Pharmacokinetic analysis identifies a factor VIII immunogenicity threshold after AAV gene therapy in hemophilia A mice

Correlation of antigen expression with epigenetic modifications after rAAV delivery of a human factor IX variant in mice and rhesus macaques

We investigated long-term human coagulation factor IX (huFIX) expression of a novel variant when delivered into mice and rhesus macaques and compared transduction efficiencies using two different adeno-associated virus (AAV) capsids. In hemophilic mice injected with KP1-packaged recombinant AAV (rAAV) expressing the hyperactive FIX variant specific activity plasma levels were 10-fold or 2-fold enhanced when compared with wild-type or Padua huFIX injected mice, respectively. In rhesus macaques AAV-LK03 capsid outperformed AAV-KP1 in terms of antigen expression and liver transduction. Two animals from each group showed sustained low-level huFIX expression at 3 months after administration, while one animal from each group lost huFIX mRNA and protein expression over time, despite comparable vector copies. We investigated whether epigenetic differences in the vector episomes could explain this loss of transcription. Cut&Tag analysis revealed lower levels of activating histone marks in the two animals that lost expression. When comparing rAAV genome associated histone modifications in rhesus macaques with those in mice injected with the same vector, the activating histone marks were starkly decreased in macaque-derived episomes. Differential epigenetic marking of AAV genomes may explain different expression profiles in mice and rhesus macaques, as well as the wide dose response variation observed in primates in both preclinical and human clinical trials.

A review of the rationale for gene therapy for hemophilia A with inhibitors: one-shot tolerance and treatment?

The therapeutic landscape for people living with hemophilia A (PwHA) has changed dramatically in recent years, but many clinical challenges remain, including the development of inhibitory antibodies directed against factor VIII (FVIII) that occur in approximately 30% of people with severe hemophilia A. Emicizumab, an FVIII mimetic bispecific monoclonal antibody, provides safe and effective bleeding prophylaxis for many PwHA, but clinicians still explore therapeutic strategies that result in immunologic tolerance to FVIII to enable effective treatment with FVIII for problematic bleeding events. This immune tolerance induction (ITI) to FVIII is typically accomplished through repeated long-term exposure to FVIII using a variety of protocols. Meanwhile, gene therapy has recently emerged as a novel ITI option that provides an intrinsic, consistent source of FVIII. As gene therapy and other therapies now expand therapeutic options for PwHA, we review the persistent unmet medical needs with respect to FVIII inhibitors and effective ITI in PwHA, the immunology of FVIII tolerization, the latest research on tolerization strategies, and the role of liver-directed gene therapy to mediate FVIII ITI.

Hemophilic Arthropathy: Barriers to Early Diagnosis and Management

Hemophilia is a congenital coagulopathy characterized by a deficiency of one of the clotting factors. It is characterized by the development of hematomas and hemarthrosis, either spontaneously or after minor trauma. The recurrence of hemarthroses leads to progressive and degenerative joint damage from childhood (hemophilic arthropathy). This arthropathy is characterized by disabling physical effects that limit the functionality and quality of life of these patients. Medical progress achieved over the last decade in the drug treatment of hemophilia has improved the medium and long-term prospects of patients with more effective and long-lasting drugs. The universal use of safer, more effective and prolonged prophylactic treatments may promote the prevention of bleeding, and also therefore, of the development of hemarthrosis and joint damage. A number of imaging instruments have been developed for the assessment of hemarthrosis and hemophilic arthropathy, using ultrasound, magnetic resonance imaging and simple radiology. Different physical examination scores and questionnaires allow the assessment of joint health, self-perceived activity and functionality of patients with hemophilia. The approach to these patients should be interdisciplinary. Assessment of the processes that affect pain in these patients and the development of pain education models should be implemented. Expert advice and information to patients with hemophilia should be based on individual functional prevention diagnoses, advice on available therapies and sports practice, as well as health recommendations.