There is a growing consensus that clinical practice in the areas of bone marrow (BM) transplantation and gene therapy will rely on the ex vivo expansion of hematopoietic cells. We report here on the development of continuously perfused culture systems (bioreactor systems) that expand human stem and progenitor cells from BM mononuclear cell (MNC) populations obtained without cell enrichment. In three separate experiments, 10 bioreactors were each inoculated with 3 x 10(7) BM MNC from patients undergoing marrow harvest for autologous transplantation. At various times thereafter (between days 6 and 16), duplicate bioreactors were harvested and cells were analyzed. The bioreactors contained three cell populations that were analyzed separately: nonadherent cells; cells that were loosely adherent to the endogenously formed stromal layer; and an adherent cell layer that required trypsinization for removal. Total cell numbers increased continuously to give an overall 10-fold (range, 8- to 11-fold) expansion by day 14. The adherent stromal layer significantly expanded to more than 2 x 10(7) cells, but remained less than 6% of the total cell population. Colony-forming unit-granulocyte-macrophage (CFU-GM) numbers expanded 21-fold (range, 12- to 34-fold) by day 14 and, because this expansion was greater than that for total cells, CFU-GM were enriched by as much as fourfold by day 14. Burst-forming unit-erythroid (BFU-E) numbers peaked earlier than did CFU-GM numbers, with a 12-fold (range, 6- to 18-fold) expansion obtained on day 8. In contrast to CFU- GM, which were predominantly nonadherent, BFU-E were more evenly distributed between the three cell populations. Stem cell activity was measured by the long-term culture-initiating cell (LTC-IC) limiting dilution assay. The number of LTC-IC per reactor consistently increased with time in all cultures, resulting in a 7.5-fold (range, 3.4- to 9.8- fold) expansion. In summary, more than 3 billion cells, containing 12 million CFU-GM, were reproducibly generated from the equivalent of a 10 to 15 ml BM aspirate. These data indicate that small numbers of BM MNC can be readily expanded ex vivo in continuous perfusion cultures, and that such ex vivo expansion may have direct applications in clinical and experimental BM transplantation.

Expansion of hematopoietic progenitor cells in the mononuclear cell (MNC) fraction of human cord blood was evaluated under atmospheres containing reduced (5%) and normal (20%) oxygen tensions. Cells were cultured with synergistic cytokine combinations in suspension (without stroma) and on irradiated bone marrow stroma. Addition of interleukin (IL)-3 and IL-6 (IL-3/IL-6) provided a greater expansion of both total and progenitor cells than IL-1 and IL-3 (IL-1/IL-3). IL-3/IL-6 maintained a higher level of progenitors throughout the 8-week culture period, whereas progenitors disappeared earlier from cultures with IL- 1/IL-3. This indicates that an earlier cell type was affected by IL- 3/IL-6, and/or that IL-3/IL-6 favored self-renewal while IL-1/IL-3 induced differentiation. Reduced oxygen tension enhanced the productivity of these long-term hematopoietic cultures (LTHC) under all conditions tested. In suspension cultures, reduced oxygen increased cumulative total cell production by 125% and 167%, and cumulative progenitor production by 68% and 21%, with IL-1/IL-3 and IL-3/IL-6, respectively. The presence of irradiated stroma increased cumulative progenitor cell production almost threefold in cultures without cytokines. In cultures with cytokines, the beneficial effect of stroma was less significant, but was greater under 20% O2 than 5% O2. Cultures under 5% O2 provided more progenitors and often maintained progenitors for 1 to 2 weeks longer than those under 20% O2. To quantitate more precisely the shift in cell populations induced by IL-3/IL-6 and stroma in cultures under 5% O2, flow cytometry analysis was used. By week 3, the addition of IL-3/IL-6 stimulated a 15-fold and 25-fold expansion of promyelocytes (CD15+CD11b-) in suspension and stromal cultures, respectively. Addition of IL-3/IL-6 also increased mature granulocyte (CD15hiCD11b+) and monocyte (CD15loCD11b+) numbers, while no effect was seen on T-(CD3+) or B- (CD19+) lymphocytes. Endogenous production of IL- 6 was significantly higher under 5% O2 in both suspension and stromal cultures, and IL-6 production was increased threefold by the addition of IL-1/IL-3. Very little IL-1 beta was produced in these cultures, and endogenous IL-3 and tumor necrosis factor (TNF)-alpha were undetectable by enzyme-linked immunosorbent assay (ELISA) analysis.

Expansion of hematopoietic progenitor cells in the mononuclear cell (MNC) fraction of human cord blood was evaluated under atmospheres containing reduced (5%) and normal (20%) oxygen tensions. Cells were cultured with synergistic cytokine combinations in suspension (without stroma) and on irradiated bone marrow stroma. Addition of interleukin (IL)-3 and IL-6 (IL-3/IL-6) provided a greater expansion of both total and progenitor cells than IL-1 and IL-3 (IL-1/IL-3). IL-3/IL-6 maintained a higher level of progenitors throughout the 8-week culture period, whereas progenitors disappeared earlier from cultures with IL- 1/IL-3. This indicates that an earlier cell type was affected by IL- 3/IL-6, and/or that IL-3/IL-6 favored self-renewal while IL-1/IL-3 induced differentiation. Reduced oxygen tension enhanced the productivity of these long-term hematopoietic cultures (LTHC) under all conditions tested. In suspension cultures, reduced oxygen increased cumulative total cell production by 125% and 167%, and cumulative progenitor production by 68% and 21%, with IL-1/IL-3 and IL-3/IL-6, respectively. The presence of irradiated stroma increased cumulative progenitor cell production almost threefold in cultures without cytokines. In cultures with cytokines, the beneficial effect of stroma was less significant, but was greater under 20% O2 than 5% O2. Cultures under 5% O2 provided more progenitors and often maintained progenitors for 1 to 2 weeks longer than those under 20% O2. To quantitate more precisely the shift in cell populations induced by IL-3/IL-6 and stroma in cultures under 5% O2, flow cytometry analysis was used. By week 3, the addition of IL-3/IL-6 stimulated a 15-fold and 25-fold expansion of promyelocytes (CD15+CD11b-) in suspension and stromal cultures, respectively. Addition of IL-3/IL-6 also increased mature granulocyte (CD15hiCD11b+) and monocyte (CD15loCD11b+) numbers, while no effect was seen on T-(CD3+) or B- (CD19+) lymphocytes. Endogenous production of IL- 6 was significantly higher under 5% O2 in both suspension and stromal cultures, and IL-6 production was increased threefold by the addition of IL-1/IL-3. Very little IL-1 beta was produced in these cultures, and endogenous IL-3 and tumor necrosis factor (TNF)-alpha were undetectable by enzyme-linked immunosorbent assay (ELISA) analysis.