Expression and immunogenicity of secreted forms of bovine ephemeral fever virus glycoproteins applied to subunit vaccine development

A novel epitope tag from rabies virus has versatile in vitro applications

Fusion tag technology is an important tool for rapid separation, purification, and characterization of proteins. Combined with monoclonal antibodies, tag epitope systems can be rapidly adapted to many assay systems. A monoclonal antibody that reacts with the matrix protein of the rabies virus CVS-11 strain was reported. The epitope (termed M) targeted by this antibody contains only six amino acids. We examine whether this specific sequence epitope can be applied as a protein tag. We show ectopic expression of M-tagged proteins has little impact on cell viability or major signaling pathways. The M tag system can be used for western blotting, immunoprecipitation, immunofluorescence staining, and flow cytometry assays. The results indicate the specificity, sensitivity, and versatility of this novel epitope tag system are comparable to the widely used FLAG tag system, providing researchers with an additional tool for molecular analysis. KEY POINTS: • A short peptide (Pro Pro Tyr Asp Asp Asp) can be applied as a new tag. • The new epitope-tagging fusion system has no effect on the main cellular signaling pathway. • The epitope-tagging fusion system can be widely used for western blotting, immunoprecipitation, immunofluorescence, flow cytometry, etc.

Immunogenicity of a secreted, C-terminally truncated, form of bovine viral diarrhea virus E2 glycoprotein as a potential candidate in subunit vaccine development

Both current live, attenuated, and killed virus vaccines for bovine viral diarrhea virus (BVDV) have their limitations. Here, we report the development of a BVDV subunit vaccine by (i) the expression of a secreted form of a recombinant E2 glycoprotein using BHK21 cells and (ii) determination of the immune responses in mice. The E2 glycoprotein was modified by deletion of the C-terminal transmembrane anchor domain and fusion to a V5 epitope tag. This allowed detection using anti-V5 monoclonal antibodies together with simple purification of the expressed, secreted, form of E2 from the cell media. Furthermore, we genetically fused green fluorescent protein (GFP) linked to E2 via a Thosea asigna virus 2A (T2A) ribosome skipping sequence thereby creating a self-processing polyprotein [GFP-T2A-BVDV-E2^trunk-V5], producing discrete [GFP-T2A] and [E2^trunk-V5] translation products: GFP fluorescence acts, therefore, as a surrogate marker of E2 expression, BALB/c mice were inoculated with [E2^trunk-V5] purified from cell media and both humoral and cellular immune responses were observed. Our antigen expression system provides, therefore, both (i) a simple antigen purification protocol together with (ii) a feasible strategy for further, large-scale, production of vaccines.

Development and validation of a DIVA ELISA for differentiating BEFV infected from vaccinated animals

Inactivated vaccine is considered safe and used for prevention of bovine ephemeral fever in several endemic countries. To differentiate between BEFV-infected and vaccinated animals, we developed an ELISA capable of detecting infection-related antibodies against BEFV. Recombinant proteins, including N, P, M, L, G_NS, α2, β and γ, were expressed in E. coli and screened by Western blotting and ELISA. The results showed G_NS, α2 and β specifically reacted with sera from BEFV infected cattle but not sera from vaccinated cattle. A DIVA ELISA based on a C-terminal truncated form of G_NS was developed, with 100% sensitivity and 98.0% specificity at a sample to positive-control optical density ratio (S/P) threshold of 0.18. Specificity analysis showed that the assay has no cross-reactivity with antisera of other common bovine viruses. Anti-G_NS antibody appears at 3-4 days post infection (dpi) and persists up to 240-300 dpi in the experimentally infected cattle. Sero-epidemiological survey using sera collected from vaccinated cattle in an endemic area in Jiangsu Province revealed sero-positive rate of 2.36% (6/254), indicating that the DIVA ELISA could be used as a reliable diagnostic tool for differentiating BEFV infected from vaccinated animals.

The Development of Dual Vaccines against Lumpy Skin Disease (LSD) and Bovine Ephemeral Fever (BEF)

Dual vaccines (n = 6) against both lumpy skin disease (LSD) and bovine ephemeral fever (BEF) were constructed, based on the BEFV glycoprotein (G) gene, with or without the BEFV matrix (M) protein gene, inserted into one of two different LSDV backbones, nLSDV∆SOD-UCT or nLSDVSODis-UCT. The inserted gene cassettes were confirmed by PCR; and BEFV protein was shown to be expressed by immunofluorescence. The candidate dual vaccines were initially tested in a rabbit model; neutralization assays using the South African BEFV vaccine (B-Phemeral) strain showed an African consensus G protein gene (Gb) to give superior neutralization compared to the Australian (Ga) gene. The two LSDV backbones expressing both Gb and M BEFV genes were tested in cattle and shown to elicit neutralizing responses to LSDV as well as BEFV after two inoculations 4 weeks apart. The vaccines were safe in cattle and all vaccinated animals were protected against virulent LSDV challenge, unlike a group of control naïve animals, which developed clinical LSD. Both neutralizing and T cell responses to LSDV were stimulated upon challenge. After two inoculations, all vaccinated animals produced BEFV neutralizing antibodies ≥ 1/20, which is considered protective for BEF.