4"-O-Alkylated alpha-Galactosylceramide Analogues as iNKT-Cell Antigens: Synthetic, Biological, and Structural Studies.

Invariant natural killer T-cells (iNKT) represent a unique subset of T-lymphocytes that play an important regulatory role in the protection against tumour cells, auto-immune diseases and certain infections. iNKT cells recognize the prototypical ligand α-galactosylceramide (α-GalCer), a synthetic glycolipid, presented by the MHC class I-like non-polymorphic glycoprotein CD1d. After recognition by the T-cell receptor (TCR) and formation of a ternary CD1d-glycolipid-TCR complex, the iNKT cells secrete vast amounts of Th1- and Th2-cytokines, which serve as small-protein modulators in the immune system. This presentation will focus on our attempts to design α-GalCer analogues that polarize the cytokine response towards Th1, which is desirable for defense against tumours and various intracellular pathogens. Towards this end we carefully investigated modifications of the galactose ring, in particular the 4"-position, which has remained underexplored up until now. We will demonstrate the ability of analogues modified at the 4’’-position of the galactose ring to induce a polarized Th1 response in an in vivo mouse model. Crystallographic studies indicate that benzyl-type ethers, such as p-ClBn-α-GalCer, undergo additional Vanderwaals interactions with CD1d. In all, we have shown that judiciously chosen modifications of the carbohydrate moiety of α-GalCer may lead to an enhanced release of Th1-cytokines in mice.