P07.05 Intravenous delivery of oncolytic reovirus to brain tumours in patients to immunologically prime for sequential checkpoint blockade

Abstract Introduction: Therapies targeting T-cell inhibitory checkpoint signalling pathways are redefining cancer survival in many solid malignancies. Unfortunately only a minority of patients respond, with mounting evidence that tumour response and patient survival are significantly associated with the presence of tumour PD-L1 expression, which prevents immune activation in situ within the tumour. We hypothesised that pre-conditioning of the tumour immune microenvironment using targeted, virus-mediated interferon stimulation, would upregulate PD-L1 protein expression and improve the efficacy of sequential checkpoint blockade. Oncolytic viruses (OV) stimulate anti-tumour immunity, and represent a promising novel form of cancer immunotherapy. However almost all brain tumour studies to date administer OV via intra-lesion injection, following a largely untested belief that intra-venous (IV) administration will not deliver virus to this site, due to exclusion by the blood brain barrier. Materials and Methods: In this window-of-opportunity clinical study 9 patients were injected IV once with 1x1010 TCID50 of oncolytic human Orthoreovirus (reovirus) ahead of planned surgical resection of their brain tumour. Following resection, tumour tissue was analysed by RNAseq and virus presence assayed by IHC, in-situ-hybridisation, electron microscopy and qPCR. Virus regulated expression of PD1/PDL1 axis was determined in ex vivo brain tumour culture, and intracranial tumour models were used to assess combination treatment of OV and checkpoint therapy. Results: Here we show that IV injection of reovirus leads to infection of tumour cells both in high grade glioma and brain metastases. Reovirus σ3 protein and RNA were detected in all tumour samples by at least one detection method. RNAseq analysis indicated reovirus upregulates interferon-regulated gene expression in tumours, and we further show in stem-like cell lines and ex vivo primary human tumour cultures that the PD-1/PD-L1 axis is altered across both target tumour and immune effector cells via an IFN-mediated mechanism. Finally, in a pre-clinical glioma model we demonstrate significantly enhanced clinical therapy using combination treatment of PD-1 blockade and reovirus. CONCLUSION: These results support the development of novel combination, systemic immuno-virotherapy strategies for the treatment of both primary and secondary tumours in the brain.