Spark Therapeutics announced data from its Phase 1/2 clinical trial of investigational SPK-8011 in hemophilia A. The study found that, at a median efficacy follow-up of 33.4 months (range, 3.7-47.6), 16 of 18 study participants had sustained factor VIII (FVIII), which permitted prophylaxis cessation and reduction in bleeding episodes. The latest results were published online in the New England Journal of Medicine (NEJM). The updated analysis (cutoff May 3, 2021) of all 18 study participants, following the initial data presentation at the International Society of Thrombosis and Hemostasis (ISTH) 2021 Virtual Congress in July, demonstrated a 91.5% reduction (95% CI: [88.8, 94.1]) in annualized bleed rate (ABR) and a 96.4% reduction (95% CI: [95.7, 97.1]) in annualized number of FVIII infusions. In the safety analysis, 33 treatment-related adverse events (AEs) occurred in 8 participants of which 17 were vector-related, including one serious AE, and 16 were glucocorticoid-related. As previously reported, two participants lost all FVIII expression due to an anti-AAV capsid cellular immune response, unresponsive to immunosuppression. The remaining 16 participants maintained FVIII expression, of which 12 were followed for over 2 years and demonstrated no apparent decrease in one-stage FVIII activity over time. About SPK-8011 for hemophilia A Investigational SPK-8011, a novel bio-engineered adeno-associated viral (AAV) vector utilizing the AAV-LK03 capsid, also referred to as Spark200, contains a codon-optimized human factor VIII gene under the control of a liver specific promoter. The Food and Drug Administration (FDA) granted orphan-disease designation and breakthrough therapy designation in the U.S., while the European Commission has granted orphan designation to SPK-8011. The Phase 1/2 study, titled ?A Gene Transfer Study of SPK-8011 for Hemophilia A,? is being conducted by Spark Therapeutics, Inc. to determine the safety and efficacy of the factor VIII gene transfer treatment with SPK-8011 in individuals with hemophilia A. (Trial identifier NCT03003533).