HLA-matched CD56⁺ cells show cytotoxicity restricted to leukemic CD34⁺ cells. CD56⁺ cells were cultured with either recipient CD34⁺ CML cells or autologous CD34⁺ cells. (A-B) Colony inhibition assay of electronically sorted autologous or HLA-matched NK or NK-T cells as indicated on patient 7 CD34⁺ CML cells. (C) Cytotoxicity assay of IL-2–stimulated HLA-matched donor CD56⁺ cells on CD34⁺ CML cells of patient 4 (□) or autologous normal CD34⁺ cells (▪). (D) Cytotoxicity assay of IL-2– and IL-15–stimulated donor HLA-matched CD56⁺ cells on CD34⁺ CML cells of patient (□) or autologous normal CD34⁺ cells (▪). IL-2–stimulated CD56-negative PBLs versus recipient CD34⁺ CML cells indicated by ○. Error bars indicate plus or minus standard deviation (SD).