ERVW-1 and infection: Our results together with those from a previous work that reported inefficient infection of viruses from LTNP-ECs (11) could indicate that the ability of HIV-1 to establish efficient infection determines the in vivo progression of the infection, and as we specifically described here, inefficient Env-mediated functions appear to be responsible for the LTNP-EC phenotype in this cluster of HIV-1+ individuals.