A simian-adenovirus-vectored rabies vaccine suitable for thermostabilisation and clinical development for low-cost single-dose pre-exposure prophylaxis

Abstract

BackgroundEstimates of current global rabies mortality range from 26,000 to 59,000 deaths per annum. Although pre-exposure prophylaxis using inactivated rabies virus vaccines (IRVs) is effective, it requires two to three doses and is regarded as being too expensive and impractical for inclusion in routine childhood immunization programmes.Methodology/ Principal FindingsHere we report the development of a simian-adenovirus-vectored rabies vaccine intended to enable cost-effective population-wide pre-exposure prophylaxis against rabies. ChAdOx2 RabG uses the chimpanzee adenovirus serotype 68 (AdC68) backbone previously shown to achieve pre-exposure protection against rabies in non-human primates. ChAdOx2 differs from AdC68 in that it contains the human adenovirus serotype 5 (AdHu5) E4 orf6/7 region in place of the AdC68 equivalents, enhancing ease of manufacturing in cell lines which provide AdHu5 E1 proteins in trans.We show that immunogenicity of ChAdOx2 RabG in mice is comparable to that of AdC68 RabG and other adenovirus serotypes expressing rabies virus glycoprotein. High titers of rabies virus neutralizing antibody (VNA) are elicited after a single dose. The relationship between levels of VNA activity and rabies glycoprotein monomer-binding antibody differs after immunization with adenovirus-vectored vaccines and IRV vaccines, suggesting routes to further enhancement of the efficacy of the adenovirus-vectored candidates. We also demonstrate that ChAdOx2 RabG can be thermostabilised using a low-cost method suitable for clinical bio-manufacture and ambient-temperature distribution in tropical climates. Finally, we show that a dose-sparing effect can be achieved by formulating ChAdOx2 RabG with a simple chemical adjuvant. This approach could lower the cost of ChAdOx2 RabG and other adenovirus-vectored vaccines.Conclusions/ SignificanceChAdOx2 RabG may prove to be a useful tool to reduce the human rabies death toll. We have secured funding for Good Manufacturing Practice-compliant bio-manufacture and Phase I clinical trial of this candidate.Author summaryRabies was, after smallpox, the second human disease for which an efficacious vaccine was developed, by Pasteur in 1885. Although it is eminently preventable, with highly efficacious vaccines available for both humans and animals, it still causes considerable mortality in low and middle-income countries. It is a particular problem in areas with the weakest healthcare and veterinary infrastructure, where achieving prompt post-exposure vaccination or high-coverage dog vaccination are challenging.Here, we report the development of a new candidate rabies vaccine, designed to enable low-cost single-dose pre-exposure human rabies prophylaxis in such settings. ChAdOx2 RabG is based upon a simian adenovirus-vectored candidate previously shown to achieve protection after a single dose in non-human primates, now modified to allow clinical-grade bio-manufacture. We show that it induces a potent immune response in mice, that this response can be further enhanced by clinically-relevant adjuvant, and that we can stabilise it such that it can withstand temperatures of up to 45 °C for a month. We will be performing a clinical trial of this candidate in the near future.

Characterisation of factors contributing to the performance of nonwoven fibrous matrices as substrates for adenovirus vectored vaccine stabilisation

“…We have now dried full human doses (5×10 10 virus particles, approximately 5×10 8 infectious units [IU]) of a simian adenovirus vectored rabies vaccine (ChAdOx2 RabG) upon 1 cm 2 of the matrix, with <0.1 log 10 -fold loss in-process (i.e. during desiccation) and approximately 0.3 log 10 -fold loss after thermochallenge at 30°C for a month (Figure 1C) 28 . For explanation of the log 10 -fold loss metric, please see Methods.…”

“…Simian adeno virus vectors ChAd63-METRAP and ChAdOx2-RabGP were prepared, purified and tested for quality by the Jenner Institute Viral Vector Core Facility, as previously described 28, 29 . Viruses were dialysed against either a previously used storage buffer (10mM Tris, 7.5 % w/v sucrose, pH 7.8) or unbuffered 0.5M trehalose and sucrose and stored at −80°C as stock.…”

“…Other groups have reported improvement in stability by drying vaccines using lyophilisation 20, 21 , spray drying 22–24 , and nano-patch technology 25 . We have previously reported that drying a formulation of adenovirus in glass forming sugars upon a fibrous matrix such as paper or a wetlaid nonwoven fabric permitted full recovery of viable and immunogenic virus, even after six months at 45°C 26–28 . We refer to this method as sugar-matrix thermostabilisation (SMT).…”

Immunogenicity of replication-deficient vesicular stomatitis virus based rabies vaccine in mice

“…Most human cases of rabies are the result of dog bites (Fooks et al, 2017) . There is a strong argument for investment in dog vaccination: the feasibility and cost-effectiveness of rabies control and human rabies elimination by dog vaccination has been demonstrated in some countries (Wang, C. et al, 2018) . Several inactivated preparations of RABV are available as vaccines to immunize humans and domestic animals.…”

“…Not only inactivated vaccines, but also other recombinant vaccines trials are reported elsewhere. Recently, a simian adenovirus-vectored candidate showed that single-dose vaccination induced strong neutralizing antibodies in mice (Wang, C. et al, 2018) . Also, other rabies vaccine candidates using viral vectors have been reported (Abreu-Mota et al, 2018;Chen et al, 2019;Ramya et al, 2011;Wang, X. et al, 2019) .…”