A recombinant chimeric La Crosse virus expressing the surface glycoproteins of Jamestown Canyon virus is immunogenic and protective against challenge with either parental virus in mice or monkeys

Abstract

La Crosse virus (LACV) and Jamestown Canyon virus (JCV), family Bunyaviridae, are mosquito-borne viruses that are endemic in North America and recognized as etiologic agents of encephalitis in humans. Both viruses belong to the California encephalitis virus serogroup, which causes 70 to 100 cases of encephalitis a year. As a first step in creating live attenuated viral vaccine candidates for this serogroup, we have generated a recombinant LACV expressing the attachment/fusion glycoproteins of JCV. The JCV/LACV chimeric virus contains full-length S and L segments derived from LACV. For the M segment, the open reading frame (ORF) of LACV is replaced with that derived from JCV and is flanked by the untranslated regions of LACV. The resulting chimeric virus retained the same robust growth kinetics in tissue culture as observed for either parent virus, and the virus remains highly infectious and immunogenic in mice. Although both LACV and JCV are highly neurovirulent in 21 day-old mice, with 50% lethal dose (LD₅₀) values of 0.1 and 0.5 log₁₀ PFU, respectively, chimeric JCV/LACV is highly attenuated and does not cause disease even after intracerebral inoculation of 10³ PFU. Parenteral vaccination of mice with 10¹ or 10³ PFU of JCV/LACV protected against lethal challenge with LACV, JCV, and Tahyna virus (TAHV). The chimeric virus was infectious and immunogenic in rhesus monkeys and induced neutralizing antibodies to JCV, LACV, and TAHV. When vaccinated monkeys were challenged with JCV, they were protected against the development of viremia. Generation of highly attenuated yet immunogenic chimeric bunyaviruses could be an efficient general method for development of vaccines effective against these pathogenic viruses.

Fig 1

Growth kinetics in Vero cells. Growth kinetics of JCV, rLACV, and rJCV/LACV in Vero cells infected at an MOI of 0.01. Each point represents the mean titer for three replicates. The standard error of any mean is ≤0.28.

Fig 2

Chimeric rJCV/LACV replicates at very low levels in the CNS of mice compared to those of parental JCV and rLACV. Mice were inoculated intracerebrally with 100 PFU of JCV, rLACV, or rJCV/LACV, and six mice were sampled from each treatment group each day. Data shown are the mean virus titers/g in the brain (A) or spinal cord (B) for each treatment group. All mice in the rLACV or JCV treatment groups had succumbed to disease prior to the day 5 sampling. The lower limit of virus detection was 1.7 log₁₀ PFU/g for brain samples and 2.7 log₁₀ PFU/g for spinal cord samples and is indicated by a dotted line. To assess the genetic stability of rJCV/LACV after replication in mouse brain, virus was isolated and sequenced on indicated days (↓).