32.3:
Cell Lines
Primary cell cultures obtained directly from normal tissue samples can only divide a limited number of times.
To evade this problem, scientists chemically or genetically manipulate cells to create cell lines—immortalized cells that can proliferate indefinitely.
Cell lines can also be propagated directly from cancerous cells.
Besides immortality, such cell lines have higher growth rates and can continue to grow even when surrounded by other cells or not attached to a solid surface.
Primary cell lines can acquire spontaneous mutations in cancer-associated genes or be deliberately exposed to cancer-inducing viruses or chemicals, creating cancerous cell lines.
Over time, cell lines can undergo phenotypic and genetic changes. They are also prone to cross-contamination in the lab.
Despite their limitations, they are easy to handle and cost-effective and bypass many ethical issues associated with animal research.
Therefore, labs routinely use cell lines to model diseases, test drugs, and mass-produce antibodies and vaccines.
32.3:
Cell Lines
A cell line is a population of cells grown in vitro that can be subcultured over several generations. Normal cells cease to divide after a certain number of cell divisions, a process known as replicative senescence. This number, called the Hayflick limit, was conceptualized by Leonard Hayflick in 1961 when he observed that fetal cells grown in culture could only divide 40-60 times. This limit is due to the shortening of the telomeres during each round of cell division, preventing cell division beyond insufficient telomere length. Overexpression of the enzyme telomerase prevents telomere shortening, and is one of the methods to produce immortal cell lines.
Types of Cell Lines
Primary cell lines obtained directly from animal tissue retain the approximate genotypic and phenotypic characteristics of their cells of origin. For example, human lung cell line BEAS2B and retinal cell line RPE1 have close to the normal number of 46 chromosomes. In contrast, cell lines obtained from cancer cells can proliferate indefinitely and are called transformed cell lines. These cell lines show additional attributes like anchorage independence and lack of contact inhibition. Transformed cell lines also commonly have an altered number of chromosomes. For example, the SW480 and A549 cell lines can have up to 56 and 66 chromosomes, respectively.
Validating Cell Lines
Cell lines are prone to genomic instability and cross-contamination in the lab. Therefore, it is essential to validate them routinely. Techniques such as spectral karyotyping help identify numerical and structural chromosomal aberrations and detect cross-contamination. Cell lines can also be validated at the molecular level by STR profiling, a method used to analyze the number of short tandem repeats (STR) in DNA which are unique to each cell line.
Suggested Reading
- American Type Culture Collection Standards Development Organization Workgroup ASN-0002 j. masters@ ucl. ac. uk. "Cell line misidentification: the beginning of the end." Nature Reviews Cancer 10.6 (2010): 441-448.
- Butler, Michael. "Animal cell cultures: recent achievements and perspectives in the production of biopharmaceuticals." Applied microbiology and biotechnology 68.3 (2005): 283-291.