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Final Activity Report Summary - MC-PIAID (Marie-Curie grant on Primary Immunodeficiencies and AutoImmune Diseases)

Over the last four years, we found six new genetic defects in primary immunodeficiency diseases, which are rare and often severe hereditary conditions. After the initial discovery of dominant-negative mutations in the signal transducer STAT3 in autosomal-dominant hyper-IgE syndrome (HIES) (Holland et al., NEJM, 2007), the study of additional 165 DNA samples from HIES patients confirmed the role of STAT3 in the pathogenesis of the disease and enabled us to propose new guidelines for the diagnosis of STAT3 deficiency (Woellner et al., JACI, 2010). In patients with autosomal-recessive HIES, we found mutations in the gene dedicator of cytokinesis 8 (DOCK8) (Engelhardt et al., JACI, 2009).

Further analysis of patients showed that DOCK8 mutations are the most common cause of AR-HIES, and provided a better understanding of the phenotype of DOCK8 deficiency, which helps in the diagnosis of patients. As a consequence, these patients now receive bone marrow transplantation for treatment. In a large family diagnosed with Chronic Mucocutaneous Candidiasis, we found mutations of the Caspase Recruitment Domain containing protein 9 (CARD9). Functional tests with the patients' immune cells confirmed a reduced antifungal immune response of mutated CARD9 (Glocker et al., NEJM, 2009). We were also the first group to discover a genetic defect in children with early-onset colitis. In two children suffering from colitis we found mutations in the IL-10 receptor, which result in a breakdown of IL-10-mediated immunosuppressive properties, giving rise to a severe auto-inflammation of the large intestine (Glocker et al., NEJM, 2009). Later, we found mutations in the gene encoding IL-10 in two other children with early-onset colitis and showed that an in vitro synthesised version of the mutated protein is non-functional (Glocker et al., Lancet, 2010).

Finally, we found homozygous mutations in a novel gene causing a severe form of common variable immunodeficiency (Lopez Herrera et al., submitted). Our results underline the importance of discovering new genetic defects. On the one hand, until now DOCK8 had not been known to play a role in the immune system. Thus, our findings pave the way for a better understanding of the human immune defence against pathogens. On the other hand, we and others showed that hematopoietic stem cell or bone marrow transplantation was successful in patients with mutations in IL10RB and IL10 (Glocker et al., 2009 and 2010), STAT3 (Goussetis et al., JACI 2010) and DOCK8 (Gatz et al., BMT, 2010), who were cured from their respective symptoms. Thus, our results provide a basis for diagnosis and improvement of patient care. As in PIDs the susceptibility to infections often goes along with the development of autoimmune conditions, we explored this link in the most prevalent primary immunodeficiency, common variable immunodeficiency (CVID), which is associated in up to 10% of cases with mutations in the TNF-like B cell receptor TACI.

We sequenced the TACI gene in 291 patients with autoimmune and lymphoproliferative diseases. However, from all SNPs and missense mutations detected, only the heterozygous C104R mutation found in two Non-Hodgkin samples has been shown to impair the function of TACI signalling (Salzer et al., 2007). To evaluate our hypothesis that the phenotype of hypogammaglobulinemia in TACI deficiency is an effect of an autoimmune condition against B cells, we set up a FACS-based assay to screen sera from CVID patients for auto-antibodies directed against B cells. We screened 36 CVID patients with low B cell numbers and/or autoimmunity but found no auto-antibodies against B cells.

Finally, we have established a robust in vitro assay to induce class-switch in memory B cells; this assay will facilitate the diagnosis of CVID, may help identify carriers of the disease and possible affected individuals without a clear phenotype and may improve the treatment of CVID patients in future.

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UNIVERSITY COLLEGE LONDON
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United Kingdom
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