The American Academy of Allergy, Asthma & Immunology (AAAAI) and the American College of Allergy, Asthma & Immunology (ACAAI) have jointly accepted responsibility for establishing the "Practice parameter for the diagnosis and management of primary immunodeficiency." This is a complete and comprehensive document at the current time. The medical environment is a changing environment, and not all recommendations will be appropriate for all patients. Because this document incorporated the efforts of many participants, no single individual, including those who served on the Joint Task Force, is authorized to provide an official AAAAI or ACAAI interpretation of these practice parameters. Any request for information about or an interpretation of these practice parameters by the AAAAI or ACAAI should be directed to the Executive Offices of the AAAAI, the ACAAI, and the Joint Council of Allergy, Asthma & Immunology. These parameters are not designed for use by pharmaceutical companies in drug promotion.

Iconographies supplémentaires de l'article : Practice parameter for the diagnosis and management of primary immunodeficiency

/pdf/discovery-of-atg5-atg7-independent-alternative-su6l22ol35.pdf

Discovery of Atg5/Atg7-independent alternative macroautophagy

T cell activation requires a costimulation signal, which is typically provided by CD28 binding to CD80 or CD86; hence CD80/CD86 availability is tightly regulated, in part through their removal from APCs by Treg CTLA4-dependent transendocytosis. We aimed to model the impact of changes in CD80/CD86 availability upon T cell proliferation and phenotype and to validate a quantitative assay of transendocytosis, to explore the regulation of this process. Finally, we aimed to explore the role of Treg, CTLA4 and CD80/CD86 in autoimmune hepatitis (AIH). // We demonstrated that Treg proliferation and phenotype were more sensitive to CD86 than to CD80. Although CD80 and CD86 are often considered interchangeable, we observed greater Treg proliferation, CTLA4, ICOS, and OX40 expression and reduced IL2 requirements, akin to stronger CD28 signals, following costimulation with CD86. We demonstrated that CTLA4 impaired Treg costimulation by CD80, potentially explaining why CD86 was a more effective ligand for CD28 despite its lower affinity. This suggested that the two ligands have differing roles in Treg homeostasis. // We also established an assay to quantitatively measure Treg transendocytosis of CD80, which reflected clinically significant CTLA4 mutations, and we demonstrated that IL2 and IL10 positively regulate transendocytosis. // The liver has a high degree of immunological tolerance, but when this breaks down autoimmunity can occur. We observed that the regulated immune microenvironment in the liver might be highly Treg/CTLA4-dependent and that in AIH there was an imbalance in CD80 and CD86 control, despite maintained Treg frequency and function. // In summary, we present evidence for a fundamentally different role for CD80 and CD86 in Treg homeostasis and a tool to quantitatively measure Treg transendocytosis, We present some of the 1st functional data from intrahepatic Treg in AIH and evidence of an imbalance in the control of CD28 costimulation, suggesting this pathway as a potential therapeutic target.

CD4 regulatory T cells: their requirement for CD80 and CD86 costimulation and their role in autoimmune hepatitis

The immune system represents the body’s defense against infectious organisms. Inborn defects of the immune system, called primary immunodeficiencies (PIDs), are a heterogeneous group of Mendelian disorders. Clinically, PIDs can cause isolated to broad susceptibility to pathogens, severe hyperinflammation, autoimmunity, allergy, and cancer. The studies in this thesis take advantage of the recent development in DNAsequencing technologies and of our increased understanding of genetic variability to further explore the genetic architecture and phenotypic spectrum of hemophagocytic lymphohistiocytosis (HLH), an inborn error of lymphocyte cytotoxicity, and to elucidate the genetic factors behind autoimmunity and hematological malignancies in selected families. Familial HLH (FHL) is a severe hyperinflammatory condition, genetically heterogeneous, caused by defective perforin-mediated lymphocyte cytotoxic activity. In paper I we use a high-throughput sequencing panel covering 12 HLH-related genes in 58 prospectively recruited patients with HLH and achieve a molecular diagnosis in 22 cases (38%). In paper II we show that perforin-deficiency due to biallelic PRF1 missense variants is associated with broad intra-familial variability and clinical presentations seemingly unrelated to HLH, such as Hodgkin lymphoma. Using exome sequencing, in paper III, we identify biallelic pathogenic variants in IFNGR1 and INFGR2, respectively, in two patients with HLH and disseminated mycobacterial infection. Previous studies have shown that HLH pathology is largely driven by IFN-γ. Instead, our findings suggest the existence of IFN-γ-independent mechanisms for the development of HLH. In paper IV, we uncover biallelic coding and non-coding variants in RAB27A, the gene responsible for Griscelli syndrome type 2 (GS2), in five unrelated patients with atypical HLH, normal pigmentation, and a functional defect suggestive of FHL. A complex structural variant disrupting the transcriptional start site (TSS) of one RAB27A transcript was shared among the patients. We show that the disrupted TSS is less predominantly used by melanocytes compared to lymphocytes, explaining the lack of hypopigmentation in these patients, otherwise present in GS2. In paper V we report the beneficial effect of hematopoietic stem cell transplantation in a 14-year-old boy with LRBA deficiency and a seven-year history of severe autoimmmune disorders. In paper VI we uncover germline heterozygous missense variants in SAMD9L, a gene located on 7q21, in two families with multiple individuals affected by cytopenia, immunodeficiency, myelodysplastic syndrome (MDS) with cytogenetic aberrations of chromosome 7, and neurologic disease. We show a gain-of-function (GOF) effect of the mutants, which inhibit cell proliferation. Germline SAMD9L GOF variants were lost in MDS cells and hematopoietic revertant mosaicism occurred frequently among less severely affected carriers. Our results indicate a strong selective advantage for hematopoietic cells that, through different somatic events, overcome the growthinhibiting effect of germline SAMD9L GOF variants. Taken together, these studies add to our understanding of the phenotypic and genetic spectrum of HLH, display the power of high-throughput sequencing in diagnostics of individuals affected by severe inflammation, autoimmunity, and hematological malignancies, and highlight SAMD9L as an important gene for regulation of hematopoietic cell proliferation.

Genetic studies of susceptibility to inflammation, autoimmunity, and hematological malignancy

Functional genomics uses high throughput genome-wide technologies to investigate the functional consequences of genetic variants on gene expression and protein products. In the context of disease, using integrative functional genomic approaches to understand the genetic variation which underlies disease susceptibility and aetiology may contribute to better diagnosis, treatment and prevention. This thesis investigated genetic determinants of variation in response to infection by applying a functional genomics approach to investigate three clinical cohorts: patients with severe sepsis, an influenza challenge study and patients with common variable immune deficiency disorders. The transcriptomic response to severe sepsis is reported here for the largest known adult severe sepsis community acquired pneumonia cohort. Two clusters within the cohort, based on gene expression signatures, which have different survival rates and identify individuals with distinct immune responses to sepsis, highlight the value of functional genomics for identifying heterogeneity within patient cohorts. This was further complemented by the resolution of gene expression signatures in healthy individuals following influenza challenge which identified individuals with moderate to severe disease. Shared gene expression signatures between the cohorts highlighted components of the immune response to viral infection important across multiple clinical settings and may assist with the identification of viral infections in the sepsis patients. Gene expression was mapped as a quantitative trait (eQTL). Comparison to data sets for healthy individuals and from innate immune stimulated cells identified regulatory variants specific to the context of sepsis. Whole genome sequencing for a cohort of patients with common variable immune deficiency disorders was performed. This identified novel variants and pathways which may play a role in the underlying immunopathogenesis of disease. Integration with RNA-seq for a small number of patients allowed prioritisation of non-coding variants based on evidence of altered gene expression. Comparison to the sepsis cohort analysis identified key immune related genes involved in rare and common responses to bacterial infection. This thesis has demonstrated the value of integrating multiple functional genomic techniques to further our understanding of the mechanisms underlying variation in the response to infection.

Functional genomics of variation in response to infection : insights into severe sepsis and common variable immune deficiency disorders

Most autosomal genetic causes of childhood-onset hypogammaglobulinemia are currently not well understood. Most affected individuals are simplex cases, but both autosomal-dominant and autosomal-recessive inheritance have been described. We performed genetic linkage analysis in consanguineous families affected by hypogammaglobulinemia. Four consanguineous families with childhood-onset humoral immune deficiency and features of autoimmunity shared genotype evidence for a linkage interval on chromosome 4q. Sequencing of positional candidate genes revealed that in each family, affected individuals had a distinct homozygous mutation in LRBA (lipopolysaccharide responsive beige-like anchor protein). All LRBA mutations segregated with the disease because homozygous individuals showed hypogammaglobulinemia and autoimmunity, whereas heterozygous individuals were healthy. These mutations were absent in healthy controls. Individuals with homozygous LRBA mutations had no LRBA, had disturbed B cell development, defective in vitro B cell activation, plasmablast formation, and immunoglobulin secretion, and had low proliferative responses. We conclude that mutations in LRBA cause an immune deficiency characterized by defects in B cell activation and autophagy and by susceptibility to apoptosis, all of which are associated with a clinical phenotype of hypogammaglobulinemia and autoimmunity.

N Rezai

Papers

Mutations in lrba are associated with a syndrome of immune deficiency and autoimmunity