Fifteen Years since the Development of KRN7000 – Structure-Activity Relationship Studies on Novel Glycosphingolipids Which Stimulate Natural Killer T Cells

Abstract

Invariant natural killer (NK) T cells bridge innate and acquired immunity and play an important role in both protective and regulatory responses. NKT cell responses are induced by recognition of a complex of glycolipid antigens with CD1d, an antigen presenting protein of the immune system, with its invariant T cell receptors. KRN7000, an α-galactosyl ceramide developed by KIRIN Brewery Co. in 1995, stimulates NKT cells strongly to induce the production of a large amount of cytokines, and is used as a standard reagent for a positive control of NKT cell studies. At the beginning, KRN7000 was developed as an anticancer drug candidate. However, it induces both helper T (Th)1-type cytokines, which induce immunostimulatory activity, and Th2-type ones, which induce immunosuppressive activities, in large quantities at the same time. Its therapeutical use, therefore, is limited. Fifteen years has passed since the discovery of KRN7000, and a number of analogues of KRN7000 have been developed worldwide to solve the above problem. Many researchers are also trying to understand how NKT cells recognize the structure of glycolipids and induce cytokines. In this minireview, we discuss the structure-activity relationship studies on novel glycolipids which stimulate NKT cells efficiently.