To analyze Gag expression, in brief, 1610 6 HEK293 cells were infected with various vectors at 100 IFU per cell. Cell lysates were collected after 24 hours and subjected to four freeze-thaw cycles to obtain crude cell lysate. 10 mg of protein was boiled in Laemmli sample buffer for 10 minutes and resolved on 4 to 15% sodium dodecyl sulfate-polyacrylamide gel. The proteins were transferred to polyvinylidene fluoride membrane and staining was performed with Gag antibody (1:1,000) (Affi-anti-HIV matrix IgY, Genway Biotech, Inc.), followed by secondary staining with HRP-linked goat-chicken IgY (1:2,000) (Aves Lab, Inc). The proteins were detected on the polyvinylidene fluoride membrane by staining with 3939-diaminobenzidine tablets (Sigma-Aldrich, St. Louis, MO).