107. Tracking Target Cell Fate After Oncolytic Herpes Simplex Virus Infection

Abstract

Oncolytic virus (OV) cancer therapy relies on virus-mediated selective killing of cancer cells and subsequent secondary effects that involve induction of anti-tumor immunity. Although cell death induction is a prerequisite in this therapeutic process, experimental evidence is lacking as to whether OV infection of cancer cells results in their inevitable death. To address this issue, we developed an experimental platform that allows us to track the fate of a cell following OV infection. This system is composed of: 1) Recombinant oncolytic herpes simplex viruses derived from G47delta (ICP6-, gamma34.5-, alpha47-) and MG18L (ICP6-, Us3-) that express a Cre recombinase-EGFP fusion protein (G47delta-CreGFP and MG18L-CreGFP), and 2) tumor cell lines that have been engineered to stably carry a reporter construct, in which Cre-mediated excision of a polyA STOP sequence converts the cell into an expresser of the mCherry fluorescence protein. Using patient-derived and established T98 glioblastoma lines, we show that upon G47delta-CreGFP or MG18L-CreGFP infection, the reporter cells become mCherry positive, indicating virus-induced Cre recombination in the host genome. Monitoring of these cells in culture revealed that although an overwhelming majority of the cells die, a small fraction of mCherry+ cells survive and eventually proliferate. Our results demonstrate the existence of “resistance” after OV infection of cancer cells. Our experimental platform should have versatile utilities for tracking the fate of both neoplastic and non-neoplastic cells during OV therapy in in vitro and in vivo settings.