The isolated CD133 + and CD133 2 cells were cultured in a 96well cell culture cluster (Corning Costar, Acton, MA) at a density of 3610 3 cells/well with 100 ml culture medium. At specific time points during cultivation, the medium was discarded and replaced with an equal volume (100 ml) of fresh medium containing 0.2 mg/ml of 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS, Promega, Madison, WI) and 0.038 mg/ml of phenazine methosulfate (PMS; Promega) and incubated for additional 1.5 hours in 37uC 5% CO 2 . Cell viability proportionate to optical density (OD) was measured by colorimetric assay in terms of mitochondria activity to convert tetrazolium salt into a colored soluble formazan product in the medium. The OD values were measured at the wavelength of 490 nm with a 1420 multilabel counter VICTOR from Wallac (PerkinElmer Wallac, Turku, Finland).