Encapsidated-CpG ODN enhances immunogenicity of porcine circovirus type 2 virus-like particles.

A DNA fragment containing CpG motifs (CpG ODN) is one of the potent immunopotentiators used to improve vaccine efficacy. It can enhance a protective immunity by stimulating both innate and adaptive immune responses. In this study, we designed and constructed a recombinant plasmid carrying the combined CpG ODN to generate an immunopotentiator for boosting the immunogenicity of porcine circovirus type 2 (PCV2) virus-like particles (VLPs). The capsid protein of PCV2b was expressed in insect cells and purified by affinity chromatography. The purified capsid protein was incubated with the CpG ODN in the reaction that allowed VLPs formation and encapsidation of the CpG ODN to occur simultaneously. Morphology of the reassembled VLPs was similar to the PCV2 virions as observed using an electron microscope. When the CpG ODN-encapcidated VLPs was treated with DNase I, the VLPs could protect the packaged CpG ODN from the enzyme digestion. Moreover, we immunized mice subcutaneously with VLPs, CpG ODN-loaded VLPs, or phosphate buffer saline for three times at two-week intervals. The results showed that the CpG ODN-loaded VLPs could elicit significantly higher levels of PCV2-specific neutralizing antibodies and interferon gamma (IFN-γ) expression in the immunized mice compared to those conferred by the VLPs alone. Conclusively, we have proved that the CpG ODN incorporated in VLPs can serve as a potent immunopotentiator for PCV2 vaccine development.

The immunogenicity of the secretory GΔTM protein of bovine ephemeral fever virus stably expressed by mammalian cells.

Bovine ephemeral fever virus (BEFV) causes an acute febrile disease in cattle and water buffalo. The disease has an impact on dairy and beef production in tropical and subtropical countries. Vaccination is used for disease prevention and control. In this study, we developed a recombinant lentivirus to produce mammalian stable cells expressing histidine-tagged BEFV G protein with a deleted transmembrane domain (GΔTM) as a secretory protein. In addition, guinea pigs were immunised with the purified GΔTM protein and booster immunised at a 3-week interval. The mammalian stable cells were able to continuously produce GΔTM protein for a minimum of 25 passages. All of the mammalian stable cells expressing GΔTM protein could react specifically with a BEFV convalescent bovine serum. Serum samples from the immunised guinea pigs could react strongly and specifically with the purified GΔTM protein. Moreover, post-immunised guinea pig sera contained antibodies that could neutralise BEFV. These results indicate that the G protein without a transmembrane domain can be used as a subunit vaccine for the prevention and control of BEFV. The availability of the mammalian stable cells, which constitutively express GΔTM protein, could facilitate the potential use of the secretory protein for BEFV diagnosis and vaccine development.