Here he witnessed the first establishment of the Lgr5+ cell-derived intestinal organoid culture system pioneered by Dr. Toshiro Sato and Prof. Hans Clevers. In the following years Dr. Koo has utilised this novel culture system to perform sophisticated gene correction studies, to unravel the molecular regulation of adult stem cells and to proof the stem cell properties of a Troy+, quiescent reserve stem cell population in the stomach. Together with his group at the University of Cambridge he is now developing novel genetic tools to further investigate how proliferating and quiescent adult epithelial stem cell populations are regulated both in homeostasis and during injury mediated repair.