Abstract
Simian immunodeficiency viruses infecting sooty mangabeys (SIVsmm) gave rise to nine groups of human immunodeficiency virus type 2 (HIV-2). Two of these (A and B) spread substantially with an estimated 1-2 million individuals affected. The evolutionary adaptations that facilitated HIV-2's spread in humans are still poorly understood. Here, we report that diverse SIVsmm strains efficiently infect primary human T cells. However, they are more sensitive to interferon than HIV-2, indicating that interferon-stimulated genes (ISGs) pose a barrier to the successful spread of SIVsmm in humans. One of the best-known antiviral ISGs is the zinc finger antiviral protein (ZAP), which targets CpG dinucleotides in RNA. To evade ZAP-mediated restriction, many viruses, including HIV-1, suppress their CpG content. Unexpectedly, we found that HIV-2 is more resistant to ZAP restriction than HIV-1 and SIVsmm despite having 33% more CpGs. Identification of ZAP-binding sites using RNA enhanced crosslinking immunoprecipitation and analyses of chimeric HIV-2/SIVsmm viruses revealed that the determinants of ZAP resistance map to the nef/U3 region and promote HIV-2 replication in primary human T cells. Our results indicate that HIV-2 evolved a CpG-independent ZAP resistance mechanism which might have been facilitated by relaxed functional constraints acting on Nef in the human host.