An Open-Label Study to Assess the Safety & Efficacy of Leniolisib in Japanese Patients With APDS

Inclusion Criteria: * Patient is Japanese. * Patient is male or female and 12 to 75 years of age (inclusive) at the time of the first study procedure. * Patient weighs ≥35 kg at baseline. * Patient has a PI3Kδ genetic mutation of either the PIK3CD (APDS1) or PIK3R1 (APDS2) gene. * Patient has at least 1 measurable nodal lesion on computed tomography (CT) or magnetic resonance imaging (MRI) scan within 6 months of Screening. * Patient has nodal and/or extranodal lymphoproliferation and clinical findings and manifestations consistent with APDS (e.g., a history of repeated oto-sino-pulmonary infections and/or organ dysfunction consistent with APDS). * At Screening, patient has sitting vital signs (with patient rested for at least 3 minutes) within the following ranges: * Systolic blood pressure, 90-160 mm Hg * Diastolic blood pressure, 50-95 mm Hg * Pulse rate, 40-100 bpm; up to 110 bpm in adolescents Exclusion Criteria: \- Patient has previous or concurrent use of immunosuppressive medication such as the following: 1. A mammalian target of rapamycin inhibitor (e.g., sirolimus, rapamycin, or everolimus) or a PI3Kδ inhibitor (selective or non-selective phosphoinositide 3-kinase inhibitors) within 6 weeks prior to first dose. \- Short-term use for up to a total of 5 days is allowed but only up to 1 month prior to enrollment in the study. 2. B-cell depleters (e.g., rituximab) within 6 months prior to first dose of study treatment. \- If patient has received prior treatment with a B-cell depleter, absolute B lymphocyte counts in the blood must have regained normal values. 3. Belimumab or cyclophosphamide within 6 months prior to first dose of study treatment. 4. Cyclosporine A, mycophenolate, 6-mercaptopurine, azathioprine, or methotrexate within 3 months prior to first dose of study treatment. 5. Glucocorticoids above 25 mg prednisone or equivalent per day within 2 weeks prior to first dose of study treatment. 6. Other immunosuppressive medications where effects are expected to persist at start of dosing of study treatment. * Patient has had a hematopoietic stem-cell transplant, hematopoietic cell transplant, or bone marrow transplant. * Patient is currently using a medication known to be a strong inhibitor or moderate or strong inducer of isoenzyme cytochrome P450 (CYP)3A if treatment cannot be discontinued or switched to a different medication prior to starting study treatment. * Patient is currently using medications that are metabolized by isoenzyme CYP1A2 and have a narrow therapeutic index (drugs whose exposure response indicates that increases in their exposure levels by the concomitant use of potent inhibitors may lead to serious safety concerns \[e.g., Torsades de Pointes\]). * Patient had been administered a live vaccine (this includes any attenuated live vaccines) starting from 6 weeks before the anticipated first dose of study treatment, during the treatment period, and up to 7 days after the last dose of leniolisib. * Patient is a pregnant or nursing (lactating) woman, where pregnancy is defined as the state of a female after conception and until the termination of gestation, confirmed by a positive human chorionic gonadotropin laboratory test. * Patient is a woman of child-bearing potential, defined as a woman physiologically capable of becoming pregnant, unless she is using highly effective methods of contraception during dosing of study treatment and for 30 days after the last study procedure.