Plasma Factor IX Activity Research Articles

Recombinant factor IX Fc for the treatment of hemophilia B.

Current hemophilia B treatment guidelines recommend routine prophylaxis with factor IX (FIX) replacement products, tailored to maintain plasma activity at levels that will prevent bleeds. However, plasma FIX activity may not be the primary determinant or best indicator of hemostatic efficacy due to its extravascular distribution. FIX replacement therapy has evolved to include extended half-life (EHL) products that provide effective bleed protection when administered at intervals of 7 days or longer. rFIXFc is a recombinant fusion protein with an extended circulation time. rFIXFc has a biodistribution profile consistent with distribution into extravascular space, where it may support hemostasis at sites of vessel injury independent of circulating plasma activity levels. The safety and efficacy of rFIXFc prophylaxis is well established in adults, adolescents and children including previously untreated patients with hemophilia B, with substantial evidence from clinical trials and real-world clinical practice. This review describes the pharmacokinetic characteristics of rFIXFc, summarizes available safety and efficacy data, and evaluates the use of rFIXFc in special populations. Current hemophilia B treatment challenges, including target FIX plasma levels, perioperative use, and management of patients with comorbidities, are discussed together with the potential role of EHL products in the future treatment landscape of hemophilia B.

Random X-Chromosome Inactivation in Adult Hemophilia B Carriers Does Not Attenuate Bleeding Risk

Introduction: The X-linked bleeding disorder Hemophilia B (HB) results from deficiency in coagulation Factor IX (FIX). In contrast to Hemophilia A, genotype-phenotype correlations in HB males are complex, as some F9 variants in males are associated with low plasma FIX activity (FIX:C) but milder than expected bleeding phenotypes. At least 75% of FIX is extravascular and not adequately measured from plasma. Hemostasis is likely influenced by this extravascular FIX which is bound reversibly to type IV collagen in the subendothelial basement membrane. We predict that genotype-phenotype correlations in female carriers of F9 mutations may have additional complexity as the mutant FIX can competitively interfere with wild type (WT) FIX for extravascular binding sites. F9 expression in female HB carriers is influenced by X-chromosome inactivation (XCI), a process that silences one X in XX females. XCI results in cells that randomly inactivate either the X carrying the mutant or wild type F9, although skewed XCI (>80:20) is found in ~25% of the general population. XCI skewing in HB carriers can lead to preferential expression of the X carrying the F9 mutation, which in turn influences plasma and extravascular levels of FIX and bleeding tendency. How frequently XCI is skewed in HB carriers, and the role of XCI in modulating FIX levels and bleeding phenotypes, remains poorly understood. We sought to determine whether XCI skewing may further differentiate bleeding risk in HB carriers. Methods: Subjects were enrolled in a prospective, observational cross-sectional study with informed consent. Both the Condensed MCMDM-1 bleeding assessment tool (BAT) and Pictorial Blood-loss Assessment Chart (PBAC) were completed at the time of the visit. F9 mutation analysis confirmed carrier status. FIX:C and FIX antigen ELISA assays were performed on all subjects. XCI skewing was assessed using established assays at the Androgen Receptor (AR) and Fragile X Mental Retardation (FMR1) loci. Results: A total of 15 subjects (11 adults) were confirmed F9 mutation carriers; six missense mutations and one frameshift mutation were identified. Abnormal bleeding is frequent in adult HB carriers, with 5/11 (45%) having BAT scores >4. Heavy menstrual bleeding (HMB) is particularly frequent, with all adult HB carriers reporting PBAC > 100, and 8/11 with BAT HMB subcategory score >1. FIX assessment by activity (mean 56% ± 28) and antigen (mean 0.55 IU/mL ± 0.2) assays are highly correlated (r 2= 0.83, p < 0.0001). Notably, only two adult HB carriers with significant bleeding have FIX levels < 50%, while two HB carriers with FIX levels < 50% have BAT scores < 4, indicating that neither FIX:C nor FIX antigen levels adequately predict bleeding risk in all HB carriers. Indeed, for all 11 adult HB carriers, no significant differences in either FIX:C or FIX antigen were observed between those with BAT scores ≥ 4 and < 4. We asked if XCI explained FIX levels or bleeding phenotypes. Nearly half (5/11) of the adult carriers have moderately skewed XCI (> 70:30); only one is extremely XCI skewed (> 80:20), and of the individuals with skewed XCI, 3/5 have BAT scores ≥ 4. Although random XCI is proposed to attenuate HB carrier bleeding phenotype, 2/6 HB carriers with random XCI also have BAT scores ≥ 4. XCI weakly correlated with FIX antigen (n = 15; r 2= 0.27, p < 0.05) but not FIX:C. When assessing this relationship for only the individuals with F9 c.1025C>T (n = 6), there was significant correlation with FIX:C (R 2= 0.73, p < 0.05) but not with FIX antigen or bleeding phenotype. The lack of correlation between XCI and FIX antigen in individuals with an identical F9 mutation argues for additional influences on intravascular, and likely extravascular, FIX levels and will require further investigation. Conclusions: Bleeding tendency in HB carriers is not rare and does not correlate with plasma FIX:C or FIX antigen. Random XCI is not fully protective against abnormal bleeding. Future studies are needed to better understand bleeding phenotypes in HB carriers that consider XCI, F9 mutation type and influences on circulating levels of WT and mutant FIX.

Mathematical modelling of gene delivery in patients with haemophilia B

Haemophilia B is a bleeding disorder resulting from a deficiency of coagulation factor IX (FIX). Although gene therapy is a potentially curative treatment option, optimising the dosing of therapeutic genes for patients remains a challenge. Detailed simulation of gene delivery systems is required for an improved understanding of the system. Hence, the purpose of this paper is to develop a modelling framework to predict the physiological response of a subject affected by type B haemophilia to a dose of the vector. To address this, an integrated pharmacokinetic/pharmacodynamic (PK/PD) modelling platform was developed based on in vivo clinical data for three patients with severe haemophilia B, whose functional plasma levels of FIX are less than 1% of the normal value. The plasma FIX activity was considered as the pharmacological effect, while the level of serum alanine aminotransferase (ALT) demonstrated the hepatocellular toxicity. Both an individual-based modelling approach and a population modelling approach were used to estimate the physiological parameters of the developed PK/PD models. The models were then validated using data from the clinical study before being used in a simulation-based modelling approach to provide dosing recommendations. The results obtained from the study demonstrate a good prediction of the pharmacokinetics and pharmacodynamics of the vector. Model-based simulations were subsequently performed to guide initial dose selection to provide clinicians with better tools to simplify the decision-making process for designing more effective treatment plans.

BAX 335 Hemophilia B Gene Therapy Phase 1/2 Clinical Trial: Long-Term Safety and Efficacy Follow-up

Background: BAX 335 is an adeno-associated virus serotype 8 (AAV8)-based clotting factor IX (FIX) Padua (R338L) gene therapy for the treatment of hemophilia B. A phase 1/2 safety and efficacy study dosed 8 participants with BAX 335 between 2013 and 2015 (NCT01687608). Infusions with BAX 335 were generally well tolerated; however, 7 of 8 participants did not achieve significant levels of durable transgene expression despite the use of glucocorticoids and resumed FIX replacement by 52 weeks (Konkle et al, Blood 2021;137:763-74). A root-cause analysis identified CpG content in the vector as a potential immunogenic trigger for the innate immune response, resulting in loss of expression. One participant demonstrated high levels of durable FIX expression, with detectable FIX activity levels between 0.1 and 0.4 IU/mL after 4 years and was found to have a missense variant in the IL6R gene. This study is the longest ongoing clinical gene therapy trial using a FIX R338L transgene. Aims: (1) To report long-term safety and participant disposition; (2) to describe persistence of endogenous FIX R338L transgene expression; and (3) to report long term persistence of neutralizing anti-capsid antibodies. Methods: Eight adult male participants with hemophilia B (FIX activity ≤2%) received BAX 335 in 1 of 3 intravenous dose cohorts (2.0 x 1011, 1.0 x 1012, or 3.0 x 1012 vector genomes/kg). The primary study objective was to assess the safety of BAX 335. Secondary assessments included the kinetics of plasma FIX activity, the need for exogenous FIX replacement, and systemic immune responses to BAX 335 and vector transgene protein. FIX clotting activity was measured using the one-stage clotting assay at the central laboratory. Serum neutralizing antibodies against the AAV8 and AAV2 capsids were measured to Year 5 following BAX 335 infusion using an in vitro transduction inhibition assay. Laboratory and in-person assessments were conducted for the first 5 years after BAX 335 infusion (one unscheduled visit was made at 7.2 Years). This was followed by annual liver ultrasound scans and telephone questionnaires assessing health status with the aim of completing 15 years of follow-up per participant. The study was approved by the institutional review boards of all participating sites, and all participants provided written informed consent. Results: Of 8 participants enrolled (aged 20-69 years), 2 discontinued from the study approximately 1 and 3 years after receiving BAX 335 infusion, and another participant withdrew consent 2 weeks prior to the data cutoff of May 6, 2022. Data from the 6 participants who had >5 years of long-term safety follow-up were included in this analysis. At data cutoff, 176 adverse events (AEs) were reported in all 8 dosed participants, most (72%) occurred in Years 1 and 2. In total, 6 serious adverse events (SAEs) were reported in 3 participants, of these 2 SAEs (post-procedural hemorrhage, arthritis) were reported after the interim analysis reported by Konkle et al. 2021. None were considered to be related to BAX 335 and all resolved. Although long-term hemostatic protection from bleeds was not observed in most of the participants in this analysis, 1 participant had continued FIX activity (Figure 1), with a most recent value of 0.078 IU/mL at 7.2 years after BAX 335 infusion. This participant has neither experienced any bleeds nor needed FIX replacement therapy after the second week of vector infusion. No FIX inhibitors have been observed. At Year 5, AAV neutralizing antibodies persisted at high titers in most participants (reciprocal of serum dilution: AAV2, <5 to 10,240; AAV8, 80 to 40,960). Conclusions: No additional BAX 335-related AEs, malignancy or thrombosis were reported in this long-term follow-up analysis of a phase 1/2 study. One participant achieved persistent FIX transgene activity in the circulation for 7.2 years and remains free from bleeding and the need for FIX replacement therapy. This is the longest duration of FIX R338L expression reported. Consistent with other studies, AAV neutralizing antibodies remained persistent at titers that would limit re-dosing with current AAV platforms. Future studies should explore patient-specific factors that may predict persistent transgene expression. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Identification of coagulation factor IX variants with enhanced activity through ancestral sequence reconstruction

AbstractOrthologous proteins contain sequence disparity guided by natural selection. In certain cases, species-specific protein functionality predicts pharmacological enhancement, such as greater specific activity or stability. However, immunological barriers generally preclude use of nonhuman proteins as therapeutics, and difficulty exists in the identification of individual sequence determinants among the overall sequence disparity. Ancestral sequence reconstruction (ASR) represents a platform for the prediction and resurrection of ancient gene and protein sequences. Recently, we demonstrated that ASR can be used as a platform to facilitate the identification of therapeutic protein variants with enhanced properties. Specifically, we identified coagulation factor VIII (FVIII) variants with improved specific activity, biosynthesis, stability, and resistance to anti-human FVIII antibody–based inhibition. In the current study, we resurrected a panel of ancient mammalian coagulation factor IX (FIX) variants with the goal of identifying improved pharmaceutical candidates. One variant (An96) demonstrated 12-fold greater FIX activity production than human FIX. Addition of the R338L Padua substitution further increased An96 activity, suggesting independent but additive mechanisms. after adeno-associated virus 2 (AAV2)/8-FIX gene therapy, 10-fold greater plasma FIX activity was observed in hemophilia B mice administered AAV2/8-An96–Padua as compared with AAV2/8-human FIX–Padua. Furthermore, phenotypic correction conferred by the ancestral variant was confirmed using a saphenous vein bleeding challenge and thromboelastography. Collectively, these findings validate the ASR drug discovery platform as well as identify an ancient FIX candidate for pharmaceutical development.

In Vivo CRISPR/Cas9-Targeted Genome Editing Recovers Factor IX Expression Restoring Haemostasis in a Mouse Model

CRISPR/Cas9 is a robust genome engineering tool due to its high editing efficiency and simple design principle. Taking advantage of DNA repair mechanism, namely homology directed recombination (HDR) with donor templates provided, this technology has a great promise to correct genetic defects at the molecular level for therapeutic purposes.Haemophilia B (HB) is an inherited disease caused by multiple loss-of-function mutations in the factor IX (FIX) gene. CRISPR mediated genome editing provides a potential treatment for HB, yet hardly any attempts have achieved efficacy in vivo so far. In this context, we developed a therapeutic strategy with CRISPR/SaCas9 targeted genome editing in combination with HDR events, and demonstrate efficient corrective replacement of a mutant fragment in the murine FIX (m FIX) genome in vivo .For the study, a mouse model of HB was employed, in which the part between 1kb upstream of the transcription start site (TSS) and intron 3 of the m FIX gene was replaced by an artificial mutant fragment. Through AAV vector delivery, CRISPR/SaCas9 targeted at specific sites around the mutant fragment in the m FIX gene and generated double-strand breaks (DSB) efficiently both in vitro and in vivo . Among all CRISPR candidates, a distinctive CRISPR efficiently inducing DSB at the site within intron 4 was chosen. Subsequently a comprehensive design of targeting vectors was performed. The replacement constructs contain a common insert of m FIX exons 1 to 4 coding sequence under the control of a synthetic liver-specific regulatory element to re-gain the full-length mRNA transcription. Multiple targeting constructs shared the 3' arm adjacent to the targeting site, whilst differed in the 5' arms either right adjacent to the targeting site, or containing the 5' UTR region bypassing the mutant fragment. In presence of CRISPR/SaCas9 genome editing, both targeting vectors mediated correction of the defective m FIX gene. As a consequence, the plasma levels of FIX coagulant activity were covered to over 15-20% of normal murine plasma level, whereas the mice receiving targeting vectors harboring the 5' arm bypassing the mutant fragment achieved higher activity compared to other groups. In addition, incorporation of miRNA622, which supposed to suppress non-homologous end joining and facilitate HR-mediated DSB repair, into SaCas9-expressing vector further improved the plasma FIX activity levels in the HB mice.In total, our results demonstrate that CRISPR/SaCas9 mediated genome targeting combining homology-directed recombination has the capability to correct genetic defects in the m FIX genome in vivo to re-gain gene expression and recover haemostasis in the mouse model of HB. It provides a cure solution in treatment of inherited diseases including haemophilia B as well as the rationale for clinic translation of the technology. DisclosuresNo relevant conflicts of interest to declare.

Evaluation of the Human Factor IX Gene Therapy Vector TAK-748 in Hemophilia: Results from Non-Clinical Studies in Factor IX Knockout Mice and Rhesus Monkeys

Introduction: Adeno-associated virus (AAV)-based factor IX (FIX) gene therapy has the potential to provide clinical benefit in patients with hemophilia B. TAK-748 is a novel next-generation AAV vector for FIX gene therapy. The vector design includes the insertion of 3 hepatocyte-specific cis-regulatory elements to increase the strength of the liver-specific transthyretin promoter driving expression of a human FIX transgene. Aims: The objectives of this study were to investigate the TAK-748 dose-response relationship for FIX activity, and evaluate its efficacy, in FIX knockout (KO) mice and rhesus monkeys. Methods: Male FIX KO mice (N=12/group) received single intravenous doses of TAK-748 (7.4×1010, 1.5×1011, 7.4×1011, or 1.5×1012 vector genomes [vg]/kg) or buffer. Blood samples were taken on days 7, 14, 28, 42, and 56 for the analysis of plasma FIX activity. At the end of the observation period, the bleeding phenotype was assessed by a tail-tip bleeding assay. The viral transduction efficiency of TAK-748 in liver tissue was analyzed by quantitative real-time polymerase chain reaction. Safety assessments included monitoring for clinical signs, and histopathological analysis of selected organs (liver, spleen, kidney, and heart). Male rhesus monkeys (N=3/group) were administered single TAK-748 intravenous bolus injections (3.8×1011, 9.5×1011, or 1.9×1012 vg/kg). Blood samples were collected before dosing and weekly after dosing up to week 18. Plasma FIX activity, human (hu)FIX antigen, and anti-hu-Padua FIX neutralizing antibodies were analyzed. Results: No clinical signs or deaths were recorded in animals treated with TAK-748, and there were no TAK-748-related histopathological findings in the tissues collected from the mice. FIX activity levels in plasma from FIX KO mice treated with buffer were below the lower limit of quantification. Administration of TAK-748 resulted in a dose-dependent increase in mean plasma FIX activity, and supraphysiologic mean FIX levels up to 41.0 IU/mL (1.5×1012 vg/kg). In the tail-tip bleeding assay, blood loss was significantly reduced in the TAK-748 groups at dose levels above 7.4×1010 vg/kg (P&lt;0.05 vs. buffer control). Administration of TAK-748 to rhesus monkeys resulted in a dose-dependent increase in mean plasma FIX activity and antigen, and peak levels of huFIX expression were detected 2-4 weeks after treatment. Mean huFIX activity was 0.3, 0.6, and 1.9 IU/mL after treatment with 3.8×1011 vg/kg, 9.5×1011 vg/kg, and 1.9×1012 vg/kg TAK-748, respectively. A significant reduction in FIX activity and huFIX protein was observed in most of the animals starting about 4 weeks after dosing with TAK-748. In most animals, anti-huFIX Padua neutralizing antibody titers were detected at about week 6 of the study and correlated with the preceding reductions in huFIX expression. Conclusions: Treatment with TAK-748 resulted in dose-dependent increases in plasma FIX activity and was efficacious in FIX KO mice and rhesus monkeys. There were no treatment-related safety findings. Disclosures Weiller: Baxalta Innovations GmbH, a Takeda company: Employment. Wang:Shire US Inc., a Takeda company: Employment, Equity Ownership. Coulibaly:Baxalta Innovations GmbH, a Takeda company: Employment. Schuster:Baxalta Innovations GmbH, a Takeda company: Employment. Rottensteiner:Baxalta Innovations GmbH, a Takeda company: Employment, Equity Ownership. Sun:Shire US Inc., a Takeda company: Employment. Chuah:Shire, a Takeda company: Consultancy, Research Funding; Catalyst Bio: Consultancy, Research Funding; Pfizer: Research Funding. Vandendriessche:Shire, a Takeda company: Consultancy, Honoraria, Research Funding; Catalyst Bio: Consultancy, Research Funding; Pfizer: Research Funding; Biotest: Honoraria. Scheiflinger:Baxalta Innovations GmbH, a Takeda company: Employment, Equity Ownership. Höllriegl:Baxalta Innovations GmbH, a Takeda company: Employment, Equity Ownership.

Co-Prevalence of Pre-Existing Immunity to Different Serotypes of Adeno-Associated Virus (AAV) in Adults with Hemophilia

Background: Recombinant and synthetic adeno-associated virus (AAV) vectors are in development for gene transfer in patients with hemophilia A (HA) or hemophilia B (HB). These include liver-directed recombinant AAV8 vectors BAX 888/SHP654/TAK-754 factor VIII (FVIII) gene therapy (GT) for severe HA, and SHP648/TAK-748 factor IX (FIX) GT for HB (Baxalta US Inc., a Takeda company, Lexington, MA, USA). However, environmental exposure to wild-type AAVs can result in individuals developing antibodies and cell-mediated immune responses to the naturally occurring AAV. While natural exposure to AAV does not result in any known disease in humans, presence of preexisting immunity can block delivery and prevent sustained expression of the transgene by an AAV-based vector in a gene therapy setting. Of the AAV serotypes, AAV2 is the most frequently encountered natural human infection and AAV5 and AAV8 have been the most commonly used vectors for hemophilia GT. Therefore, it is important to assess the prevalence and co-prevalence of antibody and T cell-mediated responses against each of these AAV serotypes and to better characterize the association between humoral and cellular immunity in people with hemophilia. Aims: To determine the prevalence of preexisting antibody-mediated immunity against AAV2, AAV5 and AAV8 and the association between AAV8-specific humoral and cell-mediated responses in adult patients with HA and HB in an international prospective, epidemiological study. Methods: This ongoing seroprevalence study involved adult male patients (18-75 years of age) with severe HA (&lt;1% plasma FVIII activity) or severe/moderate HB (≤2% plasma FIX activity) recruited from hemophilia treatment centers in the United States and Europe (NCT03185897). Participants consented to collection of peripheral blood at either a single or multiple annual outpatient study visits, in order to explore fluctuations of the immune response over time. Local ethics committee approval was obtained. Titers for anti-AAV2, anti-AAV5 and anti-AAV8 neutralizing antibodies (NAbs) were determined using a cell-based transduction inhibition assay, with seropositivity defined as a titer ≥1:5. Titers for anti-AAV2, anti-AAV5 and anti-AAV8 binding antibodies (BAbs) were quantitated by indirect enzyme-linked immunosorbent assay (ELISA), with seropositivity defined as a titer ≥1:80. Cell-mediated immune responses to AAV8 peptide antigens were measured in peripheral blood mononuclear cells using an interferon-γ enzyme-linked immunospot (ELISpot) assay. Samples with a signal ≥3 times background and &gt;60 spots per million cells were defined as positive. Results: Here we present data from patients who completed at least a single visit at the time of the interim, one year data cut (November 9, 2018). Of 242 patients enrolled (mean ± SD age: 35.3 ± 11.4 years), 194 patients had HA and 48 patients had HB. The overall co-prevalence of NAbs and BAbs to AAV2, AAV5 and AAV8 was 39.7% (HA: 38.1%, 72/189; HB: 45.8%, 22/48) and 16.1% (HA: 16.5%, 31/188; HB: 14.6%, 7/48) respectively, with further details shown in Table 1. Overall, 38.3% of patients (82/214) exhibited a T cell-mediated immune response to AAV8 peptide antigens (HA: 35.9%, 61/170; HB: 47.7%, 21/44). Among patients with AAV-8-specific NAbs, 37.9% (39/103) demonstrated positive AAV8-specific ELISPOT results. (HA: 35.7%, 30/84; HB: 47.4%, 9/19). Conclusion: The findings from this ongoing study demonstrate that approximately 50% of patients with hemophilia have preexistent NAb responses to AAV2, AAV5 or AAV8 with 40% demonstrating co-prevalence to all 3 evaluated AAV serotypes. Similar percentages of patients exhibited a positive cellular response to AAV8 antigens. Further, patients with HB demonstrated a slightly higher co-prevalence and a higher cellular response than patients with HA. In the combined HA and HB cohorts, co-prevalence was almost 40% for AAV8-specific humoral and T-cell mediated immunity. These data will add to our appreciation of preexisting AAV immunity that prevent patient participation in gene therapy trials. Disclosures Rajavel: Baxalta US Inc., a Takeda company: Employment, Equity Ownership. Ayash-Rashkovsky:Baxalta US Inc., a Takeda company: Employment, Equity Ownership. Tang:Baxalta US Inc., a Takeda company: Employment, Equity Ownership. Gangadharan:Baxalta Innovations GmbH, a Takeda company: Employment. de la Rosa:Baxalta Innovations GmbH, a Takeda company: Employment. Ewenstein:Baxalta US Inc., a Takeda company: Employment, Equity Ownership, Other: a Takeda stock owner.

Spontaneous Bleeding and Poor Bleeding Response with Extended Half-Life Factor IX Products: A Survey of Select US and Canadian Hemophilia Treatment Centers

Background: Factor IX (FIX) has distinct pharmacokinetic properties compared to factor VIII including significant distribution to the extravascular space. Extravascular distribution and binding to type IV collagen is important in hemostasis but not readily measureable in clinical practice for patients with hemophilia B receiving factor products. We previously reported data regarding use of EHL-FIX products in a cohort of patients who demonstrated issues with spontaneous bleeding and poorly controlled bleeding events; we now report data from an expanded cohort including performance of all EHL-FIX products available in US and Canada. Aims: To characterize the use and performance of EHL-FIX in clinical practice at six hemophilia treatment centers (HTCs). Methods: An electronic survey regarding center specific use of EHL-FIX amongst patients with severe hemophilia B (HB) was sent in summer 2019, including 4 previously surveyed centers and 2 additional centers. Providers were asked if patients utilizing EHL-FIX for prophylaxis had experienced 1) spontaneous/minimally traumatic bleeding events at factor levels &gt;10% or 2) poorly controlled bleeding events requiring more frequent/higher doses of EHL-FIX than anticipated in addition to patterns of EHL-FIX product switching. Results: Surveyed HTCs cared for 90 patients with HB including 67 (74%) who utilized EHL-FIX, including 26 (39%) recombinant factor IX (FIX) albumin fusion protein (rFIX-FP), 37 (55%) recombinant factor IX Fc fusion protein (rFIXFc), and 4 (6%) received glycopegylated recombinant FIX (rFIX-GP). All patients had severe hemophilia B with the exception of one smaller center also contributing data regarding moderate HB patients on prophylaxis. All centers reported having patients with unexpected spontaneous/minimally traumatic bleeding and poorly controlled bleeding which did not seem to be dependent on age (median age 14.5 years, range 1.4-44). This occurred in 18 patients on prophylaxis, including 16 of 26 (62%) patients using rFIX-FP, and 2 of 4 (50%) of patients using rFIX-GP. Conclusions: Although plasma FIX activity levels have driven prophylaxis and bleed management decisions, clinical experience suggests novel properties of EHL-FIX may impact hemostasis. Although achieving seemingly adequate FIX plasma troughs (&gt;10%), limited clinical experience suggests patients with SHB may have a differential response to EHL-FIX, noted in our cohort with FIX-FP and rFIX-GP. Successful bleed prevention or control in SHB may be predicted by the distribution of FIX in circulation and extravascular space, and the presence of FIX in tissues at time of injury. These data demonstrate the importance of real-world monitoring of efficacy of new FIX products and suggest the need for more robust mechanisms to understand the hemostatic performance of products. Disclosures Malec: Bayer: Honoraria; Spark: Honoraria; CSL: Honoraria; Sanofi: Consultancy, Honoraria, Speakers Bureau; Takeda: Honoraria. Croteau:Novo Nordisk: Consultancy, Honoraria, Research Funding; Shire: Consultancy, Honoraria; Bayer: Consultancy, Honoraria; Bayer: Consultancy, Honoraria; Octapharma: Honoraria; Octapharma: Honoraria; Genentech: Consultancy, Honoraria; Pfizer: Research Funding; Spark Therapeutics: Research Funding; Novo Nordisk: Consultancy, Honoraria, Research Funding; Spark Therapeutics: Research Funding; Pfizer: Research Funding; Genentech: Consultancy, Honoraria; CSL Behring: Consultancy, Honoraria; CSL Behring: Consultancy, Honoraria; Shire: Consultancy, Honoraria. Callaghan:Biomarin, Bioverativ, Grifols, Kedrion, Pfizer, Roche/Genentech, Shire, and Spark Therapeutics: Consultancy; Alnylum: Equity Ownership; Bayer: Consultancy, Speakers Bureau; Takeda: Consultancy, Research Funding; Sanofi: Consultancy; Global Blood Therapeutics: Consultancy; Novonordisk: Consultancy, Speakers Bureau; Octapharma: Consultancy; Pfizer: Research Funding; Roche: Research Funding; Shire/Takeda: Speakers Bureau; Roche/Genentech: Speakers Bureau. Matino:Bayer: Honoraria, Research Funding; Sobi: Honoraria, Research Funding; Pfizer: Honoraria, Research Funding; Roche: Research Funding; Bioviiix: Honoraria; Sanofi: Honoraria. Friedman:CSL: Consultancy; Bayer: Consultancy; Genentech: Consultancy; Instrumentation Laboratory: Consultancy; Siemens: Consultancy. Sidonio:Grifols: Membership on an entity's Board of Directors or advisory committees, Research Funding; Genetech: Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda-Shire: Membership on an entity's Board of Directors or advisory committees, Research Funding; Bioverativ: Membership on an entity's Board of Directors or advisory committees, Research Funding; Octapharma: Membership on an entity's Board of Directors or advisory committees, Research Funding; Uniqure: Membership on an entity's Board of Directors or advisory committees; Novo Nordisk: Membership on an entity's Board of Directors or advisory committees; Biomarin: Membership on an entity's Board of Directors or advisory committees; Kedrion: Research Funding.

Pharmacokinetics, Efficacy, and Safety of Nonacog Alfa in Previously Treated Patients with Moderately Severe to Severe Hemophilia B

PurposeNonacog alfa, a recombinant factor IX (FIX) product, is used for FIX replacement in the treatment and prevention of bleeding events in patients with hemophilia B. This study aimed to provide supplemental pharmacokinetic (PK), efficacy, and safety data for nonacog alfa when administered as part of usual hemophilia care, including on-demand treatment, routine prophylaxis, and surgical prophylaxis. MethodsMen with previously treated severe or moderately severe hemophilia B (FIX activity ≤2%) were enrolled in this prospective, open-label, nonrandomized, multicenter study. An initial 72-hour PK assessment was performed wherein patients received a single dose of nonacog alfa (75 IU/kg) as an infusion over 10 minutes. A final 72-hour PK assessment was performed at the patient’s last visit, after a minimum washout period of 4 days. Correlations between Cmax after the first dose and body weight and body mass index (BMI) were assessed post hoc using Spearman test after evaluating normality. FindingsIn total, 23 patients (age, 12–59 years; weight, 44–173 kg; and BMI, 16.3–45.1) with previous exposure to FIX products (median, 460 days; range, 150–2400 days) were enrolled; 21 were evaluable for efficacy. The median number of exposure days per efficacy-evaluable patient in this study was 48 (range, 31–103). The FIX activity profiles showed multiphasic disposition characteristics, with initial mean (SD) PK profiles as follows: Cmax, 61.4 (12.5) IU/dL; AUC∞, 1055 (227) IU·h/dL; t½, 23.7 (5.6) hours; and recovery, 0.818 (0.167) IU/dL. Mean plasma FIX activity versus time profiles were essentially identical upon initial exposure and after repeated use (n = 17), and bioequivalence was confirmed. No apparent relationship was observed between Cmax and either body weight (P > 0.1732) or BMI (P > 0.1235). ImplicationsThe FIX activity profile after administration of nonacog alfa is predictable and is not altered after repeated exposure during usual hemophilia care. PK parameters are consistent with nonacog alfa use for FIX replacement in on-demand treatment, routine prophylaxis, and surgical prophylaxis in patients with hemophilia B.

Pharmacokinetic Results of Two Phase III Clinical Studies of Coagulation Factor IX (Recombinant) Albumin Fusion Protein (rIX-FP) in Previously Treated Patients with Hemophilia B (PROLONG-9FP)

A recombinant fusion protein linking recombinant coagulation factor IX (FIX) with recombinant human albumin (rIX-FP) has been developed to extend the plasma half-life of FIX, thus improving hemophilia B treatment by allowing less frequent dosing than required with standard plasma-derived (pd) and recombinant (r) FIX products. The PROLONG-9FP clinical program aims to evaluate the use of rIX-FP for prophylaxis and on-demand treatment of bleeding in patients with severe hemophilia B. In a completed Phase I pharmacokinetic (PK) study in subjects aged 15 to 58 years (y), the mean half-life of rIX-FP was 92 hours, 5 times longer than the half-life of the FIX products previously used by the subjects. The mean trough FIX activity after injection of rIX-FP was 7.4% (day 7) at a dose of 25 IU/kg, and 13.4% (day 7) and 5.5% (day 14) at a dose of 50 IU/kg (Santagostino E, et al. Blood 2012; 120:2405-11). A Phase II study demonstrated the efficacy of weekly prophylaxis with rIX-FP, with excellent safety and an improved PK profile.Following completion of these studies, 2 Phase III, open-label, multicenter studies have been conducted in previously treated patients (PTPs) with severe hemophilia B, aged 12 to 65 years (NCT01496274) and < 12 years (NCT01662531). Both studies, which were designed to evaluate the long term safety and efficacy of rIX-FP for both prophylaxis and on-demand treatment of bleeding episodes, consisted of an initial PK evaluation period followed by a treatment period during which subjects were administered rIX-FP as prophylaxis and on-demand treatment. Subjects from 42 hemophilia treatment centers in 12 countries participated; to date, the PROLONG-9FP clinical program encompasses over 100 hemophilia B subjects for the PK evaluation. Here, we report on the PK results from these 2 studies.During the 14-day PK evaluation periods, blood samples for PK analysis were taken before dosing, and then at 30 minutes, 3, 24, 48, 72, 120, 168, 240 and 336 hours after injection of 50 IU/kg rIX-FP. A subgroup of subjects also completed a PK evaluation of their previously used Factor IX products (pdFIX and rFIX), with sampling before dosing, and then at 30 minutes, 3, 6, 12, 24 and 48 hours after 50 IU/kg FIX injection. Plasma FIX activity (FIX:C) was measured by a one-stage clotting assay (CSL Behring central laboratory).The mean plasma FIX half-life after injection of 50 IU/kg rIX-FP was 105, 92 and 84 hours in the respective age groups of 12 to 61 years (n = 46), 6 to 11 years (n = 15) and 1 to 5 years (n = 12); the baseline corrected mean incremental recovery (IR) was 1.3, 1.1 and 1.0 IU/dL per IU/kg, the mean area under the curve (AUC) was 7,360, 4,949 and 4,358 IU*hr/dL, and the clearance was 0.7, 1.1 and 1.3 mL/h/kg in the respective age groups. The time to 5% FIX:C after injection of 50 IU/kg rIX-FP administration was Day 10 for children and Day 14 for adults; at Day 14, the mean trough FIX activity in children was 3%. Compared with the FIX products previously used by the subjects, rIX-FP had a 30 to 40% higher incremental recovery, > 5-times longer half-life, larger AUC and lower clearance.In conclusion, compared with standard FIX products, rIX-FP demonstrated an improved PK profile with a prolonged half-life in all age groups (1 to 61 years). At 14 days after injection of rIX-FP, the mean trough FIX activity is 3% in children and above 5% in adults, supporting a treatment interval of 14 days for routine prophylaxis. Treatment intervals of 7-, 10- and 14 days for routine prophylaxis were tested in the pivotal Phase III studies; every 21 day regimen will be tested in selected age groups during the Phase IIIb extension study. Detailed PK results will be presented during the meeting. DisclosuresSantagostino:CSL: Honoraria, Speakers Bureau. Jacobs:CSL Behring: Employment. Voigt:Csl Behring: Employment. Feussner:CSL Behring: Employment. Limsakun:CSL Behring: Employment.

Employing a gain-of-function factor IX variant R338L to advance the efficacy and safety of hemophilia B human gene therapy: preclinical evaluation supporting an ongoing adeno-associated virus clinical trial.

Vector capsid dose-dependent inflammation of transduced liver has limited the ability of adeno-associated virus (AAV) factor IX (FIX) gene therapy vectors to reliably convert severe to mild hemophilia B in human clinical trials. These trials also identified the need to understand AAV neutralizing antibodies and empty AAV capsids regarding their impact on clinical success. To address these safety concerns, we have used a scalable manufacturing process to produce GMP-grade AAV8 expressing the FIXR338L gain-of-function variant with minimal (<10%) empty capsid and have performed comprehensive dose–response, biodistribution, and safety evaluations in clinically relevant hemophilia models. The scAAV8.FIXR338L vector produced greater than 6-fold increased FIX specific activity compared with wild-type FIX and demonstrated linear dose responses from doses that produced 2–500% FIX activity, associated with dose-dependent hemostasis in a tail transection bleeding challenge. More importantly, using a bleeding model that closely mimics the clinical morbidity of hemophilic arthropathy, mice that received the scAAV8.FIXR338L vector developed minimal histopathological findings of synovitis after hemarthrosis, when compared with mice that received identical doses of wild-type FIX vector. Hemostatically normal mice (n=20) and hemophilic mice (n=88) developed no FIX antibodies after peripheral intravenous vector delivery. No CD8+ T cell liver infiltrates were observed, despite the marked tropism of scAAV8.FIXR338L for the liver in a comprehensive biodistribution evaluation (n=60 animals). With respect to the role of empty capsids, we demonstrated that in vivo FIXR338L expression was not influenced by the presence of empty AAV particles, either in the presence or absence of various titers of AAV8-neutralizing antibodies. Necropsy of FIX–/– mice 8–10 months after vector delivery revealed no microvascular or macrovascular thrombosis in mice expressing FIXR338L (plasma FIX activity, 100–500%). These preclinical studies demonstrate a safety:efficacy profile supporting an ongoing phase 1/2 human clinical trial of the scAAV8.FIXR338L vector (designated BAX335).

Pharmacokinetics Of Recombinant Factor IX Fc Fusion Protein (rFIXFc) In Pediatric Subjects With Hemophilia B: An Interim Analysis Of The Kids B-LONG Study

IntroductionProphylaxis with factor IX (FIX) is the optimal treatment for patients with hemophilia B; however, due to the short half-life of currently available FIX products, frequent injections may be required to prevent bleeding episodes. To prolong half-life and reduce injection frequency, a long-acting recombinant FIX Fc fusion protein (rFIXFc) consisting of one rFIX molecule covalently linked to the Fc domain of immunoglobulin G1 (IgG1) was developed. In a phase 3 study in adults and adolescents, rFIXFc had a 2.43-fold increase in half-life and 50% reduction in clearance (CL) compared with FIX (BeneFIX®) (J Thromb Haemost. 2013;11[2]:241). The Kids B-LONG study (NCT01440946) was designed to evaluate the pharmacokinetics (PK), safety, and efficacy of rFIXFc prophylaxis in previously treated pediatric subjects with hemophilia B. The objective of this planned interim analysis was to determine the PK parameters of rFIXFc in subjects enrolled in Kids B-LONG and compare these parameters to their pre-study FIX PK parameters. MethodsThis multicenter, open-label, phase 3 study is currently enrolling previously treated subjects aged<12 years with severe hemophilia B (≤2 IU/dL endogenous FIX), at least 50 exposure days (EDs) to FIX products, and no inhibitors to FIX. Subjects are stratified into two age cohorts (<6 and 6 to<12 years of age). A weekly prophylactic regimen of 50-60 IU/kg of rFIXFc is administered to all subjects, with subsequent dose and interval adjustments based upon PK data and bleeding frequency. Subjects will continue treatment until they achieve 50 EDs. The primary endpoint is the incidence of inhibitor formation. A sequential PK analysis is performed to compare the PK parameters of rFIXFc with that of pre-study FIX products. PK sampling of pre-study FIX occurs at baseline prior to first dose of FIX (50 IU/kg) and at 5 additional time points through 48 hours. PK sampling of rFIXFc occurs prior to first dose of 50 IU/kg rFIXFc and at 7 additional time points through 168 hours following the first dose; a washout period of 96 hours is required before the first dose of both pre-study FIX and rFIXFc. Plasma FIX activity is measured using the one-stage clotting assay calibrated against a commercially available FIX plasma standard and the FIX activity-over-time profiles are analyzed by non-compartmental analysis (NCA) using the PK data analysis software Phoenix™ WinNonlin 6.2.1.51. A data cut-off date of 23 April 2013 was used to report PK data in this interim analysis. ResultsAt the time of this interim analysis, 24 subjects were enrolled and had received at least one dose of pre-study FIX and/or rFIXFc. Of 18 subjects with evaluable PK profiles, 15 had complete PK profiles for both pre-study FIX (BeneFIX®, Haemosolvex®, or Alphanine®) and rFIXFc. A comparison of PK parameters for rFIXFc versus FIX for both age cohorts is presented in Table 1. rFIXFc had a more than 3-fold prolongation in half-life and a more than 60% reduction in CL compared to the FIX products.Table 1PK of FIX products and rFIXFc in pediatric subjects (Geometric mean [95% CI])Half-life (hr)CL (mL/dL/kg)IR (IU/dL per IU/kg)Vss (mL/kg)< 6 yrsFIX (pre-study) n=518.1 (15.6 - 20.9)11.8 (9.27 - 15.0)0.525 (0.447 - 0.617)293 (247 - 348)rFIXFc (on-study) n=663.6 (42.1 – 96.2)4.36 (3.56 – 5.34)0.593 (0.494 - 0.711)344 (276 - 429)rFIXFc/FIX Ratio n=43.70 (2.56 - 5.34)0.385 (0.280 - 0.529)1.13 (0.981 - 1.31)1.21 (1.18 - 1.25)6 to<12 yrsFIX (pre-study) n=1317.8 (16.0 – 19.8)8.76 (7.35 - 10.5)0.638 (0.502 - 0.812)217 (165 - 286)rFIXFc (on-study) n=1370.4 (61.0 - 81.3)3.51 (3.01 – 4.09)0.718 (0.612 - 0.841)290 (237 - 354)rFIXFc/FIX Ratio n=113.99 (3.36 - 4.74)0.386 (0.322 - 0.462)1.16 (0.942 - 1.42)1.31 (0.992 - 1.74) ConclusionIn comparison to currently available FIX products, rFIXFc had a prolonged half-life and reduced CL in pediatric subjects, which was similar to previous observations in adults and adolescents. The final analysis of the Kids B-LONG study will provide further PK information and evaluate the safety and efficacy of rFIXFc in children. Disclosures:Fischer:Biogen Idec, Baxter, Novo Nordisk, Bayer: Membership on an entity's Board of Directors or advisory committees; Baxter, Bayer, Novo Nordisk, Pfizer: Research Funding. Kulkarni:Biogen Idec, Novo Nordisk, Baxter : Membership on an entity's Board of Directors or advisory committees. Ragni:Biogen Idec: Membership on an entity's Board of Directors or advisory committees; Bristol Myers Squibb, Smith Kline Glaxo, Tacere Benitec: Consultancy; Baxter, Bayer, Biogen Idec, Bristol Myers Squibb, CSL Behring, Merck, Novo Nordisk, Pfizer, Smith Kline Glaxo: Research Funding. Rangarajan:Baxter, Pfizer: Research Funding; Biogen Idec : Membership on an entity's Board of Directors or advisory committees. Dong:Biogen Idec: Employment, Equity Ownership. Li:Biogen Idec: Employment, Equity Ownership. Jiang:Biogen Idec: Employment, Equity Ownership. Nugent:Biogen Idec: Employment, Equity Ownership. Pierce:Biogen Idec: Employment, Equity Ownership. Allen:Biogen Idec: Employment, Equity Ownership.

Glycopegylated Factor IX Enables Prolonged Efficacy After Subcutaneous Injection But Requires a Higher Than Expected Plasma Activity To Prevent Bleeding In Hemophilia B Mice

BackgroundReduced frequency of administration as well as subcutaneous (s.c.) injection would improve the treatment of Hemophilia B. Conjugation to polyethylene glycol (PEG) has been shown to increase the half-life of i.v. dosed Factor IX (FIX), but s.c. dosing of PEGylated FIX was not previously evaluated. Because s.c. dosing is limited by volume and bioavailability, we evaluated the combination of PEGylation with the increased specific activity variant R338A to reduce the amount of protein needed to provide therapeutic levels of FIX. MethodsFIX-R338A was PEGylated on N-linked glycans in the activation peptide by periodate oxidation of sialic acid residues followed by conjugation to amino-oxy functionalized PEG. Pharmacokinetic (PK) profiles were determined in hemophilia B mice and cynomologous monkeys. Allometric scaling was used to predict dose regimens in humans. Prophylactic efficacy was determined in a Hemophilia B mouse tail bleeding model. Results60kDaPEG-R338A had prolonged terminal half-life in mice (3-fold) and monkeys (5-fold) and the s.c. bioavailability was 44% and 35%, respectively. The volume of distribution was reduced 5-fold. To achieve a trough level of 3% FIX activity, s.c. dosing at weekly, bi-monthly and monthly intervals was predicted to require doses of 7, 25 and 220 IU/kg in patients. However, in a tail vein transection injury model, approximately 10-fold higher plasma FIX activity levels of PEGylated proteins were found to be needed to protect hemophilia B mice against bleeding than was required for i.v. dosed un-PEGylated recombinant FIX. This difference was observed for PEGylated wild-type and R338A proteins, dosed i.v or s.c. We hypothesize that this is related to the reduced distribution of PEGylated FIX to the extravascular compartment. Trough levels of 30% FIX activity were predicted to be achievable in humans after weekly and bi-monthly s.c. dosing at 70 and 260 IU/kg. ConclusionsThe PEGylation of FIX led to a significant improvement in both i.v. and s.c. PK. Unexpectedly, a 10-fold higher plasma activity was needed for PEGylated FIX to provide protection against bleeding in Hemophilia B mice, suggesting that trough levels of 10 to 30% of PEGylated FIX activity may be needed in patients to provide efficacy equivalent to current therapy of recombinant or plasma derived FIX. Nevertheless, 60kDaPEG-R338A has the potential to treat hemophilia B patients with once weekly or twice monthly subcutaneous injection. Disclosures:Sim:Bayer HealthCare: Employment. Brooks:Bayer HealthCare: Employment. Mallari:Bayer HealthCare: Employment. Xu:Bayer HealthCare: Employment. Feldman:Bayer HealthCare: Employment. Schneider:Bayer HealthCare: Employment. Patel:Bayer HealthCare: Employment. Blasko:Bayer HealthCare: Employment. Ho:Bayer HealthCare: Employment. Su:Bayer HealthCare: Employment. Liu:Bayer HealthCare: Employment. Laux:Bayer HealthCare: Employment. Murphy:Bayer HealthCare: Employment.

Population Pharmacokinetic Modeling of BeneFIX in Pediatric and Adult Patients with Hemophilia B Demonstrates Weight as An Important Factor Contributing to Inter-Patient PK Variability.

Clinical trials in patients with hemophilia B have demonstrated considerable inter-patient variability in the pharmacokinetics (PK) of Factor IX (FIX) replacement therapy, including the recovery, an important PK parameter from which individualized clinical dosing decisions are calculated. In clinical trials of plasma-derived and recombinant factor IX replacement therapies, the age of the patient has been demonstrated to affect recovery (younger patients have lower recovery values than older patients), however the specific contribution of age, as well as additional covariates such as body weight and race to PK variability has not been systematically evaluated. We analyzed an extensive database of BeneFIX PK data collected from 8 separate clinical trials conducted over 13 years. A systematic approach involving population PK modeling and simulation was utilized for the first time to estimate the effects of individual-specific covariate factors on PK of BeneFIX in the pooled population that included pediatric and adult patients. A total of 4025 plasma FIX activity PK data sets collected from 191 patients, aged 0 to 69 years were used for the analysis. There were 111 children (£15 years) including 53 infants <2 years, and 80 adults (>15 years) in the pooled data. The majority (84%) of patients were Caucasian. The remaining patients were African American (7%), Hispanic (4%), Asian/Japanese (3%), and other ethnicity (3%).The data were analyzed using nonlinear mixed-effects modeling with the NONMEM software system. Age, weight, and race were examined as covariates for the ability to explain inter-individual variability in the BeneFIX PK. The PK in pediatric and adult patients was described by a two-compartment model with first-order elimination and a zero-order input using the following parameters: clearance (CL), volume of central compartment (V1), volume of peripheral compartment (V2) and inter-compartmental clearance (Q). Population predicted BeneFIX PK parameters, standardized to a 70 kg patient, were 7.46 (standard error; 0.20) mL/hr/kg, 131 (4.4) mL/kg, 71.5 (2.1) mL/kg and 12.1 (1.1) mL/h/kg, for CL, V1, V2 and Q, respectively. The final model was able to simulate data in close agreement with the actual study observations.Variability (%CV) in BeneFIX PK was explained most significantly by allometrically scaled body weight (Figure 1a), while age and race had no discernible effects on BeneFIX PK in the population studied. Observed recovery values were slightly lower in children (£15 years) compared with those in adults (>15 years) since the initial volume of distribution (V1), normalized to body weight, was slightly higher in children than in adults, while the variability in the observed recovery values was comparable between children and adults (Figure 1b).In conclusion, the present analysis, for the first time, systematically describes and quantifies the sources of age-dependent variability of factor IX PK, using BeneFIX data, and provides a better understanding of the importance of body weight in the disposition of BeneFIX. This confirms existing weight-based dosing recommendations and further supports consideration of dosing adjustments that are individualized based on the patient's body weight in the context of the achieving the desired clinical response, such as recovery. This also may be important in pediatric patients during growth periods associated with significant weight change. [Display omitted] [Display omitted]

Therapeutic Effects of Hepatocyte Transplantation on Hemophilia B

Hepatocyte transplantation offers an alternative therapeutic approach in the treatment of liver-related diseases. Hemophilia B is a bleeding disorder lacking factor IX (FIX) production in the liver, and achieving more than 1% coagulation activity results in significant improvement in the quality of life of the patients. The aim of this study was to investigate the efficacy of hepatocyte transplantation in the mouse model of hemophilia B. We transplanted isolated normal mouse hepatocytes into the liver of FIX knock-out mice. In some recipient mice, additional hepatocyte transplantations were performed 15 days after the first transplant. The recipient plasma FIX activities increased at 1% to 2% and persisted throughout the experimental period. An additional increase was achieved by the repeated transplantation. Close correlation between FIX messenger RNA levels of the liver and plasma FIX activity levels was observed. These results demonstrate that hepatocyte transplantation can provide therapeutic benefits in the treatment of hemophilia B.