Optimizing cord blood unit selection to improve survival after single-unit unrelated cord blood transplantation for adult myelodysplastic syndrome.

Unrelated cord blood transplantation (CBT) is an important alternative donor option for adult patients with myelodysplastic syndrome (MDS); however, the prognostic significance of cord blood unit characteristics following CBT remains unclear and may vary according to disease risk. We conducted a nationwide retrospective study of 1767 adult patients with MDS who underwent first single-unit CBT between 1999 and 2023, including 529 patients with low-risk and 1238 with high-risk disease at transplantation. Cord blood unit characteristics were not significantly associated with disease-free survival (DFS) in patients with low-risk MDS. In contrast, in patients with high-risk MDS, higher cryopreserved cluster of differentiation (CD)34+ cell dose and higher colony-forming unit-granulocyte/macrophage dose were associated with improved DFS, whereas human leucocyte antigen (HLA) serological one-locus mismatch and female-to-male donor-recipient sex mismatch were independently associated with inferior DFS. Restricted cubic spline Cox regression demonstrated a significant non-linear association between CD34+ cell dose and DFS, as well as relapse, in high-risk MDS. These findings demonstrate that the prognostic impact of cord blood unit characteristics after single-unit CBT differs according to MDS risk status and support a risk-adapted approach to cord blood unit selection, particularly for patients with high-risk MDS.