Stem cell therapy and research have been a debated topicin recent years. Regardless of the usefulness and great potential of
stem cells in the fields of tissue engineering and regenerative medicine, preservation techniques suitable for stem cells have not yet been
established. We attempted to develop a preservation solution that can enhance the viability of stem cells after preservation.
Cryopreservation is a standard technique for long-term cell storage, but the toxicity of conventional cryoprotective agents (CPAs) such as
dimethylsulfoxide(DMSO) make it difficult to recover cells after thawing. ε-poly-L-lysine (PLL), in which the amino groups were converted
to carboxyl groups at an appropriate ratio (more than 50mol % to 80mol %), was shown to have higher cryopreservation efficiency
and lower cytotoxicity than current cryoprotective agents (CPAs). Using PLL with 65 mol% [PLL(0.65)] carboxylation, the protective effect
on mouse induced pluripotent stem (iPS) cells under hypothermic preservation (4°C and -196°C) was investigated.
After preservation, iPS cells retained their proliferation capacity and expressed markers of undifferentiated cells. Thus, we concluded that
an effective and safe CPA was developed. PLL(0.65) can therefore be a valuable component of a DMSO-free, xeno-free, and chemically
defined preservation solution for stem cells that also can be utilized at 4°C.