101 Facts About Ageing #17: Immortalised Human Cell Lines

As Daniel Patrick Moynihan, an American sociologist, politician, and diplomat once said: “Everyone is entitled to his own opinion, but not his own facts”. And we wholeheartedly agree. A shared set of facts is the first step to building a better world with longevity for all. In that spirit, we are creating a series that covers 101 indisputable facts about ageing, health and longevity.

Due to telomere shortening, every cell in our bodies will eventually lose its ability to replicate when it enters the state known as senescence. This is why human cells cultured in a lab can only divide a certain number of times, this number being known as the Hayflick limit. However, the capacity for immortality exists within our cells, and can be brought about by random or deliberately induced mutations in the genetic code. Mutations that allow a cell to avoid entering senescence allow it to continue to divide indefinitely, resulting in an immortalised cell line. Certain stem cells within multicellular organisms also have the capacity to divide indefinitely during normal development, but this ability is not retained.

The most commonly occurring immortal human cell lines are cancers. Since cancer cells divide rapidly and uncontrollably, they must also acquire mutations that allow them to divide indefinitely, or they would quickly reach their replication limit and die out. The first ever immortal human cell line – HeLa – came from a cancer. The original HeLa cells were taken (without her knowledge or consent, as was common at that time) from Henrietta Lacks, an African-American woman who died of cervical cancer at 31 in 1951. This cell line has been maintained ever since, effectively making it 100 years old, and continues to be used in research to this day.

Immortal cell lines can also be induced through deliberate genetic alterations, for example by enhancing the expression of telomerase, an enzyme that repairs telomeres and thereby allows cells to avoid senescence. Mice that are modified to produce telomerase throughout life have slightly increased rates of cancer in return for a reduced rate of ageing.