Summary of DNA analysis (A) and frequency of human CFC (B) in the BM of NOD/SCID mice receiving transplants of freshly isolated CB cells and those isolated after 1 to 2 weeks of culture on stroma. Each symbol represents the level of engraftment (A) or CFC concentration (B) in a single mouse. Solid symbols represent mice receiving transplants of cultured cells treated with trypsin. Open symbols represent mice receiving transplants of cultured cells treated with CDB. The horizontal lines indicate the mean level of engraftment. *Statistically significant differences in the mean level of engraftment in mice receiving transplants of CB cells cultured for 2 weeks (P < .05) compared with uncultured CB cells.