Establishment of an in vitro equine papillomavirus type 2 (EcPV2) neutralization assay and a VLP-based vaccine for protection of equids against EcPV2-associated genital tumors.

This study investigates the role of the Equus caballus papillomavirus type 2 (EcPV2) in the development of genital squamous cell carcinoma (gSCC) in horses. The researchers established a test, developed a vaccine based on virus-like particles (VLPs) of EcPV2, and evaluated its potential to prevent the infection and related disease.

Context and Objective of the Study

• This research is situated in the context of equine health. Specifically, the scientists explore the connection between Equus caballus papillomavirus type 2 (EcPV2) and genital squamous cell carcinoma (gSCC), a type of cancer affecting horses.
• Given the consistent presence of EcPV2 DNA and mRNA in the tumors, they hypothesized that EcPV2 might play a causative role in the disease development. The main objective of this research is to validate this assumption and test a potential vaccine for EcPV2 infection.

EcPV2 Neutralization Assay

• Firstly, the researchers developed an EcPV2 pseudo-virion (PsV) neutralization assay, a test aiming to measure the amount of EcPV2-neutralizing serum antibodies.
• They found that all animals affected by gSCC (6 out of 6) exhibited EcPV2-neutralizing antibodies according to the PsV assay. However, among those without tumors, only a minority (3 out of 20) showed similar results.

Development of EcPV2 L1 VLP-based Vaccine

• The researchers created a vaccine consisting of EcPV2 L1 virus-like particles (VLP). VLPs are molecules that closely resemble viruses but are non-infectious as they lack viral genetic material.
• By using two different kinds of booster substances (Freund’s for rabbits and alum for mice), they induced a strong immune response in the vaccinated animals (with antibody titer ranging from 1600 to 12,800).

Prophylactic Efficacy Evaluation

• The protective effect of the new vaccine was examined through experiments involving passive transfer with rabbit EcPV2-VLP immune sera. This method involves transferring immunity from one organism to another through serum.
• Mice that received this treatment were fully protected against a subsequent experimental infection by EcPV2.

Conclusion

• The study’s findings endorse the proposed role of EcPV2 in the development of gSCC in horses. Furthermore, the robust efficacy of the EcPV2 L1 VLP-based vaccine put it forth as a promising strategy to protect equids against EcPV2 infection and associated disease.