Optimization of Natural Killer T Cell-Mediated Immunotherapy in Cancer Using Cell-Based and Nanovector Vaccines

α-Galactosylceramide (α-GalCer) represents a new class of immune stimulators and vaccine adjuvants that activate type I natural killer T (NKT) cells to swiftly release cytokines and to exert helper functions for acquired immune responses. This unique property prompted clinicians to exploit the antitumor potential of NKT cells. Here, we review the effects of α-GalCer in (pre)clinics and discuss current and future strategies that aim to optimize NKT cell-mediated antitumor therapy, with a particular focus on cell-based and nanovector vaccines.