Experimental schema overview.

CD34⁺/CD38⁻ cells were isolated from normal human bone marrow and transplanted into immunodeficient bnxmice. Marrow was harvested from the primary recipients 8 to 12 months after transplantation and analyzed by FACS, immunohistochemistry, RT-PCR, and CFU and LTCIC cell assays. No human CD34⁺ cells were detected. Samples of marrow from the primary mice were then transplanted into secondary NOD/SCID recipients. The secondary recipients were killed 6 to 8 weeks later, and the marrow was subjected to FACS analysis for CD34 and human hematopoietic lineage development. Multilineage human hematopoietic development and human CD34⁺ cells were detected in the secondary recipients.