Joy Kong, MD, explains how stem cells divide: each division produces one self-renewing stem cell and one daughter cell that loses potential. At the four-cell stage, only one of four is a true stem cell. Labs often mistake cultured cell mixtures for pure stem cells when they're mostly differentiated daughters.
Stem cells have a lot of variations. So every step of the way, they gain function and lose potential. And that's called differentiation. So once you gain some function, you also lose some potential. But the thing is, the stem cell develop into a copy that gains function and another copy of itself. So then if you have a whole soup of stem cells and they keep dividing, if each original cell is dividing into a daughter cell that's gained function and the copy of itself, and then the one that's a copy of self will divide into a copy of self. And a daughter cell that's gained, of course, cannot go backward, so it will develop into more daughter cells. You can already see at a four cell stage, you only have one out of the four cells that's actually a stem cell, right? So then you just keep going and you end up with a big soup of majority daughter cells. But then the people who are giving these stem cells, they don't think that all those are daughter cells, and they think, oh, I've got all these stem cells, because they all look the same under microscope. So then they would take a little portion out of this big soup that they just grew and give that to patients, not realizing only a small fraction actually are still the original stem cell.
