[refurb]

If you don't kill off the existing bone marrow, you end up with a couple problems:

1. You only give the patient a small number of edited cells. You want those cells to multiply and replace the existing cells. If you don't remove the existing cells, the edited cells aren't going to reproduce very fast because the body has a feedback loop and is saying "we have enough bone marrow cells now, so no need to make more".

2. Host versus graft disease. The old immune system will attack the new immune system cells.

[enchiridion]

Do these patients have to be revaccinated?

[refurb]

I’m not a doctor, but I would say yes, you’d lose any acquired immunity since you kill off all the memory b-cells that store that information.

But you’d also gain the donor’s immunity, and if they’ve been vaccinated, the recipient would have that immunity as well.

[rnet85]

That is not correct. Trained B cells are predominantly stored in lymph nodes. You also don’t gain host immunity by marrow transfer.

[enchiridion]

So B cells are what responsible for learned immunity?