There are two ways to do bone marrow transplantation. One is indeed using CD34+ stem and progenitor enrichment to get rid of all the mature T cells in order to prevent GVHD (graft versus host disease).
However this graft is weaker and can be rejected by residual host T cells and other immune cells which survived host preconditioning with total body irradiation and chemotherapy. This graft aslo lacks the graft bersus leukemia effect induced by donoe T cells. The 2nd and more common way to transplant is without CD34+ selection or T cell depletion and these grafts are stronger, biggerr but in addtion to their graft versus leukemia effect they also induce graft versus host disease which even when supressed can be lethal.
I hope this info will be of help.
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