Malignant cells display phenotypic and functional properties characteristic of natural killer cells.

(A) FACS light scatter profile and CD45 expression of freshly isolated cells from the patient's peripheral blood leukopheresis product. Cells located in region I represent malignant leukocytes. Cells located in region II represent normal lymphocytes. (B) FACS analysis of cells in region I demonstrates that a majority of neoplastic cells express CD16/56 but lack CD3 surface expression consistent with the phenotype of a NK cell. (C) Percentage of specific lysis of NK-sensitive K562 cells by unstimulated patient malignant cells (▪) versus control peripheral blood mononuclear cells (■) at various effector-to-target ratios as determined by a standard 4-hour chromium release NK cell assay.