A Variant allele in Varicella-Zoster Virus Glycoprotein B, Selected during Production of the Varicella Vaccine, Contributes to its Attenuation. A Variant allele in Varicella-Zoster Virus Glycoprotein B

Attenuation of the live varicella Oka vaccine (vOka) has been attributed to mutations in the genome acquired during cell culture passage of pOka (parent strain); however, the precise mechanisms of attenuation remain unknown. Comparative sequence analyses of several vaccine batches showed that over 100 single-nucleotide polymorphisms (SNPs) are conserved across all vaccine batches; six SNPs are fixed or nearly fixed, suggesting that these SNPs are responsible for attenuation. By contrast, prior analysis of chimeric vOka and pOka recombinants indicates that loci other than these six SNPs contribute to attenuation. Here, we report that pOka consists of a heterogenous population of virus sequences with two nearly equally represented bases, G or A, at nucleotide 2096 of ORF31 which encodes glycoprotein B (gB) resulting in arginine (R) or glutamine (Q), respectively, at amino acid 699 of gB. While 2096A/699Q is dominant in vOka (99.99 to 100%). gB699Q/gH/gL showed significantly less fusion activity than gB699R/gH/gL in a cell-based fusion assay. Recombinant pOka with gB-669Q (rpOka-gB699Q) had a similar growth phenotype as vOka during lytic infection in cell culture; however, rpOka-gB699R showed a growth phenotype similar to pOka. rpOka-gB699R entered neurons from axonal terminals more efficiently than rpOka-gB699Q in the presence of cell membrane-derived vesicles containing gB. Strikingly, when a mixture of pOka with both alleles equally represented was used to infect human neurons from axon terminals, pOka with gB699R was dominant for virus entry. These results identify a variant allele in gB that contributes to attenuation of vOka.