Vaccination with virus-like particles induces long lasting protection from experimentally induced sarcoid-like tumours in horses

Reasons for performing study:

We have already demonstrated that vaccination with empty BPV1 capsids termed virus-like particles (VLP) protects horses from experimental infection with BPV1 virion. Long-term monitoring of antibody titres in experimental horses and data from other species suggest that this protection is long lasting.

Objectives:

To test protection against experimental infection with BPV-1 virion in horses that were vaccinated with BPV-1 L1 VLP approximately 5 years earlier. Study design: Controlled experiment.

Methods:

Seven horses, vaccinated 3 times (boosters after 4 weeks and 6 months) in 2007/2008 with doses of BPV1 L1 VLP ranging from 50 µg to 150 µg/dose and 3 unvaccinated control horses were challenged by intra-dermal inoculation with cow wart derived BPV1 virion (5x107 BPV-1 virions per wheal, 10 wheals per horse). Inoculation sites were monitored for 10 weeks. Blood for serum antibody titre determination by pseudovirion neutralisation assay was taken on the day of challenge and after 6 months.

Results:

Six of 7 vaccinated horses had measurable serum antibody titres (1:50 to 1:400). These titres were boosted by inoculation (about one step of dilution). Two of 3 unvaccinated controls remained sero-negative. One control horse showed sero-conversion. All control horses developed tumours at all 10 inoculation sites. Tumours appeared approximately 2 weeks after inoculation and reached maximum sizes of up to 8 mm. Regression was complete by 8 weeks after their first appearance in all horses. All vaccinated horses remained completely free from tumours. No influence of dose rate or antibody titre on the level of protection could be determined.

Conclusions:

BPV-1 L1 VLP vaccination proves to be fully effective in protecting horses from experimental infection and tumour formation 5 years post immunisation. The protection was complete even in horses with low or unmeasurable antibody titres. This is another step towards establishing a vaccination against equine sarcoids.