To be honest Dore,
I have long thought about spleens and transplants. From my understanding,transplanting some of the donors cells into the recipients spleen may reduce the chance of rejection for bmts.
I also think that if enough of the donors cells were implanted into the recipient's spleen that much of the problem with thalassemia may be reduced because the spleen is capable of extra medullary hematopoiesis (which is why the spleen increases in size due to low hemoglobin - in attempts to increase it's own surface area, in hopes to produce more red blood cells in order to assist the bone marrow to increase hg - of course in thalassemia this effort is futile because the beta gene is missing) - but if the donor cells in the spleen can make red blood cells it may reduce the anemia. Furthermore, cells implanted in the spleen also tend to migrate into the bone marrow - causing engraftment.
If the spleen has accepted donor cells the body tends to accept them too.
Of course these are all theories circulating in my own head, and I don't know what practical significance they would have. I hope to discuss them with doctors in Oakland in the future.
Sharmin