In vitro effects of stromal cells expressing different levels of Jagged-1 and Delta-1 on the growth of primitive and intermediate CD34+ cell subsets from human cord blood

In trying to contribute to our knowledge on the role of Notch and its ligands within the human hematopoietic system, we have assessed the effects of the OP9 stroma cell line – naturally expressing Jagged-1 – transduced with either the Delta-1 gene (OP9-DL1 cells) or with vector alone (OP9-V), on the in vitro growth of two different hematopoietic cell populations. Primitive (CD34+ CD38− Lin−) and intermediate (CD34+ CD38+ Lin−) CD34+ cell subsets from human cord blood were cultured in the presence of 7 stimulatory cytokines under four different conditions: cytokines alone (control); cytokines and mesenchymal stromal cells; cytokines and OP9-V cells; cytokines and OP9-DL1 cells. Proliferation and expansion were determined after 7 days of culture. Culture of CD34+ CD38− Lin− cells in the presence of OP9-V or OP9-DL1 cells resulted in a significant increase in the production of new CD34+ CD38− Lin− cells (expansion), which expressed increased levels of Notch-1; in contrast, production of total nucleated cells (proliferation) was reduced, as compared to control conditions. In cultures of CD34+ CD38+ Lin− cells established in the presence of OP9-V or OP9-DL1 cells, expansion was similar to that observed in control conditions, whereas proliferation was also reduced. Interestingly, in these latter cultures we observed production of CD34+ CD38− Lin− cells. Our results indicate that, as compared to MSC, OP9 cells were more efficient at inducing self-renewal and/or de novo generation of primitive (CD34+ CD38− Lin−) cells, and suggest that such effects were due, at least in part, to the presence of Jagged-1 and DL1.