醣脂質α-GalCer衍生物構造與活性關聯之研究

Abstract

Invariant NKT cells (iNKT cells) produce both Th1 and Th2 cytokines in response to α-Galactosylceramide (α-GalCer) stimulation and are thought to be the important effectors in the regulation of both innate and adaptive immunity involved in autoimmune disorders, microbial infections and cancers. However, the anticancer effects of α-GalCer were limited in early clinical trial. In the first study, several analogs of α-GalCer, containing phenyl groups in the lipid tails were found to stimulate murine and human iNKT cells to secrete Th1-skewed cytokines and exhibit greater anticancer efficacy in mice than α-GalCer. We explored the possibility of different Vβ usages of murine Vα14+ iNKT or human Vα24+ iNKT cells, accounting for differential cytokine responses. However, TCR Vβ analysis revealed no significant differences in Vβ usages by α-GalCer and these phenyl glycolipid analogs. On the other hand, these phenyl glycosphingolipids (GSLs) showed greater binding avidity and stability for iNKT TCR when complexed with CD1d. These findings suggest that CD1d-phenyl glycolipid complexes may interact with the same population of iNKT cells but with different avidity and stability to drive Th1 polarization. Thus, this study provides a key to the rational design of Th1 biased CD1d reactive glycolipids in the future. Further, we replaced their glycan heads with α-Glc or α-Man. Regardless of lipid tail modifications, GSLs with α-Glc head were stronger than those with α-Gal head for humans but weaker for mice in the induction of cytokines/chemokines and expansion/activation of immune cells. The immune-stimulatory potencies were associated with the strength of ternary interaction for each species. It was the iNKT TCR rather than CD1d that dictated the species-specific responses, as demonstrated by mCD1d vs. hCD1d swapping assay. Computer modeling of the ternary complexes provided further insight into the species differences in the TCR structure contributing to the differential binding avidities. In comparison, neither murine nor human iNKT TCR could recognize the GSL with α-Man head. Using Jα18 KO mice, we showed that most cytokines/chemokines induced by GSLs with either α-Glc or α-Gal head were iNKT-dependent. However, there was also iNKT-independent induction of chemokines by the GSL with α-Glc head, which might be mediated by activated monocytes. Thus, our studies showed different effects of the glycan head in mice vs. humans in the ternary interaction and bioactivities, suggesting that immune responses in mice cannot be translated to those in humans.