EIAV envelope diversity: shaping viral persistence and encumbering vaccine efficacy

Equine infectious anemia virus (EIAV) and its associated disease have presented a considerable challenge to veterinary medicine worldwide ever since its identification in the 19th century. Furthermore EIAV, along with its fellow animal lentiviruses, has been utilized as an animal model of HIV-1/AIDS research since the latters identification in the late 20th century. Like all lentiviruses, EIAV has been shown to have a high propensity for genomic sequence and antigenic variation, principally in its envelope (Env) proteins. However, unlike other lentiviruses, EIAV possesses a unique and dynamic disease presentation that enables consummate analyses of the interactions between a virus, host immune system, and the effects of viral evolution on vaccine efficacy. Hence, EIAV provides a novel animal lentivirus system with which to dissect the viral and immune correlates of vaccine efficacy and a system with which to examine vaccine candidates for the ability to elicit broadly protective vaccine immunity. The current review summarizes the key findings that have thus far provided a fundamental understanding of the role of the viral Env in immune control of infection, disease, and vaccine efficacy.