CD48 knockout renders ATLL cells resistant to YT1-mediated direct cytotoxicity. (A) Cell surface expression of CD48, CCR4, and CD58. Mean fluorescence intensity were evaluated in the sgRNA-transduced ST1 ATLL cells by flow cytometry. (B) Normalized live-cell numbers of sgRNA-transduced ATLL cells under the cocultivation with YT1. After the indicated incubation times, numbers of the live target ATLL cells were determined with flow cytometry by gating on propidium iodide⁻ cells representing live cells and by gating on GFP⁺ cells representing sgRNA-transduced ATLL cells, which excluded GFP-negative effector YT1 cells. The number of beads normalized the number of live cells. The numbers at different E:T ratios were normalized by the one at the E:T ratio of 0:1. (C) Normalized live-cell numbers of sgCD58-transduced ATLL cells under the cocultivation with YT1. sgAAVS1-, sgCD48-, and sgCCR4-transduced ATLL cells are also shown for comparison. Data were obtained as shown in (B). (D) Normalized live-cell numbers of sgRNA-transduced ATLL cells under the cocultivation with YT1 in the presence of mogamulizumab. Data were obtained as shown in (B). (E) Schematic design of the animal study. (F) Tumor volume of irradiated YT1–NK-cell–treated or control tumors of ED40515(−) ATLL cells with sgAAVS1 or sgCD48#3 in NOG mice. Error bars represent the SEM of replicates. ∗P < .05, ∗∗P < .01, and ∗∗∗P < .001, Welch 2-sample t test. All experiments were repeated ≥2 times except for (F).