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Abstract
HIV-1 does not persistently infect macaques due in part to restriction by several macaque host factors. This has been partially circumvented by generating chimeric SIV/HIV-1 viruses (SHIVs) that encode SIV antagonist of known restriction factors. However, most SHIVs replicate poorly in macaques unless they are further adapted in culture and/or macaques (adapted SHIVs). Therefore, development of SHIVs encoding HIV-1 sequences derived directly from infected humans without adaptation (unadapted SHIVs) has been challenging. In contrast to the adapted SHIVs, the unadapted SHIVs have lower replication kinetics in macaque lymphocytes and are sensitive to type-1 interferon (IFN). The HIV-1 Envelope (Env) in the chimeric virus determines both the reduced replication and the IFN-sensitivity differences. There is limited information on macaque restriction factors that specifically limit replication of the more biologically relevant, unadapted SHIV variants. In order to identify the IFN-induced host factor(s) that could contribute to the inhibition of SHIVs in macaque lymphocytes, we measured IFN-induced gene expression in immortalized pig-tailed macaque (Ptm) lymphocytes using RNA-Seq. We found 147 genes that were significantly upregulated upon IFN treatment in Ptm lymphocytes and 31/147 were identified as genes that encode transmembrane helices and thus are likely present in membranes where interaction with viral Env is plausible. Within this group of upregulated genes with putative membrane-localized proteins, we identified several interferon-induced transmembrane protein (IFITM) genes, including several previously uncharacterized Ptm IFITM3-related genes. An evolutionary genomic analysis of these genes suggests the genes are IFITM3 duplications not found in humans that are both within the IFITM locus and also dispersed elsewhere in the Ptm genome. We observed that Ptm IFITMs are generally packaged at higher levels in unadapted SHIVs when compared to adapted SHIVs. CRISPR/Cas9-mediated knockout of Ptm IFITMs showed that depletion of IFITMs partially rescues the IFN sensitivity of unadapted SHIV. Moreover, we found that the depletion of IFITMs also increased replication of unadapted SHIV in the absence of IFN treatment, suggesting that Ptm IFITMs are likely important host factors that limit replication of unadapted SHIVs. In conclusion, this study shows that Ptm IFITMs selectively restrict replication of unadapted SHIVs. These findings suggest that restriction factors including IFITMs vary in their potency against different SHIV variants and may play a role in selecting for viruses that adapt to species-specific restriction factors.
Highlights
The macaque models of HIV-1 infection have been critical to the understanding of retroviral pathogenesis as well as for testing antiretroviral therapies and candidate vaccines for HIV-1
HIV-1 does not persistently infect macaques due to inhibition of the virus by several macaque-specific restriction factors necessitating the use of chimeric SIV/HIV-1 viruses (SHIVs)
Existing SHIV/ macaque models typically employ SHIVs that encode HIV-1 sequences from viruses amplified in culture and further adapted in macaques
Summary
The macaque models of HIV-1 infection have been critical to the understanding of retroviral pathogenesis as well as for testing antiretroviral therapies and candidate vaccines for HIV-1. SHIVs encoding HIV-1 sequences derived directly from humans typically require further adaptation in vitro in macaque cells and/or in vivo by serial macaque-passage [1] in order to obtain pathogenic viruses that establish persistent infection in macaques. These variant chimeric viruses used in the SHIV/macaque models are “adapted” SHIVs. We have previously determined that most circulating, transmitted HIV-1 Envelope (Env) variants, including the transmitted/founder variants, do not use macaque CD4 entry receptor efficiently [4] and SHIVs generated using these Envs replicate poorly in macaque cells. The adaptation of SHIV Env sequences in macaques increases replication and pathogenicity of SHIVs [5,6,7,8,9,10,11] and leads to antigenic changes in Env that can limit their utility for vaccine and therapeutic
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