Restriction of HIV type 1 infection in macrophages heterozygous for a deletion in the CC-chemokine receptor 5 gene

The role of genetic variants of Stromal cell-Derived Factor 1 in pediatric HIV-1 infection and disease progression

Stromal cell-Derived Factor 1 (SDF1) is the natural ligand of CXCR4, the coreceptor of HIV-1 X4 viruses. This study investigated the role of the single nucleotide polymorphism (SNP) rs1801157 (NM_000609.5:c.*519G>A) of the SDF1 gene in the natural history of mother-to-child transmission of HIV-1 and disease progression of HIV-1-infected children. The study was conducted in 428 children born to HIV-1-seropositive mothers, who had not undergone antiretroviral therapy (ART) during pregnancy, and in 120 HIV-1-infected children for whom the end-point was the onset of AIDS or the initiation of ART; 16 children developed early AIDS (<24 months of life), 13 from 24 to 84 months of age, and 14 had late AIDS (>84 months). The rs1801157 SNP was not associated with risk of perinatal infection in any genetic models tested. By contrast, this SNP influenced disease progression in a time-dependent manner. rs1801157 GA heterozygous children had a higher risk of late AIDS (HR = 6.3, 95%CI 1.9–20.7, p = 0.002) than children with the rs1801157 GG genotype. Children were studied for viral coreceptor usage at birth, after 84 months of age and/or at AIDS onset. While R5 viruses using CCR5 coreceptor were predominant at birth (94%) and at early AIDS (85%), viruses using CXCR4 coreceptor emerged during the course of infection and were detected in 49% of children older than 84 months and in 62% of late AIDS. The rs1801157 SNP did not influence the emergence of R5X4 viruses, but children with the rs1801157 GA genotype and R5X4 viruses were at significantly higher risk of late AIDS than children with rs1801157 GG genotype (OR = 8.0, 95% CI 1.2–52.2, p = 0.029). Our results indicate that the rs1801157 SNP does not influence perinatal infection, but impacts disease progression. This effect is time-dependent and linked to the coreceptor-usage of viral variants that undergo evolution during the course of HIV-1 infection.

HIV-1 and the macrophage

Macrophages and CD4+ T cells are natural target cells for HIV-1, and both cell types contribute to the establishment of the viral reservoir that is responsible for continuous residual virus replication during antiretroviral therapy and viral load rebound upon treatment interruption. Scientific findings that support a critical role for the infected monocyte/macrophage in HIV-1-associated diseases, such as neurological disorders and cardiovascular disease, are accumulating. To prevent or treat these HIV-1-related diseases, we need to halt HIV-1 replication in the macrophage reservoir. This article describes our current knowledge of how monocytes and certain macrophage subsets are able to restrict HIV-1 infection, in addition to what makes macrophages respond less well to current antiretroviral drugs as compared with CD4+ T cells. These insights will help to find novel approaches that can be used to meet this challenge.

Host hindrance to HIV-1 replication in monocytes and macrophages

Monocytes and macrophages are targets of HIV-1 infection and play critical roles in multiple aspects of viral pathogenesis. HIV-1 can replicate in blood monocytes, although only a minor proportion of circulating monocytes harbor viral DNA. Resident macrophages in tissues can be infected and function as viral reservoirs. However, their susceptibility to infection, and their capacity to actively replicate the virus, varies greatly depending on the tissue localization and cytokine environment. The susceptibility of monocytes to HIV-1 infection in vitro depends on their differentiation status. Monocytes are refractory to infection and become permissive upon differentiation into macrophages. In addition, the capacity of monocyte-derived macrophages to sustain viral replication varies between individuals. Host determinants regulate HIV-1 replication in monocytes and macrophages, limiting several steps of the viral life-cycle, from viral entry to virus release. Some host factors responsible for HIV-1 restriction are shared with T lymphocytes, but several anti-viral mechanisms are specific to either monocytes or macrophages. Whilst a number of these mechanisms have been identified in monocytes or in monocyte-derived macrophages in vitro, some of them have also been implicated in the regulation of HIV-1 infection in vivo, in particular in the brain and the lung where macrophages are the main cell type infected by HIV-1. This review focuses on cellular factors that have been reported to interfere with HIV-1 infection in monocytes and macrophages, and examines the evidences supporting their role in vivo, highlighting unique aspects of HIV-1 restriction in these two cell types.

Viral tropism, fitness and pathogenicity of HIV-1 subtype C

The majority of studies on HIV-1 pathogenesis have been conducted on subtype B HIV-1 (B-HIV) strains. However, B-HIV strains constitute the minority of HIV-1 cases worldwide, and are not common in regions that stand to benefit the most from advances in HIV-1 research such as southern Africa and Asia, where the HIV-1 pandemic is at its worst. The majority of individuals with HIV-1 are infected with subtype C HIV-1 (C-HIV) and reside in Southern Africa and Central Asia. Relatively little is known about C-HIV, but current evidence suggests the pathogenesis of C-HIV is distinct from B-HIV and other HIV-1 subtypes. This article summarizes what is currently known about the viral tropism, fitness and pathogenicity of C-HIV, and compares and contrasts these features to B-HIV. A thorough understanding of the molecular pathogenesis of C-HIV is important for a targeted approach to developing vaccines and novel drugs optimized for effectiveness in populations that are most in need.

Human immunodeficiency virus type 1 V1-to-V5 envelope variants from the chronic phase of infection use CCR5 and fuse more efficiently than those from early after infection

Human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein modifications over the course of infection have been associated with coreceptor switching and antibody neutralization resistance, but the effect of the changes on replication and host cell receptor usage remains unclear. To examine this question, unique early- and chronic-stage infection envelope V1-to V5 (V1-V5) segments from eight HIV-1 subtype A-infected subjects were incorporated into an isogenic background to construct replication-competent recombinant viruses. In all subjects, viruses with chronic-infection V1-V5 segments showed greater replication capacity than those with early-infection V1-V5 domains in cell lines with high levels of both the CD4 and the CCR5 receptors. Viruses with chronic-infection V1-V5s demonstrated a significantly increased ability to replicate in cells with low CCR5 receptor levels and greater resistance to CCR5 receptor and fusion inhibitors compared to those with early-infection V1-V5 segments. These properties were associated with sequence changes in the envelope V1-V3 segments. Viruses with the envelope segments from the two infection time points showed no significant difference in their ability to infect cells with low CD4 receptor densities, in their sensitivity to soluble CD4, or in their replication capacity in monocyte-derived macrophages. Our results suggest that envelope changes, primarily in the V1-V3 domains, increase both the ability to use the CCR5 receptor and fusion kinetics. Thus, envelope modifications over time within a host potentially enhance replication capacity.

Donor variation in in vitro HIV-1 susceptibility of monocyte-derived macrophages

Primary human cells from different donors vary in their susceptibility to in vitro infection with HIV-1. In order to perform genetic analysis to identify host factors that affect HIV-1 susceptibility, it is important that a clear phenotype is defined. Here, we report a standardized method to study variation for in vitro HIV-1 infection in monocyte-derived macrophages (MDM) from large numbers of individuals. With this assay, HIV-1 susceptibility of MDM from 489 different donors shows more than 3 log variation and a good correlation with the 32 base pair deletion in the CCR5 co-receptor (ccr5 Delta 32 genotype) of the donors. However, in 7 of 12 donors completely resistant to infection with CCR5-using HIV-1, this was not explained by the ccr5 Delta 32 genotype, showing evidence that other host factors are likely to influence HIV-1 replication in MDM. Infections with VSV-G pseudotyped HIV-1 indeed confirmed the existence of post-entry level restrictions in MDM.

HIV-1 with multiple CCR5/CXCR4 chimeric receptor use is predictive of immunological failure in infected children

BACKGROUND

HIV-1 R5 viruses are characterized by a large phenotypic variation, that is reflected by the mode of coreceptor use. The ability of R5 HIV-1 to infect target cells expressing chimeric receptors between CCR5 and CXCR4 (R5(broad) viruses), was shown to correlate with disease stage in HIV-1 infected adults. Here, we ask the question whether phenotypic variation of R5 viruses could play a role also in mother-to-child transmission (MTCT) of HIV-1 and pediatric disease progression.

METHODOLOGY/PRINCIPAL FINDINGS

Viral isolates obtained from a total of 59 HIV-1 seropositive women (24 transmitting and 35 non transmitting) and 28 infected newborn children, were used to infect U87.CD4 cells expressing wild type or six different CCR5/CXCR4 chimeric receptors. HIV-1 isolates obtained from newborn infants had predominantly R5(narrow) phenotype (n = 20), but R5(broad) and R5X4 viruses were also found in seven and one case, respectively. The presence of R5(broad) and R5X4 phenotypes correlated significantly with a severe decline of the CD4+ T cells (CDC stage 3) or death within 2 years of age. Forty-three percent of the maternal R5 isolates displayed an R5(broad) phenotype, however, the presence of the R5(broad) virus was not predictive for MTCT of HIV-1. Of interest, while only 1 of 5 mothers with an R5X4 virus transmitted the dualtropic virus, 5 of 6 mothers carrying R5(broad) viruses transmitted viruses with a similar broad chimeric coreceptor usage. Thus, the maternal R5(broad) phenotype was largely preserved during transmission and could be predictive of the phenotype of the newborn's viral variant.

CONCLUSIONS/SIGNIFICANCE

Our results show that R5(broad) viruses are not hampered in transmission. When transmitted, immunological failure occurs earlier than in children infected with HIV-1 of R5(narrow) phenotype. We believe that this finding is of utmost relevance for therapeutic interventions in pediatric HIV-1 infection.

Modeling HIV quasispecies evolutionary dynamics

BACKGROUND

During the HIV infection several quasispecies of the virus arise, which are able to use different coreceptors, in particular the CCR5 and CXCR4 coreceptors (R5 and X4 phenotypes, respectively). The switch in coreceptor usage has been correlated with a faster progression of the disease to the AIDS phase. As several pharmaceutical companies are starting large phase III trials for R5 and X4 drugs, models are needed to predict the co-evolutionary and competitive dynamics of virus strains.

RESULTS

We present a model of HIV early infection which describes the dynamics of R5 quasispecies and a model of HIV late infection which describes the R5 to X4 switch. We report the following findings: after superinfection (multiple infections at different times) or coinfection (simultaneous infection by different strains), quasispecies dynamics has time scales of several months and becomes even slower at low number of CD4+ T cells. Phylogenetic inference of chemokine receptors suggests that viral mutational pathway may generate a large variety of R5 variants able to interact with chemokine receptors different from CXCR4. The decrease of CD4+ T cells, during AIDS late stage, can be described taking into account the X4-related Tumor Necrosis Factor dynamics.

CONCLUSION

The results of this study bridge the gap between the within-patient and the inter-patients (i.e. world-wide) evolutionary processes during HIV infection and may represent a framework relevant for modeling vaccination and therapy.

Human immunodeficiency virus type 1 V1-V2 envelope loop sequences expand and add glycosylation sites over the course of infection, and these modifications affect antibody neutralization sensitivity

Over the course of infection, human immunodeficiency virus type 1 (HIV-1) continuously adapts to evade the evolving host neutralizing antibody responses. Changes in the envelope variable loop sequences, particularly the extent of glycosylation, have been implicated in antibody escape. To document modifications that potentially influence antibody susceptibility, we compared envelope variable loops 1 and 2 (V1-V2) from multiple sequences isolated at the primary phase of infection to those isolated around 2 to 3 years into the chronic phase of infection in nine women with HIV-1 subtype A. HIV-1 sequences isolated during chronic infection had significantly longer V1-V2 loops, with a significantly higher number of potential N-linked glycosylation sites, than the sequences isolated early in infection. To assess the effects of these V1-V2 changes on antibody neutralization and infectivity, we created chimeric envelope sequences, which incorporated a subject's V1-V2 sequences into a common subtype A envelope backbone and then used them to generate pseudotyped viruses. Compared to the parent virus, the introduction of a subject's early-infection V1-V2 envelope variable loops rendered the chimeric envelope more sensitive to that subject's plasma samples but only to plasma samples collected >6 months after the sequences were isolated. Neutralization was not detected with the same plasma when the early-infection V1-V2 sequences were replaced with chronic-infection V1-V2 sequences, suggesting that changes in V1-V2 contribute to antibody escape. Pseudotyped viruses with V1-V2 segments from different times in infection, however, showed no significant difference in neutralization sensitivity to heterologous pooled plasma, suggesting that viruses with V1-V2 loops from early in infection were not inherently more neutralization sensitive. Pseudotyped viruses bearing chimeric envelopes with early-infection V1-V2 sequences showed a trend in infecting cells with low CD4 concentrations more efficiently, while engineered viruses with V1-V2 sequences isolated during chronic infection were moderately better at infecting cells with low CCR5 concentrations. These studies suggest that changes within the V1-V2 envelope domains over the course of an infection influence sensitivity to autologous neutralizing antibodies and may also impact host receptor/coreceptor interactions.

Modeling Evolutionary Dynamics of HIV Infection

We have modelled the within-patient evolutionary process during HIV infection. We have studied viral evolution at population level (competition on the same receptor) and at species level (competitions on different receptors). During the HIV infection, several mutants of the virus arise, which are able to use different chemokine receptors, in particular the CCR5 and CXCR4 coreceptors (termed R5 and X4 phenotypes, respectively). Phylogenetic inference of chemokine receptors suggests that virus mutational pathways may generate R5 variants able to interact with a wide range of chemokine receptors different from CXCR4. Using the chemokine tree topology as conceptual framework for HIV viral speciation, we present a model of viral phenotypic mutations from R5 to X4 strains which reflect HIV late infection dynamics. Our model investigates the action of Tumor Necrosis Factor in AIDS progression and makes suggestions on better design of HAART therapy.

Combined effect of CCR5-Delta32 heterozygosity and the CCR5 promoter polymorphism -2459 A/G on CCR5 expression and resistance to human immunodeficiency virus type 1 transmission

Exposed seronegative individuals (ES) with persistent high-risk sexual behavior may be less susceptible to human immunodeficiency virus type 1 (HIV-1) infection because they carry the chemokine receptor (CR) gene alleles CCR5 open reading frame (ORF) Delta32, CCR5 promoter -2459G, or CCR2 ORF 64I (CCR2-64I), all of which have been found to diminish HIV-1 infectivity and/or disease progression. To investigate this, we determined the haplotypes for these three genetic loci in 93 ES and 247 low-risk control individuals. To test if protective haplotypes exert their effect by modulating CR expression, we measured the protein expression of CCR5 and CXCR4 on circulating CD4+ T cells and CD14+ monocytes in 71 ES and 92 controls. To avoid investigator bias, the analysis was performed without knowledge of each subject's risk and genotype. The CCR5 -2459G allele was significantly enriched in ES Caucasian men, who constituted the majority (84%) of the ES cohort, compared to the control Caucasian men (P = 0.02). This increase was mostly attributable to a higher frequency of the -2459 A/G versus the -2459 A/A genotype in individuals heterozygous for the delta32 allele (P = 0.012). No protective influence of the CCR2-64I allele was observed. The haplotypes CCR5 ORF delta32/CCR5 -2459A (in complete linkage disequilibrium) and CCR5 ORF wt/CCR5 -2459G had a cumulative negative effect on the expression of CCR5, since we measured significantly reduced CCR5 densities on both T-helper cells and monocytes only when both haplotypes were present. Densities of CCR5 on lymphocytes and monocytes were correlated (r = 0.59; P < 0.0001), indicating concordance of CCR5 expression patterns across different cell types. We conclude that the CCR5 ORF delta32/wt-CCR5 -2459 A/G genotype combination offers an advantage in resisting sexual HIV-1 transmission and that this effect is mediated by a relative paucity of CCR5 on potential target cells of HIV-1.

Uncoupling coreceptor usage of human immunodeficiency virus type 1 (HIV-1) from macrophage tropism reveals biological properties of CCR5-restricted HIV-1 isolates from patients with acquired immunodeficiency syndrome

The mechanisms underlying the pathogenicity of CCR5-restricted (R5) human immunodeficiency virus type-1 (HIV-1) strains are incompletely understood. Acquisition or enhancement of macrophage (M)-tropism by R5 viruses contributes to R5 HIV-1 pathogenesis. In this study, we show that M-tropic R5 viruses isolated from individuals with acquired immunodeficiency syndrome (late R5 viruses) require lower levels of CD4/CCR5 expression for entry, have decreased sensitivity to inhibition by the entry inhibitors TAK-779 and T-20, and have increased sensitivity to neutralization by the Env MAb IgG1b12 compared with non-M-tropic R5 viruses isolated from asymptomatic, immunocompetent individuals (early R5 viruses). Augmenting CCR5 expression levels on monocyte-derived macrophages via retroviral transduction led to a complete or marginal restoration of M-tropism by early R5 viruses, depending on the viral strain. Thus, reduced CD4/CCR5 dependence is a phenotype of R5 HIV-1 associated with M-tropism and late stage infection, which may affect the efficacy of HIV-1 entry inhibitors.

Multiple domains of the SIV Env protein determine virus replication efficiency and neutralization sensitivity

SIVmac239 and SIVmac1A11 are wild-type viruses encoding Env proteins with full-length or truncated cytoplasmic tails (CTs), respectively. A mutant designated SIVmac239T has a site-specific mutation which introduces a stop codon in the env gene resulting a truncated protein of similar length to SIVmac1A11 Env. To investigate the role of specific sequence differences in these Env proteins, we constructed SIV mutants encoding 1A11 or 239 Env proteins with reciprocal exchanges of the CT or exchanges of both the surface unit (SU) and CT sequences. A truncated CT in the context of the 1A11 SU subunit was found to significantly enhance replication in CEMx174 (human T-cell line) and rhesus PBMCs. However, similar Env CT truncation did not enhance replication of SIVmac239 in human or monkey cells. SIVmac1A11 with a full-length SIVmac239 CT did not replicate in human T-cell lines, but truncation of the CT by a stop codon resulted in replication. We also observed that these viruses differed significantly in sensitivity to neutralization by antibody. Taken together, the results indicated that the length of the CT domain as well as specific sequence differences in the SU domain affect viral replication capacity as well as sensitivity to neutralization.

Protecting from R5-tropic HIV: individual and combined effectiveness of a hammerhead ribozyme and a single-chain Fv antibody that targets CCR5

The CCR5 chemokine receptor is important for most clinical strains of HIV to establish infection. Individuals with naturally occurring polymorphisms in the CCR5 gene who have reduced or absent CCR5 are apparently otherwise healthy, but are resistant to HIV infection. With the goal of reducing CCR5 and protecting CCR5+ cells from R5-tropic HIV, we used Tag-deleted SV40-derived vectors to deliver several anti-CCR5 transgenes: 2C7, a single-chain Fv (SFv) antibody; VCKA1, a hammerhead ribozyme; and two natural CCR5 ligands, MIP-1alpha and MIP-1beta, modified to direct these chemokines, and hence their receptor to the endoplasmic reticulum. These transgenes were delivered using recombinant, Tag-deleted SV40-derived vectors to human CCR5+ cell lines and primary cells: monocyte-derived macrophages and brain microglia. All transgenes except MIP-1alpha decreased CCR5, as assayed by immunostaining, Northern blotting, and cytofluorimetry (FACS). Individually, all transgenes except MIP-1alpha protected from low challenge doses of HIV. At higher dose HIV challenges, protection provided by all transgenes diminished, the SFv and the ribozyme being most potent. Vectors carrying these two transgenes were used sequentially to deliver combination anti-CCR5 genetic therapy. This approach gave approximately additive reduction in CCR5, as measured by FACS and protected from higher dose HIV challenges. Reducing cell membrane CCR5 using anti-CCR5 transgenes, alone or in combinations, may therefore provide a degree of protection from R5-tropic strains of HIV.

HIV and the CCR5-Δ32 resistance allele

The combination of molecular biology, epidemiology, virology, evolutionary and population genetics has enabled us to understand the delicate interplay between HIV and the CCR5-Delta32 HIV resistance allele. We here review and collect from the different approaches to show how they can be combined to elucidate the interaction between host and pathogen genetics in this system. We will present an overview of the normal role of CCR5, its involvement in HIV, the molecular biology of the CCR5-Delta32 allele and its probable origins. By focusing on this well-documented and important system we hope to demonstrate the power that such a "holistic" approach might offer in the study of infectious diseases.

Role for CCR5Delta32 protein in resistance to R5, R5X4, and X4 human immunodeficiency virus type 1 in primary CD4+ cells

CCR5Delta32 is a loss-of-function mutation that abolishes cell surface expression of the human immunodeficiency virus (HIV) coreceptor CCR5 and provides genetic resistance to HIV infection and disease progression. Since CXCR4 and other HIV coreceptors also exist, we hypothesized that CCR5Delta32-mediated resistance may be due not only to the loss of CCR5 function but also to a gain-of-function mechanism, specifically the active inhibition of alternative coreceptors by the mutant CCR5Delta32 protein. Here we demonstrate that efficient expression of the CCR5Delta32 protein in primary CD4(+) cells by use of a recombinant adenovirus (Ad5/Delta32) was able to down-regulate surface expression of both wild-type CCR5 and CXCR4 and to confer broad resistance to R5, R5X4, and X4 HIV type 1 (HIV-1). This may be important clinically, since we found that CD4(+) cells purified from peripheral blood mononuclear cells of individuals who were homozygous for CCR5Delta32, which expressed the mutant protein endogenously, consistently expressed lower levels of CXCR4 and showed less susceptibility to X4 HIV-1 isolates than cells from individuals lacking the mutation. Moreover, CD4(+) cells from individuals who were homozygous for CCR5Delta32 expressed the mutant protein in five of five HIV-exposed, uninfected donors tested but not in either of two HIV-infected donors tested. The mechanism of inhibition may involve direct scavenging, since we were able to observe a direct interaction of CCR5 and CXCR4 with CCR5Delta32, both by genetic criteria using the yeast two-hybrid system and by biochemical criteria using the coimmunoprecipitation of heterodimers. Thus, these results suggest that at least two distinct mechanisms may account for genetic resistance to HIV conferred by CCR5Delta32: the loss of wild-type CCR5 surface expression and the generation of CCR5Delta32 protein, which functions as a scavenger of both CCR5 and CXCR4.

Risk associated HIV-1 cross-clade resistance of whole peripheral blood mononuclear cells from exposed uninfected individuals with wild-type CCR5

Highly HIV exposed, persistently uninfected individuals (EUs) may hold clues to the generation of effective vaccine induced acquired immunity against HIV, and considerable effort has been devoted to detecting and characterizing HIV specific immune responses in EU cohorts. When searching for such clues, it is important to exclude individuals with genetically determined absence of receptors, as this protective mechanism could not be induced by HIV specific vaccines. Homozygosity for the DeltaC32 mutation of CCR5 prevents R5 HIV infection, independent of any virus-specific immune responses that may be acquired by exposure, while heterozygosity influences susceptibility to low level exposure. Reports on the in vitro susceptibility of EU cells compared to controls have been conflicting. Therefore, we studied 14 EUs with homozygous wild type CCR5, using a newly developed in vitro challenge assay (IVCA) to measure the magnitude and breadth of resistance to infection among EUs. CD8+ cells were relatively increased compared to controls, and were largely responsible for resistance to challenge, which depended on dose of virus inoculum, and extended across clades. Consistent with some EU cohort studies, resistance waned among individuals who reduced their high-risk behavior.

Increased CCR5 affinity and reduced CCR5/CD4 dependence of a neurovirulent primary human immunodeficiency virus type 1 isolate

Most human immunodeficiency virus type 1 (HIV-1) viruses in the brain use CCR5 as the principal coreceptor for entry into a cell. However, additional phenotypic characteristics are necessary for HIV-1 neurotropism. Furthermore, neurotropic strains are not necessarily neurovirulent. To better understand the determinants of HIV-1 neurovirulence, we isolated viruses from brain tissue samples from three AIDS patients with dementia and HIV-1 encephalitis and analyzed their ability to induce syncytia in monocyte-derived macrophages (MDM) and neuronal apoptosis in primary brain cultures. Two R5X4 viruses (MACS1-br and MACS1-spln) were highly fusogenic in MDM and induced neuronal apoptosis. The R5 viruses UK1-br and MACS2-br are both neurotropic. However, only UK1-br induced high levels of fusion in MDM and neuronal apoptosis. Full-length Env clones from UK1-br required lower CCR5 and CD4 levels than Env clones from MACS2-br to function efficiently in cell-to-cell fusion and single-round infection assays. UK1-br Envs also had a greater affinity for CCR5 than MACS2-br Envs in binding assays. Relatively high levels of UK1-br and MACS2-br Envs bound to CCR5 in the absence of soluble CD4. However, these Envs could not mediate CD4-independent infection, and MACS2-br Envs were unable to mediate fusion or infection in cells expressing low levels of CD4. The UK1-br virus was more resistant than MACS2-br to inhibition by the CCR5-targeted inhibitors TAK-779 and Sch-C. UK1-br was more sensitive than MACS2-br to neutralization by monoclonal antibodies (2F5 and immunoglobulin G1b12 [IgG1b12]) and CD4-IgG2. These results predict the presence of HIV-1 variants with increased CCR5 affinity and reduced dependence on CCR5 and CD4 in the brains of some AIDS patients with central nervous system disease and suggest that R5 variants with increased CCR5 affinity may represent a pathogenic viral phenotype contributing to the neurodegenerative manifestations of AIDS.

Distribution of chemokine receptor CCR2 and CCR5 genotypes and their relative contribution to human immunodeficiency virus type 1 (HIV-1) seroconversion, early HIV-1 RNA concentration in plasma, and later disease progression

At the CC (beta) chemokine receptor 2 (CCR2) and CCR5 loci, combinations of common single-nucleotide polymorphisms (SNPs) and a 32-bp deletion (Delta32) form nine stable haplotypes (designated A through G*2). The distribution of these CCR2-CCR5 haplotypes was examined among 703 participants in the Multicenter AIDS Cohort Study (MACS), the District of Columbia Gay (DCG) Study, and the San Francisco Men's Health Study (SFMHS). Highly exposed and persistently seronegative (HEPS; n = 90) Caucasian men from MACS more frequently carried heterozygous G*2 (Delta32) genotypes (especially A/G*2) and less frequently carried the homozygous E/E genotype compared with 469 Caucasian seroconverters (SCs) from the same cohort (P = 0.004 to 0.042). Among 341 MACS Caucasian SCs with 6- to 12-month human immunodeficiency virus type 1 (HIV-1) seroconversion intervals and no potent antiretroviral therapy, mean plasma HIV-1 RNA level during the initial 42 months after seroconversion was higher in carriers of the E/E genotype and lower in those with the 64I-bearing haplotype F*2 or the Delta32-bearing haplotype G*2 (and especially genotypes A/G*2 and F*2/G*2). A multivariable model containing these CCR markers showed significant composite effects on HIV-1 RNA at each of four postconversion intervals (P = 0.0004 to 0.050). In other models using time to AIDS as the endpoint, the same markers showed more modest contributions (P = 0.08 to 0.24) to differential outcome during 11.5 years of follow-up. Broadly consistent findings in the larger MACS Caucasian SCs and the smaller groups of MACS African-American SCs and the DCG and SFMHS Caucasian SCs indicate that specific CCR2-CCR5 haplotypes or genotypes mediate initial acquisition of HIV-1 infection, early host-virus equilibration, and subsequent pathogenesis.

Macrophage tropism of human immunodeficiency virus type 1 isolates from brain and lymphoid tissues predicts neurotropism independent of coreceptor specificity

The viral determinants that underlie human immunodeficiency virus type 1 (HIV-1) neurotropism are unknown, due in part to limited studies on viruses isolated from brain. Previous studies suggest that brain-derived viruses are macrophage tropic (M-tropic) and principally use CCR5 for virus entry. To better understand HIV-1 neurotropism, we isolated primary viruses from autopsy brain, cerebral spinal fluid, blood, spleen, and lymph node samples from AIDS patients with dementia and HIV-1 encephalitis. Isolates were characterized to determine coreceptor usage and replication capacity in peripheral blood mononuclear cells (PBMC), monocyte-derived macrophages (MDM), and microglia. Env V1/V2 and V3 heteroduplex tracking assay and sequence analyses were performed to characterize distinct variants in viral quasispecies. Viruses isolated from brain, which consisted of variants that were distinct from those in lymphoid tissues, used CCR5 (R5), CXCR4 (X4), or both coreceptors (R5X4). Minor usage of CCR2b, CCR3, CCR8, and Apj was also observed. Primary brain and lymphoid isolates that replicated to high levels in MDM showed a similar capacity to replicate in microglia. Six of 11 R5 isolates that replicated efficiently in PBMC could not replicate in MDM or microglia due to a block in virus entry. CD4 overexpression in microglia transduced with retroviral vectors had no effect on the restricted replication of these virus strains. Furthermore, infection of transfected cells expressing different amounts of CD4 or CCR5 with M-tropic and non-M-tropic R5 isolates revealed a similar dependence on CD4 and CCR5 levels for entry, suggesting that the entry block was not due to low levels of either receptor. Studies using TAK-779 and AMD3100 showed that two highly M-tropic isolates entered microglia primarily via CXCR4. These results suggest that HIV-1 tropism for macrophages and microglia is restricted at the entry level by a mechanism independent of coreceptor specificity. These findings provide evidence that M-tropism rather than CCR5 usage predicts HIV-1 neurotropism.

Adaptation to blockade of human immunodeficiency virus type 1 entry imposed by the anti-CCR5 monoclonal antibody 2D7

The second extracellular loop (ECL2) domain of CC-chemokine receptor 5 (CCR5) has been proposed as a specific target site for therapeutic agents aimed at blocking CCR5-dependent entry by human immunodeficiency virus type I (HIV-1). We have adapted two CCR5-using HIV-1 isolates, prototypic JR-CSF, and a primary isolate, 11-121, to replicate in vitro in the presence of high concentrations of a monoclonal antibody (MAb 2D7) specific for the CCR5 ECL2 domain. The 75% inhibitory concentrations (IC(75)) for the two 2D7-adapted isolates were approximately 100-fold higher than those for corresponding control isolates passaged without the MAb. Adapted isolates did not acquire the ability to use CXCR4, CCR3, or CCR1. Env clones derived from MAb 2D7-adapted JR-CSF showed several gp120 mutations that were not found in any of the control JR-CSF clones. The in vitro observations suggest that CCR5-using HIV-1 strains might also be able to adapt in vivo to evade an ECL2-blocking therapeutic agent.

HIV type 1 chemokine receptor usage in mother-to-child transmission

To investigate the role of the HIV-1 phenotype in mother-to-child HIV-1 transmission, we evaluated coreceptor usage and replication kinetics in chemokine receptor-expressing U87MG.CD4 cells of primary isolates from 32 HIV-1-infected mothers of Italian origin, none under preventive antiretroviral therapy, and from their infected infants. Five of 15 mothers of infected children and 2 of 17 mothers of uninfected children harbored viruses able to use CXCR4 as coreceptor. However, all isolates used CCR5, alone or in association with CXCR4. The replicative capacity in coreceptor-expressing cells of the viral isolates did not differ between the two groups of mothers. All mothers with an R5 virus transmitted a virus with the same coreceptor usage, whereas those four with a multitropic virus transmitted such a virus in one case. Although the presence of a mixed viral population was documented in the mothers, we did not observe transmission solely of X4 viruses. Interestingly, the only child infected with a multitropic virus carried a defective CCR5 allele. Analysis of the env V3 region of the provirus from this child revealed infection with multiple viral variants with a predominance of R5-type over X4-type sequences. These findings show that CCR5 usage of a viral isolate is not a discriminating risk factor for vertical transmission. Furthermore, X4 viruses can be transmitted to the newborn, although less frequently. In particular, we document the transmission of multiple viral variants with different coreceptor usage in a Delta32 CCR5 heterozygous child, and demonstrate that the heterozygous genotype per se does not contribute to the restriction of R5-type virus spread.

Viral protein U (Vpu)-mediated enhancement of human immunodeficiency virus type 1 particle release depends on the rate of cellular proliferation

Viral protein U (Vpu) is a 17-kDa phosphoprotein that enhances the release of viral particles from human immunodeficiency virus type 1-infected cells. This study shows that the effect of Vpu on efficient particle release depends on the rate of cell proliferation. Cells arrested by contact inhibition, chemical arresting agents, or terminal differentiation (i.e., macrophages) all exhibited a striking dependence on Vpu for efficient particle release, as shown by examination of particle production from transfections with full-length clones, infections, and the vaccinia virus expression system. In contrast, actively proliferating cells did not exhibit enhanced particle release with Vpu expression. This study demonstrates the necessity of Vpu for efficient viral particle release from quiescent cells.

The level of CD4 expression limits infection of primary rhesus monkey macrophages by a T-tropic simian immunodeficiency virus and macrophagetropic human immunodeficiency viruses

The entry of primate immunodeficiency viruses into cells is dependent on the interaction of the viral envelope glycoproteins with receptors, CD4, and specific members of the chemokine receptor family. Although in many cases the tropism of these viruses is explained by the qualitative pattern of coreceptor expression, several instances have been observed where the expression of a coreceptor on the cell surface is not sufficient to allow infection by a virus that successfully utilizes the coreceptor in a different context. For example, both the T-tropic simian immunodeficiency virus (SIV) SIVmac239 and the macrophagetropic (M-tropic) SIVmac316 can utilize CD4 and CCR5 as coreceptors, and both viruses can infect primary T lymphocytes, yet only SIVmac316 can efficiently infect CCR5-expressing primary macrophages from rhesus monkeys. Likewise, M-tropic strains of human immunodeficiency virus type 1 (HIV-1) do not infect primary rhesus monkey macrophages efficiently. Here we show that the basis of this restriction is the low level of CD4 on the surface of these cells. Overexpression of human or rhesus monkey CD4 in primary rhesus monkey macrophages allowed infection by both T-tropic and M-tropic SIV and by primary M-tropic HIV-1. By contrast, CCR5 overexpression did not specifically compensate for the inefficient infection of primary monkey macrophages by T-tropic SIV or M-tropic HIV-1. Apparently, the limited ability of these viruses to utilize a low density of CD4 for target cell entry accounts for the restriction of these viruses in primary rhesus monkey macrophages.