Report of the Italian Cohort with Activated Phosphoinositide 3-Kinase δ Syndrome in the Target Therapy Era

BackgroundActivated Phosphoinositide 3-Kinase (PI3K) delta Syndrome (APDS), an inborn error of immunity due to upregulation of the PI3K pathway, leads to recurrent infections and immune dysregulation (lymphoproliferation and autoimmunity).MethodsClinical and genetic data of 28 APDS patients from 25 unrelated families were collected from fifteen Italian centers.ResultsPatients were genetically confirmed with APDS-1 (n = 20) or APDS-2 (n = 8), with pathogenic mutations in the PIK3CD or PIK3R1 genes. The median age at diagnosis was 15.5 years, with a median follow-up of 74 months (range 6-384). The main presenting symptoms were respiratory tract infections alone (57%) or associated with lymphoproliferation (17%). Later, non-clonal lymphoproliferation was the leading clinical sign (86%), followed by respiratory infections (79%) and gastrointestinal complications (43%). Malignant lymphoproliferative disorders, all EBV-encoding RNA (EBER)-positive at the histological analysis, occurred in 14% of patients aged 17-19 years, highlighting the role of EBV in lymphomagenesis in this disorder. Diffuse large B-cell lymphoma was the most frequent. Immunological work-up revealed combined T/B cell abnormalities in most patients. Treatment strategies included immunosuppression and PI3K/Akt/mTOR inhibitor therapy. Rapamycin, employed in 36% of patients, showed efficacy in controlling lymphoproliferation, while selective PI3K delta inhibitor leniolisib, administered in 32% of patients, was beneficial on both infections and immune dysregulation. Additionally, three patients underwent successful HSCT due to recurrent infections despite ongoing prophylaxis or lymphoproliferation poorly responsive to Rapamycin.ConclusionsThis study underscores the clinical heterogeneity and challenging diagnosis of APDS, highlighting the importance of multidisciplinary management tailored to individual needs and further supporting leniolisib efficacy.