MBP NK cells exhibit enhanced anti-tumor effects compared to parental NK cells. (A) MBP NK mediated cancer cell killing. K562 (left) and A549 cells (right) that stably expressed luciferase were co-cultured with NK-92 or MBP NK cells at an E:T ratio of 5:1. The percentage of dead tumor cells was determined by quantifying bioluminescence. The statistical significance was determined by one-way ANOVA with Tukey's multiple comparison test. *, p = 0.0280, **, p = 0.0018; ****, p < 0.0001. (B) The expression level of B7H6 on the surface of K562 (top) and A549 cells (bottom), which is one of the major activating immune ligands on cancer cells. NKp30 expressed by NK cells can recognize and kill B7H6 expressing tumor cells. (C) The quantitative measurement of lytic granules released from NK-92 and MBP NK cells by ELISA. The concentrations of secreted granzyme B (left) and perforin (right) from NK-92 cells (absence or presence of IL-2) and MBP NK cells were measured in the supernatant from the co-culture with K562 cells. The statistical significance was determined by ordinary one-way ANOVA with Tukey's multiple comparison test. *, p = 0.0138; **, p = 0.0091; ***, p = 0.001. (D) Fold change in CD107a expression analyzed by flow cytometry. The plot was generated by Prism 8 software. The statistical significance was determined by ordinary one-way ANOVA with Tukey's multiple comparison test. **, p = 0.0075; ***, p = 0.0003; ****, p < 0.0001. From all the analyses, statistically insignificant (ns) results are not shown.