ALDH1A1 and acute myeloid leukemia: Exposure of primary human AML cells to isatin analog KS99 that primarily inhibits ALDH1A1, suppresses clonogenicity, and yields a dose-dependent apoptotic response in primary human leukemic stem cells, identified by the markers CD34+, CD34+CD38−, CD34+CD38+, CD123+, or CD34+CD123+.