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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

Survival following vaccination and challenge of adult mice.Five-week-old CD1 mice were vaccinated with 105 PFU of VEEV TC-83 or IRES-based viruses. Challenge was performed 6 weeks post-vaccination by SC inoculation of 104 PFU of VEEV IC strain 3908, with daily monitoring of animals. No deaths occurred after day 11 post-challenge.
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pntd-0002197-g009: Survival following vaccination and challenge of adult mice.Five-week-old CD1 mice were vaccinated with 105 PFU of VEEV TC-83 or IRES-based viruses. Challenge was performed 6 weeks post-vaccination by SC inoculation of 104 PFU of VEEV IC strain 3908, with daily monitoring of animals. No deaths occurred after day 11 post-challenge.

Mentions: In a second experiment, adult mice were vaccinated SC with a single dose of 105 PFU of each vaccine strain. No viremia was detected in VEEV/mutSG/IRES/1- and VEEV/IRES/C-vaccinated groups at days 1 and 2 post-vaccination. In the TC-83-vaccinated group, 3 out of 5 animals were viremic on days 1 and 2 with mean titers of 2×103 and 2×102 PFU/ml, respectively. No significant weight changes were detected in any of the groups post-vaccination (data not shown). Animals were bled 2 months later and neutralizing antibody titers were determined. In the TC-83 vaccinated group, 100% of the animals seroconverted and PRNT titers all exceeded the endpoint of 1280. Although the titers in the IRES-recombinants vaccinated groups were lower than those in the TC-83 group, mean PRNT80 and PRNT50 titers were 2.5 times higher in the VEEV/IRES/C group (184±184 and 424±482, respectively) compared to VEEV/mutSG/IRES/1 group (74±98 and 160±195 respectively), with 80% seroconversion in VEEV/IRES/C-vaccinated animals and 70% in the VEEV/mutSG/IRES/1 cohort (Table 3). A challenge was performed 6 weeks post-vaccination with 104 PFU of wild-type VEEV strain 3908. All sham-vaccinated animals died between days 7 and 9 post-challenge, whereas all animals vaccinated with VEEV TC-83 or VEEV/IRES/C were protected. One VEEV/mutSG/IRES/1-vaccinated animal died on day 10 post-challenge (Fig. 9). All sham-vaccinated animals had detectable viremia up to 4 days post-challenge, reaching an average of 1.3×107 PFU/ml on day 3 (Table 4). In the VEEV/IRES/C-vaccinated group, viremia was recorded in 1, 3 and 1 animals out of 10 on days 1, 2 and 3 post-challenge, respectively, with average titers of 1×102 PFU/ml on days 1 and 3, and 1×103 PFU/ml on day 2. Challenge viremia was detected in 2 out of 10 animals vaccinated with VEEV/mutSG/IRES/1 on days 1 and 3, with average titers of 1×104 PFU/ml and 1×102 PFU/ml respectively. No virus was detected after challenge in animals vaccinated with TC-83 (Table 4). No significant difference was observed in weight change among the vaccinated groups (data not shown).


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)

Survival following vaccination and challenge of adult mice.Five-week-old CD1 mice were vaccinated with 105 PFU of VEEV TC-83 or IRES-based viruses. Challenge was performed 6 weeks post-vaccination by SC inoculation of 104 PFU of VEEV IC strain 3908, with daily monitoring of animals. No deaths occurred after day 11 post-challenge.
© Copyright Policy
Related In: Results  -  Collection

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

pntd-0002197-g009: Survival following vaccination and challenge of adult mice.Five-week-old CD1 mice were vaccinated with 105 PFU of VEEV TC-83 or IRES-based viruses. Challenge was performed 6 weeks post-vaccination by SC inoculation of 104 PFU of VEEV IC strain 3908, with daily monitoring of animals. No deaths occurred after day 11 post-challenge.
Mentions: In a second experiment, adult mice were vaccinated SC with a single dose of 105 PFU of each vaccine strain. No viremia was detected in VEEV/mutSG/IRES/1- and VEEV/IRES/C-vaccinated groups at days 1 and 2 post-vaccination. In the TC-83-vaccinated group, 3 out of 5 animals were viremic on days 1 and 2 with mean titers of 2×103 and 2×102 PFU/ml, respectively. No significant weight changes were detected in any of the groups post-vaccination (data not shown). Animals were bled 2 months later and neutralizing antibody titers were determined. In the TC-83 vaccinated group, 100% of the animals seroconverted and PRNT titers all exceeded the endpoint of 1280. Although the titers in the IRES-recombinants vaccinated groups were lower than those in the TC-83 group, mean PRNT80 and PRNT50 titers were 2.5 times higher in the VEEV/IRES/C group (184±184 and 424±482, respectively) compared to VEEV/mutSG/IRES/1 group (74±98 and 160±195 respectively), with 80% seroconversion in VEEV/IRES/C-vaccinated animals and 70% in the VEEV/mutSG/IRES/1 cohort (Table 3). A challenge was performed 6 weeks post-vaccination with 104 PFU of wild-type VEEV strain 3908. All sham-vaccinated animals died between days 7 and 9 post-challenge, whereas all animals vaccinated with VEEV TC-83 or VEEV/IRES/C were protected. One VEEV/mutSG/IRES/1-vaccinated animal died on day 10 post-challenge (Fig. 9). All sham-vaccinated animals had detectable viremia up to 4 days post-challenge, reaching an average of 1.3×107 PFU/ml on day 3 (Table 4). In the VEEV/IRES/C-vaccinated group, viremia was recorded in 1, 3 and 1 animals out of 10 on days 1, 2 and 3 post-challenge, respectively, with average titers of 1×102 PFU/ml on days 1 and 3, and 1×103 PFU/ml on day 2. Challenge viremia was detected in 2 out of 10 animals vaccinated with VEEV/mutSG/IRES/1 on days 1 and 3, with average titers of 1×104 PFU/ml and 1×102 PFU/ml respectively. No virus was detected after challenge in animals vaccinated with TC-83 (Table 4). No significant difference was observed in weight change among the vaccinated groups (data not shown).

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