Several molecular barriers, including members of the tripartite interaction motif (TRIM) family, members of the apolipoprotein B editing complex (APOBEC) class of cytidine deaminases, and CD317 (Tetherin, BST-2), are frequently up-regulated by host cells in response to viral (e.g., HIV-1) infection, and impose particularly effective barriers in the context of cross-species transmission of viruses (Brehm et al., 2014). This evidence concerns the gene BST2 and HIV-1 infection.