Role of MEF feeder cells in direct reprogramming of mousetail-tip fibroblasts.

Pluripotent stem cells can be induced from somatic cells by the transcription factors Oct3/4, Sox2, c-Myc and Klf4 when co-cultured with mouse embryonic fibroblast (MEF) feeder cells. To date, the role of the feeder cells in the reprogramming process remains unclear. In this study, using a comparative analysis, we demonstrated that MEF feeder cells did not accelerate reprogramming or increase the frequency of induced pluripotent stem (iPS) cell colonies. However, feeder conditions did improve the growth of primary iPS colonies and were necessary for passaging the primary colonies after reprogramming was achieved. We further developed a feeder-free culture system for supporting iPS growth and sustaining pluripotency by adding bFGF and activin A (bFA) to the medium. These data will facilitate the generation of human iPS cells without animal feeders for regenerative medicine.