Background Glioblastoma is an aggressive primary brain tumor typically resistant to currently available immunotherapies. A deeper understanding of the underlying immunoregulatory mechanisms in glioblastoma is needed to enhance future immunotherapeutic approaches. Natural killer T (NKT) cells are unconventional T cells that recognize lipid antigens presented by MHC-like molecules, CD1d. We hypothesize that NKT cell activation by glioblastoma-specific lipids may lead them to mediate immunoregulatory functions. Our research aims to identify potential lipid antigens enriched in glioblastoma and determine the nature of their interactions with NKT cells.
Methods We used five human glioblastoma cell lines, two human low grade glioma cell lines, and a normal human astrocyte cell line in the study. The lipid profiles of these cells were identified and compared using an LC-MS based lipidomics platform. A human NKT cell line was stimulated with the glioblastoma cell lines expressing CD1d to measure the antigenic activities of glioblastoma endogenous lipids. These NKT cells were also stimulated by a human leukemic cell line presenting individual synthetic lipid antigens identified in the lipidomic analysis.
Results Human glioblastoma stem cells transfected with CD1d were able to activate human NKT cells in vitro, suggesting that human glioblastoma may produce lipid antigens recognized by NKT cells. Multiple lipid species were found to be highly enriched in the glioblastoma cell lines compared with low-grade gliomas and normal human astrocytes. Antigenic activities of the glioblastoma-enriched lipids were examined by in vitro NKT stimulation assays. These assays demonstrated that multiple lipid species, when presented by CD1d, successfully activated NKT cells in a dose-dependent manner.
Conclusions These findings demonstrate the existence of glioblastoma-specific lipid antigens for NKT cell activation and the potential for modulating immune responses through the lipid antigens produced by the glioblastoma cells. Next steps include determining functional responses of glioblastoma lipid-activated NKT cells, as well as modulating the lipid profile of glioblastoma cells in order to enhance NKT cell function.
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