Clinical and immunologic phenotype associated with activated phosphoinositide 3-kinase delta syndrome 2: A cohort study

Background: Activated phosphoinositide 3-kinase delta syndrome (APDS) 2 (p110 delta-activating mutations causing senescent T cells, lymphadenopathy, and immunodeficiency [PASLI]-R1), a recently described primary immunodeficiency, results from autosomal dominant mutations in PIK3R1, the gene encoding the regulatory subunit (p85 alpha, p55 alpha, and p50 alpha) of class IA phosphoinositide 3-kinases. Objectives: We sought to review the clinical, immunologic, and histopathologic phenotypes of APDS2 in a genetically defined international patient cohort. Methods: The medical and biological records of 36 patients with genetically diagnosed APDS2 were collected and reviewed. Results: Mutations within splice acceptor and donor sites of exon 11 of the PIK3R1 gene lead to APDS2. Recurrent upper respiratory tract infections (100%), pneumonitis (71%), and chronic lymphoproliferation (89%, including adenopathy [75%], splenomegaly [43%], and upper respiratory tract lymphoid hyperplasia [48%]) were the most common features. Growth retardation was frequently noticed (45%). Other complications were mild neurodevelopmental delay (31%); malignant diseases (28%), most of them being B-cell lymphomas; autoimmunity (17%); bronchiectasis (18%); and chronic diarrhea (24%). Decreased serum IgA and IgG levels (87%), increased IgM levels (58%), B-cell lymphopenia (88%) associated with an increased frequency of transitional B cells (93%), and decreased numbers of naive CD4 and naive CD8 cells but increased numbers of CD8 effector/memory T cells were predominant immunologic features. The majority of patients (89%) received immunoglobulin replacement; 3 patients were treated with rituximab, and 6 were treated with rapamycin initiated after diagnosis of APDS2. Five patients died from APDS2-related complications. Conclusion: APDS2 is a combined immunodeficiency with a variable clinical phenotype. Complications are frequent, such as severe bacterial and viral infections, lymphoproliferation, and lymphoma similar to APDS1/PASLI-CD. Immunoglobulin replacement therapy, rapamycin, and, likely in the near future, selective phosphoinositide 3-kinase delta inhibitors are possible treatment options. European Union's 7th RTD Framework Programme (ERC advanced grant PID-IMMUNE) - 249816 French National Research Agency (ANR) - ANR-10-IAHU-01 Centre de Reference Deficits Immunitaires Hereditaires (CEREDIH) French National Research Agency (ANR)-European Commission - ANR-15-CE15-0020 Gebert Ruf Stiftung program "Rare Diseases-New Approaches'' - GRS-046/10 European Commission - CELL-PID HEALTH-261387 Zurich Centre for Integrative Human Physiology (ZIHP) Gottfried und Julia Bangerter-Rhyner-Stiftung Rossi Stiftung European Research Council (ERC)-European Commission - 260477 European Commission - 261441 National Institute for Health Research (NIHR) Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT)-Japan Society for the Promotion of Science Ministry of Health, Labour and Welfare, Japan Ministry of Defense Japan Agency for Medical Research and Development (AMED) National Institute for Health Research-Leeds Musculoskeletal Biomedical Research Unit (and Leeds Teaching Hospitals Charitable Foundation) National Children's Research Centre, Our Lady's Children's Hospital Crumlin, Dublin, Ireland United States Department of Health & Human Services/National Institutes of Health (NIH) - USA/NIH National Institute of Allergy & Infectious Diseases (NIAID) Postdoctoral Research Associate (PRAT) Fellowship, National Institute of General Medical Sciences(NIGMS)/NIH EU-FP7 NET4CGD UK Research & Innovation (UKRI)/Medical Research Council UK (MRC)/European Commission - MR/M012328 - MR/M012328/2 UK Research & Innovation (UKRI)/Medical Research Council UK (MRC) - MR/M012328/2 - MR/M012328/1 Institut National de la Sante et de la Recherche Medicale (Inserm) Fondation pour la Recherche Medicale - ING20130526624 la Ligue Contre le Cancer (Comite de Paris)