Immunotherapeutic targeting of shared melanoma-associated antigens in a murine glioma model

Immune-based treatments for central nervous system gliomas have traditionally lagged behind those of more immunogenic tumors such as melanoma. The relative paucity of defined glioma-associated antigens that can be targeted by the immune system may partially account for this situation. Antigens present on melanomas have been extensively characterized, both in humans and in murine preclinical models. Melanocytes and astrocytes are both derived embryologically from the neural ectoderm. Their neoplastic counterparts, malignant melanomas and gliomas, have been shown in humans to share common antigens at the RNA level. However, little is known concerning whether gliomas can be targeted by immune-based strategies that prime T cells to epitopes from melanoma-associated antigens (MAAs). In this study, we provide evidence that two common murine glioma cell lines (GL26 and GL261) express the melanoma antigens gp100 and tyrosinase-related protein 2 (TRP-2). To understand the immunogenicity of marine gliomas to CD8(+) T cells, we examined the ability of a MAA-specific CTL cell line to lyse the glioma cells, as well as the in vivo expansion of MAA-specific CD8(+) T cells in animals harboring gliomas. Both glioma cell lines were lysed by a human gp100-specific CTL cell line in vitro. Mice harboring s.c. GL26 gliomas possessed TRP-2-specific CD8(+) T cells, providing further evidence that these gliomas express the protein products in the context of MHC class I. Furthermore, MAA peptide-pulsed dendritic cells could prime T cells that specifically recognize GL26 glioma cells in vitro. Lastly, mice that were prevaccinated with human gp100 and TRP-2 peptide-pulsed dendritic cells had significantly extended survival when challenged with tumor cells in the brain, resulting in >50% long-term survival. These results suggest that shared MAAs on gliomas can be targeted immunotherapeutically, pointing the way to a new potential treatment option for patients with malignant gliomas.