For decades, the generation of soluble mimics of Env was challenging due to its inherent metastability, in part because of the non-covalent association of the Env subunits, gp120 and gp41, due to furin cleavage of the precursor gp160 during natural infection to attain its fusion-active conformation (Berger et al., 1991, Moore et al., 1990). This evidence concerns the gene ERVW-1 and infection.