Placental/umbilical cord blood for unrelated-donor bone marrow reconstitution: relevance of nucleated red blood cells.

Placental/umbilical cord blood (PCB) is a source of hematopoietic stem cells for bone marrow reconstitution. Engraftment speed and survival are related to the total nucleated cell (TNC) dose of the graft. This study explored the possible influence on engraftment of nucleated red blood cells (NRBCs) in the graft. Automated hematology analyzers were used to enumerate TNCs. NRBCs were counted by visual examination or by using an automated analyzer. Hematopoietic progenitor cells were enumerated as either colony-forming cells or CD34(+) cells. Transplant centers reported on transplant outcome in 1112 patients given PCB grafts through September 2001. NRBCs correlated with progenitor cell numbers. Both white blood cell and NRBC dose were independently predictive of myeloid engraftment speed. Because NRBC dose predicted engraftment speed, inclusion of NRBCs in the TNC count does not reduce the effectiveness of the prefreezing TNC count as an index of the quality of a PCB unit as a graft. The correlation between the number of NRBCs and the number of hematopoietic progenitor cells probably reflects the involvement of early stem cells in erythroid responses.