MSCs have no effect on cytolytic killing of virally infected target cells by virus-specific CTL. (A) EBV-CTL or (B) CMV-CTL cultured with EBV or CMV antigens, respectively, for 5 days in the presence or absence of MSCs were analyzed for cytolytic activity of autologous LCL or pp65-pulsed LCL, respectively, by a standard ⁵¹Cr release assay. Allogeneic LCL and HSB-2 cells were used to control for MHC-restricted killing. (C) Negligible killing of MSCs cultured together with LCL or pulsed with pp65 peptides by virus-specific CTL. The bars show the mean specific lysis by 5 different EBV-CTL (A), 2 different CMV-CTL lines (B), and 2 EBV-CTL and 2 CMV-CTL (C). Error bars illustrate SEM.