Chimerism after allogeneic hematopoietic cell transplantation in childhood acute lymphoblastic leukemia.

Leukemic relapse after allogeneic bone marrow transplantation or allogeneic peripheral blood progenitor cell transplantation arises normally from residual malignant host hematopoiesis. The lack of specific tumor markers in acute lymphoblastic leukemia presents a problem for detection of residual disease post-infusion. In the present prospective study, we used PCR amplification of variable numbers of tandem repeat genetic regions for close follow-up of chimeric status in order to try to distinguish those patients at high risk of relapse. We found that chimeric status evolution was different between the long-term surviving patients and relapsed patients. The former showed either donor chimerism (DC) or transient mixed chimerism (tMC), while the latter always showed a recipient-growing MC (r.gMC). In addition, we found that complete substitution of hematopoiesis was achieved better with radiation-containing regimens, and that chronic graft-versus-host disease never appeared in MC patients. We conclude that very close follow-up of serial samples can facilitate the early detection of those leukemic children with a poor outcome after hematopoietic cell transplantation.