Exploring the role of single nucleotide polymorphisms in varicella zoster virus vaccine attenuation in skin

Abstract

Varicella zoster virus (VZV) is a disease that can be detrimental to the health of children in its primary form, chicken pox, and later in the elderly as its reactivated form, shingles. Before the advent of the vaccine, Varivax, VZV was endemic in the United States as it is highly contagious and can be spread through both direct contact and aerosol particles. Varivax, or vOka, is a live attenuated vaccine, and while effective, has side effects ranging from rashes to possible VZV reactivation. While the vaccine has reduced the incidence and severity of VZV, there is still little known about the mechanism of its attenuation in skin. vOka is genetically heterogeneous with hundreds of single nucleotide polymorphisms (SNPs) that are a mixture of wild-type and vOka nucleotides. Previous studies have demonstrated the key to attenuation may be through five SNPs in the open reading frame (ORF) 62 region found to be fixed and stable across different licensed vOka preparations around the world. ORF62 contains the gene for IE62, a transactivator protein responsible for regulating the expression of viral genes and the host gene for KRT15, a cytokeratin protein. This project focused on if two SNPs, located in the loci positions 106262 and 107252, that are found to be almost 100% conserved across all variations of vOka are responsible for the attenuation in human skin and induction of KRT15. We evaluated four mutant viruses with SNPs found in vOka and discovered that a double SNP mutation stunted virus growth in HFF cells. In addition, we found no significant difference in the growth of our viruses in skin but variability in successful infection. Furthermore, in infected skin, we found that VZV-ORF57-Luc and single mutant virus, 68-958, upregulate KRT15 expression with VZV infection while single mutant virus, 68-62S-A, may downregulate KRT15 expression with VZV infection. This project is important because it may reveal the molecular basis of attenuation of the licensed varicella vaccine. This information could be used to make a vaccine that contains only the attenuated genotype.