From the definition of cell line, they are indefinitely propagated/subcultured.
However, in practice beyond a certain passage number, they are said to loose characteristic gene profile, for e.g. SHSY5Y beyond PN 20 are no longer dopaminergic.
So my question is, are these cell lines re-established every time they lose their genetic profile and subcultured and sold to us? This is my assumption; I couldn't find any information that clearly support or disapproves of this idea.
Hello Sanjukta,
Once a cell line has been developed or acquired and validated (i.e., shown to be authentic and uncontaminated), the first step to ensuring a reliable and reproducible supply of cells is the cryopreservation of these cells in 1ml ampoules, each containing 1–5 × 10^6 cells.
This will help to provide a ready supply for many years. Usually, a tiered system is used namely,
(a) a MCB or seed stock, containing 10–20 ampoules, which should be protected and not distributed,
(b) a distribution stock generated from the seed stock, which is used to provide the end users with cultures from which they will generate their own frozen stock. This user stock should contain sufficient ampoules to provide at least one ampoule for every 3 months of the proposed experimental period plus sufficient ampoules for contingencies.
So, if one has frozen enough stock called the seed stock, and sufficient number of distribution stock made from the seed stock which are meant for distribution, the need to re-establish the cell lines doesn't arise because the frozen stock distributed to the Institutions and laboratories who purchase them are in the early passages. Thus, the cell lines losing their genetic profile doesn't arise.
It is true that on repeated subculturing the cell lines show genetic drift due selective pressure. But once the developed cell line has been validated, it is immediately cryopreserved by the cell banks to ensure supply of cell lines of early passages. For instance, SHSY5Y cells are cryopreserved in cell banks at an early passage (say PN2 or PN3).
So, you will have to purchase a new vial at an early passage and after thawing the vial, you will have to first prepare a stock of these cells to be stored in liquid nitrogen so that these frozen vials will come useful for your experiments when your current cells in culture have crossed PN10/PN15 and are no longer useful. The cancerous cell lines generated earlier may have been cryopreserved at an early passage and therefore do not show any genetic drift.
For more information you may want to refer to the article attached below.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4453835/
Best.
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