IMMU-44. CIRCULATING CELL-FREE DNA DIRECTLY INHIBITS T CELL FUNCTION AND CONTRIBUTES TO PERIPHERAL IMMUNOSUPPRESSION IN EXPERIMENTAL GBM

Abstract

Abstract Glioblastoma (GBM) is aggressive form of brain cancer that is associated with severe peripheral immunosuppression. This immunosuppression is a critical barrier to patient survival and the success of immunotherapies. Immunocompetent mice harboring intracranial gliomas present with the hallmark features of peripheral immunosuppression observed in GBM patients, including T cell lymphopenia. Using parabiosis, we determined that T cell lymphopenia can be transferred from glioma-bearing to healthy mice via circulation This led to the identification of a high molecular weight immunosuppressive factor in sera of glioma-bearing mice that inhibits T cell proliferation ex vivo. Proteomics analysis identified 119 proteins uniquely upregulated in the sera of glioma-bearing mice compared to controls. These proteins are associated with pathways involved in DNA response elements, cell death, and DNA-histone complexes which imply DNA release. Additional analysis revealed serum isolated from glioma-bearing mice harbor significantly higher concentrations of double stranded cell free DNA (cfDNA) compared to controls. Reducing DNA content using DNase partially reverses the proliferation defects observed in T cells when exposed to serum of glioma-bearing mice. This is while, addition of cfDNA purified from serum of glioma-bearing mice, but not genomic DNA, potently inhibited T cell function. These results were AIM2 independent implicating a novel pathway of cfDNA sensing in T cells. We contend that cfDNA induces immunosuppressive effects in experimental GBM. Devising strategies to reduce circulating cfDNA is therefore a therapeutic approach that could improve outcomes in GBM patients.