CNSC-30. CD4 T CELLS MEDIATED UPREGULATION OF CCL4 CHEMOKINE DRIVES GLIOBLASTOMA TUMOR MICROENVIRONMENT REPROGRAMMING FOLLOWING TREATMENT WITH A NOVEL MRNA VACCINE

Intra-tumoral immunosuppression is a major cause of treatment failure for patients with glioblastoma (GBM). Our group has developed a proprietary vaccine that combines mRNA encapsulated in lipid nanoparticles with PEG hydrogel and a chemokine (CXCL9). This hydrogel-chemokine-mRNA (HCM) vaccine is delivered subcutaneously (SQ) and results in significant anti-tumor efficacy in syngeneic murine glioma models. The objective of this study was to evaluate the effects of the vaccine on the tumor microenvironment (TME).

C57BL/6 mice underwent intracranial implantation of KR158-luc tumor cells and underwent SQ injection of the HCM vaccine using total tumor mRNA. Tumors were collected for analysis. Q-PCR and flow cytometry were done to evaluate the differential gene expression and CCR5 expression (receptor for CCL4) in the TME.

CCL4 was found to be upregulated in tumor-bearing animals treated with HCM vaccine using PCR. In a separate experiment, CCL4 blockade was given prior to HCM vaccination and this resulted in abrogation of the survival benefit of the vaccine. Next, flow cytometry was performed and microglia in the TME had the highest expression of the CCR5 receptor. CD4 T cells in the TME had significantly increased CCL4 expression after treatment with HCM vaccine.

The HCM vaccine results in significant anti-tumor efficacy in murine syngeneic murine glioma which is dependent on upregulation of CCL4 in the TME driven by CD4 T cells. The CCL4 exerts its effect through microglia expressing CCR5 in the TME. Further analysis of the effects of vaccination on microglia phenotype and function are underway.