In vitro and in vivo evidence for the long-term multilineage (myeloid, B, NK, and T) reconstitution capacity of ex vivo expanded human CD34(+) cord blood cells.

The aim of the present report is to describe clinically relevant culture conditions that support the expansion of primitive hematopoietic progenitors/stem cells, with maintenance of their hematopoietic potential as assessed by in vitro assays and the NOD-SCID in vivo repopulating capacity.CD34(+) cord blood (CB) cells were cultured in serum-free medium containing stem cell factor, Flt3 ligand, megakaryocyte growth and development factor, and granulocyte colony-stimulating factor. After 14 days, the primitive functions of expanded and nonexpanded cells were determined in vitro using clonogenic cell (colony-forming cells, long-term culture initiating cell [LTC-IC], and extended [E]-LTC-IC) and lymphopoiesis assays (NK, B, and T) and in vivo by evaluating long-term engraftment of the bone marrow of NOD-SCID mice. The proliferative potential of these cells also was assessed by determining their telomere length and telomerase activity. Levels of expansion were up to 1,613-fold for total cells, 278-fold for colony-forming unit granulocyte-macrophage, 47-fold for LTC-IC, and 21-fold for E-LTC-IC. Lymphoid B-, NK, and T-progenitors could be detected. When the expanded populations were transplanted into NOD-SCID mice, they were able to generate myeloid progenitors and lymphoid cells for 5 months. These primitive progenitors engrafted the NOD-SCID bone marrow, which contained LTC-IC at the same frequency as that of control transplanted mice, with conservation of their clonogenic capacity. Moreover, human CD34(+)CDl9(-) cells sorted from the engrafted marrow were able to generate CD19(+) B-cells, CD56(+)CD3(-) NK cells, and CD4(+)CD8(+)alphabetaTCR(+) T-cells in specific cultures. Our expansion protocol also maintained the telomere length in CD34(+) cells, due to an 8.8-fold increase in telomerase activity over 2 weeks of culture. These experiments provide strong evidence that expanded CD34(+) CB cells retain their ability to support long-term hematopoiesis, as shown by their engraftment in the NOD-SCID model, and to undergo multilineage differentiation along all myeloid and the B-, NK, and T-lymphoid pathways. The expansion protocol described here appears to maintain the hematopoietic potential of CD34(+) CB cells, which suggests its relevance for clinical applications.