The future of recombinant coagulation factors

Advances and challenges in the purification of recombinant coagulation factors: A review

Hemostasis is a complex process for the cessation of bleeding from an injured blood vessel, involving the interplay of 12 coagulation factors in the coagulation cascade with activated blood platelets and the vessel wall. Hence, the coagulation factors are important to control hemorrhage. However, the low abundance of many coagulation factors in human plasma proteins limited their production in therapeutic drugs and their clinical applications. With the development of modern biotechnology, commercially manufactured recombinant coagulation factors became available as hemostatic therapeutics, emerging a huge potential in pharmaceutical manufacturing market. Unlike antibodies, whose standard operation unit or platform purification processes in the industrial-scale downstream processing has been well-established, the complexity in post-translational modification and differences in structures of the coagulation factors posed specific challenges with respect to the downstream processing, which have long been limiting their industrial-scale production. This review presents a comprehensive overview of the technological development of commercially manufactured recombinant coagulation factors, with emphasis on their advances and challenges in the separation and purification processes. Firstly, the licensed products of the plasma derived and recombinant coagulation factors are summarized. Then, typical recombinant coagulation factors, i.e. factors VII, VIII and IX, are introduced with detailed discussion on their preparative separation procedures for both the licensed products of industrial-scale and the experimental cases of laboratory-scale. Finally, perspectives and challenges in the future development of the purification technology of recombinant coagulation factors are highlighted to provide new insight into the design of cost-effective purification processes of recombinant coagulation factors.

Autologous bone marrow-derived MSCs engineered to express oFVIII-FLAG engraft in adult sheep and produce an effective increase in plasma FVIII levels

Introduction

Hemophilia A (HA) is the most common X-linked bleeding disorder, occurring in 1 in 5,000 live male births and affecting >1 million individuals worldwide. Although advances in protein-based HA therapeutics have improved health outcomes, current standard-of-care requires infusion 2-3 times per week for life, and 30% of patients develop inhibitors, significantly increasing morbidity and mortality. There are thus unmet medical needs requiring novel approaches to treat HA.

Methods

We tested, in a highly translational large animal (sheep) model, whether the unique immunological and biological properties of autologous bone marrow (BM)-derived mesenchymal stromal cells (MSCs) could enable them to serve as cellular delivery vehicles to provide long-term expression of FVIII, avoiding the need for frequent infusions.

Results

We show that autologous BM-MSCs can be isolated, transduced with a lentivector to produce high levels of ovine (o)FVIII, extensively expanded, and transplanted into adult animals safely. The transplanted cells engraft in multiple organs, and they stably produce and secrete sufficient quantities of FVIII to yield elevated plasma FVIII levels for at least 15 weeks.

Discussion

These studies thus highlight the promise of cellular-based gene delivery approaches for treating HA.

Past, present and future of hemophilia: a narrative review

Over the past forty years the availability of coagulation factor replacement therapy has greatly contributed to the improved care of people with hemophilia. Following the blood-borne viral infections in the late 1970s and early 1980, caused by coagulation factor concentrates manufactured using non-virally inactivated pooled plasma, the need for safer treatment became crucial to the hemophilia community. The introduction of virus inactivated plasma-derived coagulation factors and then of recombinant products has revolutionized the care of these people. These therapeutic weapons have improved their quality of life and that of their families and permitted home treatment, i.e., factor replacement therapy at regular intervals in order to prevent both bleeding and the resultant joint damage (i.e. primary prophylaxis). Accordingly, a near normal lifestyle and life-expectancy have been achieved. The main current problem in hemophilia is the onset of alloantibodies inactivating the infused coagulation factor, even though immune tolerance regimens based on long-term daily injections of large dosages of coagulation factors are able to eradicate inhibitors in approximately two-thirds of affected patients. In addition availability of products that bypass the intrinsic coagulation defects have dramatically improved the management of this complication. The major challenges of current treatment regimens, such the short half life of hemophilia therapeutics with need for frequent intravenous injections, encourage the current efforts to produce coagulation factors with more prolonged bioavailability. Finally, intensive research is devoted to gene transfer therapy, the only way to ultimately obtain cure in hemophilia.

Knowledge and therapeutic gaps: a public health problem in the rare coagulation disorders population

Rare coagulation disorders (RCDs) present a considerable and multifaceted public health risk. Although inherited RCDs affect a minor segment of any local healthcare delivery system, their global impact is major and highlight the challenges of delivering healthcare services to any rare disease population. These include but are not limited to: (1) a general lack of knowledge about and familiarity with the genetic and clinical implications of the disorder among affected patients, and both urgent and specialty care providers; (2) the potential for preventable morbidity and mortality related to delayed diagnosis and treatment; (3) the lack of safe and effective therapies; and (4) minimal research activity to establish and improve standards of care. A multiagency national partnership has established an approach to address these problems through development of a clinical, genetic, and treatment-related web-based data-collection tool that will: (1) generate a reliable, sufficient knowledge base for these disorders; (2) facilitate new product licensure through subject identification and access to comparative historical treatment data; and (3) serve as an effective tool for outcomes research and post-licensure product surveillance. To maximize impact, this database is being harmonized with a European data-collection effort. Database development and harmonization is in progress. A resource library was completed and disseminated to major national and international bleeding disorder websites to provide state-of-the-art patient and provider education on each RCD. We believe that this model is effective and adaptable to other rare conditions.

The case for wider use of recombinant factor VIII concentrates

The introduction of clotting factor concentrates led to major advances in hemophilia care. Rather than simply providing an alternative to plasma-derived concentrates, the introduction in the 1990s of recombinant concentrates added value to replacement therapy particularly with respect to prophylaxis and immune-tolerance induction. While the safety of plasma-derived concentrates has improved considerably, these concentrates may still pose an infectious risk through as-yet unknown pathogens and poor impurity constituent characterization. Recombinant concentrates are increasingly used because of their benefits in pathogen safety, convenience and the potential for unfettered supply. Yet worldwide they remain accessible only to a limited number of patients due to fear of the potential for inhibitor development, overestimation of their costs and underestimation of their benefits. This article reviews the characteristics and properties of recombinant FVIII concentrates to help physicians and patient representatives promote the right of access of patients to the safest products.

Comparison of factor VIII transgenes bioengineered for improved expression in gene therapy of hemophilia A

Successful gene therapy of hemophilia A depends on the sustained expression of therapeutic levels of factor VIII (fVIII). Because of mRNA instability, interactions with resident endoplasmic reticulum (ER) chaperones, and the requirement for carbohydrate-facilitated transport from the ER to the Golgi apparatus, fVIII is expressed at much lower levels from mammalian cells than other proteins of similar size and complexity. A number of bioengineered forms of B domain-deleted (BDD) human fVIII have been generated and shown to have enhanced expression. Previously, we demonstrated that recombinant BDD porcine fVIII exhibits high-level expression due to specific sequence elements that increase biosynthesis via enhanced posttranslational transit through the secretory pathway. In the current study, high-expression recombinant fVIII constructs were compared directly in order to determine the relative expression of the various bioengineered fVIII transgenes. The data demonstrate that BDD porcine fVIII expression is superior to that of any of the human fVIII variant constructs tested. Mean fVIII expression of 18 units/10(6) cells/24 hr was observed from HEK-293 cells expressing a single copy of the porcine fVIII transgene, which was 36- to 225-fold greater than that of any human fVIII transgene tested. Furthermore, greater than 10-fold higher expression was observed in human cells transduced with BDD porcine fVIII versus BDD human fVIII-encoding lentiviral vectors, even at low proviral copy numbers, supporting its use over other human fVIII variants in future hemophilia A gene therapy clinical trials.

Delivery of factor VIII gene into skeletal muscle cells using lentiviral vector

PURPOSE

This study was designed to investigate whether transduction of lentiviral vectors (LV) carrying human coagulation factor VIII (hFVIII) cDNA into skeletal muscle could increase circulating hFVIII concentrations.

MATERIALS AND METHODS

A LV containing bacterial LacZ gene as a control or human FVIII gene was intramuscularly administered into the thigh muscle of 5 weeks old Sparague-Dawley rats. The plasma human FVIII concentration and neutralizing anti-FVIII antibodies were measured for up to 12 weeks in these experimental animals.

RESULTS

The plasma human FVIII levels in the rats injected with LV carrying FVIII cDNA peaked at post-injection 1st week (5.19 +/- 0.14 ng/mL vs. 0.21 +/- 0.05 ng/mL in control rats , p < 0.05). Elevated hFVIII concentrations were maintained for 4 weeks (2.52 +/- 0.83 ng/mL vs. 0.17 +/- 0.08 ng/mL in control rats, p < 0.05) after a single intramuscular injection. In the Bethesda assay, neutralizing antibodies for FVIII protein were detected only in FVIII-LV injected rats by the 10th week, but not in control rats.

CONCLUSION

This study suggested that a single administration of an advanced generation LV carrying the human FVIII cDNA resulted in elevation of FVIII level in immune competent rats, and that this gene transfer approach to the skeletal muscle could be an effective tool in treatment of hemophilia A.

Ethical considerations in clinical investigation: exploring relevance in haemophilia research

Painful controversy has so far been largely absent from the history of haemophilia-related clinical research. However, the investigative methods now needed to realize evidence-based clinical practice, therapeutic advance, and a progressive standard of care for patients worldwide will be accompanied by the potential for ethical dilemma and transgression. From the current vantage point, three primary ethical issues merit special consideration: (i) the therapeutic misconception inherent to all clinical research and the randomized trial in particular; (ii) high risk and potentially non-beneficial novel technology research in children; and (iii) a collaborative partnership approach to research in the developing world. This study will focus on a discussion of each of these, drawing from the research ethics literature to offer a potential template for future deliberations in clinical trial design.

Development of a Peptidomimetic Ligand for Efficient Isolation and Purification of Factor VIII via Affinity Chromatography

Hemophilia A, one of the most severe bleeding disorders, results from an inherited deficiency of factor VIII (FVIII) function. Treatment by injection of FVIII has been a common procedure for decades. Nevertheless, the production and purification of FVIII remains a challenging task. Current procedures using immunoaffinity chromatography are expensive and suffer from the instability of the applied antibody ligands, which elute along with the product and contaminate it. Recently, FVIII was purified by use of octapeptide ligands, but their low protease-resistance limits their application. We here report the systematic rational and combinatorial optimization procedure that allowed us to transfer the octapeptide ligands into a small peptidomimetic. This compound is the smallest ligand known for separation of such a large protein (330 kDa). It not only binds and purifies FVIII with high efficiency but also is stable, protease-resistant, and cheap to produce in preparative scale. Hence it offers a valuable alternative to antibody-based purification procedures.

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.

Ethical issues in haemophilia

Ethical issues surrounding both the lack of global access to care as well as the implementation of advancing technologies, continue to challenge the international haemophilia community. Haemophilia is not given the priority it deserves in most developing countries. Given the heavy burdens of sickness and disease and severe resource constraints, it may not be possible to provide effective treatment to all who suffer from the various 'orphan' diseases. Nevertheless, through joint efforts, some package of effective interventions can be deployed for a significant number of those who are afflicted with 'orphan' diseases. With cost-effective utilization of limited resources, a national standard of care is possible and affordable. Gene-based diagnosis carries attendant ethical concerns whether for clinical testing or for research purposes, even as the list of its potential benefits to the haemophilia community grows rapidly. As large-scale genetic sequencing becomes quicker and cheaper, moving from the research to the clinic, we will face decisions about the implementation of prenatal, neonatal and other screening programs. Such debates will require input from not just the health care professionals but from all stakeholders in the haemophilia community. Finally, long-term therapeutic success gene transfer in small and large animal models raises the question of when and in which patient population the novel therapeutic approach should first be studied in humans with haemophilia. Although gene therapy represents a worthy goal, the central question for the haemophilia community should be whether it wishes to volunteer itself as a model for a much broader set of innovations.

The protein structure and effect of factor VIII

Factor VIII (FVIII) is a key component of the fluid phase of the blood coagulation system. The proteases efficiently cleave FVIII at three sites, two within the heavy and one within the light chain resulting in alteration of its covalent structure and conformation and yielding the active cofactor, FVIIIa. FVIIIa is a trimer composed of A1, A2 and A3-C1-C2 subunits. The role of FVIIIa is to markedly increase the catalytic efficiency of factor IXa in the activation of factor X. Variants of these factors frequently also lead to severe bleeding disorders.

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.

A Glu113Ala mutation within a factor VIII Ca2+-binding site enhances cofactor interactions in factor Xase

We recently identified an acidic-rich segment in the A1 domain of factor VIII (residues 110-126) that functions in the coordination of Ca(2+), an ion necessary for cofactor activity [Wakabayashi et al. (2004) J. Biol. Chem. 279, 12677-12684]. Mutagenesis studies showed that replacement of residue Glu113 with Ala (E113A) yielded a factor VIII point mutant possessing increased specific activity as determined by a one-stage clotting assay. Mutagenesis at this site suggested that substitution with relatively small, nonpolar residues was well tolerated, whereas replacement with a number of polar or charged residues appeared detrimental to activity. Ala substitution resulted in the greatest enhancement, yielding an approximately 2-fold increased specific activity. Time course experiments following reaction with thrombin revealed similar rates of activation and inactivation of E113A as observed for the wild type. Results from factor Xa generation assays showed minimal differences in kinetic parameters and factor IXa affinity for E113A and wild-type factor VIIIa when run in the presence of synthetic phospholipid vesicles, whereas factor VIIIa E113A displayed an approximately 4-fold greater affinity for factor IXa compared with factor VIIIa wild type in reactions run on the platelet membrane surface. This latter effect may be attributed, in part, to a 2-fold increased affinity of factor VIIIa E113A for the platelet membrane. Considering that low levels of factors VIIIa and IXa are generated during clotting in plasma, the increased cofactor specific activity observed for E113A factor VIII may result from its enhanced affinity for factor IXa on the physiological membrane.

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.

Haemophilia A: from mutation analysis to new therapies

Haemophilia is caused by hundreds of different mutations and manifests itself in clinical conditions of varying severity. Despite being inherited in monogenic form, the clinical features of haemophilia can be influenced by other genetic factors, thereby confounding the boundary between monogenic and multifactorial disease. Unlike sufferers of other genetic diseases, haemophiliacs can be treated successfully by intravenous substitution of coagulation factors. Haemophilia is also the most attractive model for developing gene-therapy protocols, as the normal life expectancy of haemophiliacs allows the side effects of gene therapy, as well as its efficiency, to be monitored over long periods.

Mutating factor VIII: lessons from structure to function

Factor VIII, a metal ion-dependent heterodimer, circulates in complex with von Willebrand factor. At sites of vessel wall damage, this procofactor is activated to factor VIIIa by limited proteolysis and assembles onto an anionic phospholipid surface in complex with factor IXa to form the intrinsic factor Xase; an enzyme complex that efficiently converts factor X to factor Xa during the propagation phase of coagulation. Factor Xase activity is down-regulated by mechanisms that include self-dampening by dissociation of a critical factor VIIIa subunit and proteolytic inactivation by the activated protein C pathway. Recent studies identify putative metal ion coordination sites as well as ligands involved in the catabolism of the activated and procofactor forms of the protein. Our knowledge of these multiple intra- and inter-molecular interactions has been facilitated by the application of naturally occurring and site-directed mutations to study factor VIII structure and function. In this review, we document important and novel contributions following this line of investigation.

Therapy for haemophilia: recent advances and goals for the future

In the 20th century, haemophilia evolved from a life-threatening, crippling disease to one for which the prognosis is excellent and many patients lead normal, productive lives. Although dramatic achievements in the treatment of haemophilia have occurred, the current therapies have significant drawbacks. Among these is the relatively high incidence of inhibitor development, the requirement for frequent intravenous infusions to prevent bleeding complications, the lack of effective treatment for established joint disease, and the high cost of treatment. The future goal of haemophilia treatment first and foremost is curing this genetic condition via gene therapy. As this goal is likely many years away, improvements in the current factor products in order to reduce the development of inhibitors and to reduce the frequency of therapy are more immediately achievable goals. Finally, improving the treatment of bleeding complications, particularly in inhibitor patients, and developing novel adjunctive therapies for the management of joint disease are also important goals for the near future. This review will discuss in detail the cu-rrent and future goals of haemophilia therapy.

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.

New Perspectives in Hemophilia Treatment

A variety of factor concentrates are currently available for replacement therapy for patients with hemophilia. These differ by several parameters, including source (pooled from pooled blood vs recombinant), purity, pathogen inactivation, and by the presence or absence of extraneous proteins such as albumin. The choice of replacement product reflects both safety issues of pathogen transmission or inhibitor development, and personal preferences of the patient and the physician. In general, currently available products are viral pathogen-free, although there is debate about the risk of transmission of parvovirus B19 and prion pathogens. Because of this very small risk, recombinant factor is the treatment of choice in previously untreated patients. In addition, a subset of concentrates contain factor that is activated during manufacture, yielding activated products that can be used in the treatment of patients with inhibitors. Such activated products, especially recombinant factor VIIa (rFVIIa), have also acquired several off-label indications in the management of bleeding in non-hemophiliac patients. The management of hemophilia patients with inhibitors is an ongoing challenge. Immune tolerance induction using a desensitization technique is successful in up to 90% of patients with alloantibodies against factor VIII, with greatest success seen in patients with low titer inhibitors who are treated soon after detection of an alloantibody and in whom treatment includes administration of immunosuppression along with repeated infusions of high titer concentrates. Such therapy is less successful in patients with factor IX alloantibodies. Non-hemophiliac patients with acquired inhibitors represent a unique patient population that requires special management. These patients have a mortality rate that approaches 25% because of the association of acquired inhibitors with severe bleeding complications, occurrence in a largely elderly population, and the frequent presence of an underlying, often serious, primary medical condition. Treatment consists of immunosuppression with steroids, chemotherapy, or intravenous immunoglobulin. Recent studies using rituximab for selective B-cell depletion in these patients have been very promising, although prospective controlled studies have not yet been performed. Finally, although hemophilia A and B appear to be ideal diseases to target with gene therapy approaches, the promise of this therapy remains to be realized.

New high-technology products for the treatment of haemophilia

This review will focus on new technologies in development that promise to lead to further advances in haemophilia therapeutics. There has been continued interest in the bioengineering of recombinant factor VIII (rFVIII) and factor IX (rFIX) with improved function to overcome some of the limitations in current treatment, the high costs of therapy and to increase availability to a broader world haemophilia population. Bioengineered forms of rFVIII, rFIX or alternative haemostatic molecules may ultimately have an impact on improving the efficacy of therapeutic strategies for the haemophilias by improving biosynthesis and secretion, functional activity, half-life and immunogenicity. Preventing and suppressing inhibitors to factor (F) VIII remain a challenge for both clinicians and scientists. Recent experiments have shown that it is possible to obtain anti-idiotypic antibodies with a number of desirable properties: (i) strong binding avidity to FVIII inhibitors; (ii) neutralization of inhibitory activity both in vitro and in vivo; (iii) cross-reactivity with antibodies from unrelated patients, and (iv) no interference with FVIII function. An alternative, although complementary approach, makes use of peptides derived from filamentous-phage random libraries. Mimotopes of FVIII can be obtained, which bind to the paratope of inhibitory activity and neutralize their activity both in vitro and in vivo. In this paper, we review advanced genetic strategies for haemophilia therapy. Until recently the traditional concept for gene transfer of inherited and acquired haematological diseases has been focused on how best to obtain stable insertion of a cDNA into a target-cell genome, allowing expression of a therapeutic protein. However, as gene-transfer vector systems continue to improve, the requirement for regulated gene transcription and hence regulated protein expression will become more critical. Inappropriate protein expression levels or expression of transferred cDNAs in non-intended cell types or tissues may lead to target-cell toxicity or activation of unwanted host immune responses. Regulated protein expression requires that the transferred gene be transferred with its own regulatory cassette that allows for gene transcription and translation approaching that of the normal gene in its endogenous context. New molecular techniques, in particular the use of RNA molecules, now allow for transcription of corrective genes that mimic the normal state.

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.

Bioengineering of coagulation factor VIII for improved secretion

Factor VIII (FVIII) functions as a cofactor within the intrinsic pathway of blood coagulation. Quantitative or qualitative deficiencies of FVIII result in the inherited bleeding disorder hemophilia A. Expression of FVIII (domain structure A1-A2-B-A3-C1-C2) in heterologous mammalian systems is 2 to 3 orders of magnitude less efficient compared with other proteins of similar size compromising recombinant FVIII production and gene therapy strategies. FVIII expression is limited by unstable mRNA, interaction with endoplasmic reticulum (ER) chaperones, and a requirement for facilitated ER to Golgi transport through interaction with the mannose-binding lectin LMAN1. Bioengineering strategies can overcome each of these limitations. B-domain-deleted (BDD)-FVIII yields higher mRNA levels, and targeted point mutations within the A1 domain reduce interaction with the ER chaperone immunoglobulin-binding protein. In order to increase ER to Golgi transport we engineered several asparagine-linked oligosaccharides within a short B-domain spacer within BDD-FVIII. A bioengineered FVIII incorporating all of these elements was secreted 15- to 25-fold more efficiently than full-length FVIII both in vitro and in vivo. FVIII bioengineered for improved secretion will significantly increase potential for success in gene therapy strategies for hemophilia A as well as improve recombinant FVIII production in cell culture manufacturing or transgenic animals.

Blood Products for Hemophilia

Hemophilia is an inherited bleeding disorder, which in its severe form is characterized by recurrent hemarthrosis and internal bleeding. In the absence of effective treatment the prognosis is poor, but the development of blood products in the last few decades has transformed the outlook, and patients can now live essentially normal lives. Treatment options vary around the world, with cryoprecipitate still the mainstay of therapy in many developing countries. Many patients were infected with hepatitis and/or HIV through the use of coagulation factor concentrates before the introduction of physical methods of viral inactivation in the mid-1980s. In more affluent countries, the debate in recent years has focused on the relative merits of plasma versus recombinant products. Coagulation factor concentrates are expensive, and cost-benefit and quality-of-life studies will assume an increasing importance in guiding the selection of products. Looking to the future, genetic engineering offers the potential to create coagulation factors with enhanced properties, such as reduced immunogenicity and prolonged half-life. Transgenic animals are a potential source of therapeutic materials. Several trials of gene therapy for hemophilia are already underway.

Hemophilia: treatment options in the twenty-first century

In the last three decades, hemophilia has moved from the status of a neglected and often fatal hereditary disorder to that of a fully defined group of molecular-pathological entities for which safe and effective treatment is available. Hemophilia is likely to be the first widespread severe genetic condition to be cured by gene therapy in the third millennium. In the socio-economic arena it remains a challenge to humanity to know that four-fifths of the world's hemophiliacs still receive no treatment at all. Production of factor (F) VIII and IX in the milk of transgenic farmyard animals could provide a source of less expensive replacement therapy for developing countries. Affordable gene transfer will be the ultimate solution for hemophilia in the third world as in the first. Thus it may be confidently predicted that the early new millennium will see an end to this ancient scourge.