Hemophilia: New Protein Therapeutics

Associated comorbidities, healthcare utilization & mortality in hospitalized patients with haemophilia in the United States: Contemporary nationally representative estimates

INTRODUCTION

Current in-hospital burden and healthcare utilization patterns for persons with haemophilia (PWH) A and B, including both children (ages < 18 years) and adults (ages ≥ 18 years), in the United States (US) are lacking.

AIM

To evaluate healthcare utilization, the prevalence of comorbidities, and mortality in hospitalized paediatric and adult PWH using a contemporary nationally representative cohort.

METHODS

Hospitalizations of PWH either as the primary reason for admission (principal diagnosis) or one of all listed diagnoses were identified using ICD-10 codes from the 2017 Nationwide Inpatient Sample (NIS), the largest publicly available all-payer inpatient discharge database in the US. Sampling weights were applied to generate nationally representative estimates.

RESULTS

The contemporary cohort included 10,555 hospitalizations (paediatrics, 18.3%; adults, 81.7%) among PWH as one-of-all listed diagnoses (n = 1465 as principal diagnosis). Median age (interquartile range) was 46 (24-66) years overall; adults, 54 (35-70) years and paediatric, 4 (1-11). The most common comorbidities in adults were hypertension (33.4%), hyperlipidaemia (23.6%), and diabetes (21.1%). In children, hemarthrosis (11.4%), contusions (9.6%), and central line infections (9.3%) were the most common. The overall mortality rate was 2.3%. Median hospital charges per haemophilia admission were $52,616 ($24,303-$135,814) compared to $26,841 ($12,969-$54,568) for all-cause admissions in NIS.

CONCLUSION

Bleeding and catheter-related infections are the significant reasons for paediatric haemophilia admissions. Adult haemophilia admissions tend to be associated with age-related comorbidities. Costs for haemophilia-related hospitalizations are higher than the national average for all-cause hospitalizations.

Evaluating the psychometric properties of the EQ-5D-5L and SF-6D among patients with haemophilia

OBJECTIVE

The aim of this study was to evaluate the psychometric properties of the EQ-5D-5L and SF-6D, and to compare their performance among patients living with haemophilia in China.

METHODS

A total of 875 Chinese patients completed the EQ-5D-5L, SF-6D, and Haem-A-QoL questionnaires. Construct validity of the EQ-5D-5L and SF-6D dimensions and indices was assessed by testing hypotheses relating these measures to Haem-A-QoL and clinical measures. The Spearman correlation coefficient was used to assess convergent validity, and one-way analysis of variance (F statistic) was used to assess the known-groups validity (discriminatory power). The agreement between EQ-5D-5L and SF-6D indices was assessed using the intraclass correlation coefficient (ICC) and the Bland-Altman plot.

RESULTS

Both the EQ-5D-5L and SF-6D indices showed acceptable ceiling and floor effects. As hypothesised, both EQ-5D-5L and SF-6D were significantly correlated with Haem-A-QoL (both dimensions and overall score). EQ-5D-5L and SF-6D indices as well as EQ-VAS differentiated patients are known to differ in severity of haemophilia, bleeding status, disabling levels, and comorbidity. The F statistics in the known-groups comparisons suggested that the EQ-5D-5L was slightly more discriminative than the SF-6D. ICC (0.41) and Bland-Altman plot confirmed that the agreement between the EQ-5D-5L and SF-6D indices was poor.

CONCLUSION

Both EQ-5D-5L and SF-6D showed satisfactory construct validity in the measurement of the HRQoL among patients with haemophilia. However, the two instruments may not be used interchangeably in this patient population due to their poor agreement and differing discriminatory power.

FVIII proteins with a modified immunodominant T-cell epitope exhibit reduced immunogenicity and normal FVIII activity

Factor VIII (FVIII)-neutralizing antibodies (inhibitors) are a serious complication in hemophilia A (HA). The peptide FVIII2194-2213 contains an immunodominant HLA-DRA*01-DRB1*01:01 (DRB1*01:01)-restricted epitope recognized by CD4+ T-effector cells from HA subjects. The aim of this study was to identify amino acid substitutions to deimmunize this epitope while retaining procoagulant function and expression levels comparable to those of wild-type (WT) FVIII proteins. The shortest DRB1*01:01-binding peptide was FVIII2194-2205, and residues important for affinity were identified as F2196, M2199, A2201, and S2204. T-cell proliferation experiments with Ala-substituted FVIII2194-2205 peptides identified F2196A as a substitution that abrogated proliferation of clones specific for the WT sequence. T-cell clones that were stimulated by recombinant WT-FVIII-C2 (rWT-FVIII-C2) protein did not proliferate when cultured with rFVIII-C2-F2196A, indicating the immunogenic peptide includes a naturally processed T-cell epitope. Additional amino acid substitutions at F2196 and M2199 were evaluated by peptide-MHC class II (MHCII)-binding assays, T-cell proliferation assays, epitope prediction algorithms, and sequence homologies. Six B-domain-deleted (BDD)-FVIII proteins with substitutions F2196A, F2196L, F2196K, M2199A, M2199W, or M2199R were produced. Proliferation of T-cell clones and polyclonal lines in response to rBDD-FVIII-F2196K and rBDD-FVIII-M2199A was reduced compared with responses to WT-BDD-FVIII. The BDD-FVIII-F2196K sequence modification appears to be the most promising sequence variant tested here, due to its effectiveness at eliminating DRB1*01:01-restricted immunogenicity, low potential immunogenicity in the context of other MHCII alleles, expression level comparable to WT-BDD-FVIII, and retained procoagulant activity. These results provide proof of principle for the design of less immunogenic FVIII proteins targeted to specific subsets of HA patients.

Binding of Factor VIII to Lipid Nanodiscs Increases its Clotting Function in a Mouse Model of Hemophilia A

Background

Hemophilia A is a congenital bleeding disorder caused by defective or deficient factor VIII (FVIII). The active form of FVIII is the co-factor for the serine protease factor IXa (FIXa) in the membrane-bound intrinsic tenase (FVIIIa-FIXa) complex. The assembly of the FVIIIa-FIXa complex on the activated platelet surface is critical for successful blood clotting.

Objectives

To characterize the role of lipid nanodiscs (ND) for on FVIII function in vivo and test the lipid ND as a delivery system for FVIII. To evaluate the potential of binding recombinant FVIII to ND as improved treatment for Hemophilia A.

Methods

Recombinant porcine FVIII (rpFVIII) was expressed and characterized in solution, and when bound to ND. The rpFVIII, ND and rpFVIII-ND complexes were characterized via transmission electron microscopy. Functional studies were carried out using aPTT tests and time resolved tail snip studies of hemophilic mice.

Results

Functional rpFVIII was successfully assembled on lipid ND. When injected in hemophilic mice, the rpFVIII-ND complexes showed a pronounced pro-coagulant effect, which was stronger than that of rpFVIII alone. While injection of the ND alone showed a pro-coagulant effect this effect was not additive, implying that the rpFVIII-ND complexes have a synergistic effect on the clotting process in hemophilic mice.

Conclusions

Binding of rpFVIII to ND prior to its injection in hemophilic mice significantly improves the therapeutic function of the protein. This represents a meaningful step towards a new approach to modulate blood coagulation at the membrane-bound FVIII level and the assembly of the intrinsic tenase complex.

Dimeric Organization of Blood Coagulation Factor VIII bound to Lipid Nanotubes

Membrane-bound Factor VIII (FVIII) has a critical function in blood coagulation as the pro-cofactor to the serine-protease Factor IXa (FIXa) in the FVIIIa-FIXa complex assembled on the activated platelet membrane. Defects or deficiency of FVIII cause Hemophilia A, a mild to severe bleeding disorder. Despite existing crystal structures for FVIII, its membrane-bound organization has not been resolved. Here we present the dimeric FVIII membrane-bound structure when bound to lipid nanotubes, as determined by cryo-electron microscopy. By combining the structural information obtained from helical reconstruction and single particle subtomogram averaging at intermediate resolution (15-20 Å), we show unambiguously that FVIII forms dimers on lipid nanotubes. We also demonstrate that the organization of the FVIII membrane-bound domains is consistently different from the crystal structure in solution. The presented results are a critical step towards understanding the mechanism of the FVIIIa-FIXa complex assembly on the activated platelet surface in the propagation phase of blood coagulation.

Hemostatic agents of broad applicability produced by selective tuning of factor Xa zymogenicity

There is a clinical need to develop safe therapeutic strategies to mitigate bleeding. Previously, we found that a novel zymogen-like factor Xa variant (FXa-I16L) was effective in correcting the coagulation defect in hemophilic mice. Here we expand the mutational framework to tune the FX(a) zymogen-like state. Alteration of FXa zymogenicity yields variants (V17M, I16L, I16M, V17T, V17S, and I16T) with a wide range (≤1000-fold) of reduced function toward physiologic substrates and inhibitors. The extent of zymogen-like character, including resistance to antithrombin III, correlates well with plasma half-life (<2 minutes to >4 hours). Importantly, biologic function, including that of the most zymogen-like variant (FXa-I16T), was greatly enhanced when bound to FVa membranes. This resulted in improvement of clotting times and thrombin generation in hemophilic plasma. The FXa variants were remarkably effective in mouse injury models. In these systems, the data show that the more active the protease, the more difficult it is to overcome the protective mechanism of circulating inhibitors to achieve a therapeutic benefit. Depending on the treatment situation, the more zymogen-like variants (V17S and I16T) were most useful when given before injury whereas variants exhibiting greater activity but shorter half-lives (I16L and I16M) were most effective when administered after injury. This new class of FXa variants provides a useful and flexible platform for selectively bioengineering biologic function and half-life to target different clinical bleeding scenarios.

Factor VIII organisation on nanodiscs with different lipid composition

Nanodiscs (ND) are lipid bilayer membrane patches held by amphiphilic scaffolding proteins (MSP) of ~10 nm in diameter. Nanodiscs have been developed as lipid nanoplatforms for structural and functional studies of membrane and membrane associated proteins. Their size and monodispersity have rendered them unique for electron microscopy (EM) and single particle analysis studies of proteins and complexes either spanning or associated to the ND membrane. Binding of blood coagulation factors and complexes, such as the Factor VIII (FVIII) and the Factor VIIIa - Factor IXa (intrinsic tenase) complex to the negatively charged activated platelet membrane is required for normal haemostasis. In this study we present our work on optimising ND, specifically designed to bind FVIII at close to physiological conditions. The binding of FVIII to the negatively charged ND rich in phosphatidylserine (PS) was followed by electron microscopy at three different PS compositions and two different membrane scaffolding protein (MSP1D1) to lipid ratios. Our results show that the ND with highest PS content (80 %) and lowest MSP1D1 to lipid ratio (1:47) are the most suitable for structure determination of the membrane-bound FVIII by single particle EM. Our preliminary FVIII 3D reconstruction as bound to PS containing ND demonstrates the suitability of the optimised ND for structural studies by EM. Further assembly of the activated FVIII form (FVIIIa) and the whole FVIIIa-FIXa complex on ND, followed by EM and single particle reconstruction will help to identify the protein-protein and protein-membrane interfaces critical for the intrinsic tenase complex assembly and function.

AAV liver expression of FIX-Padua prevents and eradicates FIX inhibitor without increasing thrombogenicity in hemophilia B dogs and mice

Emerging successful clinical data on gene therapy using adeno-associated viral (AAV) vector for hemophilia B (HB) showed that the risk of cellular immune response to vector capsid is clearly dose dependent. To decrease the vector dose, we explored AAV-8 (1-3 × 10(12) vg/kg) encoding a hyperfunctional factor IX (FIX-Padua, arginine 338 to leucine) in FIX inhibitor-prone HB dogs. Two naïve HB dogs showed sustained expression of FIX-Padua with an 8- to 12-fold increased specific activity reaching 25% to 40% activity without antibody formation to FIX. A third dog with preexisting FIX inhibitors exhibited a transient anamnestic response (5 Bethesda units) at 2 weeks after vector delivery following by spontaneous eradication of the antibody to FIX by day 70. In this dog, sustained FIX expression reached ∼200% and 30% of activity and antigen levels, respectively. Immune tolerance was confirmed in all dogs after challenges with plasma-derived FIX concentrate. Shortening of the clotting times and lack of bleeding episodes support the phenotypic correction of the severe phenotype, with no clinical or laboratory evidence of risk of thrombosis. Provocative studies in mice showed that FIX-Padua exhibits similar immunogenicity and thrombogenicity compared with FIX wild type. Collectively, these data support the potential translation of gene-based strategies using FIX-Padua for HB.

Helical organization of blood coagulation factor VIII on lipid nanotubes

Cryo-electron microscopy (Cryo-EM)(1) is a powerful approach to investigate the functional structure of proteins and complexes in a hydrated state and membrane environment(2). Coagulation Factor VIII (FVIII)(3) is a multi-domain blood plasma glycoprotein. Defect or deficiency of FVIII is the cause for Hemophilia type A - a severe bleeding disorder. Upon proteolytic activation, FVIII binds to the serine protease Factor IXa on the negatively charged platelet membrane, which is critical for normal blood clotting(4). Despite the pivotal role FVIII plays in coagulation, structural information for its membrane-bound state is incomplete(5). Recombinant FVIII concentrate is the most effective drug against Hemophilia type A and commercially available FVIII can be expressed as human or porcine, both forming functional complexes with human Factor IXa(6,7). In this study we present a combination of Cryo-electron microscopy (Cryo-EM), lipid nanotechnology and structure analysis applied to resolve the membrane-bound structure of two highly homologous FVIII forms: human and porcine. The methodology developed in our laboratory to helically organize the two functional recombinant FVIII forms on negatively charged lipid nanotubes (LNT) is described. The representative results demonstrate that our approach is sufficiently sensitive to define the differences in the helical organization between the two highly homologous in sequence (86% sequence identity) proteins. Detailed protocols for the helical organization, Cryo-EM and electron tomography (ET) data acquisition are given. The two-dimensional (2D) and three-dimensional (3D) structure analysis applied to obtain the 3D reconstructions of human and porcine FVIII-LNT is discussed. The presented human and porcine FVIII-LNT structures show the potential of the proposed methodology to calculate the functional, membrane-bound organization of blood coagulation Factor VIII at high resolution.

Phase I study of BAY 94-9027, a PEGylated B-domain-deleted recombinant factor VIII with an extended half-life, in subjects with hemophilia A

BACKGROUND

BAY 94-9027 is a B-domain-deleted recombinant factor VIII (rFVIII) with site-specific attachment of poly(ethylene glycol) that has shown an extended half-life in animal models of hemophilia.

OBJECTIVES

To assess the pharmacokinetics and safety of BAY 94-9027 after single and repeated administration in subjects with severe hemophilia A.

PATIENTS/METHODS

This 8-week, prospective, multicenter, open-label, phase I trial was conducted in 14 subjects aged 21–58 years with FVIII of < 1%, ≥ 150 days of exposure to FVIII, and no history of FVIII inhibitors. After a ≥ 3-day washout, subjects received a single dose of sucrose-formulated rFVIII (rFVIII-FS) (cohort 1 [n = 7], 25 IU kg−1; cohort 2 [n = 7], 50 IU kg−1) for a 48-h pharmacokinetic (PK) study. After another ≥ 3-day washout, cohort 1 received twice-weekly BAY 94-9027 at 25 IU kg−1 (16 doses), and cohort 2 received once-weekly BAY 94-9027 at 60 IU kg−1 (nine doses). A 168-h PK study was performed after the first and last BAY 94-9027 doses.

RESULTS

BAY 94-9027 showed equivalent recovery and an improved PK profile vs. rFVIII-FS, with a half-life of ~ 19 h (vs. ~ 13.0 h for rFVIII-FS). BAY 94-9027 was well tolerated, and no immunogenicity was observed.

CONCLUSIONS

This phase I study demonstrates that BAY 94-9027 has an extended half-life in subjects with hemophilia A and, after multiple dosing, was well tolerated with no immunogenicity during the 8-week trial. A phase III study in a larger number of subjects is underway to fully characterize how this prolonged half-life will permit less frequent prophylaxis dosing for patients with hemophilia.

Progress towards gene therapy for haemophilia B

Haemophilia B is an X-linked recessive bleeding disorder, arising from a deficiency of coagulation factor IX. It has been a target for gene therapy ever since the factor IX gene was cloned in 1982. Several distinct approaches have been evaluated in humans over the last 30 years, but none has resulted in tangible corrections of the bleeding phenotype in humans until recently. Our group has now shown that lasting clinical improvement of the bleeding phenotype in patients with haemophilia B is possible following a single systemic administration of a self-complementary adeno-associated virus vector to deliver an optimised factor IX expression cassette to the liver. Success in this trial raises hope for patients with severe haemophilia B as well as others with inherited monogenetic disorders of the liver where current treatment options are limited.

Phase 3 study of recombinant factor IX Fc fusion protein in hemophilia B

BACKGROUND

Prophylactic factor replacement in patients with hemophilia B improves outcomes but requires frequent injections. A recombinant factor IX Fc fusion protein (rFIXFc) with a prolonged half-life was developed to reduce the frequency of injections required.

METHODS

We conducted a phase 3, nonrandomized, open-label study of the safety, efficacy, and pharmacokinetics of rFIXFc for prophylaxis, treatment of bleeding, and perioperative hemostasis in 123 previously treated male patients. All participants were 12 years of age or older and had severe hemophilia B (endogenous factor IX level of ≤2 IU per deciliter, or ≤2% of normal levels). The study included four treatment groups: group 1 received weekly dose-adjusted prophylaxis (50 IU of rFIXFc per kilogram of body weight to start), group 2 received interval-adjusted prophylaxis (100 IU per kilogram every 10 days to start), group 3 received treatment as needed for bleeding episodes (20 to 100 IU per kilogram), and group 4 received treatment in the perioperative period. A subgroup of group 1 underwent comparative sequential pharmacokinetic assessments of recombinant factor IX and rFIXFc. The primary efficacy end point was the annualized bleeding rate, and safety end points included the development of inhibitors and adverse events.

RESULTS

As compared with recombinant factor IX, rFIXFc exhibited a prolonged terminal half-life (82.1 hours) (P<0.001). The median annualized bleeding rates in groups 1, 2, and 3 were 3.0, 1.4, and 17.7, respectively. In group 2, 53.8% of participants had dosing intervals of 14 days or more during the last 3 months of the study. In groups 1, 2 and 3, 90.4% of bleeding episodes resolved after one injection. Hemostasis was rated as excellent or good during all major surgeries. No inhibitors were detected in any participants receiving rFIXFc; in groups 1, 2, and 3, 73.9% of participants had at least one adverse event, and serious adverse events occurred in 10.9% of participants. These events were mostly consistent with those expected in the general population of patients with hemophilia.

CONCLUSIONS

Prophylactic rFIXFc, administered every 1 to 2 weeks, resulted in low annualized bleeding rates in patients with hemophilia B. (Funded by Biogen Idec; ClinicalTrials.gov number, NCT01027364.).

Future of coagulation factor replacement therapy

Over a million patients worldwide currently suffer from hemophilia and other congenital clotting factor deficiencies. Patients affected with hemophilia A and B are treated by intravenous replacement therapy of factor VIII and factor IX, respectively. Current hemophilia treatments have favorably supported their efficacy, tolerability, and safety profiles. The onset of alloantibodies inactivating the infused coagulation factor is the main problem in hemophilia patients rendering replacement therapies ineffective; another disadvantage is the short half-life of the infused clotting factors with the need for multiple and frequent infusions to manage a bleeding episode. Now, the challenge in the management of hemophilia treatment is the prolongation of the half-life and reduction in the immunogenicity of recombinant clotting factors. The bioengineering strategies, previously applied successfully to other therapeutic proteins, encourage the current efforts to produce novel coagulation factors with more prolonged bioavailability, with increased potency and resistance to inactivation and potentially reduced immunogenicity.

Management of joint bleeding in hemophilia

Hemarthrosis, the hallmark of severe hemophilia, is the major cause of serious bleeding events, disability and reduced quality of life in patients with factor VIII or factor IX deficiency. Joint bleeding is one of the greatest challenges confronting individuals treating hemophilia, and its economic impact is enormous. This article reviews the current management of hemophilic joint bleeding and discusses the potential impact of novel therapies.

Minimal modification in the factor VIII B-domain sequence ameliorates the murine hemophilia A phenotype

Recombinant canine B-domain deleted (BDD) factor VIII (FVIII) is predominantly expressed as a single-chain protein and exhibits greater stability after activation compared with human FVIII-BDD. We generated a novel BDD-FVIII variant (FVIII-RH) with an amino acid change at the furin cleavage site within the B domain (position R1645H) that mimics the canine sequence (HHQR vs human RHQR). Compared with human FVIII-BDD, expression of FVIII-RH protein revealed a 2.5-fold increase in the single-chain form. Notably, FVIII-RH exhibited a twofold increase in biological activity compared with FVIII-BDD, likely due to its slower dissociation of the A2-domain upon thrombin activation. Injection of FVIII-RH protein in hemophilia A (HA) mice resulted in more efficacious hemostasis following vascular injury in both the macro- and microcirculation. These findings were successfully translated to adeno-associated viral (AAV)-based liver gene transfer in HA mice. Expression of circulating FVIII-RH was approximately twofold higher compared with AAV-FVIII-BDD-injected mice. Moreover, FVIII-RH exhibits superior procoagulant effects compared with FVIII-BDD following a series of hemostatic challenges. Notably, the immunogenicity of FVIII-RH did not differ from FVIII-BDD. Thus, FVIII-RH is an attractive bioengineered molecule for improving efficacy without increased immunogenicity and may be suitable for both protein- and gene-based strategies for HA.

New challenges in hemophilia: long-term outcomes and complications

For the past 5 decades, the care for hemophilia patients has improved significantly to the point that a newborn with hemophilia living in a developed nation can expect to have a normal lifespan and a high quality of life. Despite this, there are several new challenges that the hemophilia community will face in the coming years. First, the hemophilia community will soon be challenged with adopting a variety of new agents into clinical practice. Second, the normalization of patients' lives as a result of improved treatment has led to new problem areas, including obese/overweight hemophiliacs and osteoporosis. In addition, although mortality rates are similar to those of the healthy population, morbidities such as hemophilic arthropathy still occur. Third, the cost of care continues to rise, both due to the development of expensive new therapies and to the costs of managing problems such as obesity and osteoporosis. Finally, most patients in the world with hemophilia receive little to no care and although this is an enormous challenge, it must be confronted. This review discusses some new challenges facing developing nations and their care for hemophilia patients. In summary, in hemophilia in the coming few years, several new challenges will need to be confronted.

Population pharmacokinetic modeling for dose setting of nonacog beta pegol (N9-GP), a glycoPEGylated recombinant factor IX

BACKGROUND

nonacog beta pegol (N9-GP) is a glycoPEGylated recombinant factor IX (rFIX) molecule with a prolonged half-life.

OBJECTIVES

To provide information on potential dose regimens for N9-GP for phase 3 pivotal and surgery trials.

METHODS

A population pharmacokinetic model was developed from single-dose data derived from the first human-dose trial with N9-GP in hemophilia B patients, and was used to extrapolate to steady-state conditions for different N9-GP dose regimens for prophylaxis. The model was also used to compare prophylaxis using N9-GP with standard prophylactic regimens using rFIX or plasma-derived (pd) FIX (40 IU kg(-1) every third day). Plasma activity following dosing with N9-GP, rFIX and pdFIX for surgery and on-demand treatment of bleeds was also simulated.

RESULTS

A linear two-compartmental model best described the pharmacokinetic profiles of N9-GP, rFIX and pdFIX. A prophylactic regimen of 10 U kg(-1) N9-GP once weekly predicted mean peak and trough levels of 18 and 4.2 U dL(-1) , while 40 U kg(-1) once weekly predicted values of 72 and 17 U dL(-1) , respectively. Standard prophylactic regimens with rFIX and pdFIX predicted mean peak and trough levels of 34 and 3.9 IU dL(-1) for rFIX, and mean values of 43 and 2.1 IU dL(-1) for pdFIX. Additional simulations predicted significantly reduced dosing frequency and factor concentrate consumption for N9-GP vs. rFIX and pdFIX for surgery and the treatment of bleeds.

CONCLUSIONS

N9-GP may allow prophylaxis, surgical dosing regimens and on-demand treatment of bleeding episodes with less frequent injections and lower factor concentrate consumption; this possibility is being investigated in prospective clinical trials.

Mortality, health care utilization and associated diagnoses in hospitalized patients with haemophilia in the United States: first reported nationwide estimates

To describe the in-hospital epidemiology of haemophilia A and B in the US we analysed the National Inpatient Sample (NIS), a stratified probability sample of 20% of all hospital discharges in the US for the year 2007. We applied sampling weights to represent all hospital discharges for haemophilia A and B identified using ICD-9 codes 286.0 and 286.1, respectively. Haemophilia (A or B) was one of all the listed diagnoses in 9737 discharges and principal diagnosis in 1684 discharges. The most common associated diagnoses in discharges with Haemophilia in adults and children were hypertension (28.1 ± 1.6%) and central line infections (15.2 ± 1.8%) respectively. No Hepatitis C or HIV was reported in children. Among 212 deaths, associated diagnoses included sepsis (37.9%), heart failure (30.2%), respiratory failure (28.3%), pneumonia (24.5%), HIV (14.2%), hepatic coma (5.2%) and intracranial haemorrhage (2.3%). All fifteen reported paediatric deaths occurred on day zero of life, the commonest associated diagnoses being Intraventricular haemorrhage and newborn haemorrhage-NOS (33% each). Median age of in-hospital mortality for diagnosis of Haemophilia was 68.3 years as compared to 72.3 years for all males for all hospitalizations in NIS combined. Mean hospital charges for haemophilia of $76823 ± 5530 were significantly higher than those from all causes of hospitalization of $26,120 ± 562. In-hospital mortality is rare in children with haemophilia beyond the neonatal period and age of mortality in adults is approaching that of the general male population. Hospitalization in children is most often due to central line infections and hospitalization and death in adults is primarily due to age-related illnesses.

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.

Biological rationale for new drugs in the bleeding disorders pipeline

Since the introduction of replacement coagulation factor infusions for the treatment of hemophilia in the 1970s and subsequent improvements in the safety profile of available factor VIII (FVIII) and factor IX (FIX) concentrates, mortality among patients with hemophilia has improved considerably and now parallels that of the noncoagulopathic population in developed countries. Substantial morbidity, however, continues from the development of inhibitory antibodies, a recognized complication of clotting factor replacement; from infections and thrombosis complicating placement of central venous catheters, which are required in children with hemophilia due to frequent prophylactic infusions of coagulation factors with defined half-lives; and from disabling joint disease in individuals without access to costly prophylaxis regimens. In response to the need for long-acting, more potent, less immunogenic, and more easily administered therapies, an impressive array of novel agents is nearly ready for use in the clinical setting. These therapeutics derive from rational bioengineering of recombinant coagulation factors or from the discovery of nonpeptide molecules that have the potential to support hemostasis through alternative pathways. The number of novel agents in clinical trials is increasing, and many of the initial results are promising. In addition to advancing treatment of bleeding episodes or enabling adherence to prophylactic infusions of clotting factor concentrate, newer therapeutics may also lead to improvements in joint health, quality of life, and tolerability of iatrogenic or comorbidity-associated bleeding challenges.