ERVW-1 and infection: The results of infection experiments showed that HIV-1NL4–3 Env enabled HIV-1BH10 to replicate in IFITM1-expressing cells, whereas inserting the Env of HIV-1BH10 into HIV-1NL4–3 dramatically reduced virus replication in the presence of IFITM1 (Fig. 5C), supporting the role of NL4–3 Env in overcoming IFITM1 inhibition.