CyT203 (ViaCyte - (Novocell) San Diego, CA)

Maintain undifferentiated hES cells on mouse embryo fibroblast feeder layers (Specialty Media) in DMEM/F12 supplemented with KnockOut serum replacement (20% (v/v)), nonessential amino acids (1 mM), Glutamax (x1), penicillin/streptomycin (x1), 2-mercaptoethanol (0.55 mM), recombinant human FGF2 (4 ng/ml) and activin A (10–25 ng/ml). Passage cells manually at a 1:4–1:8 split ratio, every 5–7 d.