ECFC clonogenicity and genomic stability. ECFCs after large-scale expansion representing more than or equal to 20 population doublings of the colony-initiating cells were subjected to an endothelial colony assay in triplicate in a seeding density of 10 ECFCs/cm² in EGM/10% pHPL. (A) Colony assays were performed with ECFCs from 3 different donors each for 10 () or 14 days (). Colony plates were then fixed and stained before photo documentation. Precise cell numbers of all imaged colonies were counted in ImageJ software. (B) Examples of typical LPP and HPP colonies²⁰  are depicted (Figure S2). Representative chromosome G-banding derived from ECFC nuclei after large-scale expansion of (C) female and (D) male ECFCs and corresponding sorted (E) female and (F) male karyograms are shown. Representative array CGH depiction of constitutional initial white blood cell–derived DNA compared with ECFC-derived DNA post large-scale expansion and after passage 4 of the same (G) female and (H) male volunteers as shown in panels C and E and D and F, respectively (further examples in Figure S4).