Bioluminescent proteins for in vivo optical imaging are enzymes that upon interaction with a substrate emit light. Commonly used enzymes are firefly luciferase, renilla, gaussia, clickbeetle and bacterial luciferase. Easy to use lentivirus vectors encoding firefly luciferase luc2 pGL4 are readily available to generate stable luciferase cell lines for in vivo bioluminescence imaging.