ERVW-1 and HIV-1 infection: In addition, replication-competent virus carrying the env gene from the CCR5-tropic BaL strain did not induce type I IFNs when the transfection procedure included a step to remove the transfection input (Fig. S2b) These results indicate that the observed induction of type I IFNs upon HIV-1 infection is caused independently from the VSV-G protein.