In vitro anti-tumour activity of α-galactosylceramide-stimulated human invariant Vα24+NKT cells against melanoma

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 V alpha 24+NKT-cells. We hypothesized that human V alpha 24+NKT-cells activated by alpha -GalCer might exhibit anti-tumour activity against human melanoma. To investigate this, V alpha 24+NKT-cells were generated from the peripheral blood of patients with melanoma after stimulation with alpha -GalCer pulsed monocyte-derived dendritic cells (Mo-DCs). V alpha 24+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 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 pulsed Mo-DCs exhibited similar anti proliferative 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 V alpha 24+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 V alpha 24+NKT-cells may contribute to clinical anti-tumour effects of alpha -GalCer. (C) 2001 Cancer Research Campaign.