Venezuelan Equine Encephalitis Virus V3526 Vaccine RNA-Dependent RNA Polymerase Mutants Increase Vaccine Safety Through Restricted Tissue Tropism in a Murine Model.

Clint A Haines,Shannan L Rossi,K Lane Warmbrod,Rafael K Campos,Sasha R Azar,Naomi L Forrester,Tiffany F Kautz

doi:10.15212/zoonoses-2021-0016

Abstract

Venezuelan equine encephalitis virus (VEEV) is an arbovirus endemic to the Americas. There are no approved vaccines or antivirals. TC-83 and V3526 are the best-characterized vaccine candidates for VEEV. Both are live-attenuated vaccines and have been associated with safety concerns, albeit less so for V3526. A previous attempt to improve the TC-83 vaccine focused on further attenuating the vaccine by adding mutations that altered the error incorporation rate of the RNA-dependent RNA polymerase (RdRp). The research presented here examines the impact of these RdRp mutations in V3526 by cloning the 3X and 4X strains, assessing vaccine efficacy against challenge in adult female CD-1 mice, examining neutralizing antibody titers, investigating vaccine tissue tropism, and testing the stability of the mutant strains. Our results show that the V3526 RdRp mutants exhibited reduced tissue tropism in the spleen and kidney compared to wild-type V3526, while maintaining vaccine efficacy. Illumina sequencing showed that the RdRp mutations could revert to wild-type V3526. The observed genotypic reversion is likely of limited concern because wild-type V3526 is still an effective vaccine capable of providing protection. Our results indicate that the V3526 RdRp mutants may be a safer vaccine design than the original V3526.

Highlights

Venezuelan equine encephalitis virus (VEEV) is a member of the Alphavirus genus in the family Togaviridae with an 11.5 kb positive-sense single-stranded RNA genome [1,2].Venezuelan equine encephalitis (VEE) commonly causes mild flu-like symptoms, but severe symptoms can occur in approximately 4–14% of cases in humans [3,4,5,6]
Multiple VEEV outbreaks have occurred across Central and South America; the most recent outbreak occurred in Peru in 2006 [9,10,11,12,13,14,15].A Central American outbreak between 1969 and 1972 resulted in the deaths of 50,000 equines and 93 humans, and hundreds of additional cases of human disease were reported [13].The outbreak reached southern Texas in 1971, resulting in 1,500 equine deaths and 110 cases of human disease [12]
Our study indicated that V3526 3X and 4X have less tissue tropism than wild type (WT) V3526, thereby indicating improved vaccine safety without sacrificing immunogenicity

Summary

Introduction

Venezuelan equine encephalitis virus (VEEV) is a member of the Alphavirus genus in the family Togaviridae with an 11.5 kb positive-sense single-stranded RNA genome [1,2].Venezuelan equine encephalitis (VEE) commonly causes mild flu-like symptoms, but severe symptoms can occur in approximately 4–14% of cases in humans [3,4,5,6]. Multiple VEEV outbreaks have occurred across Central and South America; the most recent outbreak occurred in Peru in 2006 [9,10,11,12,13,14,15].A Central American outbreak between 1969 and 1972 resulted in the deaths of 50,000 equines and 93 humans, and hundreds of additional cases of human disease were reported [13].The outbreak reached southern Texas in 1971, resulting in 1,500 equine deaths and 110 cases of human disease [12] Another major outbreak in Venezuela between 1992 and 1995 resulted in 4,000 equine deaths and between 75,000 and 100,000 cases of human disease [14].The virus tends to recede and emerge in epizootic (outbreak) cycles every 14–20 years and to cause disease in humans and equids [9,14]. A previous attempt to improve the TC-83 vaccine focused on further attenuating the vaccine by adding mutations that alter the error-incorporation rate of the RNA-dependent RNA polymerase (RdRp)

Methods

Results

Conclusion