alpha-galactosylceramide (
KRN 7000,
alpha-GalCer) has shown potent in vivo anti-tumour activity in mice, including against
melanoma and the highly specific effect of inducing proliferation and activation of human Valpha24+NKT-cells. We hypothesized that human Valpha24+NKT-cells activated by
alpha-GalCer might exhibit anti-tumour activity against human
melanoma. To investigate this, Valpha24+NKT-cells were generated from the peripheral blood of patients with
melanoma after stimulation with
alpha-GalCer pulsed monocyte-derived dendritic cells (Mo-DCs). Valpha24+NKT-cells did not exhibit cytolytic activity against the primary autologous or allogeneic
melanoma cell lines tested. However, proliferation of the
melanoma cell lines was markedly suppressed by co-culture with activated Valpha24+NKT-cells (mean +/- SD inhibition of proliferation 63.9 +/- 1.3%). Culture supernatants of activated Valpha24+NKT-cell cultures stimulated with
alpha-GalCer pulsed Mo-DCs exhibited similar antiproliferative activities against
melanoma cells, indicating that the majority of the inhibitory effects were due to soluble mediators rather than direct cell-to-cell interactions. This effect was 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
cytokines had less antiproliferative effects. These in vitro results show that Valpha24+NKT-cells stimulated by
alpha-GalCer-pulsed Mo-DCs have anti-tumour activities against human
melanoma through antiproliferative effects exerted by soluble mediators rather than cytolytic effects as observed against some other tumours. Induction of local
cytokine release by activated Valpha24+NKT-cells may contribute to clinical anti-tumour effects of
alpha-GalCer.