Potent immune-modulating and anticancer effects of NKT cell stimulatory glycolipids

α-Galactosylceramide (α-GalCer), a glycolipid that stimulates natural killer T (NKT) cells to produce both T helper (Th)1 and Th2 cytokines, has shown antitumor effects in mice but failed in clinical trials. We evaluated 16 analogs of α-GalCer for their CD1-mediated T cell receptor (TCR) activation of naïve human NKT cells and their anticancer efficacy. In vitro, glycolipids containing an aromatic ring in their acyl tail or sphingosine tail were more effective than α-GalCer in inducing Th1 cytokines/chemokines, TCR activation, and human NKT cell expansion. None of these glycolipids could directly stimulate human dendritic cell maturation, except for a glycolipid with an aromatic ring on the sphingosine tail. Here, we show that glycolipids activated the TCR of NKT cells with phosphorylation of CD3ε, ERK1/2, or CREB, which correlated with their induction of Th1 cytokines. Notably, the extent of NKT cell activation when glycolipid was presented by antigen-presenting cells was greater than when glycolipid was presented by non-antigen-presenting cells. In vivo, in mice bearing breast or lung cancers, the glycolipids that induced more Th1-biased cytokines and CDS/CD4 T cells displayed significantly greater anticancer potency than α-GalCer. These findings indicate that α-GalCer analogs can be designed to favor Th1-biased immunity, with greater anticancer efficacy and other immune-enhancing activities than α-GalCer itself.