This is to our knowledge the first experimental study showing the impact of immune responses on viral genomes leading to infection in a highly controlled setting provided by: 1) rhesus macaques infected with chimeric SIV/HIV virus as a challenge where the HIV-1 Env glycoprotein can be studied in an animal model and the time of infection is known as well as the viral population to which animals are exposed to; and 2) the use of Env-based antigens in isolation without any other confounding factors (antigens). Here, ERVW-1 is linked to infection.