In Vivo Inverse Correlation in the Activation of Natural Killer T Cells Through Dual-Signal Stimulation via a Combination of α-Galactosylceramide-Loaded Liposomes and Interleukin-12

Alpha-galactosylceramide (GC) represents a potentially new class of adjuvant because GC strongly induces interferon (IFN) gamma production from natural killer T (NKT) cells, leading to the induction of strong antitumor immunity. Interleukin (IL)-12 is another stimulating signal that induces IFN-γ production by NKT cells. We report herein on an investigation of the effect of recombinant IL-12 on NKT cell activation, when used in combination with GC-loaded octaarginine modified liposomes (GC-Lip). IFN-γ production from splenocytes simulated with GC-Lip was dose dependently enhanced in the presence of IL-12 in vitro. In contrast, IFN-γ production in vivo was enhanced at a low dose of IL-12. Enhanced IFN-γ production was observed in the case of low doses (0.5 μg and 2.5 μg) of GC-Lip but not a high dose (5 μg), that is, the IL-12 combination enhanced NKT cell activation at a 10-fold lower GC dose. The use of the above combination also enhanced the expansion of the NKT cell population. These findings indicate that in vivo IFN-γ production is inversely correlated with the dose of IL-12 during dual signal stimulation of NKT cells via both GC-Lip and IL-12, indicating that the dose of GC-Lip can be reduced without weakening NKT cell activation.