Umbilical cord blood progeny cells that retain a CD34+phenotype after ex vivo expansion have less engraftment potential than unexpended 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, limi ting-dilution analysis was used in nonobese diabetic mice with severe combi ned immunodeficiency (NOD/SCID) to compare the engraftment potential of pro geny cells expressing the CD34+ phenotype after expansion with that of uncu ltured CD34+ cells. STUDY DESIGN AND 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 liga nd. 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 ov er input values by 180 +/- 59-fold, CD34+ cell numbers by 44 +/- 13-fold, C FU activity by 23 +/- 5-fold, and long-term culture-initiating cell activit y 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 -1:1,1 00,000). 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 o f progeny CD34+ cells were significantly tower than those in mice receiving equivalent numbers of uncultured CD34+ cells (p<0.05). CONCLUSION: Umbilical cord blood progeny cells retaining a CD34+ phenotype after ex vivo expansion have less engraftment potential than do unexpanded CD34+ cells.