ABCC4 and cystic fibrosis: This emphasizes that further investigation of ABCC4 and PDE-4 inhibitors as a potential add-on combinatorial therapy should be performed in primary human airway epithelial cells from a large subset of CF subjects, covering a wide-range of CFTR variants with compromised CFTR expression or function, in order to determine which patient populations could benefit from cAMP modulation therapy.