Lonza just published their Protocol for Cryopreservation of NucleofectionTM Competent Cells . This comes unsurprisingly, considering the favorable results the CoolCell freezing container demonstrated when Lonza did an independent study and compared to an alcohol-based freezing container. In all 4 cell types studied; HeLa, CHO-K, K562 and NIH3T3, CoolCell freezing method produced high levels of cell viability and GFP transfection efficiency without the use of alcohol. see slide 10 of this CoolCell presentation for more details about the independent Lonza study.
Lonza’s latest protocol recommends that all cell aliquots be frozen in a controlled manner by decreasing the temperature by 1°C per minute down to at least to -80°C (recommendation: use a manual device e.g. CoolCell®, Biocision for this purpose). The cells can be stored at -80°C for up to 24 hours prior to the transfer to the cryogenic storage.