Chronic mucocutaneous candidiasis (CMC): Genotype heterogeneity, pathogenesis and development of therapeutic options

Gain of function mutations of STAT1 represent the most important cause of Chronic Mucocutaneous Candidiasis (AD-CMCD) and can be inherited as autosomal dominant trait. The hyperphosphorylation of STAT1 induce an augmented response to IFN-a, IFN-g, IL27 and an increased expression of STAT1-related genes. This disease is very complex and can be associated to fungal infections, bacterial and viral infiltrations, progressive lymphopenia, augmented risk of anheurism and/or tumors and autoimmunity. The present work aimed at characterizing the immunological features of our cohort of patients diagnosed with STAT1-GOF syndrome, focusing on investigating the pathogenesis of lymphopenia throughout experimental in vitro functional assays on cells of affected subjects, compared to healthy controls. We studied the effect of Ruxolitinib, a JAK inhibitor, as a potential tool to treat progressive lymphopenia. In order to prove that the identified mutations were gain-of-function, we investigated IFNα- and IFNγ-induced pSTAT1 by cytometry from peripheral blood mononuclear cells (PBMCs) of our patients compared to healthy controls. Our results show that STAT1 is not constitutively activated, but the increase of phosphorylation is observed after IFNα and IFNγ stimulation. We observed a normal ratio of CD4/CD8, a low percentage of memory B cells with a reduction of both un-switched and switched subsets. In order to investigate the potential causes of progressive lymphopenia we stimulated PBMC with anti-CD3, CD28 and IFN-a and we observed that the patients had an increased positivity to annexin V staining after 48h of stimulation with IFNa (p<0.05). Then we tested the role of Ruxolitinib in the treatment of hyperphosphorylation of STAT1 induced by IFN-a. We carried out a dose-response curve on whole blood of patients and healthy subjects and we observed that the phosphorylation of STAT1 decreased proportionally with the increase of Ruxolitinib concentration. We also wanted to test the potentiality of Ruxolitinib in the downregulation of apoptosis. We observed that patients' CD3 T cells stimulated with IFN-a decreased the positivity to Annexin V considerably after the treatment with Ruxolitinib. The pathogenic role of IFNa was confirmed also with a Real Time assay, actually we observed an augmented expression of CASP3. We investigated the possible pathway involved and we observed an increase of IRF1 expression. However we noticed that Ruxolitinib is able to downregulate the expression of CASP3 and IRF1 after the stimulation with IFNa. We can conclude that STAT1-GOF patients have increased risk to develop progressive lymphopenia in adolescence and adult age and our results suggest a possible pathogenetic role of IFN-a in T cell apoptosis. Ruxolitinib has proved to be a potential tool to traditional treatments for hyperphosphorylation and progressive lymphopenia in CMCD patients.