A human colon cancer cell capable of initiating tumour growth in immunodeficient mice

Abstract

Two papers in this issue report the identification of a specific type of colon cancer cell that initiates tumour growth in mice. This lends support to the theory that only a few cells within a tumour, the cancer stem cells, are responsible for tumour formation and maintenance. The finding highlights the importance of finding therapeutics to target cancer stem cells. Colon cancer is one of the best-understood neoplasms from a genetic perspective1,2,3, yet it remains the second most common cause of cancer-related death, indicating that some of its cancer cells are not eradicated by current therapies4,5. What has yet to be established is whether every colon cancer cell possesses the potential to initiate and sustain tumour growth, or whether the tumour is hierarchically organized so that only a subset of cells—cancer stem cells—possess such potential6,7. Here we use renal capsule transplantation in immunodeficient NOD/SCID mice to identify a human colon cancer-initiating cell (CC-IC). Purification experiments established that all CC-ICs were CD133+; the CD133- cells that comprised the majority of the tumour were unable to initiate tumour growth. We calculated by limiting dilution analysis that there was one CC-IC in 5.7 × 104 unfractionated tumour cells, whereas there was one CC-IC in 262 CD133+ cells, representing >200-fold enrichment. CC-ICs within the CD133+ population were able to maintain themselves as well as differentiate and re-establish tumour heterogeneity upon serial transplantation. The identification of colon cancer stem cells that are distinct from the bulk tumour cells provides strong support for the hierarchical organization of human colon cancer, and their existence suggests that for therapeutic strategies to be effective, they must target the cancer stem cells.