HFs were infected daily for five days with tetracycline-inducible lentiviruses expressing OCT4, SOX2, KLF4, cMYC and LIN28, driven by a sixth lentivirus expressing the reverse tetracycline transactivator (rtTA)7. Cells from a single well of a six-well dish were split onto a 10-cm plate containing 1 million mouse embryonic fibroblasts (mEFs). Cells were switched to HUES media (KO-DMEM (Invitrogen), 10% KO-Serum Replacement (Invitrogen), 10% Plasminate (Talecris), 1x Glutamax (Invitrogen), 1x NEAA (Invitrogen), 1x 2 mercaptoethanol (Sigma) and 20 ng/ml FGF2 (Invitrogen)). 1 µg/ml Doxycycline (Sigma) was added to HUES media at for the first 21–28 days of reprogramming.
