P12.06 Clinicopathological evaluation of PD-L1 expression and cytotoxic T-lymphocyte infiltrates across intracranial molecular subgroups of ependymomas

Abstract

Abstract BACKGROUND Immune check-point blockade targeting programmed cell death ligand-1 (PD-L1)/programmed death-1 (PD-1) axis has created paradigm shift in the treatment of advanced cancer. The prognosis of the ‘ST-RELA’ and ‘PF-A’ molecular subgroups of ependymomas (EPN) remains poor. This study aims to understand the potential candidature of EPNs for ICB. MATERIAL AND METHODS All supratentorial (ST) Grade II/III EPNs were classified into ST-RELA, ST-YAP and ST-not otherwise specified (NOS), based on L1CAM protein expression and/or presence of RELA/YAP1 fusion transcripts by RT-PCR. All posterior fossa (PF) BEPNs were classified into PF-A and PF-B based on H3K27me3 protein expression and chromosome 1q gain. Immunohistochemistry for PD-L1 (SP263, Ventana) and CD8 was performed. RelA protein enrichment at PDL1 promoter site was analysed by chromatin immunoprecipitation-qPCR (ChIP-qPCR) in three ST-RELA samples. RESULTS A total of 83 intracranial EPNs were included as follows: ST-RELA (n=32), ST-YAP (n=1), ST-NOS (n=11), ST-subependymoma (n=1), PF-A (n=25) and PF-B (n=13). Median tumor infiltrating CD8+ cytotoxic T-lymphocyte (CTL) density was 6/mm2, and was higher in ST EPNs (median 10/mm2) as compared to PF EPNs (median 3/mm2). PD-L1 protein expression in ≥1% tumor cells was noted in 17/83 (20%) of all EPNs, including 12/32 (37%) of ST-RELA and rare ST-NOS (2/11), PF-A (2/25) and PF-B (1/13) tumors. Twelve intracranial EPNs (14%, 12/83) showed high CTL density and concurrent PD-L1 positivity, of which majority (83%, 10/12) were ST-RELA EPNs. Enrichment of RelA protein was seen at PD-L1 promoter. CONCLUSION Increased CTL densities and upregulation of PD-L1 in ST-RELA ependymomas suggests potential candidature for immunotherapy.