The protein cytotoxic T lymphocyte antigen-4 (CTLA-4) is an essential negative regulator of immune responses and its loss causes fatal autoimmunity in mice. We investigated a large autosomal-dominant family with five individuals presenting with a complex immune dysregulation syndrome characterized by hypogammaglobulinemia, recurrent infections and multiple autoimmune features. We identified a heterozygous nonsense mutation in exon 1 of CTLA4. Screening of 71 unrelated patients with comparable clinical phenotypes identified five additional families (nine individuals) with novel splice site and missense mutations in CTLA4. While clinical penetrance was incomplete (eight adults of a total of 19 CTLA4 mutation carriers were considered unaffected), CTLA-4 protein expression was decreased in regulatory T cells (Treg cells) in patients and carriers with CTLA4 mutations. Whilst Treg cells were generally present at elevated numbers, their suppressive function, CTLA-4 ligand binding and transendocytosis of CD80 were impaired. Mutations in CTLA4 were also associated with decreased circulating B cell numbers and antibody levels. Taken together, mutations in CTLA-4 resulting in CTLA-4 haploinsufficiency or impaired ligand binding results in a complex syndrome with features of both autoimmunity and immunodeficiency.

BackgroundActivated phosphoinositide 3-kinase δ syndrome (APDS) is a recently described combined immunodeficiency resulting from gain-of-function mutations in PIK3CD, the gene encoding the catalytic subunit of phosphoinositide 3-kinase δ (PI3Kδ).ObjectiveWe sought to review the clinical, immunologic, histopathologic, and radiologic features of APDS in a large genetically defined international cohort.MethodsWe applied a clinical questionnaire and performed review of medical notes, radiology, histopathology, and laboratory investigations of 53 patients with APDS.ResultsRecurrent sinopulmonary infections (98%) and nonneoplastic lymphoproliferation (75%) were common, often from childhood. Other significant complications included herpesvirus infections (49%), autoinflammatory disease (34%), and lymphoma (13%). Unexpectedly, neurodevelopmental delay occurred in 19% of the cohort, suggesting a role for PI3Kδ in the central nervous system; consistent with this, PI3Kδ is broadly expressed in the developing murine central nervous system. Thoracic imaging revealed high rates of mosaic attenuation (90%) and bronchiectasis (60%). Increased IgM levels (78%), IgG deficiency (43%), and CD4 lymphopenia (84%) were significant immunologic features. No immunologic marker reliably predicted clinical severity, which ranged from asymptomatic to death in early childhood. The majority of patients received immunoglobulin replacement and antibiotic prophylaxis, and 5 patients underwent hematopoietic stem cell transplantation. Five patients died from complications of APDS.ConclusionAPDS is a combined immunodeficiency with multiple clinical manifestations, many with incomplete penetrance and others with variable expressivity. The severity of complications in some patients supports consideration of hematopoietic stem cell transplantation for severe childhood disease. Clinical trials of selective PI3Kδ inhibitors offer new prospects for APDS treatment.

Affected mutation carriers with CTLA-4 insufficiency can present in any medical specialty. Family members should be counseled because disease manifestation can occur as late as 50 years of age. EBV- and cytomegalovirus-associated complications must be closely monitored. Treatment interventions should be coordinated in clinical trials.

This report describes the largest cohort of patients with LRBA deficiency and offers guidelines for physicians to identify LRBA deficiency, supporting appropriate clinical management.