Hemophilia Therapy Research Articles

Gene therapy for hemophilia

Concept Gene therapy with adeno-associated virus (AAV) vectors treats hemophilia A or B by delivering a functional F8 or F9 gene to hepatocytes. This single infusion enables endogenous production of FVIII or FIX protein, reducing bleeding in patients. Evolution Long-term clinical studies have provided insight into the efficacy, safety, and durability of AAV-mediated gene therapies for hemophilia A and B. Gene therapies have now been approved for hemophilia A (valoctocogene roxaparvovec) and hemophilia B (etranacogene dezaparvovec; fidanacogene elaparvovec) in select regions. Application The approved gene therapies are associated with a strong reduction in bleeding tendency and increased FVIII or FIX activity levels, without the need for additional FVIII or FIX replacement therapies, in the vast majority of patients. Future Steps Improvements in AAV technology, protein expression, and immunogenicity may render AAV-mediated gene therapies more efficient, longer lasting and safer for people with hemophilia A or B.

Efficient generation of liver sinusoidal endothelial-like cells secreting coagulation factor VIII from human induced pluripotent stem cells

Liver sinusoidal endothelial cells (LSECs) and LSEC progenitor cells (LPCs) derived from human pluripotent stem cells (PSCs) are expected as valuable cell sources for the development of cell therapy for hemophilia A, a congenital deficiency of coagulation factor VIII (FVIII), as LSECs are responsible for FVIII production. However, there is room for improvement in the efficiency of LSECs and LPCs differentiation from PSCs. In this study, we sought to optimize the method of mesoderm differentiation induction, the initial step of LSEC differentiation from PSCs, to efficiently induce LSEC-like cells capable of secreting FVIII from human induced pluripotent stem cells (iPSCs). Following optimization of the concentration and stimulation period of CHIR99021 (glycogen synthase kinase 3β inhibitor), bone morphogenetic protein 4, fibroblast growth factor 2, and Activin A in the mesoderm induction step, approximately 65% and 54% of cells differentiated into LPCs and LSEC-like cells, respectively. Furthermore, we observed substantial FVIII protein secretion from LSEC-like cells in vitro. In conclusion, we established an efficient method for obtaining LPCs and functional LSEC-like cells from iPSCs in vitro.

Reviewing The Latest Treatments for Haemophilia

Abstract: Advancements in haemophilia treatment have been significant in the first 20 years of the 21st century. However, the progress started with the fractionation of plasma in 1946. The first concentrates were developed after discovering FVIII in frozen plasma cryoprecipitate and FIX in the supernatant in the early 1960s, leading to initial attempts at replacement therapy. Unfortunately, due to the lack of screening methods for viral pathogens, people with haemophilia (PWH) received contaminated concentrates, leading to infections with the hepatitis A virus, hepatitis C virus, and human immunodeficiency virus. Thankfully, by 1985, viral screening methods and virucidal techniques were developed, making concentrates safe. The introduction of chromatography steps with monoclonal antibodies in the production process led to increasingly pure products. However, the problem of immunogenicity of administered concentrates persists. The development of alloantibodies against FVIII in a significant percentage of PWH is a serious adverse effect of replacement therapy. The next major advancement came with cloning the F8 and F9 genes, which allowed the production of factor concentrates using recombinant DNA technology. The injected FVIII and FIX molecules have a relatively short circulating half-life in the plasma of people with haemophilia A and B, approximately 12 and 18 hours, respectively. Methods such as conjugating the factor molecule with fragment crystallizable of IgG1, albumin, or adding polyethylene glycol have been applied to prolong the plasma half-life and extend the interval between injections, especially for risk. The next frontier in haemophilia therapy is the development of durable and potentially curative treatments, such as gene addition therapy. Experiments in haemophilia B have shown promising long-lasting responses. However, the results of gene therapy for haemophilia A have not been as remarkable, and the durability of the treatment is yet to be demonstrated. The long-term safety, predictability, durability, and efficacy of gene therapy for haemophilia A and B remain open questions. Currently, only healthy adult PWH has been enrolled in gene therapy clinical trials, and further studies are needed before gene therapy can be widely applied to children and those with pre-existing antibodies against the delivery vector.

Drug-induced liver injury related to gene therapy: A new challenge to be managed.

Gene therapy is being successfully developed for the treatment of several genetic disorders. Various methods of gene transfer have been developed to enable the production of the deficient enzyme or protein. One of the most important is adeno-associated virus vectors, which have been shown to be viable for use in invivo gene therapy. Several gene therapies have already been approved. They are also promising for acquired diseases. Important examples include gene therapy for haemophilia A and B, X-linked myotubular myopathy, spinal muscular atrophy and several liver diseases such as Criggler-Najjar disease, alpha-1 antitrypsin deficiency and Fabry disease. However, the introduction of a foreign compound into hepatocytes leads to hepatic reactions with heterogeneous phenotypic expression and a wide spectrum of severity, ranging from mild transaminase elevation to acute liver failure. Several mechanisms appear to be involved in liver injury, including an immune response, but also direct toxicity depending on the method of gene transfer. As a result, the incidence, expression and severity of liver injury vary from indication to indication and from patient to patient. Patients treated for haemophilia A are more prone to transaminase elevation than those treated for haemophilia B. Corticosteroids are successfully used to correct liver reactions but also to prevent degradation of the transferred gene and loss of therapeutic activity. The aim of this review is to describe the risk of liver injury according to the indication for gene therapy and the short- and long-term management currently proposed to prevent or correct liver reactions in clinical practice.

Liver-related aspects of valoctocogene roxaparvovec gene therapy for hemophilia A: expert guidance for clinical practice

AbstractAdeno-associated virus–based gene therapy (valoctocogene roxaparvovec) is an attractive treatment for hemophilia A. Careful clinical management is required to minimize the risk of hepatotoxicity, including assessment of baseline liver condition to determine treatment eligibility and monitoring liver function after gene therapy. This article describes recommendations (developed by a group of hemophilia experts) on hepatic function monitoring before and after gene therapy. To prevent harmful liver-related effects, gene therapy is contraindicated in patients with uncontrolled liver infections, autoimmune hepatitis, liver stiffness ≥8 kPa, or cirrhosis. Before using gene therapy in patients with liver steatosis or other liver disorders, the risk of liver damage should be considered using a highly individualized approach. Treatment is not recommended in patients with abnormal liver enzymes, including alanine aminotransferase (ALT) at any level above the upper limit of normal (ULN). Therefore, pretreatment assessment of liver health should include laboratory tests, abdominal ultrasound, and liver stiffness measurements by transient elastography (TE). In the first year after therapy, ALT levels should be monitored 1 to 2 times per week to detect elevations ≥1.5× ULN, which may require immunosuppressant therapy. Patients with ALT elevation should receive prednisone 60 mg/d for 2 weeks, followed by stepwise tapering when ALT returns to baseline. ALT monitoring should continue long term (every 3-6 months), along with abdominal ultrasound (every 6 months) and TE (yearly) evaluations. When patients with good liver health are selected for treatment and closely monitored thereafter, ALT elevations can be promptly treated and are expected to resolve without long-term hepatic sequelae.

Evaluating clinically translatable conditioning for platelet gene therapy in murine hemophilia A with inhibitors

BackgroundPlatelet gene therapy is effective in hemophilia A (HA) mice even with inhibitors. Fludarabine (Flu), along with busulfan (Bu) or melphalan (Mel), preconditioning has been shown to be highly effective for hematopoietic stem cell transplantation in the clinic. ObjectivesTo evaluate the efficacy of Bu–Flu and Mel–Flu preconditioning in platelet gene therapy of HA with inhibitors. MethodsBu–Flu and Mel–Flu were used to condition HA mice preimmunized with recombinant human factor (F)VIII. An optimal 660 centigray total body irradiation was used as a control regimen in parallel. Platelet–FVIII expression was introduced by transplantation of 2bF8 lentivirus (LV)-transduced hematopoietic stem cells. Animals were analyzed by fluorescence-activated cell sorting, quantitative polymerase chain reaction, FVIII assays, and tail bleeding tests. ResultsBu–Flu, but not Mel–Flu, enabled successful 2bF8 gene therapy. All recipients achieved >55% chimerism post hematopoietic stem cell transplantation in both Bu–Flu and 660 centigray groups, with comparable copy numbers of 2bF8 cassette and the platelet–FVIII levels. The bleeding phenotype was rescued in 2bF8LV-transduced recipients. FVIII inhibitor titers declined with time, with comparable disappearance time of inhibitors between the 2 groups. When animals were rechallenged with recombinant human FVIII after the titers dropped to undetectable levels, no inhibitors were detected in 2bF8LV-transduced recipients. In contrast, all untransduced transplanted control mice produced inhibitors. These data demonstrate that immune tolerance was established in 2bF8LV-transduced primed HA mice under Bu–Flu conditioning. ConclusionBu–Flu preconditioning allows for successfully introducing platelet–FVIII expression to restore hemostasis and induce immune tolerance in primed HA mice, suggesting that this approach is a promising clinically translatable strategy for gene therapy of HA with inhibitors.

The impact of capping health system cost savings on the projected cost-effectiveness of etranacogene dezaparvovec compared with factor IX prophylaxis for the treatment of hemophilia B.

This viewpoint discusses cost-effectiveness estimates for EtranaDez, a gene therapy for hemophilia B, using the Institute for Clinical and Economic Review's (ICER) framework for single and short-term therapies (SSTs). EtranaDez offers long-term benefits from a single administration, in contrast to the high costs and frequent dosing required by current factor IX prophylaxis. However, the projected gains in health from EtranaDez are small relative to the cost implications of the therapy, and consequently, how the cost offsets associated with EtranaDez are counted has a substantial impact on assessing its cost-effectiveness. Strategies for assessing cost offsets used in the ICER SST framework include a 50/50 cost-sharing model between the health care system and the manufacturer and a cap of $150,000 annually on health care cost offsets. Results from the standard full cost-offset analysis as reported by ICER depicted EtranaDez as a dominant therapy with substantial cost savings compared with factor IX prophylaxis. However, while considering the ICER SST framework, particularly the $150,000 annual cap scenario, the cost-effectiveness was significantly reduced. The incremental cost-effectiveness ratio varied notably between these scenarios, challenging the conventional perception of value of gene therapy in health care. These cost-sharing scenarios highlight the potential of the ICER SST framework to help curtail inefficient health care spending. In cases in which the cost of existing treatment is exceedingly high, the application of such frameworks would improve efficiency in resource allocation, fostering a balance between incentives for innovation and economic sustainability in managed care systems.

Hemophilia Healing with AAV: Navigating the Frontier of Gene Therapy.

Gene therapy for hemophilia has advanced tremendously after thirty years of continual study and development. Advancements in medical science have facilitated attaining normal levels of Factor VIII (FVIII) or Factor IX (FIX) in individuals with haemophilia, thereby offering the potential for their complete recovery. Despite the notable advancements in various countries, there is significant scope for further enhancement in haemophilia gene therapy. Adeno-associated virus (AAV) currently serves as the primary vehicle for gene therapy in clinical trials targeting haemophilia. Subsequent investigations will prioritize enhancing viral capsid structures, transgene compositions, and promoters to achieve heightened transduction efficacy, diminished immunogenicity, and more predictable therapeutic results. The present study indicates that whereas animal models have transduction efficiency that is over 100% high, human hepatocytes are unable to express clotting factors and transduction efficiency to comparable levels. According to the current study, achieving high transduction efficiency and high levels of clotting factor expression in human hepatocytes is still insufficient. It is also crucial to reduce the risk of cellular stress caused by protein overload. Despite encountering various hurdles, the field of haemophilia gene therapy holds promise for the future. As technology continues to advance and mature, it is anticipated that a personalized therapeutic approach will be developed to cure haemophilia effectively.

Long-term clinical outcomes of prophylaxis with an rFVIIIFc or rFIXFc in adults aged ≥50 years with hemophilia A or B

Advances in therapies for hemophilia have led to an increased life expectancy for people with hemophilia. Limited data exist on the aging population of people with hemophilia who face additional challenges of age-related comorbidities. Efmoroctocog alfa (a recombinant factor VIII Fc fusion protein [herein referred to as rFVIIIFc]) and eftrenonacog alfa (a recombinant factor IX Fc fusion protein [rFIXFc]) are extended half-life factor replacements for hemophilia A and B, respectively, with demonstrated long-term safety and efficacy. The objective of this post hoc analysis was to describe long-term outcomes in participants 50+ years of age treated with rFVIIIFc or rFIXFc in pivotal Phase 3 trials and their extension studies: A-LONG (NCT01181128; n=21) and ASPIRE (NCT01454739; n=20 [95%]); B-LONG (NCT01027364; n=26) and B-YOND (NCT01425723; n=16 [62%]). Approximately half of participants (48%) with hemophilia A and 62% of participants with hemophilia B had a comorbidity at baseline. More than half of the participants were taking 1+ concomitant medication at baseline, with arthropathy and joint pain reported as the most common indications. Prophylaxis with rFVIIIFc or rFIXFc in individuals 50+ years of age with hemophilia A or B, respectively, resulted in low annualized bleed rates and improvements in joint health. Positive impacts on health-related quality of life were observed in individuals on either rFVIIIFc or rFIXFc prophylaxis. The results for the older subgroups were consistent with the overall study populations, demonstrating that prophylaxis with rFVIIIFc or rFIXFc provides long-term clinical benefits irrespective of age and presence of target joints in patients with severe hemophilia.

Human umbilical cord mesenchymal stem cell-based gene therapy for hemophilia B using scAAV-DJ/8-LP1-hFIXco transduction

BackgroundHemophilia B is an X-linked bleeding disorder caused by a mutation in the gene responsible for encoding coagulation factor IX (FIX). Gene therapy offers promising potential for curing this disease. However, the current method of relatively high dosage of virus injection carries inherent risks. The purpose of this study was to introduce a novel scAAV-DJ/8-LP1-hFIXco vector transduced human umbilical cord blood derived mesenchymal stem cells (HUCMSCs) as an alternative cell-based gene therapy to conventional gene therapy for Hemophilia B.MethodsThe LP1-hFIXco gene structure was designed by us through searching the literature from NCBI and the scAAV-DJ/8-LP1-hFIXco vector was constructed by a commercial company. The HUCMSCs were cultivated in routine approach and transduced with scAAV-DJ/8-LP1-hFIXco vector. The human FIX activation system was employed for detection of hFIXco activity. The RNA and protein expression levels of the hFIXco were evaluated using PCR and western blot techniques. In animal studies, both NSG and F9-KO mice were used for the experiment, in which clotting time was utilized as a parameter for bleeding assessment. The immunohistochemical analysis was used to assess the distribution of HUCMSCs in mouse tissue sections. The safety for tumorigenicity of this cell-based gene therapy was evaluated by pathological observation after hematoxylin-eosin staining.ResultsThe transduction of HUCMSCs with the scAAV-DJ/8-LP1-hFIXco vector results in consistent and sustainable secretion of human FIXco during 5 months period both in vitro and in mouse model. The secretion level (hFIXco activity: 97.1 ± 2.3% at day 7 to 48.8 ± 4.5% at 5 months) was comparable to that observed following intravenous injection with a high dose of the viral vector (hFIXco activity: 95.2 ± 2.2% to 40.8 ± 4.3%). After a 5-month observation period, no clonal expansions of the transduced cells in tissues were observed in any of the mice studied.ConclusionsWe have discovered a novel and safer HUCMSCs mediated approach potentially effective for gene therapy in hemophilia B.

Recent Advances in Gene Therapy for Hemophilia: Projecting the Perspectives.

One of the well-known X-linked genetic disorders is hemophilia, which could be hemophilia A as a result of a mutation in the F8 (factor VIII) gene or hemophilia B as a result of a mutation in the F9 (factor IX) gene, leading to insufficient levels of the proteins essential for blood coagulation cascade. In patients with severe hemophilia, factor VIII or factor IX activities in the blood plasma are considerably low, estimated to be less than 1%. This is responsible for spontaneous or post-traumatic bleeding episodes, or both, leading to disease complications and death. Current treatment of hemophilia relies on the prevention of bleeding, which consists of expensive lifelong replacement infusion therapy of blood plasma clotting factors, their recombinant versions, or therapy with recombinant monoclonal antibodies. Recently emerged gene therapy approaches may be a potential game changer that could reshape the therapeutic outcomes of hemophilia A or B using a one-off vector in vivo delivery and aim to achieve long-term endogenous expression of factor VIII or IX. This review examines both traditional approaches to the treatment of hemophilia and modern methods, primarily focusing on gene therapy, to update knowledge in this area. Recent technological advances and gene therapeutics in the pipeline are critically reviewed and summarized. We consider gene therapy to be the most promising method as it may overcome the problems associated with more traditional treatments, such as the need for constant and expensive infusions and the presence of an immune response to the antibody drugs used to treat hemophilia.

Exploring the Low Uptake of Gene Therapy in Hemophilia.

Exploring the Low Uptake of Gene Therapy in Hemophilia.

The longitudinal kinetics of AAV5 vector integration profiles and evaluation of clonal expansion in mice

Adeno-associated virus (AAV)-based vectors are used clinically for gene transfer and persist as extrachromosomal episomes. A small fraction of vector genomes integrate into the host genome, but the theoretical risk of tumorigenesis depends on vector regulatory features. A mouse model was used to investigate integration profiles of an AAV serotype 5 (AAV5) vector produced using Sf and HEK293 cells that mimics key features of valoctocogene roxaparvovec (AAV5-hFVIII-SQ), a gene therapy for severe hemophilia A. The majority (95%) of vector genome reads were derived from episomes, and mean (± standard deviation) integration frequency was 2.70±1.26 and 1.79±0.86 integrations per 1000 cells for Sf- and HEK293-produced vector. Longitudinal integration analysis suggested integrations occur primarily within 1 week, at low frequency, and their abundance was stable over time. Integration profiles were polyclonal and randomly distributed. No major differences in integration profiles were observed for either vector production platform, and no integrations were associated with clonal expansion. Integrations were enriched near transcription start sites of genes highly expressed in the liver (P = 1x10−4) and less enriched for genes of lower expression. We found no evidence of tumorigenesis or fibrosis caused by the vector integrations.

AAV vectors for long-term gene therapy of hemophilia B: Are we there yet?

AAV vectors for long-term gene therapy of hemophilia B: Are we there yet?

Patient Perspective on Disease Burden and Gene Therapy for Hemophilia A and B: The "Haemvolution for Patients" Italian Survey.

Hemophilia is a rare X-linked congenital bleeding disorder due to a deficiency of factor VIII (hemophilia A [HA]) or factor IX (hemophilia B [HB]). Replacement and nonreplacement treatments are available but have limitations. Gene therapy (GT) provides an effective, long-term, single-dose treatment option, now approaching clinical practice. This study aimed to understand patient perspectives on GT for HA and HB in Italy using a qualitative questionnaire distributed through Italian patient associations, addressing patient views on daily life, treatments, unmet needs, quality of life (QoL), and GT for hemophilia. In total, 141 participants had HA, and 14 had HB (severe 78.6%). Daily life was most affected by pain and/or joint function limitations (57.5% of participants), high infusion frequency (42.5%), management of breakthrough bleeding episodes (40.3%), and anxiety/fear of severe or sudden bleeding (38.8%). Despite current treatments, about half of the participants experienced three or more annual bleeding episodes. Most participants knew of GT (87.2%) and expected improvements in QoL (60.5%), reduced frequency of current treatments (53.5%), and a permanent cure (49.1%); 46.4% were unaware of its once-off dosage and 46.4% were not concerned about the costs they anticipated to be associated with GT. Although several fears were reported, 25.0% of participants were willing to undergo GT with the support of a multidisciplinary team. This survey provided valuable insight into patient perspectives on hemophilia and GT in Italy. Overall, relevant proportions of patients still experience limitations affecting their daily life. Most were positive about GT and anticipated improvements in their clinical outcomes and QoL.

Strategies for Performing Factor Assays in the Presence of Emicizumab or Other Novel/Emerging Hemostatic Agents.

For several decades, therapeutic options for inherited deficiencies of factor VIII or IX (hemophilia A or B, respectively) have largely been the replacement of the missing clotting factor with plasma-derived or recombinant products. Hemostasis laboratories use standard activated partial thromboplastin time (aPTT)-based clotting or chromogenic assays to monitor plasma factor levels to guide therapy. The emergence in the past 10 years of extended half-life replacement products and other novel therapies for hemophilia has led to a reappraisal of assay suitability, with studies of product measurement showing some existing assay types or reagents to be unsuitable for some products. The hemostasis laboratory must adapt to the changing landscape by adding new assays or modifying existing assays to ensure accurate results for product measurement. These strategies include switching from a chromogenic assay to a clotting assay, or vice versa, changing an aPTT reagent brand, or introducing product specific calibrators. This article evaluates the effects of some of the newer treatment options on the laboratory testing of factor levels and related assays.

Beqvez - another gene therapy for hemophilia B.

Fidanacogene elaparvovec-dzkt (Beqvez – Pfizer), an adeno-associated virus (AAV) vector-based gene therapy, has been approved by the FDA for treatment of adults with moderate to severe hemophilia B who do not have neutralizing antibodies to AAV serotype Rh74var and currently receive factor IX prophylaxis therapy or have had life-threatening hemorrhage or repeated, serious, spontaneous bleeding episodes. Beqvez is the second single-dose gene therapy to be approved in the US for treatment of hemophilia B; Hemgenix was the first.

Bleeding phenotype according to factor level in 825 children with nonsevere hemophilia: data from the PedNet cohort

BackgroundInformation on bleeding phenotype in nonsevere hemophilia may be used to determine target factor levels for prophylaxis or gene therapy in severe hemophilia. ObjectivesTo assess the association between endogenous factor level and bleeding phenotype in children with nonsevere (factor [F]VIII/FIX activity 1%-25%) hemophilia A (HA) and B without prophylaxis. MethodsData on annualized bleeding rate (ABR), annualized joint bleeding rate (AJBR), and onset of bleeding were extracted from the international PedNet cohort including children born since 2000. Mean ABR and AJBR were modeled and compared according to FVIII/FIX endogenous activity (1%-2%, 3%-5%, 6%-10%, 11%-15%, 16%-20%, and 21%-25%) using negative binomial regression. Onset of bleeding was analyzed using Kaplan–Meier survival curves. ResultsEight hundred twenty-five children (40% with moderate hemophilia; 87% with HA) with median follow-up of 7.4 years/child were included. The median age at onset of bleeding and median bleeding rates changed with increasing endogenous activity. From endogenous FVIII 1% to 2% to 21% to 25%, the age at onset of bleeding changed from a median of 1.4 to 14.2 years, ABR from 1.6 to 0.1/y, and AJBR from 0.5 to 0.0/y. From endogenous FIX 1% to 2% to 16% to 25%, the onset of bleeding changed from a median of 1.7 to 6.1 years, ABR from 0.5 to 0.1/y, and AJBR from 0.1 to 0.0/y. The negative correlation between AJBR and factor level was most strongly pronounced up to a factor level of 6% in HA and hemophilia B. ConclusionEndogenous factor activity of >5% was identified as a threshold to significantly lower joint bleeding rate, while FVIII levels >15% and FIX levels >10% were sufficient to achieve the goal of 0 bleeds in this pediatric cohort.

Inhibitory hemophilia: contemporary treatment with emicizumab. Considerations for pediatric practice

Introduction. This article provides an overview of current knowledge and global experience regarding the use of emicizumab, with a focus on its specific considerations in pediatric practice. Emicizumab, a monoclonal antibody, operates uniquely compared to other therapies. It has been approved in Moldova since 2019 for preventing bleeding in hemophilia patients. Significant data from clinical studies and accumulated clinical practice provide answers to most questions physicians have when prescribing emicizumab. The article presents recommendations based on current information and global experience to aid decision-making in emicizumab usage. The purpose of this article is to provide information on management tactics for pediatric patients with hemophilia A receiving emicizumab. Materials and methods. Over 40 publications were reviewed, consisting of recommendations, study results, and observations related to emicizumab use in pediatric patients with Hemophilia A. Results. In 2017, emicizumab became the first registered non-factorial therapy for Hemophilia A. It was approved for use in treating the inhibitory form of the condition. In 2018, indications for emicizumab were expanded to include patients with the inhibitory form of hemophilia A and severe hemophilia A without inhibitors. Emicizumab is used to prevent bleeding and is not intended to stop an already occurring bleeding. If bleeding has occurred, the patient will need to be prescribed FVIII or bypassing agents. Emicizumab is administered as a loading dose of 3 mg/kg once a week for the first 4 weeks, followed by a maintenance dose of 1.5 mg/kg once a week, 3 mg/kg once every two weeks, or 6 mg/kg once every four weeks. The dose is based on the patient’s body weight, which needs regular monitoring. If a dose is missed, it should be administered as soon as possible before the next scheduled dose, and the injection schedule should not be altered. Emicizumab can be used in children under one year to prevent bleeding. Conclusions. Hemophilia, caused by a deficiency in coagulation factors VIII or IX, is a bleeding disorder. The main treatment-related complication in hemophilia patients is the development of inhibitors – alloantibodies that neutralize the procoagulant activity of infused FVIII or factor IX. The reasons why only 20%-30% of Hemophilia A patients develop inhibitors remain a challenge. Emicizumab, a bispecific monoclonal antibody, bridges the gap between activated factor IX and factor X to replace the missing activated factor VIII, thereby restoring hemostasis.

Gene Therapy for Hemophilia B: Achievements, Open Issues, and Perspectives.

Hemophilia B is the first bleeding disorder for which gene therapy clinical programs began. Presently, adenovirus-associated vectors represent the best means to deliver the transgene, and their administration by intravenous route has been used in recent clinical trials. The natural occurring factor IX (FIX) Padua variant, which allows for a 5- to 8-fold higher activity of FIX, while maintaining a normal protein concentration, was subsequently used to enhance the level of transgene expression. All the recent trials using this variant showed good results, and accumulating data suggest that long-term expression durability could be maintained at a significant hemostatic level. However, the risk of loss of transgene expression associated to immune response with liver enzymes elevation remains a concern, especially as to the efficacy and duration of immunosuppressive treatment. Notwithstanding this limitation, the results of clinical trials suggest that gene therapy in hemophilia B has the potential to provide long-term benefits with sustained factor activity levels predicted to last several years in many patients.