K562 lysis is reduced in patients with MDS by direct cytotoxicity of target cells. Results are shown for 5-hour 51Cr-release assays using K562 as a target. (A) The graphic representation of the percent specific lysis at a 50:1 E/T ratio is shown using normal PBMCs (n = 37) and PBMCs from patients with MDS (n = 48). (B) Percent specific lysis of K562 at a 50:1 E/T ratio versus percentage of NK cells in the sample for 26 patients and the percent specific lysis of K562 at a 50:1 E/T ratio versus the absolute number of NK cells in the peripheral blood. (C) Percent specific lysis by highly enriched NK cells (NK) and PBMCs at 50:1, 25:1, 12:1, and 6:1 E/T ratios are shown from 3 healthy controls and 2 MDS patients. Samples used for these assays were never frozen. The graphs represent the average of triplicate samples; standard deviation is indicated by the error bars, and the asterisks represent statistical significance at P ≤ .001 as determined by the nonparametric Wilcoxon rank sum test.
