TAMI-40. TUMOR MICROBIOME AND GLIOBLASTOMA (GBM)

Abstract Bacteria have been found to play major roles in many physiologic/disease processes including cancer. The presence of bacteria within brain tumors has never been explored. The aim of this study was to examine the microbiome of Glioblastoma. A cohort of 40 glioblastoma samples (FFPE), from two medical centers served for DNA extraction using a specialized extraction protocol that includes a bead beating step to ensure complete bacterial DNA recovery. A set of negative controls was introduced at different steps of the assay to identify and monitor contaminating bacterial DNA. We measured the levels of bacterial DNA in the samples using a RT-qPCR assay, amplifying the bacterial 16S rRNA gene and detected bacterial DNA in over 40% of the samples. To characterize the bacterial taxa that are present in GBM tumors, we applied 16S DNA sequencing on the samples. After implementing a stringent set of filters on the sequencing data, eliminating contaminating signal, we detected a total of 22 bacterial taxa in GBM tumors. To visualize bacteria in GBM tissues and learn about their localization within the tissue we used immunohistochemistry staining with anti-lipopolysaccharide (LPS) and anti-lipoteichoic acid (LTA) antibodies detecting gram negative and gram positive bacteria (correspondingly). Bacteria were also visualized by staining bacterial RNA using a 16S rRNA in situ hybridization assay. Staining of a human GBM tissue microarray (TMA) containing 32 cases of GBM showed that the majority of cases stained positive for LPS and ~40% were positive for 16S rRNA staining. Bacterial LPS and 16S rRNA were localized mainly inside the tumor cells. Our study demonstrates, for the first time, that bacteria or bacterial components are present in human Glioblastoma tumors. We are currently expanding our study cohort in order to better define the bacteria found within glioblastoma samples and assess their possible effects