The body is a rather large collection of cells and all these cells are continuously replaced/renewed. Stem cells produce progenitor cells by differentiating. The body needs these differentiated cells to prosper and survive. Progenitor cells can turn into any cell in your body (depending on the type of stem cell) such as blood, cartilage, bone, organ tissue, skin or any other kind of tissue.
One could say that stem cells (each and every one of them) are in fact the production facility of our body.
As we age, the number of active stem cells decreases. This is thought to be one of the key elements of aging. It is actually called “cell depletion”. It causes a lack of differentiated progenitor cells to replace the cells that are dying due to exhaustion.
Hendrikje van Andel-Schipper was a Dutch lady that once was the oldest person alive. She died at the age of 115 and donated her body to science. It turned out that she had only 2 hematopoietic (blood forming) stem cells left in her body. Cord blood is actually a rich source of these hematopoietic stem cells.
One of the conclusions of the research was that if you, earlier in life, would preserv a number of these hematopoietic stem cells and reinfuse them at a later date you could replenish the number of active cells and keep the production of blood going: thedailystar.net
There is no donor alternative for such a case. Only your own bodies stem cells can replenish lost cells unless you undergo a full donor stem cell transplant.