hESC-derived NK cells protect against K562 metastasis. (A) Representative images of micrometastasis foci in liver, lungs, spleen, and kidneys as identified by bioluminescent imaging. (B) Quantification of luciferase activity (p/s) from isolated organs. Luciferase intensity from each well was quantified using LivingImage software. Mean ± SEM from indicated organs is shown.