RARE DISEASE
Hemophilia B Leyden
Hemophilia B Leyden
Hemophilia B Leyden
Synonyms: F9 deficiency, Leyden type, Factor IX deficiency, Leyden type
Synonyms: F9 deficiency, Leyden type, Factor IX deficiency, Leyden type
Synonyms: F9 deficiency, Leyden type, Factor IX deficiency, Leyden type
Drug discovery
1,455
papers
On emerging therapies
Overview
Hemophilia B Leyden (HBL) is an X-linked recessive subtype of hemophilia B caused by mutations in the F9 gene promoter, impairing factor IX production in childhood. Hormonal activation of intact promoter regions during puberty drives progressive factor IX elevation, often normalizing by midlife [1][2][12]. It accounts for ~3% of hemophilia B cases and presents with severe childhood bleeding that ameliorates with age [1][14][19].
Burden
Childhood: High bleeding risk (joints, soft tissues) necessitates frequent infusions, impacting quality of life [1][13].
Economic: Annual hemophilia B treatment costs exceed $600,000 USD in severe cases, though HBL costs decline with age [3][9].
Long-term: Reduced arthropathy risk compared to classic hemophilia B due to endogenous factor correction [9][13].
Therapies
Factor IX replacement: Prophylaxis in early childhood; transition to episodic treatment as levels rise [1][8].
Antifibrinolytics (e.g., tranexamic acid): Adjunct therapy for mucosal bleeding [1][18].
Monitoring: Regular factor IX assays to guide dose reduction or discontinuation in adulthood [2][17].
Categories: rare genetic diseases, rare hematological diseases
Research Papers
1,455 drug discovery papers about Hemophilia B Leyden. Recent publications:
1,455 drug discovery papers about Hemophilia B Leyden. Recent publications:
categories:
Small molecules
small molecules
2026-09-07 | Catheter salvage with antibiotic lock therapy for central venous port infection due to Pseudoxanthomonas sp. in a child with hemophilia B.
Catheter-related bloodstream infections (CRBSIs) generally necessitate prompt catheter removal, which poses significant hemorrhagic risks in patients with hemophilia. Consequently, catheter salvage utilizing antibiotic lock therapy (ALT) serves as a critical adjunctive strategy. We describe an exceptionally rare case of CRBSI caused by Pseudoxanthomonas sp., an environmental Gram-negative bacillus, and its successful management. A 4-year-old boy with severe hemophilia B developed persistent bacteremia originating from an implanted central venous access port. The pathogen was identified as Pseudoxanthomonas sp. utilizing matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and 16S rRNA gene sequencing. Catheter removal was deemed high-risk due to the patient's underlying hemophilia B and associated risk of major bleeding. Therefore, a catheter salvage strategy was pursued through a combination of systemic antimicrobial therapy and ALT. The patient received systemic antibiotics, adapting through piperacillin/tazobactam, ceftazidime, and trimethoprim-sulfamethoxazole. ALT was administered concurrently, initially using a ceftazidime-heparin lock solution, and later transitioning to a ciprofloxacin-heparin lock following an episode of suspected drug fever. Despite initial persistent bacteremia, this dual approach effectively eradicated the intraluminal infection. The central venous port was successfully retained with no recurrence observed over four months post-therapy. Systemic antimicrobial therapy combined with ALT can be an effective catheter-preserving strategy for high-risk patients with device-related infections caused by rare environmental non-fermenting Gram-negative organisms such as Pseudoxanthomonas sp.
2026-09-03 | Transforming Hemophilia Treatment With Novel Rebalancing Agents: Clinical Studies and Practical Perspectives.
While conventional prophylaxis with clotting factor concentrates (CFC) is the standard of care for hemophilia A and B, its challenges include frequent intravenous administration, factor level fluctuations, and potential inhibitor development. Rebalancing agents, including fitusiran (antithrombin-lowering small interfering ribonucleic acid), concizumab and marstacimab (tissue factor pathway inhibitor antagonists), are novel nonfactor therapies that restore hemostatic balance by targeting natural anticoagulants rather than replacing missing clotting factors. Clinical trials demonstrate that these three rebalancing agents provide effective prophylaxis for people with hemophilia (PwH) with or without inhibitors through subcutaneous administration. Rebalancing agents thus provide subcutaneous alternatives to current treatment regimens and offer effective prophylaxis for people with hemophilia B with inhibitors who previously had limited therapeutic options. Their novel mechanism of action may necessitate individualized dose optimization and unique approaches for managing breakthrough bleeds and surgeries. Those conditions require reduced dosing of CFC or bypassing agents to mitigate potential thrombotic risk. In addition, the use of rebalancing agents in pediatric patients (<12 years old) remains under investigation. While promising, successful implementation depends on individualized treatment approaches, appropriate monitoring protocols, and thorough patient education to improve current care for PwH.
2026-03-14 | Balancing the benefits and risks of rebalancing coagulation in haemophilia.
Rebalancing agents represent a novel therapeutic class in haemophilia, designed to restore the deficient thrombin generation that underlies bleeding. Unlike factor replacement or factor VIII mimetic therapies, rebalancing agents act by downregulating natural anticoagulants. By partially inhibiting these physiological brakes of coagulation, they induce a controlled and reversible procoagulant shift. These agents have shown clinically meaningful reductions in bleeding rates across both haemophilia A and B, including in patients with inhibitors. However, their therapeutic window appears narrow; excessive thrombin generation might lead to thrombosis, whereas conservative dosing could fail to fully prevent bleeding. The optimal balance between efficacy and safety, therefore, remains to be defined. Current or potential future indications include haemophilia B with inhibitors, young children in whom venous access limits prophylaxis, patients with suboptimal bleed control despite standard therapies, or those with other bleeding disorders. Tissue factor pathway inhibitor inhibition might confer specific benefits in reducing joint bleeding and synovitis, due to its local tissue expression. Overall, rebalancing agents broaden the therapeutic landscape but require judicious patient selection, individualised monitoring, and continued evaluation of their long-term safety and clinical positioning.
2026-01-31 | Evidence-based dental management strategies for individuals with congenital hemophilia: a systematic review.
BACKGROUND: People with hemophilia commonly present with a range of bleeding symptoms, from minor oral cavity bleeds to life-threatening events such as intracranial hemorrhage. People with hemophilia often exhibit poor oral health, attributed to disease-specific barriers and a fear of dental procedures, which may exacerbate their oral disease burden. This systematic review aimed to evaluate the various dental procedures performed in patients with hemophilia and the corresponding clotting factor concentrate replacement regimens used for individuals with mild, moderate, and severe forms of the disease. METHODS: An electronic database search was carried out using MEDLINE by PubMed, Scopus, Google Scholar, Web of Science, ProQuest, CINAHL, EBSCO Dental collection and EMBASE databases from inception to March 2025 for studies published in English language. The search strategy terms included were “hemophilia A”, “hemophilia A”, “hemophilia B”, “hemophilia B”, “dental care”, “oral surgery”, “complications”, “bleeding”. Case control studies, randomized controlled trials, observational studies and case reports addressing the dental treatments for people with hemophilia A/hemophilia B were included. Cases of acquired hemophilia and cases of hemophilia who are inhibitor positive were excluded. RESULTS: A total of 23 studies were included for the final review. Majority of the studies have ensured to achieve 30% to 50% factor correction for dental procedures. Routine dental care procedures like restoration and dental scaling with the necessary technical specifications can be safely performed. Dental extractions can be safely performed using local infiltration anesthesia; however, administering nerve blocks typically necessitates prior administration of clotting factors due to the elevated bleeding risk. Adjuvant systemic anti-fibrinolytics like Epsilon-aminocaproic acid (EACA) and tranexamic acid greatly reduces the need for additional factor infusion. CONCLUSIONS: The use of prophylactic clotting factors during dental interventions in hemophilia patients showed notable inconsistencies across studies. This inconsistency underscores the importance of conducting larger, prospective clinical studies to better understand the rationale behind clotting factor use and its effects on dental treatment outcomes in patients with varying degrees of hemophilia severity.
2025-10-27 | Suppressing microtubule detyrosination augments adeno-associated virus 2 endosomal escape and gene delivery.
Adeno-associated virus (AAV) is a widely used vector for gene delivery, yet the host intracellular trafficking barriers often limit its therapeutic efficacy. Here, we identify microtubule detyrosination - a microtubule post-translational modification - as a key regulator of AAV2 endo-lysosomal processing. Using super-resolution microscopy (SIM/STORM), we show that upon AAV2 endocytosis, the host upregulates microtubule detyrosination via the GSK3β-CLASP2 signaling axis. Single-particle tracking of recombinant virus reveals that detyrosinated microtubules form a physical and functional barrier, restricting AAV2 motility and promoting lysosomal trapping. Restoring microtubule tyrosination via tubulin-tyrosine ligase overexpression or pharmacological inhibition of detyrosination with parthenolide, enhances endosomal escape and perinuclear accumulation of AAV2, translating to improved gene delivery in host cells. Notably, a clinically relevant pro-drug of parthenolide (DMAPT) also displayed a similar trend of enhancing AAV2-driven coagulation factor IX expression in hemophilia B mouse models. Our findings uncover a host mechanism that reshapes the microtubule landscape to restrict AAV2 trafficking and identify microtubule detyrosination as a novel druggable target to improve AAV-based gene therapy.
proteins
2026-09-25 | Personalized Treatment of Hemophilia: Matching Therapies to Patient Needs in a Rapidly Evolving Landscape.
The therapeutic landscape of hemophilia, a rare inherited bleeding disorder, has rapidly evolved, introducing several novel modalities: extended half-life (EHL) coagulation factor concentrates, non-factor therapies, hemostasis-rebalancing agents, and gene therapy. These advances have improved clinical outcomes by reducing bleeding and treatment burden. However, individualizing treatment in routine practice has become more complex. This narrative review aims to provide a practical summary of available treatment options for pharmacologists, policymakers, and other readers who are not hemophilia specialists. A practical decision framework integrates available data with the clinical indication (regular prophylaxis, management of breakthrough bleeding, and perioperative care), patient-specific modifiers (age, lifestyle, inhibitor status, venous access, joint phenotype, comorbidities, and thrombosis risk). Drug therapies are discussed according to clinical evidence, including pivotal phase 3 trials, long-term extension studies, real-world data, and late-stage development programs. Factor replacement remains critical for hemostatic control during acute bleeding, surgery, and other interventions where predictable and measurable exposure is needed, whereas non-factor and rebalancing therapies provide low-burden prophylactic alternatives with distinct safety profiles and monitoring challenges. Direct comparisons between treatment classes are limited, making treatment individualization essential. Gene therapy has demonstrated more durable outcomes in hemophilia B than in hemophilia A. This review supports shared decision-making and individualized treatment selection in modern hemophilia care. While clinical trial evidence is limited by the scarcity of head-to-head comparisons and incomplete integration of real-world determinants, registry data collection will be essential.
2026-08-27 | Physiologically Based Pharmacokinetic (PBPK) Modeling of FIX in Pediatric Hemophilia B: Extravascular Distribution and Dosing Optimization.
Background: Prophylaxis in children with hemophilia B (HB) lacks quantitative approaches that integrate both plasma exposure and tissue distribution. This study aimed to develop and validate a physiologically based pharmacokinetic (PBPK) model of factor IX (FIX) for pediatric HB. The model incorporated the binding of FIX to type IV collagen (Col4) to characterize its distribution in both plasma and extravascular tissues. Methods: A total of 20 children with severe HB were included, contributing 219 plasma samples. The base PBPK model was first established and verified using adult and plasma-derived FIX (pdFIX) data. It was subsequently extrapolated to children by integrating FIX-CTBB parameters and pediatric observations for model calibration. The validated model was used to characterize plasma pharmacokinetics, predict tissue distribution and target attainment, and simulate alternative prophylactic dosing regimens. Results: The model adequately described the plasma pharmacokinetics of FIX in children and predicted substantial extravascular distribution. Total extravascular exposure was approximately sixfold higher than plasma exposure. Marked heterogeneity in target attainment was identified across tissues. Lower target attainment was observed in the colon, pancreas, and brain, whereas delayed attainment occurred in bone and muscle. Simulations of prophylactic dosing regimens suggested that 75 IU/kg twice weekly may provide a favorable balance among sustained FIX exposure, tissue-level target attainment, and treatment burden. Conclusions: This PBPK model provides a mechanistic and quantitative framework for characterizing plasma and tissue exposure to FIX in children with HB and may support individualized optimization of FIX prophylactic dosing.
2026-08-16 | Extravascular distribution of factor IX-review of experimental and clinical evidence, and relevance for hemophilia B replacement therapy.
Factor IX (FIX) is a relatively small molecule (55 kDa) that distributes physiologically beyond the plasma pool into the extravascular space. This contrasts with factor VIII, which is confined to the bloodstream as a consequence of its larger size (∼300 kDa) and binding to von Willebrand factor. The extravascular distribution of FIX may be significant in relation to factor replacement therapy in patients with hemophilia B. Given the increasing number of relevant publications over recent years, we critically reviewed and evaluated the experimental and clinical data relating to the extravascular distribution of FIX, considering both the native molecule and therapeutic products generated via biotechnological approaches. Endogenous FIX has an extensive distribution to tissues outside of plasma and is in dynamic equilibrium between plasma and the extravascular compartment. Approximately two-thirds of total FIX exists reversibly bound to type IV collagen in the vessel wall and extravascular space. This may produce an extravascular reservoir of FIX extending the plasma hemostatic role. Consequently, plasma FIX activity alone may not fully reflect the hemostatic potential of FIX prophylactic treatment. Extravascular FIX could be relevant for controlling and preventing both clinical and subclinical bleeds. When used as prophylactic treatment, extended half-life FIX products demonstrate similar annualized bleeding rates, but with a wide range of FIX trough levels and varying extents of extravascular distribution. Clinical implications of variation between FIX products remain to be fully understood; more knowledge is required. Further studies may help to address knowledge gaps, potentially informing treatment optimization.
2026-07-13 | Symptoms, Diagnosis, and Treatment for Women and Girls With Hemophilia: A Narrative Review.
Hemophilia is an X-linked bleeding disorder previously thought to present only in men. This sentiment is rapidly changing as the information around women and girls' experiences of bleeding symptoms has evolved, sparking intense discussion among researchers, clinicians, patients, and patient advocates regarding appropriate nomenclature. The primary objective of this narrative review is to build a comprehensive understanding of how women with hemophilia experience symptoms, how those symptoms are managed, navigate barriers to care, as well as discuss what can be done to alleviate barriers amongst this population. This is a qualitative narrative review which incorporates literature search strategies alongside testimonial from patient advocates to inform study priorities. This review identified multiple barriers to care for women and girls with hemophilia, including recognizing symptoms of abnormal bleeding, feeling comfortable asking for help, dealing with stigma from clinicians, getting an appropriate referral, accessing screening, facing challenges along the diagnostic pathway, and receiving treatment for symptoms. Another challenge is the wide variety of places a woman or girl may go to seek care for her bleeding symptoms, including primary care providers, gynecologists, hematologists, emergency medicine physicians, and rheumatologists. We conclude that while important strides have been made in this area in research and understanding, gaps remain. The research gaps in the differential symptom presentation when compared to men, potential efficacy and effectiveness of treatments in women as well as gender based behavioral difference are crucial to improving care and mitigating barriers for this cohort. This literature review combines information on symptoms, blood and genetic screening, diagnosis, treatment, current barriers to care, and next steps into a comprehensive perspective of the current available research. Evidence indicates that women with hemophilia are more likely than men to experience concerns related to family planning. In addition, women, in general, are more likely to engage in presenteeism rather than absenteeism when managing menstrual symptoms, attending work or school while unwell, which can result in reduced productivity. While screening techniques exist, novel rapid assays are being developed that could be more effective for screening women, particularly those who require multiple screenings before a diagnosis can be established. This can be combined with increased screening protocols to systematically identify carriers within families affected by hemophilia to ensure diagnosis. However, current efforts tend to focus on women of childbearing age, although premenarchal girls also experience hemophilia-related symptoms. The modalities of care for women and girls with hemophilia are numerous including pharmaceuticals such as factor replacement therapy, desmopressin, antifibrinolytic drugs, nonfactor therapy, and hormonal therapy. Additionally, assistance from physiotherapists, rheumatologists, and orthopedic surgeons can help manage joint related complications. Even with many care options, significant barriers to care persist, including the minimization of symptoms, avoidance of medical care, normalization of symptoms due to family history, and difficulties accessing care because of caregiving responsibilities. Existing care structures should be leveraged to provide better support for women and girls with hemophilia and symptomatic carriers. These could include more information provided within caregiving support groups, changes in guidelines, and wider understanding from the medical community as women and girls with hemophilia may seek assistance for their symptoms at a wide variety of clinical locations.
2026-07-11 | Immunopeptidomics of blood coagulation factor IX: a core peptide derived from the protease domain is promiscuously presented on HLA-DR.
Hemophilia B is an X-linked bleeding disorder that results in a qualitative or quantitative factor IX (FIX) deficiency. A subset of hemophilia B patients treated with FIX replacement therapy develop antibodies against FIX. The development of FIX inhibitors can present as allergic or anaphylactic reactions in some patients. It is currently unknown why a subset of hemophilia B patients develop inhibitors. CD4+ T cells recognizing FIX-derived peptides on major histocompatibility complex (MHC) class II on antigen-presenting cells are crucial for the development of class-switched, high-affinity anti-FIX antibodies. In this study, we explored MHC class II presentation of FIX-derived peptides by antigen presenting cells. We incubated purified FIX with monocyte derived dendritic cells of healthy, human leukocyte antigen-typed donors. MHCII peptide complexes were immunopurified, followed by peptide elution and mass spectrometry-based analysis of eluted peptides. We analyzed 12 healthy donors; of them, 8 presented FIX-derived peptides. The majority of FIX peptides were derived from the serine protease domain of FIX. With the exception of 1 donor, all of them presented at least one peptide containing the same core sequence, "NVIRIIPHHN" (residues 295-306 of FIX). Taken together, we identified a promiscuously presented peptide derived from the protease domain of FIX. Based on its frequent presentation in multiple donors, we speculate that this peptide may be recognized by FIX-specific CD4+ T cells that develop in hemophilia B patients with inhibitors. Peptides identified in our study can be used for inhibitor risk stratification and development of novel therapies to induce tolerance.
antibodies
2026-09-18 | Subcutaneous MG1113 in severe hemophilia A and B: phase 1b study for safety, pharmacokinetics, and pharmacodynamics.
MG1113 is an immunoglobulin G4 monoclonal antibody targeting the Kunitz-2 domain of tissue factor pathway inhibitor (TFPI), developed as a hemostatic rebalancing agent for patients with hemophilia A or B. We aimed to investigate the safety, pharmacokinetics (PK), pharmacodynamics, and preliminary hemostatic effects of MG1113. This phase 1b clinical trial was conducted in a multicenter, prospective, stepwise dose-escalating (2.0, 3.0, and 3.3 mg/kg) design. MG1113 was administered subcutaneously once weekly for 8 weeks. Fifteen male patients (n = 5/cohort) diagnosed with severe hemophilia A (n = 14) or B (n = 1) without inhibitors were enrolled. MG1113 was well tolerated, with an adverse event (AE) rate of 40.0% (6/15). No serious AEs, early withdrawals, or dose interruptions occurred. PK analysis demonstrated a nonlinear profile, with the peak plasma concentration at 33 to 48 hours post dose. Free TFPI and diluted prothrombin time (PT) decreased from baseline, while thrombin generation markers increased. Exploratory analysis showed a notable numerical reduction in annualized total bleeding rates at higher doses: 91.7% at 3.0 mg/kg and 76.2% at 3.3 mg/kg. The zero bleeding rate was 20.0%, 60.0%, and 40.0% at doses of 2.0, 3.0, and 3.3 mg/kg, respectively. MG1113, administered subcutaneously as a prophylaxis in patients with severe hemophilia A or B without inhibitors for 8 weeks, demonstrated an acceptable safety profile with a PK profile suitable for once-a-week dosing. The pharmacodynamics marker changes were consistent with TFPI inhibition, which was associated with reductions in bleeding events. This trial was prospectively registered at www.ClinicalTrials.gov (#NCT05493631).
2026-07-30 | Concizumab prophylaxis in a 2-year-old patient with severe hemophilia B and inhibitor: a case report.
Hemophilia B is a rare X-linked congenital bleeding disorder characterized by a deficiency in coagulation factor IX (FIX). Standard management relies on exogenous factor replacement; however, the development of neutralizing alloantibodies (inhibitors) against infused clotting factor can significantly reduce therapeutic efficacy and complicate long-term management. Consequently, patients turn to bypassing agents or non-factor therapies to help achieve adequate hemostatic control. Concizumab is a novel subcutaneous non-factor therapy for hemophilia A and B that targets the tissue factor pathway inhibitor (TFPI). While it is approved for patients >12 years old, data remains sparse in younger children. Prophylactic treatment with concizumab reduces several limitations associated with inhibitor development and variability in treatment response with conventional therapies, especially in pediatric populations. We report a toddler with hemophilia B who developed a low-titer inhibitor following treatment with recombinant coagulation factor IX agents, resulting in recurrent bleeding complications and consistent subtherapeutic hemostatic control on standard bypassing agents. The patient was transitioned to concizumab for long-term prophylaxis, with dose adjustments based on clinical response and concizumab drug levels. Following the initiation of concizumab, the patient demonstrated a marked reduction in bleeding episodes. We highlight an individualized early drug-level-guided dose escalation approach in a very young child, demonstrating that pharmacokinetic monitoring can be utilized proactively to optimize therapeutic response in this age group, leading to effective drug levels and excellent clinical response. This case supports the role of concizumab in potentially reducing treatment burden and improving hemostatic outcomes in young patients with severe hemophilia B and inhibitors.
2026-06-18 | A plain language summary of the BASIS study looking at people living with severe hemophilia A or B with inhibitors and being treated with marstacimab.
What is this summary about? This summary describes a clinical study looking at how well marstacimab works in people living with hemophilia with inhibitors. The study was published in the medical journal Blood. Hemophilia is caused by not having enough blood clotting factors, which are proteins found in the blood that help form a clot and stop bleeding. People living with hemophilia either don't make these proteins, have low amounts of these proteins, or these proteins do not work well. Hemophilia is usually inherited from biological parents, meaning it is passed on to their children through genes. In some cases, hemophilia happens even if no one in the family has it. There are some treatments to replace the missing clotting factor. This type of treatment is called factor replacement therapy and contains the missing clotting factor proteins. Some people make antibodies against the replacement clotting factors, so the replacement clotting factors do not work as well as they need to for the blood to clot. This is called hemophilia with inhibitors. People who have hemophilia with inhibitors need to take medicines called bypassing agents instead of replacement clotting factors. These medicines aim to activate the body's blood clotting system, but do not always work well. They also need to be injected into a vein, known as intravenous infusion, or IV infusion for short. IV infusions are taken several times a week. Different options to IV factor replacement therapy for people living with hemophilia A or hemophilia B are called non-factor replacement therapy. A protein in the blood called Tissue Factor Pathway Inhibitor, or TFPI, can also prevent blood clotting. Marstacimab is a type of non-factor replacement therapy that attaches to TFPI and stops its activity. For people living with hemophilia, marstacimab can help blood to form a clot when needed. Marstacimab is injected under the skin. This can be an easier way to receive medicine than an injection into a vein. Marstacimab offers a new way to treat people living with hemophilia. What were the results of the study? The study showed that people living with hemophilia with inhibitors who were treated with marstacimab had fewer bleeding events over 1 year compared to previous therapy with bypassing agents. Most side effects with marstacimab treatment were minor or could be easily managed. One person stopped taking marstacimab treatment because they developed a skin rash that got better over time. What do the results mean? The study showed that marstacimab could help prevent bleeding in people living with hemophilia A or B with inhibitors.
2026-06-12 | The Dilemma of Providing Advanced Hemophilia Treatments in Developing Countries - For Whom, by Whom and Where?
Hemophilia, a congenital deficiency of factor VIII (hemophilia A) or factor IX (hemophilia B), leads to recurrent bleeding episodes that may cause progressive joint damage and long-term disability. Traditional management relies on intravenous factor replacement therapy; however, limited half-life, immunogenicity, venous access challenges, and the burden of frequent infusions have prompted the development of extended half-life (EHL) factor products. Although EHL therapies represent an important advancement, they only partially reduce treatment burden and do not fully meet expectations for improved convenience and sustained bleed protection. Recent innovations are reshaping the therapeutic landscape. Nonfactor subcutaneous therapies such as anti-TFPI molecules, antithrombin reducing agents, and anti-protein C agents offer simplified administration with the potential for improved adherence. Gene therapy provides the prospect of a long-term therapeutic effect in selected patients. In Türkiye, hemophilia care remains largely factor-based; however, clinical trial participation and recent regulatory approvals for selected novel therapies have begun to expand real-world experience with these emerging treatment options. As global practice shifts toward individualized, less invasive treatment approaches, expanding availability of novel therapies and optimizing patient-specific treatment strategies will be essential. This review examines current and evolving treatment options, key challenges, and future opportunities shaping the trajectory of hemophilia management.
2026-06-11 | Discovery and optimization of marstacimab, a human monoclonal antibody targeting tissue factor pathway inhibitor for the treatment of hemophilia A and B.
We report the discovery and optimization of marstacimab, a novel monoclonal antibody targeting tissue factor pathway inhibitor (TFPI), for the treatment of hemophilia A and B. Hybridoma and phage display approaches identified antibodies that blocked the TFPI: coagulation factor Xa (FXa) interaction. Antibodies bound TFPI with nanomolar affinity to multiple epitopes, including one that covered the entire FXa binding surface and others that partially overlapped the interface from different sides of the TFPI-K2 domain. Several antibodies reduced bleeding in a hemophilia A mouse injury model for up to 96 h following a single dose. Rabbit pharmacokinetic studies indicated that antibodies with ≤~1 nM TFPI-binding affinity were cleared rapidly from circulation, whereas TFPI-23 (5.72 nM) had a longer plasma residence time. Pharmacokinetic-pharmacodynamic modeling indicated that this intermediate affinity allowed circulating concentrations of antibodies such as TFPI-23 to maintain concentrations required for 50% residual activity; in contrast, higher-affinity antibodies quickly decreased to concentrations that would not effectively neutralize TFPI. The end-to-end process leading to final candidate selection incorporated rigorous assessment of biophysical properties, including thermal stability, aggregation propensity, viscosity, predicted immunogenicity, stable cell line productivity, and nonspecific binding. An optimized derivative of TFPI-23, TFPI-106 (PF-06741086, known as marstacimab), had the functional and biophysical properties with other characteristics suitable for clinical development and was selected as the final candidate. TFPI-106 elicited enhanced hemostasis in hemophilic plasma, shortened clotting time, and enhanced thrombin generation velocity. Marstacimab is now approved for patients with hemophilia A or B with or without inhibitors.
gene therapies
2026-09-25 | Advancements in CRISPR-based in vivo gene therapy for hemophilia.
Hemophilia is an X-linked hereditary bleeding disorder caused by loss-of-function mutations in the genes encoding coagulation factors, leading to excessive bleeding and potentially being life-threatening. Currently, regular treatment for hemophilia is the infusion of recombinant blood coagulation factors. This approach is not only costly but can also give rise to complications such as the development of neutralizing antibodies (Nabs), which impede the therapeutic outcome. Hemophilia is a monogenic disease, making gene therapy a promising curative measure that includes gene addition and gene editing approaches. Adeno-associated virus (AAV) vectors have gained massive attention as the premier delivery vehicle for clinical gene therapy due to their diverse tissue tropisms dictated by the natural and engineered AAV capsids, their excellent safety profile since AAVs do not cause any known human diseases, low immunogenicity, and long-lasting gene expression. Several AAV-based gene addition therapies have been approved for hemophilia B and hemophilia A, and dozens of similar AAV-based clinical trials are underway. Gene editing technologies, like Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/CRISPR-associated protein 9 (Cas9), have shown immense potential in the treatment of genetic diseases. CRISPR/Cas9-mediated transgene integration provides critical advantages over regular gene insertion therapy by enabling site-specific, targeted genomic integration rather than random integration. Clinical trials focusing on AAV-CRISPR/Cas9-mediated knock-in of human genes represent the frontier of in vivo genetic medicine, and one such prominent ongoing clinical trial for hemophilia B is designed to insert the human Factor IX gene into hepatocytes. This review outlines recent advances and feasible strategies of CRISPR/Cas9-based genome editing for hemophilia therapy, highlights the potential applications of next-generation gene editing and vector delivery technologies, and offers new insights for the advantages, limitations, and future directions for these novel treatment modalities.
2026-09-17 | Factor IX Padua AAV gene therapy in adolescents with hemophilia B: a phase 1 trial.
Adeno-associated virus (AAV)-mediated factor IX Padua gene therapy has demonstrated good safety and efficacy in adult patients with hemophilia B, but its safety and efficacy in adolescent patients with hemophilia B remain unknown. Here we report a multicenter, single-arm, phase 1 study involving 11 adolescent participants (aged 12-18 years) with severe or moderately severe hemophilia B (factor IX coagulant activity (FIX:C) ≤2 IU dl-1) in China. All of them received the AAV gene therapy BBM-H901 at a dose of 5 × 1012 vector genomes per kilogram of body weight and were then enrolled in a 52-week follow-up. The primary endpoint was safety. No dose-limiting toxicity was observed throughout the study. The most common adverse events included elevation of white blood cell count, elevation of neutrophil count and rash associated with corticosteroid use. One serious adverse event and two grade 3 adverse events occurred. Abnormal liver function was observed in one participant, with elevated alanine aminotransferase (197.0 U l-1) and aspartate aminotransferase (75.0 U l-1) levels, which returned to normal 4 weeks after immunosuppression therapy. The key secondary endpoints included the mean (s.d.) FIX:C at week 52 following infusion, which was 41.8 (30.1) IU dl-1 (one-stage SynthASil method), and the mean annualized bleeding rate, which decreased from 13.9 to 0.5. In this study, we show that the gene therapy drug BBM-H901 for hemophilia B is safe in adolescent patients, providing initial insights into its efficacy. ClinicalTrials.gov identifier: NCT05709288 .
2026-07-27 | Hemophilia in Mexico: Updated Consensus Recommendations on Diagnosis, Treatment and Gene Therapy.
Hemophilia is an X-linked inherited bleeding disorder, classified as type A or type B. Therapeutic advances offer new treatment options that improve disease control and reduce associated complications, including inhibitor development and hemophilic arthropathy. This document aims to update the Mexican hemophilia consensus, reviewing current evidence on diagnosis and management, and addressing gaps in the treatment and follow-up of patients in Mexico, aligning local needs with international recommendations. A PubMed literature search covering the last five years (up to September 2025) was conducted, prioritizing consensus statements, guidelines, and systematic reviews. Using the Delphi methodology, a structured questionnaire was submitted electronically to forty-four experts. Aspects without initial agreement were discussed at an in-person meeting. Consensus was defined as at least 80% of votes in favor. Recommendations were issued across six domains: laboratory diagnosis, genetic testing, management of hemophilia A and B without and with inhibitors, adjuvant treatments, and gene therapy. The recommendations address prophylaxis with coagulation factor concentrates, non-factor therapies, immune tolerance induction, perioperative management, pain management, and eligibility criteria and follow-up protocols for gene therapy with adeno-associated viral vectors. This consensus provides updated, evidence-based recommendations adapted to the Mexican healthcare context, identifying priority areas, including timely access to non-factor therapies and gene therapy, development of a national referral network for complex cases, and inclusion of novel therapeutic agents in the institutional essential medicines list, with the aim of improving the quality of life of people with hemophilia in Mexico.
2026-07-03 | Increased Gene Therapy Efficacy Through the Use of Extended Half-Life Clotting Factors.
The development of more effective gene therapy strategies for hemophilia B remains essential, as results of multiple clinical trials show significant interpatient variability in clinical outcomes, with a fraction of patients (up to 13%) even returning to prophylaxis. Another major challenge in current AAV based gene therapy for hemophilia B pertains to dose-dependent vector-related immune responses, requiring immune suppression. We investigated whether combining gene therapy with transgenes encoding extended half-life (EHL) coagulation factors could enhance therapeutic efficacy. Adeno-associated viral (AAV) vectors encoding a hyperactive factor IX variant R338L (i.e., FIX-Padua), genetically fused to a mutant human albumin (FIX-R338L-ALB(QMP)), were administered to both wild-type and hemophilia B mice. These chimeric transgenes were codon-optimized and driven by a hepatocyte-specific promoter. The AAV-FIX-R338L-ALB(QMP) vector demonstrated significantly improved efficacy compared to the control AAV-FIX-R338L vector, resulting in a sustained 4-fold and 3-fold increase in FIX antigen levels and activity, respectively. These increases were consistent with durable correction of the bleeding phenotype. Importantly, immunogenicity or liver toxicity was not increased, as no anti-FIX antibodies, alanine transaminase elevations, or liver immune infiltrations were detected following treatment. Furthermore, immune tolerance was achieved in the majority of hemophilia B mice treated with AAV-FIX-R338L-ALB(QMP), even after active immunization with FIX protein and adjuvant, which was found to be mediated by regulatory T cells. Additionally, no increase in thrombogenic risk was observed, indicated by stable D-dimer levels. These findings support the potential of FIX-R338L-ALB(QMP) fusion constructs encoding extended half-life FIX as a promising next-generation gene therapy for hemophilia B.
2026-06-21 | Development of an Agent-Based Model to Investigate Durability of Factor IX Activity in Hemophilia B Patients Treated With Etranacogene Dezaparvovec.
Many currently approved gene therapies use adeno-associated virus (AAV) to deliver DNA sequences encoding protein(s)-of-interest into cells. The AAV viral genome forms stable, circular DNA structures called episomes after entering the nuclei. Therapeutic proteins are then generated in vivo from transcription and translation of these episomes, and long-term durability thus depends on episome stability. Prior modeling work has utilized differential equation-based models to characterize AAV uptake and subsequent protein production. However, episome loss associated with target cell turnover is poorly described with these models. Here, an agent-based model (ABM) to overcome this shortcoming is developed. The liver was used as the example organ as it is known to be self-renewing and has been a common target for gene therapies. In this model, each hepatocyte is an agent, capable of division and death. When transduced, these agents acquire and carry episomes. During cell division, episomes are passed from mother to daughter cells. All episomes are presumed lost when transduced cells die. The ABM was applied to etranacogene dezaparvovec (formerly AMT-061 or CSL222), a liver-targeting gene therapy for hemophilia B consisting of AAV serotype 5 particles encoding a transgene for the Padua variant (R338L) of coagulation factor IX (FIX). ABM-simulated FIX activity in patients receiving this therapy was consistent with clinical observations over more than 2 years following treatment. This ABM was then used to generate 20-year predictions and explore biological mechanisms underlying long-term durability. The ABM framework and approach should be applicable to investigating durability of other AAV-based gene therapies.
other
2026-04-18 | Pseudoexon inclusion induced by three deep intronic variants in hemophilia B and correction achieved through an antisense oligonucleotide-based strategy.
Although studies have identified deep intronic variants associated with hemophilia B in patients undiagnosed by conventional genetic testing, knowledge in this field remains limited. Long range-PCR of entire F9 gene was used to screen variants of three unrelated genetically unresolved severe hemophilia B patients. In silico analysis and minigene assay with two minigene plasmid construction methods were conducted to explore the effects of candidate deep intronic variants on splicing. Three novel putative pathogenic deep intronic variants (c.278-765_278-764ins6.1kb, c.392-903A>G and c.724-751T>G) and one variant of uncertain significance (c.723+2708del) in F9 were identified in three patients. All the three putative pathogenic variants created de novo donor splice site and utilized cryptic acceptor splice site to generate pseudoexon. We successfully developed antisense oligonucleotide-mediated exon-skipping correction strategies for the three identified putative pathogenic variants and the previously reported c.392-864T>G. However, the results obtained from minigene assay revealed certain discrepancies with the clinical phenotype. It is still challenging to accurately characterize the pathogenicity of deep intronic variants in vitro. Overall, our results highlight the complementary role of whole-gene sequencing of F9 to conventional genetic diagnosis. Furthermore, we provide insight into a potential therapeutic approach based on antisense oligonucleotide technology-mediated exon-skipping.
2026-01-09 | Molecular mechanisms and therapeutic strategies for the recurrent F9 (c.520 + 13 A > G) variant in hemophilia B.
Hemophilia B (HB), an X-linked recessive disorder, results from variants in the coagulation factor IX gene (F9). The F9 c.520 + 13 A > G variant is a recurrent intronic variant in HB patients, accounting for 15.05% of all documented F9 intronic variants. Despite prior predictions of its impact, the molecular mechanism associated with moderate to mild HB remains undissected. In silico predictions and splicing-competent cDNA constructs were used to assess the impact of F9 c.520 + 13 A > G on mRNA splicing. Factor IX (FIX) variant (p.V174delinsGHNLM) expression in HEK293T cells was evaluated using activated partial thromboplastin time, enzyme-linked immunosorbent assay, Western blot analysis, and immunofluorescence analyses. Structural modeling and molecular dynamics simulations were performed to evaluate the structural impact of the variant. Engineered U1 small nuclear RNA (U1snRNA) was challenged with F9 full-length splicing-competent constructs to evaluate splicing correction. The F9 c.520 + 13 A > G variant caused nearly complete aberrant splicing, producing the F9 c.520_521insGTCATAATCTGA insertion and the in-frame FIX p.V174delinsGHNLM variant. A small amount (approximately 10%) of wild-type FIX was also detected. We characterize the p.V174delinsGHNLM variant, which exhibited impaired secretion and increased intracellular accumulation. Interestingly, an engineered U1snRNA partially rescued aberrant splicing, restoring functional FIX levels to approximately 40%. This study elucidates the molecular mechanism of the F9 c.520 + 13 A > G variant, which activates a cryptic 5' splice site in intron 5, leading to an in-frame FIX (p.V174delinsGHNLM) with secretion defects and loss of protein function. And Engineered U1snRNA partially rescued the splicing defect.
2025-12-08 | Liver-Specific Biocompatible Lipid Nanoparticle-Enabled mRNA Therapy for Haemophilia B.
The standard treatment for Haemophilia B (HB) involves frequent intravenous (IV) infusions of recombinant factor IX (FIX), which imposes a significant financial burden on patients. FIX delivery as messenger RNA using lipid nanoparticles (LNPs) presents a promising alternative, but achieving prolonged and effective protein expression remains challenging. To this end, we developed Galactosylated Lipid Nucleic Acid complex (GaLiNAx) to enhance the delivery of chemically modified FIX mRNAs. The nanocarrier encompasses an ionizable galactosylated lipid to enable receptor-mediated endocytosis and a transfection-competent cationic lipid for optimal mRNA complexation. We incorporated truncated albumin UTRs and base modifications in functional FIX mRNA to enhance hepatic translation. In an HB mouse model, GaLiNAx demonstrated therapeutically relevant FIX protein expression for about one month after single dose offering a cost-effective option. Safety assessments indicated that multiple doses of GaLiNAx could be administered without toxicity to any major organs. These results highlight the potential of long-lasting mRNA therapy as an effective protein replacement strategy for HB, paving the way for future mRNA therapeutics targeting other monogenic liver disorders.
2025-09-07 | A precision gene-engineered B cell medicine producing sustained levels of active factor IX for hemophilia B therapy.
Hemophilia B gene therapy treatments have not addressed the need for predictable, durable, active, and redosable factor IX (FIX). Unlike conventional gene therapy, engineered B cell medicines (BCMs) are durable, redosable, and titratable and thus have the potential to address significant unmet needs in the hemophilia B treatment paradigm. BE-101 is an autologous BCM comprising expanded and differentiated B lymphocyte lineage cells genetically engineered ex vivo to secrete factor IX (FIX)-Padua. CRISPR-Cas9-mediated gene editing at the C-C chemokine receptor type 5 (CCR5) locus was used to facilitate transgene insertion of an adeno-associated virus 6-encoded DNA template via homology-directed repair. Transgene insertion did not alter B cell biology, viability, or differentiation into plasma cells. Appreciable levels of BE-101-derived FIX-Padua were detected within 1 day after IV administration in mice, and steady state was reached within 2 weeks and persisted for over 184 days. Redosing produced an increase in FIX-Padua production close to linear dose proportionality. Comprehensive genotoxicity analysis found no off-target issues of concern. No safety signals were observed in animal tolerability and Good Laboratory Practice toxicology studies. In conclusion, BE-101 produces sustained levels of active FIX-Padua with the ability to engraft without host preconditioning and with the potential for redosing and titratability.
2025-03-29 | Enhancing hemostasis potency in hemophilia with a small interfering ribonucleic acid targeting protein S.
One hemophilia treatment concept focuses on rebalancing coagulation and anticoagulation to restore normal blood clotting. Targeting the coagulation regulator, protein S (PS), in hemophilia shows promise to increase the generation of thrombin, a critical enzyme in the clotting process. This study aimed to: (1) assess whether inhibiting PS increases thrombin generation (TG) in plasma from individuals with hemophilia A (HA) and B (HB); and (2) develop a hepatocyte-targeted PS small interfering RNA (siRNA) therapy using N-acetylgalactosamine conjugation to restore hemostasis in hemophilia without increasing thromboembolic risks. We assessed TG in plasma from patients with HA and HB. To target the liver specifically, we developed a PS-siRNA conjugated with N-acetylgalactosamine. This approach ensures that PS levels remain adequate in other cells, thereby minimizing the risk of thrombosis. Additionally, we evaluated the therapeutic potential of PS-siRNA in preclinical models. Inhibiting PS with a polyclonal antibody in plasma resulted in a 3- to 5-fold increase in TG in HA and a 4- to 9-fold increase in HB plasma, with a 70% reduction in plasma PS. In preclinical models, subcutaneous PS-siRNA therapy in HA mice and nonhuman primates successfully lowered PS levels and improved clot formation. It also prevented bleeding in both saphenous vein puncture and knee injury models in HA mice. Notably, it enhanced clotting without triggering widespread clot formation. Reducing PS levels enhances TG in hemophilia models, and PS-siRNA therapy shows promise in improving hemostasis. This approach warrants further clinical investigation as a potential treatment for hemophilia.
small molecules
2026-09-07 | Catheter salvage with antibiotic lock therapy for central venous port infection due to Pseudoxanthomonas sp. in a child with hemophilia B.
Catheter-related bloodstream infections (CRBSIs) generally necessitate prompt catheter removal, which poses significant hemorrhagic risks in patients with hemophilia. Consequently, catheter salvage utilizing antibiotic lock therapy (ALT) serves as a critical adjunctive strategy. We describe an exceptionally rare case of CRBSI caused by Pseudoxanthomonas sp., an environmental Gram-negative bacillus, and its successful management. A 4-year-old boy with severe hemophilia B developed persistent bacteremia originating from an implanted central venous access port. The pathogen was identified as Pseudoxanthomonas sp. utilizing matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and 16S rRNA gene sequencing. Catheter removal was deemed high-risk due to the patient's underlying hemophilia B and associated risk of major bleeding. Therefore, a catheter salvage strategy was pursued through a combination of systemic antimicrobial therapy and ALT. The patient received systemic antibiotics, adapting through piperacillin/tazobactam, ceftazidime, and trimethoprim-sulfamethoxazole. ALT was administered concurrently, initially using a ceftazidime-heparin lock solution, and later transitioning to a ciprofloxacin-heparin lock following an episode of suspected drug fever. Despite initial persistent bacteremia, this dual approach effectively eradicated the intraluminal infection. The central venous port was successfully retained with no recurrence observed over four months post-therapy. Systemic antimicrobial therapy combined with ALT can be an effective catheter-preserving strategy for high-risk patients with device-related infections caused by rare environmental non-fermenting Gram-negative organisms such as Pseudoxanthomonas sp.
2026-09-03 | Transforming Hemophilia Treatment With Novel Rebalancing Agents: Clinical Studies and Practical Perspectives.
While conventional prophylaxis with clotting factor concentrates (CFC) is the standard of care for hemophilia A and B, its challenges include frequent intravenous administration, factor level fluctuations, and potential inhibitor development. Rebalancing agents, including fitusiran (antithrombin-lowering small interfering ribonucleic acid), concizumab and marstacimab (tissue factor pathway inhibitor antagonists), are novel nonfactor therapies that restore hemostatic balance by targeting natural anticoagulants rather than replacing missing clotting factors. Clinical trials demonstrate that these three rebalancing agents provide effective prophylaxis for people with hemophilia (PwH) with or without inhibitors through subcutaneous administration. Rebalancing agents thus provide subcutaneous alternatives to current treatment regimens and offer effective prophylaxis for people with hemophilia B with inhibitors who previously had limited therapeutic options. Their novel mechanism of action may necessitate individualized dose optimization and unique approaches for managing breakthrough bleeds and surgeries. Those conditions require reduced dosing of CFC or bypassing agents to mitigate potential thrombotic risk. In addition, the use of rebalancing agents in pediatric patients (<12 years old) remains under investigation. While promising, successful implementation depends on individualized treatment approaches, appropriate monitoring protocols, and thorough patient education to improve current care for PwH.
2026-03-14 | Balancing the benefits and risks of rebalancing coagulation in haemophilia.
Rebalancing agents represent a novel therapeutic class in haemophilia, designed to restore the deficient thrombin generation that underlies bleeding. Unlike factor replacement or factor VIII mimetic therapies, rebalancing agents act by downregulating natural anticoagulants. By partially inhibiting these physiological brakes of coagulation, they induce a controlled and reversible procoagulant shift. These agents have shown clinically meaningful reductions in bleeding rates across both haemophilia A and B, including in patients with inhibitors. However, their therapeutic window appears narrow; excessive thrombin generation might lead to thrombosis, whereas conservative dosing could fail to fully prevent bleeding. The optimal balance between efficacy and safety, therefore, remains to be defined. Current or potential future indications include haemophilia B with inhibitors, young children in whom venous access limits prophylaxis, patients with suboptimal bleed control despite standard therapies, or those with other bleeding disorders. Tissue factor pathway inhibitor inhibition might confer specific benefits in reducing joint bleeding and synovitis, due to its local tissue expression. Overall, rebalancing agents broaden the therapeutic landscape but require judicious patient selection, individualised monitoring, and continued evaluation of their long-term safety and clinical positioning.
2026-01-31 | Evidence-based dental management strategies for individuals with congenital hemophilia: a systematic review.
BACKGROUND: People with hemophilia commonly present with a range of bleeding symptoms, from minor oral cavity bleeds to life-threatening events such as intracranial hemorrhage. People with hemophilia often exhibit poor oral health, attributed to disease-specific barriers and a fear of dental procedures, which may exacerbate their oral disease burden. This systematic review aimed to evaluate the various dental procedures performed in patients with hemophilia and the corresponding clotting factor concentrate replacement regimens used for individuals with mild, moderate, and severe forms of the disease. METHODS: An electronic database search was carried out using MEDLINE by PubMed, Scopus, Google Scholar, Web of Science, ProQuest, CINAHL, EBSCO Dental collection and EMBASE databases from inception to March 2025 for studies published in English language. The search strategy terms included were “hemophilia A”, “hemophilia A”, “hemophilia B”, “hemophilia B”, “dental care”, “oral surgery”, “complications”, “bleeding”. Case control studies, randomized controlled trials, observational studies and case reports addressing the dental treatments for people with hemophilia A/hemophilia B were included. Cases of acquired hemophilia and cases of hemophilia who are inhibitor positive were excluded. RESULTS: A total of 23 studies were included for the final review. Majority of the studies have ensured to achieve 30% to 50% factor correction for dental procedures. Routine dental care procedures like restoration and dental scaling with the necessary technical specifications can be safely performed. Dental extractions can be safely performed using local infiltration anesthesia; however, administering nerve blocks typically necessitates prior administration of clotting factors due to the elevated bleeding risk. Adjuvant systemic anti-fibrinolytics like Epsilon-aminocaproic acid (EACA) and tranexamic acid greatly reduces the need for additional factor infusion. CONCLUSIONS: The use of prophylactic clotting factors during dental interventions in hemophilia patients showed notable inconsistencies across studies. This inconsistency underscores the importance of conducting larger, prospective clinical studies to better understand the rationale behind clotting factor use and its effects on dental treatment outcomes in patients with varying degrees of hemophilia severity.
2025-10-27 | Suppressing microtubule detyrosination augments adeno-associated virus 2 endosomal escape and gene delivery.
Adeno-associated virus (AAV) is a widely used vector for gene delivery, yet the host intracellular trafficking barriers often limit its therapeutic efficacy. Here, we identify microtubule detyrosination - a microtubule post-translational modification - as a key regulator of AAV2 endo-lysosomal processing. Using super-resolution microscopy (SIM/STORM), we show that upon AAV2 endocytosis, the host upregulates microtubule detyrosination via the GSK3β-CLASP2 signaling axis. Single-particle tracking of recombinant virus reveals that detyrosinated microtubules form a physical and functional barrier, restricting AAV2 motility and promoting lysosomal trapping. Restoring microtubule tyrosination via tubulin-tyrosine ligase overexpression or pharmacological inhibition of detyrosination with parthenolide, enhances endosomal escape and perinuclear accumulation of AAV2, translating to improved gene delivery in host cells. Notably, a clinically relevant pro-drug of parthenolide (DMAPT) also displayed a similar trend of enhancing AAV2-driven coagulation factor IX expression in hemophilia B mouse models. Our findings uncover a host mechanism that reshapes the microtubule landscape to restrict AAV2 trafficking and identify microtubule detyrosination as a novel druggable target to improve AAV-based gene therapy.
proteins
2026-09-25 | Personalized Treatment of Hemophilia: Matching Therapies to Patient Needs in a Rapidly Evolving Landscape.
The therapeutic landscape of hemophilia, a rare inherited bleeding disorder, has rapidly evolved, introducing several novel modalities: extended half-life (EHL) coagulation factor concentrates, non-factor therapies, hemostasis-rebalancing agents, and gene therapy. These advances have improved clinical outcomes by reducing bleeding and treatment burden. However, individualizing treatment in routine practice has become more complex. This narrative review aims to provide a practical summary of available treatment options for pharmacologists, policymakers, and other readers who are not hemophilia specialists. A practical decision framework integrates available data with the clinical indication (regular prophylaxis, management of breakthrough bleeding, and perioperative care), patient-specific modifiers (age, lifestyle, inhibitor status, venous access, joint phenotype, comorbidities, and thrombosis risk). Drug therapies are discussed according to clinical evidence, including pivotal phase 3 trials, long-term extension studies, real-world data, and late-stage development programs. Factor replacement remains critical for hemostatic control during acute bleeding, surgery, and other interventions where predictable and measurable exposure is needed, whereas non-factor and rebalancing therapies provide low-burden prophylactic alternatives with distinct safety profiles and monitoring challenges. Direct comparisons between treatment classes are limited, making treatment individualization essential. Gene therapy has demonstrated more durable outcomes in hemophilia B than in hemophilia A. This review supports shared decision-making and individualized treatment selection in modern hemophilia care. While clinical trial evidence is limited by the scarcity of head-to-head comparisons and incomplete integration of real-world determinants, registry data collection will be essential.
2026-08-27 | Physiologically Based Pharmacokinetic (PBPK) Modeling of FIX in Pediatric Hemophilia B: Extravascular Distribution and Dosing Optimization.
Background: Prophylaxis in children with hemophilia B (HB) lacks quantitative approaches that integrate both plasma exposure and tissue distribution. This study aimed to develop and validate a physiologically based pharmacokinetic (PBPK) model of factor IX (FIX) for pediatric HB. The model incorporated the binding of FIX to type IV collagen (Col4) to characterize its distribution in both plasma and extravascular tissues. Methods: A total of 20 children with severe HB were included, contributing 219 plasma samples. The base PBPK model was first established and verified using adult and plasma-derived FIX (pdFIX) data. It was subsequently extrapolated to children by integrating FIX-CTBB parameters and pediatric observations for model calibration. The validated model was used to characterize plasma pharmacokinetics, predict tissue distribution and target attainment, and simulate alternative prophylactic dosing regimens. Results: The model adequately described the plasma pharmacokinetics of FIX in children and predicted substantial extravascular distribution. Total extravascular exposure was approximately sixfold higher than plasma exposure. Marked heterogeneity in target attainment was identified across tissues. Lower target attainment was observed in the colon, pancreas, and brain, whereas delayed attainment occurred in bone and muscle. Simulations of prophylactic dosing regimens suggested that 75 IU/kg twice weekly may provide a favorable balance among sustained FIX exposure, tissue-level target attainment, and treatment burden. Conclusions: This PBPK model provides a mechanistic and quantitative framework for characterizing plasma and tissue exposure to FIX in children with HB and may support individualized optimization of FIX prophylactic dosing.
2026-08-16 | Extravascular distribution of factor IX-review of experimental and clinical evidence, and relevance for hemophilia B replacement therapy.
Factor IX (FIX) is a relatively small molecule (55 kDa) that distributes physiologically beyond the plasma pool into the extravascular space. This contrasts with factor VIII, which is confined to the bloodstream as a consequence of its larger size (∼300 kDa) and binding to von Willebrand factor. The extravascular distribution of FIX may be significant in relation to factor replacement therapy in patients with hemophilia B. Given the increasing number of relevant publications over recent years, we critically reviewed and evaluated the experimental and clinical data relating to the extravascular distribution of FIX, considering both the native molecule and therapeutic products generated via biotechnological approaches. Endogenous FIX has an extensive distribution to tissues outside of plasma and is in dynamic equilibrium between plasma and the extravascular compartment. Approximately two-thirds of total FIX exists reversibly bound to type IV collagen in the vessel wall and extravascular space. This may produce an extravascular reservoir of FIX extending the plasma hemostatic role. Consequently, plasma FIX activity alone may not fully reflect the hemostatic potential of FIX prophylactic treatment. Extravascular FIX could be relevant for controlling and preventing both clinical and subclinical bleeds. When used as prophylactic treatment, extended half-life FIX products demonstrate similar annualized bleeding rates, but with a wide range of FIX trough levels and varying extents of extravascular distribution. Clinical implications of variation between FIX products remain to be fully understood; more knowledge is required. Further studies may help to address knowledge gaps, potentially informing treatment optimization.
2026-07-13 | Symptoms, Diagnosis, and Treatment for Women and Girls With Hemophilia: A Narrative Review.
Hemophilia is an X-linked bleeding disorder previously thought to present only in men. This sentiment is rapidly changing as the information around women and girls' experiences of bleeding symptoms has evolved, sparking intense discussion among researchers, clinicians, patients, and patient advocates regarding appropriate nomenclature. The primary objective of this narrative review is to build a comprehensive understanding of how women with hemophilia experience symptoms, how those symptoms are managed, navigate barriers to care, as well as discuss what can be done to alleviate barriers amongst this population. This is a qualitative narrative review which incorporates literature search strategies alongside testimonial from patient advocates to inform study priorities. This review identified multiple barriers to care for women and girls with hemophilia, including recognizing symptoms of abnormal bleeding, feeling comfortable asking for help, dealing with stigma from clinicians, getting an appropriate referral, accessing screening, facing challenges along the diagnostic pathway, and receiving treatment for symptoms. Another challenge is the wide variety of places a woman or girl may go to seek care for her bleeding symptoms, including primary care providers, gynecologists, hematologists, emergency medicine physicians, and rheumatologists. We conclude that while important strides have been made in this area in research and understanding, gaps remain. The research gaps in the differential symptom presentation when compared to men, potential efficacy and effectiveness of treatments in women as well as gender based behavioral difference are crucial to improving care and mitigating barriers for this cohort. This literature review combines information on symptoms, blood and genetic screening, diagnosis, treatment, current barriers to care, and next steps into a comprehensive perspective of the current available research. Evidence indicates that women with hemophilia are more likely than men to experience concerns related to family planning. In addition, women, in general, are more likely to engage in presenteeism rather than absenteeism when managing menstrual symptoms, attending work or school while unwell, which can result in reduced productivity. While screening techniques exist, novel rapid assays are being developed that could be more effective for screening women, particularly those who require multiple screenings before a diagnosis can be established. This can be combined with increased screening protocols to systematically identify carriers within families affected by hemophilia to ensure diagnosis. However, current efforts tend to focus on women of childbearing age, although premenarchal girls also experience hemophilia-related symptoms. The modalities of care for women and girls with hemophilia are numerous including pharmaceuticals such as factor replacement therapy, desmopressin, antifibrinolytic drugs, nonfactor therapy, and hormonal therapy. Additionally, assistance from physiotherapists, rheumatologists, and orthopedic surgeons can help manage joint related complications. Even with many care options, significant barriers to care persist, including the minimization of symptoms, avoidance of medical care, normalization of symptoms due to family history, and difficulties accessing care because of caregiving responsibilities. Existing care structures should be leveraged to provide better support for women and girls with hemophilia and symptomatic carriers. These could include more information provided within caregiving support groups, changes in guidelines, and wider understanding from the medical community as women and girls with hemophilia may seek assistance for their symptoms at a wide variety of clinical locations.
2026-07-11 | Immunopeptidomics of blood coagulation factor IX: a core peptide derived from the protease domain is promiscuously presented on HLA-DR.
Hemophilia B is an X-linked bleeding disorder that results in a qualitative or quantitative factor IX (FIX) deficiency. A subset of hemophilia B patients treated with FIX replacement therapy develop antibodies against FIX. The development of FIX inhibitors can present as allergic or anaphylactic reactions in some patients. It is currently unknown why a subset of hemophilia B patients develop inhibitors. CD4+ T cells recognizing FIX-derived peptides on major histocompatibility complex (MHC) class II on antigen-presenting cells are crucial for the development of class-switched, high-affinity anti-FIX antibodies. In this study, we explored MHC class II presentation of FIX-derived peptides by antigen presenting cells. We incubated purified FIX with monocyte derived dendritic cells of healthy, human leukocyte antigen-typed donors. MHCII peptide complexes were immunopurified, followed by peptide elution and mass spectrometry-based analysis of eluted peptides. We analyzed 12 healthy donors; of them, 8 presented FIX-derived peptides. The majority of FIX peptides were derived from the serine protease domain of FIX. With the exception of 1 donor, all of them presented at least one peptide containing the same core sequence, "NVIRIIPHHN" (residues 295-306 of FIX). Taken together, we identified a promiscuously presented peptide derived from the protease domain of FIX. Based on its frequent presentation in multiple donors, we speculate that this peptide may be recognized by FIX-specific CD4+ T cells that develop in hemophilia B patients with inhibitors. Peptides identified in our study can be used for inhibitor risk stratification and development of novel therapies to induce tolerance.
antibodies
2026-09-18 | Subcutaneous MG1113 in severe hemophilia A and B: phase 1b study for safety, pharmacokinetics, and pharmacodynamics.
MG1113 is an immunoglobulin G4 monoclonal antibody targeting the Kunitz-2 domain of tissue factor pathway inhibitor (TFPI), developed as a hemostatic rebalancing agent for patients with hemophilia A or B. We aimed to investigate the safety, pharmacokinetics (PK), pharmacodynamics, and preliminary hemostatic effects of MG1113. This phase 1b clinical trial was conducted in a multicenter, prospective, stepwise dose-escalating (2.0, 3.0, and 3.3 mg/kg) design. MG1113 was administered subcutaneously once weekly for 8 weeks. Fifteen male patients (n = 5/cohort) diagnosed with severe hemophilia A (n = 14) or B (n = 1) without inhibitors were enrolled. MG1113 was well tolerated, with an adverse event (AE) rate of 40.0% (6/15). No serious AEs, early withdrawals, or dose interruptions occurred. PK analysis demonstrated a nonlinear profile, with the peak plasma concentration at 33 to 48 hours post dose. Free TFPI and diluted prothrombin time (PT) decreased from baseline, while thrombin generation markers increased. Exploratory analysis showed a notable numerical reduction in annualized total bleeding rates at higher doses: 91.7% at 3.0 mg/kg and 76.2% at 3.3 mg/kg. The zero bleeding rate was 20.0%, 60.0%, and 40.0% at doses of 2.0, 3.0, and 3.3 mg/kg, respectively. MG1113, administered subcutaneously as a prophylaxis in patients with severe hemophilia A or B without inhibitors for 8 weeks, demonstrated an acceptable safety profile with a PK profile suitable for once-a-week dosing. The pharmacodynamics marker changes were consistent with TFPI inhibition, which was associated with reductions in bleeding events. This trial was prospectively registered at www.ClinicalTrials.gov (#NCT05493631).
2026-07-30 | Concizumab prophylaxis in a 2-year-old patient with severe hemophilia B and inhibitor: a case report.
Hemophilia B is a rare X-linked congenital bleeding disorder characterized by a deficiency in coagulation factor IX (FIX). Standard management relies on exogenous factor replacement; however, the development of neutralizing alloantibodies (inhibitors) against infused clotting factor can significantly reduce therapeutic efficacy and complicate long-term management. Consequently, patients turn to bypassing agents or non-factor therapies to help achieve adequate hemostatic control. Concizumab is a novel subcutaneous non-factor therapy for hemophilia A and B that targets the tissue factor pathway inhibitor (TFPI). While it is approved for patients >12 years old, data remains sparse in younger children. Prophylactic treatment with concizumab reduces several limitations associated with inhibitor development and variability in treatment response with conventional therapies, especially in pediatric populations. We report a toddler with hemophilia B who developed a low-titer inhibitor following treatment with recombinant coagulation factor IX agents, resulting in recurrent bleeding complications and consistent subtherapeutic hemostatic control on standard bypassing agents. The patient was transitioned to concizumab for long-term prophylaxis, with dose adjustments based on clinical response and concizumab drug levels. Following the initiation of concizumab, the patient demonstrated a marked reduction in bleeding episodes. We highlight an individualized early drug-level-guided dose escalation approach in a very young child, demonstrating that pharmacokinetic monitoring can be utilized proactively to optimize therapeutic response in this age group, leading to effective drug levels and excellent clinical response. This case supports the role of concizumab in potentially reducing treatment burden and improving hemostatic outcomes in young patients with severe hemophilia B and inhibitors.
2026-06-18 | A plain language summary of the BASIS study looking at people living with severe hemophilia A or B with inhibitors and being treated with marstacimab.
What is this summary about? This summary describes a clinical study looking at how well marstacimab works in people living with hemophilia with inhibitors. The study was published in the medical journal Blood. Hemophilia is caused by not having enough blood clotting factors, which are proteins found in the blood that help form a clot and stop bleeding. People living with hemophilia either don't make these proteins, have low amounts of these proteins, or these proteins do not work well. Hemophilia is usually inherited from biological parents, meaning it is passed on to their children through genes. In some cases, hemophilia happens even if no one in the family has it. There are some treatments to replace the missing clotting factor. This type of treatment is called factor replacement therapy and contains the missing clotting factor proteins. Some people make antibodies against the replacement clotting factors, so the replacement clotting factors do not work as well as they need to for the blood to clot. This is called hemophilia with inhibitors. People who have hemophilia with inhibitors need to take medicines called bypassing agents instead of replacement clotting factors. These medicines aim to activate the body's blood clotting system, but do not always work well. They also need to be injected into a vein, known as intravenous infusion, or IV infusion for short. IV infusions are taken several times a week. Different options to IV factor replacement therapy for people living with hemophilia A or hemophilia B are called non-factor replacement therapy. A protein in the blood called Tissue Factor Pathway Inhibitor, or TFPI, can also prevent blood clotting. Marstacimab is a type of non-factor replacement therapy that attaches to TFPI and stops its activity. For people living with hemophilia, marstacimab can help blood to form a clot when needed. Marstacimab is injected under the skin. This can be an easier way to receive medicine than an injection into a vein. Marstacimab offers a new way to treat people living with hemophilia. What were the results of the study? The study showed that people living with hemophilia with inhibitors who were treated with marstacimab had fewer bleeding events over 1 year compared to previous therapy with bypassing agents. Most side effects with marstacimab treatment were minor or could be easily managed. One person stopped taking marstacimab treatment because they developed a skin rash that got better over time. What do the results mean? The study showed that marstacimab could help prevent bleeding in people living with hemophilia A or B with inhibitors.
2026-06-12 | The Dilemma of Providing Advanced Hemophilia Treatments in Developing Countries - For Whom, by Whom and Where?
Hemophilia, a congenital deficiency of factor VIII (hemophilia A) or factor IX (hemophilia B), leads to recurrent bleeding episodes that may cause progressive joint damage and long-term disability. Traditional management relies on intravenous factor replacement therapy; however, limited half-life, immunogenicity, venous access challenges, and the burden of frequent infusions have prompted the development of extended half-life (EHL) factor products. Although EHL therapies represent an important advancement, they only partially reduce treatment burden and do not fully meet expectations for improved convenience and sustained bleed protection. Recent innovations are reshaping the therapeutic landscape. Nonfactor subcutaneous therapies such as anti-TFPI molecules, antithrombin reducing agents, and anti-protein C agents offer simplified administration with the potential for improved adherence. Gene therapy provides the prospect of a long-term therapeutic effect in selected patients. In Türkiye, hemophilia care remains largely factor-based; however, clinical trial participation and recent regulatory approvals for selected novel therapies have begun to expand real-world experience with these emerging treatment options. As global practice shifts toward individualized, less invasive treatment approaches, expanding availability of novel therapies and optimizing patient-specific treatment strategies will be essential. This review examines current and evolving treatment options, key challenges, and future opportunities shaping the trajectory of hemophilia management.
2026-06-11 | Discovery and optimization of marstacimab, a human monoclonal antibody targeting tissue factor pathway inhibitor for the treatment of hemophilia A and B.
We report the discovery and optimization of marstacimab, a novel monoclonal antibody targeting tissue factor pathway inhibitor (TFPI), for the treatment of hemophilia A and B. Hybridoma and phage display approaches identified antibodies that blocked the TFPI: coagulation factor Xa (FXa) interaction. Antibodies bound TFPI with nanomolar affinity to multiple epitopes, including one that covered the entire FXa binding surface and others that partially overlapped the interface from different sides of the TFPI-K2 domain. Several antibodies reduced bleeding in a hemophilia A mouse injury model for up to 96 h following a single dose. Rabbit pharmacokinetic studies indicated that antibodies with ≤~1 nM TFPI-binding affinity were cleared rapidly from circulation, whereas TFPI-23 (5.72 nM) had a longer plasma residence time. Pharmacokinetic-pharmacodynamic modeling indicated that this intermediate affinity allowed circulating concentrations of antibodies such as TFPI-23 to maintain concentrations required for 50% residual activity; in contrast, higher-affinity antibodies quickly decreased to concentrations that would not effectively neutralize TFPI. The end-to-end process leading to final candidate selection incorporated rigorous assessment of biophysical properties, including thermal stability, aggregation propensity, viscosity, predicted immunogenicity, stable cell line productivity, and nonspecific binding. An optimized derivative of TFPI-23, TFPI-106 (PF-06741086, known as marstacimab), had the functional and biophysical properties with other characteristics suitable for clinical development and was selected as the final candidate. TFPI-106 elicited enhanced hemostasis in hemophilic plasma, shortened clotting time, and enhanced thrombin generation velocity. Marstacimab is now approved for patients with hemophilia A or B with or without inhibitors.
gene therapies
2026-09-25 | Advancements in CRISPR-based in vivo gene therapy for hemophilia.
Hemophilia is an X-linked hereditary bleeding disorder caused by loss-of-function mutations in the genes encoding coagulation factors, leading to excessive bleeding and potentially being life-threatening. Currently, regular treatment for hemophilia is the infusion of recombinant blood coagulation factors. This approach is not only costly but can also give rise to complications such as the development of neutralizing antibodies (Nabs), which impede the therapeutic outcome. Hemophilia is a monogenic disease, making gene therapy a promising curative measure that includes gene addition and gene editing approaches. Adeno-associated virus (AAV) vectors have gained massive attention as the premier delivery vehicle for clinical gene therapy due to their diverse tissue tropisms dictated by the natural and engineered AAV capsids, their excellent safety profile since AAVs do not cause any known human diseases, low immunogenicity, and long-lasting gene expression. Several AAV-based gene addition therapies have been approved for hemophilia B and hemophilia A, and dozens of similar AAV-based clinical trials are underway. Gene editing technologies, like Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/CRISPR-associated protein 9 (Cas9), have shown immense potential in the treatment of genetic diseases. CRISPR/Cas9-mediated transgene integration provides critical advantages over regular gene insertion therapy by enabling site-specific, targeted genomic integration rather than random integration. Clinical trials focusing on AAV-CRISPR/Cas9-mediated knock-in of human genes represent the frontier of in vivo genetic medicine, and one such prominent ongoing clinical trial for hemophilia B is designed to insert the human Factor IX gene into hepatocytes. This review outlines recent advances and feasible strategies of CRISPR/Cas9-based genome editing for hemophilia therapy, highlights the potential applications of next-generation gene editing and vector delivery technologies, and offers new insights for the advantages, limitations, and future directions for these novel treatment modalities.
2026-09-17 | Factor IX Padua AAV gene therapy in adolescents with hemophilia B: a phase 1 trial.
Adeno-associated virus (AAV)-mediated factor IX Padua gene therapy has demonstrated good safety and efficacy in adult patients with hemophilia B, but its safety and efficacy in adolescent patients with hemophilia B remain unknown. Here we report a multicenter, single-arm, phase 1 study involving 11 adolescent participants (aged 12-18 years) with severe or moderately severe hemophilia B (factor IX coagulant activity (FIX:C) ≤2 IU dl-1) in China. All of them received the AAV gene therapy BBM-H901 at a dose of 5 × 1012 vector genomes per kilogram of body weight and were then enrolled in a 52-week follow-up. The primary endpoint was safety. No dose-limiting toxicity was observed throughout the study. The most common adverse events included elevation of white blood cell count, elevation of neutrophil count and rash associated with corticosteroid use. One serious adverse event and two grade 3 adverse events occurred. Abnormal liver function was observed in one participant, with elevated alanine aminotransferase (197.0 U l-1) and aspartate aminotransferase (75.0 U l-1) levels, which returned to normal 4 weeks after immunosuppression therapy. The key secondary endpoints included the mean (s.d.) FIX:C at week 52 following infusion, which was 41.8 (30.1) IU dl-1 (one-stage SynthASil method), and the mean annualized bleeding rate, which decreased from 13.9 to 0.5. In this study, we show that the gene therapy drug BBM-H901 for hemophilia B is safe in adolescent patients, providing initial insights into its efficacy. ClinicalTrials.gov identifier: NCT05709288 .
2026-07-27 | Hemophilia in Mexico: Updated Consensus Recommendations on Diagnosis, Treatment and Gene Therapy.
Hemophilia is an X-linked inherited bleeding disorder, classified as type A or type B. Therapeutic advances offer new treatment options that improve disease control and reduce associated complications, including inhibitor development and hemophilic arthropathy. This document aims to update the Mexican hemophilia consensus, reviewing current evidence on diagnosis and management, and addressing gaps in the treatment and follow-up of patients in Mexico, aligning local needs with international recommendations. A PubMed literature search covering the last five years (up to September 2025) was conducted, prioritizing consensus statements, guidelines, and systematic reviews. Using the Delphi methodology, a structured questionnaire was submitted electronically to forty-four experts. Aspects without initial agreement were discussed at an in-person meeting. Consensus was defined as at least 80% of votes in favor. Recommendations were issued across six domains: laboratory diagnosis, genetic testing, management of hemophilia A and B without and with inhibitors, adjuvant treatments, and gene therapy. The recommendations address prophylaxis with coagulation factor concentrates, non-factor therapies, immune tolerance induction, perioperative management, pain management, and eligibility criteria and follow-up protocols for gene therapy with adeno-associated viral vectors. This consensus provides updated, evidence-based recommendations adapted to the Mexican healthcare context, identifying priority areas, including timely access to non-factor therapies and gene therapy, development of a national referral network for complex cases, and inclusion of novel therapeutic agents in the institutional essential medicines list, with the aim of improving the quality of life of people with hemophilia in Mexico.
2026-07-03 | Increased Gene Therapy Efficacy Through the Use of Extended Half-Life Clotting Factors.
The development of more effective gene therapy strategies for hemophilia B remains essential, as results of multiple clinical trials show significant interpatient variability in clinical outcomes, with a fraction of patients (up to 13%) even returning to prophylaxis. Another major challenge in current AAV based gene therapy for hemophilia B pertains to dose-dependent vector-related immune responses, requiring immune suppression. We investigated whether combining gene therapy with transgenes encoding extended half-life (EHL) coagulation factors could enhance therapeutic efficacy. Adeno-associated viral (AAV) vectors encoding a hyperactive factor IX variant R338L (i.e., FIX-Padua), genetically fused to a mutant human albumin (FIX-R338L-ALB(QMP)), were administered to both wild-type and hemophilia B mice. These chimeric transgenes were codon-optimized and driven by a hepatocyte-specific promoter. The AAV-FIX-R338L-ALB(QMP) vector demonstrated significantly improved efficacy compared to the control AAV-FIX-R338L vector, resulting in a sustained 4-fold and 3-fold increase in FIX antigen levels and activity, respectively. These increases were consistent with durable correction of the bleeding phenotype. Importantly, immunogenicity or liver toxicity was not increased, as no anti-FIX antibodies, alanine transaminase elevations, or liver immune infiltrations were detected following treatment. Furthermore, immune tolerance was achieved in the majority of hemophilia B mice treated with AAV-FIX-R338L-ALB(QMP), even after active immunization with FIX protein and adjuvant, which was found to be mediated by regulatory T cells. Additionally, no increase in thrombogenic risk was observed, indicated by stable D-dimer levels. These findings support the potential of FIX-R338L-ALB(QMP) fusion constructs encoding extended half-life FIX as a promising next-generation gene therapy for hemophilia B.
2026-06-21 | Development of an Agent-Based Model to Investigate Durability of Factor IX Activity in Hemophilia B Patients Treated With Etranacogene Dezaparvovec.
Many currently approved gene therapies use adeno-associated virus (AAV) to deliver DNA sequences encoding protein(s)-of-interest into cells. The AAV viral genome forms stable, circular DNA structures called episomes after entering the nuclei. Therapeutic proteins are then generated in vivo from transcription and translation of these episomes, and long-term durability thus depends on episome stability. Prior modeling work has utilized differential equation-based models to characterize AAV uptake and subsequent protein production. However, episome loss associated with target cell turnover is poorly described with these models. Here, an agent-based model (ABM) to overcome this shortcoming is developed. The liver was used as the example organ as it is known to be self-renewing and has been a common target for gene therapies. In this model, each hepatocyte is an agent, capable of division and death. When transduced, these agents acquire and carry episomes. During cell division, episomes are passed from mother to daughter cells. All episomes are presumed lost when transduced cells die. The ABM was applied to etranacogene dezaparvovec (formerly AMT-061 or CSL222), a liver-targeting gene therapy for hemophilia B consisting of AAV serotype 5 particles encoding a transgene for the Padua variant (R338L) of coagulation factor IX (FIX). ABM-simulated FIX activity in patients receiving this therapy was consistent with clinical observations over more than 2 years following treatment. This ABM was then used to generate 20-year predictions and explore biological mechanisms underlying long-term durability. The ABM framework and approach should be applicable to investigating durability of other AAV-based gene therapies.
other
2026-04-18 | Pseudoexon inclusion induced by three deep intronic variants in hemophilia B and correction achieved through an antisense oligonucleotide-based strategy.
Although studies have identified deep intronic variants associated with hemophilia B in patients undiagnosed by conventional genetic testing, knowledge in this field remains limited. Long range-PCR of entire F9 gene was used to screen variants of three unrelated genetically unresolved severe hemophilia B patients. In silico analysis and minigene assay with two minigene plasmid construction methods were conducted to explore the effects of candidate deep intronic variants on splicing. Three novel putative pathogenic deep intronic variants (c.278-765_278-764ins6.1kb, c.392-903A>G and c.724-751T>G) and one variant of uncertain significance (c.723+2708del) in F9 were identified in three patients. All the three putative pathogenic variants created de novo donor splice site and utilized cryptic acceptor splice site to generate pseudoexon. We successfully developed antisense oligonucleotide-mediated exon-skipping correction strategies for the three identified putative pathogenic variants and the previously reported c.392-864T>G. However, the results obtained from minigene assay revealed certain discrepancies with the clinical phenotype. It is still challenging to accurately characterize the pathogenicity of deep intronic variants in vitro. Overall, our results highlight the complementary role of whole-gene sequencing of F9 to conventional genetic diagnosis. Furthermore, we provide insight into a potential therapeutic approach based on antisense oligonucleotide technology-mediated exon-skipping.
2026-01-09 | Molecular mechanisms and therapeutic strategies for the recurrent F9 (c.520 + 13 A > G) variant in hemophilia B.
Hemophilia B (HB), an X-linked recessive disorder, results from variants in the coagulation factor IX gene (F9). The F9 c.520 + 13 A > G variant is a recurrent intronic variant in HB patients, accounting for 15.05% of all documented F9 intronic variants. Despite prior predictions of its impact, the molecular mechanism associated with moderate to mild HB remains undissected. In silico predictions and splicing-competent cDNA constructs were used to assess the impact of F9 c.520 + 13 A > G on mRNA splicing. Factor IX (FIX) variant (p.V174delinsGHNLM) expression in HEK293T cells was evaluated using activated partial thromboplastin time, enzyme-linked immunosorbent assay, Western blot analysis, and immunofluorescence analyses. Structural modeling and molecular dynamics simulations were performed to evaluate the structural impact of the variant. Engineered U1 small nuclear RNA (U1snRNA) was challenged with F9 full-length splicing-competent constructs to evaluate splicing correction. The F9 c.520 + 13 A > G variant caused nearly complete aberrant splicing, producing the F9 c.520_521insGTCATAATCTGA insertion and the in-frame FIX p.V174delinsGHNLM variant. A small amount (approximately 10%) of wild-type FIX was also detected. We characterize the p.V174delinsGHNLM variant, which exhibited impaired secretion and increased intracellular accumulation. Interestingly, an engineered U1snRNA partially rescued aberrant splicing, restoring functional FIX levels to approximately 40%. This study elucidates the molecular mechanism of the F9 c.520 + 13 A > G variant, which activates a cryptic 5' splice site in intron 5, leading to an in-frame FIX (p.V174delinsGHNLM) with secretion defects and loss of protein function. And Engineered U1snRNA partially rescued the splicing defect.
2025-12-08 | Liver-Specific Biocompatible Lipid Nanoparticle-Enabled mRNA Therapy for Haemophilia B.
The standard treatment for Haemophilia B (HB) involves frequent intravenous (IV) infusions of recombinant factor IX (FIX), which imposes a significant financial burden on patients. FIX delivery as messenger RNA using lipid nanoparticles (LNPs) presents a promising alternative, but achieving prolonged and effective protein expression remains challenging. To this end, we developed Galactosylated Lipid Nucleic Acid complex (GaLiNAx) to enhance the delivery of chemically modified FIX mRNAs. The nanocarrier encompasses an ionizable galactosylated lipid to enable receptor-mediated endocytosis and a transfection-competent cationic lipid for optimal mRNA complexation. We incorporated truncated albumin UTRs and base modifications in functional FIX mRNA to enhance hepatic translation. In an HB mouse model, GaLiNAx demonstrated therapeutically relevant FIX protein expression for about one month after single dose offering a cost-effective option. Safety assessments indicated that multiple doses of GaLiNAx could be administered without toxicity to any major organs. These results highlight the potential of long-lasting mRNA therapy as an effective protein replacement strategy for HB, paving the way for future mRNA therapeutics targeting other monogenic liver disorders.
2025-09-07 | A precision gene-engineered B cell medicine producing sustained levels of active factor IX for hemophilia B therapy.
Hemophilia B gene therapy treatments have not addressed the need for predictable, durable, active, and redosable factor IX (FIX). Unlike conventional gene therapy, engineered B cell medicines (BCMs) are durable, redosable, and titratable and thus have the potential to address significant unmet needs in the hemophilia B treatment paradigm. BE-101 is an autologous BCM comprising expanded and differentiated B lymphocyte lineage cells genetically engineered ex vivo to secrete factor IX (FIX)-Padua. CRISPR-Cas9-mediated gene editing at the C-C chemokine receptor type 5 (CCR5) locus was used to facilitate transgene insertion of an adeno-associated virus 6-encoded DNA template via homology-directed repair. Transgene insertion did not alter B cell biology, viability, or differentiation into plasma cells. Appreciable levels of BE-101-derived FIX-Padua were detected within 1 day after IV administration in mice, and steady state was reached within 2 weeks and persisted for over 184 days. Redosing produced an increase in FIX-Padua production close to linear dose proportionality. Comprehensive genotoxicity analysis found no off-target issues of concern. No safety signals were observed in animal tolerability and Good Laboratory Practice toxicology studies. In conclusion, BE-101 produces sustained levels of active FIX-Padua with the ability to engraft without host preconditioning and with the potential for redosing and titratability.
2025-03-29 | Enhancing hemostasis potency in hemophilia with a small interfering ribonucleic acid targeting protein S.
One hemophilia treatment concept focuses on rebalancing coagulation and anticoagulation to restore normal blood clotting. Targeting the coagulation regulator, protein S (PS), in hemophilia shows promise to increase the generation of thrombin, a critical enzyme in the clotting process. This study aimed to: (1) assess whether inhibiting PS increases thrombin generation (TG) in plasma from individuals with hemophilia A (HA) and B (HB); and (2) develop a hepatocyte-targeted PS small interfering RNA (siRNA) therapy using N-acetylgalactosamine conjugation to restore hemostasis in hemophilia without increasing thromboembolic risks. We assessed TG in plasma from patients with HA and HB. To target the liver specifically, we developed a PS-siRNA conjugated with N-acetylgalactosamine. This approach ensures that PS levels remain adequate in other cells, thereby minimizing the risk of thrombosis. Additionally, we evaluated the therapeutic potential of PS-siRNA in preclinical models. Inhibiting PS with a polyclonal antibody in plasma resulted in a 3- to 5-fold increase in TG in HA and a 4- to 9-fold increase in HB plasma, with a 70% reduction in plasma PS. In preclinical models, subcutaneous PS-siRNA therapy in HA mice and nonhuman primates successfully lowered PS levels and improved clot formation. It also prevented bleeding in both saphenous vein puncture and knee injury models in HA mice. Notably, it enhanced clotting without triggering widespread clot formation. Reducing PS levels enhances TG in hemophilia models, and PS-siRNA therapy shows promise in improving hemostasis. This approach warrants further clinical investigation as a potential treatment for hemophilia.
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