Characterization of a recombinant chimeric yellow fever 17D vaccine - dengue-4 virus

The disease dengue is caused by four genetically and serologically related virus termed dengue virus-1 to dengue virus-4 (DENV-1 to DENV-4) There are currently no licensed therapeutics, but there is a recently licensed recombinant live attenuated tetravalent vaccine, termed Dengvaxia™ by Sanofi Pasteur, available in some countries. This vaccine was based on Chimerivax™ technology where recombinant DNA technology was used to generate vaccine viruses based on a backbone of the yellow fever virus 17D (YFV-17D) vaccine virus with the structural components premembrane and envelope (prME) of a corresponding wild-type DENV. This thesis investigated the impact of viral chimerization on a YFV-17D infectious clone where the 17D prME genes were replaced with those of the sylvatic wild-type DEN-4 strain P75-215, hereafter termed YFV 17D/DENV-4 prME chimera. Viral RNA of 17D vaccine, wild-type DENV-4, and YFV 17D/DENV-4 prME chimera were compared by Next Generation Sequencing (NGS), which indicated that the YFV-17D/DENV-4 prME chimera has a similar genetic diversity profile to YFV-17D, exemplified by a low diversity profile across the genome. However, the YFV 17D/DENV-4 prME chimera exhibited lower diversity indices than that of YFV-17D in some gene regions, including C, prM, NS2B, and NS4B, 5’UTR. Compared to WT DENV-4, the YFV- 17D/DENV-4 prME chimera was less diverse, suggesting that chimerization lowers the genetic diversity of the virus. The phenotype of the YFV-17D/DENV-4 prME chimera was investigated in cell culture and animals. Multiplication kinetics indicate that the YFV-17D/DENV-4 chimera was functionally more like that of YFV-17D than that of DENV-4, while in vivo in interferon αβγ receptor deficient (AG129) mice the chimeric YFV 17D/DENV-4 prME virus was more virulent than either YFV-17D and DENV-4 parental viruses. It is hypothesized that the process of chimerization results in reduced genetic diversity indices of viruses, which may be linked attenuation of the virus, and may be important in development of chimeric flavivirus vaccine candidates. However, the chimera was not attenuated in the mouse model used and this may be due to the immunocompromised AG129 mouse model.