P01.01 Autologous live cell vaccination prolongs survival in immunotherapy-resistant glioma models

Background High grade gliomas remain refractory to immunotherapy. Novel approaches are required to generate a durable immune response. We developed a live cell vaccination strategy and used this approach to reverse engineer the critical components of a curative anti-glioma immune response.Methods Therapeutic strategies were evaluated in the immunotherapy-resistant SB28 and CT2A glioma models. Glioma cells were implanted intracranially. For peripheral live cell vaccination, additional glioma cells were implanted subcutaneously in the flank, and subjects were treated with immune checkpoint blockade (anti-PD1, anti-CTLA4). To determine the necessary properties of the vaccine, modifications were made to the tumor cells prior to flank implantation. To determine the necessary properties of the immune response, transgenic models, antibody-based depletions, and surgical procedures were utilized to disrupt the endogenous immune response. To replicate the clinical standard of care, intracranial tumors were surgically resected on Day 16 post-implantation, processed, and re-implanted as an autologous vaccine.Results Peripheral live cell vaccination 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. Only viable tumor cells—not cell lysates, fixed cells, or heat-killed preparations—conferred protection, and live cells remained effective even when vaccination was delayed 6 days post-intracranial implantation. Therapeutic efficacy was associated with increased CD8+ T cells and reduced myeloid populations, such as Arg1+ monocytes and macrophages, in the tumor microenvironment. Depletion of CD8+ T cells, but not CD4+ T cells or NK cells, abrogated protective responses. Deficiency of conventional type 1 dendritic cells in IRF8+32kb−/− mice also disrupted anti-glioma immunity. 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 both primary disease and rechallenge. Tumor MHCI expression has also been thought to be critical. CRISPR-based knockout of β2-microglobulin, which is required for MHCI expression, revealed that tumor MHCI expression was dispensable in the peripheral vaccine for generation of immunity but required in the intracranial tumor for response to the vaccine. Finally, standard of care for patients with gliomas includes surgical resection. Translating this to our models, intracranial tumors were resected, processed and re-implanted in the flank. This autologous live cell vaccination significantly prolonged survival.Conclusion These results demonstrate that durable anti-glioma immunity is achievable with autologous live cell vaccination in translatable surgical resection models and reveal critical mechanistic insights to guide development of novel immunotherapies.