Clinical evaluation of recombinant human factor VIII (BAY w 6240) in the treatment of hemophilia A.

A pilot clinical trial was conducted in five patients with severe hemophilia A to evaluate the safety and efficacy of a recombinant human factor VIII preparation, BAY w 6240 (rFVIII). In a comparative pharmacokinetic study of rFVIII and a plasma-derived factor VIII preparation (pdFVIII), the mean t1/2 values for rFVIII at week 1 and week 13 were 16.8 and 14.4 h, while this value for pdFVIII at week -2 was 16.9 h. There were no statistical differences between these values. The mean in vivo recovery rates of rFVIII were comparable to those of pdFVIII. When rFVIII was administered prophylactically three times a week for 4 weeks, no bleeding episodes were observed. Seventy-four bleeding episodes were assessed during the 6-month treatment period. The efficacy rate of the hemostatic effect was confirmed to be 95.9%. No adverse reactions attributable to rFVIII were observed in a total of 178 infusions. Neither FVIII-inhibitors nor antibodies to foreign proteins were detected. Vital signs and laboratory findings showed no significant changes attributable to rFVIII. These results suggest that rFVIII is safe and efficacious as replacement therapy for hemophilia A.     

Allergic reaction in a cohort of haemophilia A patients using plasma‐derived factor VIII (FVIII) concentrate is rare and not necessarily triggered by FVIII

In contrast to haemophilia B, allergic manifestations are rare complications in haemophilia A (HA) patients treated with factor VIII (FVIII) concentrates. Nevertheless, it can be serious and hamper replacement therapy in these cases. The aims of this study were to evaluate the frequency of allergic reaction in a cohort of HA patients treated only with plasma‐derived FVIII (pdFVIII) concentrates, and assess the possible immune mechanisms involved. History of allergic reaction was retrospectively assessed. Patients with allergic manifestations were followed, and had plasma samples collected in different timepoints in relation to the allergic episode. These samples were analysed for the presence of inhibitor and anti‐FVIII immunoglobulins subclasses. Three of 322 HA patients (0.9%) developed allergic reaction after exposure to pdFVIII products during the last 15 years in our centre. The first patient, with severe HA, without inhibitor, had anti‐pdFVIII IgE and IgG4, but no anti‐recombinant FVIII (rFVIII) IgE. The second patient, with severe HA, and high‐responding inhibitor, presented allergic manifestation with both, pdFVIII concentrate and activated prothrombin complex concentrate. Although anti‐pdFVIII and anti‐rFVIII IgG4 were detected, no anti‐FVIII IgE was present. The third patient, with moderate HA without inhibitor, atopic, had no anti‐FVIII immunoglobulin detected, and allergic symptoms disappeared after switching to rFVIII concentrate. This study corroborates the low incidence of allergic reactions in HA patients. In the three cases presented, the anti‐FVIII immunoglobulin profile demonstrated that the allergic manifestation was triggered by other proteins contained in pdFVIII products, and not directed to FVIII.     

Kinetics of the interaction between anti‐FVIII antibodies and FVIII from therapeutic concentrates,with and without von Willebrand factor,assessed by surface plasmon resonance

The presence of VWF in plasma‐derived FVIII (pdFVIII/VWF) products has been pointed out as a key difference with recombinant FVIII (rFVIII) products with regard to immunogenicity. A Surface Plasmon Resonance (SPR) study was designed to characterize in detail the interaction between anti‐FVIII (IgGs) from a severe haemophilia A patient, and FVIII from concentrates of different sources. Full‐length rFVIII (preincubated or not with purified VWF), B domain‐deleted (BDD)‐rFVIII and pdFVIII/VWF were analysed. To ensure reproducible conditions for accurate determination of kinetic constants, a capture‐based assay format was developed using protein G surfaces for specific and reversible coupling of endogenous anti‐FVIII antibodies. Concentration ranges (nm ) of FVIII products tested were 9–0.03 (rFVIII) and 6–0.024 (pdFVIII/VWF). The association with antibodies was monitored for 3–5 min, whereas dissociation of the complex was followed for 5–20–240 min. A strong interaction of rFVIII and BDD‐rFVIII with patient's IgG was detected with the K _D values in the low picomolar range (5.9 ± 3.0 and 12.7 ± 6.9 pm , respectively) and very slow dissociation rates, while pdFVIII/VWF showed only marginal binding signals. The VWF complexed rFVIII displayed reduced binding signals compared with uncomplexed rFVIII, but the K _D was still in the picomolar range (4.1 ± 1.9 pm ) indicating insufficient complex formation. rFVIII, alone or bound to exogenously added VWF, showed high affinity for anti‐FVIII IgGs from a severe haemophilia A patient whereas pdFVIII/VWF did not. These results are in agreement with those studies that point towards rFVIII concentrates to be more immunogenic than pdFVIII concentrates.     

Successful induction of immune tolerance by continuous infusion of recombinant factor VIII in a haemophilia A patient with high-inhibitor titres

The successful and persistent abolition of the inhibitor is of significant clinical benefit, as it allows for the restoration of the usual treatment with clotting factor concentrate. We describe a successful induction of immune tolerance by continuous infusion of recombinant factor VIII (rFVIII) in a 5-year-old boy with severe haemophilia A and high-responding inhibitor. He had previously been subjected to immune tolerance induction (ITI) with rFVIII at 100 units (U) kg(-1) three times weekly. One year after the beginning of therapy tolerance was not achieved and a high titer of inhibitor was detected (15 Bethesda Units). The patient had a sudden onset of severe neck pain. The diagnosis of spinal epidural haematoma was revealed by magnetic resonance imaging, and emergency laminectomy with evacuation of the haematoma was required. The patient received sequential therapy for surgery first as bolus rFVIII injection of 500 U kg(-1) in order to overwhelm the inhibitor and then as continuous infusion at 6 to 12 U kg(-1) hour(-1) to avoid bleeding episodes in the postoperative period. After the 3 weeks of continuous infusion, the inhibitor became undetectable. Thereafter, prophylactic treatment with rFVIII was started three times weekly, and the inhibitor has remained undetectable for 6 months. The, present case suggests that continuous infusion of rFVIII may be an effective therapy to induce immune tolerance.     

Pharmacokinetics, coagulation factor consumption and clinical efficacy in patients being switched from full-length FVIII treatment to B-domain-deleted r-FVIII and back to full-length FVIII

Summary.  Concerns have been raised regarding pharmacokinetic performance, efficacy and safety of B-domain-deleted recombinant FVIII (BDD rFVIII). The objective of this study was to perform a retrospective survey of half-life measurements, efficacy and safety in patients with severe haemophilia A, switching treatment from full-length factor VIII (FL FVIII) to BDD rFVIII and then back to FL FVIII. We hypothesized that half-life of FVIII would be equal regardless of product and that total factor consumption and bleeding frequency would be indistinguishable. We report on inhibitor development and outcome following surgery. Patients with severe haemophilia A, exposed to BDD rFVIII were identified from a database. A retrospective analysis of laboratory data and medical notes was undertaken. No significant difference was detected between the half-life measurements during the switch from FL FVIII (T/2 median 9.15 h, range 6.4–22) to BDD rFVIII (T/2 median 9.7, range 4.7–16.8) and back to FL FVIII (T/2 median 9.0, range 5.0–19.5). There was no significant difference in coagulation factor usage (BDD rFVIII median 4803 IU kg⁻¹ year⁻¹, range 659–11 304; FL FVIII median 5349, range 1691–10 146), nor bleeds. Eleven received BDD rFVIII to cover surgical procedures, with no reports of excess bleeding. Thirty-three patients received significant exposure to BDD rFVIII and one developed a low titre inhibitor. BDD rFVIII was found to be equivalent to other FVIII products in terms of pharmacokinetics, clinical efficacy and safety in this study group.     

Prolonged effect of a new O‐glycoPEGylated FVIII (N8‐GP) in a murine saphenous vein bleeding model

Prophylaxis in severe haemophilia significantly increases health‐related quality of life for patients, but the dosing frequency still constitutes a challenge. Thus, there is a need for new treatment options, utilizing compounds with longer duration of action, while still maintaining potency. The objective of this study was to evaluate the acute and prolonged effects of a new glycoPEGylated recombinant factor VIII (rFVIII) (N8‐GP) in a venous bleeding model in haemophilia A mice and to compare the efficacy and potency to turoctocog alfa (rFVIII). Following intravenous administration of turoctocog alfa or N8‐GP to normal and FVIII‐deficient mice, bleeding time and blood loss from a saphenous vein incision were evaluated in an acute dose–response study and a duration of action study. In the acute setting, N8‐GP dose dependently reduced the number and duration of bleeding episodes as well as blood loss compared to FVIII‐deficient mice, reaching statistical significance at doses as low as 5–10 U kg^?1. In the duration of action study, a significantly prolonged and maintained effect of N8‐GP was found for up to 48 h after dosing, whereas the effect of rFVIII was no longer present for any end‐points 24 h after dosing. Seventy‐two hours after dosing, no significant effect of either compound was found. This study shows a prolonged haemostatic effect of N8‐GP compared to rFVIII supporting other recent studies that N8‐GP may hold a potential to increase the quality of life for patients with haemophilia A by reducing dosing frequency.     

Defining extended half‐life rFVIII—A critical review of the evidence

Introduction

Recent haemophilia treatment advances include new recombinant FVIII (rFVIII) products with improved pharmacokinetic (PK) properties that aim to reduce the burden of prophylaxis. These treatments are commonly referred to as extended half‐life rFVIII products (EHL rFVIII). There is no uniform definition of what constitutes an EHL rFVIII. Such a definition would help physicians, patients and funders understand the properties of standard and EHL rFVIIIs and thus provide clarity when selecting an EHL in clinical settings.

Aim

To critically assess the published evidence on new and emerging rFVIII products in order to propose a definition to classify EHL rFVIIIs.

Methods

We systematically searched PubMed, EMBASE and regulatory authorities (FDA/EMA/Health Canada) websites for publications and regulatory submissions describing prospective crossover PK studies evaluating rFVIIIs that demonstrate improved PK parameters in adults and adolescents with severe haemophilia A.

Results

Following critical analyses of the published data, we developed a holistic approach to defining rFVIIIs as EHLs, which requires all of the following: (i) using technology designed to extend rFVIII half‐life; (ii) lacking bioequivalence with a standard rFVIII comparator—above the FDA/EMA cut‐off of 125% for the 90% confidence intervals for area under the curve ratio; and (iii) having an extended half‐life ratio measured in a PK comparator crossover study.

Conclusion

In this systematic review, a pragmatic definition of EHL rFVIII has been proposed that should provide better clarity in clinical discussions surrounding the appropriate use of rFVIII products. At present, only products using PEGylation or Fc fusion half‐life extension technology meet the proposed criteria for definition of EHL rFVIII.     

Safety and prolonged activity of recombinant factor VIII Fc fusion protein in hemophilia A patients

Current factor VIII (FVIII) products display a half-life (t(1/2)) of ～ 8-12 hours, requiring frequent intravenous injections for prophylaxis and treatment of patients with hemophilia A. rFVIIIFc is a recombinant fusion protein composed of a single molecule of FVIII covalently linked to the Fc domain of human IgG(1) to extend circulating rFVIII t(1/2). This first-in-human study in previously treated subjects with severe hemophilia A investigated safety and pharmacokinetics of rFVIIIFc. Sixteen subjects received a single dose of rFVIII at 25 or 65 IU/kg followed by an equal dose of rFVIIIFc. Most adverse events were unrelated to study drug. None of the study subjects developed anti-rFVIIIFc antibodies or inhibitors. Across dose levels, compared with rFVIII, rFVIIIFc showed 1.54- to 1.70-fold longer elimination t(1/2), 1.49- to 1.56-fold lower clearance, and 1.48- to 1.56-fold higher total systemic exposure. rFVIII and rFVIIIFc had comparable dose-dependent peak plasma concentrations and recoveries. Time to 1% FVIII activity above baseline was ～ 1.53- to 1.68-fold longer than rFVIII across dose levels. Each subject showed prolonged exposure to rFVIIIFc relative to rFVIII. Thus, rFVIIIFc may offer a viable therapeutic approach to achieve prolonged hemostatic protection and less frequent dosing in patients with hemophilia A. This trial was registered at www.clinicaltrials.gov as NCT01027377.     

Validation of a quantitative SPR assay for recombinant FVIII

Surface plasmon resonance was employed to establish a quantitative assay for recombinant FVIII (rFVIII) products using rFVIII as standard. The anti-FVIII monoclonal antibody ESH4 was immobilized onto a carboxymethyldextran surface. A range of rFVIII concentrations were injected over the surface and the binding response enhanced by the addition of a further monoclonal antibody ESH8. Validation using National Institute of Biological Standards and Controls (NIBSC) sixth International rFVIII concentrate standard gave inter- and intra-assay coefficient of variations (CVs) of 7.5 and 3.68% respectively for ESH4-rFVIII binding alone. Enhancement of the binding signal by secondary addition of ESH8 produced inter- and intra-assay CVs of 2.75 and 1.5%. The ESH4 immobilized chip was found to retain binding capacity following regeneration for at least 75 cycles. The assay was found to be unsuitable for quantitation of plasma derived FVIII product but may prove useful for monitoring of rFVIII production.     

Continuous infusion of recombinant factor VIII formulated with sucrose in surgery: Non‐interventional,observational study in patients with severe haemophilia A

In haemophilia A, continuous infusion (CI) of FVIII perioperatively provides a more constant FVIII level than conventional bolus injections, avoiding low trough levels that could increase bleeding risk. Due to the low number of surgical cases in clinical trials, especially in haemophilia, more information on the clinical practice of CI from observational studies is helpful. We aimed to evaluate the effectiveness and safety of CI with recombinant factor VIII formulated with sucrose (rFVIII‐FS) in a typical surgery practice setting. This was a non‐interventional study in 12 centres. Patients with severe haemophilia A who received rFVIII‐FS by CI during and after surgery were included in this study if they had more than 150 exposure days (EDs) to any FVIII product and had no history of inhibitors before CI. Patients were observed during the entire course of CI, with monitoring up to 3 months thereafter. Twenty‐five patients with 28 surgeries were included in the analysis. Median age was 51.7 (range 10–75). Most (75%; 21/25) patients underwent orthopaedic surgeries. The median dose of rFVIII‐FS consumed during CI was 376 IU kg^?1 (range 157.9–3605.6 IU kg^?1) with a greater median dose for orthopaedic surgeries (424.0 IU kg^?1) compared to non‐orthopaedic surgeries (278.5 IU kg^?1). 95% of all FVIII measurements (214/224) were on target. Efficacy and tolerability were rated as good/excellent in 89.3% (25/28) of surgeries. No inhibitors were observed during or after surgery. This study demonstrates the effectiveness of CI with rFVIII‐FS during surgery in patients with severe haemophilia A in a clinical practice setting.     

Safety and efficacy of turoctocog alfa (NovoEight®) during surgery in patients with haemophilia A: results from the multinational guardian™ clinical trials

Recombinant factor VIII (rFVIII) products provide a safe and efficacious replacement therapy for prevention and treatment of bleeding episodes in patients with haemophilia A. The present investigations from the multinational, open‐label guardian^? clinical trials assessed the haemostatic response of turoctocog alfa (NovoEight^®), a rFVIII product, in patients with severe haemophilia A (FVIII ≤ 1%) undergoing surgery. All patients had a minimum of 50 exposure days to any FVIII product prior to surgery and no history of inhibitors. A total of 41 procedures (13 orthopaedic, 19 dental and 9 general) were performed in 33 patients aged 4–59 years. Of the 41 procedures, 15 were major surgeries in 13 patients and 26 were minor surgeries in 21 patients. The success rate for haemostatic response was 100% (success was defined as ‘excellent’ or ‘good’ haemostatic outcome). Turoctocog alfa consumption on the day of surgery ranged from 27 to 153 IU kg^?1. The mean daily dose declined over time, while retaining adequate FVIII coverage as measured by trough levels. Overall, no safety issues were identified. No thrombotic events were observed and none of the patients developed FVIII inhibitors. In conclusion, the present results show that turoctocog alfa was effective in controlling blood loss by obtaining a sufficient haemostatic response in patients with severe haemophilia A undergoing surgery.     

Potency measurement of factor VIII in recombinant concentrates

In preliminary studies on the stability of recombinant factor VIII (rFVIII) concentrates post reconstitution, a rise in potency to 200% of labelled values was observed in concentrates stored at 22 °C over 24 h. This was observed in potency estimates by the one-stage clotting, but not the two-stage clotting or chromogenic assays, and was not observed for intermediate-purity product derived from plasma (IPVIII). Use of human serum albumin (HSA), rather than the usual bovine material (BSA), to dilute product for the stability study abolished the rise in potency. Incorporating purified von Willebrand Factor (VWF) in the diluent buffer abolished the rise observed in BSA. A similar rise was observed upon incubating rFVIII in the presence of 10^?4 u of thrombin per mL in HSA buffer. Potency estimates using the HSA in the dilution buffer resulted in severe underpotency in relation to the label claim when using the two-stage clotting and the chromogenic assays, but not the one-stage clotting assay. Predilution in severe haemophilic plasma restored potency levels to those claimed. We conclude that (i) commercial preparations of BSA may be unsuitable for inclusion in buffers for rFVIII studies; (ii) FVIII in rFVIII concentrates is exquisitely sensitive to activation by thrombin, presumably as a result of the lack of VWF; (iii) accurate potency estimation in the two-stage assay systems requires VWF in the assay system.     

Development of a factor VIII inhibitor in a newborn haemophiliac

A major problem in the treatment of haemophilia A is the development of inhibitors (antibodies) against factor VIII. We report the case of a newborn male with no family history of haemophilia who developed an intracerebral haemorrhage. On day 10 post-delivery severe haemophilia A was diagnosed and treatment with recombinant FVIII (rFVIII) concentrate was started. Seventy-two hours later the presence of inhibitors was suspected because high doses of rFVIII were required to maintain therapeutic FVIII plasma levels. Days after, the inhibitor was detected. The quick detection of the inhibitor in this newborn haemophiliac allowed us to start the immunotolerance early, without interruption in the administration of rFVIII.     

Patients with severe von Willebrand disease are insensitive to the releasing effect of DDAVP: evidence that the DDAVP-induced increase in plasma factor VIII is not secondary to the increase in plasma von Willebrand factor

Summary It is generally held that factor VIII (FVIII) does not increase in the plasma of severe von Willebrand disease (vWD) patients treated with DDAVP because they lack von Willebrand factor (vWF), which is the plasma carrier for FVIII. To test this hypothesis, FVIII plasma levels were monitored in severe vWD patients treated with DDAVP after normalization of vWF plasma levels with infusions of cryoprecipitate. Each of four severe vWD patients underwent four different treatments at intervals of at least 15 d: (1) cryoprecipitate plus DDAVP; (2) cryoprecipitate plus saline; (3) cryoprecipitate plus recombinant FVIII (rFVIII); (4) saline plus rFVIII. Cryoprecipitate increased the plasma levels of FVIII and vWF. The infusions of saline or DDAVP after cryoprecipitate did not further increase FVIII and vWF plasma levels and had no effect on the plasma levels of tissue plasminogen activator (tPA), which are raised by DDAVP in normal subjects and in patients with vWD of other types. The infusion of rFVIII further increased by 182 ± 32 U/dl (mean ± SEM) the plasma levels attained after cryoprecipitate, which disappeared from the circulation with a half-life of 11.95 ± 0.86 h. In contrast, the infusion of rFVIII after saline increased by only 107 ± 18 U/dl the plasma levels of FVIII, which disappeared from the circulation with a half-life of 2.68 ± 0.14 h, indicating that the vWF infused with cryoprecipitate is able to bind additional FVIII. These studies indicate that DDAVP does not increase the plasma levels of FVIII in patients with severe vWD even after normalization of plasma vWF. The possibility is discussed that severe vWD patients may be insensitive to the releasing effect of DDAVP.     

Human recombinant DNA-derived antihaemophilic factor (factor VIII) in the treatment of haemophilia A: conclusions of a 5-year study of home therapy

Fifty-eight previously treated haemophilic subjects were treated exclusively with the recombinant FVIII (rFVIII-KOGENATE®) produced by Bayer Corporation (Berkeley, CA) in an international multicentre prospective study of more than 5 years duration. Fifty-four of the 58 had severe haemophilia (< 2% FVIII) and four had moderate haemophilia (2–5% FVIII); 23/58 (40%) were seropositive for HIV, while 35/58 (60%) were HIV seronegative. Patients were monitored for safety and efficacy over a median period of 4.7 years (range 0.9–5.9 years) and received 17 922 infusions totalling 25.7 million units of rFVIII. Of 7107 bleeding episodes reported in home diaries, 5831 (82%) required only one treatment with rVIII. Twenty-five invasive surgical procedures in 17 patients, including eight joint replacements, were successfully accomplished and 13 serious bleeding episodes in eight patients were successfully treated. FVIII recovery performed on 885 occasions using 39 different lots of rFVIII showed mean incremental recovery of 2.48% IU^?1 kg^?1 (± 0.64). Adverse events were associated with 42 infusions (0.2%); none caused discontinuation of therapy. Immunological parameters remained stable in HIV-seronegative subjects treated with rFVIII; a small decrease in CD4 counts was noted in HIV-seropositive individuals (mean ? 37.2 cells mm–3 yr^?1). No de novo formation of inhibitors to FVIII was noted; and no clinical allergic reactions occurred to murine or hamster proteins. These conclusions from the longest monitored safety study ever performed for a haemophilia treatment product (with more than 5 years of observation) confirm previous interim study reports that rFVIII is well tolerated over the long-term, has biological activity comparable to that of plasma-derived FVIII, and is safe and efficacious for the treatment of haemophilia A.     

First and next generation native rFVIII in the treatment of hemophilia A. What has been achieved? Can patients be switched safely?

The introduction of plasma-derived human factor VIII (FVIII) and later human recombinant FVIII (rFVIII) has potentially allowed patients suffering from hemophilia A to have a quality of life and life expectancy similar to the population at large. One of the major achievements in molecular biology over the past 15 years was the sequencing of the gene coding for FVIII, leading eventually to the ability to isolate the human gene for FVIII and transfect cells to produce human rFVIII. The first rFVIII products, which are native full-length FVIII molecules, have proved to have an excellent efficacy and safety profile in patients with hemophilia A. Initial concerns about a potential increased inhibitor formation have not been confirmed so far but long-term pharmacovigilance of inhibitor formation is still ongoing. To date, no transmission of hepatitis or human immunodeficiency virus (HIV) attributable to rFVIII products has been reported. However, a theoretical risk of transmission of infectious disease does exist as long as nonsynthetic proteins are used during the production process. The next-generation native rFVIII has been developed to minimize the exposure of patients to animal or human plasma-derived proteins. This has been achieved through major changes to the process of production of rFVIII from baby hamster kidney cells (BHK). This change has included the introduction of a solvent/detergent step and, of more importance, the introduction of a purification procedure without using albumin as a stabilizer. Finally, the rFVIII (BHK) is formulated using sucrose as the final stabilizer to produce the sucrose formulated rFVIII referred to as rFVIII-FS. This article summarizes the recently published pharmacokinetic, safety, and efficacy data for the native rFVIII-FS and compares its clinical profile with that of the first-generation rFVIII.     

Characterization of recombinant factor VIII and a recombinant factor VIII deletion mutant using a rabbit immunogenicity model system.

The use of factor VIII prepared genetically engineered cell lines (rFVIII) may avoid some of the problems inherently associated with administering plasma-derived factor VIII (pdFVIII) concentrates to hemophilia A patients. Although rFVIII may represent an improvement over traditional therapeutics, the chance exists that protein production in cell culture may result in the presence of novel epitopes that may enhance the formation of inhibitor antibodies capable of neutralizing either rFVIII or pdFVIII. To assess the differences between rFVIII and its plasma-derived homologue, a rabbit immunogenicity model system was developed. Antibodies raised to rFVIII in rabbits were tested for the presence of antibodies capable of binding rFVIII but not pdFVIII, the presence of which would suggest that novel epitope(s) were present. This analysis was performed using a competitive enzyme-linked immunosorbent assay, as well as immunoadsorption. For either technique, rFVIII-specific antibodies were not detected, indicating that differences between rFVIII and pdFVIII were not found. When a rFVIII B-region deletion mutant was similarly tested, antibodies specific for this protein were found. These specific antibodies appeared to bind in the vicinity of the deletion site and their binding was not affected by carbohydrate removal. These results indicate that the rabbit immunogenicity model system is sensitive to alterations in the factor VIII molecule and suggest that full-length rFVIII will not be any more immunogenic in human patients than pdFVIII.     

Understanding FVIII/VWF complex--report from a symposium of XXIX WFH meeting 2010

Summary. von Willebrand factor (VWF) has the capacity to form a complex with factor VIII (FVIII) which may modulate the immunogenicity of FVIII. It has been proposed that a significant fraction of recombinant FVIII (rFVIII) is unable to bind VWF. In an experimental model studied at the McMaster University in Canada, this VWF‐unbound rFVIII fraction showed no coagulant function. Sulphation of FVIII tyrosine (Tyr) 1680 has been reported as essential for the interaction with VWF. In a study performed at the Grifols and CNS‐CSIC in Spain, Tyr1680 sulphation was observed to be incomplete in rFVIII and complete in plasma‐derived FVIII (pdFVIII). This could explain the incapability of some rFVIII molecules to bind VWF. Experience with immune tolerance induction (ITI) at the Bonn Haemophilia Centre indicates that only eradication of FVIII inhibitors allows safe haemostasis control and the option of prophylactic treatment. Various clinical trials were planned to evaluate the clinical role VWF‐containing FVIII concentrates (FVIII/VWF). RES.I.ST (an acronym for REScue Immunotolerance STudy) is an international, prospective study aimed at assessing whether FVIII/VWF can induce ITI in high‐risk haemophilia patients (RES.I.ST naïve) and whether patients who previously failed ITI with FVIII alone can be rescued with FVIII/VWF (RES.I.ST experienced). Enrolment started in November 2009. In the FAIReSt.Will (Fanhdi and Alphanate Italian Retrospective Study in Willebrand disease) study, 120 von Willebrand disease (VWD) patients treated with Fanhdi^® or Alphanate^® were retrospectively analysed. Efficacy was excellent and no side effects were reported. The ongoing PRO.Will study is a prospective, multicenter trial aimed at assessing the efficacy, safety and pharmacoeconomics of secondary long‐term prophylaxis in patients with severe inherited VWD.     

Antibody formation and specificity in Bethesda‐negative brother pairs with haemophilia A

Antibodies directed towards non‐neutralizing epitopes on the factor VIII protein (FVIII) may be detected in patients with haemophilia A. We evaluated the prevalence of non‐neutralizing antibodies, in 201 inhibitor‐negative brother pairs with severe haemophilia A, enrolled in the Malmö International Brother Study and the Haemophilia Inhibitor Genetics Study. To evaluate binding specificity of the antibodies, ELISA plates were coated with two recombinant full‐length (FL) FVIII‐products and one recombinant B‐domain‐deleted (BDD) product. Seventy‐nine patients (39.3%) had a history of positive inhibitor titre measured by Bethesda assay, and FVIII antibodies were detected in 20 of them (25.3%). Additional 23 samples from subjects without a history of FVIII inhibitors were ELISA‐positive corresponding to a frequency of non‐neutralizing antibodies of 18.9%. The antibody response towards the different FVIII products was heterogenous, and was raised not only towards the non‐functional B‐domain but also towards both FL‐rFVIII and BDD‐rFVIII. In patients considered successfully treated with immune tolerance induction, 25.4% had remaining FVIII antibodies. The number of families with an antibody response in all siblings was increased when the total antibody response was taken into account, further supporting the concept of a genetic predisposition of the immune response. Further studies and careful monitoring over time are required to appreciate the immune response on the risk of inhibitor development or recurrence in the future.     

Expression of factor VIII in recombinant and transgenic systems

Deficiency in a coagulation factor VIII (FVIII) causes a genetic disorder hemophilia A, which is treated by repeated infusions of expensive FVIII products. Recombinant FVIII (rFVIII), the culmination of years of extensive international research, is an important alternative to plasma-derived FVIII (pdFVIII) and is considered to have a higher margin of safety. Advances in biotechnology allowed production of rFVIII at industrial scale, which significantly improved treatment of hemophilia A patients. We review the contemporary methods used for FVIII expression in mammalian cell culture systems and discuss the factors responsible for insufficient recoveries of rFVIII, such as inefficient accumulation of FVIII mRNA in the cell, complexity of the mechanisms of FVIII secretion, and instability of secreted FVIII. The approaches to improve the yield of rFVIII in cell culture systems include genetic engineering of B-domain-deleted FVIII, introduction of introns into FVIII cDNA constructs for more efficient processing and accumulation of FVIII mRNA, and introduction of mutations into chaperone-binding sites of FVIII to improve its secretion. Design of FVIII with prolonged half-life in vivo is considered as another promising direction in improving rFVIII protein and efficiency of hemophilia A therapy. As an alternative to expression of rFVIII in cell culture systems, we discuss production of rFVIII in transgenic animals, where high levels of rFVIII have been successfully secreted into milk. We also pay attention to the major limitations of this approach, such as safety issues associated with potential transmission of animal pathogens. Finally, we present a brief characterization of commercial recombinant FVIII products currently available on the market for hemophilia A treatment.