Engineering a novel HSV-1 strain for oncolytic therapy of solid tumors.

Oncolytic herpes simplex virus (HSV)-1-derived viruses are being developed for cancer treatment. Here, we describe the isolation of a novel strain of HSV-1 and its engineering to safely harness it as an oncolytic therapeutic. This strain (UT1a) was isolated from a de-identified consented patient biorepository. CRISPR-Cas9-based recombination was utilized to insert bacterial artificial chromosome (BAC) genes into the viral and locus, resulting in the deletion of both large and small subunits of the viral ribonucleotide reductase (RR). Subsequent deletion of viral genes encoding the neurovirulence factor γ34.5 resulted in OncoDelta (OncoD), a virus deleted for , , and both copies of . OncoD retained tumor-cell-specific cytotoxicity and replication; was safe and non-toxic in intracranial injections in naive mice up to doses of 5 × 10, the maximal injectable dose for OncoD; and showed significant anti-tumor immune-activating potential in multiple tumor models. Transcriptome profiling of OncoD showed that it impaired DNA damage repair pathways and hence synergized with radiation to improve therapeutic response and .