Propagation of mouse cytotoxic clones with characteristics of natural killer (NK) cells

Splenocytes obtained from normal mice (BALB/c nude, BALB/c, C 3H, C57Bl/6) and from mice bearing lung or pulmonary carcinomas were propagated for 1–12 months in the presence of crude or mitogen-depleted T-cell growth factor (TCGF). Clones from several TCGF-propagated lymphoid cell lines were established by limiting dilution or the soft agar techniques. All the cultured lines and the majority of the clonal populations derived from them exhibited strong cytotoxic activity in vitro ( 51Cr release assay) toward a variety of syngeneic and allogeneic tumor target cells, both freshly obtained and passaged in culture, and both lymphoid and solid in origin, and including targets usually resistant to fresh NK cells. Considerable cytotoxic activity was also observed with several rat and human cultured tumor lines. Only low cytotoxic activity was detected against normal lymphoid mouse cells. Cloned populations generally exhibited more restricted target cytotoxicity than the parental cultured lines, and the pattern of reactivity varied among the clones. Of the clones tested for surface markers, all were positive for Thy 1.2, T200, and asialo GM1 and had strong binding to peanut agglutinin (PNA), all had undetectable receptors for IgG or IgM, and some were positive for Lyt 2. The cytotoxic activity was augmented by pretreatment of the effector cells with interferon and inhibited by the presence of mannose or galactose during the assay. Several clones were capable of mediating antibody-dependent cellular cytotoxicity and lectin-induced cellular cytotoxicity (LICC), and produced relatively large quantities of interferon and lymphotoxinlike material. The findings indicated continuous culturing in TCGF of previously antigen-nonstimulated mouse lymphocytes selects for the growth of at least two distinct populations with activated NK activity, one reacting preferentially with lymphoid tumor target cells (designated CNK-L), and the second reacting effectively with both lymphoid and solid tumor targets (designated CNK-SL). Both populations have several features of both T lymphocytes and NK cells.