For example, while several groups used CD117 (c-Kit, type III tyrosine kinase receptor for stem cell factor) to isolate the undifferentiated population19,20, other authors failed to select CD117+ cells from hAFs20,21; in addition, there is evidence that unselected AF and CD117+-isolated cells differ in both differentiation potential and efficacy14,22. This evidence concerns the gene KIT and atrial fibrillation.