New high-technology products for the treatment of haemophilia

Gene therapy for hemophilias: the end of phenotypic testing or the start of a new era?

: Hemophilia comprises two distinct genetic disorders caused by missing or defective clotting factor VIII (hemophilia A) or clotting factor IX (hemophilia B). The management of these conditions has been for long based on replacement therapies, but emerging evidence garnered from recent landmark studies suggests that a promising avenue toward routine use of gene therapy is clearly progressing forward, thus generating unavoidable consequences on laboratory hemostasis, especially as pertaining to phenotypic testing. Although it seems likely that widespread use of gene therapy will be associated with a relative decrease of hemostasis tests requests in this patient population due to the relatively stable effect of transgene delivery and persistent production of endogenous clotting factor, some important aspects persuade us that conventional laboratory diagnostics, especially encompassing activated partial thromboplastin time, as well as one-stage and two-stage clotting factor assays, will not be completely voided in the gene therapy era. In particular, phenotypic testing will remain essential for excluding acquired or sporadic cases of hemophilia, for identifying and titrating factor inhibitors, as well as for defining and monitoring the long-term therapeutic effectiveness of gene transfection in hemophiliacs.

Central venous access devices in patients with hemophilia

Hemophilia is a hereditary disorder in which the major clinical manifestation is bleeding into the joints, muscles, internal organs and the CNS, often without any obvious trauma. Bleeding can be fatal as in the case of CNS hemorrhage, or severely debilitating following repeated bleeding into joints that results in crippling arthritis. Treatment for hemophilia includes the intravenous administration of clotting factor concentrates to replace the missing or defective protein. Venous access is therefore critical to the treatment of hemophilia and the prevention of complications due to bleeding. According to the US Centers for Disease Control and Prevention, approximately half of patients less than 16 years of age and one-third of all patients with hemophilia receive regular prophylactic injections of clotting factor concentrates. Prophylaxis, or the regular scheduled administration of antihemophilic factor concentrate, is effective in preventing bleeding. Among those patients with severe disease, in the absence of prophylaxis, approximately 13 bleeds, including nine joint hemorrhages, occur annually. In contrast, when prophylaxis is administered, the annual number of total and joint bleeds decreases to five and three, respectively. One of the major barriers to the more wide-spread use of prophylaxis is venous access. While peripheral venipuncture remains the first choice for venous access, central venous access devices are frequently used to facilitate repeated and/or urgent administration of clotting factor concentrates. The advantages of central venous access devices are well recognized in certain treatment regimens such as prophylaxis and immune tolerance therapy, as well as certain patient groups such as young children in whom venipuncture is often difficult and traumatic, and adults with scarred veins. Central venous access devices also allow earlier commencement of both home treatment and prophylaxis. The goal of this review is to discuss the different types of central venous access devices and their role in the management of hemophilia to provide practitioners that care for patients with hemophilia with the necessary information to make sound therapeutic recommendations to their patients.

A review of current methods for assessing hemostasis in vivo and introduction to a potential alternative approach

A validated method for assessing hemostasis in vivo is critical for testing the hemostatic efficacy of therapeutic agents in preclinical animal models and in patients with inherited bleeding disorders, such as von Willebrand disease (VWD) and hemophilia A, or with acquired bleeding disorders such as those resulting from medications or disease processes. In this review, we discuss current methods for assessing hemostasis in vivo and the associated challenges. We also present ARFI-Monitored Hemostatic Challenge; a new, potentially alternate method for in vivo hemostasis monitoring that is in development by our group.

Animal models of hemophilia

The X-linked bleeding disorder hemophilia is caused by mutations in coagulation factor VIII (hemophilia A) or factor IX (hemophilia B). Unless prophylactic treatment is provided, patients with severe disease (less than 1% clotting activity) typically experience frequent spontaneous bleeds. Current treatment is largely based on intravenous infusion of recombinant or plasma-derived coagulation factor concentrate. More effective factor products are being developed. Moreover, gene therapies for sustained correction of hemophilia are showing much promise in preclinical studies and in clinical trials. These advances in molecular medicine heavily depend on availability of well-characterized small and large animal models of hemophilia, primarily hemophilia mice and dogs. Experiments in these animals represent important early and intermediate steps of translational research aimed at development of better and safer treatments for hemophilia, such a protein and gene therapies or immune tolerance protocols. While murine models are excellent for studies of large groups of animals using genetically defined strains, canine models are important for testing scale-up and for long-term follow-up as well as for studies that require larger blood volumes.

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.

Multimerization of peptide mimotopes for blocking of factor VIII neutralizing antibodies

About 30 % of patients with severe hemophilia A develop neutralizing antibodies (inhibitors) to coagulation factor VIII (FVIII) upon treatment with exogenous factor preparations. Two peptides, C6 (NPVENMMDRDSQ) and H10 (QSPWQTWFTRAL), that mimic putative inhibitor epitopes (mimotopes), were previously selected by phage display screening of plasma samples from patients with inhibitors. Synthetic peptide mimotopes inhibited IgG binding to FVIII (IC(50): 30-50 microM). This effect was increased by an equimolar combination of both mimotopes. Mimotopes were fused to the C-terminal multimerization domain of the C4bp alpha-chain and expressed as multimers in 293T cells. Multimerized mimotopes showed improved binding to anti-FVIII IgG and prolonged in vitro half-life relative to synthetic peptides. The two mimotopes were combined in heteromultimers by co-transfection of 293T cells with respective vectors, resulting in bi-specific molecules that almost completely blocked polyclonal antibody binding to FVIII (IC(50): 2-3 microM). This strategy is capable of functionally improving synthetic peptides by multimerization and could provide a basis for novel therapeutic approaches for patients with hemophilia A and inhibitors.

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.

Efficient factor VIII affinity purification using a small synthetic ligand

BACKGROUND

Hemophilia A is currently treated by infusions of the coagulation factor (F) VIII, of which production and purification remain a challenging task. Current purification procedures using immunoaffinity chromatography are cumbersome, expensive, and suffer from the instability of the applied antibody ligands, which elute along with the product and contaminate it. Recently, FVIII was purified using octapeptide ligands, but their use is limited due to the low resistance to proteases.

OBJECTIVE

Our goal was to develop and evaluate a novel ligand for FVIII purification, overcoming the drawbacks of current procedures.

METHODS

Peptide ligands were screened for binding of (125)I-plasma-derived-FVIII (pdFVIII) in a microbead assay. A selected ligand-coated Toyopearl resin was then used for pdFVIII purification from cell-conditioned Delbucco's modified Eagle's medium (DMEM) containing fetal bovine serum. The proteolytic stability of ligand was measured by incubating with human serum and proteinase K, and its cytotoxicity towards human OV-MZ-6 cells was assayed.

RESULTS

A high-affinity octapeptidic FVIII ligand was modified into the small, highly stable and non-toxic peptidomimetic ligand L4 by rational and combinatorial design without affecting its affinity for FVIII. Using ligand L4-coated Toyopearl resin, pdFVIII was isolated from cell-conditioned medium with high purity and 89% column retention after elution with a mild buffer containing 0.6 m NaCl at pH 6.8.

CONCLUSIONS

Ligand L4 offers a valuable alternative to antibody-based procedures for laboratory and industrial production. Its synthesis by established solid-phase procedures is straightforward and considerably cheaper than the biotechnological production of antibodies, and safety concerns associated with the use of biological material are overcome.

Enhanced functional recombinant factor VII production by HEK 293 cells stably transfected with VKORC1 where the gamma-carboxylase inhibitor calumenin is stably suppressed by shRNA transfection

INTRODUCTION

Recombinant members of the vitamin K-dependent protein family (factors IX and VII and protein C) have become important pharmaceuticals in treatment of bleeding disorders and sepsis. However, because the in vivo gamma-carboxylation system in stable cell lines used for transfection has a limited capacity of post translational gamma-carboxylation, the recovery of fully gamma-carboxylated and functional proteins is low.

MATERIALS AND METHODS

In this work we have engineered recombinant factor VII producing HEK 293 cells to stably overexpress VKORC1, the reduced vitamin K gamma-carboxylase cofactor and in addition stably silenced the gamma-carboxylase inhibitory protein calumenin.

RESULTS AND CONCLUSIONS

Stable cell lines transfected with only a factor VII cDNA had a 9% production of functional recombinant factor VII. On the other hand, these recombinant factor VII producing cells when engineered to overexpress VKORC1 and having calumenin stably suppressed more than 80% by shRNA expression, produced 68% functional factor VII. The technology presented should be applicable to all vertebrae members of the vitamin K-dependent protein family and should lower the production cost of the clinically used factors VII, IX and protein C.

Over-expression of Hsp70 in BHK-21 cells engineered to produce recombinant factor VIII promotes resistance to apoptosis and enhances secretion

Production of coagulation factor VIII (FVIII) by recombinant cell lines is limited by its failure to reach or maintain the native conformation in the endoplasmic reticulum. This results in significant cytoplasmic degradation and/or aggregation of the misfolded product. The molecular chaperone Hsp70 was overexpressed in an attempt to increase the recombinant FVIII (rFVIII) secretion. The characteristics of increased Hsp70 expression were investigated by comparing a clone of BHK-21 cells expressing rFVIII (rBHK-21(host)) to a chaperone clone derived by transfection of the host clone with human Hsp70 (rBHK-21(Hsp70)) in small-scale batch cell cultures. To aid this investigation a number of fluorescence based cellular apoptosis assays were developed and optimized. These assays demonstrated sub-populations of rBHK-21(host) cells that were apoptotic in nature and were identified prior to the loss in plasma membrane integrity. Dual staining for intracellular rFVIII and caspase-3 activation showed a reduction in intracellular rFVIII in rBHK-21(host) cells that correlated with a significant increase in active caspase-3, suggesting that apoptosis was a factor limiting rFVIII secretion. In sharp contrast there was more intracellular rFVIII and less active caspase-3 in rBHK-21(Hsp70) cell cultures. Moreover when grown in batch culture, rBHK-21(Hsp70) cells released rFVIII of higher specific activity (active FVIII protein/total FVIII protein), suggesting improved product quality. Thus, increased expression of HSP70 led to an increased yield of a secreted recombinant protein by inhibition of apoptosis and promoting proper conformational maturation of rFVIII in sub-optimal bioreactor conditions.

Hemorrhagic subcutaneous nodules: an initial clinical sign of hemophilia A

A 9-month-old boy presented with multiple hemorrhagic subcutaneous nodules after treatment with oral antibiotics for an upper respiratory tract infection. Excessive bleeding after an incisional biopsy led to a diagnosis of hemophilia A. While this was an unexpected presentation of hemophilia, screening laboratory coagulation studies prior to biopsy would have revealed the etiology. Similar presentations should alert dermatologists to suspect an underlying coagulation defect prior to biopsy, thus averting bleeding complications.

Can activated recombinant factor VII be used to postpone the exposure of infants to factor VIII until after 2 years of age?

Two retrospective studies have suggested that exposure to factor VIII (FVIII) in early infancy is associated with an increased risk of FVIII inhibitor development. We prospectively studied 11 infants who needed replacement therapy for bleeding episodes before the age of 2 years. They received activated recombinant factor VII (rFVIIa) concentrate on demand, with the intention of postponing their first exposure to FVIII after 2 years of age. Thirty-three bleeding episodes were treated with 154 doses of rFVIIa with no evidence of adverse effect. Bleeding was controlled in 27 of 33 episodes. Mouth bleeds were most difficult to treat. The use of rFVIIa allowed postponement of the use of FVIII for a mean of 5.5 months (median 4, range 0-12) but in only three of 11 children could be the first exposure to factor postponed after the age of 2 years. With this modest effect of rFVIIa in postponing the first exposure to FVIII, more convincing evidence for the benefit of such a postponement will have to be demonstrated before rFVIIa could be recommended for this indication.

The promise and challenges of bioengineered recombinant clotting factors

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