Very low O2 concentration (0.1%) favors G0 return of dividing CD34+ cells

Physiological bone marrow oxygen concentrations are everywhere lower than 4% and almost null in some areas. We compared the effects of 20%, 3%, and 0.1% O-2 concentrations on cord blood CD34(+) cell survival, cycle, and functionality in serum-free cultures for 72 hours with or without interleukin-3 (IL-3). As from 24 hours, IL-3 improved cell survival and proliferation in all conditions. After 72 hours, cells were 1.5 and 2.5 times more in quiescence (G(0)) at 3% and 0.1% O-2, respectively, than at 20%; transforming growth factor-beta signaling seemed not to be involved. To explore cell cycle further, fresh CD34(+) cells were stained with PKH26 and cultured for 72 hours, and then undivided and divided cells were sorted. At 0.1% O-2, 46.5% +/- 19.1% of divided cells returned to Go compared with 7.9% +/- 0.3% at 20%. Colony formation and nonobese diabetic/severe combined immunodeficient mice engraftment efficiency were similar after 3 days at 20% and 0.1% O-2 concentrations but lower than at T-0. In conclusion, a low O-2 concentration, close to those found in bone marrow stem cell niches, induces the G(0) return of CD34(+) cells without impairing their functional capacity.