A Species-Specific Amino Acid Difference in the Macaque CD4 Receptor Restricts Replication by Global Circulating HIV-1 Variants Representing Viruses from Recent Infection

Abstract

bHIV-1 replicates poorly in macaque cells, and this had hindered the advancement of relevant nonhuman primate model systems for HIV-1 infection and pathogenesis. Several host restriction factors have been identified that contribute to this species-specific restriction to HIV-1 replication, but these do not fully explain the poor replication of most strains of HIV-1 in macaque cells. Only select HIV-1 envelope variants, typically those derived from viruses that have been adapted in cell culture, result in infectious chimeric SIVs encoding HIV-1 envelope (SHIVs). Here we demonstrate that most circulating HIV-1 variants obtained directly from infected individuals soon after virus acquisition do not efficiently mediate entry using the macaque CD4 receptor. The infectivity of these viruses is ca. 20-to 50-fold lower with the rhesus and pig-tailed macaque versus the human CD4 receptor. In contrast, culture-derived HIV-1 envelope variants that facilitate efficient replication in macaques showed similar infectivity with macaque and human CD4 receptors (within ϳ2-fold). The ability of an envelope to mediate entry using macaque CD4 correlated with its ability to mediate entry of cells expressing low levels of the human CD4 receptor and with soluble CD4 sensitivity. Species-specific differences in the functional capacity of the CD4 receptor to mediate entry mapped to a single amino acid difference at position 39 that is under strong positive selection, suggesting that the evolution of CD4 may have been influenced by its function as a viral receptor. These results also suggest that N39 in human CD4 may be a critical residue for interaction of transmitted HIV-1 variants. These studies provide important insights into virus-host cell interactions that have hindered the development of relevant nonhuman primate models for HIV-1 infection and provide possible markers, such as sCD4 sensitivity, to identify potential HIV-1 variants that could be exploited for development of better SHIV/macaque model systems.

Simian Immunodeficiency Virus SIVmac239, but Not SIVmac316, Binds and Utilizes Human CD4 More Efficiently than Rhesus CD4

“…We further show that a key determinant of the greater neutralization by human CD4-Ig is residue 39, an asparagine in human CD4 but an isoleucine in the rhesus ortholog. This observation is consistent with previous reports demonstrating that this CD4 residue can also account for the ability of various SHIVs to utilize human CD4 more efficiently than rhesus CD4 (13,15). While it is not unexpected that SHIVs, whose Envs are derived from HIV-1, would utilize human CD4 more efficiently, SIV's preference for human CD4 requires greater explanation.…”

“…We have previously observed that huCD4-Ig more efficiently neutralizes various HIV-1 Envs than does a CD4-Ig variant with rhesus CD4 and Fc domains (15). As suggested by Humes et al (13), we also observed that introduction of human CD4 asparagine 39 into this rhesus CD4-Ig construct neutralized HIV-1 isolates with efficiencies similar to huCD4-Ig (15). To focus our current studies on the CD4 domains of these constructs, here we used a common human IgG1 Fc domain for huCD4-Ig, rhCD4-Ig, and rhCD4-Ig variants.…”

“…Only a subset of SHIVs replicate efficiently in macaques, a consequence in part of the inefficiency with which most HIV-1 Envs utilize rhesus CD4 (12,13). An isoleucine at rhesus CD4 residue 39 has been identified as a major determinant of this inefficiency (13). Substitution of this isoleucine with an asparagine (I39N) present in human CD4 significantly increases infection by most SHIVs.…”

“…These chimeric viruses include the HIV-1 env and vpu genes and were developed to study the properties of HIV-1 envelope glycoprotein (Env) in the macaque model. Only a subset of SHIVs replicate efficiently in macaques, a consequence in part of the inefficiency with which most HIV-1 Envs utilize rhesus CD4 (12,13). An isoleucine at rhesus CD4 residue 39 has been identified as a major determinant of this inefficiency (13).…”

Lineage-Specific Differences between the gp120 Inner Domain Layer 3 of Human Immunodeficiency Virus and That of Simian Immunodeficiency Virus

“…Of note, while some differences between human and rhesus CD4/CCR5 have been reported (24,26,27), we decided to use both human CD4-Ig and cells expressing human CCR5 to be consistent with previous studies characterizing the HIV and SIV gp120 inner domain layers (15,16). For CCR5 binding, normalized amounts of radiolabeled SIVmac239 gp120 envelope glycoproteins were incubated in the presence or absence of 200 nM soluble CD4 (sCD4) for 1 h at 37°C.…”