Primitive human HPCs are better maintained and expanded in vitro at 1 percent oxygen than at 20 percent

BACKGROUND: The liquid culture of murine bone marrow cells at 1-percent oxygen maintains the balance between primative progenitor cell renewal and clonogenic progenitor expansion better than that at 20-percent oxygen. These results are of potential interest for the ex vivo expansion of human progenitor cells, as low O-2 tension could preserve the engraftment potential of cultured apheresis products. STUDY DESIGN AND METHODS: G-CSF-mobilized blood cells collected by apheresis, now the main source of progenitor cells for autologous transplantation, were cultured at 1-percent and 20-percent O-2 for 7 days in serum-free liquid cultures in the presence of IL-3 and SCF (5 ng/mL). The growth of the clonogenic progenitors (CFU-GM, BFU-E, CFU-Mix) and of the more primitive human HPCs that are capable of generating clongenic progenitors in secondary liquid culture, as well as the proliferation and differentiation of total and CD34+ cells, was analyzed. RESULTS: The expansion of CD34+ cells and of clonogenic progenitors was significantly lower in liquid cultures at 1-percent O-2 than at 20-percent O-2. On the contrary, the primitive human HPCs were better maintained and expanded at 1-percent O-2, although the number of CD34+ cells remaining quiescent was lower. After 7 days of liquid culture at 1-percent or 20-percent O-2 the percentage of CD34+ cells was similar. However, the CD34+ cells that divided more than four times (PKH2 staining) were more numerous in liquid cultures incubated at 1-percent O-2. CONCLUSION: When cultured at 1-percent O-2 for 7 days in presence of IL-3 and SCF, the CD34+ cells present in apheresis components underwent more cell divisions and better maintained their primitive progenitor cell potential. As suggested by previous results in mice, our data on human cells emphasize the potential interest of cultures at low O-2 tension (1%) for cell therapy protocols aimed at expanding primitive HPCs in autografts.