ERVW-1 and leukemia: During the BLV-induced leukemia progression, BLV proviral genes coding for polymerase, capsid, and envelop proteins become increasingly deleted in BLV-infected cattle to escape from the host immune response, while BLV still retains the LTR region and tax gene, which carry oncogenic potential [9, 52, 53]; it is not clear whether BLV can cause the same phenomenon in human body, considering that all the blood donors are healthy.