Cryopreservation of human adipose tissue-derived stem/progenitor cells using the silk protein sericin

Adipose tissue-derived stem/progenitor cells (ASCs) have attracted attention as a cell source that replaces marrow stromal cells (MSCs); ASCs may thus have applications in both regenerative medicine and cell transplantation. These medical treatments, however, require a high-quality supply of human ASCs. Therefore, the cryopreservation methods have been improved by changing a component of a cryopreservation medium. Sericin, a protein hydrolysate (with an average molecular weight of 30 kDa) is very rich in serine. The viability and the adipogenic/osteogenic potential of human ASCs were tested after freezing in a cryopreservation medium containing sericin. After thawing, the viability of the human ASCs frozen in the cryopreservation medium was found to be more than 95%. The proliferation rate of human ASCs frozen in CELLBANKER 2, and DMEM/Ham's F-12 medium (serum free) + 10% DMSO, 0.1 mol/L maltose, and 1% sericin was higher than that of the cells frozen in the maintenance medium + 10% DMSO. The adipogenic/osteogenic differentiation capabilities of frozen human ASCs were examined by Oil Red O staining/Von Kossa's method. The human ASCs were frozen using CELLBANKER 2, and DMEM/Ham's F-12 medium (serum free) + 10% DMSO, 0.1 mol/L maltose, and 1% sericin were positive. In conclusion, the cryopreservation medium containing sericin is therefore considered to have a beneficial effect on freezing human ASCs. This serum-free cryopreservation medium should be widely used in regenerative medicine, cell transplantation, and biological research.