Abstract
Therapies targeting immune checkpoints are effective in tumors with a high mutation burden that express multiple neo-antigens. However, glial tumors including those seen in children carry fewer mutations and there is an unmet need to identify new antigenic targets of anti-tumor immunity. SOX2 is an embryonal stem cell antigen implicated in the biology of glioma initiating cells. Expression of SOX2 by pediatric glial tumors and the capacity of the immune system in these patients to recognize SOX2 has not been previously studied. We examined the expression of SOX2 on archived paraffin-embedded tissue from pediatric glial tumors. The presence of T-cell immunity to SOX2 was examined in both blood and tumor-infiltrating T-cells in children and young adults with glioma. The nature of tumor-infiltrating immune cells was analyzed with a 37-marker panel using single-cell mass cytometry. SOX2 is expressed by tumor cells but not surrounding normal tissue in pediatric gliomas of all grades. T-cells against this antigen can be detected in blood and tumor tissue in glioma patients. Glial tumors are enriched for CD8/CD4 T-cells with tissue resident memory (TRM; CD45RO+, CD69+, CCR7-) phenotype, which co-express multiple inhibitory checkpoints including PD-1, PD-L1 and TIGIT. Tumors also contain natural killer cells with reduced expression of lytic granzyme. Our data demonstrate immunogenicity of SOX2, which is specifically overexpressed on pediatric glial tumor cells. Harnessing tumor immunity in glioma will likely require the combined targeting of multiple inhibitory checkpoints.