Schematic representation of lentiviral vector. CMV indicates cytomegalovirus immediate early promoter; cG, canine granulocyte colony-stimulating factor cDNA; ΔLTR, long terminal repeat with majority of U3 region deleted; RSV, Rous Sarcoma Virus enhancer/promoter; RRE, rev responsive element; cPPT, HIV-1 central polypurine tract; and PRE, hepatitis B virus posttranscriptional regulatory element.