Induction of NK-like activity in T cells by IL-2/anti-CD3 is linked to expression of a new antitumour receptor with specificity for acetylated mannose

The generation of MHC-unrestricted cytotoxicity of highly enriched human CD3+ T cells (95-99%) by treatment with IL-2 and/or anti-CD3 antibodies was studied. T cells obtained by positive immunomagnetic sorting (anti-CD3) developed comparable specific cytotoxicities against K562 and Daudi cells when cultured with IL-2 and anti-CD3 for 96 h (80% of donors; n = 25). This increase of MHC-unrestricted cytotoxicity correlated fairly well with an increased formation of T cell/tumour cell conjugates. Moreover, simultaneous expression of a rhamnogalacturonan-binding receptor on activated T cells could be demonstrated. Rhamnogalacturonan was reported to enhance cytotoxicity of CD56+ NK cells by effector cell/target cell bridging. Untreated CD3+ cells hardly reacted with rhamnogalacturonan and IL-2-activated T cells showed only a moderate enhancement of cytotoxicity in the presence of rhamnogalacturonan. However, when CD3+ T cells had interacted with anti-CD3 antibodies during cell-sorting or during subsequent culturing with IL-2, enhancement in cytotoxicity and increased formation of lytic effector cell/tumour cell conjugates in the presence of rhamnogalacturonan could be readily demonstrated, indicating a bridging effect analogous to CD56+ NK cells. The conjugate formation of activated T cells with tumour cells as well as the additional rhamnogalacturonan-mediated bridging must be based on the expression of receptors with acetyl mannose specificity, since enhancements of MHC-unrestricted T cell cytotoxicity and conjugate formation were inhibited in a dose-dependent manner when acetylated mannose was present in the assays.