Abstract: Objective To produce human papillomavirus(HPV) type 31 L1 virus-like particle(VLP) vaccine in baculovirus system. Methods A C-terminal 27 residues truncated HPV31 L1 gene (HPV31 L1MΔC) which optimized with Sf9 cell bias condons, was synthesized and expressed in baculovirus system. Cells infected with HPV31 L1MΔC recombinant baculovirus were lysed by sonification, or incubation with either ionic surfactant-containing buffer or nonionic surfactant-containing buffer, and the supernatants were harvested respectively for expression assays. The supernatants prepared by incubation with nonionic surfactant-containing buffer were purified by CsCl ultracentrifugation and HPV31 L1MΔC protein was identified by dynamic light scatter (DLS) and transmission electronic microscopy (TEM). BALB/c mice were immunized with 0.1 μg HPV31 L1MΔC VLP intramuscularly at weeks 0, 2 and sera at week 4 were taken for neutralization assay against HPV31 pseudovirus. Results HPV31 L1MΔC protein was expressed in all three kinds of supernatants prepared by either sonification or incubation with two different surfactant-containing buffer, and amounted for 10% of the total proteins. The yield of purified HPV31 L1MΔC was up to 11.5 mg per liter suspension medium. HPV31 L1MΔC protein showed an average hydrodynamic diameter of 103.3 nm with a mean polydispersity index of 0.190 by DLS, and presented VLP with an average diameter of 50~60 nm which is similar to native virions by TEM. HPV31 L1MΔC VLP induced high titer of HPV31 neutralizing antibody (1,440) in mice. Conclusions The VLP produced with HPV31 L1MΔC truncated gene in baculovirus system is a promising candidate for development of multivalent HPV L1VLP vaccine for its high yield and potent immunogenicity.

Key words: human papillomavirus type 31 L1, virus-like particle, neutralizing antibody, insect cells