An efficient and safe xeno-free cryopreservation method for the storage of human embryonic stem cells.

Human embryonic stem cells (hESCs) promise to revolutionize reparative medicine through their potential in developing cell replacement therapies for diseases like diabetes and parkinsonism. Most of the existing hESC lines available for research, including all National Institutes of Health-registered lines, have been derived and maintained on mouse embryonic fibroblast feeders in the presence of xenoproteins. For future clinical application, many more hESC lines derived and grown in current good manufacturing practice, good tissue culture practice, and xeno-free conditions need to be developed. Concurrently, effective cryopreservation methods that prevent or limit the accidental contact of hESCs with nonsterile liquid nitrogen during periods of long-term storage have to be formulated. We describe a safe, xeno-free cryopreservation protocol for hESCs involving vitrification in closed sealed straws using human serum albumin as opposed to fetal calf serum as the main protein source in the cryoprotectant and long-term storage in the vapor phase of liquid nitrogen. After thaw, hESCs exhibited high thaw-survival rates and low differentiation rates, remained pluripotent, and maintained normal diploid karyotypes throughout extended passage. The cryopreservation technique we describe here should complement xeno-free culture conditions for hESCs already in refinement and will prove very useful for the setting up of hESC banks throughout the world.