Recombinant factor VIII Fc fusion protein for first-time immune tolerance induction: final results of the verITI-8 study

Pharmacokinetic evaluation of efanesoctocog alfa: breakthrough factor VIII therapy for hemophilia A

INTRODUCTION

Blood coagulation factor (F)VIII functions as a cofactor in the tenase complex responsible for phospholipid-dependent FIXa-mediated activation of FX in plasma. Congenital defect of FVIII causes severe bleeding disorder, hemophilia (H) A. Intravenous FVIII replacement therapy is the gold standard therapy in patients with HA (PwHA) but requirement for frequent dosing of FVIII owing to pharmacokinetics burdens PwHA a lot. Efanesoctocog alfa is a new class of recombinant FVIII and has the ability to overcome conceivable unmet needs in treatment for PwHA.

AREAS COVERED

Efanesoctocog alfa is a B domain-deleted single-chain fusion FVIII connected to the Fc-region of human immunoglobulin G1, D'D3-fragment of von Willebrand factor (VWF), and unstructured hydrophilic recombinant polypeptides (XTEN). Owing to its novel design, it can function independently of endogenous VWF and elicits 2 to 4 times longer half-life compared to other existing FVIII products. The prolonged half-life contributes to maintain high level of FVIII activity for most of the week and has led to excellent hemostatic effect by once-weekly administration in phase 3 clinical trials.

EXPERT OPINION

Efanesoctocog alfa with outstanding pharmacological properties, well tolerated in the clinical trials, is a promising FVIII therapy for PwHA. Future studies should include long-term safety, especially in previously untreated patients.

Impacts of the COVID-19 pandemic on pediatric and adult patients with hemophilia

BACKGROUND

The coronavirus disease 2019 (COVID-19)-associated mortality rate of hemophilia patients is similar to that of the general population, but the risk of hospitalization and bleeding is higher. However, the specific impact of this infection on hemophilia patients remains unknown. We aimed to investigate the impact of the pandemic on the infection susceptibility, symptoms, drug use, and social intercourse of patients with hemophilia.

METHODS

A survey was distributed to 265 patients with hemophilia (185 adults and 80 children) in the Fujian hemophilia therapeutic center (Fuzhou City, China) during the COVID-19 pandemic, and data were collected between January 2022 and January 2023. The impacts of SARS-CoV-2 infection on hemophilia symptoms, drug use, and social intercourse of these patients were investigated, and the association between the recovery time and disease conditions was explored in infected patients.

RESULTS

During the pandemic, compared with adult patients, pediatric patients had significantly reduced social intercourse and outdoor activities because of the fear of contracting COVID-19 (85.0% vs. 66.5%). Bleeding events were also significantly fewer in children than in adults (61.2% vs. 81.1%). The SARS-CoV-2 infection rate was significantly higher in patients living in urban areas than in those living in rural areas (74.3% vs. 53.6%). The duration of symptomatic recovery from COVID-19 was not significantly associated with hemorrhage, type and classification of hemophilia, presence of inhibitors, complications, and vaccination status.

CONCLUSION

Having COVID-19 infection did not significantly influence the symptoms and treatments in patients with hemophilia. Pediatric patients had significantly fewer bleeding events than adults.

Shifting Paradigms and Arising Concerns in Severe Hemophilia A Treatment

The management of hemophilia A has undergone a remarkable revolution, in line with technological advancement. In the recent past, the primary concern associated with Factor VIII (FVIII) concentrates was the risk of infections, which is now almost resolved by advanced blood screening and viral inactivation methods. Improving patients' compliance with prophylaxis has become a key focus, as it can lead to improved health outcomes and reduced health care costs in the long term. Recent bioengineering research is directed toward prolonging the recombinant FVIII (rFVIII) coagulant activity and synthesising higher FVIII yields. As an outcome, B-domain deleted, polyethylene glycolated, single-chain, Fc-fused rFVIII, and rFVIIIFc-von Willebrand Factor-XTEN are available for patients. Moreover, emicizumab, a bispecific antibody, is commercially available, whereas fitusiran and tissue factor pathway inhibitor are in clinical trial stages as alternative strategies for patients with inhibitors. With these advancements, noninfectious complications, such as inhibitor development, allergic reactions, and thrombosis, are emerging concerns requiring careful management. In addition, the recent approval of gene therapy is a major milestone toward a permanent cure for hemophilia A. The vast array of treatment options at our disposal today empowers patients and providers alike, to tailor therapeutic regimens to the unique needs of each individual. Despite significant progress in modern treatment options, these highly effective therapies are markedly more expensive than conventional replacement therapy, limiting their access for patients in developing countries.

Factor VIII moiety of recombinant Factor VIII Fc fusion protein impacts Fc effector function and CD16+ NK cell activation

Recombinant Factor VIII-Fc fusion protein (rFVIIIFc) is an enhanced half-life therapeutic protein product used for the management of hemophilia A. Recent studies have demonstrated that rFVIIIFc interacts with Fc gamma receptors (FcγR) resulting in the activation or inhibition of various FcγR-expressing immune cells. We previously demonstrated that rFVIIIFc, unlike recombinant Factor IX-Fc (rFIXFc), activates natural killer (NK) cells via Fc-mediated interactions with FcγRIIIA (CD16). Additionally, we showed that rFVIIIFc activated CD16+ NK cells to lyse a FVIII-specific B cell clone. Here, we used human NK cell lines and primary NK cells enriched from peripheral blood leukocytes to study the role of the FVIII moiety in rFVIIIFc-mediated NK cell activation. Following overnight incubation of NK cells with rFVIIIFc, cellular activation was assessed by measuring secretion of the inflammatory cytokine IFNγ by ELISA or by cellular degranulation. We show that anti-FVIII, anti-Fc, and anti-CD16 all inhibited indicating that these molecules were involved in rFVIIIFc-mediated NK cell activation. To define which domains of FVIII were involved, we used antibodies that are FVIII domain-specific and demonstrated that blocking FVIII C1 or C2 domain-mediated membrane binding potently inhibited rFVIIIFc-mediated CD16+ NK cell activation, while targeting the FVIII heavy chain domains did not. We also show that rFVIIIFc binds CD16 with about five-fold higher affinity than rFIXFc. Based on our results we propose that FVIII light chain-mediated membrane binding results in tethering of the fusion protein to the cell surface, and this, together with increased binding affinity for CD16, allows for Fc-CD16 interactions to proceed, resulting in NK cellular activation. Our working model may explain our previous results where we observed that rFVIIIFc activated NK cells via CD16, whereas rFIXFc did not despite having identical IgG1 Fc domains.

Gene Therapy in Hemophilia A: Achievements, Challenges, and Perspectives

Strides in advancements of care of persons with hemophilia include development of long-acting factor replacement therapies, novel substitution and hemostatic rebalancing agents, and most recently approved gene therapy. Several decades of preclinical and clinical trials have led to development of adeno-associated viral (AAV) vector-mediated gene transfer for endogenous production of factor VIII (FVIII) in hemophilia A (HA). Only one gene therapy product for HA (valoctocogene roxaparvovec) has been approved by regulatory authorities. Results of valoctocogene roxaparvovec trial show significant improvement in bleeding rates and use of factor replacement therapy; however, sustainability and duration of response show variability with overall decline in FVIII expression over time. Further challenges include untoward adverse effects involving liver toxicity requiring immunosuppression and development of neutralizing antibodies to AAV vector rendering future doses ineffective. Real-life applicability of gene therapy for HA will require appropriate patient screening, infrastructure setup, long-term monitoring including data collection of patient-reported outcomes and innovative payment schemes. This review article highlights the success and development of HA gene therapy trials, challenges including adverse outcomes and variability of response, and perspectives on approach to gene therapy including shared decision-making and need for future strategies to overcome the several unmet needs.

Therapeutic Fusion Proteins

Therapeutic fusion proteins are a class of hybrid constructs that combine distinct biomolecules into a single platform with the additive effects of the components. The ability to fuse two unrelated proteins provides a means to localize mechanisms to better treat a range of diseases. Fusion proteins can be designed to impart diverse functions, including increasing half-life, providing targeting, and enabling sustained signaling. Of these, half-life extenders, which are fused to a therapeutic protein to increase exposure, are the most established group of fusion proteins, with many clinical successes. Rapid advances in antibody and antibody-derivative technology have enabled the fusion of targeting domains with therapeutic proteins. An emerging group of therapeutic fusion proteins has two separate active functions. Although most research for therapeutic fusion proteins focuses on cancer, prior successes provide a foundation for studies into other diseases as well. The exponential emergence of biopharmaceuticals gives precedence for increased research into therapeutic fusion proteins for a multitude of diseases.