Central Nervous System Compartmentalization of HIV-1 Subtype C Variants Early and Late in Infection in Young Children

Human immunodeficiency virus type 1 (HIV-1) infection in the central nervous system (CNS) is characterized by replication in macrophages or brain microglia that express low levels of the CD4 receptor and is the cause of HIV-associated dementia and related cognitive and motor disorders that affect 20 to 30% of treatment-naive patients with AIDS. Independent viral envelope evolution in the brain has been reported, with the need for robust replication in resident CD4 low cells, as well as CD4-negative cells, such as astrocytes, proposed as a major selective pressure. We previously reported giant-cell encephalitis in subtype B and C R5 simian-human immunodeficiency virus (SHIV)-infected macaques (SHIV-induced encephalitis [SHIVE]) that experienced very high chronic viral loads and progressed rapidly to AIDS, with varying degrees of macrophage or microglia infection and activation of these immune cells, as well as astrocytes, in the CNS. In this study, we characterized envelopes (Env) amplified from the brains of subtype B and C R5 SHIVE macaques. We obtained data in support of an association between severe neuropathological changes, robust macrophage and microglia infection, and evolution to CD4 independence. Moreover, the degree of Env CD4 independence appeared to correlate with the extent of astrocyte infection in vivo. These findings further our knowledge of the CNS viral population phenotypes that are associated with the severity of HIV/SHIV-induced neurological injury and improve our understanding of the mechanism of HIV-1 cellular tropism and persistence in the brain. IMPORTANCE Human immunodeficiency virus type 1 (HIV-1) infection of astrocytes in the brain has been suggested to be important in HIV persistence and neuropathogenesis but has not been definitively demonstrated in an animal model of HIV-induced encephalitis (HIVE).Here, we describe a new nonhuman primate (NHP) model of R5 simian-human immunodeficiency virus (SHIV)-induced encephalitis (SHIVE) with several classical HIVE features that include astrocyte infection. We further show an association between severe neuropathological changes, robust resident microglia infection, and evolution to CD4 independence of viruses in the central nervous system (CNS), with expansion to infection of truly CD4-negative cells in vivo. These findings support the use of the R5 SHIVE models to study the contribution of the HIV envelope and viral clades to neurovirulence and residual virus replication in the CNS, providing information that should guide efforts to eradicate HIV from the body.

Section: Characteristics Of R5 Shiv-infected Macaques With Encephalitismentioning

confidence: 80%

mentioning

confidence: 99%

Emergence of CD4 Independence Envelopes and Astrocyte Infection in R5 Simian-Human Immunodeficiency Virus Model of Encephalitis

Zhuang

Léda

Tsai

et al. 2014

“…Using these types of assay parameters, we have been able to show that most isolates of HIV-1, including the transmitted virus (28), require high levels of CD4 for entry, indicating that most of the time HIV-1 is replicating in CD4 ϩ T cells, with their high densities of surface CD4, and that the virus does not have the entry properties of viruses that have evolved to infect macrophages. We have been able to identify rare examples of viruses with intermediate entry phenotypes (56), although we do not know if this represents phenotypic variation or evolutionary intermediates. Other investigators have also used Affinofile cells to identify a low-CD4-density entry phenotype (57).…”

Section: Discussionmentioning

confidence: 99%

Quantification of Entry Phenotypes of Macrophage-Tropic HIV-1 across a Wide Range of CD4 Densities

Joseph

Arrildt

Swanstrom

et al. 2014

Self Cite

102

148

Defining a macrophage-tropic phenotype for HIV-1 to assess a role in pathogenesis is complicated by the fact that HIV-1 isolates vary continuously in their ability to enter monocyte-derived macrophages (MDMs) in vitro, and MDMs vary in their ability to support HIV-1 entry. To overcome these limitations, we identified consistent differences in entry phenotypes between five paired blood-derived, T cell-tropic HIV-1 env genes, four of which are CCR5-using (R5) and one of which is CXCR4-using (X4), and cerebrospinal fluid (CSF)-derived, R5 macrophage-tropic env genes. We performed entry assays using the CD4-and CCR5-inducible Affinofile cell line, expressing a range of CD4 levels that approximates the range from MDMs to CD4 ؉ T cells. The macrophage-tropic viruses were significantly better at infecting cells expressing low levels of CD4 than the T cell-tropic viruses from the same subjects, with the titration of CD4 providing a distinctive and quantitative phenotype. This difference in CD4 utilization was not due to macrophage-tropic viruses being CD4 independent. Furthermore, macrophage-tropic viruses did not differ from paired T cell-tropic viruses in their ability to use low levels of CCR5 (t paired ‫؍‬ ؊1.39; P ‫؍‬ 0.24) or their use of an alternative conformation of CCR5. We also infected MDMs with a panel of viruses and observed that infectivity of each virus differed across four donors and between three preparations from a single donor. We concluded that the evolutionary transition from replication in T cells to that in macrophages involves a phenotypic transition to acquire the ability to infect cells expressing low levels of CD4 and that this phenotype is more reliably measured in Affinofile cells than in macrophages. IMPORTANCEHIV-1 typically infects memory T cells by using CD4 and CCR5 to enter cells. The virus evolves to infect new cell types by changing the coreceptor from CCR5 to CXCR4 to infect naive T cells or adapting to the use of low levels of CD4 to infect macrophages. However, defining the phenotype of macrophage tropism has been difficult due to inherent variability in the use of macrophages generated in culture to support entry of HIV-1. We describe the use of Affinofile cells with inducible and variable levels of CD4 to identify a signature phenotype for macrophage-tropic HIV-1. The ability to define HIV-1 variants that have evolved an entry phenotype that allows more efficient entry into cells with low levels of CD4 sets the stage for a clearer placement of these variants in HIV-associated pathogenesis.T he HIV-1 Env protein determines the entry phenotype of the virus, typically using CD4 as the receptor and CCR5 as the coreceptor. The ability of HIV-1 to replicate in a novel cell type likely requires adaptation of the viral envelope protein to efficiently utilize the receptor and coreceptor present on that cell type. The emergence of CXCR4-using virus late in infection has long been thought to represent adaptation to infect a novel host cell (reviewed in reference 1), most likely CD...

“…We examined env gene clones generated in several studies, including previously described clones generated from the blood and CSF of five adult subjects infected with HIV-1 subtype B and diagnosed with HIV-associated neurological disease (22) and from four pediatric subjects infected with HIV-1 subtype C and diagnosed with delays in neurological development (42). We also examined new env clones that were generated from the blood and subjectmatched CSF, semen, or cervicovaginal fluid (CVF) of five subjects infected with HIV-1 subtype B or C (Table 1).…”

Section: Methodsmentioning

confidence: 99%

“…Based on these defined characteristics, we identified seven additional HIV-1 env genes cloned from compartmentalized virus in the CSF early after HIV-1 infection of infants (42) or in the genital tract of adults (E. N. Dukhovlinova and L. Ping, unpublished data) that showed a modest enhancement of entry on CD4 low Affinofile cells (i.e., "intermediate" between the values of T-tropic and M-tropic viruses) and seven subject-matched T-tropic Env proteins isolated from the blood. Viruses with intermediate CD4 usage phenotypes are rare and may provide information about the evolution of macrophage tropism.…”

Section: Identification Of Macrophage-tropic and Paired T Cell-tropicmentioning

confidence: 99%

Phenotypic Correlates of HIV-1 Macrophage Tropism

Arrildt

LaBranche

Joseph

et al. 2015

Self Cite

HIV-1 is typically CCR5 using (R5) and T cell tropic (T-tropic), targeting memory CD4؉ T cells throughout acute and chronic infections. However, viruses can expand into alternative cells types. Macrophage-tropic (M-tropic) HIV-1 variants have evolved to infect macrophages, which have only low levels of surface CD4. Most M-tropic variants have been isolated from the central nervous system during late-stage chronic infection. We used the HIV-1 env genes of well-defined, subject-matched M-tropic and T-tropic viruses to characterize the phenotypic features of the M-tropic Env protein. We found that, compared to T-tropic viruses, M-tropic viruses infect monocyte-derived macrophages (MDMs) on average 28-fold more efficiently, use low-density CD4 more efficiently, have increased sensitivity to soluble CD4 (sCD4), and show trends toward sensitivity to some CD4 binding site antibodies but no difference in sensitivity to antibodies targeting the CD4-bound conformation. M-tropic viruses also displayed a trend toward resistance to neutralization by monoclonal antibodies targeting the V1/V2 region of Env, suggesting subtle changes in Env protein conformation. The paired M-and T-tropic viruses did not differ in autologous serum neutralization, temperature sensitivity, entry kinetics, intrinsic infectivity, or Env protein incorporation. We also examined viruses with modestly increased CD4 usage. These variants have significant sensitivity to sCD4 and may represent evolutionary intermediates. CD4 usage is strongly correlated with infectivity of MDMs over a wide range of CD4 entry phenotypes. These data suggest that emergence of M-tropic HIV-1 includes multiple steps in which a phenotype of increased sensitivity to sCD4 and enhanced CD4 usage accompany subtle changes in Env conformation. IMPORTANCE HIV-1 typically replicates in CD4؉ T cells. However, HIV-1 can evolve to infect macrophages, especially within the brain. Understanding how CCR5-using macrophage-tropic viruses evolve and differ from CCR5-using T cell-tropic viruses may provide insights into viral evolution and pathogenesis within the central nervous system. We characterized the HIV-1 env viral entry gene from subject-matched macrophage-tropic and T cell-tropic viruses to identify entry features of macrophage-tropic viruses. We observed several differences between T cell-tropic and macrophage-tropic Env proteins, including functional differences with host CD4 receptor engagement and possible changes in the CD4 binding site and V1/V2 region. We also identified viruses with phenotypes between that of "true" macrophage-tropic and T cell-tropic viruses, which may represent evolutionary intermediates in a multistep process to macrophage tropism. HIV-1 host cell entry is determined solely by the virion surface protein Env. The Env protein precursor gp160 is cleaved into two proteins: the external gp120 protein and the membrane-spanning gp41 protein, which remain associated as a heterodimer and form trimers of these heterodimers. Attachment of gp120 to the host CD4 ...