One of the most promising technique for the in vitro expansion of cord blood (CB) hematopoietic stem cells (SCs) seems to be their co-culture with stromal feeder-layers. Hence, we developed and immortalized by retroviral transduction with the temperature-sensitive SV40 large T antigen three new human cell lines, two derived from bone marrow (HM1-SV40 and HM2-SV40) and one from umbilical cord (HCB1-SV40), and investigated the inductive capacity of their conditioned culture media on clonal growth of CB hematopoietic SCs. Immunocytochemistry showed that cell lines were positive to either cytokeratins or stromal markers, as well as to epidermal growth factor (EGF), fibroblast growth factor (FGF) and adrenomedullin. Moreover, cell lines expressed interleukin (IL)-1β, IL-6, granulocyte macrophage-colony stimulating factor (GM-CSF), G-CSF and stem cell factor (SCF), and secreted variable amount of IL-1β, IL-6 and GM-CSF. Collectively, these findings indicate that cell lines possess the stromal-cell phenotype. The conditioned supernatants of the three cell lines induced similar increases in the clonal growth of both fresh and cryopreserved-thawed CB hematopoietic SCs cultured on semisolid media deprived of growth factors and cytokines. However, the inductive capacity was significantly higher in the case of cryopreserved cells, where the rise in clonal growth reached that induced by the addition to the culture media of IL-3, GM-CSF and SCF. Our findings allow us to conclude that our new human stromal cell lines could be used as feeder-layers for CB hematopoietic SC expansion in vitro.

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