In vivo evolution of the gp90 gene and consistently low plasma viral load during transient immune suppression demonstrate the safety of an attenuated equine infectious anemia virus (EIAV) vaccine.

This study investigates the in vivo evolution of the Chinese equine infectious anemia virus (EIAV) vaccine, observing a decrease in diversity of the viral gp90 gene over time and consistently low levels of virus replication, even with suppressed immunity. It provides evidence supporting the safety of this weakened lentiviral vaccine.

Viral gp90 Gene Variation and Vaccine Evolution

• The study focused on the evolution of the gp90 gene of the attenuated EIAV vaccine in the body (in vivo).
• The gp90 gene of the EIAV vaccine showed a decreased diversity over time after vaccination.
• The declining diversity of the gp90 gene is reported to align with the maturation of immunity against EIAV, implying the adaptability of the vaccine to the host’s immune system.
• With the progression of time, the gp90 gene showed a high level of homology or similarity. The sequences of these predominant quasi species (viral forms within a host) were consistently detected for up to 18 months post-vaccination.

Viral Replication under Immune Suppression

• To test the safety of the vaccine under immune suppression, dexamethasone, an immune suppressant, was administered to the vaccinated horses.
• Unlike a virulent strain of the virus, which showed a 25,000-fold increase in viral load in a host with suppressed immunity, the vaccine strain maintained viral RNA copy number in the plasma consistently below the “pathogenic threshold,” even under immune suppression.
• This demonstrated that the vaccine was still functional and safe, keeping the viral replication under control even when the host’s immune response was compromised.

Implications of the Study

• This study provides the first piece of evidence attesting to the safety of this attenuated EIAV vaccine.
• It highlights the low-risk nature of the vaccine not just in normal conditions, but also under immunosuppression.
• The consistent low viral load throughout immune suppression indicates the vaccine’s effectiveness at containing the virus, thereby demonstrating its potential as a protective measure against EIAV.
• Moreover, the findings regarding the in vivo evolution of the gp90 gene contribute to our understanding of how attenuated vaccines function and evolve within the host.