Reversible induction of natural killer cell activity in cloned murine cytotoxic T lymphocytes

Natural killer (NK) activity is a poorly understood component of the immune system, generally identified as the ability to kill certain tumour cells(1,2). Perhaps the most controversial issue has been the lineage to which cells displaying this activity belong. Extensive studies of surface antigens on cells with NK activity in both mouse and man have led to enigmatic results, such cells apparently bearing markers of both T-cell (Thy-1 and E receptor) and myeloid (Mac-1 and OKM1) lineages(3–6). A fresh approach to this problem would be to take cells of known lineage and test whether they express, or could be induced to express, NK cell function. Using this approach we show here that monoclonal cytotoxic T lymphocyte (CTL) lines can be induced, by culture in high concentrations of spleen cell supernatant, to express a new lytic activity apparently identical with that of splenic cells NK activity. Preliminary evidence implicates both interleukin-2(IL-2) and interferon (IFN) as mediators of this phenomenon. These findings clearly demonstrate that cells of T cell lineage have the capacity to express NK activity.