Incorporation of a truncated form of flagellin (TFlg) into porcine circovirus type 2 virus-like particles enhances immune responses in mice

Abstract

Background: Porcine circovirus type 2 (PCV2) is an economically important pathogen in the swine industry worldwide. Vaccination remains the principal tool to control PCV2-associated diseases (PCVADs). Current vaccines do not eliminate viral shedding in the environment. To enhance the efficacy of PCV2 vaccines, recombinant viruslike particles (VLPs) of PCV2 were generated by fusing a truncated form of flagellin FliC (TFlg: 85-111aa) with the PCV2 capsid protein (Cap). Results: The recombinant proteins were expressed in Escherichia coli and detected using Western blotting. The abilities of the recombinant proteins to assemble into VLPs were observed under transmission electron microscopy (TEM). The protective immune responses of recombinant VLPs were further evaluated by immunization of mice. The results showed that insertion of TFlg into C terminal of the Cap protein did not affect the formation of VLPs and boosted both humoral and cellular immune responses in mice. After a challenge with PCV2, in the Cap-TFlg vaccinated group, viremia was milder and viral loads were lower as compared with those in the Cap vaccinated group.Conclusion: These results suggest that recombinant VLPs of PCV2 containing a TFlg adjuvant can be used as a promising PCV2 vaccine candidate.

Immunogenicity and Protective Activity of Pigeon Circovirus Recombinant Capsid Protein Virus-Like Particles (PiCV rCap-VLPs) in Pigeons (Columba livia) Experimentally Infected with PiCV

“…Similarly, VLP immunization in mice and guinea pigs was able to significantly induce specific antibody responses to PCV2 Cap [42]. Meanwhile, in another study [43], the protective immune responses of a VLP-based PCV2 vaccine enhanced by the incorporation of a truncated form of flagellin significantly reduced viral loads in lung samples from mice. PiCV viral loads in the spleens of naturally infected nonvaccinated pigeons were also reportedly higher than those of the naturally infected pigeons vaccinated with recombinant PiCV Cap vaccine formulation [1].…”

“…Specifically, the VLP group displayed a T cell proliferation stimulation index that is twice higher and IFN-γ fold change that is thrice higher as compared with the control group. A similar study on PCV2 VLPs demonstrated that after the vaccination with VLP, the level of IFN-γ production was higher than with Cap vaccine [43]. Administration of VLPs enhanced the T helper type 1 (Th1), which promotes inflammatory responses through the secretion of cytokines such as gamma interferon (IFN-γ) that activate macrophages and provide help to CD8+ cytotoxic T cells [45].…”

Targeted Delivery of Nanovaccine to Dendritic Cells via DC-Binding Peptides Induces Potent Antiviral Immunity in vivo

“…Several studies have demonstrated the potential to allow insertion or substitution of small fragments of foreign peptides of C terminal of PCV2 Cap without apparent negative effect on formation of VLPs. 19 , 37 In the present study, different DC-binding peptides were introduced into C-terminal of PCV2 Cap, and fusion proteins were expressed in soluble form. After one-step Ni-NTA affinity purification, Cap-DCbp fusion proteins form highly organized VLPs with similar morphology.…”

“…To determine the titers of anti-PCV2 neutralizing antibodies (NAbs) in serum samples, VNT was performed as described previously. 19 Briefly, 4×10 5 PK-15 cells were pre-seeded into 96-well plates and cultured in DMEM containing 10% FBS at 37°C for 24 h. Heat-inactivated serum samples were 2-fold serially diluted to 1:256. 100 μL of each diluted sample was mixed with an equal volume of PCV JH (200 TCID 50 ) and added to the cells, and allowed to interact for 1 h at 37°C.…”

“… 13 A series of strategies has been proposed to enhance the immunogenicity of the subunit vaccine, including the employment of cytokine adjuvants, 14–16 the development of Cap VLP-based vaccine 17 , 18 or chimeric Cap VLP containing small molecules as adjuvants. 19 , 20 However, deepened studies in Cap VLP delivery and the related efficacy mechanism are not widely available.…”