Cell numbers, progenitors, and engraftment levels of CD34⁺CD38^−/low cells after ex vivo cultures. Human CD34⁺CD38^−/low cells were cultured in serum-free media with cytokines as indicated and were assayed for cell numbers, progenitors, and levels of human cell engraftment. (A, I) Cell numbers. Mean increase over day 0: SCF + FL = 1.4, SCF + FL + IL6RIL6 = 6.1 (P = .02). (A, II) Progenitor levels. Mean increase over day 0: SCF + FL = 1.9, SCF + FL + IL6RIL6 = 12.8 (P = .03). Values shown are the mean ± SE from 5 independent experiments. (B) Representative Southern blots of the BM of mice transplanted with ex vivo-cultured CD34⁺CD38^−/low cells that originated from 2 different donors. DNA was extracted from the BM of transplanted mice 1 month after transplantation and hybridized with a human-specific probe. The marrow of mice transplanted with 10⁴ uncultured cells before seeding (lane 1) expanded cells cultured for 6 days with SCF + FL either alone (lane 2) or together with IL6RIL6 chimera (lane 3). The marrow of mice transplanted with 10⁴ ex vivo-cultured for 10 days with SCF + FL either alone (lane 4) or together with IL6RIL6 chimera (lane 5). (C) A summary of the levels of human cell engraftment by percentage of human DNA in the BM of mice transplanted with ex vivo-cultured CD34⁺CD38^−/low cells. NOD/SCID mice were transplanted with initial 10⁴CD34⁺CD38^−/low cells that were ex vivo-cultured for 6 to 10 days in serum-free media with SCF + FL alone compared with SCF + FL + IL-6 + sIL-6R (P = .04) or compared with SCF + FL + IL6RIL6 chimera (P = .02). Values shown are the mean ± SE from 5 independent experiments (n = 17).