Engineering, expression, and immuno-characterization of recombinant protein comprising multi-neutralization sites of rabies virus glycoprotein

Construction and evaluation of recombinant Lactobacillus plantarum NC8 delivering one single or two copies of G protein fused with a DC-targeting peptide (DCpep) as novel oral rabies vaccine

Rabies remains an important public health threat in most developing countries. To develop a more effective and safe oral vaccine against rabies, we constructed recombinant Lactobacillus plantarum NC8 carrying one or two copies of the G gene with a dendritic cell-targeting peptide (DCpep) fused at the C-terminal designated NC8-pSIP409-sRVG or NC8-pSIP409-dRVG, respectively. The immunogenicity and protective efficacy of these recombinant Lactobacillus plantarum against RABV were evaluated by oral administration in a mouse model. The results showed that recombinant NC8-pSIP409-dRVG possessed more G protein, resulting in more functional maturation of DCs. After three cycle of oral immunization, NC8-pSIP409-dRVG induced significantly higher levels of specific IgG antibody and mixed Th1/Th2 with a strong Th1-biasd immune response in mice. Most importantly, although the titers of RABV neutralizing antibody (VNA) were below the threshold of 0.5 IU/mL, the NC8-pSIP409-dRVG could protect 60 % of inoculated mice against lethal RABV challenge. These data reveal that recombinant NC8-pSIP409-dRVG may be a novel and promising oral vaccine candidate to prevent and control of animal rabies.

Recent advances in the production of recombinant subunit vaccines in Pichia pastoris

Recombinant protein subunit vaccines are formulated using defined protein antigens that can be produced in heterologous expression systems. The methylotrophic yeast Pichia pastoris has become an important host system for the production of recombinant subunit vaccines. Although many basic elements of P. pastoris expression system are now well developed, there is still room for further optimization of protein production. Codon bias, gene dosage, endoplasmic reticulum protein folding and culture condition are important considerations for improved production of recombinant vaccine antigens. Here we comment on current advances in the application of P. pastoris for the synthesis of recombinant subunit vaccines.

Molecular optimization of rabies virus glycoprotein expression in Pichia pastoris

In this work, different approaches were investigated to enhance the expression rabies virus glycoprotein (RABV-G) in the yeast Pichia pastoris; this membrane protein is responsible for the synthesis of rabies neutralizing antibodies. First, the impact of synonymous codon usage bias was examined and an optimized RABV-G gene was synthesized. Nevertheless, data showed that the secretion of the optimized RABV-G gene was not tremendously increased as compared with the non-optimized one. In addition, similar levels of RABV-G were obtained when α-factor mating factor from Saccharomyces cerevisiae or the acid phosphatase PHO1 was used as a secretion signal. Therefore, sequence optimization and secretion signal were not the major bottlenecks for high-level expression of RABV-G in P. pastoris. Unfolded protein response (UPR) was induced in clones containing high copy number of RABV-G expression cassette indicating that folding was the limiting step for RABV-G secretion. To circumvent this limitation, co-overexpression of five factors involved in oxidative protein folding was investigated. Among these factors only PDI1, ERO1 and GPX1 proved their benefit to enhance the expression. The highest expression level of RABV-G reached 1230 ng ml(-1). Competitive neutralizing assay confirmed that the recombinant protein was produced in the correct conformational form in this host.