Characterization of five cloned murine cell lines showing high cytolytic activity against YAC-1 cells

In an attempt to provide a selection procedure for the long-term growth and subsequent cloning of NK cells, mouse lymphocytes were treated with monoclonal anti-Thy-1.2 antibody and complement, incubated for 24 hr with poly I:C to boost residual NK cell activity, and then transferred into growth medium containing supernatant from Con A-stimulated mouse spleen cells. After cloning on appropriate feeder cells, to clones of C57Bl/6 origin and three CBA clones were isolated and studied in detail. They had extremely high cytotoxic activity against YAC-1 cells in a 4-hr super(51)Cr-release assay. They bore surface antigens characteristic of NK cells, namely asialo-GM1, Qa-5, and NK-1.2. In addition, cytotoxicity by these cloned cell lines was blocked by anti-Ly-5 antibody, a reagent that inhibited lysis by splenic NK cells but not by cytotoxic T lymphocytes. Morphologically, the cells were large and contained prominent azurophilic granules. The existence of two cloned cell lines expressing simultaneously characteristics of bone NK cells and cytotoxic T lymphocytes is intriguing and suggests the possibility of a close relationship between these two lineages of cells.