Replication Ability in Vitro and in Vivo of Equine Infectious Anemia Virus Avirulent Japanese Strain

Liu

et al. 2018

J Virol

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 an attenuated virus might have involved branching from EIAV quasispecies. This hypothesis was verified by 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 equine infectious anemia in China. This vaccine provides an important reference for 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 by use of 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 a decrease in virulence, which indicated that LTR variability might parallel the attenuation of virulence. Interestingly, the attenuated-virus-specific LTR variation was also detected in virulent-strain-infected horses, a finding consistent with those of previous investigations of gp90 and S2 evolution. Therefore, we present a hypothesis that the evolution of the attenuated virus may involve branching from EIAV quasispecies present in vivo.

“…6 ). These results are consistent with observations from our lab ( 27 ) and other labs ( 28 , 29 ). Interestingly, in vitro -adapted mutations were found in the LN40-infected horses.…”

Section: Discussionsupporting

confidence: 94%

Characterization of Equine Infectious Anemia Virus Long Terminal Repeat Quasispecies In Vitro and In Vivo

Liu

et al. 2018

J Virol

“…These results suggest that the S2 gene plays an important role in viral replication in vivo and in viral virulence. These two attenuated strains generate effective immunity against infection by their respective virulent parental strains, but cannot produce immunoprotection against heterologous viral strains [2,[44][45][46].…”

Section: Discussionmentioning

confidence: 99%

Genomic analysis of an effective lentiviral vaccine-attenuated equine infectious anemia virus vaccine EIAVFDDV13

et al. 2010

Virus Genes

Chinese equine infectious anemia virus (EIAV) attenuated vaccine is the first lentiviral vaccine with a successful application. In order to understand the correlation of viral genomic mutations with viral attenuation and with induced immunoprotective properties, we analyzed the proviral genome sequences of the EIAV-attenuated vaccine strain EIAV(FDDV13) (EIAV fetal donkey dermal cell-adapted vaccine) and its highly virulent parental strain EIAV(LN40). The sequences of these strains were compared with those of the major foreign EIAV strains. The results indicated a large genetic distance between the Chinese EIAV strain and the major EIAV strains in America and Japan. The Chinese strains belong to an independent phylogenetic branch. The divergence between the entire genome of the Chinese strains and that of other major EIAV strains is approximately 23%. The divergence rate in LTR is over 14%, whereas that in each open reading frame is over 20%. The gp90 exhibited a divergence of 35% in its nucleotide sequence and 40% in its amino acid sequence. The present study found that after long-term passage in vitro, EIAV(FDDV13) has accumulated many stable substitution mutations in each gene. These mutations at multiple sites in multiple genes of the vaccine strain, especially the conserved mutations, provide important references for further understanding the attenuation mechanism of Chinese EIAV-attenuated vaccine and the immunoprotection mechanism of lentiviral vaccines.

“…Although EIA is pandemic throughout the world, previous studies targeted only a few viral strains [4], mainly the American virulent strain, EIAV Wyoming , and its derived strains (EIAV PV , EIAV UK , and EIAV WSU5 ) [1,10,[14][15][16][17][18][19][20][21], the Japanese virulent strain, V70, and its attenuated strain V26, which was derived after extended culture in equine macrophage cells [22][23][24][25], and the Chinese virulent EIAV LN40 and its derived attenuated vaccine strains [26][27][28][29][30][31][32][33]. Recently, Craigo et al reported that a special EIAV strain, EIAV PA , was isolated in Pennsylvania, USA, with an Env that differs from that of EIAV Wyoming by 40% [34].…”

Section: Introductionmentioning

confidence: 99%

Unique evolution characteristics of the envelope protein of EIAVLN40, a virulent strain of equine infectious anemia virus

Lin

et al. 2011

Virus Genes

The Chinese equine infectious anemia virus (EIAV) virulent strain EIAV(LN40) is derived from a naturally occurring virus by continuously passing in horses for 16 generations. Its genome sequence is 23% different from that of the American strains or the Japanese strains, and the variation of envelope gp90 surface unit (SU) is as high as 41%. In this study, evolutions of the EIAV(LN40) gp90 gene in four infected horses were analyzed. Results showed that new quasispecies arose in the early stage of infection in all EIAV(LN40)-infected horses. These quasispecies belonged to branches different from EIAV(LN40) in a phylogenetic tree. In contrast, the gp90 sequences of viruses isolated after disease onset remained in the same phylogenetic branch as EIAV(LN40), with some having exactly the same sequences. The glycosylation sites 191NSSN and 237NNTW in the V3 and V4 region present or absent simultaneously in most of the predicted amino acid sequences. Changes in the glycosylation sites within V3, V4, and V5 regions are usually associated with the disease status. Glycosylation sites (191NSSN, 237NNTW, and 280NDTS) within these three regions were present in EIAV(LN40) and most of the quasispecies isolated after, but not before disease onset. These unique evolutionary characteristics of SU have not been reported for EIAV and other lentiviruses. Our results provide a reference for a further understanding of the mechanism underlying the persistent infection and escape from immune surveillance of EIAV.