Identification and characterization of molecular genetic bases responsible for the predisposition to chronic mucocutaneous candidiasis in humans

My project consists in the molecular and immunological identification and characterization of patients with increased susceptibility to fungal infections with Candida sp. suffering from the Mendelian syndrome of chronic mucocutaneous candidiasis (CMC).CMC is characterized by persistent or recurrent infections of the skin, nails and mucosae by Candida fungi, especially C. albicans. CMC is frequently associated with other opportunistic infections in some acquired or primary immunodeficiencies, or can be associated with autoimmune disorders. Finally, CMC may be present as an isolated form (chronic mucocutaneous candidiasis disease or CMCD) without any other severe infectious or autoimmune clinical manifestation: most reported cases are sporadic, but there are also familial cases with autosomal dominant (AD) or recessive (AR) Mendelian inheritance.Based the literature, which demonstrated a major role of IL-17 cytokines in mucocutaneous immunity with C. albicans, and our recent results, which show an impairment of IL-17 immunity in some primary immunodeficiencies associated with CMC (AD-HIES syndrome, AR APS-1, and CARD9-deficient patients), we hypothesized that among CMCD patients, some might have a genetic defect affecting specifically the IL-17-dependent immunity.At the beginning of my PhD, I participated in the identification of the first two genetic etiologies of CMCD: complete AR IL-17RA and partial AD IL-17F deficiencies. More recently, I identified the third and most common genetic etiology of CMCD by identifying gain of function mutations in the STAT1 gene following an approach exploring the whole genome (sequencing of all exons). These mutations are responsible for a "hyper-response" to type I and II interferons and IL-27, which inhibit the differentiation of IL-17-producing T cells. Impaired IL-17 immunity results in reduced mucocutaneous defenses against C. albicans in humans. In conclusion, we have identified in 2011, the first three genetic etiologies of CMCD with AR IL-17RA and AD IL-17F deficiencies and gain-of-function STAT1 mutations, all associated with an impaired IL-17-dependent immunity. Gain-of-function STAT1 mutations represent the most frequent genetic cause of CMCD with a total of 94 patients reported in the literature since 2011. We have shown that CMCD is a primary immunodeficiency associated with inborn errors of IL-17 immunity. This work has important implications in the field of immunology with the description and characterization of the biological mechanisms involved in protective immunity specific to C. albicans and a better understanding of the pathophysiological mechanisms associated with increased susceptibility to fungal infections in natural conditions of infection, and in the medical field, with the possibility of molecular diagnostics, genetic counseling for a positive diagnosis, and a better follow-up of the patients.