Delayed engraftment of nonobese diabetic severe combined immunodeficient mice transplanted with ex vivo-expanded human CD34(+) cord blood cells

The ex vivo expansion of hematopoietic progenitors is a promising approach for accelerating the engraftment of recipients, particularly when cord bloo d (CB) is used as a source of hematopoietic graft. With the aim of defining the in vivo repopulating properties of ex vivo-expanded CB cells, purified CD34(+) cells were subjected to ex vivo expansion, and equivalent proporti ons of fresh and ex vivo-expanded samples were transplanted into irradiated nonobese diabetic (NOD)/severe combined immunodeficient (SCID) mice. At pe riodic intervals after transplantation, femoral bone marrow (BM) samples we re obtained from NOD/SCID recipients and the kinetics of engraftment evalua ted individually. The transplantation of fresh CD34(+) cells generated a do se-dependent engraftment of recipients, which was evident in all of the pos ttransplantation times analyzed (15 to 120 days). When compared with fresh CB, samples stimulated for 6 days with interleukin-3 (IL-3)/IL-6/stem cell factor (SCF) contained increased numbers of hematopoietic progenitors (20-f old increase in colony-forming unit granulocyte-macrophage [CFU-GM]). Howev er, a significant impairment in the short-term repopulation of recipients w as associated with the transplantation of the ex vivo-expanded versus the f resh CB cells (CD45(+) repopulation in NOD/SCIDs BM: 3.7% +/- 1.2% v 26.2% +/- 5.9%, respectively, at 20 days posttransplantation, P < .005). An impai red short-term engraftment was also observed in mice transplanted with CB c ells incubated with IL-11/SCF/FLT-3 ligand (3.5% +/- 1.7% of CD45(+) cells in femoral BM at 20 days posttransplantation). In contrast to these data, a similar repopulation with the fresh and the ex vivo-expanded cells was obs erved at later stages posttransplantation. At 120 days, the repopulation of CD45(+) and CD45(+)/CD34(+) cells in the femoral BM of recipients ranged b etween 67.2% to 81.1% and 8.6% to 12.6%, respectively, and no significant d ifferences of engraftment between recipients transplanted with fresh and th e ex vivo-expanded samples were found. The analysis of the engrafted CD45() cells showed that both the fresh and the in vitro-incubated samples were capable of lymphomyeloid reconstitution. Our results suggest that although the ex vivo expansion of CB cells preserves the long-term repopulating abil ity of the sample, an unexpected delay of engraftment is associated with th e transplantation of these manipulated cells. (C) 1999 by The American Soci ety of Hematology.