Equine Infectious Anemia Virus Envelope Evolution In Vivo during Persistent Infection Progressively Increases Resistance to In Vitro Serum Antibody Neutralization as a Dominant Phenotype

Abstract

Equine infectious anemia virus (EIAV) infection of horses is characterized by well-defined waves of viremiaassociated with the sequential evolution of distinct viral populations displaying extensive envelope gp90 variation; however, a correlation of in vivo envelope evolution with in vitro serum neutralization phenotype remains undefined. Therefore, the goal of the present study was to utilize a previously defined panel of natural variant EIAV envelope isolates from sequential febrile episodes to characterize the effects of envelope variation during persistent infection on viral neutralization phenotypes and to define the determinants of EIAV envelope neutralization specificity. To assess the neutralization phenotypes of the sequential EIAV envelope variants, we determined the sensitivity of five variant envelopes to neutralization by a longitudinal panel of immune serum from the source infected pony. The results indicated that the evolution of the EIAV envelope sequences observed during sequential febrile episodes produced an increasingly neutralization-resistant phenotype. To further define the envelope determinants of EIAV neutralization specificity, we examined the neutralization properties of a panel of chimeric envelope constructs derived from reciprocal envelope domain exchanges between selected neutralization-sensitive and neutralization-resistant envelope variants. These results indicated that the EIAV gp90 V3 and V4 domains individually conferred serum neutralization resistance while other envelope segments in addition to V3 and V4 were evidently required for conferring total serum neutralization sensitivity. These data clearly demonstrate for the first time the influence of sequential gp90 variation during persistent infection in increasing envelope neutralization resistance, identify the gp90 V3 and V4 domains as the principal determinants of antibody neutralization resistance, and indicate distinct complex cooperative envelope domain interactions in defining sensitivity to serum antibody neutralization.

Equine Infectious Anemia Virus (EIAV): what has HIV?s country cousin got to tell us?

“…Interestingly, as previously described during HIV and SIV infections in primates [39,45,69,119], viral evolution in EIAV-gag and env genes led to CTL escape [114]. EIAV-neutralizing antibodies that are able to block the infecting strain usually emerge only after two or three months post infection [5,51,61,75,123] suggesting that they are not responsible for the termination of the acute episode. In a longitudinal study, no correlation was observed between the level of neutralizing antibodies and the course of the infection [51].…”

“…In a recent study, we determined the sensitivity of five sequential variant envelope glycoproteins [81] to neutralization by a longitudinal panel of immune sera from the source infected pony by exchanging regions of neutralization-sensitive and neutralization-resistant envelopes [61]. We demonstrated the influence of sequential gp90 variation in increasing envelope neutralization resistance, identified the V3 and V4 variable regions of gp90 as the principal determinants of neutralization resistance and suggested the importance of complex cooperative envelope domain interaction in defining this resistance [61].…”

Envelope variation as a primary determinant of lentiviral vaccine efficacy

“…The variant virus stocks were then titered and characterized for in vitro and in vivo replication kinetics (14,31). All three proviral challenge strains demonstrated typical in vitro replication kinetics that peaked in virus production at Ϸ10 days after infection (data not shown).…”

“…The two proviral clones chosen for the production of variant challenge strains were derived from plasma viral isolates that were acquired Ϸ1,000 days apart and that diverged from EIAV PV and EIAV D9 at the amino acid level by 6% and 13%. The gp90 genes of these isolates were cloned by using standard techniques (14,32) into our proviral molecular clone EIAV UK3 (33) and were termed EV6 and EV13, respectively. EIAV UK3 , which is derived from our EIAV PV biological clone (hence the envelope is homologous to EIAV PV /EIAV D9 ) was also used as a proviral challenge strain and was termed EV0.…”

“…Lentiviral antigenic variation is most pronounced in the viral Env proteins that serve as initial primary targets for host immune responses. Studies on the effect of Env variation on antigenic properties indicate that even minor changes in amino acid sequence can dramatically alter antibody and CTL specificities in in vitro assays and immune control of persistent infections in vivo (6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17). Nevertheless, even apparently extensive Env variations may not necessarily cause detectable changes in immune phenotype as measured by in vitro assays alone (18).…”