Recombinant Human Adenovirus Type 5 Vaccine Vectors Expressing Rhabdoviral Glycoproteins

Abstract

<p>Rabies is an important causative agent of disease resulting in an acute infection of the nervous system and death of the individual. Vaccination of wildlife species, which are vectors of the disease, can reduce the number of non-protected animals so that the virus is not sustained in nature. Vaccines currently distributed to North American wildlife do not effectively immunize all at-risk species. This project pursued the development of recombinant human adenovirus type 5 (hAd5) expressing rabies glycoprotein as an effective vaccine vector against rabies.</p> <p>Prevec et al. (1990) had previously described AdRG1 expressing the rabies (ERA) glycoprotein gene from the early 3 region. Low levels of rabies glycoprotein were detected in cultured cells although good titres of rabies neutralizing antibodies were measured in mice and skunks (Prevec et al., 1990; Charlton et al., 1992). Using AdRG1 as a guide, I examined conditions required for optimal rabies glycoprotein expression. Vectors AdSVRG1.3, AdRG1.2, AdRG4, AdRG1.3, and AdHCMV13RG, containing variable exogenous promoters and genomic deletions, were constructed and evaluated. Although no formula was derived to predict optimal vector structure, AdRG1.3, containing rabies glycoprotein and SV40 polyadenylation sequences in parallel orientation to the E3 promoter, demonstrated high levels of glycoprotein expression and elicited high levels of neutralizing antibodies.</p> <p>Rabies glycoprotein shares structural and functional properties with the glycoprotein of vesicular stomatitis virus, also a rhabdovirus. We predicted that chimaeric glycoprotein molecules would structurally resemble the parental glycoproteins and, thus, be useful as vaccines. Five chimaeric DNA sequences of the two glycoproteins were designed and expressed from hAd5 vectors. The chimaeric proteins were expressed at low levels in infected cultured cells yet no anti-rabies nor anti-VSV neutralizing antibodies were detected in serum from immunized BALB/c mice. A block in the post-translational processing pathway of the chimaeric proteins at the level of oligosaccharide modifications may also be a result of blocked movement of proteins.</p>