Adaptation of transgene mRNA translation boosts the anticancer efficacy of oncolytic HSV1

Abstract

BackgroundTransgenes deliver therapeutic payloads to improve oncolytic virus immunotherapy. Transgenes encoded within oncolytic viruses are designed to be highly transcribed, but protein synthesis is often negatively affected by viral infection, compromising the amount of therapeutic protein expressed. Studying the oncolytic herpes simplex virus-1 (HSV1), we found standard transgene mRNAs to be suboptimally translated in infected cells.MethodsUsing RNA-Seq reads, we determined the transcription start sites and 5'leaders of HSV1 genes and uncovered the US11 5'leader to confer superior activity in translation reporter assays. We then incorporated this 5’leader into GM-CSF expression cassette in oncolytic HSV1 and compared the translationally adapted oncolytic virus with the conventional, leaderless, virusin vitroand in mice.ResultsInclusion of the US11 5’leader in the GM-CSF transgene incorporated into HSV1 boosted translationin vitroandin vivo. Importantly, treatment with US11 5’leader-GM-CSF oncolytic HSV1 showed superior antitumor immune activity and improved survival in a syngeneic mouse model of colorectal cancer as compared with leaderless-GM-CSF HSV1.ConclusionsOur study demonstrates the therapeutic value of identifying and integrating platform-specificcis-acting sequences that confer increased protein synthesis on transgene expression.