Open-label extension study of leniolisib in activated PI3Kδ syndrome: Long-term efficacy and safety

Activated phosphoinositide 3-kinase delta syndrome (APDS) is an inborn error of immunity characterized by immune deficiency and dysregulation. Leniolisib is a selective phosphoinositide 3-kinase delta inhibitor approved to treat APDS in patients ≥12 years old. We report final results from a single-arm, open-label extension study in 37 patients with APDS (NCT02859727). Median leniolisib exposure was 4.3 years (range, 1.2-7.0 years). Adverse events (AE) were reported in 34 patients; 87% were grade 1. Serious AEs, reported in 10 patients, were deemed unrelated to leniolisib. Two patients discontinued treatment due to AEs: cardiac arrest and Hodgkin's lymphoma. There were significant reductions in annual infection (P = 0.0005) and respiratory infection (P = 0.0017) rates per year of treatment. Immunoglobulin replacement therapy (IRT) use significantly decreased per year of treatment (P = 0.0095). Clinically meaningful improvements in general health scores from the 36-Item Short Form Survey were observed. Overall, long-term use of leniolisib was generally well tolerated, and infections and IRT use reduced over time.