Introduction. Chickenpox poses a significant public health concern due to its worldwide occurrence, a substantial probability of severe clinical progression, development of complications that can lead to a fatal outcome. Routine vaccination is the only way to prevent the disease. The purpose of this study was to assess the attenuation of cold-adapted (CA) candidate virus strains of Varicella zoster and Herpes zoster by using traditional and new methods.Materials and methods. The study was performed on strains of diploid cells from human embryonic lung and musculocutaneous tissue, primary and diploid cells of guinea pig fetal fibroblasts. Two clinical isolates of the virus were obtained — from a child with chickenpox and from an adult during the reactivation of shingles. The vOka vaccine strain and Ellen strain, a laboratory strain, were used as a control. The viral infectivity was measured by using a sensitive limiting dilution assay. The virulence was measured through the analysis of chick embryo chorioallantoic membranes infected with the Varicella zoster virus.Results. The clinical isolates were sub-cultured at lower temperatures, put through comparative tests and checked for presence of attenuation biomarkers. It was found that vFiraVax, a Varicella zoster virus strain, and vZelVax, a Herpes zoster virus strain were temperature-sensitive and cold-adaptable, but they lacked virulence. Attenuated CA virus strains induced lower expression of IFN-α and IFN-γ receptors on human mononuclear cells as compared to their parental variants.Conclusion. We created and assessed two candidate vaccine strains through attenuation of clinical isolates.

Purpose: characterization of vFiraVax (the causative agent of chickenpox - VZV) and vZelVax (the causative agent of shingles - HZ) vaccine strains by their ability to bind to preparations of brain membrane receptors of SPF BALB/c mice.Materials and Methods. The study was performed on cold-adapted vFiraVax VZV and vZelVax HZ vaccine strains developed by the authors on the basis of the wild-type parental pFira VZV virus (chickenpox causative agent) and the latent parental lpZel HZ virus (shingles causative agent); vOka vaccine strains isolated from vaccines against VZV infection from two manufactures (United Kingdom and USA); the HEL-3 strain of diploid cells from human embryonic lung tissue, the MC 27 strain of diploid cells from human embryonic musculocutaneous tissue, primary and diploid cells from guinea pig fetal fibroblasts. The VZV infectivity was estimated by the limiting dilution method using MC 27 cell cultures or guinea pig fetal fibroblasts. The virus titer was measured by the hemadsorption test performed with suspensions of red blood cells from guinea pig or human type 0 positive blood. Negative staining and electron microscopy were used to study the virus preparation. The immunogenicity of vFiraVax VZV and vZelVax HZ virus strains was compared with the immunogenicity of vOka VZV virus strains from different manufacturers by using a cross-neutralization test with immune sera.Results. The Russian cold-adapted vFiraVax VZV and vZelVax HZ vaccine strains, the latent parental lpZel HZ virus and the vOka VZV vaccine strain (United Kingdom) did not bind to preparations of brain neuroreceptors of SPF BALB/c mice as distinct from the wild-type parental pFira VZV variant and vOka VZV vaccine strains (USA); the absent neurotropism of Russian vFiraVax VZV and vZelVax HZ vaccine strains is not connected with the decreased immunogenicity in relation to foreign counterparts; the electron microscope study of the vFiraVax VZV virus containing liquid concentrate detected VZV nucleocapsids.Conclusion. The differences in the VZV ability to bind to preparations of brain membrane receptors of SPF BALB/c mice can be explained by the differences in the technology of vaccine manufacturing, including attenuation techniques, obtaining of the vaccine strain, specific characteristics of the latent parental lpZel HZ virus. The absence of the binding with brain neuroreceptors of SPF mice has been proved for the Russian vFiraVax VZV and vZelVax HZ vaccine strains which was is not connected with a decrease in their immunogenicity. The method of assessment of the binding ability of VZV vaccine strains can be used as a preliminary characteristic of neurotropism for newly created vaccine strains and for vaccine products.

Until now, it has been considered that infectivity of the varicella-zoster virus (VZV) is closely related to target cell, and newly formed virus is not released into the culture medium. It is also known that it is hard to grow VZV in cell cultures, due to its slow replication rate and a limited range of sensitive cell cultures. In addition, VZV isolation depends on type of cell culture used, nature of clinical material, presence of viable virus and transport time. Objectives. To study production of infectious extracellular VZV in various cell cultures. Materials and methods. Eight cell cultures were used, including human embryonic diploid lung cells and human embryonic dermomuscular tissue (KM-27), as well as continuous human and monkey cell lines. Crusts detached from vesicular lesions were used as clinical isolates, which were placed into cryo-vials added with transport medium and transferred in liquid nitrogen. VZV infectivity was assessed in cell cultures by using hemo-adsorption assay with erythrocyte suspension isolated from guinea pig or human zero group blood and confirmed by indirect immunofluorescence with polyclonal sera from varicella or herpes zoster convalescents. Results. There were examined 27 clinical samples consisting of crusts from vesicular lesions isolated from patients with chickenpox, as well as one sample from 63-year old patient with exacerbated recurrent herpes zoster. Primary infection with clinical isolates was performed on diploid human lung embryo cells (HLEC) at low temperature. It was found that clinical samples collected within day 1–18 inclusive after the onset of skin eruption were able to induce cytopathic effects in HLEC cell monolayer such as cytolysis around dermal crusts. Specificity of cytopathic effect was confirmed by using real-time polymerase chain reaction (RT-PCR). Viral antigens were prepared on 7 cell lines infected with the laboratory strain Ellen VZV (USA) to assess the immune sera. A high anti-VZV specificity of mouse sera was detected by ELISA while all the lysates of infected cell lines were used as the solid-phase sorbent. In experiments on VZV reproduction demonstrated that extracellular virus was released into the culture medium starting from day 1 after infection of target cells, and infectivity of the virus-containing fluid ascends during further cultivation.