Interleukin 2 and interferon-γ are not sufficient to induce natural killer-like activity in human T cell clones

The role of interleukin 2 (IL2) and interferon (IFN)-γ in the maintenance of natural killer (NK)-like activity mediated by human cytolytic T cell clones was investigated. When cultured in standard supernatant (SN) obtained by phytohemagglutinin stimulation of human mononuclear cells (containing both IL2 and IFN activities), several mixed lymphocyte culture-derived clones displayed cytolytic activity directed against the K562 cell line; in addition, some of these clones also lysed specific target cells bearing the sensitizing alloantigens. When cultured in IL2-containing SN obtained from the Jurkat cell line, the NK-like activity was selectively abrogated within 4-5 days. However, by culturing cells again in standard SN the cytolytic activity was completely restored. The possibility that inhibitory molecules in Jurkat SN could be responsibe for the loss of NK-like activity was ruled out by experiments showing that cytotoxicity could be induced by mixtures of Jurkat and standard SN. In addition, a source of affinity chromatography-purified IL2 also failed to maintain NK-like activity. Moreover, addition of recombinant IFN-γ in combination with purified IL2 did not prevent the loss of NK-like activity. The present results indicate that neither IL2 nor IFN-γ are sufficient to maintain NK-like activity and suggest that other molecule(s) are required.