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

African green monkeys (AGM) and sooty mangabeys (SM) are wellstudied natural hosts of simian immunodeficiency virus (SIV) that do not progress to AIDS when infected with their species-specific viruses. Natural hosts of SIV express very low levels of the canonical entry coreceptor CCR5, and recent studies have shown that CCR5 is dispensable for SIV infection of SM in vivo and that blocking of CCR5 does not prevent ex vivo infection of peripheral blood mononuclear cells (PBMC) from SM or vervet AGM. In both hosts, CXCR6 is an efficient entry pathway in vitro. Here we investigated the use of species-matched CXCR6 and other alternative coreceptors by SIVagmSab, which infects sabaeus AGM. We cloned sabaeus CD4 and 10 candidate coreceptors. Species-matched CXCR6, CCR5, and GPR15 mediated robust entry into transfected cells by pseudotypes carrying SIVagmSab92018ivTF Env, with lower-level entry through GPR1 and APJ. We cloned genetically divergent env genes from the plasma of two wild-infected sabaeus AGM and found similar patterns of coreceptor use. Titration experiments showed that CXCR6 and CCR5 were more efficient than other coreceptors when tested at limiting CD4/coreceptor levels. Finally, blocking of CXCR6 with its ligand CXCL16 significantly inhibited SIVagmSab replication in sabaeus PBMC and had a greater impact than did the CCR5 blocker maraviroc, confirming the use of CXCR6 in primary lymphocyte infection. These data suggest a new paradigm for SIV infection of natural host species, whereby a shared outcome of virus-host coevolution is the use of CXCR6 or other alternative coreceptors for entry, which may direct SIV toward CD4 ϩ T cell subsets and anatomical sites that support viral replication without disrupting immune homeostasis and function.IMPORTANCE Natural hosts of SIV do not progress to AIDS, in stark contrast to pathogenic human immunodeficiency virus type 1 (HIV-1)-human and SIVmacmacaque infections. Identifying how natural hosts avoid immunodeficiency can elucidate key mechanisms of pathogenesis. It is known that despite high viral loads, natural hosts have a low frequency of CD4 ϩ cells expressing the SIV coreceptor CCR5. In this study, we demonstrate the efficient use of the coreceptor CXCR6 by SIVagmSab to infect sabaeus African green monkey lymphocytes. In conjunction with studies of SIVsmm, which infects sooty mangabeys, and SIVagmVer, which infects vervet monkeys, our data suggest a unifying model whereby in natural hosts, in which the CCR5 expression level is low, the use of CXCR6 or other coreceptors to

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

CXCR6-Mediated Simian Immunodeficiency Virus SIVagmSab Entry into Sabaeus African Green Monkey Lymphocytes Implicates Widespread Use of Non-CCR5 Pathways in Natural Host Infections

Wetzel

Elliott

et al. 2017

“…However, additional characterization of CD4 ϩ cell populations in AGM milk as well as of the true extent of chemokine receptor promiscuity for SIVsab milk and plasma variants could elucidate selection pressures leading to compartmentalization. Furthermore, our identification of chemokine receptor promiscuity of chronic SIVsab variants, including a T/F variant, supports the possibility of distinct target cell populations mediating transmission in infant and adult natural SIV hosts (46,(63)(64)(65). Additionally, it is possible, and has been suggested (66)(67)(68), that cell-associated virus is the source of transmitted virus in postnatal transmission.…”

Section: Discussionmentioning

confidence: 74%

“…We next assessed SIVsab variant infectivity in cell lines with distinct chemokine receptor expression of CCR5 and CXCR4, as well as GPR15, as this chemokine receptor has been reported to be utilized as a coreceptor by some SIV strains (20,(43)(44)(45)(46). Chemokine receptor expression was confirmed in the cell lines with virus controls of the CCR5-tropic Du.156.12, the CXCR4-tropic Mn.3, the CCR5-and CXCR4-tropic 89.6, the CCR5-tropic YU2, and the CCR5-and GPR15-tropic YU2-6248wt.…”

Section: Plasma and Milk Sivsabmentioning

confidence: 99%

Characterization of Simian Immunodeficiency Virus Variants Anatomically Compartmentalized in Plasma and Milk in Chronically Infected African Green Monkeys

Himes

Nguyen

et al. 2016

Unlike human immunodeficiency virus type 1 (HIV-1)-infected humans, African-origin, natural simian immunodeficiency virus (SIV) hosts, such as African green monkeys (AGMs), sustain nonpathogenic SIV infections and rarely vertically transmit SIV to their infants. Interestingly, chronically SIV-infected AGMs have anatomically compartmentalized SIV variants in plasma and milk, whereas humans and SIV-infected rhesus monkeys (RMs), Asian-origin nonnatural SIV hosts, do not exhibit this compartmentalization. Thus, it is possible that AGM SIV populations in milk have unique phenotypic features that contribute to the low postnatal transmission rates observed in this natural host species. In this study, we explored this possibility by characterizing the infectivity, tropism, and neutralization susceptibility of plasma and milk SIVsab env variants isolated from chronically SIVsab92018ivTF-infected AGMs. AGM plasma and milk SIVsab env pseudovirus variants exhibited similar infectivities, neutralization susceptibilities to autologous and heterologous plasma, and chemokine coreceptor usages for cell entry, suggesting similar abilities to initiate infection in a new host. We also assessed the cytokine milieu in SIV-infected AGM milk and compared it to that of SIV-infected RMs. MIP-1␤, granulocyte colony-stimulating factor (G-CSF), interleukin-12/23 (IL-12/23), and IL-13 trended significantly higher in SIV-infected AGM milk than in that of RMs, while IL-18 and IL-6 trended significantly higher in SIV-infected RM milk than in that of AGMs. Taken together, our findings imply that nonviral maternal factors, such as the cytokine milieu, rather than unique characteristics of SIV populations in the milk contribute to the low postnatal transmission rates observed in AGMs. IMPORTANCEDue to the ongoing global incidence of pediatric HIV-1 infections, including many that occur via breastfeeding, development of effective vaccine strategies capable of preventing vertical HIV transmission through breastfeeding remains an important goal. Unlike HIV-1-infected humans, African green monkeys (AGMs), the natural SIV host species, sustain nonpathogenic SIV infections, rarely transmit the virus postnatally to their infants, and exhibit anatomically compartmentalized SIV populations in milk and plasma. Identifying unique features of the anatomically compartmentalized milk SIV populations could enhance our understanding of how AGMs may have evolved to avoid transmission through breastfeeding. While this study identified limited phenotypic distinctions between AGM plasma and milk SIV populations, potential differences in milk cytokine profiles of natural and nonnatural SIV hosts were observed. These findings imply the potential importance of nonviral factors in natural SIV host species, such as innate SIV/HIV immune factors in milk, as a means of naturally preventing vertical transmission. N ow 4 decades into the human immunodeficiency virus type 1 (HIV-1) epidemic, more than 200,000 pediatric HIV-1 infections continue to occur annually despi...

“…Other mechanisms unique to AGMs that may contribute to disease nonprogression have also been described, including a robust but transient type I interferon response and non-CCR5 entry pathways of SIVagm (29,30). Our findings that homeostatic signals can drive CD4 downregulation give key insights on how AGMs can preserve these essential immune functions while still maintaining a diverse T cell repertoire, as one would expect a skewed representation with some T cell clones more represented than others if the CD4 Ϫ…”

Section: Cd8␣␣mentioning

confidence: 85%

Interleukin-2 Therapy Induces CD4 Downregulation, Which Decreases Circulating CD4 T Cell Counts, in African Green Monkeys

Mudd

Perkins

DiNapoli

et al. 2016

Self Cite

African green monkeys (AGMs) are natural hosts of simian immunodeficiency virus (SIV AGM ). Because these animals do not develop simian AIDS despite maintaining high viral loads, there is considerable interest in determining how these animals have evolved to avoid SIV disease progression. Unlike nonnatural hosts of SIV, adult AGMs maintain low levels of CD4؉ T cells at steady states and also have a large population of virus-resistant CD8␣␣ T cells that lack CD4 expression despite maintaining T helper cell functionalities. In recent work, we have shown that homeostatic cytokines can induce CD4 downregulation in AGM T cells in vitro. Through administering therapeutic doses of recombinant human interleukin-2 (IL-2) to AGMs, we show here that this mechanism is operative in vivo. IL-2 therapy induced transient yet robust proliferation in all major T cell subsets. Within the CD4؉ T cell population, those that were induced into cycle by IL-2 exhibited characteristics of CD4-to-CD8␣␣ conversion. In all animals receiving IL-2, circulating CD4 ؉ T cell counts and proportions tended to be lower and CD4 ؊ CD8␣␣ ؉ T cell counts tended to be higher. Despite reductions in circulating target cells, the viral load was unaffected over the course of study. IMPORTANCE The data in this study identify that homeostatic cytokines can downregulate CD4 in vivo and, when given therapeutically, can induce AGMs to sustain very low levels of circulating CD4 ؉ T cells without showing signs of immunodeficiency.A frican green monkeys (AGMs) are natural hosts of simian immunodeficiency virus (SIVagm) that progress to AIDS very rarely despite maintaining high viral loads in plasma (1). Yet, SIVagm is pathogenic in pigtail macaques when they are experimentally infected, implying a coevolution of SIVagm with its natural host (2, 3). Adult AGMs have low numbers of CD4 T cells and a large population of memory T cells that lack CD4 expression and express CD8␣ homodimers (4, 5). These CD8␣␣ T cells are uniquely different from classical CD8␣␤ T cells in that they retain characteristics of CD4 T cells, such as major histocompatibility complex class II (MHC-II) restriction, expression of Foxp3, and production of interleukin-2 (IL-2) and IL-17 (4, 6, 7). We have previously shown that these cells arise from downregulation of CD4 by canonical CD4 T cells (8). Importantly, downregulation of CD4 protects these cells from infection by SIVagm in vivo (4, 9). The maintenance of immunological function by cells that are resistant to infection is thought to, in part, underlie the nonprogressive nature of SIVagm infection in AGM.The exact mechanisms of CD4-to-CD8␣ conversion in AGMs are not entirely understood, although cellular division is likely important for this process. It is clear that cellular division through antigenic stimuli can induce CD4 downregulation in vitro and infection of AGMs with SIV can accelerate CD4-to-CD8␣ conversion in vivo (8). Yet, the conversion of CD4 to CD4 Ϫ CD8␣ ϩ T cells during infection is not entirely limited to those that a...