Creation of a Double Chimera after the Transplantation of Umbilical-Cord Blood from Two Partially Matched Unrelated Donors

To the Editor: Despite promising outcomes in the transplantation into pediatric recipients of umbilical-cord blood from unrelated donors, the low cell dose adversely affects both the rate of hematopoietic recovery and the probability of survival.1–3 The cell dose is a major limitation of the procedure, particularly in adults. An alternative to the ex vivo expansion of cells, which has yet to be shown to be efficacious, is the transplantation of 2 closely HLA-matched units of umbilical-cord blood. We transplanted 2 units of umbilical-cord blood from male infant donors into a 53-year-old, 84-kg woman with accelerated-phase chronic myelogenous leukemia and . . .