Replication-competent SIVcpz CRISPR screen identifies barriers to successful cross-species transmission

Simian immunodeficiency viruses (SIVs) have crossed from apes to humans at least four times, but only one event gave rise to the AIDS pandemic. The host barriers that pandemic HIV-1 group M (major) strains overcame to spread efficiently in humans remain poorly understood. To identify such barriers, we performed CRISPR-Cas9 screens driven by the replication efficiency of SIVcpz, the chimpanzee precursor of HIV-1. Guide RNA libraries targeting more than 500 human genes encoding potential antiviral factors were inserted into the replication-competent SIVcpz MB897 molecular clone, which is phylogenetically closely related to HIV-1 group M strains. Propagation in Cas9-expressing human SupT1 T cells significantly enriched for sgRNAs targeting AXIN1, CEACAM3, CD72, EHMT2, GRN, HMOX1, HMGA1, ICAM2, IFITM2, MEFV, PCED1B, SGOL2, SMARCA4, SUMO1, and TMEM173. These hits only partially overlapped with those identified in analogous HIV-1-based screens, indicating virus-specific restriction profiles. Functional analyses confirmed that IFITM2 (interferon-induced transmembrane protein 2), PCED1B (PC-esterase domain-containing protein 1B), MEFV (Mediterranean fever protein, pyrin/TRIM20), and AXIN1 (Axis inhibition protein 1) restrict replication of the analyzed SIVcpz strains but not HIV-1 group M strains in primary human CD4⁺ T cells. These findings reveal previously unrecognized host factors that limit SIVcpz replication in human cells and highlight barriers that at least some HIV-1 group M strains overcame during adaptation for pandemic spread.

Four independent transmission events of simian immunodeficiency viruses from chimpanzees and gorillas to humans gave rise to human immunodeficiency virus type 1, but only one led to the global AIDS pandemic. Understanding which adaptations allowed the pandemic HIV-1 M strains to spread efficiently in humans remains a key question in virus evolution and public health. In this study, we engineered replication-competent SIVcpz constructs carrying more than 1,500 single-guide RNAs to identify antiviral genes in Cas9-expressing cells. This approach revealed several cellular factors that restrict SIVcpz but not the pandemic HIV-1 M strains analyzed in primary human T cells. These findings provide new insights into antiviral defense mechanisms and the adaptations that most likely contributed to the efficient spread of HIV-1.