Natural Killer T Cells as Targets for Therapeutic Intervention in Autoimmune Diseases

Natural killer T (NKT) cells are a subset of lymphocytes that express receptors characteristic of conventional T cells together with receptors typically found on natural killer cells. A key feature of NKT cells is the expression of a semi-invariant T cell receptor that is specific for glycolipid antigens presented by the unusual major histocompatibility complex class I-like molecule CD1d. While their precise immunological functions remain unknown, NKT cells have been implicated in the regulation of adaptive immune responses, including those directed against autoantigens. These findings raise the possibility that specific stimulation of NKT cells may be exploited for therapeutic purposes. A number of laboratories have tested this hypothesis, utilizing the sea sponge-derived agent α- galactosylceramide (α-GalCer), a specific agonist of NKT cells. Administration of α-GalCer to mice results in potent activation of NKT cells, rapid and robust cytokine production, and activation of a variety of cells of the innate and adaptive immune systems. Most notably, repeated administration of α-GalCer to mice favors the generation of conventional T lymphocytes producing T helper (Th) type 2 cytokines such as IL-4 and IL-10. These findings suggest that α-GalCer can modulate inflammatory conditions that are mediated by pathogenic Th1 cells. Indeed, recent studies have demonstrated that α-GalCer modulates the development of a variety of autoimmune and inflammatory diseases. Collectively, these studies provide a solid foundation for the development of NKT cell ligands as pharmacological agents for treatment of autoimmune diseases.