The body’s bone marrow produces white blood cells
If you’ve seen a human bone before, you would have noticed the yellow-colored tissues found at the center of the bone. Those yellow-colored tissues are the white blood cells. The spongy tissues inside some bones usually contain immature cells.
The bone marrow is replenished by your body just like it replenishes cells. This means that the bone marrow cannot be sold for as much as one would sell a kidney or any other valuable organ.