An intricate Web: chemokine receptors, HIV-1 and hematopoiesis

Expression of ADP receptor P2Y12, thromboxane A2 receptor and C-type lectin-like receptor 2 in cord blood-derived megakaryopoiesis

The ADP receptor P2Y₁₂, the thromboxane A₂ receptor (TXA₂R) and the C-type lectin-like receptor 2 (CLEC-2) mediate platelet activation by different mechanisms. Only little is known about the expression of the receptors in human megakaryopoiesis. Our study aimed to establish a flow cytometry (FC) method for the measurement of P2Y₁₂, TXA₂R, and CLEC-2 on platelets of healthy donors and to monitor receptor expression in ex vivo megakaryopoiesis. We determined mean fluorescence intensity (MFI) values of FITC, PE, or APC labeled antibodies binding to the receptors on platelets of 90 healthy donors. For cord blood-derived megakaryopoiesis (CBMK) differentiation of CD34+ cells was induced by IL-3, SCF, and TPO. At 6 time points between day 0 and day 21 of cell culture the MFI values for CD34, CD41, CD61, P2Y₁₂, TXA₂R, and CLEC-2 were measured. Quantitative PCR was used for relative quantification of the corresponding mRNA. Transcription factor (TF) binding sites were predicted by in silico analysis of the genes. Platelets showed expectable high MFI values for the platelet marker CD41 (13,716 median MFI). Lower MFI was found for P2Y₁₂ (2,847 median MFI) and CLEC-2 (1,211 median MFI), whereas, binding of the TXA₂R antibody revealed even higher values (21,458 median MFI) than CD41. In CBMK the CD34+ cells were negative for P2Y₁₂, TXA₂R, and CLEC-2 at day 0. A maximum of 21-fold and 6-fold increase of P2Y₁₂ and TXA₂R MFI values, respectively, was found on day 14 to 17. MFI for CLEC-2 increased by 58-fold within the first week and reached a maximum of 1,572-fold increase within the first two weeks of CBMK. Very similar results were obtained on the RNA level. The differential regulation of receptor expression in CBMK was further supported by significant differences in the numbers and types of TF binding sites. P2Y₁₂ and TXA₂R, both upregulated only to a low extent in CBMK, probably, are dispensable for megakaryopoiesis. Furthermore, we speculate that CLEC-2 strongly upregulated in early CMBK is important for megakaryopoiesis.

HIV Impacts CD34+ Progenitors Involved in T-Cell Differentiation During Coculture With Mouse Stromal OP9-DL1 Cells

HIV-1 causes the loss of CD4⁺ T cells via depletion or impairment of their production. The latter involves infection of thymocytes, but the involvement of hematopoietic CD34⁺ cells remains unclear even though HIV-positive patients frequently manifest myelosuppression. In order to have a closer look at the impact of HIV-1 on T-lineage differentiation, this study utilized the OP9-DL1 coculture system, which supports in vitro T-lineage differentiation of human hematopoietic stem/progenitor cells. In the newly developed in vitro OP9-DL1/HIV-1 model, cord-derived CD34⁺ cells were infected with CXCR4-tropic HIV-1_NL4−3 and cocultured. The HIV-infected cocultures exhibited reduced CD4⁺ T-cell growth at weeks 3–5 post infection compared to autologous uninfected cocultures. Further assays and analyses revealed that CD34⁺CD7⁺CXCR4⁺ cells can be quickly depleted as early as 1 week after infection of the subset, and this was accompanied by the emergence of rare CD34⁺CD7⁺CD4⁺ cells. A subsequent theoretical model analysis suggested potential influence of HIV-1 on the differentiation rate or death rate of lymphoid progenitor cells. These results indicate that CXCR4-tropic HIV-1 strains may impact the dynamics of CD34⁺CD7⁺ lymphoid progenitor cell pools, presumably leading to impaired T-cell production potential.

In vivo effect of statins on the expression of the HIV co-receptors CCR5 and CXCR4

BACKGROUND

During the HIV-1 replication cycle, several molecules including chemokine receptors and cholesterol are crucial, and are therefore potential targets for therapeutic intervention. Indeed statins, compounds that inhibit cellular synthesis of cholesterol and have anti-inflammatory and immunomodulatory properties were shown to inhibit HIV-1 infection by R5 tropic strains but not by X4 strains in vitro, mainly by altering the chemokine receptor/ligands axes. Therefore, the objective of this study was to characterize in vivo, the capacity of statins to modulate in HIV seronegative and chronically HIV-1-infected adults the expression of CCR5 and CXCR4, of their ligands and the tropism of circulating HIV-1 strains.

METHODS

Samples from asymptomatic HIV-1-infected adults enrolled in a clinical trial aimed at evaluating the antiretroviral activity of lovastatin were used to evaluate in vivo the modulation by lovastatin of CCR5, CXCR4, their ligands, and the shift in plasma viral tropism over one year of intervention. In addition, ten HIV negative adults received a daily oral dose of 40 mg of lovastatin or 20 mg of atorvastatin; seven other HIV negative individuals who received no treatment were followed as controls. The frequency and phenotype of immune cells were determined by flow-cytometry; mRNA levels of chemokine receptors and their ligands were determined by real-time PCR. Viral tropism was determined by PCR and sequencing, applying the clonal and clinical model of analyses.

RESULTS

Our study shows that long-term administration of lovastatin in HIV-infected individuals does not induce a shift in viral tropism, or induce a significant modulation of CCR5 and CXCR4 on immune cells in HIV-infected patients. Similar results were found in HIV seronegative control subjects, treated with lovastatin or atorvastatin, but a significant increase in CCL3 and CCL4 transcription was observed in these individuals.

CONCLUSIONS

These findings suggest that long-term administration of statins at therapeutic doses, does not significantly affect the expression of HIV-1 co-receptors or of their ligands. In addition it is important to point out that based on the results obtained, therapeutic administration of statins in HIV-infected patients with lipid disorders is safe in terms of selecting X4 strains.

A novel approach to quantify G-protein-coupled receptor dimerization equilibrium using bioluminescence resonance energy transfer

Along with other resonance energy transfer techniques, bioluminescence resonance energy transfer (BRET) has emerged as an important method for demonstrating protein-protein interactions in cells. In the field of G-protein-coupled receptors, including chemokine receptors, BRET has been widely used to investigate homo- and heterodimerization, a feature of their interactions that is emerging as integral to function and regulation. While demonstrating the existence of dimers for a given receptor proved to be fairly straightforward, quantitative comparisons of different receptors or mutants are nontrivial because of inevitable variations in the expression of receptor constructs. The uncontrollable parameters of the cellular expression machinery make amounts of transfected DNA extremely poor predictors for the expression levels of BRET donor and acceptor receptor constructs, even in relative terms. In this chapter, we show that properly accounting for receptor expression levels is critical for quantitative interpretation of BRET data. We also provide a comprehensive account of expected responses in all types of BRET experiments and propose a framework for uniform and accurate quantitative treatment of these responses. The framework allows analysis of both homodimer and heterodimer BRET data. The important caveats and obstacles for quantitative treatment are outlined, and the utility of the approach is illustrated by its application to the homodimerization of wild-type (WT) and mutant forms of the chemokine receptor CXCR4.

Pathogen recognition in the human female reproductive tract: expression of intracellular cytosolic sensors NOD1, NOD2, RIG-1, and MDA5 and response to HIV-1 and Neisseria gonorrhea

PROBLEM

Expression patterns and regulation of cytosolic pattern recognition receptors (PRR) NOD-1, NOD-2, RIG-1, and MDA5 have not been elucidated in the human female reproductive tract (FRT).

METHOD OF STUDY

Primary epithelial cells (EC) isolated from Fallopian tube (FT), endometrium (EM), cervix (Cx), and ectocervix (Ecx) were treated with estradiol, poly(I:C), Neisseria gonorrhea (GC), and HIV-1. PRR mRNA expressions were analyzed by Real-time RT-PCR. Conditioned media were analyzed for IL-8 by ELISA.

RESULTS

EC from all FRT compartments constitutively expressed NOD1, NOD2, RIG-1, and MDA5 with highest levels expressed by FT. Stimulation with poly(I:C) resulted in upregulation of NOD2, RIG-1, and MDA5 in all FRT compartments and correlated with increased secretion of IL-8, whereas estradiol treatment had no effects. Exposure to GC and HIV-1 IIIB but not BaL resulted in selective upregulation of NOD2 and MDA5.

CONCLUSION

PRR are expressed throughout the FRT and differentially regulated by poly(I:C), GC and HIV-1.

Ccr5 deficiency regulates the proliferation and trafficking of natural killer cells under physiological conditions

Chemokines were shown to govern the trafficking of immune cells and may also play important roles in the survival and activation of these cells. We report here that under physiological conditions, the bone marrow (BM), spleen, blood and liver of Ccr5, but not of Ccr1-deficient mice, contain reduced numbers of NK cells. NK cells in the BM of Ccr5-deficient mice proliferate to a lesser extent compared to WT mice. Furthermore, spleen NK cells derived from Ccr5-deficient mice that were transplanted into irradiated recipients failed to proliferate in the host. Ccr5, but not Ccr1-deficient NK cells, failed to migrate in vitro in response to RANTES and MIP-1β but not MIP-1β or SDF-1 and had reduced activation, lower expression levels of NK cell markers and a slightly reduced capacity to adhere to target cells and stimulate their killing. Using the polyI:C mouse model for NK trafficking, we found that in the absence of Ccr5, but not Ccr1, NK cells failed to accumulate in the liver. In contrast, using the influenza viral infection as a model to evaluate NK cell proliferation, we found that Ccr5-deficient NK cells in the BM had a higher proliferation rate than WT NK cells. These results suggest a role for Ccr5 in NK cell proliferation and circulation under physiological conditions and a complex role for Ccr5 in determining the fate of NK cells under pathological conditions.

HIV-1 infection inhibits cytokine production in human thymic macrophages

OBJECTIVE

The thymus serves as a critical site of T-lymphocyte ontogeny and selection. Thymic infection by HIV-1 is known to disrupt thymocyte maturation by both direct and indirect means; however, the mechanism behind these effects remains poorly defined. Macrophages represent one of the most important peripheral targets of HIV-1 infection, are resident in the thymic stroma, and play a central role in thymocyte maturation.

MATERIALS AND METHODS

Studies presented here define three primary features and outcomes of thymic macrophages (TM) and HIV-1 infection: (1) The distinctive TM phenotype (surface markers and cytokine production measured by immunofluorescence, fluorescence-activated cell sorting, and reverse transcriptase polymerase chain reaction) relative to macrophages from other sources (blood [monocyte-derived macrophages] and bone marrow); (2) infection of TM by different HIV-1 subtypes (X4, R5, and X4/R5) measured by enzyme-linked immunosorbent assay and polymerase chain reaction; and (3) consequences of HIV-1 infection on cytokine production by TM measured by reverse transcriptase polymerase chain reaction.

RESULTS

The results demonstrate that TM display a distinctive phenotype of HIV-1 receptors (CD4(lo), CXCR4(lo), CCR5(med), CCR3(hi)), chemokine production (macrophage inflammatory protein-1α(+); regulated on activation, normal T expressed and secreted(+); macrophage inflammatory protein-1b(-); stromal cell-derived factor -1(-)); and cytokine production (tumor necrosis factor-α(+), interleukin-8(+), macrophage colony-stimulating factor(+), interleukin-6(-)) relative to either monocyte-derived macrophages or bone marrow. TM were infected in vitro with R5 and X4/R5-tropic HIV-1 subtypes, and developed syncytia formation during long-term X4/R5 culture. In contrast, TM supported only transient replication of X4-tropic HIV-1. Lastly, infection of TM with HIV-1 abolished the production of all cytokines tested in long-term in vitro cultures.

CONCLUSIONS

Taken together, these results indicate that TM are a potential direct target of in situ HIV-1 infection, and that this infection may result in the disruption of macrophage functions that govern normal thymocyte maturation.

Simvastatin restores down-regulated GATA-6 expression in pulmonary hypertensive rats

Vascular smooth muscle cell proliferation has been known to be predominant in vascular remodeling of pulmonary hypertensive. The GATA family proteins, a group of zinc finger transcription factors, play an important role during cell proliferation. The aim of present study was to investigate the expression of GATA-6 gene in experimental pulmonary hypertensive rats and explore the effect of regulation of GATA-6 expression by simvastatin on pulmonary vascular remodeling. The male Sprague-Dawley rats model was established with receiving pneumonectomy and monocrotaline (MCT) administration. Right pulmonary artery remodeling in these animals was compared with untreated rats or rats receiving simvastatin. The level of GATA-6 mRNA and protein expression was detected by reverse transcriptase–polymerase chain reaction (RT-PCR) and Western blotting, respectively. Pneumonectomized, MCT-treated rats had significantly increased mean pulmonary arterial pressure (mPAP), RV/(LV + S) ratio (ratio of the right ventricular to left ventricular and septum weights), vascular occlusion scores (VOSs), and percent media wall thickness on day 35, all the indices were significantly decreased after simvastatin administration in these rats. The level of GATA-6 mRNA and protein were markedly decreased in these pneumonectomy and MCT-treated rats, and they were significantly up-regulated in these rats after receiving simvastatin. These results indicate that the development and progression of pulmonary hypertension is prevented by simvastatin by up-regulating GATA-6 expression in the lung tissue.

Activation of Wnt5A signaling is required for CXC chemokine ligand 12-mediated T-cell migration

Chemokines mediate the signaling and migration of T cells, but little is known about the transcriptional events involved therein. Microarray analysis of CXC chemokine ligand (CXCL) 12-treated T cells revealed that Wnt ligands are significantly up-regulated during CXCL12 treatment. Real-time polymerase chain reaction and Western blot analysis confirmed that the expression of noncanonical Wnt pathway members (eg, Wnt5A) was specifically up-regulated during CXCL12 stimulation, whereas beta-catenin and canonical Wnt family members were selectively down-regulated. Wnt5A augmented signaling through the CXCL12-CXCR4 axis via the activation of protein kinase C. Moreover, Wnt5A expression was required for CXCL12-mediated T-cell migration, and rWnt5A sensitized human T cells to CXCL12-induced migration. Furthermore, Wnt5A expression was also required for the sustained expression of CXCR4. These results were further supported in vivo using EL4 thymoma metastasis as a model of T-cell migration. Together, these data demonstrate that Wnt5A is a critical mediator of CXCL12-CXCR4 signaling and migration in human and murine T cells.

Cooperative interaction between hepatocyte nuclear factor 4 alpha and GATA transcription factors regulates ATP-binding cassette sterol transporters ABCG5 and ABCG8

Cholesterol homeostasis is maintained by coordinate regulation of cholesterol synthesis and its conversion to bile acids in the liver. The excretion of cholesterol from liver and intestine is regulated by ATP-binding cassette half-transporters ABCG5 and ABCG8. The genes for these two proteins are closely linked and divergently transcribed from a common intergenic promoter region. Here, we identified a binding site for hepatocyte nuclear factor 4alpha (HNF4alpha) in the ABCG5/ABCG8 intergenic promoter, through which HNF4alpha strongly activated the expression of a reporter gene in both directions. The HNF4alpha-responsive element is flanked by two conserved GATA boxes that were also required for stimulation by HNF4alpha. GATA4 and GATA6 bind to the GATA boxes, coexpression of GATA4 and HNF4alpha leads to a striking synergistic activation of both the ABCG5 and the ABCG8 promoters, and binding sites for HNF4alpha and GATA were essential for maximal synergism. We also show that HNF4alpha, GATA4, and GATA6 colocalize in the nuclei of HepG2 cells and that a physical interaction between HNF4alpha and GATA4 is critical for the synergistic response. This is the first demonstration that HNF4alpha acts synergistically with GATA factors to activate gene expression in a bidirectional fashion.

Expression of Nef downregulates CXCR4, the major coreceptor of human immunodeficiency virus, from the surfaces of target cells and thereby enhances resistance to superinfection

Lentiviral Nef proteins are key factors for pathogenesis and are known to downregulate functionally important molecules, including CD4 and major histocompatibility complex class I (MHC-I), from the surfaces of infected cells. Recently, we demonstrated that Nef reduces cell surface levels of the human immunodeficiency virus type 1 (HIV-1) entry coreceptor CCR5 (N. Michel, I. Allespach, S. Venzke, O. T. Fackler, and O. T. Keppler, Curr. Biol. 15:714-723, 2005). Here, we report that Nef downregulates the second major HIV-1 coreceptor, CXCR4, from the surfaces of HIV-infected primary CD4 T lymphocytes with efficiencies comparable to those of the natural CXCR4 ligand, stromal cell-derived factor-1 alpha. Analysis of a panel of mutants of HIV-1(SF2) Nef revealed that the viral protein utilized the same signature motifs for downmodulation of CXCR4 and MHC-I, including the proline-rich motif P(73)P(76)P(79)P(82) and the acidic cluster motif E(66)E(67)E(68)E(69.) Expression of wild-type Nef, but not of specific Nef mutants, resulted in a perinuclear accumulation of the coreceptor. Remarkably, the carboxy terminus of CXCR4, which harbors the classical motifs critical for basal and ligand-induced receptor endocytosis, was dispensable for the Nef-mediated reduction of surface exposure. Functionally, the ability of Nef to simultaneously downmodulate CXCR4 and CD4 correlated with maximum-level protection of Nef-expressing target cells from fusion with cells exposing X4 HIV-1 envelopes. Furthermore, the Nef-mediated downregulation of CXCR4 alone on target T lymphocytes was sufficient to diminish cells' susceptibility to X4 HIV-1 virions at the entry step. The downregulation of chemokine coreceptors is a conserved activity of Nef to modulate infected cells, an important functional consequence of which is an enhanced resistance to HIV superinfection.

Solubilization, stabilization, and purification of chemokine receptors using biosensor technology

Establishing solubilization conditions for membrane-associated receptors is often a tedious empirical process. Here we describe a novel application of SPR biosensor technology to screen solubilization conditions automatically and to assess receptor activity directly. We focus on two chemokine receptors, CXCR4 and CCR5, which are important in HIV cell invasion. The autosampler in Biacore 3000 permitted whole cells expressing C-terminally tagged receptors to be automatically lysed under a given solubilization condition and the lysates to be injected over an antibody surface. The total amount of solubilized receptor could be quantitated from the antibody capture level, whereas the amount of active receptor could be quantitated using a subsequent injection of conformationally sensitive antibody or protein. Using this approach, we identified detergent/lipid/buffer combinations that enhanced and maintained receptor activity. We also used the biosensor to demonstrate CD4-dependent binding of gp120 to solubilized CCR5 and to develop affinity chromatography-based purification methods that increased receptor activity more than 300%. Together, these results illustrate the benefits of using the biosensor as a tool for isolating functional membrane receptors and for analyzing ligand/receptor interactions.

Increased keratinocyte proliferation by JUN-dependent expression of PTN and SDF-1 in fibroblasts

In skin, fibroblasts of the connective tissue play a decisive role in epidermal homeostasis and repair by contributing to the regulation of keratinocyte proliferation and differentiation. The AP-1 transcription factor subunit JUN plays a crucial role in this mesenchymal-epithelial interplay by regulating the expression of two critical paracrine-acting cytokines, keratinocyte growth factor (KGF) and granulocyte-macrophage colony-stimulating factor (GM-CSF). We have performed gene expression profiling of wild-type and Jun–/– mouse embryonic fibroblasts to identify additional players involved in this complex network, and have found pleiotrophin (PTN) and the stromal cell-derived factor 1 (SDF-1) as novel JUN-regulated factors. Both cytokines are expressed by dermal fibroblasts in vivo, as shown by semi-quantitative RT-PCR and in situ hybridization on murine skin sections. Using a heterologous feeder layer co-culture system, we demonstrated that PTN and SDF-1 exert a mitogenic effect on primary human keratinocytes. Moreover, SDF-1-induced keratinocyte proliferation could be specifically inhibited by neutralizing antibodies against SDF-1 or its receptor, CXCR4. Consistent with its role in promoting keratinocyte growth, PTN was upregulated during cutaneous wound healing in vivo. Interestingly, co-cultivation with keratinocytes stimulated PTN expression but repressed SDF-1 production in fibroblasts, demonstrating the complexity of the paracrine regulatory cytokine networks that control skin homeostasis and regeneration.

Alterations in mast cell function and survival following in vitro infection with human immunodeficiency viruses-1 through CXCR4

HIV-1 infection leads to a disease that attacks the central regulatory mechanisms of the immune response. As mucosal tissue is one of the primary sites infected with HIV in vivo, we examined the effects of HIV exposure on human mast cells, important components of mucosal defense. Using the human mast cell line, HMC-1, which expresses CXCR4 but not CCR5 on the cell surface, we found that several HIV-1 X4 tropic lab (IIIB, RF) and primary isolates but not R5 (BAL, ADA) isolates productively infected these cells. Furthermore, stem cell factor-dependent mast cells derived from primary fetal liver or cord blood cultures were also productively infected with both X4 and R5 HIV-1 strains. Infection was blocked at the level of viral entry using monoclonal antibodies to CXCR4 and CD4. Treatment of HMC-1 with TNF-alpha and TGF-beta stimulated cell surface expression of CCR5 and up-regulated expression of both CCR5 and CXCR4 on primary mast cells, leading to increased susceptibility to both X4 and R5 viral isolates. HIV-1 infection also resulted in histamine release from these mast cells, most due in part to HIV-mediated cell death. These results demonstrate that X4 viruses can use CD4 and the CXCR4 receptor to infect mast cells, suggesting that mast cell-T cell interactions may contribute to HIV mediated immune dysfunction in the mucosa.

Selective up-regulation of functional CXCR4 expression in erythroid cells by HIV-1 Tat protein

CXCR4 is the high affinity receptor for the SDF-1 alpha chemokine and represents the main coreceptor for HIV-1 T-tropic strains. The surface expression of CXCR4 was analysed in CD34+ haematopoietic progenitors, induced to differentiate along the erythroid or granulocytic lineages, in liquid cultures supplemented or not with HIV-1 Tat protein. At concentrations as low as 1-10 ng/ml, synthetic Tat protein significantly increased the surface expression of CXCR4 in erythroid but not in granulocytic cells. The Tat-mediated up-regulation of surface CXCR4 was accompanied by a concomitant increase of CXCR4 mRNA and total CXCR4 protein content in cells developing along the erythroid lineage after 6-10 days of culture. Moreover, addition of SDF-1 alpha (200 ng/ml) induced a significant higher rate of apoptosis in Tat-treated erythroid cells in comparison with control cells. These results demonstrated for the first time a direct positive role in haematopoietic gene regulation of Tat protein, and suggest the possible involvement of Tat in HIV-1-induced anaemia.

Platelet- and megakaryocyte-derived microparticles transfer CXCR4 receptor to CXCR4-null cells and make them susceptible to infection by X4-HIV

OBJECTIVE

Under some circumstances the HIV virus may infect cells that do not express receptors essential to HIV-entry. We hypothesized that platelet- and megakaryocyte-derived microparticles (MP) could play a role in such infections. MP are circular membrane fragments shed from the surface of eukaryotic cells. After adhesion to target cells, MP may transfer membrane-associated proteins to these cells. We found that peripheral blood platelet- (PMP) and megakaryocyte-derived MP (MegaMP) that highly express CXCR4 may transfer this receptor from the surface of platelets or megakaryocytes to the surface of CXCR4-null cells.

DESIGN

Since this mechanism could potentially allow CD4+/CXCR4-null cells to become infected by T-tropic HIV, we incubated several human CD4+/CXCR4-null cells such as normal erythroblasts, glioblastomas U87, MAGI and hematopoietic cell lines UT-7, HEL and TF-1 with PMP or MegaMP. We found that these cells became CXCR4+. We next exposed these cells to X4-HIV (IIIB) and evaluated their susceptibility to infection by PCR, ELISA, and morphological analysis.

RESULTS

We observed in all instances that after CD4+/CXCR4-null cell lines 'acquired' CXCR4 from PMP or MegaMP, they could became infected by X4 HIV.

CONCLUSIONS

We postulate that both PMP and MegaMP may play a novel and important role in spreading HIV-1 infection by transferring the CXCR4 co-receptor to CD4+/CXCR4-null cells.

Human Immunodeficiency Virus Hematology

The advent of potent antiretroviral therapy has altered the expected natural history of human immunodeficiency virus (HIV) infection and of many previously associated opportunistic complications, including malignancies. At the same time, HIV suppression hasn’t affected all of these complications equally and the longer expected survival of infected patients may allow the development of newer complications. Additionally, the use of potent antiretroviral combination therapy may itself lead to hematological toxicities. Together these changes affect the consultation role of the hematology-oncology specialist in comprehensive HIV care and demand ongoing education.

In Section I, Dr. Paul Volberding reviews the biology of antiretroviral drug development and the progression in discovering new agents as the viral life cycle is further elucidated. He briefly summarizes the process of combining agents to achieve the degree of viral suppression required for long-term clinical benefit.

In Section II, Dr. Kelty Baker reviews the effects of HIV and its therapy on hematologic dyscrasia and clotting disorders. She summarizes how therapy may decrease certain previously common manifestations of HIV disease while adding new problems likely to result in referral to the hematologist. In addition, she addresses the role of secondary infections, such as parvovirus, in this spectrum of disorders.

In Section III, Dr. Alexandra Levine discusses the still challenging aspects of HIV associated non-Hodgkin’s lymphoma and the association between HIV infection and Hodgkin’s disease. She addresses current controversies in the pathogenesis of HIV related lymphomas and summarizes a number of recent trials of combination chemotherapy, with or without monoclonal antibodies, in their management. Additionally, she reviews the complex relationship of HIV disease with multicentric Castleman’s disease and recent attempts to manage this disorder.

In vivo induction of human immunodeficiency virus type 1 entry into nucleus-free cells by CD4 gene transfer to hematopoietic stem cells: a hypothetical possible strategy for therapeutic intervention

As a useful alternative to employing soluble CD4 to inhibit binding of human immunodeficiency virus type 1 (HIV-1) to target cells, the introduction of CD4-bearing erythrocyte has been proposed by two study groups (see Refs. (5,6)). Prominently, Nicolau and colleagues demonstrated that the electroinserted CD4 molecules in the membranes of erythrocytes are capable of mediating HIV-1 entry. The implications of the studies are that inactivation of the integration-dependent retrovirus by the facilitation of entry into the nucleus-free cells, referred to as 'fake host trap' or 'host cell decoy', may be a possible therapeutic approach. Here we expand this concept to include genetic modification of autologous hematopoietic stem cells and review the relevant theoretical basis. Effective application of molecular technologies to induce partial replacement of hematopoiesis may be critical for this strategy.

Progress toward a human CD4/CCR5 transgenic rat model for de novo infection by human immunodeficiency virus type 1

The development of a permissive small animal model for the study of human immunodeficiency virus type (HIV)-1 pathogenesis and the testing of antiviral strategies has been hampered by the inability of HIV-1 to infect primary rodent cells productively. In this study, we explored transgenic rats expressing the HIV-1 receptor complex as a susceptible host. Rats transgenic for human CD4 (hCD4) and the human chemokine receptor CCR5 (hCCR5) were generated that express the transgenes in CD4(+) T lymphocytes, macrophages, and microglia. In ex vivo cultures, CD4(+) T lymphocytes, macrophages, and microglia from hCD4/hCCR5 transgenic rats were highly susceptible to infection by HIV-1 R5 viruses leading to expression of abundant levels of early HIV-1 gene products comparable to those found in human reference cultures. Primary rat macrophages and microglia, but not lymphocytes, from double-transgenic rats could be productively infected by various recombinant and primary R5 strains of HIV-1. Moreover, after systemic challenge with HIV-1, lymphatic organs from hCD4/hCCR5 transgenic rats contained episomal 2-long terminal repeat (LTR) circles, integrated provirus, and early viral gene products, demonstrating susceptibility to HIV-1 in vivo. Transgenic rats also displayed a low-level plasma viremia early in infection. Thus, transgenic rats expressing the appropriate human receptor complex are promising candidates for a small animal model of HIV-1 infection.

New T-lymphocytic cell lines for studying cell infectability by human immunodeficiency virus

We identified five human T-lymphoid cell lines (PB-1, Sez-4, C19PL, HUT 102B and ATL-2) which highly express CD4 in addition to CXCR4 and CCR5. In order to evaluate if these cells are infectabile by human immunodeficiency virus (HIV) and could be employed as a model in HIV research we exposed these cell lines to X4 (T-cell tropic) and R5 (macrophage tropic) and subsequently tried to correlate their infectability with (i) level of chemokine coreceptor (CXCR4 and CCR5) expression, (ii) coreceptor functionality (calcium flux, chemotaxis and phosphorylation of MAPK p42/44 and AKT) and (iii) endogenous expression and secretion of HIV-related chemokines which compete with the virus for binding to CXCR4 (SDF-1/CXCL12) or CCR5 (MIP-1beta/CCL4, MIP-1alpha/CCL3, RANTES/CCL5, MCP-2/CCL8, MCP-3/CCL7 and MCP-4/CCL13). We demonstrated that while PB-1 cells are infectable by both X4 and R5 HIV, Sez-4, C91PL, HUT 102B and ATL-2 cells were infected by X4 HIV only. Moreover, we noticed that the susceptibility of these cells to HIV did not correspond either with the level of surface expression or with the functionality of CXCR4 or CCR5; however, it was modulated to some degree by the endogenously secreted HIV-related chemokines. Thus all five mature T-cell lines described here may provide useful new models for studying various aspects of HIV infection. In addition we demonstrate that the infectability of cells by HIV is modulated by so far unidentified intrinsic factors as well as some already known endogenously secreted chemokines. The identification of these factors may be important for developing new strategies to protect cells from HIV infection.

Aggregation-independent modulation of proteoglycan binding by neutralization of C-terminal acidic residues in the chemokine macrophage inflammatory protein 1alpha

Members of the chemokine family of proteins mediate their biological effects through interaction with a family of seven-transmembrane G-protein-coupled receptors. This interaction is complicated by the biochemical properties of chemokines, such as their ability to form self aggregates and their ability to bind to proteoglycans. With some chemokines there is a clear interrelationship between these interactions; the chemokine platelet factor 4 binds preferentially to proteoglycans in its aggregated form. Little is known about the role of aggregation in the proteoglycan binding of other chemokines. Here we demonstrate that the aggregation status of the chemokine macrophage inflammatory protein 1alpha (MIP-1alpha) has no detectable effect on its affinity for proteoglycans. Furthermore, we demonstrate that the alteration of acidic amino acid residues in MIP-1alpha influences the affinity of its interactions with heparin as these residues are progressively neutralized, leading to an enhanced binding affinity for heparin. Thus, with MIP-1alpha, aggregation is not a determinant of proteoglycan binding; however, overall charge does seem to have a major role in the interaction. These results therefore add to our understanding of the nature of the interaction between MIP-1alpha and proteoglycans and suggests that the basic amino acids might not be the sole regulators of proteoglycan binding.

The limited infectability by R5 HIV of CD34(+) cells from thymus, cord, and peripheral blood and bone marrow is explained by their ability to produce beta-chemokines

The resistance of human bone marrow (BM) CD34(+) cells to human immunodeficiency virus (HIV) infection is at this point not fully understood. Recently we reported that the chemokines MIP-1alpha, MIP-1beta, and RANTES secreted by BM-derived CD34(+) cells may compete with the macrophagotropic HIV (R5 HIV) strain for the CCR5 coreceptor.In this study we extended our previous observations and examined various lympho-hematopoietic CD34(+) cells isolated from thymus (Th), cord blood (CB), mobilized peripheral blood (mPB), and BM for the expression of beta-chemokines binding to CCR5, i.e., MIP-1alpha, MIP-1beta, RANTES, MCP-2, MCP-3, and MCP-4, and the alpha chemokine SDF-1 (binding to CXCR4) as these chemokines may compete with the R5 and X4 HIV strains, respectively, for entry into cells. We found that Th-, CB-, mPB-, and BM-derived CD34(+) cells express mRNA transcripts for all the beta-chemokines tested but not for SDF-1. Using sensitive ELISA assays we found that although MIP-1alpha and MIP-1beta proteins were secreted by all the lympho-hematopoietic CD34(+) cells tested, RANTES was detectable only in media conditioned by BM- and CB-derived CD34(+) cells and not Th-derived cells. However, media conditioned by BM-, mPB- and Th-derived CD34(+) cells protected the T lymphocytic cell line (PB-1) from infection by the R5 but not the X4 HIV strain. Hence this study demonstrates that beta-chemokines are secreted by lympho-hematopoietic CD34(+) cells originating from various sources and that these endogenously secreted chemokines may limit entry of the R5 HIV strain into the cells by competing for the CCR5 coreceptor.

Biological significance of the expression of HIV-related chemokine coreceptors (CCR5 and CXCR4) and their ligands by human hematopoietic cell lines

The aim of this study was to learn more about the role of the HIV-related chemokine-chemokine receptor axes in human hematopoiesis. To address this issue we phenotyped 35 selected hematopoietic cell lines for the expression of CD4, CXCR4 and CCR5. We next evaluated the functionality of these chemokine receptors by calcium flux and chemotaxis assays, and by the ability of SDF-1, MIP-1alpha, MIP-1beta and RANTES to influence the growth of the cells expressing CXCR4 and/or CCR5. Lastly, we examined whether human hematopoietic cell lines may secrete some HIV-related chemokines, and whether endogenously secreted chemokines might interfere with the infectability. of hematopoietic cells by X4 and R5 HIV strains. These results demonstrate that: (1) HIV-related receptors are widely expressed on human hematopoietic cell lines; (2) stimulation of CXCR4 by SDF-1 induces calcium flux and chemotaxis in several hematopoietic cell lines more efficiently than stimulation of CCR5 by receptor-specific beta-chemokines; (3) chemokines do not regulate proliferation of the hematopoietic cells; and finally (4) infectability of the hematopoietic cells by HIV-1 may be auto-modulated by endogenously secreted chemokines. These data shed more light on the role of HIV-related chemokine-chemokine receptors axes in human hematopoiesis and interaction of hematopoietic cells with HIV.

The role of HIV-related chemokine receptors and chemokines in human erythropoiesis in vitro

In order to better define the role of HIV-related chemokines in human erythropoiesis we studied: A) the expression of chemokine receptors, both on human CD34(+) cells which include erythroid progenitors and on more mature erythroid cells; B) the functionality of these receptors by calcium flux, chemotaxis assay and phosphorylation of mitogen-activated protein kinases (MAPK) p42/44 (ERK1/ERK2) and AKT, and finally C) the influence of chemokines on BFU-E formation. We found that HIV-related chemokine receptor CXCR4, but not CCR5, is detectable on human CD34(+) BFU-E cells. CXCR4 surface expression decreased during erythroid maturation, although CXCR4 mRNA was still present in cells isolated from differentiated erythroid colonies. SDF-1, a CXCR4 ligand, induced calcium flux and phosphorylation of MAPK (p42/44) and AKT in CD34(+)KIT(+) bone marrow mononuclear cells which contain BFU-E, as well as chemotactic activity of both human CD34(+) BFU-E progenitors and erythroid cells isolated from day 2-6 BFU-E colonies. Responsiveness to SDF-1 decreased when the cells differentiated to the point of surface expression of the erythroid-specific marker Glycophorin-A. In contrast, the CCR5 ligands (macrophage inflammatory protein-1alpha [MIP-1alpha], MIP-1beta, and RANTES) did not activate calcium flux, MAPK and AKT phosphorylation or chemotaxis of CD34(+)KIT(+) cells or cells isolated from the BFU-E colonies. Interestingly, none of the chemokines tested in this study had any effect on BFU-E colony formation. In conclusion, only CXCR4 is functional, and its specific ligand SDF-1 may therefore play an important role in the homing and/or retention of early erythroid precursors in the bone marrow environment.

Stromal cell–derived factor-1 and macrophage-derived chemokine: 2 chemokines that activate platelets

Platelets play roles in both thrombosis and inflammation, and chemokines that are released at sites of inflammation could potentially activate platelets. Among the chemokine receptors expressed on platelets, the CXCR4 is the receptor for chemokine stromal cell-derived factor-1 (SDF-1), and the CCR4 is the receptor for macrophage-derived chemokine (MDC). Of the chemokines tested, SDF-1 and MDC were the only 2 that activated platelets. Both are weak agonists, but they enhanced response to low-dose adenosine 5′-diphosphate (ADP), epinephrine, or serotonin. When SDF-1 and MDC were added together, full and brisk platelet aggregation occurred. Platelet activation by these 2 chemokines appears to involve distinct pathways: SDF-1 inhibited an increase in cyclic adenosine monophosphate (cAMP) following prostaglandin (PG) I2, while MDC had no effect. In contrast, MDC, but not SDF-1, lead to Ca++mobilization by platelets. Further, second-wave aggregation induced by MDC in platelet-rich plasma was inhibited by aspirin, ADP scavenger creatine phosphate/creative phosphokinase (CP/CPK), and ARL-66096, an antagonist of the ADP P2TAC receptor involved in adenylyl cyclase inhibition. But the aggregation was not affected by A3P5PS, an inhibitor of the ADP P2Y receptor. SDF-1–induced aggregation was inhibited by aspirin, but it was only slightly affected by CP/CPK, ARL-66096, or A3P5PS. Finally, the presence of chemokines in platelets was determined. Reverse transcriptase–polymerase chain reaction studies with platelet RNA did not detect the presence of SDF-1 or MDC. In summary, SDF-1 and MDC are platelet agonists that activate distinct intracellular pathways. Their importance in the development of thrombosis at sites of inflammation needs to be further evaluated.

Stromal cell–derived factor-1 and macrophage-derived chemokine: 2 chemokines that activate platelets

Platelets play roles in both thrombosis and inflammation, and chemokines that are released at sites of inflammation could potentially activate platelets. Among the chemokine receptors expressed on platelets, the CXCR4 is the receptor for chemokine stromal cell-derived factor-1 (SDF-1), and the CCR4 is the receptor for macrophage-derived chemokine (MDC). Of the chemokines tested, SDF-1 and MDC were the only 2 that activated platelets. Both are weak agonists, but they enhanced response to low-dose adenosine 5′-diphosphate (ADP), epinephrine, or serotonin. When SDF-1 and MDC were added together, full and brisk platelet aggregation occurred. Platelet activation by these 2 chemokines appears to involve distinct pathways: SDF-1 inhibited an increase in cyclic adenosine monophosphate (cAMP) following prostaglandin (PG) I2, while MDC had no effect. In contrast, MDC, but not SDF-1, lead to Ca++mobilization by platelets. Further, second-wave aggregation induced by MDC in platelet-rich plasma was inhibited by aspirin, ADP scavenger creatine phosphate/creative phosphokinase (CP/CPK), and ARL-66096, an antagonist of the ADP P2TAC receptor involved in adenylyl cyclase inhibition. But the aggregation was not affected by A3P5PS, an inhibitor of the ADP P2Y receptor. SDF-1–induced aggregation was inhibited by aspirin, but it was only slightly affected by CP/CPK, ARL-66096, or A3P5PS. Finally, the presence of chemokines in platelets was determined. Reverse transcriptase–polymerase chain reaction studies with platelet RNA did not detect the presence of SDF-1 or MDC. In summary, SDF-1 and MDC are platelet agonists that activate distinct intracellular pathways. Their importance in the development of thrombosis at sites of inflammation needs to be further evaluated.

Productive infection of CD34+-cell-derived megakaryocytes by X4 and R5 HIV-1 isolates

The human immunodeficiency virus (HIV-1) causes various hematopoietic abnormalities, with thrombocytopenia (TP) occurring in 30% of infected individuals. In the present study, we aimed to determine whether HIV-1 in the bone marrow of TP patients can infect primary megakaryocytes in vitro, which may contribute to the development of thrombocytopenia. We amplified the V3 loop of HIV-1 envelope from the bone marrow of TP and non-TP patients and constructed recombinant viruses. We demonstrate that the bone marrow of TP and non-TP patients contained R5 strains, whereas X4 strains were present only in the bone marrow of TP patients. Furthermore, HIV-1 from the bone marrow of TP and non-TP patients infected megakaryocytes to similar levels, suggesting that the V3 loop of HIV-1 may not contain the viral determinants of HIV-associated TP. Chemokine receptor analysis determined that CD34+-cell-derived megakaryocytes express CD4, CXCR4, and CCR5 and are productively infected by both X4 and R5 HIV-1 isolates. Finally, we showed that CD34+-cell-derived megakaryocytes express the chemokine receptor CCR3.

Bone marrow CD34(+) cells and megakaryoblasts secrete beta-chemokines that block infection of hematopoietic cells by M-tropic R5 HIV

CD34(+) cells are nonpermissive to infection by HIV strains X4 and R5, despite the fact that many CD34(+) cells express high levels of the viral receptor protein CD4 and the coreceptor CXCR4 on their surface. In these cells, the co-receptor CCR5 protein, which, like CXCR4, is a chemokine receptor, is detected mainly intracellularly. We hypothesized that CD34(+) cells secrete CCR5-binding chemokines and that these factors interfere with HIV R5 interactions with these cells, possibly by binding CCR5 or by inducing its internalization. We found that human CD34(+) cells and CD34(+)KIT(+) cells, which are enriched in myeloid progenitor cells, expressed and secreted the CCR5 ligands RANTES, MIP-1alpha, and MIP-1beta and that IFN-gamma stimulated expression of these chemokines. In contrast, SDF-1, a CXCR4 ligand, was not detectable in the CD34(+)KIT(+) cells, even by RT-PCR. Conditioned media from CD34(+) cell culture significantly protected the T lymphocyte cell line PB-1 from infection by R5 but not X4 strains of HIV. Interestingly, the secretion of endogenous chemokines decreased with the maturation of CD34(+) cells, although ex vivo, expanded megakaryoblasts still secreted a significant amount of RANTES. Synthesis of CCR5-binding chemokines by human CD34(+) cells and megakaryoblasts therefore largely determines the susceptibility of these cells to infection by R5 HIV strains. We postulate that therapeutic agents that induce the endogenous synthesis of chemokines in human hematopoietic cells may protect these cells from HIV infection.

Coreceptor/Chemokine Receptor Expression on Human Hematopoietic Cells: Biological Implications for Human Immunodeficiency Virus–Type 1 Infection

The recent discovery of chemokine receptors as coreceptors for human immunodeficiency virus–type 1 (HIV-1) entry offers new avenues for investigating the pathogenesis of acquired immunodeficiency syndrome (AIDS)-related cytopenias. To this end, we sought to (1) phenotype human hematopoietic cells for CD4 and the HIV-1 coreceptors CXCR4, CCR5, CCR3, and CCR2b; (2) correlate CD4 and chemokine receptor expression with their susceptibility to HIV-1 infection; and (3) examine any potential interplay between inflammatory cytokines released during HIV-1 infection and regulation of chemokine receptor expression. Fluorescence-activated cell sorting (FACS) analysis of bone marrow mononuclear cells (BMMNC), cells derived from serum-free expanded hematopoietic lineages (colony-forming unit–granulocyte-macrophage [CFU-GM], colony-forming unit-megakaryocyte [CFU-Meg], and burst-forming unit-erythroid [BFU-E]), and CD34+ cells showed differential expression of chemokine receptors and CD4 with some lineage specificity. Significantly, FACS-sorted CXCR4+/CD34+ cells had the same clonogeneic potential as CXCR4−/CD34+ cells. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis of FACS-sorted human candidate stem cells (HSC; CD34+, c-kit+, Rho123low) showed the presence of CXCR4 mRNA but not CD4 mRNA. Infection studies with HIV-1 Env-pseudotyped luciferase reporter viruses indicated that X4 Env (CXCR4-using) pseudotypes infected megakaryocytic cells, whereas R5 Env (CCR5-using) pseudotypes did not. Similarly, R5 but not X4 Env-pseudotyped viruses infected granulocyte-macrophage cells in a CD4/CCR5-dependent manner. Erythroid cells were resistant to R5 or X4 viral infection. Finally, we found that γ-interferon treatment upregulated CXCR4 expression on primary hematopoietic cells. In summary, the delineation of chemokine receptor expression on primary hematopoietic cells is a first step towards dissecting the chemokine-chemokine receptor axes that may play a role in hematopoietic cell proliferation and homing. Furthermore, susceptibility of hematopoietic cells to HIV-1 infection is likely to be more complicated than the mere physical presence of CD4 and the cognate chemokine receptor. Lastly, our results suggest a potential interplay between γ-interferon secretion and CXCR4 expression.

Coreceptor/Chemokine Receptor Expression on Human Hematopoietic Cells: Biological Implications for Human Immunodeficiency Virus–Type 1 Infection

The recent discovery of chemokine receptors as coreceptors for human immunodeficiency virus–type 1 (HIV-1) entry offers new avenues for investigating the pathogenesis of acquired immunodeficiency syndrome (AIDS)-related cytopenias. To this end, we sought to (1) phenotype human hematopoietic cells for CD4 and the HIV-1 coreceptors CXCR4, CCR5, CCR3, and CCR2b; (2) correlate CD4 and chemokine receptor expression with their susceptibility to HIV-1 infection; and (3) examine any potential interplay between inflammatory cytokines released during HIV-1 infection and regulation of chemokine receptor expression. Fluorescence-activated cell sorting (FACS) analysis of bone marrow mononuclear cells (BMMNC), cells derived from serum-free expanded hematopoietic lineages (colony-forming unit–granulocyte-macrophage [CFU-GM], colony-forming unit-megakaryocyte [CFU-Meg], and burst-forming unit-erythroid [BFU-E]), and CD34+ cells showed differential expression of chemokine receptors and CD4 with some lineage specificity. Significantly, FACS-sorted CXCR4+/CD34+ cells had the same clonogeneic potential as CXCR4−/CD34+ cells. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis of FACS-sorted human candidate stem cells (HSC; CD34+, c-kit+, Rho123low) showed the presence of CXCR4 mRNA but not CD4 mRNA. Infection studies with HIV-1 Env-pseudotyped luciferase reporter viruses indicated that X4 Env (CXCR4-using) pseudotypes infected megakaryocytic cells, whereas R5 Env (CCR5-using) pseudotypes did not. Similarly, R5 but not X4 Env-pseudotyped viruses infected granulocyte-macrophage cells in a CD4/CCR5-dependent manner. Erythroid cells were resistant to R5 or X4 viral infection. Finally, we found that γ-interferon treatment upregulated CXCR4 expression on primary hematopoietic cells. In summary, the delineation of chemokine receptor expression on primary hematopoietic cells is a first step towards dissecting the chemokine-chemokine receptor axes that may play a role in hematopoietic cell proliferation and homing. Furthermore, susceptibility of hematopoietic cells to HIV-1 infection is likely to be more complicated than the mere physical presence of CD4 and the cognate chemokine receptor. Lastly, our results suggest a potential interplay between γ-interferon secretion and CXCR4 expression.