B-domain Deleted Recombinant Factor VIII Research Articles

Production and characterization of polyclonal antibodies to human recombinant domain B-free antihemophilic factor VIII.

Moroctocog alpha is a human B-domain deleted recombinant factor VIII (BDDrFVIII), which represents a new generation of pure antihemophilic products. We describe here an optimized procedure for polyclonal anti-FVIII-antibody production with the use of BDDrFVIII as an immunogen. The main immunochemical characteristics of the produced antibodies and their potential biomedical applications are also reported. Rabbits were immunized with BDDrFVIII as an emulsion with Freund's adjuvant or with antigen immobilized in polyacrylamide gel (PAAG). Antibody titers in immune sera were assayed by enzyme-linked immunosorbent assay (ELISA). IgG purification was performed by afine chromatography on protein A-sepharose. Immune sera and IgG were tested by immunoblotting with the use of human plasma of healthy donors and people with hemophilia A, platelet lysates, and commercial plasma-derived concentrates as sources of FVIII-related antigens. FVIII-producing human umbilical vein cells were processed for immunocytochemical staining with the use of purified anti-FVIII-antibodies. Immunization of rabbits with PAAG-trapped antigen induced more potent immune response compared to the standard immunization procedure with Freund's adjuvant. The lowest working amount of immune IgG, measured by ELISA, was ~50 ng. Immunoblotting demonstrated that anti-BDDrFVIII antibodies effectively recognize the whole FVIII molecule (320 kDa), as well as different truncated polypeptides thereof, and are suitable for immunocytochemical analysis of FVIII-producing cells. An optimized procedure for the production of polyclonal antibodies against FVIII with the use of PAAG-immobilized BDDrFVIII (moroctocog alpha) was proposed and successfully validated. The produced antibodies are suitable for detecting and measuring FVIII-related antigens and may have various biomedical applications.

BDDrFVIII (Moroctocog alfa [AF‐CC]) for surgical haemostasis in patients with haemophilia A: results of a pivotal study

Moroctocog alfa (AF-CC) (Xyntha, BDDrFVIII) is manufactured by a process designed to enhance the theoretical viral safety profile relative to ReFacto, its predecessor, and to provide alignment with clinical monitoring by the one-stage clotting assay. To evaluate the efficacy and safety of B-domain-deleted recombinant factor VIII (BDDrFVIII) was given as bolus injection (BI) or continuous infusion (CI) in haemophilia patients undergoing major surgery. BDDrFVIII was administered by BI or CI per investigator discretion peri-operatively for at least 6 days. Thirty patients enrolled and were treated with at least one dose of BDDrFVIII. Twenty-five patients were evaluable for efficacy. Outcomes were favourable against a background of multiple major surgical procedures. All haemostatic efficacy ratings were 'excellent' or 'good'. End-of-surgery haemostasis ratings, the primary efficacy endpoint, were excellent for 72% (18/25) and good for 28% (7/25) of patients. Haemostasis ratings following the initial postoperative period were excellent for 92% (23/25) and good for 8% (2/25) of patients. Intra-operative blood loss was rated as normal in all patients. Thirteen patients had postoperative blood loss; in 10, this was rated as normal. A low frequency of transfusion was reported in both the intra-operative and postoperative settings. Adverse events (AEs) were consistent with surgery; three were considered related to BDDrFVIII. One patient had a related AE of postoperative haemorrhage. A clinically silent low-titre inhibitor was detected in one patient, and one patient had a false-positive inhibitor titre. This study demonstrates that BDDrFVIII is safe and efficacious for surgical prophylaxis in haemophilia A patients undergoing major surgery.

Clinical evaluation of moroctocog alfa (AF‐CC), a new generation of B‐domain deleted recombinant factor VIII (BDDrFVIII) for treatment of haemophilia A: demonstration of safety, efficacy, and pharmacokinetic equivalence to full‐length recombinant factor VIII

BDDrFVIII is a B-domain deleted recombinant factor VIII (rFVIII) product for haemophilia A. Manufacture uniquely includes purification chromatography by synthetic-affinity ligand rather than murine-based monoclonal antibody, as well as an albumin-free cell culture process. BDDrFVIII was studied in 204 patients, including 62 subjects <16 years old, in two studies. A double-blind, randomized, pharmacokinetic (PK) crossover study, utilizing a central laboratory assay (one-stage (OS)) for both drug potency assignment and plasma FVIII-activity measurements, demonstrated that BDDrFVIII was PK-equivalent to a full-length rFVIII. Favourable efficacy and safety were observed: during defined routine prophylaxis in a patient population significant for preexisting target joints, nearly half (45.7%) of patients had no bleeding, and a low-annualized bleed rate (ABR) was achieved (median 1.9); 92.5% of haemorrhages (n = 187) required < or =2 infusions. Three subjects (1.5%, across both studies) developed de novo inhibitors (low-titre, transient), and the primary safety endpoint, based on a prospective Bayesian analysis, demonstrated the absence of neoantigenicity for BDDrFVIII. The PK-equivalence, based on central testing to align test and reference articles, and the novel Bayesian analysis of inhibitor safety in these investigations reflect robust experimental designs with relevance to future studies. This extensive dataset demonstrates the safety and efficacy of BDDrFVIII for haemophilia A.

Pharmacokinetics, Coagulation Factor Consumption, and Product Efficacy in Patients Crossing Over from Full-Length FVIII to B-Domain Deleted R-FVIII and Back to Full-Length FVIII.

Introduction: Treatment with B-domain deleted recombinant factor VIII (BDD-rFVIII) has proven to be effective and safe both in clinical trials and post marketing surveillance studies. However, intermittent concerns have been raised regarding the pharmacokinetic performance, efficacy and incidence of inhibitor formation with the BDD-rFVIII product.Aims: The objective of the present study was to perform a retrospective survey of half-life measurements, clinical efficacy and safety in patients with severe Haemophilia A, when switching treatment from full-length FVIII (FL-FVIII) to BDD- rFVIII and then back to full-length FVIII. We hypothesized that the biological half-life of FVIII would be equal regardless of the product used. Furthermore, we hypothesized that the total factor consumption and bleeding frequency would be indistinguishable irrespective of product used. Finally, we report on safety as evaluated by development of inhibitors and clinical outcome following surgery.Methods: Patients treated with BDD-rFVIII (between 1998 and 2008) were identified from an in-house database. Data collected included annual half-life (T/2) and recovery times (K values), total coagulation factor consumption, and number of bleeds per year as measures of clinical efficacy. Safety data consisted of surgical outcome data and incidence of inhibitor formation. The information was extracted from electronic databases and verified by a review of patients' clinical notes. The outcome data was non-parametric, hence, paired analysis was performed using Wilcoxon signed rank test and Friedman ANOVA. Data is given as a median value and range. P-value < 0.05 was set as level of statistical significance.Results: In total, 70 patients received BDD-rFVIII on at least one occasion. Following a specified list of criteria, evaluable data was obtainable for 15 males, all with verified severe Haemophilia A (FVIII:C <1%). The average age was 10.2 years (median 10, range 4–17). The median duration on BDD-rFVIII was 30 months (range 20–54). Using the one-way non-parametric ANOVA, no statistically significant difference was detected between the half-life and recovery times recorded during the switch from FL-FVIII (T/2 median 9.15 hours, range 6.4–22; K median 2.7, range 2.0–3.4) to BDD-rFVIII (T/2 median 9.7, range 4.7–16.8; K median 1.8, range 1.0–3.5) and back to FL-FVIII (T/2 median 9.0, range 5.0–19.5; K median 2.0, range 1.6–2.8). Furthermore, there was no significant difference in coagulation factor usage (BDD-rFVIII median 4803 iu/kg/year, range 659–11304; FL-FVIII median 5349, range 1691–10146), nor number of reported bleeds (BDDrFVIII median 6, range 0–24; FL-FVIII median 5.0, range 0–17). None of the 15 patients developed an inhibitor on BDD-rFVIII. Of the total 70 patients, 11 received BDD-rFVIII to cover surgical procedures (8 minor, 3 major interventions). There were no reports of excess bleeding.Conclusions: In this retrospective survey, BDD-rFVIII was found to be equivalent to other FVIII products in terms of half-life measurements, clinical efficacy and safety.

O-phospho-L-serine, multi-functional excipient for B domain deleted recombinant factor VIII

Factor VIII (FVIII) is an important cofactor in the blood coagulation cascade. A deficiency or dysfunction of FVIII causes hemophilia A, a life-threatening bleeding disorder. FVIII circulates in plasma as a heterodimer comprising 6 domains (heavy chain, A1-A2-B and light chain, A3-C1-C2). Replacement therapy using FVIII is the leading therapy in the management of hemophilia A. However, approximately 15% to 30% of patients develop inhibitory antibodies that neutralize the activity of the protein. Neutralizing antibodies to epitopes in the lipid binding region of FVIII are commonly identified in patients' plasma. In this report, we investigated the effect of O-phospho-L-serine (OPLS), which binds to the lipid binding region, on the immunogenicity of B domain deleted recombinant factor VIII (BDDrFVIII). Sandwich enzyme-linked immunosorbent assay (ELISA) studies showed that OPLS specifically bind to the lipid binding region, localized in the C2 domain of the coagulation factor. Size exclusion chromatography and fluorescence anisotropy studies showed that OPLS interfered with the aggregation of BDDrFVIII. Immunogenicity of free- vs BDDrFVIII-OPLS complex was evaluated in a murine model of hemophilia A. Animals administered subcutaneous (sc) injections of BDDrFVIII-OPLS had lower neutralizing titers compared with animals treated with BDDrFVIII alone. Based on these studies, we hypothesize that specific molecular interactions between OPLS and BDDrFVIII may improve the stability and reduce the immunogenicity of BDDrFVIII formulations.

In-Vitro Stability of B-Domain Deleted Recombinant Factor VIII in Syringe-Based Continuous Infusion Devices.

Continuous infusion (CI) factor VIII (FVIII) replacement is commonly used for serious bleeds in patients with FVIII deficiency. Clinicians lack stability information for Refacto®, a B-domain deleted recombinant FVIII (BDDrFVIII), when it is diluted or stored in CI devices for extended time periods. We studied BDDrFVIII to determine its concentration- and time-dependent stability and sterility when stored (reconstituted; reconstituted then diluted with normal saline) at ambient temperature in syringe-based CI devices (CADD-MicroTM; Baxter ColleagueTM). Three replicates of BDDrFVIII 125unit/mL and 25unit/mL admixtures were admixed aseptically then placed in CI devices that operated continuously for 48 hours. Samples (0.5ml) were obtained from control solutions (stored in the manufacturer's glass vial) or expressed from the distal end of tubing at Hour −0.25 (priming volume), 0, 1, 2, 4, 8, 12, 24 and 48. Samples were stored at −70C until assayed for Factor VIII activity using a 1-stage automated assay and Refacto® [chromogenic equivalent] Standard. Results of FVIII assays for each trio of replicates were averaged. BDDrFVIII admixtures were considered stable if they retained ≥80% baseline (control) FVIII values. Recoveries for BDDrFVIII 125unit/mL admixtures remained stable and sterile for 48 hours when stored in the manufacturer's glass vial, Baxter ColleagueTM or CADD MicroTM devices, sufficient for clinical use (Table). BDDrFVIII, when diluted to 25unit/mL, remained sterile but not stable when stored in Baxter ColleagueTM or CADD MicroTM devices, and is not recommended for CI in clinical settings. Loss of FVIII activity in BDDrFVIII 25unit/mL admixtures is thought to be due to binding of BDDrFVIII to device components.%FVIII Activity of BDDrFVIII Stored in Infusion DevicesHr 0Hr 1Hr 2Hr 4Hr 12Hr 24Hr 48Mfr Glass Vial (Control)92.59390.790.893.27680.7CADD-Micro 125unit/ml808486.378.386.38081.7Baxter Colleague 125unit/ml86.379748577.78182.3CADD-Micro 25unit/ml65.761.356.35957.559.756.3Baxter Colleague 25unit/ml18.719.33324.3272727.3

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.

Meta‐analysis of observational studies of full‐length and B‐domain‐deleted factor VIII for prophylaxis – a standard statistical approach

Summary. Meta‐analyses of observational studies have become increasingly common to support evidence‐based clinical decisions. We analyzed currently available clinical and pharmacokinetic studies of full‐length factor VIII (FL‐FVIII) vs B‐domain deleted recombinant factor VIII (BDD‐rFVIII) to investigate possible differences in clinical efficacy. A standard approach to observational study meta‐analysis was used as recommended by the Meta‐analysis Of Observational Studies in Epidemiology (MOOSE) consensus group. Data from included studies were combined using a random effects model to accommodate between‐study heterogeneity. A multivariate Poisson regression analysis was used to calculate the incidence rate ratio for bleeding. Justification for the appropriate use of this statistical approach is given. The meta‐analysis suggested reduced haemostatic efficacy during prophylaxis and shortened half‐life of BDD‐rFVIII as compared with FL‐FVIII. This analysis was rigoroulsy conducted using well‐accepted statistical methodology and presents the most comprehensive evidence‐based assessment currently available on risk factors for breakthrough bleeding under factor VIII prophylaxis. Our conclusions have been strengthened by subsequently introduced prescribing information and regulatory action for BDD‐rFVIII.

B-domain deleted recombinant factor VIII formulation and stability

B-domain deleted recombinant factor VIII (BDDrFVIII) is a deletion form of human coagulation factor VIII. A lyophilized formulation of highly purified BDDrFVIII has been developed that does not require the use of blood-derived products such as human serum albumin (HSA). By avoiding the use of blood-derived products, the BDDrFVIII formulation minimizes the risk of transmitting blood-borne pathogens that may be present in plasma-derived factor VIII or in other recombinant factor VIII products that contain HSA in their formulation. Upon reconstitution with saline (4 mL), the composition of the reconstituted product (62.5 to 250 IU/mL BDDrFVIII) is 18 mg/mL sodium chloride, 3.0 mg/mL sucrose, 1.5 mg/mL l-histidine, 0.25 mg/mL calcium chloride dihydrate, and 0.1 mg/mL polysorbate 80. The optimal combination of these excipients in the lyophilized BDDrFVIII formulation provides long-term stability, as measured by a variety of analytical methods. The formulation preserves factor VIII activity of lyophilized BDDrFVIII during storage for at least 24 months at 8 °C, and for up to 6 months at room temperature (25 °C). The reconstituted product retains its factor VIII potency for at least 100 hours at 25 °C, which would allow it to be continuously administered via an infusion pump, assuming the product is handled under aseptic conditions.

Clinical evaluation of B-domain deleted recombinant factor VIII in previously untreated patients

The safety and efficacy of B-domain deleted recombinant factor VIII (BDDrFVIII) were evaluated in previously untreated patients (PUPs) with severe hemophilia A. In an open-label multicenter study, 101 PUPs received routine prophylactic and/or on-demand treatment with BDDrFVIII, including treatment related to surgery for 50 exposure days for up to 5 years. The pharmacokinetic measurements (ie, elimination half-life and in vivo mean recovery) assessed at baseline and 12 months were stable for BDDrFVIII over time. A total of 1,362 hemorrhages occurred. Ninety-two percent ( 1,258 1,362 ) of bleeding episodes resolved after three infusions or fewer. Of the 2,375 infusions rated by investigators, 93% ( 2,215 2,375 ) were rated as providing an “excellent” or “good” response. Twenty-seven patients received routine prophylactic treatment, which significantly reduced breakthrough bleeding episodes by twofold when compared with patients who were treated on-demand. Administration in conjunction with 40 surgical procedures showed no adverse effects, and the overall assessment was either “very useful” or “useful.” The mean dose was 56 IU/kg for routine primary prophylaxis and 53 IU/kg for on-demand therapy for bleeding episodes in patients who were assessed to be inhibitor-free at the time of infusion. Thirty-two percent of patients developed inhibitors. Of these, 16 patients were high responders (peak titer ≥ 5 Bethesda units [BU]). The inhibitor risk was comparable to that seen with full-length recombinant products. BDDrFVIII was found to be effective, safe, and well tolerated.

Clinical evaluation of B-domain deleted recombinant factor VIII in previously treated patients

The pharmacokinetics, safety, and efficacy of B-domain deleted recombinant factor VIII (BDDrFVIII) were evaluated in patients with hemophilia A. In an initial 12-month study with subsequent yearly extensions over a 5-year period, 113 previously treated patients (PTPs) received on-demand and/or prophylactic treatment with BDDrFVIII, including treatment during surgery, if required. Half-life and recovery of factor VIII activity remained unchanged over the study period. The mean elimination half-life was 10.5 ± 2.6 hours at baseline and 10.4 ± 3.3 hours at month 12. A total of 7,310 hemorrhages occurred for patients who received on-demand treatment, with 71% resolving after a single infusion. Of the 11,655 rated infusions given for hemorrhages, 92% were rated by investigators and patients as providing an “excellent” or “good” response. These results are consistent with efficacy data from other trials using recombinant factor VIII products. During the prophylactic period, 12% of patients experienced no bleeding episodes, and 17% of the patients had no on-demand treatment. The mean dose was 28 IU/kg for prophylactic treatment and 30 IU/kg for on-demand treatment. The efficacy of administering BDDrFVIII in conjunction with surgery was assessed to be “very useful” or “useful” in all cases. Few adverse events were reported, and only one patient developed inhibitors to factor VIII activity. The results show that BDDrFVIII provides a safe and effective treatment of hemophilia A when given as on-demand therapy, in routine or intermittent prophylaxis, or during surgery.

Structural and functional characterization of B-domain deleted recombinant factor VIII

A new high-purity recombinant factor VIII preparation has been developed for the treatment of hemophilia A. Structurally, this factor VIII preparation, B-domain deleted recombinant factor VIII (BDDrFVIII), differs from other recombinant and plasma-derived factor VIII preparations in that most of the B-domain has been deleted. To ensure that BDDrFVIII contains the requisite structural and functional features, it has been subjected to detailed biochemical and biophysical characterization in comparison to the plasma-derived form of factor VIII. Laboratory studies have shown that the primary, secondary, and tertiary structures of BDDrFVIII and the posttranslational modifications are similar to those of the [80 + 90]-kd form of plasma-derived factor VIII. In addition, BDDrFVIII has full biologic activity compared with full-length factor VIII preparations.

Measurement of factor VIII activity of B-domain deleted recombinant factor VIII

The factor VIII activity of B-domain deleted recombinant factor VIII (BDDrFVIII) measured by activated partial thromboplastin time (APTT)-based one-stage assays is approximately 50% of the activity obtained by the chromogenic assay. Similar results have been reported for the two licensed full-length recombinant factor VIII products. In view of these findings, comprehensive studies have been undertaken to find the cause of the assay differences. Only the phospholipid reagent, used as a platelet substitute in the one-stage assay, proved to be crucial for explaining the assay difference. When platelet-rich plasma was used as the source of phospholipid in the one-stage assay, the factor VIII activity assay results correlated well with those measured by the chromogenic assay. Similar results were obtained when the platelets were replaced by liposomes prepared using platelet factor 3 (PF3) as a model that has a low content (5% to 10%) of phosphatidylserine (PS). In contrast, the use of liposomes with 20% to 30% PS, as in the crude lipid extracts used in ordinary APTT reagents, resulted in underestimation of the factor VIII activity. Antigen measurements using an enzyme-linked immunosorbent assay (ELISA) method demonstrated a good correlation between the antigen and chromogenic activity, but not always between antigen and one-stage activity results. Based on these findings and the clinical data, it can be concluded that the chromogenic assay most accurately measures the functional activity of BDDrFVIII. However, modifications of the one-stage assay, such as the use of a product-specific standard or development of a PF3-like phospholipid reagent, could address the observed assay discrepancies.

Viral safety of B-domain deleted recombinant factor VIII

The possible transmission of blood-borne pathogens has been the impetus behind the development of recombinant products formulated in the absence of human-derived components. The viral safety of Chinese hamster ovary (CHO)-cell-based pharmaceuticals is well established. Over 100 million infusions have been administered without a single known incident of CHO-related viral transmission. The manufacturing process for B-domain deleted recombinant factor VIII (BDDrFVIII) builds on this safety record by using a state-of-the-art multitiered approach to viral safety. This approach includes: (1) extensive testing of the CHO cells used to produce BDDrFVIII; (2) routine viral monitoring of the cell culture production process; (3) a purification process in which a specific viral inactivation procedure has been included; (4) a final formulation that does not incorporate human albumin as the stabilizer; and (5) a thorough validation of the viral inactivation and removal capacity of the purification process. This multifaceted viral safety program offers the hemophilia community a factor VIII product with an exceptional degree of viral safety.