Characterization of EIAV LTR quasispecies in vitro and in vivo.
Wang XF, Liu Q, Wang YH, Wang S, Chen J, Lin YZ, Ma J, Zhou JH, Wang X.
J Virol. 2018 Jan 31. pii: JVI.02150-17. doi: 10.1128/JVI.02150-17
Abstract
The equine infectious anemia virus (EIAV) attenuated vaccine was developed by long-term passaging of a field-isolated virulent strain in cross-species hosts, followed by successive cultivation in cells in vitro To explore the molecular mechanism underlying the evolution of the EIAV attenuated vaccine, a systematic study focusing on long terminal repeat (LTR) variation in numerous virus strains ranging from virulent EIAV to attenuated EIAV was performed over time both in vitro and in vivo Two hypervariable regions were identified within the U3 region in the enhancer region (EHR) and the negative regulatory element (NRE) and within the R region in the transcription start site (TSS) and the Tat-activating region (TAR). Among these sites, variation in the U3 region resulted in the formation of additional transcription factor binding sites; this variation of the in vitro-adapted strains was consistent with the loss of pathogenicity. Notably, the same LTR variation pattern was observed both in vitro and in vivo Generally, the LTR variation in both the attenuated virus and the virulent strain fluctuated over time in vivo Interestingly, the attenuated virus-specific LTR variation was also detected in horses infected with the virulent strain, supporting the hypothesis that the evolution of attenuated virus might have involved branching from EIAV quasispecies. This hypothesis was verified by the phylogenetic analysis. The present systematic study examining the molecular evolution of attenuated EIAV from EIAV quasispecies may provide an informative model reflecting the evolution of similar lentiviruses.IMPORTANCE The attenuated EIAV vaccine was the first lentiviral vaccine used to successfully control for the disease in China. This vaccine provides an important reference studying the relationship between EIAV gene variation and changes in biological characteristics. Importantly, the vaccine provides a model for the investigation of lentiviral quasispecies evolution. This study followed the "natural" development of the attenuated EIAV vaccine using a systematic analysis of LTR evolution in vitro and in vivo The results revealed that the increase in LTR variation with passaging was accompanied by decreased the virulence, which indicated that LTR variability might parallel the attenuated of virulence. Interestingly, the attenuated virus-specific LTR variation was also detected in virulent strain-infected horses, which was consistent with previously investigations of the gp90 and S2 evolution. Therefore, we present a hypothesis that the evolution of the attenuated virus may develop as a branched from EIAV quasispecies present in vivo.