One cryovial of the fibroblast cell line was thawed in fibroblast culture media (DMEM high-glucose-based medium supplemented with 10% FBS, 1:100 L-glutamine, 1:100 N.E. amino acids, 1:100 Pen/Strep, and 10 ng/mL FGF2, all reagents from Gibco Life Technologies). After centrifugation at 1000 rpm for 4 minutes, cells were plated in a tissue culture treated 75 cm2 flask (Falcon). Cells were cultured at 37°C with 5% CO2 and media was changed every three days. Cells were passed and expanded when reaching about 70% confluency using TrypLE Express (Gibco Life Technologies), following the manufacturer recommendations. The initial 75 cm2 flask was passed after two days in culture and plated in three 75 cm2 flasks. Three days later, cells were passed to five 175 cm2 flasks using the same procedure. Four days later, the cells were passed to twenty 175 cm2 flasks. After five days, the cells were passed again to forty 175 cm2 flasks. After five days, the cells were trypsinized as above, the pellets were resuspended in fresh fibroblast culture media and counted using a manual hemocytometer. Cells were resuspended in Recovery Freezing media (Gibco Life Technologies) at a density of 3 million cells per mL. A total of 52 cryovials with 2 mL each (6 million cells per vial) were produced at passage 6 to minimize culture-acquired mutations.