From bomb to blood
What do atomic bombs and stem cells have in common?
The idea of a stem cell has been around for quite a long time having appeared in the scientific literature as early as 1868, but it took many years before it was possible to produce hard evidence to support the theory. We did not have the proof of the existence of stem cells until the work of James Till and Ernest McCulloch in the 1960s.
The first evidence of the existence of stem cells came after the atomic bombs dropped on Hiroshima and Nagasaki during World War II, which resulted in unparalleled destruction and loss of life.
In the event of an explosion of a nuclear weapon, the intense heat can cause bodies to completely evaporate, but the consequences can be seen a long time after a nuclear explosion. Radioactivity will spread both in the area around the explosion and, depending on the weather and wind, also far away from the explosion site. This is called nuclear fallout. People can be affected by the fallout directly by being touched by the fine dust that rains down. They can also ingest radioactive particles by, among other things, drinking milk from cows that have grazed contaminated grass or through food, via plants and animals that have absorbed radioactive substances.
In the days to weeks following the bombing of Japan, victims began to die in a second wave, not from injuries or burns caused by the explosion itself, but from mysterious symptoms that included hair loss, low white blood cells, destruction of the stomach and intestinal lining and internal bleeding. This caused scientists to begin investigating why these people were dying, and they discovered that radiation was the cause.
Radiation injures cells, causes cell death and disrupts the cell’s ability to divide to create new cells. Without cells that can divide and form new cells, body parts such as hair and blood cannot be renewed. Early radiation experiments therefore led to the discovery of stem cells, especially hematopoietic stem cells, the blood-forming stem cells that are found in umbilical cord blood, among other places in the human body.
(Since different types of radiation (alpha, beta and gamma) have different biological effects, in medical contexts the unit Sievert is most often used as a measure of the biological effect of the radiation. The unit is named after Rolf Sievert who was a radio physicist at Karolinska Institutet.)
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Till JE, McCulloch EA. A direct measurement of the radiation sensitivity of normal mouse bone marrow cells. 1961. Radiat Res. 2012 Aug;178(2):AV3-7. doi: 10.1667/rrav01.1. PMID: 22870977.
Becker, A., McCulloch, E. & Till, J. Cytological Demonstration of the Clonal Nature of Spleen Colonies Derived from Transplanted Mouse Marrow Cells. Nature 197, 452–454 (1963). https://doi.org/10.1038/197452a0