Simian Immunodeficiency Virus SIVagm Efficiently Utilizes Non-CCR5 Entry Pathways in African Green Monkey Lymphocytes: Potential Role for GPR15 and CXCR6 as Viral Coreceptors.

UNLABELLED: African green monkeys (AGM) are natural hosts of simian immunodeficiency virus (SIV), and infection in these animals is generally nonpathogenic, whereas infection of nonnatural hosts, such as rhesus macaques (RM), is commonly pathogenic. CCR5 has been described as the primary entry coreceptor for SIV in vivo, while human-derived CXCR6 and GPR15 also appear to be used in vitro. However, sooty mangabeys that are genetically deficient in CCR5 due to an out-of-frame deletion are infectible with SIVsmm, indicating that SIVsmm can use alternative coreceptors in vivo. In this study, we examined the CCR5 dependence of SIV strains derived from vervet AGM (SIVagmVer) and the ability of AGM-derived GPR15 and CXCR6 to serve as potential entry coreceptors. We found that SIVagmVer replicated efficiently in AGM and RM peripheral blood mononuclear cells (PBMC) in the presence of the CCR5 antagonist maraviroc, despite the fact that maraviroc was capable of blocking the CCR5-tropic strains SIVmac239, SIVsmE543-3, and simian-human immunodeficiency virus SHIV-AD8 in RM PBMC. We also found that AGM CXCR6 and AGM GPR15, to a lesser extent, supported entry of pseudotype viruses bearing SIVagm envelopes, including SIVagm transmitted/founder envelopes. Lastly, we found that CCR5, GPR15, and CXCR6 mRNAs were detected in AGM and RM memory CD4(+) T cells. These results suggest that GPR15 and CXCR6 are expressed on AGM CD4(+) T cells and are potential alternative coreceptors for SIVagm use in vivo. These data suggest that the use of non-CCR5 entry pathways may be a common feature of SIV replication in natural host species, with the potential to contribute to nonpathogenicity in these animals. IMPORTANCE: African green monkeys (AGM) are natural hosts of SIV, and infection in these animals generally does not cause AIDS, whereas SIV-infected rhesus macaques (RM) typically develop AIDS. Although it has been reported that SIV generally uses CD4 and CCR5 to enter target cells in vivo, other molecules, such as GPR15 and CXCR6, also function as SIV coreceptors in vitro. In this study, we investigated whether SIV from vervet AGM can use non-CCR5 entry pathways, as has been observed in sooty mangabeys. We found that SIVagmVer efficiently replicated in AGM and RM peripheral blood mononuclear cells in the presence of the CCR5 antagonist maraviroc, suggesting that non-CCR5 entry pathways can support SIVagm entry. We found that AGM-derived GPR15 and CXCR6 support SIVagmVer entry in vitro and may serve as entry coreceptors for SIVagm in vivo, since their mRNAs were detected in AGM memory CD4(+) T cells, the preferred target cells of SIV.

Development of neurological disease is associated with increased immune activation in simian immunodeficiency virus-infected macaques.

Simian immunodeficiency virus (SIV) infection of macaques can result in central nervous system disorders, such as meningitis and encephalitis. We studied 10 animals inoculated with brain-derived virus from animals with SIV encephalitis. Over half of the macaques developed SIV-induced neurologic disease. Elevated levels of systemic immune activation were observed to correlate with viral RNA in the cerebral spinal fluid but not with plasma viral load, consistent with a role for SIV in the pathogenesis of neurologic disease.

Correction of a carboxyl terminal simian immunodeficiency virus Nef frameshift mutation restores virus replication in macaques.

Previous studies demonstrated that the nef gene is a critical determinant of the pathogenicity of simian immunodeficiency virus (SIV) in macaques. In the present study, we evaluated the effect of a spontaneous frameshift mutation in the C-terminus of the nef gene of the minimally pathogenic SIVsmH4i clone. This clone exhibited a single nucleotide deletion in the nef gene relative to pathogenic SIV clones that resulted in a frameshift and addition of 46 amino acids to the C-terminus of Nef. We generated a corrected version of this clone, SIVsmH4i Nef+ that restored Nef protein expression. Inoculation of macaques with SIVsmH4i resulted in delayed and low levels of peak viremia. This contrasted with improved kinetics and robust peak viremia in macaques inoculated with the corrected version. Despite the restoration of in vivo replication ability, neither clone resulted in memory CD4+ T cell loss or disease in a period of two years.

Adaptive evolution of simian immunodeficiency viruses isolated from 2 conventional-progressor macaques with encephalitis.

Simian immunodeficiency virus-infected macaques may develop encephalitis, a feature more commonly observed in macaques with rapid progressive disease than in those with conventional disease. In this report, an analysis of 2 conventional progressors with encephalitis is described. Phylogenetic analyses of viruses isolated from the cerebrospinal fluid and plasma of both macaques demonstrated compartmentalization. Furthermore, these viruses appear to have undergone adaptive evolution to preferentially replicate in their respective cell targets of monocyte-derived macrophages and peripheral blood mononuclear cells. A statistically significant loss of potential N-linked glycosylation sites in glycoprotein 160 was observed in viruses isolated from the central nervous system.

Loss of naïve cells accompanies memory CD4+ T-cell depletion during long-term progression to AIDS in Simian immunodeficiency virus-infected macaques.

Human immunodeficiency virus and simian immunodeficiency virus (SIV) induce a slow progressive disease, characterized by the massive loss of memory CD4+ T cells during the acute infection followed by a recovery phase in which virus replication is partially controlled. However, because the initial injury is so severe and virus production persists, the immune system eventually collapses and a symptomatic fatal disease invariably occurs. We have assessed CD4+ T-cell dynamics and disease progression in 12 SIV-infected rhesus monkeys for nearly 2 years. Three macaques exhibiting a rapid progressor phenotype experienced rapid and irreversible loss of memory, but not naïve, CD4+ T lymphocytes from peripheral blood and secondary lymphoid tissues and died within the first 6 months of virus inoculation. In contrast, SIV-infected conventional progressor animals sustained marked but incomplete depletions of memory CD4+ T cells and continuous activation/proliferation of this T-lymphocyte subset. This was associated with a profound loss of naïve CD4+ T cells from peripheral blood and secondary lymphoid tissues, which declined at rates that correlated with disease progression. These data suggest that the persistent loss of memory CD4(+)T cells, which are being eliminated by direct virus killing and activation-induced cell death, requires the continuous differentiation of naïve into memory CD4+ T cells. This unrelenting replenishment process eventually leads to the exhaustion of the naïve CD4+T-cell pool and the development of disease.

Highly pathogenic SHIVs and SIVs target different CD4+ T cell subsets in rhesus monkeys, explaining their divergent clinical courses.

In contrast to simian immunodeficiency viruses (SIVs), which induce immunodeficiency over a 1- to 3-year period, highly pathogenic simian-human immunodeficiency viruses (SHIVs) cause a complete, irreversible, and systemic depletion of CD4(+) T lymphocytes in rhesus monkeys within weeks of infection. By using small-molecule competitors specific for CCR5 and CXCR4 in ex vivo assays, we found that highly pathogenic SHIV(DH12R) exclusively uses CXCR4 for infection of rhesus peripheral blood mononuclear cells, whereas SIV(mac239) and SIV(smE543) use CCR5 for entry into the same cells. During the period of peak virus production in SHIV(DH12R)- or SHIV(89.6P)-infected rhesus monkeys, massive elimination of CXCR4(+) naïve CD4(+) T cells occurred. In contrast, circulating CCR5(+) memory CD4(+) T cells were selectively depleted in rapidly progressing SIV-infected monkeys. At the time of their death, two SIV rapid progressors had experienced a nearly complete loss of the memory CD4(+) T cell subset from the blood and mesenteric lymph nodes. Thus, pathogenic SHIVs and SIVs target different subsets of CD4(+) T cells in vivo, with the pattern of CD4(+) T lymphocyte depletion being inextricably linked to chemokine receptor use. In the context of developing an effective prophylactic vaccine, which must potently control virus replication during the primary infection, regimens that suppress SHIVs might not protect monkeys against SIV or humans against HIV-1.

Characterization and comparison of recombinant simian immunodeficiency virus from drill (Mandrillus leucophaeus) and mandrill (Mandrillus sphinx) isolates.

Since simian immunodeficiency virus (SIV) was found to be the source of the human AIDS pandemic, a major goal has been to characterize the diversity of SIV strains in the wild and to assess their potential for crossover into humans. In the present study, SIV was isolated from a seropositive drill (Mandrillus leucophaeus) and three seropositive mandrills (Mandrillus sphinx) by using macaque peripheral blood mononuclear cells (PBMC). Full-length sequences were obtained from a drill and mandrill and designated SIVdrl1FAO and SIVmnd5440, respectively. A 182-bp fragment of the pol genes of the two remaining mandrill SIV isolates was also analyzed. Phylogenetic analyses demonstrated that SIVdrl1FAO formed a monophyletic clade with SIVmnd5440 and SIVmndM14, recently designated SIVmnd type 2. Both the SIVdrl and SIVmnd type 2 genomes carried a vpx gene and appeared to share a common ancestor with SIVrcm in the 5' region of the genome and with SIVmndGB1 (type 1) in the 3' region of the genome. A statistically significant recombination breakpoint was detected at the beginning of envelope, suggesting that the viruses were descendents of the same recombinant. Phylogenetic analysis of vpx and vpr genes demonstrated that the vpx genes formed a monophyletic cluster that grouped with vpr from SIVagm. In addition, both SIVdrl1FAO and SIVmnd5440 replicated in human PBMC and therefore could pose a risk of transmission to the human population.