514P Immunophenotypic profile of glioblastoma microenvironment: A cohort study

Glioblastoma (GBM) is the most aggressive brain tumor in adults and is characterized by an immunosuppressive microenvironment. Different factors shaping its tumor microenvironment (TME) regulate tumor initiation, progression, and treatment response. The aim of this study was to characterize the TME and the expression of immunomodulatory targets in patients (pts) with GBM. Immunohistochemistry for CD3, CD4, CD8, programed death ligand 1 (PD-L1) and programed death 1 (PD1) was performed on surgical tumor specimens from pts diagnosed with GBM, according to the CNS WHO 2021 criteria. A descriptive statistic was applied to the data set. OS and PFS were estimated through the Kaplan-Meier method and analyzed by the means of a log-rang test. We included 30 pts, with median age of 59.8 years [range 40.2-69.1 years]. All pts were treated with surgery followed by temozolomide concurrent with and adjuvant to radiotherapy. MGMT was methylated in 46.7% of pts and unmethylated in 53.3% of pts. Overall CD4+ lymphocytes, both intratumoral and perivascular, were significantly more represented than CD8+ lymphocytes in the GBM TME (p= 0.01). A lower density of CD4+ lymphocytes (<10%) was found to be a favorable prognostic factor for GBM outcome (p= 0.02). Pts with MGMT methylated and unmethylated tumors exhibited a distinct TME composition, with a significant higher number of perivascular CD8+ lymphocytes (p= 0.002), intratumoral CD8+ lymphocytes (p= 0.0024) and perivascular CD4+ lymphocytes (p=0.014) in MGMT unmethylated compared to MGMT methylated tumors. PD-L1 expression in GBM cell surface was 13.3% (n=4) and PD1 was expressed in 30% (N=9) of the GBM-infiltrating T cells, with predominantly perivascular distribution. CD4+ lymphocytes lower density (<10%) correlates with improved survival. Given the small numbers of our cohort, the prognostic value of CD4+ lymphocytes density needs to be validated in large-scale studies. MGMT methylated and unmethylated tumors exhibit different immune profiles, reflecting the different biology of these tumors. The expression of PD-L1 and PD1 in GBM patients is confined to a small subpopulation.