Abstract 2648: CD155 regulates cell growth and immune evasion in diffuse midline glioma

Abstract There is an unmet need for effective treatment strategies for diffuse midline glioma (DMG), a devastating brain tumour arising in children and young adults. While immunotherapy is emerging as a powerful approach for treatment of other cancers, clinical trials with immune checkpoint inhibitors have failed to show a survival benefit for DMG patients. In this study, we analysed the expression of known immune checkpoint molecules on the surface of human and murine DMG cells by flow cytometry and identified CD155 and B7-H3 as the most highly expressed checkpoint molecules, with minimal expression of others, including PD-L1 and PD-L2. These findings were confirmed in primary patient samples from pediatric brain tumours (gliomas, medulloblastomas and ependymomas). To test whether CD155 regulates susceptibility to CD8+ T cell killing, we cultured murine DMG cells expressing ovalbumin (OVA) with CD8+ T cells from OT-I mice, which express T cell receptors specific for OVA. shRNA mediated silencing of CD155 led to a strong increase in T cell-mediated killing. In vivo, adoptive transfer of OT-I T cells into OVA-positive DMG-bearing immuno-compromised mice resulted in delayed tumour growth, and this effect was enhanced when tumours lacked CD155. Strikingly, CD155-deficient DMG cells failed to grow at all in immuno-competent mice, and depletion of CD8 T cells allowed these tumours to grow, highlighting a role for CD8 T cells in rejection of CD155-deficient cells. In addition to its effects on susceptibility to T cells, CD155 also exerted cell-autonomous effects on tumour cells: silencing of CD155 led to induction of apoptosis of DMG cells in vitro and to delayed tumour growth in vivo, even in immune-compromised mice. These studies demonstrate that CD155 functions as an immune checkpoint and as a regulator of tumour cell survival in DMG, and suggest that targeting CD155 could be a valuable double-pronged therapeutic strategy for this devastating disease. Citation Format: Theophilos Tzaridis, Tanja Eisemann, Augusto Faria Andrade, Jennifer L. Hope, Oren Becher, Nada Jabado, Linda M. Bradley, Peter Adams, Robert Wechsler-Reya. CD155 regulates cell growth and immune evasion in diffuse midline glioma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2648.