Sustained activation and tumor targeting of NKT cells using a CD1d–anti-HER2–scFv fusion protein induce antitumor effects in mice

Invariant NKT (iNKT) cells are potent activators of DCs, NK cells, and T cells, and their antitumor activity has been well demonstrated.A single injection of the high-affinity CD1d ligand α-galactosylceramide (αGalCer) leads to short-lived iNKT cell activation followed, however, by long-term anergy, limiting its therapeutic use.In contrast, we demonstrated here that when αGalCer was loaded on a recombinant soluble CD1d molecule (αGalCer/sCD1d), repeated injections led to sustained iNKT and NK cell activation associated with IFN-γ secretion as well as DC maturation in mice.Most importantly, when αGalCer/sCD1d was fused to a HER2specific scFv antibody fragment, potent inhibition of experimental lung metastasis and established s.c.tumors was obtained when systemic treatment was started 2-7 days after the injection of HER2-expressing B16 melanoma cells.In contrast, administration of free αGalCer at this time had no effect.The antitumor activity of the CD1d-anti-HER2 fusion protein was associated with HER2-specific tumor localization and accumulation of iNKT, NK, and T cells at the tumor site.Targeting iNKT cells to the tumor site thus may activate a combined innate and adaptive immune response that may prove to be effective in cancer immunotherapy.