Spark Therapeutics announced updated data from the ongoing Phase 1/2 clinical trial of investigational SPK-8011 in hemophilia A during the International Society of Thrombosis and Hemostasis (ISTH) 2021 Virtual Congress (July 17-21). The data will be shared as an oral presentation on, July 21 at 10:12 a.m. EST.(Abstract OC 67.2). Eighteen participants in the Phase 1/2 trial received a single administration of investigational SPK-8011 in four dose cohorts, ranging from 5x1011 vg/kg to 2Ã--1012 vg/kg. In the 16 patients with sustained FVIII expression, there was a 91.2% reduction in annualized bleed rate (ABR) and 97% reduction in annualized FVIII infusion rate (AIR) after vector administration. Administration of SPK-8011 in patients with hemophilia A resulted in an acceptable safety profile with no deaths and no FVIII inhibitor development with up to 4 years of follow-up. As previously disclosed, two of the 17participants with over one year of data lost FVIII expression due to a presumed cellular immune response to the AAV capsid that was unresponsive to immunosuppression. Seven participants reported transient, asymptomatic liver function test (LFT) elevations. All LFT elevations were mild or moderate and have resolved. One participant experienced a mild to moderate acute infusion reaction, which presented as four nonserious adverse events (AEs) (pyrexia, myalgia, vomiting, and back pain) and were resolved. One participant experienced Grade 2 transaminitis, which resulted in elective hospitalization for IV steroid administration, qualifying as a serious AE.