There are very few actual laws about anything related to genetic engineering in the US, if you are not working with a "select agent" and are obviously working towards a useful and peaceful purpose. That said, there are lots of guidelines set forth by the NIH if you are receiving funding through them, and they are designed to maximize safety when handling viruses etc. An incompetent lentivirus is just another piece of DNA until you pair it with a helper virus that replicates. All the commercial lentiviral transfection systems contain both and are thus biosafety level 2, requiring a laminar flow hood and a negative pressure room. Seeing as how efficiently they transform mammalian cells, I would not want to work with them outside a BSL2 facility.