Overexpression of SPI6 protects mouse MSCs from CTL killing. (A) FACS showing the transduction of MigR1-PI9 into WT MSCs for overexpression of SPI6 compared with MigR1 (empty vector) as control. Transduced MSCs were incubated with increasing E/T ratios of primed CTLs (n = 3 experiments). (B) MSCs with MigR1-PI9 displayed significant protection against cytotoxic killing at the E/T ratios examined (P < .01).