A phase 1/2 safety and efficacy study of TAK-754 gene therapy: The challenge of achieving durable factor VIII expression in haemophilia A clinical trials

IntroductionHaemophilia A is an X-linked bleeding disorder resulting from a deficiency of factor VIII (FVIII). To date, multiple gene therapies have entered clinical trials with the goal of providing durable haemostatic protection from a single dose. TAK 754 (BAX 888) is an investigational AAV8-based gene therapy containing a FVIII transgene. Reduction in CpG motifs was performed to reduce immunogenicity based on prior observations. Here, we describe the results of the first two cohorts treated with TAK 754.AimTo report clinical and translational results of the TAK-754 phase 1/2 AAV gene therapy study for the treatment of haemophilia A.MethodsA phase 1/2 single arm open-label dose escalation study of TAK-754 was performed in participants with severe haemophilia A (NCT03370172). Participants were monitored for safety events, endogenous FVIII activity and bleeding rates. Glucocorticoids were implemented to preserve transgene expression. A transcriptomics analysis was performed to evaluate immunogenicity along with additional post-hoc analyses.ResultsFour participants were dosed in two cohorts. Infusion of TAK 754 was well-tolerated. All participants developed mild transient transaminase elevation and subsequent loss of FVIII expression within the first 12 months of treatment despite use of glucocorticoids. Transcriptomic analysis did not demonstrate significant changes in immunogenicity signals in peripheral blood. One serious adverse event of hypophosphatemia occurred in the second cohort without obvious risk factors.ConclusionsSustained FVIII expression remains a challenge in haemophilia A AAV gene therapy trials. Mechanisms of transgene expression loss require further study as clinical studies enter long term follow-up periods.