Novel TNFα-based strategies to overcome immune evasion in diffuse intrinsic pontine glioma
Hematology, Oncology
Pediatric and Adolescent Medicine
Final Report Abstract
Diffuse midline glioma (DMG) is a devastating brain tumour arising in children and young adults. With a two-year survival rate of less than 10% there is an unmet need for effective treatment strategies for these patients. 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 DMG cells by flow cytometry and identified B7- H3 and CD155 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). Our murine DMG models expressed CD155, but not B7-H3. Since we were interested in the function of these molecules in the context of an intact immune system, we focused on CD155, and investigated its role in immune evasion of DMG cells. 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 in OVA-positive DMG tumour cells led to a strong increase in T cell-mediated killing. In vivo, adoptive transfer of OT-I T cells into OVA-positive DMG-bearing immunocompromised 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 immunocompetent 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 in immunocompromised mice. Notably, FOXM1 was a top differentially downregulated master regulator in the absence of CD155, and Thiostrepton, an agent leading to not only reduced expression, but also diminished transcriptional activity of FOXM1, impaired viability of DMG cells, as opposed to healthy fibroblasts. 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 patients with this devastating disease.
Publications
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“CD155 regulates cell growth and immune evasion in diffuse intrinsic pontine glioma” in the International Symposium on Pediatric Neuro-Oncology (ISPNO), Hamburg, Germany, 2022
Theophilos Tzaridis
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"CD155 regulates cell growth and immune evasion in diffuse midline glioma” in the Annual Trainee Symposium of Sanford Burnham Prebys Medical Discovery Institute, San Diego, USA, 2023
Theophilos Tzaridis
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“CD155 regulates cell growth and immune evasion in diffuse midline glioma” in the Conference of the American Association of Cancer Research (AACR), San Diego, USA, 2024
Theophilos Tzaridis
