. Of 285 patients (PTPs, 257; PUPs, 28) in the effectiveness set, 112 received on-demand treatment for 1161 bleeding episodes (effectiveness rate, 93.7%) and 185 received routine prophylaxis (effectiveness rate, 95.5%). No spontaneous bleeding was observed in 52.4% of patients during prophylactic treatment. Median ABR was lower during routine prophylaxis (2.0) vs the rest of the observation period (8.3). A weak negative correlation was found between body weight and the reciprocal of rFIX recovery. Eleven adverse drug reactions occurred in 7 PTPs (2.2% [7/312]); recurrence of inhibitor was observed in 1 patient, but no new inhibitor developed in PTPs or PUPs.

CONCLUSION

Nonacog alfa therapy is safe and effective in the real-world scenario in Japan.

Advances in Antiplatelet Therapy for Dentofacial Surgery Patients: Focus on Past and Present Strategies

BACKGROUND

Nowadays, patients involved in antiplatelet therapy required special attention during oral surgery procedures, due to the antiplatelet drugs assumption. The motivations of the assumption may be different and related to the patient's different systemic condition. For this reason, accordingly to the current international guidelines, different protocols can be followed. The aim of this work is to analyze how the dentist's approach to these patients has changed from the past to the present, evaluating the risk exposure for the patients.

METHODS

This review paper considered different published papers in literature through quoted scientific channels, going in search of "ancient" works in such a way as to highlight the differences in the protocols undertaken. The analyzed manuscripts are in the English language, taking into consideration reviews, case reports, and case series in such a way as to extrapolate a sufficient amount of data and for evaluating the past therapeutic approaches compared to those of today.

RESULTS

Colleagues in the past preferred to subject patients to substitution therapy with low molecular weight anticoagulants, by suspending antiplatelet agents to treatment patients, often for an arbitrary number of days. The new guidelines clarify everything, without highlighting an increased risk of bleeding during simple oral surgery in patients undergoing antiplatelet therapy.

CONCLUSION

Either patients take these medications for different reasons, because of cardiovascular pathologies, recent cardiovascular events, or even for simple prevention, although the latest research shows that there is no decrease of cardiovascular accidents in patients who carry out preventive therapy. Surely, it will be at the expense of the doctor to assess the patient's situation and risk according to the guidelines. For simple oral surgery, it is not necessary to stop therapy with antiplatelet agents because the risk of bleeding has not increased, and is localized to a post-extraction alveolus or to an implant preparation, compared to patients who do not carry out this therapy. From an analysis of the results it emerges that the substitutive therapy should no longer be performed and that it is possible to perform oral surgery safely in patients who take antiplatelet drugs, after a thorough medical history. Furthermore, by suspending therapy, we expose our patients to more serious risks, concerning their main pathology, where present.

A Highly Productive CHO Cell Line Secreting Human Blood Clotting Factor IX

Hemophilia B patients suffer from an inherited blood-clotting defect and require regular administration of blood-clotting factor IX replacement therapy. Recombinant human factor IX produced in cultured CHO cells is nearly identical to natural, plasma-derived factor IX and is widely used in clinical practice. Development of a biosimilar recombinant human factor IX for medical applications requires the generation of a clonal cell line with the highest specific productivity possible and a high level of specific procoagulant activity of the secreted factor IX. We previously developed plasmid vectors, p1.1 and p1.2, based on the untranslated regions of the translation elongation factor 1 alpha gene from Chinese hamster. These vectors allow one to perform the methotrexate- driven amplification of the genome-integrated target genes and co-transfect auxiliary genes linked to various resistance markers. The natural open reading frame region of the factor IX gene was cloned in the p1.1 vector plasmid and transfected to CHO DG44 cells. Three consecutive amplification rounds and subsequent cell cloning yielded a producer cell line with a specific productivity of 10.7 ± 0.4 pg/cell/day. The procoagulant activity of the secreted factor IX was restored nearly completely by co-transfection of the producer cells by p1.2 plasmids bearing genes of the soluble truncated variant of human PACE/furin signal protease and vitamin K oxidoreductase from Chinese hamster. The resulting clonal cell line 3B12-86 was able to secrete factor IX in a protein-free medium up to a 6 IU/ml titer under plain batch culturing conditions. The copy number of the genome- integrated factor IX gene for the 3B12-86 cell line was only 20 copies/genome; the copy numbers of the genome-integrated genes of PACE/furin and vitamin K oxidoreductase were 3 and 2 copies/genome, respectively. Factor IX protein secreted by the 3B12-86 cell line was purified by three consecutive chromatography rounds to a specific activity of up to 230 IU/mg, with the overall yield > 30%. The developed clonal producer cell line and the purification process employed in this work allow for economically sound industrial-scale production of biosimilar factor IX for hemophilia B therapy.

Inhibitor development in haemophilia according to concentrate

Inhibitor development represents the most serious side effect of haemophilia treatment. Any difference in risk of inhibitor formation depending on the product used might be of clinical relevance. It was this study’s objective to assess inhibitor development according to clotting factor concentrate in severe haemophilia A and B. The European Haemophilia Safety Surveillance (EUHASS) was set up as a study monitoring adverse events overall and according to concentrate. Since October 2008, inhibitors were reported at least quarterly. Number of treated patients was reported annually, specifying the number of patients completing 50 exposure days (Previously Untreated Patients, PUPs) without inhibitor development. Cumulative incidence, incidence rates and 95 % confidence intervals (CI) were calculated. Data from October 1, 2008 to December 31, 2012 were analysed for 68 centres that validated their data. Inhibitors developed in 108/417 (26 %; CI 22–30 %) PUPs with severe haemophilia A and 5/72 (7 %; CI 2–16%) PUPs with severe haemophilia B. For Previously Treated Patients (PTPs), 26 inhibitors developed in 17,667 treatment years [0.15/100 treatment years; CI 0.10–0.22) for severe haemophilia A and 1/2836 (0.04/100; (CI 0.00–0.20) for severe haemophilia B. Differences between plasma-derived and recombinant concentrates, or among the different recombinant FVIII concentrates were investigated. In conclusion, while confirming the expected rates of inhibitors in PUPs and PTPs, no class or brand related differences were observed.

[Immune tolerance induction in a case of hemophilia B with inhibitor with prothrombin complex concentrate and rituximab]

Objective: To explore the immune tolerance induction (ITI) in a case of severe hemophilia B patient with inhibitor. Methods: The F Ⅸ∶C was detected using a one-stage method and FIX inhibitor was assayed using Bethesda method. ITI was performed with prothrombin complex concentrates (PCC) in combination with rituximab. Results: His past exposure days (ED) with PCC were 20 ED and his peak FⅨ inhibitor titer was 56 BU/ml. When his FIX inhibitor titer decreased to 10.4 BU/ml in Nov. 2015 and after receiving the informed consent from his parents, ITI was started. PCC with low dose rituximab successfully eradicated the high titer inhibitor within 17 months. There was no anaphylaxis, thrombotic event and infection. Conclusion: This is the first case report for successful immune tolerance induction therapy in Chinese hemophilia B patient. ITI using PCC combined with rituximab is an effective choice to induce immune tolerance of hemophilia B with inhibitor.

Evolution of the Treatments for Hemophilia

Although hemophilia has been recognized for centuries as an inherited disorder primarily affecting males, advances in treatments have been very recent. Initial availability of plasma-derived therapies offered significant improvements in morbidity and mortality, but the transmission of viruses quickly negated the benefit of early factor replacement products. After developing successful viral inactivation methods and subsequently developing recombinant technology, the manufacturing of factor concentrates became much safer. Access to safer factor products allowed for a shift from the treatment of bleeds to prevention, called prophylaxis. Although dosing and interval vary, prevention of joint disease is now a realistic goal. Unfortunately, despite advances in the safety of therapy, some patients are unable to use factor replacement products because they develop antibodies, known as inhibitors. Eradication of inhibitors is possible in the majority of patients, but it is expensive and takes time. Management of acute bleeding may require significantly higher doses of factor replacement or the use of a bypassing agent. As a result, patients with inhibitors are at increased risk for sequelae, including joint disease, life-threatening bleeding, infectious complications with central vascular access devices, and thrombotic complications.

The prevalence of factor VIII and IX inhibitors among Saudi patients with hemophilia: Results from the Saudi national hemophilia screening program

Hemophilia A and B are X-linked diseases that predominantly affect male patients. Patients can develop coagulation factor inhibitors, which exponentially increases the treatment cost. However, the prevalence of factor VIII and IX inhibitors in Saudi Arabia is unclear.This study aimed to determine the Saudi prevalence of factor VIII and IX inhibitors.This 4-year, 7-center, cross-sectional study evaluated the Saudi prevalences of hemophilia A and B. We collected the patients' clinical data, evaluated their disease, and tested for factor inhibitors.We included 202 patients with hemophilia (median age at diagnosis: 0.13 years, range: birth-34.8 years). The patients included 198 male patients (98%), 148 patients with hemophilia A (73.3%), and 54 patients with hemophilia B (26.7%). The patients exhibited severe factor VIII activity (<1%; 121 patients; 5.2%), moderate activity (1-5%; 7 patients; 4.9%), and mild activity (14 patients; 9.9%). Among the patients with care-related data, most patients were treated for episodic bleeding (76.8%) or received prophylaxis (22.6%); 1 patient received both treatments. Among the patients with source-related data, the factor replacements were derived from plasma (48.4%), recombinant concentrates (22.9%), both sources (14.6%), or fresh frozen plasma (14.1%). Factor VIII inhibitors were observed in 43 (29.3%) of the 147 patients, and only 1 of the 54 patients developed factor IX inhibitors. Most patients who developed inhibitors had severe hemophilia (40/44; 90.9%), and inhibitors were also common among patients who received recombinant products (14/43; 32.6%).The Saudi prevalence of factor inhibitors was similar to those among other ethnic populations.

The current state of adverse event reporting in hemophilia

INTRODUCTION

Replacement of the missing clotting factor is the mainstay of hemophilia treatment. Whilst historically many hemophilia patients were infected with blood-borne viruses transmitted via plasma-derived products, nowadays the formation of alloantibodies against the missing clotting factor is the main adverse event of treatment. Areas covered: This paper provides an overview of the current national and international adverse event reporting systems, what these surveillance schemes taught us about side effects of the products presently in use, and elaborates on how to adapt these systems to the challenges we face with the changing treatment landscape. Expert commentary: Treatment of inherited bleeding disorders was accompanied by severe complications in the past, resulting in major morbidity and mortality. Current products are much safer, but still require monitoring via efficient safety surveillance systems. Adverse events are reported in national and international systems. With many new products entering the market, as well as non-factor replacement therapies, new safety issues may arise. It is important to identify potential adverse events early by making surveillance systems suitable to pick up unknown or unexpected effects, and to recognize and communicate patterns of adverse events rapidly.

New developments in the management of moderate-to-severe hemophilia B

Hemophilia B is an X-linked genetic deficiency of coagulation factor IX (FIX) activity associated with recurrent deep tissue and joint bleeding that may lead to long-term disability. FIX replacement therapy using plasma-derived protein or recombinant protein has significantly reduced bleeding and disability from hemophilia B, particularly when used in a prophylactic fashion. Although modern factor replacement has excellent efficacy and safety, barriers to the broader use of prophylaxis remain, including the need for intravenous (IV) access, frequent dosing, variability in individual pharmacokinetics, and cost. To overcome the requirement for frequent factor dosing, novel forms of recombinant FIX have been developed that possess extended terminal half-lives. Two of these products (FIXFc and rIX-FP) represent fusion proteins with the immunoglobulin G1 (IgG1) Fc domain and albumin, respectively, resulting in proteins that are recycled in vivo by the neonatal Fc receptor. The third product has undergone site-specific PEGylation on the activation peptide of FIX, similarly resulting in a long-lived FIX form. Clinical trials in previously treated hemophilia B patients have demonstrated excellent efficacy and confirmed less-frequent dosing requirements for the extended half-life forms. However, gaps in knowledge remain with regard to the risk of inhibitor formation and allergic reactions in previously untreated patient populations, safety in elderly patients with hemophilia, effects on in vivo FIX distribution, and cost-effectiveness. Additional strategies designed to rebalance hemostasis in hemophilia patients include monoclonal-antibody-mediated inhibition of tissue factor pathway inhibitor activity and siRNA-mediated reduction in antithrombin expression by the liver. Both of these approaches are long acting and potentially involve subcutaneous administration of the drug. In this review, we will discuss the biology of FIX, the evolution of FIX replacement therapy, the emerging FIX products possessing extended half-lives, and novel “rebalancing” approaches to hemophilia therapy.

Inhibitor development in non-severe haemophilia across Europe

Evidence about inhibitor formation in non-severe haemophilia and the potential role for clotting factor concentrate type is scant. It was the aim of this study to report inhibitor development in non-severe haemophilia patients enrolled in the European Haemophilia Safety Surveillance (EUHASS) study. Inhibitors are reported quarterly and total treated patients annually. Incidence rates and 95% confidence intervals (95% CI) were calculated according to diagnosis and concentrate used. Between 1-10-2008 and 31-12-2012, 68 centres reported on 7,969 patients with non-severe haemophilia A and 1,863 patients with non-severe haemophilia B. For haemophilia A, 37 inhibitors occurred in 8,622 treatment years, resulting in an inhibitor rate of 0.43/100 treatment years (95% CI 0.30-0.59). Inhibitors occurred at a median age of 35 years, after a median of 38 exposure days (EDs; P25-P75: 20-80); with 72% occurring within the first 50 EDs. In haemophilia B, one inhibitor was detected in 2,149 treatment years, resulting in an inhibitor rate of 0.05/100 years (95% CI 0.001-0.26). This inhibitor developed at the age of six years, after six EDs. The rate of inhibitors appeared similar across recombinant and plasma derived factor VIII (FVIII) concentrates. Rates for individual concentrates could not be calculated at this stage due to low number of events. In conclusion, inhibitors in non-severe haemophilia occur three times more frequently than in previously treated patients with severe haemophilia at a rate of 0.43/100 patient years (haemophilia A) and 0.05/100 years (haemophilia B). Although the majority of inhibitors developed in the first 50 EDs, inhibitor development continued with increasing exposure to FVIII.

Hemophilia B: molecular pathogenesis and mutation analysis

Hemophilia B is an X-chromosome-linked inherited bleeding disorder primarily affecting males, but those carrier females with reduced factor IX activity (FIX:C) levels may also experience some bleeding. Genetic analysis has been undertaken for hemophilia B since the mid-1980s, through linkage analysis to track inheritance of an affected allele, and to enable determination of the familial mutation. Mutation analysis using PCR and Sanger sequencing along with dosage analysis for detection of large deletions/duplications enables mutation detection in > 97% of patients with hemophilia B. The risk of the development of inhibitory antibodies, which are reported in ~ 2% of patients with hemophilia B, can be predicted, especially in patients with large deletions, and these individuals are also at risk of anaphylaxis, and nephrotic syndrome if they receive immune tolerance induction. Inhibitors also occur in patients with nonsense mutations, occasionally in patients with small insertions/deletions or splice mutations, and rarely in patients with missense mutations (p.Gln237Lys and p.Gln241His). Hemophilia B results from several different mechanisms, and those associated with hemophilia B Leyden, ribosome readthrough of nonsense mutations and apparently 'silent' changes that do not alter amino acid coding are explored. Large databases of genetic variants in healthy individuals and patients with a range of disorders, including hemophilia B, are yielding useful information on sequence variant frequency to help establish possible variant pathogenicity, and a growing range of algorithms are available to help predict pathogenicity for previously unreported variants.

Gene therapy in an era of emerging treatment options for hemophilia B

Factor IX deficiency (hemophilia B) is less common than factor VIII deficiency (hemophilia A), and innovations in therapy for hemophilia B have generally lagged behind those for hemophilia A. Recently, the first sustained correction of the hemophilia bleeding phenotype by clotting factor gene therapy has been described using recombinant adeno-associated virus (AAV) to deliver factor IX. Despite this success, many individuals with hemophilia B, including children, men with active hepatitis, and individuals who have pre-existing natural immunity to AAV, are not eligible for the current iteration of hemophilia B gene therapy. In addition, recent advances in recombinant factor IX protein engineering have led some hemophilia treaters to reconsider the urgency of genetic cure. Current clinical and preclinical approaches to advancing AAV-based and alternative approaches to factor IX gene therapy are considered in the context of current demographics and treatment of the hemophilia B population.

Risk factors associated with inhibitor development in Chinese patients with haemophilia B

INTRODUCTION

Inhibitor development is a severe complication of factor IX substitution treatment for haemophilia B (HB). Current research examined the association between inhibitor development and F9 genotypes and polymorphisms in immune response genes in Chinese HB patients.

MATERIALS AND METHODS

11 inhibitor-positive HB patients and 41 inhibitor-negative HB patients were enrolled. Direct sequencing, copy number variation (CNV) detection and fragment length analysis were applied to identify F9 genotypes and 15 polymorphisms in immune response genes.

RESULTS

7 patients developed high titer inhibitors, with 5 of them having histories of consecutive exposure to FIX products on demand for at least 5 days. Allergic reactions/anaphylaxis to prothrombin complex concentrates (PCC) occurred in 3 patients before inhibitors were detected. Five nonsense mutations (E54X, R75X, Q185X, R298X and R379X), two large deletions (E1~6del and E1~8del) and one missense mutation (S411G) were identified in patients with inhibitors. Missense mutations had a low odds ratio for FIX inhibitors development (IOR) of 0.078 (P = 0.02), while nonsense mutation presented a high IOR of 8.500 (P = 0.0044). The frequency of allele T in CD44(95102) (A/T) was significantly higher in inhibitor-negative patients, with OR of 0.324 (P = 0.04).

CONCLUSIONS

Nonsense mutations conferred a higher risk for while allele T in CD44(95102) (A/T) might play a protective role against inhibitor development in Chinese HB patients.

Emerging genetic and pharmacologic therapies for controlling hemostasis: beyond recombinant clotting factors

For more than 3 decades, the scientific community has pursued gene correction of hemophilia, with the goal that an individual with congenitally deficient factor VIII or factor IX might synthesize adequate endogenous clotting factor to be relieved of burdensome repeated clotting factor infusions, as well as the emotional weight of continuous hemorrhage risk. Recent reports of successful factor IX gene therapy and partial correction of the bleeding phenotype have raised the bar for success for a robust crop of new clinical gene therapy efforts for both hemophilia A and B. At the same time that gene therapy is gaining momentum, suggesting the possibility of relief from regular intravenous coagulation protein replacement, a number of innovative technologies that enhance hemostatic potential independently of replacement factor administration are demonstrating success in human clinical application. Human clinical trial progress is reviewed regarding a recombinant bispecific IgG antibody to factors IXa and X that mimics factor VIII cofactor activity, as well as monoclonal antibody and short interfering RNA strategies that demonstrate hemostatic efficacy via opposing inhibitors of coagulation. These strategies, associated with prolonged hemostatic potential following subcutaneous (ACE910, ALN-AT3, Concizumab) or single administration (eg, gene therapy) make it possible to imagine a day when recombinant clotting factor administration, rather than being a daily preoccupation, is relegated to an adjunctive role in supporting more novel standard of care therapies.

Inhibitors in haemophilia: what have we learned from registries? A systematic review

Congenital haemophilia A and B are genetic disorders affecting factor VIII and factor IX production, respectively. Factor replacement is the only effective treatment for these deficiencies, but a patient's immune system can develop inhibitory antibodies which bind and interfere with the function of the replaced factor in a variety of ways. The main treatment goal for patients with inhibitors is to induce immune tolerance to the injected factor. If not successful, a different treatment termed bypass therapy is needed to treat bleeds. The goal of this review is to demonstrate the usefulness of haemophilia registries as information sources to supplement available evidence regarding predictors of inhibitor development and immune tolerance induction (ITI) outcomes. In this systematic review, relevant keywords were used to search online academic databases during February 2014. Inclusion criteria were original publication and data obtained from a haemophilia or ITI registry with a minimum of 30 patients. A data collection form was created to extract information from selected manuscripts. Titles, abstracts and then full texts were screened to determine the eligibility of reports for this review. Eleven manuscripts from nine registries were determined eligible and included in the study. Registries have reported on some core variables, but are inconsistent in reporting less practiced predicting variables. Variables that may affect inhibitor and ITI outcomes were each divided into two categories: patient characteristics (such as age and family history) and treatment-related variables (including exposure days, treatment duration and dose). It is recommended that, in addition to exploratory hypothesis testing, a minimum set of variables should be collected and reported by registries. International collaboration and well-designed prospective registries are of major importance to advance this field in order to determine inhibitor risks and ITI outcomes and facilitate the development of new treatments.

Recombinant factor IX (BAX326) in previously treated paediatric patients with haemophilia B: a prospective clinical trial

A newly developed recombinant factor IX (BAX326(1) ) was investigated for prophylactic use in paediatric patients aged <12 years with severe (FIX level <1%) or moderately severe (FIX level 1-2%) haemophilia B. The aim of this prospective clinical trial was to assess the safety, haemostatic efficacy and pharmacokinetic profile of BAX326 in previously treated paediatric patients. BAX326 was administered as prophylaxis twice a week for a period of 6 months, and on demand for treatment of bleeds. Safety was assessed by the occurrence of related AEs, thrombotic events and immunologic assessments. Efficacy was evaluated by annualized bleeding rate (ABR), and by treatment response rating (excellent, good, fair, none). PK was assessed over 72 h. None of the 23 treated paediatric subjects had treatment-related SAEs or AEs. There were no thrombotic events, inhibitory or specific binding antibodies against FIX, rFurin or CHO protein. Twenty-six bleeds (19 non-joint vs. 7 joint bleeds) occurred (mean ABR 2.7 ± 3.14, median 2.0), of which 23 were injury-related. Twenty subjects (87%) did not experience any bleeds of spontaneous aetiology. Haemostatic efficacy of BAX326 was excellent or good for >96% of bleeds (100% of minor, 88.9% of moderate and 100% of major bleeds); the majority (88.5%) resolved after 1-2 infusions. Longer T1/2 and lower IR were observed in younger children (<6 years) compared to those aged 6 to 12 years. BAX326 administered as prophylactic treatment as well as for controlling bleeds is efficacious and safe in paediatric patients aged <12 years with haemophilia B.

Toward optimal therapy for inhibitors in hemophilia

Treatment of patients with hemophilia A and B has undergone significant advances during the past 2 decades. However, despite these advances, the development of antibodies that inhibit the function of infused clotting factor remains a major challenge and is considered the most significant complication of hemophilia treatment. This chapter reviews current tools available for the care of patients with inhibitors and highlights areas where progress is imminent or strongly needed. For management of bleeding, bypassing agents remain the mainstay of therapy. Recombinant factor VIIa and activated prothrombin complex concentrates are similarly effective in populations of patients with hemophilia and inhibitors; however, individuals may show a better response to one agent over another. Recent studies have shown that prophylaxis with bypassing agents can reduce bleeding episodes by ∼50%-80%. The prophylactic use of bypassing agents is an important tool to reduce morbidity in patients before they undergo immune tolerance induction (ITI) and in those with persistent high titer inhibitors, but cost and lack of convenience remain barriers. Because of the significant burden that inhibitors add to the individual patient and the health care system, inhibitor eradication should be pursued in as many patients as possible. ITI is an effective tool, particularly in patients with severe hemophilia A and good risk profiles, and leads to a return to a normal factor VIII response in ∼60% of patients. However, for the group of patients who fail to respond to ITI or have hemophilia B, new and improved tools are needed.

Toward optimal therapy for inhibitors in hemophilia

Treatment of patients with hemophilia A and B has undergone significant advances during the past 2 decades. However, despite these advances, the development of antibodies that inhibit the function of infused clotting factor remains a major challenge and is considered the most significant complication of hemophilia treatment. This chapter reviews current tools available for the care of patients with inhibitors and highlights areas where progress is imminent or strongly needed. For management of bleeding, bypassing agents remain the mainstay of therapy. Recombinant factor VIIa and activated prothrombin complex concentrates are similarly effective in populations of patients with hemophilia and inhibitors; however, individuals may show a better response to one agent over another. Recent studies have shown that prophylaxis with bypassing agents can reduce bleeding episodes by ∼50%-80%. The prophylactic use of bypassing agents is an important tool to reduce morbidity in patients before they undergo immune tolerance induction (ITI) and in those with persistent high titer inhibitors, but cost and lack of convenience remain barriers. Because of the significant burden that inhibitors add to the individual patient and the health care system, inhibitor eradication should be pursued in as many patients as possible. ITI is an effective tool, particularly in patients with severe hemophilia A and good risk profiles, and leads to a return to a normal factor VIII response in ∼60% of patients. However, for the group of patients who fail to respond to ITI or have hemophilia B, new and improved tools are needed.