CypA is a molecular barrier to HIV emergence from Eastern chimpanzees.

Of the two lineages of lentivirus that endemically infect chimpanzees, only one has served as a source of infections in humans. Using HIV-CRISPR screening, we identify factors that limit the replication of lentivirus from Eastern chimpanzees. We find that CypA restricts nonzoonotic Eastern chimpanzee lentivirus due to a unique feature encoded in capsid. The ability of CypA to restrict lentivirus replication is surprising given that CypA is a host factor exploited by HIV to promote its replication. The selective ability of CypA to restrict this virus provides a molecular explanation as to why lentivirus from Eastern Chimpanzees has never been observed to infect humans. Our work has important implications for understanding the origins of HIV-1 and the potential for novel zoonosis of primate lentiviruses.