1241 Sustained Localized Delivery of Anti-PD-1 to Tumor Draining Lymph Nodes Increases Survival and Reverses Immunosuppression in Murine Glioblastoma Models

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INTRODUCTION: Despite the advent of immunotherapy as a promising therapeutic, glioblastoma (GBM) remains resistant to using checkpoint blockade against programmed cell death protein 1 (PD-1) on T cells. The highly immunosuppressive tumor milieu of GBM prevents rescue of inactivated T cells due to decreased numbers of infiltrating T cells at the tumor site as well as increased recruitment of myeloid cells. Moreover, the current strategy of using antibodies against PD-1 (anti-PD-1) requires multiple intravenous infusions every two or three weeks with debilitating systemic effects. METHODS: Mice orthotopically implanted with GL261 glioma cells were injected with PCL:PEG:PCL hydrogel polymers loaded with anti-PD-1 in one of the following locations: cervical lymph nodes, inguinal lymph nodes, and the tumor site. Mice treated systemically with anti-PD-1 were used as comparative controls. Kaplan-Meier curves were generated for all arms, with subsequent ex vivo flow cytometric staining for CD4, CD8, IFN-y, TNF-a, Foxp3, and PD-1. RESULTS: Mice implanted with PCL:PEG:PCL hydrogels carrying anti-PD-1 at the site of their lymph nodes showed significantly improved survival outcomes compared to mice systemically treated with three doses of anti-PD-1 (p < 0.001). Flow cytometric analysis of lymph nodes and brain tissue in mice injected with this gel demonstrated increased levels of IFN-y, indicating greater reversal of immunosuppression compared to standard treatment. CONCLUSIONS: Our data demonstrates proof of principle of the advantages of using localized therapy that targets lymph nodes for GBM. We propose a paradigm shift for developing new sustained local treatments with immunotherapy that are able to eliminate the need for multiple systemic infusions and their off-target effects.