Background: SB623 cells are expanded from marrow stromal cells (MSCs) transfected with a Notch intracellular domain (NICD)-expressing plasmid. In stroke-induced animals, these cells reduce infarct size and promote functional recovery. SB623 cells resemble the parental MSCs with respect to morphology and cell surface markers despite having been in extended culture. MSCs are known to have immunosuppressive properties; whether long-term culture of MSCs impact their immunomodulatory activity has not been addressed.
Methods: To assess the possible senescent properties of SB623 cells, we performed cell cycle related assays and beta-galactosidase staining. To assess the immunomodulatory activity of these expanded NICD-transfected MSCs, we performed co-cultures of SB623 cells or MSCs with either enriched human T cells or monocytes and assessed cytokine production by flow cytometry. In addition, we monitored the immunosuppressive activity of SB623 cells in both allogenic and xenogenic mixed lymphocyte reaction (MLR).
Results: Compared to MSCs, we showed that a small number of senescent-like cells appear in each lot of SB623 cells. Nevertheless, we demonstrated that these cells suppress human T cell proliferation in both the allogeneic and xenogeneic mixed lymphocyte reaction (MLR) in a manner comparable to MSCs. IL-10 producing T cells were generated and monocyte-dendritic cell differentiation was dampened by co-culture with SB623 cells. Compared to the parental MSCs, SB623 cells appear to exert a greater inhibitory impact on the maturation of dendritic cells as demonstrated by a greater reduction in the surface expression of the co-stimulatory molecule, CD86.
Conclusion: The results demonstrated that the immunosuppressive activity of the expanded NICD-transfected MSCs is comparable to the parental MSCs, in spite of the appearance of a small number of senescent-like cells.