In this respect, we recently set up a method to assay CFTR activity in peripheral blood mononuclear cells (PBMCs) by using a GST-tagged iodine-sensitive yellow fluorescent protein (YFP) recombinant protein (HS-YFP assay) able to detect differential iodine transport between healthy and CF cells [23]. The gene discussed is CFTR; the disease is cystic fibrosis.