with 10 μg/ml mitomycin-C) were cultured in T-25
flasks (Iwaki) with addition of ES medium for 7
days. Buffalo fibroblast-conditioned medium was
collected every day, centrifuged at 200 g for 3 minutes,
filtered with a 0.2 μm syringe filter (Millipore,
Watford, England) and frozen at -80˚C. After
thawing, the medium was equilibrated for 2 hours
at 5% CO2 and 37˚C and then used for the feederfree
culture of human ES cells.