Design of an interferon-resistant oncolytic HSV-1 incorporating redundant safety modalities for improved tolerability

Abstract Development of next-generation oncolytic viruses requires the design of vectors that are potently oncolytic, immunogenic in human tumors, and well tolerated in patients. Starting with a joint-region deleted HSV-1 to create large transgene capability, we retained a single copy of the ICP34.5 gene, introduced mutations in UL37 to inhibit retrograde axonal transport, and inserted cell type-specific microRNA target cassettes in HSV-1 genes essential for replication or neurovirulence. Ten microRNA candidates highly expressed in normal tissues and with low or absent expression in malignancies were selected from a comprehensive profile of 800 microRNAs with an emphasis on protection of the nervous system. Among the genes essential for viral replication identified using a siRNA screen, we selected ICP4, ICP27, and UL8 for microRNA attenuation where a single microRNA is sufficient to potently attenuate viral replication. Additionally, a neuron-specific microRNA target cassette was introduced to control ICP34.5 expression. This vector is resistant to Type I interferon compared to an ICP34.5 deleted oncolytic HSVs, and in cancer cell lines, the oncolytic activity of the modified vector is equivalent to its parental virus. In vivo, this vector potently inhibits tumor growth while being well tolerated, even at high intravenous doses, compared to parental wild-type HSV-1.