Poster Presentation NSW State Cancer Conference 2023

Features of immunotherapy response are prevalent in melanoma brain metastases compared to high grade gliomas (#161)

Bernadette Pedersen 1 2 , Elena shklovskaya 1 2 3 , Mal Irvine 1 2 , Brindha Shivalingam 2 4 5 , Kimberly L Alexander 3 4 6 , Georgina V Long 2 6 7 8 , Richard A Scolyer 2 6 9 , Helen Rizos 1 2
  1. Faculty of Medicine, Health and Human Sciences, Macquarie University, Sydney, NSW, Australia
  2. Melanoma Institute Australia, The University of Sydney, NSW, Sydney, Australia
  3. Department of Neurosurgery, Royal Prince Alfred Hospital, Sydney, NSW, Australia
  4. Department of Neurosurgery, Chris O’Brien Lifehouse, Sydney, NSW, Australia
  5. Department of Neurosurgery, Royal Prince Alfred Hospital, Sydney, NSW, Australia
  6. Faculty of Medicine and Health, The University of Sydney, Sydney, NSW, Australia
  7. Department of Medical Oncology, Northern Sydney Cancer Centre, Royal North Shore Hospital, Sydney, NSW, Australia
  8. Mater Hospital, Sydney, NSW, Australia
  9. Department of Tissue Pathology and Diagnostic Oncology , Royal Prince Alfred Hospital and New South Wales Health Pathology, Sydney, NSW, Australia

Introduction. The PD-1 and CTLA-4 Immune checkpoint inhibitors have dramatically improved outcomes for patients with advanced melanoma, including patients with asymptomatic melanoma brain metastases. In contrast, patients with high-grade glioma continue to  have poor prognosis, and anti-PD1 immunotherapy has failed to improve patient outcomes.

Methods. To gain insights  into immunotherapy response features in gliomas and melanoma brain metastases, we utilised multiparameter flow cytometry to profile melanoma brain metastases (MBM, n=27) and high-grade gliomas (n=30). Surgically resected MBM (n=27) or gliomas (n=14) were enzymatically digested and cryopreserved; alternatively, cryopreserved Cavitron Ultrasonic Surgical Aspirator (CUSA) fluids collected during glioma surgical resections, were used (n=16). All samples were stained for viable cells, definitive tumour markers (MBM: SOX-10; glioma: SOX-2) and immune fraction (CD45). Viable tumour cells (either SOX-2+ or SOX-10+) and immune cells (CD45+) were collectively considered “total live events”, subjected to downstream analyses.

Results. Immune (CD45+) fraction was elevated in gliomas (median, 72.6% of total) compared to MBM (median, 25.3%, Mann Whitney’s p<0.0001). However, T cells were more prevalent in the MBM samples (median, 45% of CD45+ cells, compared to 28.3% in glioma, p<0.01). There was a superior T-cell tumour reactivity (as measured by PD-1 expression and proliferation of T-cells) in MBM compared to glioma: Median PD-1 expression/proliferation was 92.8/23.4% (MBM) versus 64.4/6% (glioma) for CD8 T cells (p<0.0001). Tumour expression of MHC class I, MHC class II and PD-L1 was similar for the two tumour types, but tumour PD-L2 expression was 5-fold higher in glioma compared to melanoma cells. High PDL2 expression was maintained in 7/7 cell lines established from dissociated gliomas, and was further elevated in 6/7 lines after a 24-hour exposure to gamma-interferon.

Conclusion. This study confirms a prevalence of antigen-experienced T cells in MBM compared to gliomas, and suggest that high expression of the PD-L2 immune checkpoint in glioma may represent a targetable immune escape mechanism.