The virus constructed is activated by doxycycline. In order to activate the virus, we wait 2 weeks after retro-orbital injection to ensure the virus has been taken up by the cells, and then begin doxycycline treatment. The mice receive a doxycycline feed daily, as well as a doxycycline injection of 2mg/kg twice weekly. The mice remain on this doxycycline diet and injections until they are culled.