Cell Lines: Types, Selection and Maintenance

In this nomenclature of cell lines post we have briefly explained about cell line nomenclature, cell line types, choosing a correct cell line, maintenance of cell line.

Cell line is created when a primary culture is subcultured (or passaged). This term refers to the occurrence of many cell lineages with comparable or distinct phenotypes. A cell strain is created when one cell lineage is selected via cloning, physical cell separation or any other selection approach to have particular specific features that have been recognized in the bulk of the cells in the culture.

Nomenclature of Cell Lines

New cell lines should be given a code name or designation, such as normal human brain NHB; a cell strain or cell line number (if multiple cell lines were produced from the same source, then NHB1, NHB2, and so on); and, if cloned, a clone number (NHB2-1, NHB2-2, etc.). When identifying the cell lines, it is critical to make sure that each cell line name is distinct so that there is no confusion when the reports are published. Furthermore, the cell line should be prefixed with a designation denoting the laboratory from where it was taken at the time of publication, such as NCI for National Cancer Institute and Wl for Wistar Institute.

Cell Line Types and Examples

a. Finite Cell Lines

Finite cell lines are cell lines that have a restricted culture life span and act in a predictable manner. Before senescence, they grow for a limited number of cell generations, usually between 20 and 80 cell population doublings. The number of doublings varies depending on species and cell lineage, clonal variation, and culture circumstances, but it is stable for a single cell line cultivated under the same conditions.

Cell Lines: Types, Selection and Maintenance

b. Continuous Cell Lines

Continuous cell lines have escaped from senescence control, so the generation number becomes less important and is usually replaced with the number of passages since last thawed from storage becomes more important. In addition, because of the increased cell proliferation rate and saturation density, split ratios become much greater (1:20–1:100) and cell concentration at subculture becomes much more critical.

Selecting a Correct Cell Line

Apart from specific functional requirements, there are a number of general parameters to consider in selecting a cell line.

a. Finite

In comparison to finite culture, a continuous cell line (figure 1) is easier to maintain, develops quicker, clones more easily, generates a larger cell yield per flask, and is more quickly acclimated to serum free medium.

b. Normal

Immortal cells that aren’t tumorigenic, such as 3T3-Swiss cells or BHK21-C13, would be conceivable.

c. Species

A nonhuman cell line will have fewer biohazard restrictions and have the advantage that the tissue from which it was derived may be more accessible.

d. Characteristics

Population doubling duration, saturation density, plating efficiency, growth fraction, and ability to develop in suspension are all variables to consider.

e. Availability

Are there enough stocks accessible if you need to employ a finite cell line, or would you have to create your own? Are authenticated stocks accessible if you choose a continuous cell line?

f. Validation

It is vital to eliminate the possibility of cross-contamination before embarking on a program of work with a cell line.

g. Stability

How stable is the cell line? Has it been cloned? If not, can you clone it, and how long would this cloning process take to generate sufficient frozen and usable stocks?. The cell lines must have cells with the appropriate phenotypic expression.

Maintenance of Cell Line

Once a culture has been established, whether it is a primary culture or a subculture of a cell line, it will require frequent medium changes (feeding or refreshing) and, if the cells are multiplying, subculture. The medium in nonproliferating cultures will still need to be changed on a regular basis since the cells will continue metabolise and some medium ingredients will become depleted or disintegrate spontaneously. The health of the cells in the culture, the lack of contamination, and any other major issues must all be checked on a frequent basis (toxins in medium, inadequate nutrients etc.).

a. Replacing Media

The preservation of cell lines in culture, whether proliferating or non-proliferating, necessitates a change of media on a regular basis. When compared to non-proliferating cells, proliferating cells require more frequent media changes. The length of time between medium changes is determined by cell growth and metabolism. For example, the medium for rapidly growing transformed cells (such as HeLa) should be replaced twice a week, whereas the medium for slowly growing non-transformed cells (such as IMR-90) should be changed once a week. Furthermore, sub-culturing is required more frequently for rapidly proliferating cells than for slowly proliferating cells.

b. Cell concentration

Cultures with a high cell concentration use the nutrients in the medium more quickly than those with a low concentration, necessitating more frequent medium changes for the former.

c. Decrease in pH

A drop in the pH of the medium indicates that it has to be changed. At a pH of 7.0, most cells can develop optimally, while at a pH of 6.5, they nearly cease developing. A further dip in pH (between 6.5 and 6.0) may cause the cells to die. For each cell line in a given medium, the rate of pH decrease is commonly approximated. Even if the medium is not changed quickly, there is no danger if the pH falls by less than 0.1 pH units every day. However, if the pH level drops by 0.4 pH units each day, the medium should be changed right away.

d. Culture Type

Embryonic cells, transformed cells, and continuous cell lines develop quickly, necessitating more frequent subculturing and media changes. Normal cells, on the other hand, develop more slowly.

d. Morphology

In culture techniques, it is critical to examine cell morphology on a regular basis. Any change in cell shape has the potential to cause permanent cell harm. To entirely eliminate the potential of cell injury, the medium must be changed.