With increasing culture time and passage number, cell lines become prone to cellular senescence, apparent in genetic variations and permanent cell-cycle arrest.
In addition to cell biological effects, your cultures are always at risk of
microbial contamination as well as cross contamination
. It is therefore necessary to establish backup stocks of quality cell lines, especially for the purpose of long term cultivation. Cryopreservation is a vital method to preserve cell lines in order to have access to fresh cell stocks when required.