Flt3L induces the ex-vivo amplification of umbilical cord blood committed progenitors and early stem cells in short-term cultures

Umbilical cord blood (UCB) has been successfully used for haemopoietic stem cell transplantation, although its use has been cautiously limited to paed iatric patients because of the reduced volume produced. The clinical result s hare confirmed that either engraftment or survival significantly correlat e with cell dose infused, We have standardized a culture method providing i n a short time a significant amplification of both committed progenitors an d primitive stem cells for clinical use. Eight-day culture of UCB cells with flt3L/SCF/PIXY 321 induced a 10-fold am plification of CD34(+) cells and the expansion of multipotent (CFU-GEMM) an d committed (CFU-GM. BFU-E) progenitors respectively of 5-, 7- and 9-fold o ver input cells, As to the early stern cell pool, the primitive CD34(+)Thy- 1(+) cell fraction increased 6-fold and the LTC-IC were amplified 17-fold. Furthermore, the ill vitro proliferation was detected by the gradual loss o f fluorescence of the CD34(+) cells tracked at day 0 with the dye PKH26. Af ter 8 d of amplification > 6% of the CD34(+) cells remained intensely fluor escent. This subpopulation represents a deeply quiescent cell fraction unre sponsive to cytokines and very enriched of primitive stem cells. These cell s are most likely to be responsible for long-term reconstitution after tran splant.