In vitro anti-tumour activity of alpha-galactosylceramide-stimulated humaninvariant V alpha 24+NKT cells against melanoma

alpha -galactosylceramide (KRN 7000, alpha -GalCer) has shown potent in viv o anti-tumour activity in mice, including against melanoma and the highly s pecific effect of inducing proliferation and activation of human V alpha 24 +NKT-cells. We hypothesized that human V alpha 24+NKT-cells activated by al pha -GalCer might exhibit anti-tumour activity against human melanoma. To i nvestigate this, V alpha 24+NKT-cells were generated from the peripheral bl ood of patients with melanoma after stimulation with alpha -GalCer pulsed m onocyte-derived dendritic cells (Mo-DCs). V alpha 24+NKT-cells did not exhi bit cytolytic activity against the primary autologous or allogeneic melanom a cell lines tested. However, proliferation of the melanoma cell lines was markedly suppressed by co-culture with activated V alpha 24+NKT-cells (mean +/- SD inhibition of proliferation 63.9 +/- 1.3%). Culture supernatants of activated V alpha 24+NKT-cell cultures stimulated with alpha -GalCer pulse d Mo-DCs exhibited similar anti proliferative activities against melanoma c ells, indicating that the majority of the inhibitory effects were due to so luble mediators rather than direct cell-to-cell interactions. This effect w as predominantly due to release of IFN-gamma, and to a lesser extent IL-12. Other cytokines, including IL-4 and IL-10, were released but these cytokin es had less antiproliferative effects. These in vitro results show that V a lpha 24+NKT-cells stimulated by alpha -GalCer-pulsed Mo-DCs have anti-tumou r activities against human melanoma through antiproliferative effects exert ed by soluble mediators rather than cytolytic effects as observed against s ome other tumours. Induction of local cytokine release by activated V alpha 24+NKT-cells may contribute to clinical anti-tumour effects of alpha -GalC er. (C) 2001 Cancer Research Campaign.