Introduction

Bovine papillomaviruses types 1 and 2 (BPV1, BPV2) induce semi-malignant skin tumours termed sarcoids in horses. Sarcoids seriously compromise the health and welfare of affected individuals due to their high propensity to progress upon accidental or iatrogenic trauma, and to reoccur in a more severe, multiple form following ineffective treatment.

Materials and Methods

We have developed recombinant influenza (Flu) A and B viruses harbouring a partially deleted NS1 gene (iNS1) assuring live attenuation, and shuffled BPV1 E6 and E7 antigens as immunotherapeutic vaccines.

Results

In a phase I trial involving 12 healthy horses, intradermal administration of vaccines proved safe with the only transient side effect being mild fever in four horses following injection with iNS1-FluA-BPV1-E6E7 virus. Importantly, vaccine candidates also proved biologically safe: repeated screening of secretions and faeces by RT-PCR and focus forming assay during the trial testified to the absence of virus shedding. In an ongoing patient trial involving horses bearing multiple, partly recurrent sarcoids, one lesion per horse is intralesionally injected with the influenza A virus, and then boosted with the influenza B virus. Per January 2020, treatment led to highly significant tumour regression or eradication in seven, and stable disease in two of the nine patients treated thus far. Intriguingly, treatment also induced a systemic anti-tumour response in all individuals as revealed by synchronous regression or growth arrest of non-injected lesions located at different sites of the horses’ integument.

Conclusions

To our knowledge, this is the first immunotherapeutic approach showing significant reduction of the tumour burden in equine sarcoid patients.