HNK induces cytotoxicity in MM cell lines and tumor cells from patients with MM, but not in normal PBMNCs. (A, B) Growth inhibition in MM cell lines by HNK was assessed by colorimetric assay after 48-hour culture. Data represent mean plus or minus the standard deviation (SD) of 3 independent experiments (^*P < .05 versus untreated cells). (C) Viability of PBMNCs derived from 7 healthy subjects was assessed by colorimetric assay after 48-hour culture. Data represent mean plus or minus SD of triplicate cultures (^*P < .05 versus untreated cells). (D) Cytotoxicity of HNK against patient MM cells was determined by comparison of percentage of CD38^high cells after culture with HNK (4, 6, 8, and 10 μg/mL) versus media for 48 hours. HNK induced cytotoxicity to patient MM cells in a dose-dependent manner (n = 6, values represent the mean plus or minus SD, ^*P < .005 versus untreated cells). Double asterisks indicate statistical significance in 2 lines; triple asterisks, in 3 lines.