I have googled about this, and the most I can really find is that donating bone marrow/blood stem cells is not harmful in the long run, but I want to know why and how much is really known about this.

My question “stems” from my maybe cartoonish notion that you have all the stem cells you’ll ever have at the beginning of your life and that their depletion relates strongly to aging.

In my googling, I have read studies that lifespans of older mice can be extended with bone marrow stem cell transplants from younger mice. Based on my cartoon, I guessed that perhaps older mice have some depletion of and/or damage to their own hematopoietic stem cells that reduces overall formed element production, and this is the state that a transplant helps to fix. With this frame of mind, I have a hard time imagining that even a young donor of blood stem cells is not harmed in the long run. Hasn’t their pool of stem cells effectively been aged somewhat by the donation? Or is damage to the population of cells over time by environmental factors much more significant, more the “bottleneck” in cell health than the gradual deterioration caused by repeated division? Is it that donation effectively only forces something on the order of one extra division per cell? I also wonder whether that “bottleneck” could vary depending on the typical longevity of the animal under study.

Regarding my question about what is known—I suppose I’m asking what kinds of principles or studied effects are likely being referenced in laypersons’ articles declaring that donors do not experience long term harm.

I’m sure that I am probably saying some nonsense things because biology is not my field. Any corrections and disentangled conflations would be appreciated!

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    $\begingroup$ Hematopoietic stem cells (HSCs) can regenerate themselves, with no loss of "stem-ness". When bone marrow (which contains high numbers of these cells) is harvested for a transplant, the remaining HSCs divide and eventually repopulate the area that the marrow was harvested from, leaving it no different than before. There is absolutely no identifiable difference between the "old" and "new" HSCs - they both have the same lifetime, the same markers, the same functionality, etc. There is no long-term damage to the donor. $\endgroup$ – MattDMo 2 days ago

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