We report the case of a 32-year-old man with poor risk acute myeloid leukemia (AML) who received transplantation of
an UCB graft following myeloablative conditioning but unfortunately relapsed after one year with complete loss of donor
chimerism. As this patient did not have an HLA - matched sibling donor or a volunteer MUD, he went on to receive a
second transplant with haploidentical CD34 cells from his mother following a non-myeloablative conditioning. After initial
engraftment with the haploidentical donor cells, the patient became progressively pancytopenic and chimerism analysis
revealed decreased level of cells derived from the haploidentical graft. However, there was a concurrent increasing ratio of
the UCB derived cells from the first transplant. The patient had eventual recovery and stabilization of his full blood count
and repeat chimerism analysis demonstrated successful re-engraftment with the previous UCB graft. To the best of our
knowledge, no such similar cases have been reported in the literature. Thus, cord blood cells from a prior transplant could
remain present in small quantities at the phase ofleukemia relapse and re-emerge to establish long term hematopoiesis even
after graft failure from a subsequent haploidentical transplant
