ALDH activity was measured by flow cytometry using the ALDEFLUOR kit (STEMCELL Technologies 01700) according to manufacturer's instructions. Cells were ALDEFLUOR stained at a concentration of 5 × 10 5 cells/mL for 45 minutes at 37 o C in the presence or absence of 60 µM DEAB. The cell suspension was passed through a 35 µM filter and kept on ice prior to analysis. Flow cytometry was performed on a BD FACSMelody using FACS Chorus software (488 nm laser and 527/32 bandpass filter), followed by analysis with FlowJo. A minimum of 10,000 events were collected for each sample. Data were gated post-acquisition based on forward (FS) and side scattering (SS) profiles to include only single cell events and to exclude cellular debris.