Prophylactic Vaccination Against Papillomavirus-Induced Tumour Disease

Abstract

The Papillomaviridae family comprises a large number of genetically heterogeneous papillomaviruses (PVs) that are the causative agents of benign lesions or cancer in humans and a wide range of animal species. Early research in animal PV systems has disclosed several important characteristics of PVs and led to the recognition of human papillomaviruses (HPVs) as carcinogenic viruses in 1995. One of the most crucial findings in animals was that in vitro generated PV major capsid proteins spontaneously self-assemble to empty viral capsids termed virus-like particles (VLPs) that are safe and highly immunogenic. This discovery paved the way for the establishment and commercial release of highly effective polyvalent VLP-based vaccines for the prevention of HPV-induced tumour disease in humans. In addition, it encouraged veterinary scientists to work on the establishment of analogous, VLP-based vaccines for the protection of horses and other equids from common PV-induced cutaneous and mucosal tumours that is bovine PV type 1/2 (BPV1/2)-associated sarcoids and equine PV type 2 (EcPV2)-induced squamous cell carcinomas (SCCs). So far, BPV1 and EcPV2 VLPs were shown to be safe and highly immunogenic in horses. Furthermore, immunisation of horses with BPV1 VLPs conferred complete protection from experimental BPV1 infection and associated pseudo-sarcoid formation and also elicited cross protection from BPV2 infection. Similarly, the protective potential of EcPV2 VLPs against experimental infection with EcPV2 pseudo-virions was shown in a murine model. Taken together, these findings indicate that BPV1 and EcPV2 VLPs are safe and highly effective in protecting equids from PV-induced sarcoids and SCCs.