Stable high-level expression of truncated human papillomavirus type 16 L1 protein in Drosophila Schneider-2 cells.

To improve the existing human papillomavirus type 16 (HPV16) virus-like particle (VLP) preparation, the Drosophila inducible/secreted expression system, a highly efficient, economical method, was used to produce HPV16 VLPs. Drosophila Schneider-2 cells were cotransfected with pMT/BiP/V5-His expression vector containing the target gene encoding HPV16L1 protein without nucleus localization sequence and the selection vector pCoHygro plasmids at the ratio of 4:1. The stabled hygromycin-resistant cell line was obtained 1 month later, and the protein expression was induced by copper sulfate. The molecular mass of expressed HPV16L1 protein was 66 kDa, as revealed by SDS-PAGE, and confirmed by Western blot analysis. The yield of HPV16L1 protein was 0.554 mg per 1x10(7) cells. The characteristics of HPV16L1 protein were further analyzed by mouse erythrocyte hemagglutination assay, hemagglutination inhibition assay, and transmission electron microscopy. Results showed that the truncated protein was as biologically active as natural HPVL1 protein, inducing murine erythrocyte agglutination and VLP formation. These findings indicate that the Drosophila inducible/secreted expression system is promising as a convenient and economical method for the preparation of HPV16 VLP vaccine.