Single Versus Repeated Intravenous Oncolytic Virus Infusions: Implications for Rationalised Scheduling of Therapy in Hepatocellular Carcinoma.

Scheduling of oncolytic virus (OV) therapy has never been correlated with immunological /clinical response. In hepatocellular carcinoma (HCC) patients, where background liver is frequently chronically injured, repeated dosing may have deleterious implications, resulting in off-target immune-mediated damage, thereby tipping the balance between favourable clinical response and hepatotoxicity. Elucidation of the optimum dosing regime is paramount to ensure therapy, whilst limiting damage to background liver. We expand upon our experience in neoadjuvant OV therapy to compare immunological responses from single versus repeated doses of reovirus in cancer patients. The impact of OV on HCC outcomes was examined in vivo following a high-fat diet or induced liver fibrosis in the context of abnormal background liver. Furthermore, we assess the potential immune-mediated toxicity of single versus multiple virus infusions in combination with PD-1/PD-L1 blockade. Data indicate that a single dose of reovirus is equivalent or superior to repeated doses in achieving: (a) induction of an inflammatory cytokine/chemokine response; (b) peripheral blood immune cell activation; (c) migration of activated CD8+ CTLs. Repeated doses on consecutive days do not improve the amplitude of immune response following virus infusion. Furthermore, without improving therapeutic efficacy, repeated viral dosing leads to an unwanted influx of activated T-cells into background liver, alongside elevated liver enzymes associated with aberrant liver function. A single dose of reovirus is as effective as multiple doses when combined with anti-PD-L1 therapy in limiting tumour growth and extending survival in vivo, whilst simultaneously avoiding undesirable toxicities in background liver, in the context of HCC. Novelty and Impact StatementIn solid malignancies, the optimum dosing schedule of oncolytic virotherapy thus far has not been correlated with clinical or immunological response. In hepatocellular carcinoma, background liver is frequently injured and repeated viral infusions may have harmful repercussions, tipping the balance from favourable clinical response to further hepatotoxicity. Here, we provide pivotal data that elucidates a rationalised reovirus dosing regimen, with and without checkpoint inhibition, which ensures therapy whilst limiting damage to compromised background liver.