*3.3. Dynamics of Cytokine Production in Transfected MSCs*

Next, we measured levels of cytokines IL-2, IL-6, IL-10, IL-12, IFN-γ, and TNF-α secreted by MSCs in vitro after transfection of cells with pcNS3-NS5B and sequential selection using G-418. The nontransfected MSCs secreted three cytokines: IFN-γ, IL-2, and IL-6, whereas the other cytokines were not detected in the conditioned medium. The concentration of IFN-γ increased up to the third day post-transfection, and then gradually decreased until the limit of detection at day 15 (end of cell selection) (Figure 3a). Different kinetics was observed in the case of IL-2: after an initial decrease in its level at day 3, its levels were increased at days 6–9 with a second decrease afterwards (Figure 3b). On the contrary, secretion of IL-6 was significantly increased during the entire observation period and exceeded by eightfold at day 15th the levels in the case of the untransfected MSCs (Figure 3c).

**Figure 3.** Levels of cytokines secreted by MSC in vitro after transfection with pcNS3-NS5B. The MSCs were transfected with pcNS3-NS5B, selected with G-418 for two weeks with changing medium every three days, and cytokine levels were quantified in a conditioned medium. The concentrations of IFN-γ (**a**), IL-2 (**b**), and IL-6 (**c**) are expressed in pg/ml. Values on each diagram are means ± SD of four measurements done in three independent experiments, \* *p* < 0.05 compared to the non-transfected MSC (gray bars).
