Comparative effectiveness of full-length and B-domain deleted factor VIII for prophylaxis--a meta-analysis

The self-reactive FVIII T cell repertoire in healthy individuals relies on a short set of epitopes and public clonotypes

Non-mutated FVIII-specific CD4 T cell epitopes have been recently found to contribute to the development of inhibitors in patients with hemophilia A (HA), while auto-reactive CD4 T cells specific to FVIII circulate in the blood of healthy individuals at a frequency close to the foreign protein ovalbumin. Thus, although FVIII is a self-protein, the central tolerance raised against FVIII appears to be low. In this study, we conducted a comprehensive analysis of the FVIII CD4 T cell repertoire in 29 healthy donors. Sequencing of the CDR3β TCR region from isolated FVIII-specific CD4 T cells revealed a limited usage and pairing of TRBV and TRBJ genes as well as a mostly hydrophobic composition of the CDR3β region according to their auto-reactivity. The FVIII repertoire is dominated by a few clonotypes, with only 13 clonotypes accounting for half of the FVIII response. Through a large-scale epitope mapping of the full-length FVIII sequence, we identified 18 immunodominant epitopes located in the A1, A3, C1, and C2 domains and covering half of the T cell response. These epitopes exhibited a broad specificity for HLA-DR or DP molecules or both. T cell priming with this reduced set of peptides revealed that highly expanded clonotypes specific to these epitopes were responsible individually for up to 32% of the total FVIII repertoire. These FVIII T cell epitopes and clonotypes were shared among HLA-unrelated donors tested and previously reported HA patients. Our study highlights the role of the auto-reactive T cell response against FVIII in HA and its similarity to the response observed in healthy individuals. Thus, it provides valuable insights for the development of new tolerance induction and deimmunization strategies.

Considerations on activity assay discrepancies in factor VIII and factor IX products

New modified coagulation factor VIII (FVIII) and factor IX (FIX) products have been designed to improve the treatment of individuals with hemophilia A and B by increasing the interval between dosing. Although these FVIII and FIX molecules have been structurally modified to improve the circulation time, the changes have also influenced their behavior in functional assays in comparison with traditional plasma-derived or recombinant coagulation factors. The assignment of potencies for these products can be problematic because discordance in factor activity values between the commonly used one-stage clotting and chromogenic substrate assays is often observed. Discrepancies in potency assay values also exist when different assay kits and reagents are used in the same assay type. Ideally, all FVIII and FIX products should be calibrated against the World Health Organization (WHO) International Standards (IS) because the assignment of potencies in international units (IU) helps maintain treatment tradition and meaningful references for manufacturers, patients, and clinicians. The discrepant measurements, attributed to the modified structural and functional properties of these products, are manifested in their lack of commutability with the WHO IS for FVIII or FIX. Herein, we discuss the considerations upon which an assay is chosen for potency assignment and postadministration monitoring of a new factor product, which include the validity of the assay calibrated with the IS, the meaning of the potency values in IU, standards of care for patients, clinical relevance between the assigned potency value and recovery value from clinical laboratories, and patient safety.

Restoration of FVIII expression by targeted gene insertion in the FVIII locus in hemophilia A patient-derived iPSCs

Target-specific genome editing, using engineered nucleases zinc finger nuclease (ZFN), transcription activator-like effector nuclease (TALEN), and type II clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9), is considered a promising approach to correct disease-causing mutations in various human diseases. In particular, hemophilia A can be considered an ideal target for gene modification via engineered nucleases because it is a monogenic disease caused by a mutation in coagulation factor VIII (FVIII), and a mild restoration of FVIII levels in plasma can prevent disease symptoms in patients with severe hemophilia A. In this study, we describe a universal genome correction strategy to restore FVIII expression in induced pluripotent stem cells (iPSCs) derived from a patient with hemophilia A by the human elongation factor 1 alpha (EF1α)-mediated normal FVIII gene expression in the FVIII locus of the patient. We used the CRISPR/Cas9-mediated homology-directed repair (HDR) system to insert the B-domain deleted from the FVIII gene with the human EF1α promoter. After gene targeting, the FVIII gene was correctly inserted into iPSC lines at a high frequency (81.81%), and these cell lines retained pluripotency after knock-in and neomycin resistance cassette removal. More importantly, we confirmed that endothelial cells from the gene-corrected iPSCs could generate functionally active FVIII protein from the inserted FVIII gene. This is the first demonstration that the FVIII locus is a suitable site for integration of the normal FVIII gene and can restore FVIII expression by the EF1α promoter in endothelial cells differentiated from the hemophilia A patient-derived gene-corrected iPSCs.

A strategy to restore the expression of the gene encoding blood clotting factor VIII (FVIII) offers new hope to patients with hemophilia A. Hemophilia A is a rare bleeding disorder caused by a variety of mutations in the FVIII gene which affect the function of FVIII protein. At present, the main treatment option relies on the injection of expensive clotting-factor concentrates to restore functional levels of the FVIII. Dong-Wook Kim and colleagues at Yonsei University in Seoul, South Korea, have used genome editing techniques to insert a corrected version of the FVIII gene into stem cells derived from a patient with severe hemophilia A. When these cells differentiated into the cells lining blood vessels they were able to produce and secrete active FVIII protein. This approach offers the attractive possibility of correcting all hemophilia-causing FVIII mutations.

Safety of recombinant coagulation factors in treating hemophilia

INTRODUCTION

During the last decade, new FVIII/IX concentrates have been developed for the treatment of patients affected by hemophilia A/B. Significant progress has been achieved regarding their half-life, but the old issue of immunogenicity and new concerns about safety need to be addressed.

AREAS COVERED

After the implementation of virucidal methods, both plasma-derived and recombinant clotting factor concentrates achieved a very safe profile. The development of anti-FVIII antibodies is the major adverse event of replacement therapy with both FVIII concentrates. Furthermore, the new extended half-life concentrates, protein fused or pegylated, raised some concerns about their side effects.

EXPERT OPINION

The treatment of hemophilia A with inhibitors by induction of immunotolerance and using by-passing concentrates, improved the quality of life of patients but did not allow them to have a life expectancy like that of patients without inhibitors. The new humanized monoclonal antibody (MAb) ACE910, mimicking FVIII function, seems to be able to reduce the bleedings of hemophilia A patients with inhibitors. The post-marketing surveillance will clarify if the adverse events observed during the phase III clinical trials and compassionate use were due to the association with a Prothrombin activated complex concentrate or to the prothrombotic effect of the drug itself.

Performing and interpreting individual pharmacokinetic profiles in patients with Hemophilia A or B: Rationale and general considerations

OBJECTIVES

In a separate document, we have provided specific guidance on performing individual pharmacokinetic (PK) studies using limited samples in persons with hemophilia with the goal to optimize prophylaxis with clotting factor concentrates. This paper, intended for clinicians, aims to describe how to interpret and apply PK properties obtained in persons with hemophilia.

METHODS

The members of the Working Party on population PK (PopPK) of the ISTH SSC Subcommittee on Factor VIII and IX and rare bleeding disorders, together with additional hemophilia and PK experts, completed a survey and ranking exercise whereby key areas of interest in the field were identified. The group had regular web conferences to refine the manuscript's scope and structure, taking into account comments from the external feedback to the earlier document.

RESULTS

Many clinical decisions in hemophilia are based on some form of explicit or implicit PK assessment. Individual patient PK profiles can be analyzed through traditional or PopPK methods, with the latter providing the advantage of fewer samples needing to be collected on any prophylaxis regimen, and without the need the for a washout period. The most useful presentation of PK results for clinical decision making are a curve of the factor activity level over time, the time to achieve a certain activity level, or related parameters like half-life or exposure (AUC). Software platforms have been developed to deliver this information to clinicians at the point of care. Key characteristics of studies measuring average PK parameters were reviewed, outlining what makes a credible head-to-head comparison among different concentrates. Large data collections of PK and treatment outcomes currently ongoing will advance care in the future.

CONCLUSIONS

Traditionally used to compare different concentrates, PK can support tailoring of hemophilia treatment by individual profiling, which is greatly simplified by adopting a PopPK/Bayesian method and limited sampling protocol.

2017 Clinical trials update: Innovations in hemophilia therapy

A surge in therapeutic clinical trials over recent years is paving the way for transformative treatment options for patients with hemophilia. The introduction of recombinant factor concentrates in the early 1990s facilitated the use of prophylactic replacement as standard care for hemophilia rather than on-demand treatment. This has revolutionized health outcomes for hemophilia patients, enabling participation in physical activities and reducing debilitating, chronic joint damage. Challenges of prophylactic factor infusion include the frequency of infusions needed to maintain factor levels greater than 1%, patient adherence, reliable intravenous access, and development of neutralizing alloantibodies ("inhibitors"). Novel therapeutics seek to improve upon current factor concentrates by several different mechanisms: (1) extending the half-life of circulating exogenous factor protein, (2) replacing the gene necessary for production of endogenous factor protein, (3) employing bispecific antibody technology to mimic the coagulation function of factor VIII, (4) disrupting anticoagulant proteins, such as tissue factor pathway inhibitor (TFPI) or antithrombin (AT3) with antibodies, aptamers, or RNA interference technology. Emerging treatment options may reduce the frequency of (extended half-life products) or eliminate (gene therapy) the need for scheduled factor concentrate infusions, or provide a subcutaneous administration option (bispecific antibody, AT3, and TFPI targeting therapies). In addition, the nonfactor replacement strategies provide a promising treatment option for patients with inhibitors, presently the greatest unmet medical need in hemophilia. This review highlights current and recently completed clinical trials that are driving a paradigm shift in our approach to hemophilia care for patients with and without inhibitors. Am. J. Hematol. 91:1252-1260, 2016. © 2016 Wiley Periodicals, Inc.

The use of pharmacokinetics in dose individualization of factor VIII in the treatment of hemophilia A

INTRODUCTION

Hemophilia A is a bleeding disorder resulting from a lack of clotting factor VIII (FVIII), and treatment typically consists of prophylactic replacement of the deficient factor. However, high between subject variability precludes the development of a 'one size fits all' dosing strategy and necessitates an individualized approach. We sought to summarize the data on the pharmacokinetics of FVIII available as a basis for the development of population pharmacokinetic models to be used in dose tailoring. Areas covered: We reviewed the pharmacokinetics of FVIII as used for the treatment of hemophilia A, with a focus on the variability observed between patients and the application of pharmacokinetic methods to dose individualization. We also explored the covariates affecting pharmacokinetic parameters, the differences between plasma-derived and recombinant FVIII and the development of extended half-life products. Expert opinion: The pharmacokinetics of factor VIII in patients with hemophilia shows a high interpatient variability, and is affected by age, weight, level of von Willebrand factor, and blood group. A population approach to estimating individual pharmacokinetics is likely to provide the most successful strategy to tailor factor concentrate dosing to the individual needs and to ensure optimal patient outcomes, while also improving the cost-effectiveness of prophylactic replacement therapy.

Recommendations for authors of manuscripts reporting inhibitor cases developed in previously treated patients with hemophilia: communication from the SSC of the ISTH

Aim The scope of this recommendation is to provide guidance for reporting of inhibitor cases in previously treated patients (PTPs) with hemophilia A. This guidance is intended to improve transparency and completeness of reporting of observed events; it does not cover planning, executing or analyzing original studies aimed at the assessment of inhibitor rates. Recommendation We recommend that for each case of inhibitor development reported in a published paper, a paragraph or a table is included in the main publication reporting as a minimum the underlined data fields in Table . We recommend transparent reporting when any of the suggested information is not available. We recommend that particular care is used in reporting the timeline of events by clearly identifying a reference time-point. We suggest that journals in the field adopt this guidance as instructions for the authors and as a guide for reviewers. Conclusion Development of inhibitors in PTPs is a very rare event. Standardized reporting of inhibitor characteristics will contribute to generating a body of evidence otherwise not available. Case by case reporting of the recommended data elements may shed light on the natural history and risk factors of inhibitor development in PTPs and be useful for tailoring care in similar future cases.

Efficacy, Safety, and Pharmacokinetics of Beroctocog Alfa in Patients Previously Treated for Hemophilia A

PURPOSE

Beroctocog alfa is a second generation recombinant factor VIII manufactured by removing the B-domain from factor VIII. This prospective clinical trial was conducted to evaluate the efficacy, safety, and pharmacokinetics of beroctocog alfa in patients of ages ≥12 years previously treated for severe hemophilia A.

MATERIALS AND METHODS

Seventy subjects received beroctocog alfa as an on-demand treatment for acute hemorrhage.

RESULTS

The final hemostatic effect was excellent in 35 subjects (50%) and good in 26 subjects (37.1%). The drug showed an overall efficacy rate of 87.1%. The majority of acute hemorrhages was treated by administering the study drug once (86.2%) or twice (10.0%), and the mean dose administered per single infusion was 28.55±6.53 IU/kg. Ten subjects underwent 12 surgical procedures, and hemostatic efficacy was excellent in seven cases (58.3%) and good in five cases (41.7%), showing a 100% efficacy rate. A total of 52 of 88 subjects (59.0%) experienced 168 adverse events. There were 18 serious adverse events (10.7%) in 11 subjects, and two (mild dyspnea and facial edema) in one subject were related to the study drug. Only one subject formed a de novo factor VIII inhibitor, for an occurrence rate of 1.4% (one-sided 95% upper confidence limit: 3.85%). The final elimination half-life was 13.3 h and 12.6 h at baseline and 6 months after administration, respectively.

CONCLUSION

Our results suggest that beroctocog alfa is safe and efficacious as either an on-demand treatment for acute hemorrhage or a surgical prophylaxis in patients with hemophilia A.

Soy phosphatidylinositol containing nanoparticle prolongs hemostatic activity of B-domain deleted factor VIII in hemophilia A mice

Factor VIII (FVIII) replacement therapy in hemophilia A (HA) is complicated by a short half-life and high incidence of inhibitory antibody response against the protein. Phosphatidylinositol (PI) containing lipidic nanoparticles have previously been shown to reduce the immunogenicity and prolong the half-life of full length FVIII. It has not been established whether this prolongation in half-life improves hemostatic efficacy and whether this approach could be extended to the B-domain deleted form of FVIII (BDD FVIII). In the current study, we evaluated the pharmacokinetics (PK), hemostatic efficacy, and immunogenicity of BDD FVIII associated with PI nanoparticles (PI-BDD FVIII) in HA mice. Comparative human PK was predicted using an "informed scaling" approach. PI-BDD FVIII showed an approximate 1.5-fold increase in terminal half-life compared with free BDD FVIII following i.v. bolus doses of 40 IU/kg. PI-BDD FVIII-treated animals retained hemostatic efficacy longer than the free FVIII-treated group in a tail vein transection model of hemostasis. PI association reduced the development of inhibitory and binding antibodies against BDD FVIII after a series of i.v. injections. The combined improvements in circulating half-life and hemostatic efficacy could significantly prolong the time above clinically established therapeutic thresholds of prophylactic FVIII replacement therapy in humans.

Functional roles of the factor VIII B domain

Unravelling the structure, function and molecular interactions of factor VIII (FVIII) throughout its life cycle from biosynthesis to clearance has advanced our understanding of the molecular mechanisms of haemophilia and the development of effective treatment strategies including recombinant replacement therapy. These insights are now influencing bioengineering strategies toward novel therapeutics. Whereas available molecular models and crystal structures have helped elucidate the structure and function of the A and C domains of FVIII, these models have not included detailed structural information of the B domain. Therefore, insights into the role of the FVIII B domain have come primarily from expression studies in heterologous systems, biochemical studies on bioengineered FVIII variants and clinical studies with B domain-deleted FVIII. This manuscript reviews the available data on the potential functional roles of the FVIII B domain. A detailed literature search was performed, and the data extracted were qualitatively summarized. Intriguing emerging evidence suggests that the FVIII B domain is involved in intracellular interactions that regulate quality control and secretion, as well as potential regulatory roles within plasma during activation, platelet binding, inactivation and clearance.

Recombinant factor VIII in the management of hemophilia A: current use and future promise

Hemophilia A is a rare inherited bleeding disorder due to mutation of the gene that encodes the coagulation protein factor VIII. Historically, prior to the availability of treatment with factor VIII preparations, most boys died from uncontrolled bleeding, either spontaneous bleeding or after injury, before reaching 20 years of age. One of the most impressive triumphs of modern medicine is that with current recombinant factor VIII replacement therapy, a boy born in the 21st century with severe hemophilia A can anticipate a normal life expectancy with essentially no permanent complications from bleeding. For severe hemophilia A, current optimal treatment should have two goals: first, to provide sufficient factor VIII to prevent spontaneous bleeding, and second, to provide sufficient factor VIII to have normal coagulation function after any trauma. However, the replacement therapy requires tremendous resources for effective use, and remains extraordinarily expensive. Thus there are opportunities for further advances in therapy for hemophilia A. Two major concerns continue to trouble current optimal treatment approaches: some patients will develop neutralizing antibodies during the first 50 infusions of therapeutic factor VIII, and second, to administer therapeutic factor VIII every other day in young boys often requires placement of a central venous access device, and such use carries the life-threatening risks of infection and thrombosis. Because of the effectiveness of current therapy, any new developments in treatment will require significant concerns for safety, both immediate and in the long term. A number of research groups seek to prolong the biological efficacy of infused recombinant factor VIII. Currently, one such promising development is in the advanced stages of clinical trial. The goals will be to improve further the quality of life of an individual with severe hemophilia A, and to reduce the burden of current treatment strategies on families and medical resources. Hopefully, the hemophilia community will continue to participate actively in the clinical trials needed to address these new challenges.

ReFacto and Advate: a single-dose, randomized, two-period crossover pharmacokinetics study in subjects with haemophilia A

ReFacto is a recombinant B-domain-deleted, monoclonal antibody-purified, solvent-detergent-treated factor VIII (BDDrFVIII) with no albumin added to the final formulation. Although ReFacto has been shown to be bioequivalent to a plasma-derived FVIII product (Hemophil-M) in a randomized, crossover pharmacokinetic (PK) study, the comparability of ReFacto with the full-length (complete sequence) recombinant FVIII (FLrFVIII, Advate) product has not been previously examined in this manner. The primary objective of this study was to compare the PKs of ReFacto with those of Advate in patients with severe haemophilia A. This was a third-party unblinded, randomized, multicentre, two-period crossover PKs study of ReFacto and Advate in subjects with severe haemophilia A (FVIII:C < or =1%). Blood samples were collected over a 48-h period after i.v. administration of each of the FVIII products. FVIII:C was determined using the chromogenic substrate assay (CSA) in a central laboratory. The plasma FVIII:C PK parameters of ReFacto and Advate were determined using non-compartmental analysis. Bioequivalence was assessed on maximum plasma concentration (C(max)) and the area under the plasma concentration vs. time curves (AUCs) using an anova. The two products were judged to be equivalent if the 90% confidence limits of the ratio of the geometric mean values of C(max) and AUCs fell within the interval of 80-125%. Results from this PKs comparison of two different rFVIII products, using chromogenic substrate assay to measure FVIII:C, showed that ReFacto and Advate are bioequivalent to each other.

Disulfide bond-stabilized factor VIII has prolonged factor VIIIa activity and improved potency in whole blood clotting assays

BACKGROUND

Genetically engineered disulfide bonds in B-domain-deleted factor (F) VIII variants (C662-C1828 FVIII and C664-C1826 FVIII) improve FVIIIa stability by blocking A2 domain dissociation because the new disulfide covalently links the A2 and A3 domains in FVIIIa.

AIM

The aim of this study was to assess the hypothesis that these variants have physiologically relevant properties because of prolonged thrombin generation and improved clot formation in whole blood.

METHODS

Clot-formation properties in whole blood were measured in thromboelastogram assays. The thrombin generation capabilities of the wild-type (WT) FVIII and FVIII variants were determined, and half-lives of FVIIIa variants were determined in fresh whole blood serum.

RESULTS

Thromboelastogram assays were performed with fresh, severe hemophilia whole blood reconstituted with variant and WT FVIII. The two disulfide bond-stabilized FVIII variants and WT FVIII had comparable clotting times at all studied concentrations. However, when compared with WT FVIII at low concentrations, the two FVIII variants required only 10% as much FVIII to achieve comparable clot-formation rates, clot-formation times and clot firmness values. The differences between WT and FVIII variants were quite pronounced at low FVIII concentrations. Measurement of the endogenous thrombin potential in FVIII-deficient plasma supplemented with these FVIII variants confirmed that the disulfide bond-stabilized variants supported high levels of thrombin generation at lower concentrations than did WT FVIII. During the course of clot generation in whole blood, the disulfide bond-stabilized FVIIIa variants had approximately 5-fold increased half-lives relative to WT FVIIIa.

CONCLUSION

C662-C1828 FVIII and C664-C1826 FVIII have physiologically relevant superior clot-forming properties in a whole blood environment, most likely due to the increased half-life of these FVIIIa variants in whole blood.

Role of the B domain in proteolytic inactivation of activated coagulation factor VIII by activated protein C and activated factor X

Hereditary deficiency of factor VIII (FVIII), haemophilia A, is treated by plasma-derived FVIII (pd-FVIII) or recombinant FVIII (rFVIII) infusions. B-domain-deleted FVIII (BDD-rFVIII), although generally safe and effective, was less effective than pd-FVIII in prophylaxis -- evidenced by a 2.5-fold higher bleeding incidence. Assessment of BDD-rFVIII activity in chromogenic and one-stage clotting assays gives up to 50% difference in activity values. As earlier studies demonstrated identical activation and cofactor activity of BDD-rFVIII and pd-FVIII, we decided to study susceptibility of thrombin-activated pd-FVIII, full-length rFVIII and BDD-rFVIII to proteolytic inactivation by activated protein C (APC) and activated factor X (FXa) in a purified system. Proteolysis was monitored by Western blot using monoclonal antibodies C5 and R8B12 specific for the A1 and A2 domains, respectively. Inactivation was monitored by measuring the residual cofactor activity of FVIII forms in a one-stage clotting assay. Proteolysis of A1 and A2 domains of activated BDD-rFVIII proceeded 11 or 13 times faster than that of pd-FVIII or full-length rFVIII. Inactivation of activated BDD-rFVIII was two to three times faster by APC and five to six times faster by FXa. We suggest that differences in proteolytic inactivation may contribute to differences between BDD-rFVIII and pd-FVIII in assaying and in clinical use.

A postmarketing surveillance study of the safety and efficacy of ReFactoR (St Louis-derived active substance) in patients with haemophilia A

This clinical trial evaluated the safety and efficacy of ReFacto (St Louis-derived active substance) in patients with severe or moderately severe haemophilia A over a period of 6 months or 50 exposure days (EDs), whichever occurred first. Sixty patients, 58 previously treated and two previously untreated, were enrolled into this study. This was an open-label, multicentre, postmarketing surveillance study in which patients received prophylaxis or on-demand treatment as determined by their doctor. Surgical prophylaxis was evaluated in seven patients requiring elective surgery. Thirty-two patients aged <1 to 66 years (median 19.5) received prophylaxis and 28 patients, aged 1-71 years (median 33.5), received on-demand treatment. The majority of patients had severe haemophilia A (FVIII:C < 2%): 84.4% in the prophylaxis group and 85.7% in the on-demand group. Prophylaxis with ReFacto was associated with a median of 6.7 bleeds per year (range: 0-37). The investigator's assessment of final outcome for prophylactic treatment was excellent or effective for 93.1% of patients. ReFacto resolved 92.8% of bleeds with one or two infusions. The investigator's assessment was excellent or good for 98.2% of bleeds treated with ReFacto. Haemostasis was achieved for all seven surgical cases and ReFacto gave an excellent or good response for each. The nature and incidence of adverse events was as expected and no new safety concerns emerged. One previously treated patient (PTP) developed a high-titre inhibitor (maximum 75 BU) and one minimally treated patient (MTP) developed a low-titre inhibitor while on the study but eventually achieved high titres (maximum 30 BU) after immune tolerance therapy was initiated with a plasma-derived FVIII product. One previously untreated patient (PUP) developed a transient low-titre inhibitor (0.4 BU). Other serious adverse events (SAEs) were unrelated to study treatment. There were no allergic events. The results of this study are consistent with the previously published ReFacto pivotal studies.

Treating haemophilia A with recombinant blood factors: a comparison

The mainstay in the treatment of haemophilia A is replacement therapy with repeated infusions of plasma-derived Factor VIII (FVIII) concentrates or recombinant FVIII products. While modern plasma-derived FVIII concentrates have an excellent safety profile, there is an inexorable shift towards the use of recombinant products, especially in affluent countries. Recombinant FVIII products have demonstrated excellent haemostatic efficacy and higher safety with regard to the transmission of blood-borne pathogens. The experience in haemophilia A treatment with five currently available recombinant FVIII products, including the first third-generation product, Advate, which is completely free from human or animal proteins, is summarised. Some unresolved problems concerning the efficacy and assaying of recombinant factors and future perspectives of both recombinant and plasma-derived FVIII products in global haemophilia care, are also discussed.

B-domain deleted recombinant factor VIII preparations are bioequivalent to a monoclonal antibody purified plasma-derived factor VIII concentrate: a randomized, three-way crossover study

BACKGROUND

Deletion of the B-domain of recombinant blood coagulation factor VIII (BDDrFVIII) increases the manufacturing yield of the product but does not impair in vitro or in vivo functionality. BDDrFVIII (ReFacto) has been developed with the additional benefit of being formulated without human albumin.

OBJECTIVE

The primary objective of this three-way crossover-design study was to compare the pharmacokinetic (PK) parameters of two BDDrFVIII formulations (one reconstituted with 5 mL of sterile water, the other reconstituted with 4 mL sodium chloride 0.9% USP) with those of a plasma-derived, full-length FVIII preparation (Hemofil M) in patients with haemophilia A to determine bioequivalence.

METHODS

A series of blood samples were collected over a period of 48 h after i.v. administration of each of the FVIII preparations. Plasma FVIII activity was determined using a validated chromogenic substrate assay. Plasma FVIII activity vs. time curves was characterized for a standard set of PK parameter estimates. Two parameter estimates, the maximum plasma concentration (Cmax) and the area under plasma concentration vs. time curves (AUCs), were used to evaluate bioequivalence. The two preparations were considered bioequivalent if the 90% confidence intervals for the ratio of geometric means for Cmax and AUCs fell within the bioequivalence window of 80% to 125%.

RESULTS/CONCLUSION

Results show that each BDDrFVIII formulation is bioequivalent to Hemofil M and the two formulations of BDDrFVIII are bioequivalent to each other.

Meta-analytic evidence of increased breakthrough bleeding during prophylaxis with B-domain deleted factor VIII

A recent meta-analysis of 13 observational studies suggested reduced haemostatic efficacy during prophylaxis and shortened half-life of B-domain deleted factor VIII (BDD-rFVIII) as compared with full-length factor VIII (FL-FVIII). The meta-analysis included a multivariate model that took both dose and age into account. In addition, several assumptions and interpretations were required in order to conduct the meta-analysis. It is important to test the impact of such assumptions and interpretations through sensitivity analysis. In the published meta-analysis, results of several sensitivity analyses were described involving the effect of study design; heterogeneity of subjects in some studies; type of assay used for half-life determinations; and year of publication. In two subsequent brief reports, additional sensitivity analyses addressed choice of median-to-mean conversion factor over a wide range of scenarios and use of age at start of prophylaxis vs mean age during prophylaxis in the multivariate model. A recognized inherent difficulty in the meta-analysis of multiple published reports from similar studies is the possibility of some subject or data overlap. Therefore, the present communication details further sensitivity analyses encompassing assumptions regarding the possibility of subject duplication in a subgroup of subjects from one study and possible duplication of pharmacokinetic data from two smaller studies within the reports of two larger studies. All the sensitivity analyses support the main conclusions of the meta-analysis, namely, that BDD-rFVIII substantially increases the risk of breakthrough bleeding during prophylaxis, possibly at least partly because of shorter half-life than that of FL-FVIII.

Increased breakthrough bleeding during prophylaxis with B-domain deleted factor VIII - a robust meta-analytic finding

Meta-analyses of observational studies have become increasingly common to support evidence-based clinical decisions. We analyzed currently available clinical studies of full-length factor VIII (FL-FVIII) vs. B-domain deleted recombinant factor VIII (BDD-rFVIII) using a random effects model to investigate possible differences in clinical efficacy in patients treated during prophylaxis. Some studies reported breakthrough bleeding incidence as mean annual total bleeds, whereas others reported median bleeds. In accord with the consensus recommendations by the Meta-analysis of Observational Studies in Epidemiology (MOOSE) group, all available studies where included. For analysis, data were combined by converting median to mean annual total bleeds using a conversion factor of 2.6, based on clinical data previously compiled by the Universal Data Collection Program of the U.S. Centers for Disease Control and Prevention. To evaluate the sensitivity of our model upon the choice of conversion factor, we re-estimated incidence rate ratios for breakthrough bleeding over a wide range of conversion factors from 1.4-2.6. Even at the lowest extreme conversion factor of 1.4, bleeding incidence was statistically higher in patients treated with BDD-rFVIII compared with FL-FVIII. We also examined the impact of reported patient age on our multivariate model. Exposure to BDD-rFVIII remained an independent predictor of bleeding, regardless of patient age at start or mean age during prophylaxis. These analyses further support the robustness of our meta-analysis and its conclusions.

Safety and supply of haemophilia products: worldwide perspectives

The survival and well-being of people with haemophilia depends on the supply of safe therapeutic products. Safety and supply are entirely intertwined principles; in the absence of adequate amounts of coagulation products, safety measures may be compromised in order to enhance supply, leading to risks which may result in morbidity and mortality. As haemophilia therapy has emerged through the development of blood transfusion and plasma fractionation, the safety of the blood supply in general has had a strong effect on haemophilia care. Despite the gradual detachment of haemophilia care from blood transfusion through the use of recombinant products, the majority of the world's population with haemophilia in the developing world will be reliant on blood products for the foreseeable future. It is, therefore, important to continue efforts for a safe and sufficient blood supply worldwide. As such a blood supply develops, possibly in tandem with an independent plasma fractionation industry, the level of haemophilia care should improve with the gradual introduction of concentrates for the ultimate goal of covering all aspects of care. Constant vigilance for the threat of blood-borne pathogens should be linked to considerations of how these products are to be manufactured. This should be governed entirely by considerations of safety and pharmaceutical competence. Of equal importance is a governmental capacity to oversee the entry and maintenance of these products on the market. While it is not possible for all countries to have a regulatory authority of the same status as that of the developed countries, it is perfectly feasible to develop a set of basic principles which allow an assessment of basic product safety, quality and efficacy to be made.