Britannica Sources used in this answer

How can primary cells become immortal cell lines?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

tissue culture Tissue culture often requires sterile working conditions and thus is typically performed in a laminar flow cabinet (or tissue culture hood), which circulates filtered air to reduce the risk of culture contamination.

Primary cells, which are typically mortal and have a finite life span, can become immortal cell lines through processes that allow them to overcome the Hayflick limit—the point at which cells stop dividing due to replicative senescence.1

This transformation into an immortal state generally occurs through the following mechanisms:

Genetic Mutation: Occasionally, cells in a primary culture undergo mutations, such as chromosomal rearrangements or changes in chromosome number, that result in the loss of growth-limiting factors. These mutations allow a subclone of the population to bypass normal growth controls and achieve indefinite replication.21
Telomerase Activation: Normal cells have limited replication capacity because their telomeres—DNA segments at the ends of chromosomes—shorten with each division. In many immortalized or cancer cells, the enzyme telomerase becomes activated. This enzyme adds nucleotides to telomeres, preventing them from shortening further and thereby enabling the cells to escape senescence and replicate indefinitely.34
Malignant Transformation: Cells can also be immortalized through malignant transformation, often induced by the integration of viral DNA into the host cell's chromosomes. This process can impede programmed cell death (apoptosis), allowing for uncontrolled, indefinite growth.5