There's no reason for them to do it, although I admit it might happen out of pure ignorance.

The stem cells in this case are reprogrammed and grafted from the adult patient's own body.

I expect the answer will be "both"—anything involving the immune system seems to be full of feedback loops for homeostasis.

I'm going to guess millions or thousands of parsecs, which are each about 3.26 light years.

Imagine that computer RAM or a classic hard-drive are like a bunch of tiles an Othello/Reversi game board.

When you delete a picture, only the tiles that say "photo.jpg is inside tiles X to Y" are erased and flipped to be white-side up.

The actual tiles in spaces X to Y that had all of the pixels are usually left untouched, unless we have a paranoid reason to go through and change them.

In no case are any tiles being removed from the table--that would represent damage to the system.

Later those X-Y tiles may be changed, but usually because we've decided to put something new there.

Many of the cells in your body have stopped dividing, they've settled into specialized roles and positions and will not "fill in the gaps" by duplicating to replace missing neighbors. The shape of everything else around them and the signals from their neighbors cause them to act in certain narrow ways. When they don't do that and start dividing again, that's often cancer.

New cells are usually generated from deeper spots, from special cells with the job of just churning out certain kinds of gradual replacements.

So if you choose a random zone of tissue and kill some cells in it, those gaps or weaknesses may persist in that area until everything around it is pushed out and replaced by the march of fresh cells from further in.

If you damage one of those special zones where new cells are still being made, the damage could be permanent, like getting a scar on your skin that lasts even when almost all of the cells have been replaced over time.

Another metaphor:

Suppose you have a thousand planks of wood in nice stacks. You can store them and still be okay if a random 10% become rotted and must be thrown out.

Now imagine you store a house made out of a thousand planks of wood, and again 10% of it rots. It might become dangerously weak, and it will be very expensive to check and replace the bad parts.