Potentiating Oncolytic Virus-Induced Immune-Mediated Tumor Cell Killing Using Histone Deacetylase Inhibition.

Victoria A Jennings,Hardev Pandha,Brian Keller,Richard G Vile,Oliver Donnelly,Gemma Migneco,Gina B Scott,Ailsa M.S Rose,Alan A Melcher,Karen J Scott,Donald Dewar,Kevin J Harrington,Katrina Reilly,Fiona Errington-Mais,Adel Samson,Howard Peach

doi:10.1016/j.ymthe.2019.04.008

Abstract

A clinical oncolytic herpes simplex virus (HSV) encoding granulocyte-macrophage colony-stimulating factor (GM-CSF), talimogene laherparepvec, causes regression of injected and non-injected melanoma lesions in patients and is now licensed for clinical use in advanced melanoma. To date, limited data are available regarding the mechanisms of human anti-tumor immune priming, an improved understanding of which could inform the development of future combination strategies with improved efficacy. This study addressed direct oncolysis and innate and adaptive human immune-mediated effects of a closely related HSV encoding GM-CSF (HSVGM-CSF) alone and in combination with histone deacetylase inhibition. We found that HSVGM-CSF supported activation of anti-melanoma immunity via monocyte-mediated type I interferon production, which activates NK cells, and viral maturation of immature dendritic cells (iDCs) into potent antigen-presenting cells for cytotoxic T lymphocyte (CTL) priming. Addition of the histone deacetylase inhibitor valproic acid (VPA) to HSVGM-CSF treatment of tumor cells increased viral replication, viral GM-CSF production, and oncolysis and augmented the development of anti-tumor immunity. Mechanistically, VPA increased expression of activating ligands for NK cell recognition and induced expression of tumor-associated antigens, supporting innate NK cell killing and CTL priming. These data support the clinical combination of talimogene laherparepvec with histone deacetylase inhibition to enhance oncolysis and anti-tumor immunity.

Highlights

Oncolytic viruses (OVs) are naturally occurring or genetically engineered viruses with specific anti-tumor effects mediated both by direct oncolysis and activation of innate and adaptive anti-tumor immunity
Representative histograms and the mean fold increase in expression compared with isotype controls + SEM are shown (n = 4). (E) Supernatants from melanoma cells treated with or without HSVGM-CSF and co-cultured with immature dendritic cells (iDCs) were collected, and the concentrations of GM-CSF, IL-10, and tumor necrosis factor alpha (TNF-a) were determined by ELISA
To confirm that natural killer (NK) cells were responsible for melanoma target cell death, in the context of PBMCs, we have shown that (1) depletion of NK cells from PBMCs significantly reduced killing of MEL888 cells (Figure S1A) and (2) that killing was mediated by perforin and granzyme because cell lysis was abrogated by EGTA, a calcium chelator that prevents the activity of calciumdependent perforin (Figure S1B)

Summary

Introduction

Oncolytic viruses (OVs) are naturally occurring or genetically engineered viruses with specific anti-tumor effects mediated both by direct oncolysis and activation of innate and adaptive anti-tumor immunity. A range of OVs has progressed to clinical studies, and some viruses (e.g., herpes simplex, vaccinia, and reovirus) have reached evaluation in randomized clinical trials.[1] The most clinically advanced agent (approved for use in the United States, Europe, and Australasia) is a genetically modified double-stranded DNA herpes simplex virus (HSV; JS-1 strain) called talimogene laherparepvec (T-Vec) This virus has been rendered tumor-selective through functional deletion of ICP34.5; further deletion of ICP47 enhances antigen presentation and brings the viral US11 gene under the control of the ICP47 immediate-early promoter, enhancing tumor-selective replication.[2] In addition, the ICP34.5 gene has been replaced with a cassette encoding human GM-CSF to facilitate priming of an anti-tumor immune response,[3] and an initial clinical report has confirmed that the virus can convert an immunologically suppressive “cold” tumor microenvironment (TME) into an immune-activating “hot” milieu.[4] T-Vec has a dual mode of action, causing direct tumor cell lysis and bystander activation of an anti-tumor immune response

Methods

Results

Conclusion