EXTH-48. ADENO-ASSOCIATED VIRUS TARGETING OF THE TUMOR MICROENVIRONMENT TO IMPROVE LYMPHOCYTE RECRUITMENT IN GLIOBLASTOMA

Abstract BACKGROUND Glioblastoma (GBM) is notoriously devoid of lymphocytes driven in part by a paucity of lymphocyte trafficking factors necessary to prompt their recruitment, infiltration, and activation. We have developed a novel recombinant adeno-associated virus (AAV) gene therapy strategy that enables focal and stable reconstitution of the GBM tumor microenvironment (TME) with C-X-C motif ligand 9 (CXCL9), a powerful call-and-receive chemokine for cytotoxic T lymphocytes (CTLs). By increasing lymphocyte recruitment in GBM, we HYPOTHESIZE that these tumors will be more responsive to immunotherapy. METHODS 3D fluorescence microscopy was used to characterize the distribution, tropism, and durability of AAV6 transgene expression in preclinical GBM. Flow cytometry and 3D fluorescence microscopy was used to quantify T cell infiltration and visualize their biodistribution in preclinical GBM treated with AAV-CXCL9 in combination with anti-PD-1 immune checkpoint blockade (ICB). Single-cell RNA sequencing was used to characterize intratumor lymphocyte subsets following treatment. Survival studies with and without lymphocyte depletion were done to evaluate immunogenic responsiveness of therapy. RESULTS Focal delivery of CXCL9 with AAV6 results in stable transduction of peri-tumoral astrocytes. When combined with anti-PD-1 ICB, lymphocyte infiltration was improved, with cells found disseminated across the tumor stroma and within the tumor parenchyma. CXCR3, the chemokine receptor for CXCL9, was expressed across lymphocyte subsets and NKT cells, validating treatment selectivity of AAV6-CXCL9 for lymphocytes. Combination treatment considerably improved overall survival in two distinct GBM models, with durable responses dependent on CD8 T-lymphocyte infiltration. CONCLUSIONS By manipulating local chemokine directional guidance, AAV-CXCL9 increases tumor infiltration by CD8-postive cytotoxic lymphocytes, sensitizing GBM to anti-PD-1 ICB. These effects are accompanied by immunologic signatures evocative of an inflamed and responsive TME. These findings support targeted AAV gene therapy as a promising adjuvant strategy for reconditioning GBM immunogenicity given its excellent safety profile, TME-tropism, modularity, and off-the-shelf capability.