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.