The Influence of Codon Optimization on the Immune Response and Protective Efficacy of DNA Vaccines based on the Dengue Envelope and NS1 Proteins

Dengue is a pan-tropical arthropod-borne disease, endemic in over 100 countries. The dengue virus comprises four antigenic serotypes (DENV 1-4). The envelope (E) and non-structural 1 (NS1) proteins are highly immunogenic, and the E protein carries epitopes eliciting neutralizing antibodies. In previous studies, mice immunizations with two DNA vaccines encoding the E ectodomain (pE1D2) and NS1 proteins (pcTPANS1) from DENV2 induced high protection. Based on these findings, we constructed new plasmids containing the codon-optimized genes from these proteins for expression in mouse and human cells, named pEotmD2 and pNS1otmD2. Compared to the pE1D2, the pEotmD2 mediated lower expression of the recombinant protein in human and mouse cell lines, while the pNS1otmD2 plasmid was slightly more efficient than the pcTPANS1 in these cells. Immunogenicity and protection were evaluated in BALB/c mice immunized with the original and codon-optimized plasmids followed by challenged with DENV2. In accordance with the in vitro experiments, the antibody response and protection elicited by the pE1otmD2 plasmid was lower than those observed with the pE1D2. In contrast, the pNS1otmD2 vaccine enabled slightly higher levels of the humoral and protective responses than the pcTPANS1. Overall, our study revealed different effects of codon optimization on these two dengue DNA vaccines.