Encapsidating artificial human papillomavirus-16 mE7 protein in human papillomavirus-6b L1/L2 virus like particles.

Background: Human papillomaviruses (HPVs) can infect squamous or mucosal epithelia and cause cervical cancer or genital warts. Coinfection with multiple HPV types is a common finding of many epidemiological studies. Therefore, it is necessary to develop a vaccine, which can eradicate established HPV infections and prevent other HPV infections. In this study, we generated chimeric virus like particles (cVLPs) composed of HPV-6b L1, HPV-6b L2 and one artificial HPV-16 mE7 proteins.

Methods: The artificial HPV-16 mE7 gene was designed by codon modification, point mutation and gene shuffling then chemically synthesized and subcloned behind HPV-6b L2. HPV-6b L1 and L2-mE7 were expressed in insect cells by using Bac-to-Bac system. The generated cVLPs were purified by CsCl gradient ultracentrifuge and analyzed by immunoblot, electron microscope and haemagglutination assay.

Results: The HPV-6b L1 and L2-mE7 proteins were well expressed in insect cells and could selfassemble into cVLPs, whose diameter was about 55 nm and similar to that of HPV-6b L1/L2 VLPs. Intact cVLPs could be recognized by H6.M48 neutralizing monoclonal antibody and HPV-6b L2 polyclonal antibody, while the denatured cVLPs, but not the intact cVLPs, were reactive to HPV-16 E7 polyclonal antibody. HPV-6b L1/L2-mE7 cVLPs haemagglutinated mouse erythrocytes as efficiently as HPV-6b L1/L2 VLPs did.

Conclusions: The insertion of the 158 amino acid HPV-16 mE7 protein behind L2 did not disrupt the correct assembling of cVLPs. The morphological characteristics and haemagglutinating activity of cVLPs were similar to those of HPV-6b L1/L2 VLPs. The cVLPs retained conformational B cell epitopes of HPV-6 VLPs and HPV-16 mE7 protein had an internal location in the cVLPs. Therefore, large modified E7 protein with higher immunogenicity could be incorporated into cVLPs by fusing to the C-terminus of L2, which would help to improve the therapeutic effects of L1/L2-E7 cVLPs.