CTIM-34. PARAPROGRESSION DEFINES A DAMAGE RESPONSE FROM SYSTEMIC MRNA IMMUNOTHERAPY IN MALIGNANT GLIOMA

Abstract INTRODUCTION Malignant glioma (MG) is a devastating brain tumor with insufficient treatment. Our group has developed a treatment modality for this disease and others, using mRNA wrapped into clusters of lipid particle aggregates (LPAs) for enhanced immunogenicity and anti-tumor efficacy (Cell, 2024 May 9;187(10):2521-2535.e21). These RNA-LPAs have shown survival benefit in preclinical models of diffuse midline glioma (DMG), as well as in pet dogs with canine glioma. Among long-term survivors, there is development of increased lesion size which we hypothesized was due to tandem immunologic and direct cytotoxic responses. Objective: We aimed to understand the immunologic and cytotoxic components driving increased lesion size in responding tumors across murine, canine and human GBM patients treated with RNA-LPAs. METHODS We treated neonatally implanted K2 DMGs with RNA-LPAs generated from tumor specific mRNA and used RNA sequencing and superspectral imaging to evaluate local tumor and tumor microenvironment (TME) damage response pathways in immunocompetent and immunocompromised mice. In canines and humans, we obtained pre-and post biopsy samples with serial MRI imaging following RNA-LPA treatment. RESULTS Treatment with RNA-LPAs elicits a local damage response detected by RNA sequencing in mice and canines. Treated mice have infiltrating innate and adaptive immune cell populations and patterns of reactive gliosis, as demonstrated by sequencing and superspectral imaging. Canines exhibited increases in damage response pathways including OAS/RNAase-L, CDK2NA and p53. Activation of damage response pathways drives immature monocytes towards an effector rather than suppressor phenotype enabling reprogramming of the glioma TME. Mobilization of myeloid cells associates with improved outcomes in an initial cohort of human glioblastoma patients undergoing RNA-LPA therapy per NCT04573140. In one patient, we observed a radiographically enlarging lesion revealed to be gliosis following biopsy, rather than tumor. CONCLUSION Tandem cytotoxic damage with immunologic response defines paraprogression, a novel imaging feature following RNA-LPA therapy.