Inhibition of MICA/B shedding enhances memory-like NK cell–mediated cytotoxicity against MM. (A) MICA, MICB, PDIA6 (ERp5), and ADAM10 gene expression levels in 1389 tumor cell lines from the Cancer Cell Line Encyclopedia database. Gene expression levels are presented as log2(transcripts per million [TPM] + 1). (B) MICA/B surface expression in 10 different HMCLs, as measured by flow cytometry. (C) MICA/B gene expression levels in 9 different HMCLs from the publicly available Broad CCLE data set. (D) Dose-dependent increase in MICA/B surface expression in HMCL MM.1S in response to 7C6 treatment. Significance was calculated using the t test. (E) Shed MICB was determined using sandwich enzyme-linked immunosorbent assay. A decrease in soluble MICB was seen in response to the 7C6 mAb treatment. For functional assays, effector cells (conventional or memory-like NK cells) were cocultured with MM.1S at a 5:1 effector-to-target ratio for 6 hours. (F) Increased CD107a degranulation (n = 7), IFN-γ production (n = 10), and tumor necrosis factor-α (TNF-α) production (n = 7) measured by flow cytometry in response to 7C6 treatment of cNK cells. (G) Summary of cytotoxicity (n = 9) of cNK and memory-like NK cells upon 7C6 mAb treatment of MM.1S cells. Data are depicted as the mean ± standard deviation. Significance was calculated using the Wilcoxon test for comparison of IC and 7C6 treatment conditions, and the Mann-Whitney U test was used for the remainder of the comparisons; ns, P > .05; ∗P ≤ .05; ∗∗P ≤ .01; ∗∗∗P ≤ .001; ∗∗∗∗P ≤ .0001. E:T, effector:target; IC, isotype control; ns, not significant.