Flt3L enhances the early stem cell compartment after ex vivo amplification of umbilical cord blood CD34+ cells.

: Umbilical cord blood (UCB) transplant represents a promising therapeutic approach, nevertheless this procedure has been so far almost exclusively used in pediatric patients because of the reduced volume of UCB units. The availability of larger numbers of early and late hematopoietic progenitors by ex vivo amplification procedure may allow the use of UCB in adults and improve the rate and time to engraftment. We describe a stroma-free liquid culture system that induces a 10-fold increase of CD34+ cells and hematopoietic progenitors after 8 days in vitro amplification. The presence of flt3L is essential to preserve and amplify the early stem cell compartment identified by the phenotype CD34+Thy-1+CD45RO+.