The limited in vitro lifetime of human diploid cell strains
clinical paper · 1965
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SUMMARY
Hayflick's 1965 follow-up establishing that the finite replicative capacity of normal human cells is an intrinsic property tied to the age of the organism from which cells were derived: adult lung fibroblasts (from donors aged 58–87) underwent approximately 20 doublings before senescence, while fetal lung fibroblasts underwent approximately 50 doublings. Hayflick proposed that cell populations carry a 'molecular memory' of how many divisions they have completed, unaffected by freezing and thawing. The paper also demonstrated that mixing old and young cells did not affect the young cells' replicative lifespan, ruling out humoral or medium-borne causes of cell senescence — exactly the mechanism Carrel had invoked to explain why his cultures allegedly avoided aging. This paper generalized and named the Hayflick limit and launched the field of cellular senescence.
NOTES
This 1965 paper extended and consolidated Hayflick’s 1961 findings, providing additional evidence that normal cell mortality is intrinsic rather than extrinsic. By comparing cells from young and old donors, Hayflick showed that replicative capacity decreases with donor age — a result inconsistent with Carrel’s hypothesis that cells freed from the body’s internal environment could live indefinitely. Critically, Hayflick’s mixing experiments ruled out any “bad fluid” explanation for cell senescence, directly falsifying the mechanism Carrel had proposed for his supposed immortal tissue culture.