Bioengineered molecules for the management of haemophilia: Promise and remaining challenges.

Recombinant DNA technology has led to accelerating introduction of novel therapeutics for the treatment of haemophilia. This technology has driven the development of recombinant clotting factors, extended half-life clotting factors, alternative biologics to promote haemostasis and enabled the launch of the gene therapy era for haemophilia. At the core of this technology is the ability to study the structure and function of the native molecules and to apply rational bioengineering to overcome limitations to the existing therapies. Through the study of haemophilia-causing mutations, site-directed mutagenesis, detailed structural models and a wide repertoire of animal models, new bioengineering strategies are helping overcome some of the remaining limitations and challenges of traditional clotting factor concentrates. Some of these bioengineering strategies are now being partnered with improvements in vectorology leading to the first wave of successful gene therapy approaches. This study will review past and present bioengineered molecules that are advancing care for haemophilia as well as novel approaches that promise to continue to improve care and outcomes for patients with haemophilia.

Recombinant factor VIII Fc fusion protein for immune tolerance induction in patients with severe haemophilia A with inhibitors-A retrospective analysis.

INTRODUCTION: Immune tolerance induction (ITI) is the gold standard for eradication of factor VIII inhibitors in severe haemophilia A; however, it usually requires treatment for extended periods with associated high burden on patients and healthcare resources. AIM: Review outcomes of ITI with recombinant factor VIII Fc fusion protein (rFVIIIFc) in patients with severe haemophilia A and high-titre inhibitors. METHODS: Multicentre retrospective chart review of severe haemophilia A patients treated with rFVIIIFc for ITI. RESULTS: Of 19 patients, 7 were first-time ITI and 12 were rescue ITI. Of 7 first-time patients, 6 had at least 1 high-risk feature for ITI failure. Four of 7 first-time patients were tolerized in a median of 7.8 months. The remaining 3 patients continue on rFVIIIFc ITI. Of 12 rescue patients, 7 initially achieved a negative Bethesda titre (≤0.6) in a median of 3.3 months, 1 had a decrease in Bethesda titre and continues on rFVIIIFc ITI and 4 have not demonstrated a decrease in Bethesda titre. Of these 4, 3 continue on rFVIIIFc ITI and 1 switched to bypass therapy alone. Two initially responsive patients transitioned to other factors due to recurrence. Overall, 16 of 19 patients remain on rFVIIIFc (prophylaxis or ITI). For those still undergoing ITI, longer follow-up is needed to determine final outcomes. No adverse events reported. CONCLUSIONS: Recombinant factor VIII Fc fusion protein demonstrated rapid time to tolerization in high-risk first-time ITI patients. For rescue ITI, rFVIIIFc showed therapeutic benefit in some patients who previously failed ITI with other products. These findings highlight the need to further evaluate the use of rFVIIIFc for ITI.

Association of peak factor VIII levels and area under the curve with bleeding in patients with haemophilia A on every third day pharmacokinetic-guided prophylaxis.

INTRODUCTION: We previously showed that pharmacokinetic-guided prophylaxis (PKP) allows the dosing interval to be extended while maintaining a specific trough level. However, the associations of peak factor VIII (FVIII) levels and area under the curve (AUC) with breakthrough bleeding have not been investigated. AIM: The aim of this study was to analyse data from the PKP arm to determine whether peak FVIII levels, AUC and time with FVIII levels in a haemostatically effective range are independent predictors of bleeding during prophylaxis. METHODS: Post hoc analysis of the association of FVIII levels and AUC with annualized bleeding rate in 34 patients on PKP. RESULTS: During 1 year of PKP, 131 bleeding episodes occurred in 24/34 patients. Average peak FVIII levels ranged from 24 to 168 IU dL(-1) , with higher values associated with a decreased risk for all bleeding (joint and non-joint; P < 0.01) and joint bleeding (P < 0.01). Following rFVIII infusion, median percent of time spent with FVIII levels >20 IU dL(-1) was 22%; median AUC was 1363. Both values were significantly associated with a lower ABR when targeting a 1% trough at 72 h. CONCLUSION: When PKP was administered every third day, higher peak FVIII levels, higher AUC and more time spent per week with FVIII levels >20 IU dL(-1) provided increased protection from joint and non-joint bleeding. These data highlight the potential impact of variability in individual pharmacokinetic and bleeding risk and support the need for high peak levels and AUC in some patients treated every third day. The findings do not necessarily apply to alternate-day or other prophylactic dosing regimens.

Extending the pharmacokinetic half-life of coagulation factors by fusion to recombinant albumin.

The prophylactic treatment of haemophilia B and the management of haemophilia A or B with inhibitors demand frequent administrations of coagulation factors due to the suboptimal half-lives of the products commercially available and currently in use, e.g. recombinant factor IX (rFIX) and recombinant factor VIIa (rFVIIa), respectively. The extension of the half-lives of rFIX and rFVIIa could allow for longer intervals between infusions and could thereby improve adherence and clinical outcomes and may improve quality of life. Albumin fusion is one of a number of different techniques currently being examined to prolong the half-life of rFIX and rFVIIa. Results from a phase I clinical trial demonstrated that the recombinant fusion protein linking FIX to albumin (rIX-FP) has a five-times longer half-life than rFIX, and preclinical studies with the recombinant fusion protein linking FVIIa to albumin (rVIIa-FP) suggest that rVIIa-FP possesses a significantly extended half-life versus rFVIIa. In this review, we describe albumin fusion technology and examine the recent progress in the development of rIX-FP and rVIIa-FP.

Outcomes of mentored, grant-funded fellowship training in haemostasis /thrombosis: findings from a nested case-control survey study.

Successful strategies by which to effectively recruit and retain academic subspecialists in benign haematology have not been established. To evaluate the effectiveness of a grant-funded, mentored fellowship with respect to retention and early career goals in haemostasis/thrombosis, we sought to compare outcomes for graduates of a grant-funded, mentored fellowship training programme in haemostasis/thrombosis [the National Hemophilia Foundation (NHF)-Baxter Clinical Fellowship Award] during conventional haematology/oncology fellowship training (cases), vs. their training peers who were graduates of conventional haematology/oncology fellowship training alone (controls), via a nested case-control survey study. Survey response rate was 85% (11/13) for cases and 90% (9/10) for controls. All respondents had pursued careers in academic haematology/oncology. Median (range) percent time spent in benign haematology postfellowship was 98% (70-100%) for cases vs. 0% (0-20%) for controls. Time spent in research was significantly greater among cases than controls (median 80% [range: 42-90%] vs. 55% [10-80%], respectively; P = 0.01). By years 3-4 postfellowship, median annual number of peer-reviewed publications was higher for cases than controls (3.5 vs. 1.0; P = 0.01). Cases were also more successful in grant funding (including K-awards). These data suggest that a grant-funded, mentored fellowship training programme in haemostasis/thrombosis may be superior to conventional haematology/oncology fellowship training alone with respect to outcomes of retention in clinical care/research, early-career grant funding and publication productivity.

Healthcare resource utilization among haemophilia A patients in the United States.

Advances in therapy have improved life expectancy and quality of life of patients with haemophilia A. Due to the chronic and complex management of this disease, particularly, the development of inhibitors, little is known about their health resource utilization in the real-life setting over time. The aim was to assess the distribution and trend of healthcare resource utilization among US haemophilia A patients with and without inhibitors. The MarketScan® Database, was queried to identify individuals with ≥1 year continuous enrolment, two medical diagnoses of haemophilia A and claims for factor VIII or bypassing agent (to infer inhibitor status) during 2001-2007. Haemophilia-related cost was estimated from inpatient, outpatient and pharmacy claims. Annual cost differences were assessed by age and over a 4-year period for those with continuous enrolment. Among 51 million covered lives, 1044 haemophilia patients were identified, of whom 981 (94%; mean age = 21.2 years) did not have an inhibitor. The median haemophilia-related cost for these patients was $63,935 per patient per year. When normalized by weight, annual cost was stable (no statistically significant differences) among 312 non-inhibitor patients (mean age = 21.8 years) with 4-year continuous data. While there was a wide distribution of haemophilia-related cost among the 63 individuals with an inhibitor (mean age = 15.4 years), only 0.6% of the total haemophilia patients had costs exceeding $1 million per patient per year. This study indicated that most haemophilia A patients were inhibitor-free with relatively stable annual costs over time. There was a wide distribution of haemophilia-related cost for inhibitor patients, while the proportion of patients who incurred extreme high cost was low.

Functional factor VIII made with von Willebrand factor at high levels in transgenic milk.

BACKGROUND: Current manufacturing methods for recombinant human factor VIII (rFVIII) within mammalian cell cultures are inefficient, hampering the production of sufficient amounts for affordable, worldwide treatment of hemophilia A. However, rFVIII has been expressed at very high levels by the transgenic mammary glands of mice, rabbits, sheep, and pigs. Unfortunately, it is secreted into milk with low specific activity, owing in part to the labile, heterodimeric structure that results from furin processing of its B domain. OBJECTIVES: To express biologically active rFVIII in the milk of transgenic mice through targeted bioengineering. METHODS: Transgenic mice were made with a mammary-specific FVIII gene (226/N6) bioengineered for efficient expression and stability, encoding a protein containing a B domain with no furin cleavage sites. 226/N6 was expressed with and without von Willebrand factor (VWF). 226/N6 was evaluated by ELISA, SDS-PAGE, western blot, and one-stage and two-stage clotting assays. The hemostatic activity of immunoaffinity-enriched 226/N6 was studied in vivo by infusion into hemophilia A knockout mice. RESULTS AND CONCLUSIONS: With or without coexpression of VWF, 226/N6 was secreted into milk as a biologically active single-chain molecule that retained high specific activity, similar to therapeutic-grade FVIII. 226/N6 had > 450-fold higher IU mL(-1) than previously reported in cell culture for rFVIII. 226/N6 exhibited similar binding to plasma-derived VWF as therapeutic-grade rFVIII, and intravenous infusion of transgenic 226/N6 corrected the bleeding phenotype of hemophilia A mice. This provides proof-of-principle for the study of expression of 226/N6 and perhaps other single-chain bioengineered rFVIIIs in the milk of transgenic livestock.

Most factor VIII B domain missense mutations are unlikely to be causative mutations for severe hemophilia A: implications for genotyping.

BACKGROUND & OBJECTIVE: The factor VIII (FVIII) B domain shares very little amino acid homology with other known proteins and is not directly necessary for procoagulant activity. Despite this, missense mutations within the B domain have been reported in patients with hemophilia A. Given that the B domain is dispensable for secretion and function of FVIII, we hypothesized that these mutations should not be causative of hemophilia A in these patients. METHODS: Plasmid vectors containing B domain missense mutations that were reported to be associated with moderate/severe hemophilia A (T751S, D826E, V993L, H1047Y, T1353A, N1441K, L1462P, E1579D, A1591S, P1641L and S1669L) were analyzed for their effect on synthesis and secretion compared with FVIII wild-type (WT) following transient transfection into COS-1 and CHO cells in vitro. Further, H1047Y, N1441K and E1579D mutants were expressed in vivo in a hemophilia A mouse model by hydrodynamic tail-vein injection. RESULTS: FVIII activity and antigen levels for all mutants expressed into the conditioned media of COS-1 and CHO cells were similar to FVIII WT. Also, plasma expression of these mutants was similar to FVIII WT in hemophilia A mice. An in vivo tail clip bleeding assay also demonstrated that blood loss from hemophilia A mice expressing FVIII WT, H1047Y, N1441K and E1579D was similar. CONCLUSIONS: We conclude that most missense mutations within the FVIII B domain would be unlikely to lead to severe hemophilia A and that the majority of such missense mutations represent polymorphisms or non-pathologic mutations.

Prophylactic therapy with Fibrogammin P is associated with a decreased incidence of bleeding episodes: a retrospective study.

SUMMARY: Congenital factor XIII (FXIII) deficiency is an extremely rare, yet potentially life-threatening, bleeding disorder, with a 30% rate of spontaneous intracranial haemorrhage. Routine prophylactic management is recommended for all individuals with clinically relevant (FXIII) deficiency and for all symptomatic individuals with congenital factor deficiency. Fibrogammin P is a purified, pasteurized concentrate of FXIII that appears to carry negligible risk of viral transmission, unlike other unprocessed products containing FXIII. An ongoing Phase II/III study of Fibrogammin P in patients with congenital FXIII deficiency is being conducted to evaluate the prophylactic efficacy and long-term safety of this product. Using retrospective chart review data from subjects enrolled in the Phase II/III study, the current analysis was designed to compare spontaneous bleed-event rates prior to and after the initiation of Fibrogammin P prophylaxis. Seven subjects were evaluable for comparison, having received no other prophylactic FXIII-containing product during the 24 months prior to study entry. The mean annual number of spontaneous bleeds was 2.5 events per year prior to Fibrogammin P prophylaxis and 0.2 events per year during Fibrogammin P prophylaxis (P = 0.01). Patients reported no severe bleeds during Fibrogammin P therapy. This small sample supports a consistent and clinically meaningful reduction in spontaneous bleeding with prophylactic use of Fibrogammin P.

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.

Experience with a third generation recombinant factor VIII concentrate (Advate) for immune tolerance induction in patients with haemophilia A.

The development of an inhibitor represents one of the most challenging complications in patients with haemophilia A. Optimal management is immune tolerance induction (ITI), typically through the administration of high doses of factor VIII (FVIII) concentrate. Among 12 patients who underwent ITI using Advate, a third-generation recombinant FVIII product that is free of animal and human protein additives, tolerance was achieved in nine (75%), including seven of 10 patients (70%) with high-titre inhibitors. ITI is ongoing in two patients and not yet successful; immune tolerance failed in the third patient. The median time to success was 4.0 months for group as a whole and for patients with high-titre inhibitors. Treatment was well tolerated, and no adverse events were observed. Advate was found to be equivalent to other FVIII products with regard to both ITI success rates and the incidence of adverse effects when used in these immune tolerance regimens.

Interlaboratory agreement in the monitoring of unfractionated heparin using the anti-factor Xa-correlated activated partial thromboplastin time.

BACKGROUND: In an effort to improve interlaboratory agreement in the monitoring of unfractionated heparin (UFH), the College of American Pathologists (CAP) recommends that the therapeutic range of the activated partial thromboplastin time (APTT) be defined in each laboratory through correlation with a direct measure of heparin activity such as the factor Xa inhibition assay. Whether and to what extent this approach enhances the interlaboratory agreement of UFH monitoring has not been reported. OBJECTIVES: We conducted a cross-validation study among four CAP-accredited coagulation laboratories to compare the interlaboratory agreement of the anti-FXa-correlated APTT with that of the traditional 1.5-2.5 times the midpoint of normal (1.5-2.5:control) method for defining the therapeutic APTT range. PATIENTS AND METHODS: APTT and FXa inhibition assays were performed in each laboratory on plasma samples from 44 inpatients receiving UFH. RESULTS: Using the anti-FXa-correlation method, there was agreement among all four laboratories as to whether a sample was subtherapeutic, therapeutic or supratherapeutic in seven (16%) patient samples. In contrast, consensus was achieved in 23 (52%) samples when the 1.5-2.5:control method was employed. CONCLUSIONS: The anti-FXa-correlation method does not appear to enhance interlaboratory agreement in UFH monitoring as compared with the traditional 1.5-2.5:control method. Adoption of the anti-FXa-correlation method produces considerable disparity in UFH dosing decisions among different centers, although the clinical impact of this disparity is not known.

Mild/moderate haemophilia A: new insights into molecular mechanisms and inhibitor development.

In mild/moderate haemophilia A (MHA) patients, many factor VIII (FVIII) gene defects, mainly missense mutations, have been identified and greatly improved the understanding of the structure and function of FVIII molecule. Characterization of the molecular mechanisms involved in MHA has helped to identify regions critical for proper FVIII biosynthesis, thrombin activation, intramolecular stability as well as binding regions for important intermolecular interactions with von Willebrand factor, factor IXa and the phospholipid surface. Some missense mutations were also recognized as contributing factors to inhibitor development in MHA, in parallel to acquired factors such as inflammatory state or intensity of treatment. Treatment of MHA with inhibitor patients raises questions on how best to stop or prevent bleeding episodes and eradicate the inhibitor. Longitudinal data collection is currently being conducted in France and Belgium to enhance our knowledge in this field and to further help make treatment decision. The description of mutations in MHA finally contributed to the identification of epitopes involved in the immune response to FVIII. In some patients, the epitope specificity of inhibitor antibodies recognizing normal exogenous FVIII alone and not patient ('self') FVIII was described. This distinguished epitope specificity could also be demonstrated at the T-cell clonal level. One might expect that these molecular studies will have a major impact on development of new FVIII products in the future.

Establishment of embryonic stem cells secreting human factor VIII for cell-based treatment of hemophilia A.

BACKGROUND: Hemophilia A is an X-chromosome-linked recessive bleeding disorder resulting from an F8 gene abnormality. Although various gene therapies have been attempted with the aim of eliminating the need for factor VIII replacement therapy, obstacles to their clinical application remain. OBJECTIVES: We evaluated whether embryonic stem (ES) cells with a tetracycline-inducible system could secrete human FVIII. METHODS AND RESULTS: We found that embryoid bodies (EBs) developed under conditions promoting liver differentiation efficiently secreted human FVIII after doxycycline induction. Moreover, use of a B-domain variant F8 cDNA (226aa/N6) dramatically enhanced FVIII secretion. Sorting based on green fluorescent protein (GFP)-brachyury (Bry) and c-kit revealed that GFP-Bry(+)/c-kit(+) cells during EB differentiation with serum contain an endoderm progenitor population. When GFP-Bry(+)/c-kit(+) cells were cultured under the liver cell-promoting conditions, these cells secreted FVIII more efficiently than other populations tested. CONCLUSION: Our findings suggest the potential for future development of an effective ES cell-based approach to treating hemophilia A.