Umbilical cord blood progeny cells that retain a CD34+ phenotype after ex vivo expansion have less engraftment potential than unexpanded CD34+ cells.
BACKGROUND
Because of the limitation of cell numbers associated with cord blood harvests, there is a need to determine the efficacy of using ex vivo-expanded cord blood cells in a transplantation setting. In this study, limiting-dilution analysis was used in nonobese diabetic mice with severe combined immunodeficiency (NOD/SCID) to compare the engraftment potential of progeny cells expressing the CD34+ phenotype after expansion with that of uncultured CD34+ cells.


METHODS
Cord blood CD34+ cells were cultured in Iscove's modified Dulbecco medium supplemented with 10-percent fetal calf serum (FCS) and IL-6, SCF, megakaryocyte growth and development factor, and Flt3 ligand. The resulting ex vivo-expanded products were assessed for total numbers of nucleated cells, CD34+ cells, and CFUs and long-term culture-initiating cell activity. The engraftment potentials of cultured progeny CD34+ cells and uncultured CD34+ cells were determined by using NOD/SCID mice.


RESULTS
After 14 days of culture, total nucleated cell counts increased over input values by 180 +/- 59-fold, CD34+ cell numbers by 44 +/- 13-fold, CFU activity by 23 +/- 5-fold, and long-term culture-initiating cell activity by 20 +/- 6-fold (mean +/- SD; n = 6). The frequency of SCID-repopulating cells (SRC) in mice transplanted with uncultured products was 1 per 20,000 CD34+ cells (95% CI, 1:10,000-1:38,000) and that in mice receiving ex vivo-expanded products was 1 per 418,000 progeny CD34+ cells (95% CI, 1:158,000-1:1,100,000). Taken together, these data indicated that, after 2 weeks of culture, there was a modest twofold increase in the total number of SRCs. However, the levels of human CD45 cell engraftment in NOD/SCID recipients of progeny CD34+ cells were significantly lower than those in mice receiving equivalent numbers of uncultured CD34+ cells (p<0.05).


CONCLUSIONS
Umbilical cord blood progeny cells retaining a CD34+ phenotype after ex vivo expansion have less engraftment potential than do unexpanded CD34+ cells.
Blood Systems Research Laboratory, Tempe, Arizona, USA.
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Xu
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Reems
D000818:Animals; D018952:Antigens, CD34 / Q000097:blood* / Q000235:genetics*; D002478:Cells, Cultured; D005312:Fetal Blood / Q000166:cytology* / Q000276:immunology*; D018380:Hematopoietic Stem Cell Transplantation; D006801:Humans; D051379:Mice; D016688:Mice, Inbred NOD; D016513:Mice, SCID; D010641:Phenotype
D018952:Antigens, CD34