Post-transplant transient abnormal myelopoiesis evolving from a GATA1 mutant clone in umbilical cord blood.

Transient abnormal myelopoiesis (TAM) generally affects newborns with Down syndrome and is associated with constitutional trisomy 21 and a somatic GATA1 mutation. Here we describe a case of TAM which evolved after umbilical cord blood transplantation (UCBT), whose origin was identified as a GATA1 mutation-harboring clone in umbilical cord blood (UCB) by detailed genetic analyses. A 58-year-old male who received UCBT for peripheral T-cell lymphoma presented progressive anemia and thrombocytopenia, and leukocytosis with blast cells in the peripheral blood (PB). Bone marrow (BM) aspiration showed granulocytic and megakaryocytic dysplasia with excess blasts whose karyotype was trisomy 21. Short tandem repeat analysis showed complete donor chimerism. He was initially diagnosed as donor-derived myelodysplastic syndrome (MDS) and treated with azacitidine, followed by secondary transplantation using unrelated BM, providing durable complete remission. Retrospective targeted-capture sequencing analysis of PB/BM samples collected at multiple timepoints identified trisomy 21 and a GATA1 mutation, suggestive of a diagnosis of donor cell-derived TAM (DC-TAM). Importantly, a minor clone with the same GATA1 mutation was detected in UCB by droplet digital PCR. DC-TAM is a rare UCBT-related complication which resembles MDS, but the identification of GATA1 mutation may be useful for its diagnosis. Our genetic analyses revealed that a pre-existing clone in UCB may contribute to the development of donor cell-derived hematologic neoplasms, highlighting the potential relevance of genetic screening of donor UCB.