HIV-1 coreceptor usage, transmission, and disease progression

HIV-1 coreceptor usage is believed to play a critical role in pathogenesis. To initiate infection, HIV-1 interacts with two cell surface receptors; CD4 is the primary receptor and the beta-chemokine receptors CCR5 and CXCR4 usually serve as secondary receptors. HIV-1 strains transmitted in vivo generally use CCR5. Viruses that use CCR5 (R5 viruses) appear to be associated with relatively stable infection. Years after chronic infection is established, CXCR4 utilizing strains emerge in approximately 50% of infected individuals. Viruses that use the coreceptor CXCR4 (X4 viruses) are associated with rapid CD4+ cell decline and disease progression. However, the mechanism by which X4 viruses are associated with accelerated disease progression has never been properly elucidated. For example, the association between X4 virus and acceleration of HIV-1 disease progression has been ascribed to the expanded spectrum of CXCR4+ precursor cells susceptible to infection by X4 strains. It has also been postulated that the decline of the host immune system associated with clinical AIDS may allow X4 viruses to evolve and replicate freely in late-stage infection. Discriminating between these and other alternatives is central to increasing our understanding of the fundamental pathogenic processes involved in HIV-1 infection. In this article, we critically review those studies published over the last few years that purport to examine the relationship between HIV-1 coreceptor usage, transmission, CD4+ T-cell depletion, and disease progression.

Establishment of a novel CCR5 and CXCR4 expressing CD4+ cell line which is highly sensitive to HIV and suitable for high-throughput evaluation of CCR5 and CXCR4 antagonists

BACKGROUND

CCR5 and CXCR4 are the two main coreceptors essential for HIV entry. Therefore, these chemokine receptors have become important targets in the search for anti-HIV agents. Here, we describe the establishment of a novel CD4+ cell line, U87.CD4.CCR5.CXCR4, stably expressing both CCR5 and CXCR4 at the cell surface.

RESULTS

In these cells, intracellular calcium signalling through both receptors can be measured in a single experiment upon the sequential addition of CXCR4- and CCR5-directed chemokines. The U87.CD4.CCR5.CXCR4 cell line reliably supported HIV-1 infection of diverse laboratory-adapted strains and primary isolates with varying coreceptor usage (R5, X4 and R5/X4) and allows to investigate the antiviral efficacy of combined CCR5 and CXCR4 blockade. The antiviral effects recorded in these cells with the CCR5 antagonist SCH-C and the CXCR4 antagonist AMD3100 were similar to those noted in the single CCR5- or CXCR4-transfected U87.CD4 cells. Furthermore, the combination of both inhibitors blocked the infection of all evaluated HIV-1 strains and isolates.

CONCLUSIONS

Thus, the U87.CD4.CCR5.CXCR4 cell line should be useful in the evaluation of CCR5 and CXCR4 antagonists with therapeutic potential and combinations thereof.

An absence of CCR5 on donor cells results in acceleration of acute graft-vs-host disease

OBJECTIVE

Chemokines have been postulated to play a role in the pathogenesis of graft-vs-host disease (GVHD) after allogeneic hematopoietic transplantation. Recent reports have indicated that the absence of donor expression of CCR5 on T cells ameliorates GVHD in models using no conditioning of the recipient. We therefore assessed the role of CCR5 on donor cells in models where intensive conditioning of the recipient occurs, thus more appropriately mirroring the clinical experience.

METHODS

Lethally irradiated mice received allogeneic bone marrow transplants. Recipients were given full MHC-mismatched donor bone marrow and splenocytes from CCR5 knockout (KO) mice vs wild-type (WT) control donors.

RESULTS

Recipients of CCR5 KO donor cells succumbed to acute GVHD at an accelerated rate compared to mice receiving WT cells. Donor CD8+ T cells expanded to a significantly greater extent in recipients of CCR5 KO vs WT control cells. T cells recovered from recipients of CCR5 KO cells produced more IFN-gamma and TNF-alpha and proliferated to a T-cell mitogen at a significantly greater level then T cells from recipients of WT cells, indicating that CCR5 plays a role in downregulating donor alloreactive CD8+ T-cell expansion. Histological assessment of the mice indicated pathological lesions in the kidneys and a greater degree of liver pathological changes in mice that received CCR5 KO donor grafts.

CONCLUSIONS

These results indicate that the role of CCR5 in allogeneic bone marrow transplants and GVHD is more complex than initially thought. In a murine transplant model with intensive conditioning, the overall effect of absent CCR5 expression on donor cells results in greater GVHD and donor T-cell expansion.

Inhibition of airway inflammation by amino-terminally modified RANTES/CC chemokine ligand 5 analogues is not mediated through CCR3

Chemokines play a key role in the recruitment of activated CD4(+) T cells and eosinophils into the lungs in animal models of airway inflammation. Inhibition of inflammation by N-terminally modified chemokines is well-documented in several models but is often reported with limited dose regimens. We have evaluated the effects of doses ranging from 10 ng to 100 micro g of two CC chemokine receptor antagonists, Met-RANTES/CC chemokine ligand 5 (CCL5) and aminooxypentane-RANTES/CCL5, in preventing inflammation in the OVA-sensitized murine model of human asthma. In the human system, aminooxypentane-RANTES/CCL5 is a full agonist of CCR5, but in the murine system neither variant is able to induce cellular recruitment. Both antagonists showed an inverse bell-shaped inhibition of cellular infiltration into the airways and mucus production in the lungs following allergen provocation. The loss of inhibition at higher doses did not appear to be due to partial agonist activity because neither variant showed activity in recruiting cells into the peritoneal cavity at these doses. Surprisingly, neither was able to bind to the major CCR expressed on eosinophils, CCR3. However, significant inhibition of eosinophil recruitment was observed. Both analogues retained high affinity binding for murine CCR1 and murine CCR5. Their ability to antagonize CCR1 and CCR5 but not CCR3 was confirmed by their ability to prevent RANTES/CCL5 and macrophage inflammatory protein-1beta/CCL4 recruitment in vitro and in vivo, while they had no effect on that induced by eotaxin/CCL11. These results suggest that CCR1 and/or CCR5 may be potential targets for asthma therapy.

Chemokine receptor 5 is dispensable for innate and adaptive immune responses to Listeria monocytogenes infection

Chemokine receptor 5 (CCR5) binds macrophage inflammatory protein 1alpha (MIP-1alpha), MIP-1beta, RANTES, and members of the monocyte chemotactic protein family and is also a receptor for human immunodeficiency virus (HIV). CCR5 ligands can suppress HIV-1 entry into cells. In humans, homozygous mutations of the ccr5 gene confer resistance to HIV-1 infection. The role of CCR5 in defense against microbial infection is unclear. In this study we examined the innate and adaptive immune responses of CCR5-deficient mice to the intracellular bacterial pathogen Listeria monocytogenes. We found that migration of monocytic cells, formation of L. monocytogenes-containing lesions, and bacterial clearance occurred normally in the spleens and livers of CCR5-deficient animals. Activation of macrophages and dendritic cells during the first 3 days postinfection was normal in the absence of CCR5, as demonstrated by intact expression of inducible nitric oxide synthase (iNOS) and production of the cytokines tumor necrosis factor alpha, gamma interferon, and interleukin-12. Priming of L. monocytogenes-specific CD8 T cells also occured independently of CCR5 expression. Previously immunized, CCR5-deficient animals mounted normal secondary CD8 T-cell responses and cleared bacteria from infected organs similarly to wild-type controls, suggesting that CCR5 is dispensable for migration and activation of memory CD8 T cells. Our data indicate that CCR5-mediated chemotaxis is not required for defense against infection with L. monocytogenes.

Cutting edge: IL-16/CD4 preferentially induces Th1 cell migration: requirement of CCR5

IL-16 binds to CD4 and induces a migratory response in CD4(+) T cells. Although it has been assumed that CD4 is the sole receptor and that IL-16 induces a comparable migratory response in all CD4(+) T cells, this has not been investigated. In this study, we determined that IL-16 preferentially induces a migratory response in Th1 cells. Because chemokine receptor CCR5 is expressed predominantly in Th1 cells and is physically associated with CD4, we investigated whether IL-16/CD4 stimulation was enhanced in the presence of CCR5. Using T cells from CCR5(null) mice, we determined that IL-16-induced migration was significantly greater in the presence of CCR5. The presence of CCR5 significantly increased IL-16 binding vs CD4 alone; however, IL-16 could not bind to CCR5 alone. Because CD4(+)CCR5(+) cells are prevalent at sites of inflammation, this intimate functional relationship likely plays a pivotal role for the recruitment and activation of Th1 cells.

Antagonism of RANTES Receptors Reduces Atherosclerotic Plaque Formation in Mice

Increasing evidence supports the involvement of inflammation in the early phases of atherogenesis. Recruitment of leukocytes within the vascular wall, controlled by chemokines, is an essential process in the development of this common disease. In this study, we report that blocking a chemokine pathway in vivo with the CC chemokine antagonist Met-RANTES reduces the progression of atherosclerosis in a hypercholesterolemic mouse model. The reduction of lesions was correlated with a diminution of expression of several major chemokines and chemokine receptors, a decrease in leukocyte infiltration, and an increase of collagen-rich atheroma, features associated with stable atheroma. Treatment was well tolerated and serum lipid profiles were not affected. Whereas genetically engineered mice with deletion of either a CC chemokine or its receptor have demonstrated resistance to disease, to our knowledge, this is the first demonstration that treatment with a chemokine receptor antagonist limits the progression of atherosclerosis in vivo. Thus, our findings indicate that blockade of chemokine receptor/ligand interactions might become a novel therapeutic strategy to reduce the evolution of this common disease.

Construction and characterization of CD4-independent infectious recombinant HIV-2 molecular clones

Human immunodeficiency virus type 1 (HIV-1) and type 2 (HIV-2) differ in their pathogenic mechanisms as evidenced by lower rate of disease progression, lower transmission rates and lower viral load in peripheral blood for HIV-2. One of the many factors that are involved in these characteristics is the interaction between viral glycoproteins and cellular receptors. The study of these interactions in an HIV-2 model could lead to important conclusions regarding pathogenesis and transmission mechanisms of HIV-2 infection. Here we report the design of a method enabling the construction of recombinant proviral HIV-2 DNAs in a moderate copy number plasmid that allows the analysis of env gene structure and functionality. This method constitutes an important tool for the study of HIV-2 env glycoproteins and for the mappings of genetic determinants of HIV-2 coreceptor usage and CD4-independent interaction. Furthermore, this knowledge will help towards the understanding of the different pathogenic mechanisms of HIV-1 and HIV-2.

Combined blockade of the chemokine receptors CCR1 and CCR5 attenuates chronic rejection

BACKGROUND

Chemokine-chemokine receptor interaction and the subsequent recruitment of T-lymphocytes to the graft are early events in the development of chronic rejection of transplanted hearts or cardiac allograft vasculopathy (CAV). In this study, we sought to determine whether blockade of chemokine receptors CCR1 and CCR5 with Met-RANTES affects the development of CAV in a murine model.

METHODS AND RESULTS

B6.CH-2(bm12) strain donor hearts were transplanted heterotopically into wild-type C57BL/6 mice (myosin heavy chain II mismatch). Recipients were treated daily with either Met-RANTES or vehicle starting on postoperative day 4 and were euthanized on postoperative days 24 and 56. We found that Met-RANTES significantly reduced intimal thickening in this model of chronic rejection and that Met-RANTES markedly decreased the infiltration of CD4 and CD8 T lymphocytes and MOMA-2+ monocytes/macrophages into transplanted hearts. Met-RANTES also suppressed the ex vivo and in vitro proliferative responses of recipient splenocytes to donor antigens. Finally, Met-RANTES treatment was associated with a marked reduction in RANTES/CCL5 and monocyte chemoattractant protein-1 gene transcript levels in the donor hearts.

CONCLUSIONS

Antagonism of the chemokine receptors CCR1 and CCR5 with Met-RANTES attenuates CAV development in vivo by reducing mononuclear cell recruitment to the transplanted heart, proliferative responses to donor antigens, and intragraft RANTES/CCL5 and monocyte chemoattractant protein-1 gene transcript levels. These findings suggest that chemokine receptors CCR1 and CCR5 play significant roles in the development of chronic rejection and may serve as potential therapeutic targets.

CXCR4‐Tropic HIV‐1 Suppresses Replication of CCR5‐Tropic HIV‐1 in Human Lymphoid Tissue by Selective Induction of CC‐Chemokines

In infected individuals, human immunodeficiency virus type 1 (HIV-1) exist as a "swarm" of quasi species compartmentalized in tissues where individual viral variants may interact locally. We have used human lymphoid tissue, where the critical events of HIV disease occur, to study local interactions in model HIV-1 binary swarms ex vivo. We infected tissue blocks with binary mixtures consisting either of CCR5-dependent and CXCR4-dependent variants or of 2 dual-tropic HIV-1 variants, of which one is skewed to utilization of CXCR4 and the other of CCR5. HIV-1 variants that use CXCR4 suppress replication of CCR5-dependent HIV-1 variants, whereas CCR5-dependent HIV-1 variants do not affect replication of CXCR4-dependent HIV-1. CC-chemokines that inhibit replication of CCR5-dependent HIV-1 variants were up-regulated by CXCR4-dependent HIV-1, thus possibly contributing to this suppression. Tissue-specific chemokine/cytokine network modulations triggered by individual HIV-1 variants may be an important mechanism of local interactions among HIV-1 quasi species in infected tissue.

The N-terminal of the V3 loop in HIV type 1 gp120 is responsible for its conformation-dependent interaction with cell surface molecules

The V3 loop of HIV-1 gp120 plays an important role in the interaction of the viral envelope with cellular coreceptors and/or with other cell surface molecules. To clarify this interaction we used a panel of monoclonal antibodies (MAbs) against V3 loop and synthetic looped V3 peptides V3-BH10, V3-ADA, and V3-89.6, derived from the V3 regions of the BH10 clone of IIIB (X4-tropic), ADA (R5-tropic), and 89.6 (R5X4-tropic), respectively. A linear mutant peptide, V3-BH10/CA, was also synthesized as a control. Biotinylated V3-BH10, -BH10/CA, and-ADA were also made. The binding abilities of the biotinylated and nonbiotinylated peptides to various types of cells were investigated by using flow cytometry. Subsequently, the principal region of the V3 loop involved in cell surface binding was analyzed by using MAbs against the tip (447-52D and 694-98D), N-termini (IIIB-V3-21) or C-termini (IIIB-V3-01) of the V3 loop in flow cytometry and enzyme-linked immunoabsorbent assay. We demonstrate that looped V3 peptides of both X4 and R5X4 HIV (V3-BH10 and V3-89.6) can bind to various types of cells irrespective of their CD4 and/or coreceptor expression in a conformation-dependent manner. In contrast, the V3 loop of R5 HIV (V3-ADA) can scarcely bind to the cells. Using MAbs whose epitopes cover the entire V3 loop we found that MAb IIIB-V3-21 can react with platebound but not cell-bound peptides, and the MAb blocked biotin-V3-BH10 binding suggesting that the N-terminal of the V3 loop interacts directly with cell surface molecule(s).

Chemokine-induced cell death in CCR5-expressing neuroblastoma cells

CCR5 is expressed in neurons but its function in this cellular context is hitherto poorly understood. We have generated CCR5-expressing SH-SY5Y neuroblastoma cells. CCR5 ligands induced cell death in these cells, but not in control neuroblastoma cells or in CCR5-expressing fibroblasts. CCR5-dependent killing of neuroblastoma cells occurred through apoptosis, since it was accompanied by caspase-3 activation and could be prevented by a caspase-3 inhibitor. Finally, cell killing by activated microglia was more rapid and extensive in CCR5-expressing neuroblastoma cells than in control cells. In summary, CCR5 may act as a death receptor in cells of neuronal lineage and therefore be involved in inflammatory neurodegeneration.

Contrasting use of CCR5 structural determinants by R5 and R5X4 variants within a human immunodeficiency virus type 1 primary isolate quasispecies

Macrophagetropic R5 human immunodeficiency virus type 1 (HIV-1) isolates often evolve into dualtropic R5X4 variants during disease progression. The structural basis for CCR5 coreceptor function has been studied in a limited number of prototype strains and suggests that R5 and R5X4 Envs interact differently with CCR5. However, differences between unrelated viruses may reflect strain-specific factors and do not necessarily represent changes resulting from R5 to R5X4 evolution of a virus in vivo. Here we addressed CCR5 domains involved in fusion for a large set of closely related yet functionally distinct variants within a primary isolate swarm, employing R5 and R5X4 Envs derived from the HIV-1 89.6(PI) quasispecies. R5 variants of 89.6(PI) could fuse using either N-terminal or extracellular loop CCR5 sequences in the context of CCR5/CXCR2 chimeras, similar to the unrelated R5 strain JRFL, but R5X4 variants of 89.6(PI) were highly dependent on the CCR5 N terminus. Similarly, R5 89.6(PI) variants and isolate JRFL tolerated N-terminal CCR5 deletions, but fusion by most R5X4 variants was markedly impaired. R5 89.6(PI) Envs also tolerated multiple extracellular domain substitutions, while R5X4 variants did not. In contrast to CCR5 use, fusion by R5X4 variants of 89.6(PI) was largely independent of the CXCR4 N-terminal region. Thus, R5 and R5X4 species from a single swarm differ in how they interact with CCR5. These results suggest that R5 Envs possess a highly plastic capacity to interact with multiple CCR5 regions and support the concept that viral evolution in vivo results from the emergence of R5X4 variants with the capacity to use the CXCR4 extracellular loops but demonstrate less-flexible interactions with CCR5 that are strongly dependent on the N-terminal region.

Structure and function of CC-chemokine receptor 5 homologues derived from representative primate species and subspecies of the taxonomic suborders Prosimii and Anthropoidea

A chemokine receptor from the seven-transmembrane-domain G-protein-coupled receptor superfamily is an essential coreceptor for the cellular entry of human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus (SIV) strains. To investigate nonhuman primate CC-chemokine receptor 5 (CCR5) homologue structure and function, we amplified CCR5 DNA sequences from peripheral blood cells obtained from 24 representative species and subspecies of the primate suborders Prosimii (family Lemuridae) and Anthropoidea (families Cebidae, Callitrichidae, Cercopithecidae, Hylobatidae, and Pongidae) by PCR with primers flanking the coding region of the gene. Full-length CCR5 was inserted into pCDNA3.1, and multiple clones were sequenced to permit discrimination of both alleles. Compared to the human CCR5 sequence, the CCR5 sequences of the Lemuridae, Cebidae, and Cercopithecidae shared 87, 91 to 92, and 96 to 99% amino acid sequence homology, respectively. Amino acid substitutions tended to cluster in the amino and carboxy termini, the first transmembrane domain, and the second extracellular loop, with a pattern of species-specific changes that characterized CCR5 homologues from primates within a given family. At variance with humans, all primate species examined from the suborder Anthropoidea had amino acid substitutions at positions 13 (N to D) and 129 (V to I); the former change is critical for CD4-independent binding of SIV to CCR5. Within the Cebidae, Cercopithecidae, and Pongidae (including humans), CCR5 nucleotide similarities were 95.2 to 97.4, 98.0 to 99.5, and 98.3 to 99.3%, respectively. Despite this low genetic diversity, the phylogeny of the selected primate CCR5 homologue sequences agrees with present primate systematics, apart from some intermingling of species of the Cebidae and Cercopithecidae. Constructed HOS.CD4 cell lines expressing the entire CCR5 homologue protein from each of the Anthropoidea species and subspecies were tested for their ability to support HIV-1 and SIV entry and membrane fusion. Other than that of Cercopithecus pygerythrus, all CCR5 homologues tested were able to support both SIV and HIV-1 entry. Our results suggest that the shared structure and function of primate CCR5 homologue proteins would not impede the movement of primate immunodeficiency viruses between species.

Genetic and functional analysis of full-length human immunodeficiency virus type 1 env genes derived from brain and blood of patients with AIDS

The genetic evolution of human immunodeficiency virus type 1 (HIV-1) in the brain is distinct from that in lymphoid tissues, indicating tissue-specific compartmentalization of the virus. Few primary HIV-1 envelope glycoproteins (Envs) from uncultured brain tissues have been biologically well characterized. In this study, we analyzed 37 full-length env genes from uncultured brain biopsy and blood samples from four patients with AIDS. Phylogenetic analysis of intrapatient sequence sets showed distinct clustering of brain relative to blood env sequences. However, no brain-specific signature sequence was identified. Furthermore, there was no significant difference in the number or positions of N-linked glycosylation sites between brain and blood env sequences. The patterns of coreceptor usage were heterogeneous, with no clear distinction between brain and blood env clones. Nine Envs used CCR5 as a coreceptor, one used CXCR4, and two used both CCR5 and CXCR4 in cell-to-cell fusion assays. Eight Envs could also use CCR3, CCR8, GPR15, STRL33, Apj, and/or GPR1, but these coreceptors did not play a major role in virus entry into microglia. Recognition of epitopes by the 2F5, T30, AG10H9, F105, 17b, and C11 monoclonal antibodies varied among env clones, reflecting genetic and conformational heterogeneity. Envs from two patients contained 28 to 32 N-glycosylation sites in gp120, compared to around 25 in lab strains and well-characterized primary isolates. These results suggest that HIV-1 Envs in brain cannot be distinguished from those in blood on the basis of coreceptor usage or the number or positions of N-glycosylation sites, indicating that other properties underlie neurotropism. The study also demonstrates characteristics of primary HIV-1 Envs from uncultured tissues and implies that Env variants that are glycosylated more extensively than lab strains and well-characterized primary isolates should be considered during development of vaccines and neutralizing antibodies.

The relative activity of CXCR3 and CCR5 ligands in T lymphocyte migration: concordant and disparate activities in vitro and in vivo

In chronic inflammatory reactions such as rheumatoid arthritis and multiple sclerosis, T cells in the inflamed tissue express the chemokine receptors CXCR3 and CCR5, and the chemokine ligands (CCL) of these receptors are present in the inflammatory lesions. However, the contribution of these chemokines to T cell recruitment to sites of inflammation is unclear. In addition, the relative roles of the chemokines that bind CXCR3 (CXCL9, CXCL10, CXCL11) and CCR5 (CCL3, CCL4, CCL5) in this process are unknown. The in vitro chemotaxis and in vivo migration of antigen-activated T lymphoblasts and unactivated spleen T cells to chemokines were examined. T lymphoblasts migrated in vitro to CXCR3 ligands with a relative potency of CXCL10 > CXCL11 > CXCL9, but these cells demonstrated much less chemotaxis to the CCR5 ligands. In vivo, T lymphocytes were recruited in large numbers with rapid kinetics to skin sites injected with CXCL10 and CCL5 and less to CCL3, CCL4, CXCL9, and CXCL11. The combination of CCL5 with CXCL10 but not the other chemokines markedly increased recruitment. Coinjection of interferon-gamma, tumor necrosis factor alpha, and interleukin-1alpha to up-regulate endothelial cell adhesion molecule expression with CXCL10 or CCL5 induced an additive increase in lymphoblast migration. Thus, CXCR3 ligands are more chemotactic than CCR5 ligands in vitro; however, in vivo, CXCL10 and CCL5 have comparable T cell-recruiting activities to cutaneous sites and are more potent than the other CXCR3 and CCR5 chemokines. Therefore, in vitro chemotaxis induced by these chemokines is not necessarily predictive of their in vivo lymphocyte-recruiting activity.

Viral and host cofactors facilitate HIV-1 replication in macrophages

Human immunodeficiency virus type 1 (HIV-1) infection of CD4+ T lymphocytes leads to their progressive loss, whereas HIV-1-infected macrophages appear to resist HIV-1-mediated apoptotic death. The differential response of these two host-cell populations may be critical in the development of immunodeficiency and long-term persistence of the virus. Multiple contributing factors may favor the macrophage as a resilient host, not only supporting infection by HIV-1 but also promoting replication and persistence of this member of the lentivirus subfamily of primate retroviruses. An encounter between macrophages and R5 virus engages a signal cascade eventuating in transcriptional regulation of multiple genes including those associated with host defense, cell cycle, nuclear factor-kappaB regulation, and apoptosis. It is important that enhanced gene expression is transient, declining to near control levels, and during this quiescent state, the virus continues its life cycle unimpeded. However, when viral replication becomes prominent, an increase in host genes again occurs under the orchestration of viral gene products. This biphasic host response must fulfill the needs of the parasitic virus as viral replication activity occurs and leads to intracellular and cell surface-associated viral budding. Inroads into understanding how HIV-1 co-opts host factors to generate a permissive environment for viral replication and transmission to new viral hosts may provide opportunities for targeted interruption of this lethal process.

Macrophage activation through CCR5- and CXCR4-mediated gp120-elicited signaling pathways

Macrophages are major targets for infection by human immunodeficiency virus type 1 (HIV-1). In addition to their role as productive viral reservoirs, inappropriate activation of infected and uninfected macrophages appears to contribute to pathogenesis. HIV-1 infection requires initial interactions between the viral envelope surface glycoprotein gp120, the cell-surface protein CD4, and a chemokine receptor CCR5 or CXCR4. Besides their role in HIV-1 entry, CCR5 and CXCR4 are G protein-coupled receptors that can activate multiple intracellular signaling pathways. HIV-1 gp120 has been shown to activate signaling pathways through the chemokine receptors in several cell types including lymphocytes, neurons, and astrocytes. In some cell types, these consequences may cause cellular injury. In this review, we highlight our data demonstrating diverse signaling events that occur in primary human macrophages in response to gp120/chemokine receptor interactions. These responses include K+, Cl-, and nonselective cation currents, intracellular Ca2+ increases, and activation of several kinases including the focal adhesion-related tyrosine kinase Pyk2, mitogen-activated protein kinases (MAPK), and phosphoinositol-3 kinase. Activation of the MAPK leads to gp120-induced expression of chemokines such as monocyte chemoattractant protein-1 and macrophage-inflammatory protein-1beta and the proinflammatory cytokine tumor necrosis factor alpha. These responses establish a complex cytokine network, which may enhance or suppress HIV-1 replication. In addition, dysregulation of macrophage function by gp120/chemokine receptor signaling may contribute to local inflammation and injury and further recruit additional inflammatory and/or target cells. Targeting these cellular signaling pathways may have benefit in controlling inflammatory sequelae of HIV infection such as in neurological disease.

Early control of highly pathogenic simian immunodeficiency virus/human immunodeficiency virus chimeric virus infections in rhesus monkeys usually results in long-lasting asymptomatic clinical outcomes

In contrast to simian immunodeficiency viruses (SIVs), which induce immunodeficiency over a 1- to 2-year period, highly pathogenic simian-human immunodeficiency viruses (SHIVs) cause an irreversible and systemic depletion of CD4(+) T lymphocytes in macaque monkeys within weeks of inoculation. Nonetheless, the seemingly more aggressive SHIVs have proven to be easier to control by the same vaccine regimens which fail to contain SIV. Because early events during in vivo infections may determine both the pathogenic consequences of the challenge virus and its sensitivity to interventions that prevent disease, we have evaluated the effects of inoculum size and a potent antiretroviral drug on the development of disease in monkeys infected with SHIV(DH12R). The results obtained show that in a majority of inoculated animals, suppression of SHIV replication during the first 2 weeks of infection, which prevents complete loss of CD4(+) T cells, leads to very low to undetectable postpeak viremia and an asymptomatic clinical course for periods up to 4 years.

Interfering with RNA: kill the messenger

A number of scientific papers were published in 2002 describing the discovery of a process called RNA interference, or RNAi. The newly discovered process, whereby small strands of RNA can block the development of new genetic material, was called the "breakthrough of the year" in 2002 by Science magazine. RNAi has excited AIDS researchers because it has both short- and long-term potential for significantly improving the treatment of HIV disease.

Early- and intermediate-stage variants of simian immunodeficiency virus replicate efficiently in cells lacking CCR5

Primate lentiviruses are thought to use the chemokine receptor CCR5 as the major coreceptor for entry into cells. Here we show that some variants of simian immunodeficiency virus (SIV) replicate efficiently in peripheral blood mononuclear cells (PBMCs) lacking a functional CCR5. There were differences in the replication patterns of sequential variants that evolved during SIVMne infection; the late-stage pathogenic variants were unable to replicate in PBMCs lacking CCR5, whereas the early- and intermediate-stage viruses replicated as well in PBMCs lacking CCR5 as they did in cells with wild-type CCR5. The coreceptor specificities of these sequential variants were compared using indicator cell lines expressing known SIV coreceptors. Among the known SIV coreceptors, there were none that were functional for the early and intermediate variants but not the late-stage variants, suggesting that the coreceptor used for replication in PBMCs may be a coreceptor that has not yet been described. Because some variants replicate with high efficiency in peripheral blood cells using this as yet uncharacterized cellular receptor, this coreceptor may be important for viral entry of some target cell populations in the host.

A novel cyclic peptide immunization strategy for preventing HIV-1/AIDS infection and progression

A novel synthetic peptide immunogen targeting the human immunodeficiency virus type-1 (HIV-1) coreceptor CXCR4 was evaluated for its capacity to induce CXCR4-specific antibodies with anti-HIV-1 activity in BALB/c mice and cynomolgus monkeys. A cyclic closed-chain dodecapeptide mimicking the conformation-specific domain of CXCR4 (cDDX4) was prepared in which Gly-Asp, as the dipeptide forming a spacer arm, links the amino and carboxyl termini of the decapeptidyl linear chain (linear DDX4, Asn176 to Ile185) derived from the undecapeptidyl arch (UPA; Asn176 to Cys186) of extracellular loop 2 (ECL-2) in CXCR4. Immunization of BALB/c mice with cDDX4 conjugated with a multiple-antigen peptide (cDDX4-MAP) induced conformational epitope-specific antibodies, and monoclonal antibody IA2-F9 reacted with cDDX4, but not with linear DDX4, as determined by real-time biomolecular interaction analysis using surface plasmon resonance. The antibody also reacted with cells expressing CXCR4 but not with cells expressing the other HIV coreceptor, CCR5. Furthermore, the antibody inhibited the replication of HIV-1 X4 virus (using CXCR4), as shown by an infection assay using both MAGIC-5 cells and MT4 cells, but not that of HIV-1 R5 virus (using CCR5). The antibody weakly interfered with chemotaxis induced by stromal cell-derived factor-1 alpha in THP-1 cells or moderately inhibited the chemotaxis of Molt4#8 cells under the same conditions. In addition, immunization of cynomolgus monkeys also induced cDDX4-specific antibodies with anti-HIV activity. Taken together, these results indicate that cDDX4 conjugated with a multi-antigen peptide induces the conformational epitope-specific antibodies to the undecapeptidyl arch of CXCR4 may be a novel candidate immunogen for preventing disease progression in HIV-1-infected individuals.

Identification and characterization of HIV-2 strains obtained from asymptomatic patients that do not use CCR5 or CXCR4 coreceptors

In vivo, human immunodeficiency virus type 2 (HIV-2) infection reveals several unique characteristics when compared to HIV-1 infection, the most remarkable of which is the extraordinarily long asymptomatic period. Here we describe two HIV-2 primary isolates, obtained from asymptomatic individuals, which do not infect any coreceptor-expressing cell lines tested. In those cells, we show that the absence of replication is directly related to cell entry events. Furthermore, productive infection observed in peripheral blood mononuclear cells (PBMC) was not inhibited by natural ligands and monoclonal antibodies directed to CCR5 and CXCR4. Finally, viral entry efficiency and viral progeny production of these viruses are markedly impaired in PBMC, indicating a reduced replicative fitness of both viruses. In conclusion, our data suggest that in some HIV-2 asymptomatic individuals, the circulating viruses are unable to use the major coreceptors to infect PBMC. This fact should have important implications in HIV-2 pathogenesis and transmission.

CCR5 mediates specific migration of Toxoplasma gondii-primed CD8 lymphocytes to inflammatory intestinal epithelial cells

BACKGROUND & AIMS

Toxoplasma gondii, an obligate intracellular parasite, can invade intestinal epithelial cells and elicit a robust Th1 immune response. In this model of intestinal inflammation, CD8(+) intraepithelial lymphocytes (IELs) secrete transforming growth factor (TGF)-beta, which appears necessary for the maintenance of homeostasis in the intestine. However, the mechanism responsible for the IEL migration to the inflamed intestine is still unclear.

METHODS

An in vitro coculture cell system was used to quantify the IEL attraction by an infected intestinal epithelial cell line (m-IC(cl2)). We used CCR5-deficient mice to determine which chemokine receptor-chemokine interaction could be responsible for the recruitment of antigen-specific CD8(+) IELs to the small intestine for the promotion of parasite clearance and host recovery.

RESULTS

We observed increased expression of several chemokine receptors (CCR1, CCR2, CCR5, CXCR3) in the infected ileum. In particular, CCR5 expression was markedly increased in antigen-primed CD8(+) IELs. Experiments using recombinant chemokines as well as blocking antibodies showed that macrophage inflammatory protein (MIP)-1alpha and MIP-1beta were critical for their homing. CD8(+) IELs isolated from CCR5-deficient mice (CCR5-/-), despite their high production of TGF-beta and overexpression of activation markers, were impaired in their ability to migrate in vitro to the m-IC(cl2) monolayer or in vivo to the inflamed intestine after adoptive transfer.

CONCLUSIONS

Our data emphasize the biologic role of CCR5 as an important component in the migration of intraepithelial CD8(+) T cells and the regulation of the inflammatory response following parasite infection.