518 Identification of Tumor Infiltrating Leukocytes in Glioblastoma and Clinical Outcomes

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INTRODUCTION: Glioblastoma (GBM) accounts for 60% of all malignant brain tumors in adults with a dismal 5-year survival rate of 5%. Treatment challenges stem from GBM’s intricate biology, therapy-resistant tumor cells, favorable milieu, invasive properties, and immunosuppressive tumor-infiltrating leukocytes (TIL). These cells are pro-repair and provide an immune inhibitory function, thereby conferring an elusive and protective phenotype to malignant cells. The clinical association with outcomes and response of these cell types to chemotherapeutics remains largely uncharacterized. METHODS: Fresh GBM tumor samples were collected. Using flow cytometry, tumor-specific and TIL-specific antibodies are used to label these cells. GBM and TIL phenotype within each sample is correlated to patient outcome to understand how those are related to the successes and failures of treatment. In addition, these cells are subjected to a different chemotherapeutics to assess their response to therapy. RESULTS: Patients’ mean age was 66.3 y, 15 patients (62%) were female. There was variable expression of EFGR and PDFRA within and between tumors. TIL represent approximately 20% of the cells in the samples. Myeloid cells represent most TIL (86%) in most samples. MGMT promoter un-methylated status was associated with high proportion of MDSC (34%) and poor survival. Correlations between TIL and GBM immunophenotypes were observed such as an inverse correlation between EGFR expression and MDSCs. Drug-screening is currently underway. CONCLUSIONS: The MDSC and EGFR inverse correlation suggests a possible relationship between tumor cells and TIL, supported by studies showing a release of pro-repair cytokines with EGFR signaling. Similarly, T-cells were positively correlated with EGFR expression. These findings strengthen the evidence of the protective role of TIL in GBM. Chemotherapeutics are being currently studied to assess impact on tumor viability.