7004 Background: Asparaginase is a cornerstone in the treatment of ALL, but its utility is limited by toxicities including hypersensitivity. Clinical allergy is associated with inactivation of asparaginase by antibodies (A-Abs), which can also neutralize asparaginase without any clinical signs of hypersensitivity (silent inactivation). ERY001 improves pharmacokinetics, tolerability and maintain circulating asparaginase (ASPA) activity due to the protective barrier of the erythrocyte membrane. Methods: This open, randomized international Phase 3 study enrolled pts with relapsed ALL. The co-primary endpoints were the duration of ASPA activity > 100IU/L and the incidence of ASPA hypersensitivity during induction. Key secondary endpoints were complete remission (CR), minimal residual disease (MRD), event free survival (EFS) and overall survival (OS).The study was powered to detect 3-fold difference in the incidence of allergic reactions between treatments. Pts (n = 80), aged 1-55 years were randomized to ERY0...