No, not how you feel when the cells don’t behave! This relates to keeping your cell cultures in a happy state.
1. Cell passage history
Each time you sub culture your cells you probably faithfully record on the new flask various bits of information such as the name of the cell line, date, the medium used and passage number. This last item ideally relates to the number of times the cells have been sub cultured since they were first isolated. However, it is unlikely that this is the case for many cell lines.Passage histories may become lost over the years and often this number simply refers to the first time the cells were cultured in your own laboratory.
2. Is cell passage history important?
In our opinion, passage history is a bit of a red herring. What is more important is the continued good health of your cell line. Healthy cells are productive cells, whether you are producing high titre virus or subsequently using that virus for recombinant protein production.
If you try to minimize the number of times you sub culture or passage your cells by setting up very thinly seeded flasks and then growing them for as long as possible you are not really being very kind to them. If you harvest the cells when they are very thick they will almost certainly be in a stationary phase in a medium nearly exhausted of nutrients and effectively on a starvation diet. If you then plunge them into fresh medium to a low density they will often display a marked reluctance initially to grow at a logarithmic rate. This is particularly true for cells grown in serum-free media, which seem to hate being over diluted. We don’t really understand why but it is thought that these media types have to be “conditioned” by actively growing cells to provide the necessary growth factors.
3. Keeping your cells in good health!
So, rather than see sawing your cell concentrations between very low and very high levels, sub culture your flasks more regularly to maintain the cells in a healthy condition. This might mean splitting your cells several times a week. Your passage number may rack up, but your cells will remain in an ideal state for subsequent use.
With the festive season approaching you may be thinking about how to keep your cells viable over this period. Look out for our Christmas blog next week when we will give some tips on how to maintain cell cultures in a healthy state while you partake of the seasonal goodies!