Proliferation of human hematopoietic progenitors in long-term bone marrow cultures in gas-permeabile plastic bags is enhanced by colony-stimulating factors

We compared the recovery of human hematopoietic progenitors in long-term bone marrow culture (LTBMC) initiated in tissue culture (TC) flasks to that in 'Lifecell' bags, which are gas-permeable plastic bags in which feeder-layer cells cannot adhere. Our results showed that granulocyte-macrophage colony-forming unit (CFU-GM) and erythroid burst-forming unit (BFU-E) cumulative recovery in cultures from normal donor marrow, expressed as a percent of the initial inoculum, was not statistically different in the two culture systems up to week 8, when the cultures were terminated: 31.5 ± 19 (flask) vs 30 ± 14 (bag) and 15.5 ± 12 (flask) vs 11.5 ± 8 (bag), respectively. The effects of weekly addition of recombinant human (r-hu)-interleukin 1 (IL1) and r-hu-interleukin 3 (IL3) were then studied, alone and combined, at two different concentrations. Addition of IL1, either alone or combined with IL3, in LTBMC established in flasks induced an increase of hematopoietic progenitors for the first week, but BFU-E and CFU-GM were no longer detectable at weeks 4 and 6, respectively. Analysis of adherent layer cells showed a decreased cellularity, no adipogenesis, and early disappearance of bone marrow (BM) progenitors, whereas the cycling rate of myeloid precursors, by cytosine arabinoside (Ara-C) suicide assay, was similar to that of untreated cultures. Conversely, IL3 alone (5 ng/ml) resulted in 3.6- and 5.4-fold peak increases for CFU-GM and BFU-E, respectively, at week 1 (adherent plus nonadherent cells), and the recovery of BM cells was still higher than that of control flasks at week 8. By comparison, stimulation with colony-stimulating factors (CSFs) of BM cells grown in bags never affected the longevity of the culture. Addition of IL3 (5 ng/ml) induced a higher recovery of total cells, CFU-GM (range: 1.6- to 15-fold peak increase during the culture), and BFU-E (1.2- to 3-fold) compared to the untreated controls. Bags treated with IL1 alone demonstrated only transient beneficial effects, and the number of hematopoietic precursors fell below the level of control bags during the culture. IL1 and IL3 induced 1.8- and 5.3-fold peak increases in BFU-E and CFU-GM at weeks 1 and 4, respectively. Simultaneous flow cytometric analysis of CD34⁺/CD33⁺ cells and DNA content showed increased numbers and proliferation of the committed BM progenitors when CSFs were added to the bag. Our results indicate that long-term production of hematopoietic cells can be sustained in the absence of a feeder layer in plastic gas-permeable bags, and stimulation with CSFs induces a higher recovery of BM progenitors while the longevity of hematopoiesis is not altered. This novel approach may have significant implications for the clinical use of the LTBMC method for autologous bone marrow transplantation.