FDA Grants Priority Review to Leniolisib for Children With APDS

The U.S. Food and Drug Administration has accepted a supplemental New Drug Application from Pharming Group N.V. seeking approval of leniolisib for children 4 to 11 years old with activated phosphoinositide 3-kinase delta syndrome, commonly known as APDS, and has granted the filing Priority Review. The company, based in Leiden, the Netherlands and listed on Euronext (PHARM) and Nasdaq (PHAR), said the application was accepted in materials dated October 1, 2025 and reiterated in a company summary dated January 9, 2026. The FDA set a Prescription Drug User Fee Act target action date of January 31, 2026.

Leniolisib is an oral, selective PI3K delta inhibitor that Pharming is proposing to use to correct the immune dysregulation that defines APDS. The supplemental filing is supported by data from a multinational, single-arm Phase III study in children aged 4 to 11. Over 12 weeks, the trial recorded reductions in lymphadenopathy and increases in naive B cells, changes the company said “indicate a correction of the underlying immune defect.” The submission also included safety data from up to eight months of treatment.

Pharming emphasized that there are currently no approved treatments globally for children with APDS under 12 years of age and said leniolisib would be the first and only therapy indicated for this population if approved. The FDA’s Priority Review designation signals that regulators consider the application potentially significant for the treatment of a serious condition, and it advances the regulatory timetable toward the late January decision date.

The clinical evidence in the sNDA rests on a single-arm trial, a study design commonly used in rare diseases where randomized trials are challenging to conduct. That design can demonstrate biological activity and clinically meaningful changes in small patient populations, but it offers less comparative context than randomized controlled trials. Regulators will weigh the magnitude and durability of the reported improvements and the safety profile observed during the eight-month follow-up when assessing benefit-risk for pediatric use.

Families and clinicians caring for children with APDS have few therapeutic options, generally relying on symptom management and infection prevention. An approved targeted therapy for young children would shift treatment toward addressing the underlying immune pathway, potentially reducing infections and lymphoid complications. At the same time, long-term safety and monitoring will be critical if the drug reaches the market, as most pediatric immunomodulatory therapies require ongoing assessment of growth, infection risk, and immune function.

Pharming provided corporate governance information in its October release and named its executive committee and board members in accompanying materials. With the FDA decision now days away, patients, clinicians, and investors will be watching the agency’s review of the Phase III findings and safety data ahead of the January 31, 2026 PDUFA target date.