Genetic variants of EcPV2 E6 and E7 in equine genital and oronasal squamous cell carcinoma

Background Since its discovery in 2008, equine papillomavirus type 2 (EcPV2) has been detected in up to 100% of equine genital and up to 40% of equine oronasal squamous cell carcinomas (SCCs). Preliminary sequence data point to the existence of EcPV2 E6 and E7 oncogene variants compared to the British reference sequence from 2008.Objectives To Identify E6 and E7 sequence variations in EcPV2-positive tumours of horses from Continental Europe and Iceland.Study Design Cross-sectional study.Methods EcPV2 E6 and E7 were amplified from DNA of 60 EcPV2-positive SCCs/SCC precursor lesions. Amplicons were gel-purified and submitted to bidirectional Sanger sequencing. Resulting 5 '-and 3 '-sequences were aligned with each other and then to EcPV2 sequences in the GenBank to determine sequence variations on DNA and predicted protein level.Results Eight E6 gene variants were identified, predicting four E6 protein variants compared to the reference sequence. One E6 variant predominantly occurred in Icelandic horses imported from Iceland. Detected genetic variations in E6 were unlikely to affect known functional motifs. The E7 gene was highly conserved. None to three SNPs were detected per lesion, and only one E7 sequence contained a SNP predicted to be non-synonymous.Main Limitations Low number of oronasal SCCs (n = 10) included in the study.Conclusions The detected E6 and E7 variants point to the existence of different EcPV2 sublineages. Interestingly, one E6-E7 sequence was significantly associated with SCC-bearing Icelandic horses imported from Iceland, suggesting that a specific EcPV2 sublineage may have evolved on the island. Provided that this theory can be confirmed, the long period between initial EcPV2 infection in Iceland and tumour development would indicate that EcPV2 can induce chronic infections that are reactivated in the older horse. Obtained sequence data are currently implemented in the generation of an immunotherapeutic vaccine targeting EcPV2 E6 and E7.