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IRES-driven expression of the capsid protein of the Venezuelan equine encephalitis virus TC-83 vaccine strain increases its attenuation and safety.

Guerbois M, Volkova E, Forrester NL, Rossi SL, Frolov I, Weaver SC - PLoS Negl Trop Dis (2013)

Bottom Line: Here we describe a second generation of the recombinant TC-83 in which the subgenomic promoter is maintained and only the capsid protein gene is translated from the IRES.This VEEV/IRES/C vaccine candidate did not infect mosquitoes, was stable in its attenuation phenotype after serial murine passages, and was more attenuated in newborn mice but still as protective as TC-83 against VEEV challenge.Thus, by using the IRES to modulate TC-83 capsid protein expression, we generated a vaccine candidate that combines efficient immunogenicity and efficacy with lower virulence and a reduced potential for spread in nature.

View Article: PubMed Central - PubMed

Affiliation: Institute for Human Infections and Immunity, Sealy Center for Vaccine Development, and Department of Pathology, University of Texas Medical Branch, Galveston, Texas, United States of America.

ABSTRACT
The live-attenuated TC-83 strain is the only licensed veterinary vaccine available to protect equids against Venezuelan equine encephalitis virus (VEEV) and to protect humans indirectly by preventing equine amplification. However, TC-83 is reactogenic due to its reliance on only two attenuating point mutations and has infected mosquitoes following equine vaccination. To increase its stability and safety, a recombinant TC-83 was previously engineered by placing the expression of the viral structural proteins under the control of the Internal Ribosome Entry Site (IRES) of encephalomyocarditis virus (EMCV), which drives translation inefficiently in insect cells. However, this vaccine candidate was poorly immunogenic. Here we describe a second generation of the recombinant TC-83 in which the subgenomic promoter is maintained and only the capsid protein gene is translated from the IRES. This VEEV/IRES/C vaccine candidate did not infect mosquitoes, was stable in its attenuation phenotype after serial murine passages, and was more attenuated in newborn mice but still as protective as TC-83 against VEEV challenge. Thus, by using the IRES to modulate TC-83 capsid protein expression, we generated a vaccine candidate that combines efficient immunogenicity and efficacy with lower virulence and a reduced potential for spread in nature.

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Related in: MedlinePlus

Neurovirulence in 6-day-old mice following IC injection of VEEV TC-83 and IRES-based viruses.Animals received 1×106 PFU of indicated viruses, and were monitored for survival (A) and weight change (B) for 2 weeks, with no deaths recorded after day 14 post-infection.
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pntd-0002197-g007: Neurovirulence in 6-day-old mice following IC injection of VEEV TC-83 and IRES-based viruses.Animals received 1×106 PFU of indicated viruses, and were monitored for survival (A) and weight change (B) for 2 weeks, with no deaths recorded after day 14 post-infection.

Mentions: To assess neurovirulence, six-day-old mice were inoculated intracranially with 1×106 PFU of virus. Similar to that observed after subcutaneous inoculation, there was no significant difference between VEEV/mutSG/IRES/1 and VEEV/IRES/C cohorts in mortality, with 60% and 67% of the animals surviving, respectively (Logrank test, P = 0.45), whereas 100% mortality was observed at 6 days post-inoculation in the TC-83 group (P<0.0001, Fig. 7A). The mortality observed in the VEEV/mutSG/IRES/1 and VEEV/IRES/C groups was also delayed compared to TC-83. Nevertheless, animals inoculated with VEEV/mutSG/IRES/1 showed more signs of illness than animals inoculated with VEEV/IRES/C, illustrated by the observation of more delayed growth compared to the PBS group (P = 0.01, Fig. 7B) and neurological signs such as ataxia, paralysis and lethargy in most mice infected with VEEV/mutSG/IRES/1. Thus, in this model VEEV/IRES/C appeared to be less virulent than VEEV/mutSG/IRES/1.


IRES-driven expression of the capsid protein of the Venezuelan equine encephalitis virus TC-83 vaccine strain increases its attenuation and safety.

Guerbois M, Volkova E, Forrester NL, Rossi SL, Frolov I, Weaver SC - PLoS Negl Trop Dis (2013)

Neurovirulence in 6-day-old mice following IC injection of VEEV TC-83 and IRES-based viruses.Animals received 1×106 PFU of indicated viruses, and were monitored for survival (A) and weight change (B) for 2 weeks, with no deaths recorded after day 14 post-infection.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3649961&req=5

pntd-0002197-g007: Neurovirulence in 6-day-old mice following IC injection of VEEV TC-83 and IRES-based viruses.Animals received 1×106 PFU of indicated viruses, and were monitored for survival (A) and weight change (B) for 2 weeks, with no deaths recorded after day 14 post-infection.
Mentions: To assess neurovirulence, six-day-old mice were inoculated intracranially with 1×106 PFU of virus. Similar to that observed after subcutaneous inoculation, there was no significant difference between VEEV/mutSG/IRES/1 and VEEV/IRES/C cohorts in mortality, with 60% and 67% of the animals surviving, respectively (Logrank test, P = 0.45), whereas 100% mortality was observed at 6 days post-inoculation in the TC-83 group (P<0.0001, Fig. 7A). The mortality observed in the VEEV/mutSG/IRES/1 and VEEV/IRES/C groups was also delayed compared to TC-83. Nevertheless, animals inoculated with VEEV/mutSG/IRES/1 showed more signs of illness than animals inoculated with VEEV/IRES/C, illustrated by the observation of more delayed growth compared to the PBS group (P = 0.01, Fig. 7B) and neurological signs such as ataxia, paralysis and lethargy in most mice infected with VEEV/mutSG/IRES/1. Thus, in this model VEEV/IRES/C appeared to be less virulent than VEEV/mutSG/IRES/1.

Bottom Line: Here we describe a second generation of the recombinant TC-83 in which the subgenomic promoter is maintained and only the capsid protein gene is translated from the IRES.This VEEV/IRES/C vaccine candidate did not infect mosquitoes, was stable in its attenuation phenotype after serial murine passages, and was more attenuated in newborn mice but still as protective as TC-83 against VEEV challenge.Thus, by using the IRES to modulate TC-83 capsid protein expression, we generated a vaccine candidate that combines efficient immunogenicity and efficacy with lower virulence and a reduced potential for spread in nature.

View Article: PubMed Central - PubMed

Affiliation: Institute for Human Infections and Immunity, Sealy Center for Vaccine Development, and Department of Pathology, University of Texas Medical Branch, Galveston, Texas, United States of America.

ABSTRACT
The live-attenuated TC-83 strain is the only licensed veterinary vaccine available to protect equids against Venezuelan equine encephalitis virus (VEEV) and to protect humans indirectly by preventing equine amplification. However, TC-83 is reactogenic due to its reliance on only two attenuating point mutations and has infected mosquitoes following equine vaccination. To increase its stability and safety, a recombinant TC-83 was previously engineered by placing the expression of the viral structural proteins under the control of the Internal Ribosome Entry Site (IRES) of encephalomyocarditis virus (EMCV), which drives translation inefficiently in insect cells. However, this vaccine candidate was poorly immunogenic. Here we describe a second generation of the recombinant TC-83 in which the subgenomic promoter is maintained and only the capsid protein gene is translated from the IRES. This VEEV/IRES/C vaccine candidate did not infect mosquitoes, was stable in its attenuation phenotype after serial murine passages, and was more attenuated in newborn mice but still as protective as TC-83 against VEEV challenge. Thus, by using the IRES to modulate TC-83 capsid protein expression, we generated a vaccine candidate that combines efficient immunogenicity and efficacy with lower virulence and a reduced potential for spread in nature.

Show MeSH
Related in: MedlinePlus