I'm a technican in a biotech company, and my work is to purify lentivirus vectors for downstream clinical trials. I've been using anion chromatography→TFF→SEC accompanied by benzonase( I usually use it after lentivirus harvest) to purify vectors, but there's still a trouble that the quantity of DNA and protein impurities(such as BSA) exceed the standards set by WHO (DNA is below 10ng/dose and total protein is 20ug/dose ,for us ,protein standard is easier relatively to achieve. Is there any reagents that could help remove these impurities? I considered substilisin ,which has been reported to have an ability to remove all extracellular vesicle secreted by cells producing lentivirus vectors , but I don't know whether it is feasible.