Engineered soluble truncated envelope proteins block bovine leukemia virus infection

Bovine leukemia virus (BLV), a member of the delta retrovirus family, is transmitted horizontally among cows. BLV causes enzootic bovine leukosis and has great economic impact on the cattle industry. Recently, secretory-defective Env proteins (e.g., Refrex-1 and FeLIX) have been detected in domestic cats and shown to possess antiretroviral activity against gammaretroviruses via viral receptor interference. Therefore, we investigated whether BLV-derived molecules engineered similarly exhibit antiviral activity against BLV infection. We generated several proteins consisting of the BLV envelope surface unit (SU) region and signal peptide, without the transmembrane region, and tested their inhibitory effects on BLV infection. These artificial mutant Env-SU proteins were detected as secreted proteins in cultured cells. Colony formation and quantitative PCR assays revealed that the secreted Env-SU proteins exhibited an inhibitory effect on BLV infection. In conclusion, the engineered BLV Env-SU protein was found to effectively inhibit BLV infection, likely through a mechanism consistent with viral receptor interference and is expected to contribute to the development of infection-prevention methods against BLV.