Genetic loci outside the CFTR can modify the severity of Ps. aeruginosa lung disease. In a previous study (project FFC#9/2014) researchers mapped host genetic variations (modifier genes) as risk factors for Ps. aeruginosa infection in mice. In this new project, the candidate genes will be validated in disease models and in CF patients. The new tool for rapid and efficient editing of the mammalian genome (CRISPR/Cas9 system) will be used in cell colture. Next, the results will be translated into human population in association study among CF patients with or without Ps. aeruginosa infection. For this aim BIO-bank previously collected within the ECFS Gene Modifier Working Group will be available. Novel genetic information suitable for diagnostic, prognostic or therapeutic targets are expected.