EXTH-82. Live cell vaccination generates durable immunity in immunotherapy-resistant glioma models

Abstract Glioblastoma (GBM) remains refractory to immunotherapy, requiring novel approaches to overcome immune evasion. Similar to human GBM, the intracranial SB28 murine glioma model exhibits resistance to dual checkpoint blockade (anti-PD1/anti-CTLA4). In this study, we demonstrate that concurrent intracranial and subcutaneous flank tumor implantation transforms immunotherapy responsiveness in the SB28 model. This live cell vaccination strategy rendered previously resistant intracranial tumors highly sensitive to dual checkpoint therapy, achieving >80% long-term survival with durable protective immunity against rechallenge without further therapy. This effect was reproduced in immunotherapy-resistant CT2A gliomas. Using this system, we identified the vaccine features, sites, and cell types required for effective anti-glioma immune responses. Notably, only viable tumor cells—not cell lysates or heat-killed preparations—conferred protection and remained effective even when vaccination was delayed 6 days post-intracranial implantation. Cervical lymph nodes have been thought to play a critical role in intracranial anti-tumor responses, but resection of both superficial and deep cervical lymph nodes failed to disrupt anti-glioma immunity in primary disease or rechallenge. Therapeutic efficacy was associated with immune remodeling within the tumor microenvironment, characterized by substantial CD8+ T cell infiltration and reduced myeloid populations including Arg1+ monocytes and macrophages. Depletion of CD8+ T cells, but not CD4+ T cells or NK cells, abrogated protective responses. Furthermore, deficiency of conventional type 1 dendritic cells in IRF8+32kb−/− mice also disrupted anti-glioma immunity. Overall, this work demonstrates that effective anti-glioma immunity is achievable and provides a mechanistic foundation for rational design of clinically viable immunotherapies.