Engraftment of human CB CD34⁺cells at start of cultures and of their progeny after 4 to 12 weeks of expansion. The level of human engraftment was evaluated by flow cytometry by determining the percent of human CD45⁺, CD71⁺, and GpA⁺ cells within the total BM cells in individual NOD/SCID mice. Each animal was injected either with unmanipulated CD34⁺ CB cells (2 × 10⁴, •; 3.5 × 10⁴, ○) either with the cells generated by initial 2 × 10⁴ or 3.5 × 10⁴CD34⁺ cells after 4, 7 to 8, 9 to 10 or 12 weeks of cultures as described in Materials and Methods. Each circle represents an individual mouse.