Modification of the adenoviral transfer vector enhances expression of the Hantavirus fusion protein GnS0.7 and induces a strong immune response in C57BL/6 mice.

Hantavirus glycoproteins (Gn and Gc) are significant components of vaccines for haemorrhagic fever with renal syndrome (HFRS); however, they are not effective due to weak immunogenicity and low levels of production in expression systems. To circumvent this problem, a 0.7-kb fragment of the S segment was fused to Gn, and a hybrid CAG promoter/enhancer in conjunction with (or without) the WPRE (Woodchuck hepatitis virus post-transcriptional regulatory element) was used to improve the expression of fusion protein GnS0.7 in the adenoviral expression system. The expression level of the fusion protein as well as the response of mice immunized with recombinant adenoviruses containing GnS0.7 was investigated. In addition, a series of immunological assays were conducted to determine the immunogenicity of the recombinant adenoviruses. The results showed that the recombinant adenovirus with the CAG promoter/enhancer (rAd-GnS0.7-pCAG) expressed approximately 2.1-fold more GnS0.7 than the unmodified recombinant adenovirus containing GnS0.7 (rAd-GnS0.7-pShuttle). This enhanced expression level was also higher than for other modified recombinant adenoviruses studied. Animal experiments showed that rAd-GnS0.7-pCAG induced a stronger Hantaan virus (HTNV)-specific humoral and cellular immune response in mice, with the cellular immune response to the GnS0.7 being stronger than the HFRS vaccine control. These results demonstrate that the CAG promoter/enhancer improved significantly the expression of the chimeric gene GnS0.7 in the adenovirus expression system. These findings may have significant implications for the development of genetically engineered vaccines for HFRS.