Watching CSI: Miami I learned something new: that receiving a liver transplant* can change your blood type to that of the donor. I'd never heard anything about that before, so I had to do a Google search before believing it. Apparently it's actually happened; once. It seems that stem cells in the liver managed to detach and land in the bone marrow of the recipient, and take over the marrow.
This makes me wonder. If I understand the biology involved correctly, this would only be possible if the blood type changed in a particular direction. In any other direction you'd get the same effect you'd get from getting an incompatible blood transfusion. Thus my question: might this have happened before, but been misclassified as simple organ rejection?
*In theory this is probably possible with most transplants, given that it involves stem cells being transported with the organ.