CSF2 and cancer: Indeed, there is a precedent for striking improvement of oncolytic efficacy by simple backbone reengineering: T-VEC, the herpes simplex virus 1–based vector approved as cancer therapeutic in the US and Europe, was generated based on transferring cancer specificity–conferring mutations from an over-attenuated laboratory strain to a wild-type backbone and arming the virus with a gene encoding GM-CSF [17].