First-in-human Gene Therapy Study of AAVhu37 Capsid Vector Technology in Severe Hemophilia A

Background:

Gene therapy for hemophilia A has the potential to reduce the treatment burden for care-providers and patients, by eliminating the need for regular factor VIII (FVIII) prophylaxis through the long-term expression of endogenous FVIII at levels sufficient to provide bleed protection. BAY 2599023 (AAVhu37FVIII) is a non-replicating adeno-associated virus (AAV) vector, based on the AAV serotype hu37, which contains a single-stranded DNA genome encoding a B-domain deleted FVIII, under the control of a liver-specific promotor/enhancer combination optimized for transgenic expression. The AAVhu37 capsid is a member of the hepatotropic Clade E family and has been selected based on nonclinical studies demonstrating efficient liver-directed FVIII gene transfer, favorable biodistribution as well as durable FVIII expression. BAY 2599023 is the first clinical-stage AAV gene therapy vector based on the AAVhu37 serotype. This analysis reports safety and FVIII activity following a single intravenous infusion of BAY 2599023 in the first-dose cohort of a phase I/II open-label, first time in human dose-finding study (NCT03588299) of previously treated, severe hemophilia A patients.

Patients/Methods:

Two participants were enrolled sequentially; each received a single infusion of AAVhu37 (0.5 x 10¹³ GC/kg). Patients were males ≥18 years with no history of FVIII inhibitor development, no detectable immunity to the AAVhu37 capsid, and >150 exposure days to FVIII products. Primary endpoints were adverse events (AEs), serious AEs and AEs/SAEs of special interest (S/AESI); the secondary endpoint was change in FVIII activity from baseline. Informed patient consent, and ethics committee approval at each local site, were obtained.

Results:

Following more than 15 weeks of safety observation, no SAEs, AEs related to study drug, nor S/AESI were reported. Liver enzymes (alanine aminotransferase and aspartate aminotransferase) remained <1.5 of baseline. Corticosteroids were not used in either patient. Clear evidence of FVIII expression was observed in both patients with stable values of ~5% and ~17% in the first and second patient, respectively. An early read-out also indicated hemostatic efficacy in both; the first patient had successfully halted prophylaxis for 6 weeks, while the second one, treated on-demand with 99 bleeds recorded in the 12 months prior to gene transfer, has been bleed free for over 5.5 months to date.

Conclusions:

BAY 2599023 was previously shown in non-clinical studies to have a good safety profile, with the potential to achieve endogenous expression of FVIII at therapeutic levels, over an extended period of time. In this first-in-human clinical study with BAY 2599023, two patients have been treated with BAY 2599023 at the starting dose of 0.5 x 10¹³ GC/kg and no safety concerns have been reported to date. Measurable expression of endogenous FVIII and an early read-out of hemostatic efficacy have been demonstrated in both patients. Overall, data generated from this first dose cohort demonstrate that successful translation from pre-clinical to clinical development and proof-of-mechanism for BAY 2599023 was achieved.