Viral vector vaccination induces brain resident memory T cells to drive anti-glioblastoma immunity

Glioblastoma is a lethal brain tumor notable for limited spontaneous induction of CD8 + T cell responses. While viral-vector vaccines can drive particularly high magnitudes of tumor-reactive T cells, they have not been investigated for the treatment of glioblastoma. Here, we demonstrate that heterologous prime-boost vaccination with the simian adenovirus ChAdOx1 and poxvirus modified vaccinia Ankara (MVA) treats the orthotopic, syngeneic, checkpoint-inhibitor refractory SB28 murine model of glioblastoma, both in the context of the murine tumor antigen, P1A, and a newly identified tumor-associated antigen expressed by SB28. Adjuvant anti-PD-1 and anti-CTLA-4 did not further improve outcomes. Vaccination induced immunoediting of tumor antigen expression and tumor-specific recruitment of antigen-specific T cells to challenged brains, the majority of which had a CD103 + CD69 + CD8 + tissue resident memory (TRM)-like phenotype. While induction of TRMs by vaccination has been implicated in superior control of other cancers, their role in mediating anti-glioblastoma immunity was unclear. ChAdOx1/MVA-induced brain TRMs displayed superior polyfunctionality compared to circulating and non-TRM brain antigen-specific CD8 + T cells. Long-term surviving mice maintained consistent levels of antigen-specific TRM cells in their brains at days 70 and 175 post-tumor challenge, despite a three-fold decrease in circulating antigen-specific T cells, indicating durable T cell memory in the brain parenchyma. Furthermore, survivors were protected against a second orthotopic, but not subcutaneous, tumor rechallenge, demonstrating tissue-specific immunological memory. Intracranial adoptive transfer of brain-derived antigen-specific TRMs isolated from vaccinated, tumor-bearing mice was sufficient to prolong the survival of naïve mice challenged with tumors, whereas blood-derived antigen-specific non-TRMs and non-antigen-specific brain-derived CD8⁺ T cells were not. Despite peripheral administration of the vaccines, antigen-specific CD8 + T cells were induced not only in the brains of tumor-free animals, but in many tissues, including the liver, lung, skin, skull bone marrow, and meninges, with distinct phenotypes observed in different tissues. Overall, we demonstrate that ChAdOx1/MVA vaccination is a potent strategy to induce TRMs to mediate anti-glioblastoma immunity, establishing a basis for further clinical investigation of ChAdOx1/MVA vaccination to treat patients with glioblastoma.