[Maintaining Growth of Long-Term Culture Initiating Cells from Human Cord Blood on Feeder Layers of Bone Marrow Stromal Cells Transfected with FL and/or TPO Genes].

Long-tem culture initiating cells(LTC-IC), and in vitro assay of hematopoietic stem/progenitor cells, still represent a heterogeneous population in terms of proliferative capacity and sensitivity to different growth factors. Human umbilical cord (CB) is rich of hematopoietic progenitor cells measured by clonogenic assays and stem cells capable of reconstituting the marrow after transplantation. The influence of culture conditions on the in vitro behavior of LTC-IC from CB was evaluated. First, by using IRES sequence, FL and TPO cDNA were recombined with retroviral vector pLXSN by gene recombination technology. The recombinant plasmid pLFSN, pLTSN, pLFTSN were transfected into human stromal cell line HFCL. Then, LTC-IC were evaluated in long term cultures, comparing five types of stromal feeder layers: human bone marrow stromal cell, human stromal cell line HFCL, and stromal cell lines HDF tranfected with FL gene, HLT transfected with TPO gene or HFT co-transfected with FL and TPO genes. The results were demonstrated that after 8 weeks of coculture, three types of stromal cell lines that supported the maintenance of CFU-C for up to 3 weeks in vitro were identified. However, cocultivation of human bone marrow stromal cell and CB CD34(+) cells on HFT, CFU-C production continued up to 6 weeks or longer on these stroma. The absolute LTC-IC frequency in CD34(+) cells on human bone marrow stromal cell (2.65 +/- 0.76/1 000 cells) was no significant difference with on HFT (3.65 +/- 0.58/1 000 cells). Thus, HFT acts by direct contact to maintain the phenotype and function of the most primitive and quiescent human progenitors. Furthermore, HFT cell line was selected as the optimal one for supporting long-term culture feeder. It was concluded that LTC-IC progenitors from cord blood maintain growing upon the FL/TPO gene-modified stromal feeder layers in vitro.