Immune tolerance induction with high-dose FVIII and pulsed intravenous immunoglobulin

The development of neutralizing allo-antibodies against factor VIII (FVIII) or FVIII inhibitors is a severe complication in the treatment of haemophilia A. About 25% of the children with severe haemophilia A develop FVIII inhibitors. Here we report on a boy with severe haemophilia A and intron 22 inversion of the FVIII gene who was diagnosed at ten months of age. After 16 exposure days to FVIII (81 days after initial exposure) he developed a FVIII inhibitor (maximum: 9.76 BU/ml). Therapy: We started immune tolerance induction (ITI) according to the Bonn protocol with high dose plasma derived FVIII concentrate (100 IU per kg body weight) twice daily. For additional inhibitor elimination treatment the patient received intravenous immunoglobulin (ivIg) at a dose of 1-2 g/kg body weight every 4 to 6 weeks. After start of treatment a rapid decline of the inhibitor level was observed, nevertheless low FVIII inhibitor levels persisted (<5 BU/ml). Furthermore, the FVIII half-life was still accelerated. However, after every course of ivIg the inhibitor level declined and FVIII half-life was prolonged. Currently, the FVIII half-life is approaching normal values after more than seven months of ITI duration. Conclusion: Additional application of immunoglobulin is beneficial for immune tolerance induction.     

Rituximab in the treatment of acquired haemophilia A in a patient with polymyalgia rheumatica

Acquired hemophilia A is a rare but potentially life-threatening bleeding disorder. It is caused by the development of autoantibodies directed against coagulation factor VIII in adults or elderly patients, who do not have a personal or family history of bleeding. Case: A man (age: 76 years) on prednisone and leflunomide for polymyalgia rheumatica developed spontaneous severe haematomas. The patient was diagnosed with acquired factor VIII deficiency (FVIII activity 1.2%, FVIII inhibitor 31.7 BU). Due to the active bleeding diathesis, treatment was administered with activated prothrombin complex concentrates (FEIBA®, Baxter). Immunosuppressive treatment with a combination of oral prednisone (1 mg/kg daily) and cyclophosphamide (1,5 mg/kg daily) was administered to reduce the FVIII inhibitor. However, after two weeks of treatment, FVIII was only 3% and no clinical improvement was observed. Treatment with the anti CD20 monoclonal antibody rituximab intravenously at 375 mg/m2 once weekly for four consecutive weeks was started. The patient showed rapid clinical improvement following rituximab treatment. He achieved a complete remission defined as return to normal FVIII activity and undetectable FVIII inhibitor titer. After a follow-up of six months no relapse occurred. Conclusion: Rituximab appears an effective and well-tolerated treatment for patients with acquired haemophilia.     

Can B‐domain deletion alter the immunogenicity of recombinant factor VIII? A meta‐analysis of prospective clinical studies

See also Iorio A, Marcucci M, Makris M. Concentrate‐related inhibitor risk: is a difference always real? This issue, pp 2176–9. Summary. Background: As a result of the infrequency of inhibitors in previously treated patients (PTPs) with hemophilia A and the small size of available clinical studies, the immunogenicity of factor (F)VIII products has been difficult to assess. Objectives: A meta‐analysis of prospective clinical studies was conducted to test the hypothesis that de novo inhibitor incidence differs between PTPs receiving full‐length recombinant FVIII (FL‐rFVIII) and B‐domain deleted recombinant FVIII (BDD‐rFVIII). Methods: Prospective studies with data on inhibitors in PTPs receiving FL‐rFVIII or BDD‐rFVIII were sought using systematic methods including bibliographic database searches. Data were secured from published study reports and inquiries to investigators. Between‐group differences in inhibitor incidence rates were evaluated using mixed effects Cox regression. Results: Twenty‐nine studies with 3012 total PTPs were included. Patients were at risk of de novo inhibitor development for a median of 79 exposure days. A total of 35 de novo inhibitors were observed. The cumulative hazard for all de novo inhibitors was 1.25% with a 95% confidence interval (CI) of 0.63–1.88%. The corresponding rate for high‐titer de novo inhibitors [> 5 Bethesda units (BU)] was 0.29% (CI, 0.01–0.57%). Exposure to BDD‐rFVIII was associated with an increased risk of all de novo inhibitors (hazard ratio, 7.26; CI, 2.12–24.9; P = 0.0016) and of high‐titer de novo inhibitors (hazard ratio, 10.8; CI, 2.17–53.7; P = 0.0037), compared with FL‐rFVIII. Conclusions: This meta‐analysis of prospective clinical studies suggests that recombinant FVIII products may differ in immunogenicity.     

Human recombinant DNA-derived antihemophilic factor in the treatment of previously untreated patients with hemophilia A: final report on a hallmark clinical investigation.

BACKGROUND: Development of recombinant factor VIII (rFVIII) replacement therapy represents a milestone in the treatment of hemophilia A. OBJECTIVE: The objective of this long-term, multicenter study was to assess the safety, efficacy and rate of inhibitor formation of rFVIII (Kogenate) in the treatment of hemophilia A in a group of previously untreated patients (PUPs). PATIENTS AND METHODS: Between January 1989 and October 1997, 102 evaluable patients (mean age 3.9 years) were treated with rFVIII as sole therapy for prophylaxis against bleeding or for hemorrhage. Patients with mild hemophilia were treated for > or =2 years, while those with moderate or severe hemophilia were treated for > or =5 years or 100 exposure days. RESULTS: All patients responded well to therapy, so that 82% of bleeding episodes required a single infusion for treatment. Only four mild drug-related adverse events were recorded during the study for an overall rate of 0.03% (4/13 464 infusions). No viral seroconversions were observed. The inhibitor incidence in PUPs with severe hemophilia was 29% (19/65). Overall, inhibitory antibodies developed in 21 patients (20.6%). Inhibitor titers were low (<10 Bethesda Units) in nine of the 21 patients despite continued episodic treatment with rFVIII and transient in eight patients receiving episodic treatment (seven low titer, one high titer). Eight high-titer inhibitor patients were treated with immune-tolerance induction therapy; five had successful outcomes. CONCLUSIONS: The observed incidence of inhibitor formation is similar to studies of PUPs receiving plasma-derived FVIII. These results demonstrate the safety and efficacy of rFVIII in long-term treatment of hemophilia A.     

大疱性类天疱疮并获得性血友病A患者血浆IgG亚型及FⅧ结合表位鉴定

目的确定1例大疱性类天疱疮并获得性血友病 A 患者的临床和实验室诊断;通过体内外干预实验观察获得性血友病 A 患者体内的 FⅧ抑制物对正常人血浆及兔 FⅧ凝血活性(FⅧ:C)的影响;确定患者 FⅧ抑制物的 TgG 亚型和结构表位,以揭示该病发病的分子机制。方法用Ⅰ期法测定患者血浆 FⅧ:C;以 Bethesda 单位(BU)表示 FⅧ:C 抑制物滴度;用蛋白 A-琼脂糖柱纯化患者及正常人血浆 IgG;用活化部分凝血活酶时间(APTT)分析其对 FⅧ:C 的抑制作用;观察 FⅧ抑制物对兔血浆 FⅧ:C 活性的抑制作用;分别用抗 IgG_1、IgG_2、IgG_3、IgG_4抗体作 Western blot,结合灰度扫描确定患者血浆 IgG 亚型相对表达量;散射比浊法测定患者及正常人体内各 IgG 亚型浓度;用 FⅧ/FⅧ抑制物固相结合试验及 Western blot 鉴定患者 IgG 抗体(FⅧ抑制物)作用于 FⅧ的具体“表位”。结果①患者 APTT 明显延长,正常血浆不能纠正;FⅧ:C<1.5%,FⅧ抑制物滴度为147.8 BU;②纯化的患者 IgG 以剂量依赖方式抑制正常人混合血浆 FⅧ:C;动物实验显示患者血浆能以时间依赖方式延长兔血浆 APTT;③Western blot 结果显示 FⅧ抑制物成分主要为 IgG_4,其次为 IgG_1,FⅧ抑制物作用于FⅧ:C 的结构相对分子质量为44×10~3。散射比浊法测定结果显示患者体内 IgG_4、IgG_1含量明显高于正常人。结论研究结果证明大疱性类天疱疮并获得性血友病 A 患者体内 FⅧ抑制物对 FⅧ:C有抑制作用,FⅧ抑制物的 IgG 亚型主要为 IgG_4,其次为 IgG_1;患者 FⅧ抑制物作用于 FⅧ的表位为相对分子质量为44×10~3的肽段,揭示了该获得性血友病 A 发生、发展的分子机制。     

Intensive exposure to factor VIII is a risk factor for inhibitor development in mild hemophilia A

Summary.  Background : Inhibitors are rare in boys with mild hemophilia A (MHA; factor (F)VIII:C > 5%) but may arise following intense FVIII exposure, e.g. continuous infusion (CI). Objectives : To determine the impact of intense FVIII exposure in inhibitor formation in MHA at our institution and to compare this with previous reports. Patients and methods : We reviewed FVIII exposure and inhibitor development in boys (ages 0–18 years) with MHA followed at our institution from 1996 to 2001 and conducted a Medline search (1966–2002) on the experience of inhibitor development following intensive/CI exposure to FVIII. Results : We identified 54 boys with MHA. Twenty-nine (54%) had been exposed to FVIII. Seven had received FVIII by CI. Four developed inhibitors; three high titer (at ages 10 years, 16 years and 17 years) and one low titer (at 1 month old). All four had received a CI of recombinant (r) FVIII of at least 6 days within 6 weeks of developing inhibitors. Baseline FVIII levels fell to < 1% in all cases and the three with high-titer inhibitors developed severe bleeding. Immune tolerance therapy (ITT) was attempted in two boys and was successful in one. Our literature search identified 35 cases (only four children) with MHA developing inhibitors following intense FVIII exposure often in the context of surgery. Conclusions : The incidence of inhibitors in our MHA population was 7.4%. If expressed according to exposure the incidence was significantly higher: 14% (4/29) for any exposure to FVIII and 57% (4/7) for exposure by CI. A prospective study to address whether CI is associated with an increased incidence of inhibitor development in MHA is warranted.     

Rate of inhibitor development in previously untreated hemophilia A patients treated with plasma‐derived or recombinant factor VIII concentrates: a systematic review

Summary. Background: Different rates of inhibitor development after either plasma‐derived (pdFVIII) or recombinant (rFVIII) FVIII have been suggested. However, conflicting results are reported in the literature. Objectives: To systematically review the incidence rates of inhibitor development in previously untreated patients (PUPs) with hemophilia A treated with either pdFVIII or rFVIII and to explore the influence of both study and patient characteristics. Methods: Summary incidence rates (95% confidence interval) from all included studies for both pdFVIII and rFVIII results were recalculated and pooled. Sensitivity analysis was used to investigate the effect of study design, severity of disease and inhibitor characteristics. Meta‐regression and analysis‐of‐variance were used to investigate the effect of covariates (testing frequency, follow‐up duration and intensity of treatment). Results: Two thousand and ninety‐four patients (1167 treated with pdFVIII, 927 with rFVIII; median age, 9.6 months) from 24 studies were investigated and 420 patients were observed to develop inhibitors. Pooled incidence rate was 14.3% (10.4–19.4) for pdFVIII and 27.4% (23.6–31.5) for rFVIII; high responding inhibitor incidence rate was 9.3% (6.2–13.7) for pdFVIII and 17.4% (14.2–21.2) for rFVIII. In the multi‐way anova study design, study period, testing frequency and median follow‐up explained most of the variability, while the source of concentrate lost statistical significance. It was not possible to analyse the effect of intensity of treatment or trigger events such as surgery, and to completely exclude multiple reports of the same patient or changes of concentrate. Conclusions: These findings underscore the need for randomized controlled trials to address whether or not the risk of inhibitor in PUPs with hemophilia A differs between rFVIII and pdFVIII.     

Mild hemophilia A

Summary. Mild hemophilia A (HA), defined by clinical features and factor VIII coagulant activity (FVIII:C) between 0.05 and 0.40 IU mL^?1, is characteristically distinct from severe HA. Indeed, although the molecular characterization of mild HA has permitted the identification of specific underlying mutations, its clinical phenotype is strikingly different from that of patients with a severe FVIII defect, where spontaneous hemorrhages or recurrent joint bleeding are usual manifestations. With aging, mild HA patients may develop complications (i.e. cancers and cardiovascular disorders), the management of which may prove challenging due to the concomitant bleeding tendency. Furthermore, the development of inhibitors provides an additional major complication in these patients, because it increases the severity of the bleeding phenotype and complicates their management. Standard management of mild HA includes the use of desmopressin and antifibrinolytic agents for minor bleeding episodes or surgical procedures, whilst major bleeding or surgery requires replacement therapy with FVIII concentrates. As regards treatment of patients with inhibitors, bypassing agents (i.e. activated prothrombin complex concentrates and recombinant activated FVII) have proven effective in the treatment of bleeding episodes, but as there are insufficient data to determine the optimal approach to immune tolerance induction in this group of patients, their optimal management remains controversial. Rituximab is a newer, promising therapeutic option for inhibitor eradication in such patients. Many aspects concerning mild HA remain to be clarified, including the molecular basis, the natural history and the optimal diagnostic and therapeutic strategies. Only large prospective studies will shed light on this condition.     

Neutralization of antifactor VIII inhibitors by recombinant porcine factor VIII

BACKGROUND: Inhibitory antibodies to factor (F) VIII (FVIII inhibitors) present a major clinical challenge as a complication of hemophilia A and as acquired autoantibodies in non-hemophiliacs. Porcine FVIII is a potentially useful therapeutic agent because of its low crossreactivity with many inhibitors. Recombinant porcine FVIII (rpFVIII) is undergoing clinical trials in inhibitor patients. OBJECTIVES: The goals of this study were to neutralize human FVIII inhibitors in vitro with rpFVIII and to characterize the relationship between recovery of FVIII activity and the antiporcine FVIII inhibitor titer. METHODS: rpFVIII was added to 28 antihuman FVIII inhibitor plasmas and assayed either immediately or after a 2 h preincubation at 37 degrees C. The concentration of rpFVIII required for recovery of FVIII activity to 50% of normal (EC(50)) was determined by polynomial regression analysis and compared with the antiporcine FVIII inhibitor titer measured by Bethesda assay. RESULTS: Six of nine plasmas classified as non-crossreactive by Bethesda assay had detectable inhibitory activity in the FVIII recovery assay. Recovery was decreased following a 2 h preincubation compared with immediate assay for the 19 plasmas with detectable antiporcine FVIII inhibitors. There was a linear relationship between EC(50) and inhibitor titer for plasmas with antiporcine FVIII titers ranging from 0.6 to 10 BU per milliliter in both the immediate and the 2 h preincubation assays. CONCLUSION: A quantitative method for analysis of inhibitor neutralization in vitro has been developed, which may be useful for comparison with pharmacodynamic studies of rpFVIII in FVIII inhibitor patients and subsequent rational dosing in this patient population.     

The tipping point: The critical role of therapeutic apheresis in a case of refractory acquired hemophilia

Acquired hemophilia A (AHA) is a rare autoimmune disorder that leads to factor VIII (FVIII) deficiency via autoantibody formation. Standard treatment options include FVIII bypassing factors and immunosuppression. However, the role of therapeutic plasma exchange (TPE) is not clear in the treatment of AHA. We present a case of idiopathic AHA in a 66 year old female with severe bleeding and a FVIII inhibitor of 17.6 Bethesda units (BU). She failed to respond to standard treatment including maximum dose of recombinant FVIIa (rFVIIa), rituximab, and other immunosuppressive agents. Her FVIII inhibitor rapidly increased to 140 BU and FVIII was below 5%. TPE was initiated 3 weeks after admission and her bleeding stabilized after the first treatment and completely stopped after three treatments. Repeat testing revealed increased FVIII to 15% and FVIII inhibitor decreased to 2.0 BU. After an additional TPE treatment, her FVIII increased to 27% and FVIII inhibitor decreased to 0.6 BU and she was discharged without bleeding 40 days after admission. In this case, TPE played a critical role in reducing FVIII inhibitor, which resulted in a recovery of FVIII activity and hemostasis. Therefore, TPE should be initiated early in AHA patients with bleeding and high titer of FVIII inhibitor.     

B cell–activating factor modulates the factor VIII immune response in hemophilia A

Inhibitors of factor VIII (FVIII) remain the most challenging complication of FVIII protein replacement therapy in hemophilia A (HA). Understanding the mechanisms that guide FVIII-specific B cell development could help identify therapeutic targets. The B cell–activating factor (BAFF) cytokine family is a key regulator of B cell differentiation in normal homeostasis and immune disorders. Thus, we used patient samples and mouse models to investigate the potential role of BAFF in modulating FVIII inhibitors. BAFF levels were elevated in pediatric and adult HA inhibitor patients and decreased to levels similar to those of noninhibitor controls after successful immune tolerance induction (ITI). Moreover, elevations in BAFF levels were seen in patients who failed to achieve FVIII tolerance with anti-CD20 antibody–mediated B cell depletion. In naive HA mice, prophylactic anti-BAFF antibody therapy prior to FVIII immunization prevented inhibitor formation and this tolerance was maintained despite FVIII exposure after immune reconstitution. In preimmunized HA mice, combination therapy with anti-CD20 and anti-BAFF antibodies dramatically reduced FVIII inhibitors via inhibition of FVIII-specific plasma cells. Our data suggest that BAFF may regulate the generation and maintenance of FVIII inhibitors and/or anti-FVIII B cells. Finally, anti-CD20/anti-BAFF combination therapy may be clinically useful for ITI.     

Routine measurements of factor VIII activity and inhibitor titer in the presence of emicizumab utilizing anti‐idiotype monoclonal antibodies

Essentials

• Emicizumab (Emi) affects the APTT‐based assays of factor (F)VIII activity and inhibitor titer.
• A mixture of two anti‐Emi monoclonal antibodies (mAb) effectively neutralized the Emi activity.
• Anti‐Emi mAbs completely eliminated the influence of Emi on FVIII activity and inhibitor titer.
• The inclusion of anti‐Emi mAbs in routine FVIII assays would be useful for Emi‐treated patients.

Summary

Background

Emicizumab is an anti‐factor (F)IXa/X bispecific monoclonal antibody (mAb), mimicking the factor (F)VIIIa cofactor activity. Emicizumab does not require activation by thrombin and its shortening effect on the activated partial prothrombin time (APTT) is more pronounced than that of factor (F)VIII. APTT‐based FVIII activity (FVIII:C) and FVIII inhibiter titer measurements are influenced by the presence of emicizumab.

Aim

To establish a reliable APTT‐based assay to measure FVIII in the presence of emicizumab.

Methods

Plasmas from hemophilia A (HA) patients without or with inhibitors were studied using one‐stage FVIII:C and Bethesda inhibitor assays. Two recombinant anti‐idiotype mAbs to emicizumab (anti‐emicizumab mAbs) were prepared, rcAQ8 to anti‐FIXa‐Fab and rcAJ540 to anti‐FX‐Fab.

Results

The combined anti‐idiotype mAbs (2000 nm each) eliminated the effects of emicizumab on APTTs of HA plasmas without or with inhibitor by competitive inhibition of antibody binding to FIX(a)/FX(a). Measurements of FVIII coagulation activity in HA plasmas without inhibitor were overestimated in the presence of emicizumab (1 μm = ~150 μg mL^?1) at all reference levels of FVIII. The addition of anti‐emicizumab mAbs to the assay mixtures completely neutralized the emicizumab and facilitated accurate determination of FVIII:C. Anti‐FVIII inhibitor titers were undetectable in the presence of emicizumab in HA plasmas with inhibitor or normal plasmas mixed with anti‐FVIII neutralizing antibodies. These effects of emicizumab were completely counteracted by the addition of the anti‐idiotype mAbs, allowing accurate assessment of inhibitor titers.

Conclusion

The in vitro inclusion of anti‐emicizumab mAbs in the standard one‐stage coagulation assays prevented interference by emicizumab and enabled accurate measurements of FVIII:C and inhibitor titers.

     

Generation and characterization of human hematopoietic cell lines expressing factor VIII

Considering the plasticity of hematopoietic stem cells (HSC), they would be ideal targets for gene therapy of hemophilia A by virtue of their progeny providing immediate access to the bloodstream. However, several attempts to show expression of recombinant factor VIII (rFVIII) by primary hematopoietic cells and cell lines have failed; this failure was attributed to the inability of HSC to secrete rFVIII. Here we describe the generation of stable, FVIII-secreting hematopoietic cell lines representing different blood-cell types using a bicistronic lentiviral vector encoding for a B-domain-deleted FVIII (FVIII Delta B) and enhanced green fluorescence protein (EGFP). Transduced cell lines with erythroid and/or megakaryocytic background, (K562-F8 and TF-1-F8) secrete high levels of FVIII in the order of 76.4 and 41.6 ng FVIII:C/ml, whereas moderate and low levels are observed in B lymphoblastoid Raji-F8 cells and the T leukemia line Jurkat-F8 which secrete 6.73 and 1.83 ng FVIII:C/ml, respectively. The capacity to secrete rFVIII appeared to depend on factors related to the cell lineage rather than on the transduction efficacy. Stimulation of transduced cells with the protein kinase C (PKC)-activator phorbol myristate acetate (PMA) resulted in a marked augmentation of rFVIII secretion and enhanced green fluorescent protein (EGFP). Incubation with 0.1 and 1 ng/ml PMA resulted in up to 2.7-fold (K562-F8, Raji-F8) and 1.8-fold (293T-F8) increased rFVIII secretion. The established cell lines should be helpful in further elucidating mechanisms that are able to improve FVIII secretion in hematopoietic cells on a post-translational level and suggest reanalysis of hematopoietic cells as target for gene therapy of hemophilia.     

Efficacy and safety of secondary prophylactic vs. on-demand sucrose-formulated recombinant factor VIII treatment in adults with severe hemophilia A: results from a 13-month crossover study

Summary. Background: Hemarthroses in severe hemophilia precipitate physical, psychosocial and financial difficulties. Objective: To compare the effects of secondary prophylaxis with on‐demand sucrose‐formulated recombinant factor VIII (rFVIII‐FS) therapy in severe hemophilia A. Patients and methods: This open‐label study included patients aged 30–45 years with factor VIII (FVIII) coagulant activity < 1 IU dL^?1 who were using on‐demand FVIII treatment. Patients were treated with rFVIII‐FS on demand for 6 months, followed by 7 months prophylaxis (20–40 IU kg^?1, three times per week, with the first month considered a run‐in). The primary endpoint was the number of hemarthroses. Results: Twenty patients were enrolled (n = 19 completed); the mean age was 36.4 years, and 16 had target joints. The median (25–75%) number of joint bleeds decreased significantly with prophylaxis [0 (0–3)] vs. on‐demand [15 (11–26); P < 0.001] therapy. The number of all bleeds was 0 (0–3) vs. 20.5 (14–37; P < 0.001), respectively. Median (range) total Gilbert scores improved after prophylaxis [18 (3–39)] compared with on‐demand [25 (4–46)] therapy, predominantly reflecting the improved bleeding score. Median time from last prophylactic infusion to bleed was 2 days; 82.5% of bleeds occurred 2–3 days after the last infusion. Median 48‐h and 72‐h FVIII trough levels measured during months 10 and 13 were consistently > 6 and > 4 IU dL^?1, respectively. Treatment was well tolerated, and no inhibitor formation was observed. Conclusion: Secondary prophylaxis with rFVIII‐FS significantly reduced the frequency of hemarthroses compared with on‐demand therapy in adult patients with severe hemophilia A.     

Lonoctocog alfa (rVIII-SingleChain) for the treatment of haemophilia A

Introduction: The administration of factor VIII (FVIII) concentrates on-demand or on long-term prophylaxis is the effective and safe standard of care of patients with hemophilia A (HA). Development of neutralizing antibodies against exogenous FVIII and the short half-life of the current available products remain major challenges. There is currently a great interest towards newer FVIII products with the goal of reducing the inhibitor risk and increasing the half-life.

Area covered: In this review, the authors describe the efficacy and safety of rVIII-SingleChain (Lonoctocog alfa), the first and only single chain recombinant FVIII (rFVIII) molecule developed for the prevention and treatment of bleeding episodes in HA patients. The pre-clinical and clinical studies of rVIII-SingleChain as well as the results of the AFFINITY trial program in previously treated patients both adults and pediatric are presented and discussed.

Expert opinion: The results from PTP studies document the efficacy and safety profile of the rVIII-SingleChain. However, even if rFVIII-SingleChain presents advantageous pharmacokinetic features compared to conventional rFVIII, it should not be considered as an EHL-FVIII while its immunogenicity is currently being studied in PUPs. The slightly better PK profile of rFVIII-SingleChain could however allow a small number of selected patients to be treated with a less intensive regimen.     

In non‐severe hemophilia A the risk of inhibitor after intensive factor treatment is greater in older patients: a case–control study

Summary. Background: Twenty‐five percent of new anti‐factor VIII (FVIII) antibodies (inhibitors) that complicate hemophilia A occur in those with mild and moderate disease. Although intensive FVIII treatment has long been considered a risk factor for inhibitor development in those with non‐severe disease, its strength of association and the influence of other factors have remained undefined. Objective: To evaluate risk factors for inhibitor development in patients with non‐severe hemophilia A. Methods: Information on clinical and demographic variables and FVIII genotype was collected on 36 subjects with mild or moderate hemophilia A and an inhibitor and 62 controls also with mild or moderate hemophilia A but without an inhibitor. Results: Treatment with FVIII for six or more consecutive days during the prior year was more strongly associated with inhibitor development in those ≥ 30 years of age compared with those < 30 years of age [adjusted odds ratio (OR) 12.62; 95% confidence interval (CI), 2.76–57.81 vs. OR 2.54; 95% CI, 0.61–10.68]. Having previously received < 50 days of FVIII was also not statistically associated with inhibitor development on univariate or multivariate analysis. Conclusions: These findings suggest that inhibitor development in mild and moderate hemophilia A varies with age, but does not vary significantly with lifetime FVIII exposure days: two features distinct from severe hemophilia A.     

Inhibitor development in two patients with mild haemophilia A – spontaneous disappearance and no recurrence of the inhibitor after re-challenge

Inhibitors against factor VIII (FVIII) complicate the treatment of patients with haemophilia. In mild haemophilia, the development of antibodies against FVIII is rare. However, the occurrence of an inhibitor in mild haemophilia changes the bleeding phenotype from mild to severe, and thus becomes a major clinical problem. We report on two patients with mild haemophilia A (FVIII level 8 and 27%, respectively), who have a missense mutation in exon 16 (G to A transition in codon 1773) and exon 22 (T to C transition in codon 2096), respectively. Both mutations have not been described in the Haemophilia A Mutation, Structure Test and Resource Site. Our patients developed high titer inhibitors following an intensive FVIII replacement therapy due to a muscle bleeding and after a polytrauma. During the presence of the inhibitor, AICC or FVIIa was successfully used as bypassing agent. In both patients the inhibitor disappeared spontaneously. Years after the development of the inhibitor, the patients again received FVIII concentrates. Reappearance of the inhibitor was not observed in either patient. The reported cases indicate that inhibitors in patients with mild haemophilia might be transient and disappear spontaneously. Therefore, the necessity of immune tolerance therapy, which is costly and strenuous for the patients, should be critically examined for each individual patient and a watch and wait strategy might be advisable.     

The promise and challenges of bioengineered recombinant clotting factors

The past 10 years of clinical experience have demonstrated the safety and efficacy of recombinant clotting factors. With the adoption of prophylactic strategies, there has been considerable progress in avoiding the complications of hemophilia. Now, insights from our understanding of clotting factor structure and function, mechanisms of hemophilia and inhibitors, gene therapy advances and a worldwide demand for clotting factor concentrates leave us on the brink of embracing targeted bioengineering strategies to further improve hemophilia therapeutics. The ability to bioengineer recombinant clotting factors with improved function holds promise to overcome some of the limitations in current treatment, the high costs of therapy and increase availability to a broader world hemophilia population. Most research has been directed at overcoming the inherent limitations of rFVIII expression and the inhibitor response. This includes techniques to improve rFVIII biosynthesis and secretion, functional activity, half-life and antigenicity/immunogenicity. Some of these proteins have already reached commercialization and have been utilized in gene therapy strategies, while others are being evaluated in pre-clinical studies. These novel proteins partnered with advances in gene transfer vector design and delivery may ultimately achieve persistent expression of FVIII leading to an effective long-term treatment strategy for hemophilia A. In addition, these novel FVIII proteins could be partnered with new advances in alternative recombinant protein production in transgenic animals yielding an affordable, more abundant supply of rFVIII. Novel rFIX proteins are being considered for gene therapy strategies whereas novel rVIIa proteins are being evaluated to improve the potency and extend their plasma half-life. This review will summarize the status of current recombinant clotting factors and the development and challenges of recombinant clotting factors bioengineered for improved function.     

OBI-1, porcine recombinant Factor VIII for the potential treatment of patients with congenital hemophilia A and alloantibodies against human Factor VIII

Hemophilia A is caused by a deficiency in blood coagulation Factor (F)VIII. Treatment for acute bleeding in patients comprises prophylactic infusion with human plasma-derived (pd) or recombinant (r)FVIII to increase circulating FVIII levels. However, alloantibodies (inhibitor) may arise in patients, limiting the efficacy of replacement therapy, especially in patients who develop high-titer inhibitors. For these patients, FVIII-bypassing agents are proposed, but there is a rare risk of thrombotic events. Porcine pdFVIII successfully achieves hemostatic FVIII levels in patients in whom human FVIII was ineffective, but possible residual viral contamination and immunogenicity prevents routine use. OBI-1, being developed by Ipsen and Inspiration Biopharmaceuticals Inc, is a bioengineered form of porcine rFVIII that is highly purified. OBI-1 has the procoagulant and biochemical properties of porcine pdFVIII, with improvements in risk of toxicity, infection and ease of manufacture. OBI-1 demonstrated significantly less immunogenicity than pdFVIII in a murine model of hemophilia A. Moreover, in cynomolgus monkeys, OBI-1 did not generate detectable inhibitors. OBI-1 was effective in a phase II, open-label clinical trial in patients with hemophilia A and inhibitor against porcine FVIII, who were experiencing a non-life or -limb threatening bleed. OBI-1 was well tolerated, without drug-related serious adverse events and is promising for further studies.