Limited potential for mosquito transmission of genetically engineered, live-attenuated Venezuelan equine encephalitis virus vaccine candidates.

Abstract

Abstract. In an attempt to improve the current live-attenuated vaccine (TC-83) for Venezuelan equine encephalitis (VEE), specific mutations associated with attenuation of VEE virus in rodent models were identified. These mutations were inserted into full-length cDNA clones of the Trinidad donkey strain of VEE virus by site-directed mutagenesis, and isogenic virus strains with these mutations were recovered after transfection of baby hamster kidney cells with infectious RNA. We evaluated 10 of these strains for their ability to replicate in and be transmitted by Aedes taeniorhynchus, a natural vector of epizootic VEE virus. Two vaccine candidates, one containing a deletion of the PE2 furin cleavage site, the other a combination of three separate point mutations in the E2 glycoprotein, replicated in mosquitoes and were transmitted to hamsters significantly less efficiently than was either parental (wild type) VEE virus or TC-83 virus. Although the attenuated strains were transmitted to hamsters by mosquitoes, after intrathoracic inoculation, there was no evidence of reversion to a virulent phenotype. The mutations that resulted in less efficient replication in, or transmission by, mosquitoes should enhance vaccine safety and reduce the possibility of environmental spread to unintentional hosts.The current investigational new drug (IND) vaccine (TC-83) for Venezuelan equine encephalitis (VEE) strain IAB virus is a live-attenuated virus that causes reactogenicity in 20% of recipients and fails to elicit a positive seroresponse in 20% of recipients. 1 Current efforts to develop an improved live-attenuated vaccine for VEE identified specific mutations associated with attenuation of VEE virus in rodent models. 2-4 These attenuating mutations have been inserted into a fulllength cDNA clone of wild-type VEE virus (IAB) to produce selected isogenic strains containing one or more attenuating mutations. These attenuated strains are currently being evaluated for their potential as a live-attenuated VEE virus vaccine.Live-attenuated vaccines typically offer many advantages over inactivated immunogens (e.g., single immunization, more efficient induction of mucosal immunity, longer duration of immunity). However, live arbovirus vaccines have the potential to be transmitted to secondary hosts, and may revert to a more virulent virus. This reversion to virulence could occur in either the vertebrate or the arthropod host. Thus, we examined VEE virus strains that contained attenuating mutations that might be included in a live-attenuated vaccine for their ability to infect and be transmitted by mosquitoes. In addition, we evaluated these vaccine candidates for reversion to a more virulent phenotype after intrathoracic inoculation of Aedes taeniorhynchus mosquitoes. MATERIALS AND METHODS Mosquitoes. Two laboratory strains of Ae. taeniorhynchus, Vero Beach and Medical and Veterinary EntomologyResearch Laboratory (MAVERL), were used during these studies. Both of these strains have been in colonies for more than 30 years and are derive...

Genetically engineered, live attenuated vaccines for Venezuelan equine encephalitis: testing in animal models

“…Based on our results in non-human primates and those from cohort studies in rodents [17,[28][29][30] and mosquitoes [32], V3526 was selected for development into a human-use vaccine. These other studies, like this study, showed V3526 to be more safe, immunogenic and efficacious than TC-83, and without any indication of reversion to virulent phenotype.…”

Vector Infection Determinants of Venezuelan Equine Encephalitis Virus Reside within the E2 Envelope Glycoprotein

“…Interestingly, the infection rate for theIAB/IDE2 construct did differ significantly (P ϭ 0.1) from that of the IAB parent. The lack of statistical significance between parental IAB and ID viruses could be the result of small sample sizes or extensive cell culture passaging (6-Vero and 1-BHK) of the IAB virus used to generate the VEE/IC-109 clone; cell culture passage is known to reduce mosquito infectivity by subtype IAB VEEV (27). In contrast, virus from the subtype IC clone p3908acb (generated from a virus that had been passaged only once in mosquito cells) infected mosquitoes at a higher (P ϭ 0.08) rate, 84% at 7.1 log 10 PFU/ml (Table 1), than the enzootic ID virus, also of low passage (once in suckling mice and once in Vero cells).…”

Pathogenicity of a Venezuelan Equine Encephalomyelitis Serotype Ie Virus Isolate for Ponies

“…It is also possible that lack of knowledge of mutation(s) of viral genes, which can affect the virulence of the virus, might have contributed to their conclusion. [37][38][39][40][41] In addition, the possibility of infection due to increased severity of tissue tropism cannot be ruled out.…”