ALDH1A1 and malignant colon neoplasm: Thus, in a first study, Leng and coworkers isolated a colon cancer stem cell line DLD-1 from colon cancer cells expressing typical colon cancer stem cell markers such as CD133, CD166, LGR5 and ALDH1 and by the high expression of the transcription factor KLF4, a transcription factor essential for maintaining the self-renewal of adult and embryonic stem cells [437].