ALDH1A1 and colorectal carcinoma: To determine whether CM from a ‘CSC-enriched’ population of CRC cells enhances growth and survival of CRC cells, we isolated CSCs from parental HT29 cells using two separate functional assays: (1) the ‘side population assay’ based on Hoechst dye exclusion, and (2) the Aldefluor assay based on increased expression and activity of ALDH1A1 (Huang et al, 2009).