M solution and washed by Perm/Wash buffer according to fixation and pereabilization method recommended by BD bioscience, and then stained in sterile PBS containing 1.0 albumin bovine serum, 0.1 Nonidet P-40 (Sigma-Aldrich) and 3 M DAPI (4',6-diamidino-2-phenylindole). Flow cytometry was analyzed using FlowJo (Tree Star Inc, Asland, OR).Competing interests Erika von Euw, Mohammad Atefi, Narsis At