Cell surface phenotype of a cloned line of human natural killer cells

A human cell line with strong natural killer (NK) activity lacking alloreactive cytotoxicity was derived from a primary mixed lymphocyte culture (MLC). The line was developed from a single colony grown in soft agarose and subsequently expanded in liquid culture. Several subcultures with identical reactivity were established, one of which (3.3) was studied in detail. The morphologic and phenotypic characteristics of this line were distinct from those of alloreactive T lymphocytes. While reacting with a moAb to the sheep red blood cell receptor, it lacked the well-defined pan T cell markers Leu 1 and Leu 4, as well as the markers associated with functional T cell subsets Leu 2a and Leu 3a. Further morphologic, histochemical, and phenotypic characterization revealed this cell line to be strikingly similar to the larger granular lymphocyte (LGL) population, which contains the bulk of the natural killer cell activity normally found in peripheral blood. Cold target blocking studies confirmed the NK specificity of the observed cytotoxicity. Although unlabeled NK targets readily inhibited cytotoxic activity, B-LCL bearing the stimulating antigens of the original MLC failed to inhibit lysis of NK-sensitive targets. The growth of 3.3 was strictly dependent on IL 2 CM. Absorption studies with IL 2-dependent T cells and 3.3 revealed that both of these cell populations were equally effective in removing the growth-promoting factor(s) from IL 2 CM. These data suggest that at least some of MLC-generated NK activity is mediated by a population of cells similar to if not identical to LGL. These cells, in addition, appear to depend on the same growth-promoting factor(s) in IL 2 CM as do classical T lymphocytes.