Genetic immunization with codon-optimized equine infectious anemia virus (EIAV) surface unit (SU) envelope protein gene sequences stimulates immune responses in ponies.

The researchers tested a genetic immunization approach on ponies with a renewed version of equine infectious anemia virus. Despite initial successes in stimulating immune response, the approach failed to protect the subjects against the virus infection.

Background and Objective

• The study primarily aimed at dealing with the inefficacy of the native equine infectious anemia virus (EIAV)-envelope gene. It had been a weak immunogen in horses as it was poorly expressed due to some unfavorable elements. These included an unusual codon-usage bias, the possession of multiple RNA splice sites and potential adenosine-rich RNA instability elements.
• The goal was to improve the gene’s performance and, thereby, enhance the immune response against EIAV by designing and testing a synthetic version of sequences encoding the EIAV surface unit (SU) envelope glycoprotein, termed as SYNSU. The codon-usage bias of SYNSU was modified to mimic highly expressed horse and human genes for better performance.

Methods and Findings

• The researchers tested this engineered version, SYNSU, in transfected COS-1 cell cultures. They found that the expression levels of SYNSU were at least 30 times greater than the native SU sequences, indicating that their genetic modification strategy was successful.
• Subsequently, the genetically immunization strategy was performed on ponies with a mammalian expression vector encoding SYNSU. Upon doing so, EIAV-specific humoral and lymphocyte proliferation responses were observed in the ponies, indicating a successful immune response to the synthetic antigen.

Conclusion and Future Directions

• Despite the promising early results, the genetically-triggered immunological responses could not protect the ponies against infection with a virulent strain of EIAV, ultimately rendering the whole exercise futile.
• This highlights the need for more research into these issues and possibly other novel approaches to stimulate an effective immune response against EIAV. These could potentially involve further genetic modifications or perhaps a completely alternative strategy to tackle this problem.