Abstract
BACKGROUND: In a randomized phase III study for recurrent glioblastoma (GBM), combination therapy with immune checkpoint inhibitors (ICIs) nivolumab and ipilimumab failed to improve overall survival. Since ICIs appear to be dependent on host-myeloid (and not tumor-cell) expression of PD-L1 (Tang et al. JCI, 2018), we sought to assess if tumor-mRNA nanoparticles (NPs) could prime the systemic and intratumoral GBM milieu with activated PD-L1+ host-myeloid cells sensitizing immunologically ‘cold’ tumors to immunotherapy. METHODS: We systemically administered personalized tumor-derived mRNA encapsulated in translatable lipid-NPs with excess positive charge for enhanced delivery and transfection of peripheral/intratumoral antigen presenting cells (APCs) in murine and large animal canine malignant glioma models. RESULTS: RNA-NPs activate systemic immunity within twenty-four hours, inducing significant increases in the percentage of CD11c+ myeloid-cells expressing PD-L1 and CD86. After only a single RNA-NP vaccine, the bulk of APCs within the spleen, liver, lymph nodes, bone marrow and tumor display an activated phenotype. These PD-L1+ APCs (CD11c+MHC-II+CD86+PD-L1+ cells from intracranial tumors) did not suppress immunity, but rather, heightened interferon-(IFN)-γ reactivity. Addition of ICIs (to animals primed with RNA-NPs) augmented peripheral/intratumoral PD-1+CD8+ cells and mediated synergistic anti-tumor efficacy in settings where ICIs alone did not confer therapeutic benefit. These synergistic effects were mediated by type–I-interferon released from PD-L1+ plasmacytoid dendritic-cells. In translational studies, personalized mRNA-NPs (from whole tumor-transcriptome) were safe and active in a client-owned canine with a spontaneous malignant glioma. In this patient, RNA-NPs elicited robust immunologic activity with increased percentages of activated PD-L1+ APCs and IFNγ+CD8+ cells. CONCLUSION: RNA-NPs elicit widespread immune activation concomitant with inducible PD-L1 expression on intratumoral APCs that can be therapeutically exploited. Since RNA-NPs bypass cost/complexity of cellular therapeutics, are amenable to central distribution, and can be made within days of tumor resection, these formulations can be expeditiously translated as biomodulators of GBM immunogenicity.