Immune checkpoint inhibitors, including those targeting programmed cell death protein 1 (PD-1), are reshaping cancer therapeutic strategies. Evidence suggests, however, that tumor response and patient survival are determined by tumor programmed death ligand 1 (PD-L1) expression. We hypothesized that preconditioning of the tumor immune microenvironment using targeted, virus-mediated interferon (IFN) stimulation would up-regulate tumor PD-L1 protein expression and increase cytotoxic T cell infiltration, improving the efficacy of subsequent checkpoint blockade. Oncolytic viruses (OVs) represent a promising form of cancer immunotherapy. For brain tumors, almost all studies to date have used direct intralesional injection of OV, because of the largely untested belief that intravenous administration will not deliver virus to this site. We show, in a window-of-opportunity clinical study, that intravenous infusion of oncolytic human Orthoreovirus (referred to herein as reovirus) leads to infection of tumor cells subsequently resected as part of standard clinical care, both in high-grade glioma and in brain metastases, and increases cytotoxic T cell tumor infiltration relative to patients not treated with virus. We further show that reovirus up-regulates IFN-regulated gene expression, as well as the PD-1/PD-L1 axis in tumors, via an IFN-mediated mechanism. Finally, we show that addition of PD-1 blockade to reovirus enhances systemic therapy in a preclinical glioma model. These results support the development of combined systemic immunovirotherapy strategies for the treatment of both primary and secondary tumors in the brain.

Pancreatic ductal adenocarcinoma (PDAC) has a poor prognosis, with 1 and 5-year survival rates of ~18% and 7% respectively. FOLFIRINOX or gemcitabine in combination with nab-paclitaxel are standard treatment options for metastatic disease. However, both regimens are more toxic than gemcitabine alone. Pelareorep (REOLYSIN^®), a proprietary isolate of reovirus Type 3 Dearing, has shown antitumor activity in clinical and preclinical models. In addition to direct cytotoxic effects, pelareorep can trigger antitumor immune responses. Due to the high frequency of RAS mutations in PDAC, we hypothesized that pelareorep would promote selective reovirus replication in pancreatic tumors and enhance the anticancer activity of gemcitabine. Chemotherapy-naïve patients with advanced PDAC were eligible for the study. The primary objective was Clinical Benefit Rate (complete response (CR) + partial response (PR) + stable disease (SD) ≥ 12 weeks) and secondary objectives include overall survival (OS), toxicity, and pharmacodynamics (PD) analysis. The study enrolled 34 patients; results included one partial response, 23 stable disease, and 5 progressive disease. The median OS was 10.2 months, with a 1- and 2-year survival rate of 45% and 24%, respectively. The treatment was well tolerated with manageable nonhematological toxicities. PD analysis revealed reovirus replication within pancreatic tumor and associated apoptosis. Upregulation of immune checkpoint marker PD-L1 suggests future consideration of combining oncolytic virus therapy with anti-PD-L1 inhibitors. We conclude that pelareorep complements single agent gemcitabine in PDAC.

The Cystic Fibrosis Transmembrane conductance Regulator (CFTR) is a chloride channel that primarily resides in airway epithelial cells. Decreased CFTR expression and/or function lead to impaired airway surface liquid (ASL) volume homeostasis, resulting in accumulation of mucus, reduced clearance of bacteria, and chronic infection and inflammation.

Programmed death-ligand 1 (PD-L1) can reduce the immune response by inhibiting CD8 T-cell proliferation and cytotoxic activity. We studied a series of human viral (molloscum, human papillomavirus, herpes simplex, cytomegalovirus, Epstein-Barr virus, smallpox) and bacterial infections (Helicobacter pylori) for the in situ expression of PD-L1, mononuclear cell infiltration, and CD8 activity and compared this to noninfectious idiopathic inflammatory conditions to better define which immune responses may be more highly correlated with an infectious agent. Each viral and bacterial infection showed an increased PD-L1 expression that was most prominent in the mononuclear cell/CD8+ infiltrate surrounding the infection. However, the CD8 cells were mostly quiescent as evidenced by the low Ki67 index and minimal granzyme expression. Using a melanoma mouse model, acute reovirus infection increased PD-L1 expression, but decreased CD8 cytotoxic activity and Treg (FOXP3) cell numbers. In comparison, idiopathic noninfectious chronic inflammatory processes including lichen sclerosis, eczema, Sjogren’s disease, and ulcerative colitis showed a comparable strong PD-L1 expression in the mononuclear cell infiltrates but much greater Treg infiltration. However, this strong immunosuppressor profile was ineffective as evidenced by strong CD8 proliferation and granzyme expression. These data suggest that viral and bacterial infections induce a PD-L1 response that, unlike noninfectious chronic inflammatory conditions, dampens the activity of the recruited CD8 cells which, in turn, may enhance the ability of anti-PD-L1 therapy to eliminate the infectious agent.