TMIC-07. TRIPLE COCKTAIL IMMUNOMODULATION OF TUMOR DRAINING LYMPH NODES RESULTS IN SYNERGISTIC REVERSAL OF IMMUNOSUPPRESSION AND IMPROVED OVERALL SURVIVAL IN A MURINE GLIOBLASTOMA MODEL

Abstract Clinical trials involving anti-PD-1 fail to improve survival compared to standard of care in glioblastoma (GBM). Despite the advent of newer immunotherapies such as STING agonists and anti-CSF-1R, combination of these strategies is limited by necessitation of intracranial delivery (STING) or off-target side effects with systemic exposure (anti-CSF-1R + anti-PD-1). We have previously shown that delivery of anti-PD-1 to tumor draining lymph nodes via hydrogels decreases systemic exposure of anti-PD-1 and results in improved therapeutic response compared to systemic delivery. This study assesses the efficacy of combining STING agonist (STING), anti-CSF-1R (aCSF1r), and anti-PD-1 (aPD1) into a hydrogel nanoparticle that targets different components of immunosuppression in tumor draining lymph nodes. CT-2A murine glioma cells were orthotopically implanted into C57BL/6J mice with treatment on day 7 via deep cervical injection of hydrogel polymers loaded with either PBS (control), STING, aCSF1r, aPD1, or a combination of all three immunomodulators. Flow cytometry was used for immunophenotyping and Kaplan-Meier survival curves were generated to assess therapeutic efficacy. Each treatment strategy targeted a different component of immunosuppression. Compared to controls, aCSF1r resulted in the greatest decrease of immunosuppressive myeloid cells in the brain (P=0.0017) and cervical lymph nodes (P=0.0008); STING resulted in the greatest activation of intracranial dendritic cells (P=0.0001); and aPD1 resulted in the highest level of T cell activation of the monotherapies (P=0.0008) but also caused compensatory upregulation of regulatory T cells in the brain (P=0.0176). Combination therapy resulted in the greatest decrease in immunosuppression with increased T cell IFN-y production and dendritic cell activation, with resultant improvement in median and overall survival (P=0.0006). Triple combination therapy to tumor draining lymph nodes that specifically targets multiple components of immunosuppression is a safe and efficacious treatment that can be translated to clinical application.