Four Cases of Donor Cell-Derived Acute Myeloid Leukemia Following Unrelated Cord Blood Transplantation for Adult Patients; Tokyo Cord Blood Bank Experiences.

Donor cell leukemia (DCL) is considered as a rare complication following allogeneic bone marrow transplantation (BMT), whereas the actual frequency of DCL has not yet been specified. Cord blood (CB) is now recognized as an alternative source for stem cell transplantation (SCT), with more than 6000 cord blood transplants (CBTs) performed worldwide, and a few cases of DCL following CBT have also been reported. Here we report four cases of DCL developed after unrelated CBTs using 490 shipped units from Tokyo cord blood bank (TCBB). Development of DCL was informed to TCBB by attending physicians of the recipients in CBT centers as soon as definite diagnosis was made. The feed-back from CBT centers on four DCL cases is summarized in Table 1. All the donors were well at the follow-up questionnaire 6–12 months after birth, but further information of their health conditions has not yet been obtained.

The etiology of DCL is unclear and a common mechanism is unlikely according to the reported literature. There exist several possibilities including occult leukemia or preleukemic state in the donor, defect in immune surveillance, therapy-related stromal abnormalities, excess of cytokine stimulation, and DNA replication and/or repair errors associated with post-transplant expansion of stem/progenitor cells. The possibility of occult leukemia in the donor raises serious problems regarding to the ethical responsibilities of the CBB to the donor.