Characterization of single-cycle flavivirus particles for use as a vaccine to prevent West Nile disease and to examine immune responses to flavivirus infection

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Title: Characterization of single-cycle flavivirus particles for use as a vaccine to prevent West Nile disease and to examine immune responses to flavivirus infection
Author: Douglas Gregory Widman
Abstract: West Nile virus (WNV ) is responsible for the largest outbreak of viral encephalitis in the history of North America , yet there are no vaccines available to prevent this disease . To address these needs we have developed RepliVAX WN , a single -cycle flavivirus (SCFV ) -based vaccine to prevent West Nile disease . RepliVAX WN contains a C -deleted WNV genome , and is produced in trans -complementing cell lines that express WNV C . When used for vaccination , RepliVAX WN infects a single cell where the genome replicates and drives the production of highly antigenic subviral particles (SVPs ) and NS1 without producing infectious virions . Thus , RepliVAX is expected to be highly potent yet exhibit a safety profile superior to traditional live -attenuated viral vaccines . \r \nHere we demonstrate that RepliVAX WN can be safely passaged in C -expressing cell lines and that this blind passage selected for mutations used to engineer a second -generation RepliVAX WN with an enhanced in vitro growth phenotype . When evaluated in mouse and hamster models of WN disease , this second -generation RepliVAX was safe , exhibited 100 % protective efficacy , and induced significantly higher antibody levels than the parental virus . Furthermore , we observed that RepliVAX WN -induced antibody levels remain steadily at high levels for at least 6 months after vaccination of hamsters , and all animals were protected from lethal WNV challenge at this time . Evaluation in non -human primates indicated that one or two doses of RepliVAX WN was safe , induced WNV -specific antibody responses , and protected animals from WNV viremia . \r \nHaving demonstrated the usefulness of RepliVAX WN as a vaccine to prevent WN disease , we were interested in the immunological mechanisms underlying vaccine immunity . We observed that although RepliVAX WN vaccination induces high levels of interferon (IFN ) alpha , the ability to respond to either type -I or type -II IFNs was not required for the development of activated B cells , IgG , IgM , or neutralizing antibody titers . Type -I IFN signaling did , however , play a role in viral gene expression , as in vivo imaging of animals inoculated with luciferase -expressing SCFVs revealed 1000 -fold greater bioluminescence in the absence of a type -I IFN response . The affect of this IFN response on gene expression was dramatic , but short lived and did not appear to play a role in SCFV persistence , as SCFV gene expression was detectable for at least 18 days after SCFV inoculation . Taken together these results demonstrate the usefulness of SCFVs like RepliVAX WN as vaccines to prevent flavivirus disease , and tools with which to examine immune responses to viral infection .
URI: http : / /hdl .handle .net /2152 .3 /241
Date: 2009-08-28

Citation

Characterization of single-cycle flavivirus particles for use as a vaccine to prevent West Nile disease and to examine immune responses to flavivirus infection. Doctoral dissertation, The University of Texas Medical Branch. Available electronically from http : / /hdl .handle .net /2152 .3 /241 .

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