The human immunodeficiency virus: infectivity and mechanisms of pathogenesis

Predictors of atopy in HIV-infected patients

BACKGROUND

Some studies have reported an increase of atopy in HIV-infected (HIV+) patients, but the cause still remains unclear.

OBJECTIVE

To determine the prevalence of atopy in HIV+ patients and to investigate its predictors.

METHODS

Seventy-four HIV+ hospitalized patients (46 of them with AIDS) were studied prospectively for the presence of atopy, based on immediate hypersensitivity to common allergens by prick test. Serum immunoglobulins, specific IgE, lymphocyte subsets, and the expression of low affinity IgE receptor (CD23) on B cells were determined.

RESULTS

Thirty-one percent of patients presented IgE values greater than 150 ku/L (39% of patients without AIDS and 26% of AIDS patients; P = .23) and 47% showed an increase (> or = 2%) in the percentage of CD23+ B cells. Non-AIDS patients had higher IgE values than AIDS patients (346 +/- 605 versus 175 +/- 276; P = .16). Atopy prevalence was higher in non-AIDS than in AIDS patients (28% versus 11%; P = .06). Specific IgE agreed with positive prick test in 58% of cases. Multivariate analysis showed that a personal history suggestive of allergic disease and IgE > 150 ku/L were predictors of atopy, while gender, risk group, CD4+ T cells, CD23 expression on B cells, and AIDS were not associated.

CONCLUSIONS

HIV+ patients present a higher prevalence of atopy in early stages of HIV infection than general population. Since allergic reactions could accelerate HIV-infection by increasing type 2 cytokines, it is important to evaluate the atopic state in HIV+ patients with IgE > 150 ku/L or with suggestive allergic history in order to prevent it.

Targeting activated lymphocytes with an entirely human immunotoxin analogue: human pancreatic RNase1-human IL-2 fusion

A hybrid human protein was produced in E. coli by fusing the genes encoding human pancreatic RNase1 (hpRNase1) and human IL-2 (hIL-2). The recombinant hpRNase1-hIL-2 inhibited protein synthesis in HTLV-1-infected, malignant T cells, which hyperproduce high affinity IL-2 receptors, with an IC(50)of 2x10(-8) M, whereas no inhibition was detectable in control cells with lower affinity receptors. HpRNase1 alone had an IC(50)of almost 10(-3) M. A molar excess of hIL-2 blocked the protein synthesis inhibition dose-dependently. In a human mixed lymphocyte culture, hpRNase1-hIL-2 inhibited the proliferation of responder cells with potency comparable to that of cyclosporine, while non-effective doses of FK506 importantly improved its potency. Despite its short half-life in animals, hpRNase1-hIL-2 rapidly enters cells in a few minutes and arrests the protein translation in less than 10 h. Thus, hpRNase1-hIL-2 may be useful to selectively eliminate activated lymphocytes hyperproducing high affinity IL-2 receptors, as in allograft rejection, graft-versus-host disease, autoimmune disorders, adult T cell leukaemia and other lymphoproliferative or retroviral malignancies including HIV infection, without inducing general immunosuppression. As an entirely human "immunotoxin analogue" it may alleviate the dose limiting toxicity and immunogenicity of conventional immunotoxins.

Identifying HIV/AIDS research priorities for the next millennium: a Delphi study with nurses in AIDS care

The purpose of this study was to identify HIV/AIDS research priorities for the next millennium from the perspective of nurses in AIDS care. The study used a three-round Delphi technique, with study participants (the panel of experts) selected from the membership of the Association of Nurses in AIDS Care. In the first round of the Delphi study, 317 nurses identified more than 2,000 topics they viewed as important for overall HIV/AIDS research and for HIV/AIDS nursing research. Using qualitative analysis, 12 priority topics were generated in the overall research category and 12 priority topics in the nursing research category. In Round II of the Delphi survey, study participants ranked the 12 topics in categories (overall and nursing research priorities) identified in Round I. Finally, in Round III, the top five priority topics from Round II were prioritized in each category. The overall HIV/AIDS research topics identified were (a) HIV community-level education and prevention; (b) development of more tolerable drugs; (c) HIV prevention focusing on individual or specific group behavior; (d) vaccine development; and (e) development of new and more effective drugs. The HIV/AIDS nursing research priorities identified were (a) symptom management; (b) community-level HIV education and prevention; (c) quality of life issues in chronic HIV disease; (d) HIV prevention focusing on individual or specific group behavior; and (e) research related to adherence to drug therapy.

Envelope glycoprotein determinants of increased fusogenicity in a pathogenic simian-human immunodeficiency virus (SHIV-KB9) passaged in vivo

Changes in the envelope glycoprotein ectodomains of a nonpathogenic simian-human immunodeficiency virus (SHIV-89.6) that was serially passaged in vivo have been shown to be responsible for the increased pathogenicity of the resulting virus, SHIV-KB9 (G. B. Karlsson, et al., J. Exp. Med. 188:1159-1171, 1998). The 12 amino acid changes in the envelope glycoprotein ectodomains resulted in increased chemokine receptor-binding and syncytium-forming abilities. Here we identify the envelope glycoprotein determinants of these properties. A single amino acid change in the gp120 third variable (V3) loop was both necessary and sufficient for the observed increase in the binding of the SHIV-KB9 gp120 glycoprotein to the CCR5 chemokine receptor. The increased syncytium-forming ability of SHIV-KB9 involved, in addition to the V3 loop change, changes in the second conserved (C2) region of gp120 (residue 225) and in the gp41 ectodomain (residues 564 and 567). The C2 and gp41 ectodomain changes influenced syncytium formation in a cooperative manner. Changes in the V1/V2 gp120 variable loops exerted a negative effect on syncytium formation and chemokine receptor binding, supporting a previously described role of these changes in immune evasion. The definition of the passage-associated changes that determine the efficiency of chemokine receptor binding and membrane fusogenicity will allow evaluation of the contribution of these properties to in vivo CD4-positive lymphocyte depletion.

Pathogenesis of HIV-1 infection within bone marrow cells

Mononuclear phagocytic cells and CD4+ T lymphocytes represent the major targets for infection by HIV-1 in vivo. The most severe pathogenic features associated with HIV-1 infection can be attributed to malfunction or premature death of these cells that are of hematopoietic origin. Patients with acquired immunodeficiency syndrome (AIDS), suffer from many hematologic disorders, particularly those persons with long-term infection of HIV-1. These disorders include anemia, lymphocytopenia, thrombocytopenia and neutropenia. The mechanisms that lead to the induction of these disorders are multi-factorial. However, sufficient evidence has accumulated which suggests that HIV-1 infection of cells within the microenvironment of the bone marrow can lead to the induction of hematopoietic deficits. Most studies indicate that marrow-derived hematopoietic stem cells cannot be infected by HIV-1 until they undergo modest differentiation in order to express the appropriate receptors to enable virus entry and subsequent replication. Some cells within the mixed environment of the marrow stroma appear to support HIV-1 replication however. These cells include marrow microvascular endothelial cells, sometimes referred to as blanket cells, stromal fibroblasts, as well as mononuclear phagocytes. Our recent experiments suggest that the HIV-1 accessory protein, Vpr, plays some role in the activation of marrow-derived mononuclear phagocytes which appears to result in premature phagocytosis of non-adherent marrow cells present in the in vitro cultures. This phenomenon could account, in part, for the induction of cytopenias that are typical of individuals infected by HIV-1.

Upgrading of flow cytometric analysis for absolute counts, cytokines and other antigenic molecules of cynomolgus monkeys (Macaca fascicularis) by using anti-human cross-reactive antibodies

In order to effectively use cynomolgus monkeys as animal models for human diseases, more than 300 anti-human monoclonal antibodies (mAbs) were studied as to their cross-reaction with various antigens from cynomolgus monkeys (Macaca fascicularis). Two hundred twenty-nine of 339 (67.55%) anti-human mAbs that react with human antigens of CD-defined molecules, chemokine receptors, and T cell receptors were cross-reactive with the monkey antigens. Using the cross-reactive antibodies and the fluorescenced beads for calibration, the procedure for the absolute count of monkey lymphocyte subsets was developed and the mean values for CD4+ and CD8+ lymphocyte subsets in peripheral blood were 718 and 573/mm3, respectively. Moreover, intracellular cytokines, IL-2, IL-4 and IFN gamma, and intracellular apoptosis-related proteins, Bcl-2, FADD and active form of caspase-3 could be detected in peripheral blood mononuclear cells as well as various tissue cells. It is therefore practicable to detail the phenotype of leukocytes, assess the production of intracellular cytokines and enumerate T-lymphocyte subsets by using the cross-reactive human antibodies with respective antigens of cynomolgus monkeys.

How does HIV cause AIDS? The homing theory

The mechanism by which HIV causes depletion of CD4+ T cells in infected individuals remains unknown. Numerous theories have been proposed, but none can fully explain all of the events observed to occur in patients. Recent studies have shown that HIV binding to resting CD4+ T cells upregulates L-selectin, causing the cells to home from the blood into lymph nodes at an enhanced rate. It is possible that the disappearance of CD4+ T cells in the blood is actually the result of them leaving the blood, which can help explain the loss of CD4+ T cells in the blood occurring at a much faster rate than in lymphoid tissues. Furthermore, secondary signals through homing receptors received during the homing process induce many of these cells into apoptosis. These cells die in the lymph nodes without producing HIV particles, which can explain the 'bystander effect' observed in the lymph nodes of HIV infected individuals. If this scenario occurs in HIV+ patients, it might explain many of the clinical observations.

Interleukin 18 and interleukin 1beta production is decreased in HIV type 1-seropositive hemophiliacs but not in HIV type 1-seropositive nonhemophiliacs

In Japan, the proportion of hemophiliacs infected with human immunodeficiency virus type 1 (HIV-1) is 40%, whereas more than 90% are infected with hepatitis C virus (HCV). To evaluate the immunological status of hemophiliacs infected with HIV-1, we investigated the pattern of cytokine production in peripheral blood mononuclear cells (PBMCs) of HIV-1-seropositive and -seronegative hemophiliacs, HIV-1-seropositive non-hemophiliacs, and healthy individuals. The production of IL-18 and IL-1beta from PBMCs stimulated with Staphylococcus aureus Cowan strain 1 (SAC) in the HIV-1-seropositive hemophiliacs was significantly decreased in comparison with the other groups. On the other hand, IL-12 production in both HIV-1-seropositive groups was significantly lower than in HIV-1-seronegative groups. TNF-alpha and IL-6 production was similar among the four groups. In contrast, plasma levels of TGF-beta1 were increased in HIV-1-seropositive hemophiliacs, HIV-1-seropositive nonhemophiliacs, and HIV-1-seronegative hemophiliacs, with the highest levels being in HIV-1-seropositive hemophiliacs, suggesting that coinfection with HIV-1 and HCV increases the level of plasma TGF-beta in HIV-1-seropositive hemophiliacs. Treatment of PBMCs from healthy individuals with TGF-beta1 inhibited IL-18 and IL-1beta production without affecting IL-6, IL-10, or TNF-alpha production. Suppression of the expression of caspase 1 mRNA, which is known to be an IL-1beta-converting enzyme and which also cleaves the precursor of IL-18, was observed in the SAC-stimulated PBMCs from healthy individuals after treatment with TGF-beta1 and in the SAC-stimulated PBMCs from HIV-1-seropositive hemophiliacs, suggesting that the decreased production of IL-18 and IL-1beta in HIV-1-seropositive hemophiliacs may be related to the downregulation of caspase 1 mRNA induced by high levels of TGF-beta1 in plasma.

Transduction of human PBMC-derived dendritic cells and macrophages by an HIV-1-based lentiviral vector system

Professional antigen-presenting cells, such as dendritic cells (DCs) and macrophages, are target cells for gene therapy of infectious disease and cancer. However, transduction of DCs and macrophages has proved difficult by most currently available gene transfer methods. Several recent studies have shown that lentiviral vector systems can efficiently transduce many nondividing and differentiated cell types. In this study, we examined the gene transfer to DCs and macrophages using a lentiviral vector system. Human DCs were propagated from the adherent fraction of peripheral blood mononuclear cells (PBMCs) by culture in medium containing GM-CSF, IL-4, and TNF-alpha. Human macrophages were propagated from adherent PBMCs in medium containing GM-CSF. High titers of a replication-defective vesicular stomatitis virus glycoprotein G pseudotyped HIV-1-based vector encoding the enhanced yellow fluorescent protein were produced. In immature DCs (culture days 3 and 5), transduction efficiencies of 25 to 35% were achieved at a multiplicity of infection of 100. However, the transduction efficiency was decreased in more mature DCs (culture day 8 or later). Furthermore, monocyte-derived macrophages were also transduced by the lentiviral vector system. In addition, Alu-LTR PCR demonstrated the integration of the HIV-1 provirus into the cellular genome of the transduced DCs and macrophages. Allogeneic mixed lymphocyte reactions revealed similar antigen-presenting functions of untransduced and lentivirally transduced DCs. Thus, the results of this study demonstrate that both PBMC-derived DCs and macrophages can be transduced by lentiviral vectors.

Antibodies to CD4 in primary Sjögren's syndrome

OBJECTIVE

The purpose of this study was to examine whether antibodies against CD4 are present in patients with primary Sjögren's syndrome, and to explore the possible correlation between these antibodies and the CD4+ T lymphocyte depletion that is seen in some Sjögren patients.

METHODS

Sera from 214 patients with primary Sjögren's syndrome, 154 healthy blood donors, 38 age- and sex-matched controls without autoimmune disease, and 77 HIV-1-seropositive individuals were analysed by an enzyme-linked immunosorbent assay (ELISA) using recombinant soluble CD4 as the antigen.

RESULTS

Anti-CD4 antibodies were observed more frequently in patients with Sjögren's syndrome (12.6%) as compared with the control groups (0.6%) (P < 0.001), and at a level similar to that seen among the HIV-1 patients (13.0%). However, no correlation was found between the presence of anti-CD4 antibodies and CD4+ T lymphocytopenia in the Sjögren patients.

CONCLUSION

This is the first study that shows anti-CD4 antibodies in patients with primary Sjögren's syndrome. The significance of these antibodies in the immunopathogenesis of Sjögren's syndrome remains to be determined.

The nuclear receptor chicken ovalbumin upstream promoter transcription factor interacts with HIV-1 Tat and stimulates viral replication in human microglial cells

Human immunodeficiency virus type 1 (HIV-1) infects the central nervous system and plays a direct role in the pathogenesis of AIDS dementia. However, the molecular mechanisms underlying HIV-1 expression in the central nervous system are poorly understood. We have recently reported that the nuclear receptor chicken ovalbumin upstream promoter transcription factor (COUP-TF), an orphan member of the nuclear receptor superfamily, is an activator of HIV-1 gene transcription. Here, our results show that COUP-TF stimulates HIV-1 transcription in primary cultured human microglial cells, the primary target for HIV-1 infection in brain. Run-on assays indicated that COUP-TF acts on the initiation step of transcription. Results from reverse transcription-polymerase chain reaction and immunocytochemistry analysis further revealed the importance of this factor by demonstrating that overexpression of COUP-TF leads to initiation of viral replication in primary HIV-infected human microglia. In addition, COUP-TF is able to physically interact and cooperate with the viral transactivator Tat. The combination of COUP-TF and Tat leads to NF-kappaB- and Sp1-independent enhanced transcriptional stimulation. In vitro binding studies showed that COUP-TF interacts with Tat through amino acids within the N-terminal DNA-binding domain of COUP-TF. Amino acids 48-72 in the basic and C-terminal regions of Tat are required for the binding of Tat to COUP-TF. These results suggest that COUP-TF is an essential transcription factor involved in HIV-1 expression in microglia and reveal a novel interplay of Tat and COUP-TF during regulation of viral expression.

Attenuation of human immunodeficiency virus type 1 cytopathic effects by replacing a 424-bp region of envelope from a noncytopathic biological clone

We analyzed the env genes of cytopathic and noncytopathic biological clones derived from two HIV-1-infected children with discordant clinical courses. Chimeric viruses were constructed by switching env regions from V2 through V3 of the biological clones with the corresponding region from the molecular clone NL4-3. These HIV-1 chimeric viruses exhibited similar replication kinetics as well as syncytium-inducing abilities. The chimeric virus containing the env region of noncytopathic biological clone, GC6 8-4, was noncytopathic in an in vitro cell-killing assay, while the chimeric virus containing the env region of cytopathic biological clone, HC4, was cytopathic in the in vitro cell-killing assay. These studies suggest the presence of a cytopathicity determinant that maps to the envelope sequences contained within the downstream region of V2 and within the V3 region (nucleotide position 6822 to nucleotide position 7250, based on NL4-3 sequence).

Functional interactions between C/EBP, Sp1, and COUP-TF regulate human immunodeficiency virus type 1 gene transcription in human brain cells

Human immunodeficiency virus type 1 (HIV-1) infects the central nervous system (CNS) and plays a direct role in the pathogenesis of AIDS dementia. However, mechanisms underlying HIV-1 gene expression in the CNS are poorly understood. The importance of CCAAT/enhancer binding proteins (C/EBP) for HIV-1 expression in cells of the immune system has been recently reported. In this study, we have examined the role and the molecular mechanisms by which proteins of the C/EBP family regulate HIV-1 gene transcription in human brain cells. We found that NF-IL6 acts as a potent activator of the long terminal repeat (LTR)-driven transcription in microglial and oligodendroglioma cells. In contrast, C/EBPgamma inhibits NF-IL6-induced activation. Consistent with previous data, our transient expression results show cell-type-specific NF-IL6-mediated transactivation. In glial cells, full activation needs the presence of the C/EBP binding sites; however, NF-IL6 is still able to function via the minimal -40/+80 region. In microglial cells, C/EBP sites are not essential, since NF-IL6 acts through the -68/+80 LTR region, containing two binding sites for the transcription factor Sp1. Moreover, we show that functional interactions between NF-IL6 and Sp1 lead to synergistic transcriptional activation of the LTR in oligodendroglioma and to mutual repression in microglial cells. We further demonstrate that NF-IL6 physically interacts with the nuclear receptor chicken ovalbumin upstream promoter transcription factor (COUP-TF), via its DNA binding domain, in vitro and in cells, which results in mutual transcriptional repression. These findings reveal how the interplay of NF-IL6 and C/EBPgamma, together with Sp1 and COUP-TF, regulates HIV-1 gene transcription in brain cells.

HIV-1 infects and alters immune function of a monocyte subset expressing low CD14 surface phenotype

Monocytes represent a leukocyte subset that express high levels of CD14 on their surface (CD14-high). These cells play a critical role in the pathogenesis of HIV-1 infection. In the present study, we have identified a monocyte subset expressing an extremely low level of CD14 (CD14-low), and examined their susceptibility to HIV-1 infection. Phenotypic analysis by flow cytometry of these cells revealed a low level of CD4, but the absence of CD3, CD14, CD19, and CD83 surface markers. Both CD14-low and CD14-high cell populations expressed CD13 and CD33 markers on their surface, suggesting these cells to be of myeloid origin. Morphologically, CD14-low cells were indistinguishable from CD14-high cells. CD14-low cells were susceptible to infection with a monocytotropic strain of HIV-1 (HIVADA). However, like CD14-high monocytes, CD14-low cells could not be productively infected with a T cell tropic strain of HIV-1 (H9/HTLV(IIIB)). Similar to CD14-high monocytes, CD14-low cells were capable of inducing antigen-stimulated CD4+ T-cell proliferation. HIV-1 infection substantially reduced their ability to induce antigen-stimulated T-cell proliferation. These data indicate that CD14-low cells belong to the monocyte lineage and may play an important role in the immunopathogenesis of HIV-1 infection.

The use of Filgrastim in AIDS-related neutropenia

Neutropenic individuals are at high risk for bacterial and fungal infections. Filgrastim (r-metHuG-CSF, NEUPOGEN) has been shown to improve chemotherapy-induced neutropenia significantly. Because a high incidence of HIV-infected patients have neutropenia, often associated with myelosuppressive antiretroviral medication, Filgrastim is frequently used as a treatment strategy for this HIV-associated neutropenia. This review summarizes published work related to the use of Filgrastim in HIV-infected patients. Literature bases (EMBASE, MEDLINE, Int. Pharm. Abs., SciSearch, and Aidsline) from 1970 to 1998 were searched for articles describing the relationship of Filgrastim and ANC to bacterial infection rates, bacterial infection outcome, and overall survival. Thirty-five related articles were identified during this search. Filgrastim appears to have a significant role in increasing peripheral ANC and enhancing neutrophil function in patients with HIV infection and AIDS. This may translate into a clinical benefit of delivery of full-dose myelosuppressive antiretroviral therapy and decreased susceptibility to infections and increased survival in this patient population.

Differential patterns of interaction between HIV type 1 and HTLV type I in monocyte-derived macrophages cultured in vitro: implications for in vivo coinfection with HIV type 1 and HTLV type I

The interaction between human immunodeficiency virus type 1 (HIV-1) and human T cell leukemia-lymphoma virus type I (HTLV-I) has generated substantial interest. However, there is disagreement on the in vivo consequences of the double infection. We investigated the interactions between HIV-1 and HTLV-I in monocyte-derived macrophages cultured in vitro. For study, the T cell-tropic strain IIIB and the macrophagetropic strain Ada-M of HIV-1 were used. The HTLV-I was prepared from the supernatants of the virus-producing MT-2 cell line. We found that coinfection of macrophages with T cell-tropic HIV-1 and HTLV-I significantly enhanced HIV-1 replication, whereas double infection of the cells with macrophage-tropic HIV-1 and HTLV-I resulted in marked upregulation of HTLV-I production. Stimulatory interactions between HIV-1 and HTLV-I were mediated by their trans-acting proteins. Results of study on nuclear translocation of proviral DNA showed that the tax gene product of HTLV-I was able to facilitate the nuclear import of the reverse-transcribed HIV-1(IIIB) DNA. In contrast, the HIV-1 Tat protein did not increase the intranuclear trafficking of HTLV-I DNA, which suggests another mechanism for HTLV-I enhancement by the tat gene product. In conclusion, this study provides possible mechanisms whereby coinfection of an individual with HIV-1 and HTLV-I may influence the clinical outcome of double infection.

Species-specific, postentry barriers to primate immunodeficiency virus infection

By using replication-defective vectors derived from human immunodeficiency virus type 1 (HIV-1), simian immunodeficiency virus (SIV(mac)), and murine leukemia virus (MuLV), all of which were pseudotyped with the vesicular stomatitis virus (VSV) G glycoprotein, the efficiency of postentry, early infection events was examined in target cells of several mammalian species. Titers of HIV-1 vectors were significantly lower than those of SIV(mac) and MuLV vectors in most cell lines and primary cells from Old World monkeys. By contrast, most New World monkey cells exhibited much lower titers for the SIV(mac) vector compared with those of the HIV-1 vector. Prosimian cells were resistant to both HIV-1 and SIV(mac) vectors, although the MuLV vector was able to infect these cells. Cells from other mammalian species were roughly equivalent in susceptibility to the three vectors, with the exception of rabbit cells, which were specifically resistant to the HIV-1 vector. The level of HIV-1 vector expression was very low in transduced cells of rodent, rabbit, cow, and pig origin. Early postentry restriction of primate immunodeficiency virus infection exhibits patterns largely coincident with species borders and applies to diverse cell types within an individual host, suggesting the involvement of species-specific, widely expressed cellular factors.

Tackling Tat

Activation of cellular genes typically involves control of transcription initiation by DNA-binding regulatory proteins. The human immunodeficiency virus transactivator protein, Tat, provides the first example of the regulation of viral gene expression through control of elongation by RNA polymerase II. In the absence of Tat, initiation from the long terminal repeat is efficient, but transcription is impaired because the promoter engages poorly processive polymerases that disengage from the DNA template prematurely. Activation of transcriptional elongation occurs following the recruitment of Tat to the transcription machinery via a specific interaction with an RNA regulatory element called TAR, a 59-residue RNA leader sequence that folds into a specific stem-loop structure. After binding to TAR RNA, Tat stimulates a specific protein kinase called TAK (Tat-associated kinase). This results in hyperphosphorylation of the large subunit of the RNA polymerase II carboxyl- terminal domain. The kinase subunit of TAK, CDK9, is analogous to a component of a positive acting elongation factor isolated from Drosophila called pTEFb. Direct evidence for the role of TAK in transcriptional regulation of the HIV long terminal repeat comes from experiments using inactive mutants of the CDK9 kinase expressed in trans to inhibit transcription. A critical role for TAK in HIV transcription is also demonstrated by selective inhibition of Tat activity by low molecular mass kinase inhibitors. A second link between TAK and transactivation is the observation that the cyclin component of TAK, cyclin T1, also participates in TAR RNA recognition. It has been known for several years that mutations in the apical loop region of TAR RNA abolish Tat activity, yet this region of TAR is not required for binding by recombinant Tat protein in vitro, suggesting that the loop region acts as a binding site for essential cellular co-factors. Tat is able to form a ternary complex with TAR RNA and cyclin T1 only when a functional loop sequence is present on TAR.

The potential importance of HIV-induction of lymphocyte homing to lymph nodes

The mechanism by which HIV causes depletion of CD4 lymphocytes remains unknown. Recent studies have demonstrated that HIV binding to resting CD4 lymphocytes causes them to home from the blood into lymph node, and during the homing process, they are induced into apoptosis only to secondary signals through the homing receptors. If this is the principal mechanism of CD4 cell depletion, it can explain many of the events known to occur in HIV-infected individual.

Production and characterization of monoclonal antibodies against pigtailed macaque (Macaca nemestrina) cell adhesion molecules

Our previous in vitro studies indicate a significant role for cell adhesion molecules in the biology of HIV-1 and HTLV-1. Confirmation of the involvement of these molecules in the pathogenesis of retrovirus infection in vivo will require a suitable animal model. The SIV/pigtailed macaque (Macaca nemestrina) model of acquired immunodeficiency syndrome (AIDS) is an ideal system in which to study adhesion molecules and viral pathogenesis. The monoclonal antibodies (MAbs) against human adhesion molecules previously produced in our laboratory either do not react with or fail to block function of pigtailed macaque adhesion molecules. We have used papiovirus-transformed pigtailed macaque B cells as immunogen to generate murine MAbs against macaque adhesion molecules including ICAM-1, VCAM-1, and LFA-1. The specificity of the MAbs was confirmed by immunoprecipitation from lysates of vectorially iodinated cells, flow cytometry analysis of transfected cell lines and primary cells, binding assays on recombinant soluble human VCAM-1 and ICAM-1, and by inhibition of adhesion functions. MAbs against ICAM-1 and VCAM-1 showed positive staining of fixed tissue in immunohistochemistry studies. The same antibodies also blocked the function of these two adhesion molecules. The new MAbs can be used to study the tissue expression of adhesion molecules in SIV-infected animals as well as to test the involvement of these molecules in virus infection. Thus they should prove invaluable as probes of the role of cell adhesion molecules in AIDS pathogenesis in an animal model.

The presence of human immunodeficiency virus type 1 Vpr correlates with a decrease in the frequency of mutations in a plasmid shuttle vector

The human immunodeficiency virus type 1 (HIV-1) Vpr protein induces cell cycle arrest at the border of G(2) and M similar to the arrest caused by agents which damage DNA. We determined whether the presence of Vpr would affect the ability of cells to repair DNA. We developed a shuttle vector system to analyze the effect of Vpr upon the repair of UV-damaged DNA. Our results demonstrated that the presence of Vpr decreased the rate of deletions in this system. Of note, cells arrested in G(2) by other genotoxic agents also increased the frequency of DNA repair of UV-damaged shuttle vectors. We did not observe any direct effect of Vpr upon the rate of double-strand break repair and/or nucleotide excision repair of genomic DNA in cells. Our results suggest a role for HIV-1 Vpr in altering the frequency of DNA repair, a property which may have importance for HIV-1 replication and pathogenesis.

Impaired thymopoietic potential of immature CD3(-)CD4(+)CD8(-) T cell precursors from SIV-infected rhesus monkeys

Immature thymocyte subpopulations were examined for their capacity to differentiate in a newly developed xenogeneic monkey-mouse fetal thymus organ culture (FTOC) system. We provide evidence for impaired precursor function of CD3(-)CD4(+)CD8(-) thymocytes after in vivo infection with SIVmac251 as indicated by a reduced cell number per FTOC and a lower percentage of thymocytes with more mature phenotypes. Addition of recombinant SIV glycoprotein 120 (rgp120) also resulted in a dose-dependent impairment of T cell maturation in FTOC. The data suggest that in patients infected with HIV, T cell maturation and thus replenishment of peripheral pools may be compromised as a result of intrathymic infection or circulating viral gp120.

Induction of Phosphorylation and Intracellular Association of CC Chemokine Receptor 5 and Focal Adhesion Kinase in Primary Human CD4+ T Cells by Macrophage-Tropic HIV Envelope

Binding of HIV-1 envelope glycoproteins to the surface of a CD4+ cell transduces intracellular signals through the primary envelope receptor, CD4, and/or the envelope coreceptor, a seven-transmembrane chemokine receptor. Macrophage-tropic strains of HIV-1 preferentially use CCR5 as an entry coreceptor, whereas T cell-tropic strains use CXC chemokine receptor-4 for entry. Intracellular signals transduced by HIV-1 envelope may have immunopathogenic consequences, including anergy, syncytium formation, apoptosis, and inappropriate cell trafficking. We demonstrate here that a recombinant envelope protein derived from an M-tropic isolate of HIV-1 can transduce CD4-dependent as well as CCR5-dependent intracellular signals in primary human CD4+ T cells. Novel HIV-induced intracellular signals that were identified include tyrosine phosphorylation of focal adhesion kinase (FAK) and CCR5, which are involved in cell adhesion and chemotaxis, respectively. HIV envelope-induced cellular association of FAK and CCR5 was also demonstrated, suggesting that ligation of CD4 and CCR5 leads to the formation of an activation complex composed of FAK and CCR5. Activation of this signaling pathway by HIV-1 envelope may be an important pathogenic mechanism of dysregulated cellular activation and trafficking during HIV infection.

Pregnancy, HLA allogeneic challenge, and implications for AIDS etiology

Because of the large HLA genetic polymorphism, a human fetus usually has several paternal HLA antigens allogeneic to its mother. The maternal gamma-immunoglobulin (IgG) antibody response to fetal HLA alloantigens is noncytotoxic and associated with local suppression of maternal cell-mediated immunity (CMI) at the maternal-fetal interface. When mother and fetus are syngeneic for most HLA antigens, an increased risk exists for a maternal anti-placental cytotoxic CMI responses, compromising fetal survival. Local suppression of maternal CMI by an anti-HLA IgG response may have evolved to protect the fetoplacental unit from a maternal CMI cytotoxic reaction against expressed developmental neoantigens. A negative aspect of this adaptive response is that infectious organisms bearing HLA-homologous alloantigens (e.g. human immunodeficiency virus type 1, HIV-1) may generate a systemic IgG response suppressing CMI. Findings are reviewed suggesting this is an etiologic factor in the acquired immune deficiency syndrome (AIDS).

Redox and activation status of monocytes from human immunodeficiency virus-infected patients: relationship with viral load

Monocytes are precursors of tissue macrophages, which are major targets of human immunodeficiency virus type 1 (HIV-1) infection. Although few blood monocytes are infected, their resulting activation could play a key role in the pathogenesis of HIV disease by modulating their transendothelial migration and inducing the production of reactive oxygen species (ROS). ROS participate in chronic inflammation, HIV replication, and the apoptosis of immune system cells seen in HIV-infected subjects. Published data on monocyte activation are controversial, possibly because most studies have involved monocytes isolated from their blood environment by various procedures that may alter cell responses. We therefore used flow cytometry to study, in whole blood, the activation and redox status of monocytes from HIV-infected patients at different stages of the disease. We studied the expression of adhesion molecules, actin polymerization, and cellular levels of H2O2, Bcl-2, and thioredoxin. Basal H2O2 production correlated with viral load and was further enhanced by bacterial N-formyl peptides and endotoxin. The enhanced H2O2 production by monocytes from asymptomatic untreated patients with CD4(+) cell counts above 500/microliter was associated with a decrease in the levels of Bcl-2 and thioredoxin. In contrast, in patients with AIDS, Bcl-2 levels returned to normal and thioredoxin levels were higher than in healthy controls. Restoration of these antioxidant and antiapoptotic molecules might explain, at least in part, why monocyte numbers remain relatively stable throughout the disease. Alterations of adhesion molecule expression and increased actin polymerization could play a role in transendothelial migration of these activated monocytes.

Neutralizing antibody responses in Africa green monkeys naturally infected with simian immunodeficiency virus (SIVagm)

This study assessed the magnitude and cross-reactivity of the neutralizing antibody response generated by natural SIV infection in wild-caught African green monkeys. Neutralizing antibodies of variable potency, sometimes exceeding a titer of 1:1,000, were detected in 20 of 20 SIV-seropositive African green monkeys in Kenya. Detection of those neutralizing antibodies was dependent on the strain of virus and the cells used for assay, where the most sensitive detection was made with SIVagm1532 in Sup T1 cells. Potent neutralization of SIVagm1532 was seen with contemporaneous autologous serum. Potent neutralization was also detected with laboratory-passaged SIVmac251 and SIVsmB670, but not with SIVsmE660 and two additional strains of SIVagm. Serum samples from rhesus macaques (Macaca mulatta) experimentally infected with either SIVmac251 or SIVsmE660 were capable of low-level neutralization of SIVagm. These results indicate that natural infection with SIV can generate strain-specific neutralizing antibodies in African green monkeys. They also indicate that some neutralization determinants of SIVagm are partially shared with SIV strains that arose in sooty mangabys and were subsequently transmitted to rhesus macaques.

Infectious human immunodeficiency virus can rapidly penetrate a tight human epithelial barrier by transcytosis in a process impaired by mucosal immunoglobulins

Mucosal surfaces are the main natural site of entry into the body for human immunodeficiency virus (HIV). Herein, an alternative mechanism for virus spread is described. The mechanism, which involves transcytosis of endosome-internalized HIV-particles, was generated by contact of HIV-infected cells with the apical surface of an epithelial cell line. Transcytosed viruses rapidly (in 20-30 min) access the serosal side of the epithelial barrier without infecting the epithelium itself. In turn, transcytosed HIV could infect host submucosal mononucleated target cells, and thus the infection could spread. An investigation was done to determine whether mucosal antibodies could block HIV transcytosis. Both secretory IgA (S-IgA) and IgG that were purified from colostrum from HIV-seropositive women impaired HIV transcytosis, irrespective of the level of the recombinant HIV envelope anti-gp160-specific activities in an ELISA. However, specific S-IgAs were more efficient than IgG. Therefore, mucosal-specific S-IgA to HIV-1 could be relevant to reducing infectivity of HIV-1 in corporeal fluids.

Detection and enumeration of HIV-1-producing cells by ELISPOT (enzyme-linked immunospot) assay

The enzyme-linked immunospot (ELISPOT) assay was adapted to detect and enumerate HIV-1-producing cells at the single cell level. With CEM cells or peripheral blood mononuclear cells (PBMC) infected in vitro with HIV-1, the ELISPOT assay detected cells that produced HIV-1 antigens and showed that between 5.4% and 9.5% of the p24 antigen-positive CEM cells and 11.1% to 23.6% of the p24 antigen-positive PBMC were productively infected. In HIV-1-infected patients in early stage of the disease and without antiretroviral therapy, up to 4.54 HIV-1-producing cells per 10(6) CD4+ T lymphocytes were detected in peripheral blood and up to 277.75 HIV-1-producing cells per 10(6) CD4+ T lymphocytes were detected in splenic lymphoid tissue. Our results indicate that the ELISPOT assay could represent a new tool to study HIV-1 replication in vivo.

Efficient transduction of human lymphocytes and CD34+ cells via human immunodeficiency virus-based gene transfer vectors

The development of gene transfer systems for the efficient transduction of human primary cells including lymphocytes and CD34+ cells is a significant step in the advancement of gene therapy and cell marking protocols. Efficient gene transfer systems also represent useful tools for basic research. Here we show that human primary lymphocytes and CD34+ cells can be efficiently transduced using a VSV-G pseudotyped HIV-1-based gene transfer system. The enhanced green fluorescent protein (EGFP) was chosen as the marker transgene, because it can be easily visualized and quantitated using fluorescence microscopy and flow cytometry, thus eliminating the need for selection or PCR to score transduction. Vectors produced with this system did not generate replication-competent retroviruses (RCRs) and efficiently transduced human cell lines (40-90%), PBMCs (60%), mobilized CD34+ cells (39%), and CD34+ cells from umbilical cord blood (60%) as measured by flow cytometry. Cells treated with AZT prior to infection did not express EGFP, ruling out passive protein or plasmid DNA transfer. This was further confirmed in methylcellulose cultures, where expression in myeloid and erythroid colonies was maintained for at least 3 weeks. In addition, this HIV-based vector was able to efficiently transduce freshly isolated, not-prestimulated CD34+ cells (70% EGFP positive) in serum-free medium. Under these same conditions, a Moloney murine leukemia virus-based vector failed to transduce not-prestimulated CD34+ cells. These characteristics make this gene transfer system an excellent choice for both basic science and possible gene therapy applications.

B7 cosignal potentiates apoptosis of uninfected CD4+ T lymphocytic cell lines primed by HIV envelope proteins

In lymphoid organs, follicular dendritic cells (FDCs), monocytes, and macrophages are targets for HIV infection and reservoirs for infectious virus. Strikingly, the apoptotic cells in these sites are essentially uninfected CD4+ T lymphocytes, but lie in close proximity to infected cells or FDCs carrying trapped HIV virions. To decipher this apoptotic pathway, we have established a two-step experimental system that reproduces in vitro the HIV envelope protein-mediated apoptosis restricted to uninfected CD4+ T lymphocytic cell lines. In this assay, uninfected CD4+ T cell targets undergo apoptosis following an initial priming step on HeLa cells expressing functional HIV envelope proteins at their plasma membrane and a second and necessary stimulation step via the CD3-TCR complex. The CD4+ T lymphocytic cells susceptible to apoptosis are, in contrast, resistant to cell fusion mediated by HIV envelope protein and express SDF-1. FDCs and macrophages are known to be high B7 expressors. Thus in lymph nodes, the cells that have trapped HIV particles in immune complexes at the plasma membrane present both HIV envelope proteins and B7.1 at their surface. We mimicked this situation in vitro by priming CD4+ T lymphocytes on cells expressing the costimulatory molecule B7 in addition to HIV envelope proteins, and show that it resulted in an acceleration and a twofold increase in apoptosis. Finally, we characterized two enzymes, PI3Kinase and PI-PLC, which are both downstream effectors of the CD4 (HIV envelope protein receptor) and CD28 (B7 receptor) activation pathways, and that participated in the early steps of priming for apoptosis.

Establishment of persistent infection with HIV-1 abrogates the caspase-3-dependent apoptotic signaling pathway in U937 cells

Treatment of 26L cells, a subclone obtained from U937 cells, with TNF-alpha or DNA-damaging agents such as teniposide (VM26) and camptothecin (CPT) induced morphologically and biochemically typical apoptotic changes, including the activation of procaspase-3. The cells persistently infected with HIV-1 (26L/HIV), however, showed a marked resistance to VM26 and CPT, whereas they hardly lost the sensitivity to TNF-alpha. TNF-alpha-induced apoptosis of 26L/HIV cells proceeded without the increase in caspase-3 activity, indicating that signaling for apoptosis in the infected cells proceeded through an alternative caspase-3-independent pathway which could respond to TNF-alpha but not to VM26 and CPT. The evidence that p-toluenesulfonyl-l-lysine chloromethyl ketone (a trypsin-like serine protease inhibitor) blocked VM26- and CPT-induced apoptotic changes but not TNF-alpha-induced apoptosis also supported the existence of the alternative TNF-alpha-inducible pathway. The results also suggest that a TLCK-sensitive protease is involved upstream of the procaspase-3 activation process and that the protease is essential for the progress of VM26- and CPT-induced apoptosis. The similar effect of HIV-1-productive infection on the apoptosis induced by the DNA-damaging agents was also confirmed by utilizing U1 cells, which are latently HIV-1-infected U937 cells. The cells became resistant to these agents after induction of the viral production by pretreatment with PMA. These results suggest that persistent HIV-1 infection blocks an apoptotic pathway triggered by DNA damaging agents through the inhibition of the procaspase-3 activation process.

HIV vaccines

In summary, the development of HIV vaccines has progressed from simple first-generation env subunit vaccines to second-generation vaccines containing multiple subunits. Vaccines with epitopes for CMI and Ab responses have broadened the immune response and the potential efficacy of these vaccines. It is hoped that newer technologies including the development of adjuvants, new types of vaccines, such as naked DNA, and new delivery systems, such as liposomes, will evoke stronger immune responses with longer duration. Improved schedules for dosing and combinations of HIV vaccines may result in longer lasting immune responses. A phase III trial is anticipated to begin within the next 2 years. After a temporary lull, the outlook for HIV vaccine development is being met once again with strong enthusiasm and encouragement for the future.

The relative resistance of HIV type 1-infected chimpanzees to AIDS correlates with the maintenance of follicular architecture and the absence of infiltration by CD8+ cytotoxic T lymphocytes

Lymphoid tissues are the focus of critical events in HIV pathogenesis. Persistent and high levels of virus production, extensive trapping of virus particles in germinal centers, and progressive degenerative changes in lymph node architecture are characteristics of progressive HIV-1 infection. Infiltrates of granzyme B- and TIA-expressing CD8+ "cytotoxic" T lymphocytes (CTLs) precede involution of germinal centers in humans who develop AIDS. Similar to humans, HIV-1 infection in chimpanzees is active and persistent. However, in contrast to humans, they remain relatively resistant to AIDS. Lymph node biopsies from chimpanzees infected with HIV-1 or a related chimpanzee lentivirus were studied for the level and pattern of virus expression, changes in lymphoid architecture, CD8+ T cell infiltrates and the presence or absence of CTL markers. In stark contrast to HIV-1-infected humans, lymph nodes from infected chimpanzees had little virus deposition in germinal centers and a paucity of virus-expressing cells. Although some of the lymph nodes examined from infected animals had moderate follicular hyperplasia with infiltrating CD8+ T cells, none had evidence of follicular fragmentation. Most importantly, in marked contrast to infected humans, CD8+ T cells infiltrating the germinal center were negative for the CTL marker granzyme B. This evidence suggests that the infiltration of CD8+ CTLs into the germinal centers of lymph nodes may be a key determinant in AIDS pathogenesis.

HIV-1 tat protein induces the production of interleukin-8 by human brain-derived endothelial cells

This study focused on the role of the HIV-derived viral protein, tat, in activating central nervous system (CNS)-derived endothelial cells (EC) to produce interleukin-8 (IL-8), a stimulator and chemoattractant for neutrophils and lymphocytes. Human CNS-EC treated with tat (100 ng/ml) demonstrated a 2 to 3 fold upregulation in IL-8 mRNA and protein. Tumor necrosis factor-alpha (TNF) and tat were found to act additively in upregulating IL-8 production. In contrast, transforming growth factor beta (TGF beta), appeared to down modulate tat-induced IL-8 production. These data suggest that extracellular tat, especially in the presence of TNF, may be responsible for the local production of IL-8.

Suppression of feline immunodeficiency virus replication in vitro by a soluble factor secreted by CD8+ T lymphocytes

Mitogen-activated lymphoblasts isolated from the blood and lymph nodes, but not the spleen, of domestic cats acutely infected with the Petaluma or Glasgow8 isolates of feline immunodeficiency virus (FIV), suppressed the replication of FIV in the MYA-1 T-cell line in a dose-dependent manner. This effect was not limited to the homologous isolate of FIV. The suppressor activity declined with progression to chronic infection, with lower levels of activity detectable only in the lymph nodes. Immunization of domestic cats with whole inactivated FIV vaccine elicited profound suppressor activity in both the blood and lymph nodes. The suppressor activity was associated with the CD8+ T-cell subpopulation, the effect did not appear to be major histocompatibility complex-restricted, and was mediated by a soluble factor(s). This activity may be associated with the control of virus replication during both the asymptomatic stages of FIV infection, and in the protective immunity observed in cats immunized with whole inactivated virus vaccines.

Time course of antibody response to tetanus toxoid and pneumococcal capsular polysaccharides in patients infected with HIV

The temporal course of the humoral immune response to T-cell-dependent and T-cell-independent type 2 antigens was evaluated in HIV-infected patients. In all, 26 seropositive patients were vaccinated with tetanus toxoid and 23-valent pneumococcal vaccines; total IgG and IgG1 antibodies to tetanus toxoid (Ttox) and total IgG and IgG2 antibodies against 23 Streptococcus pneumoniae capsular antigens (PPS) were measured at baseline, 2 months, and 12 months after vaccination. For the Ttox, baseline levels of IgG1 (Ttox-IgG1) increased from 11.0 to 19.5 mg/L at 2 months postimmunization. Overall only 6 patients (23%) showed a significant response. At 12 months postvaccination, Ttox-IgG and T-tox-IgG1 were significantly lower than baseline levels (Ttox IgG basal; 11.0 mg/L, 12 months; 0.8 mg/L, Ttox IgG1 baseline; 13.1 mg/L, Ttox IgG1 12 months; 2.4 mg/L) and in 10 patients, antibodies that fell below protective levels (0.6 mg/L). In contrast with PPS, a significant response was observed at 2 and 12 months (PPS-IgG basal; 35.9 U/ml, 2 months; 151.4 U/ml, 12 months; 59.7 U/ml; PPS-IgG2 baseline 20.3 U/ml, 2 months; 113.2 U/ml, 12 months; 51.9 U/ml). Overall, 19 patients (76%) showed an immune response to pneumococcal polysaccharides antigens. Immunization with the Ttox T-cell-dependent antigen fails to elicit a significant immune response and may induce inhibition of antibody production in HIV-infected patients. In contrast, immunization with a T-cell-independent type 2 antigen can cause the pneumococcal polysaccharides to induce significant immune response in a high proportion of HIV-infected patients.

Safety and immunogenicity of HIV recombinant envelope vaccines in HIV-infected infants and children. National Institutes of Health-sponsored Pediatric AIDS Clinical Trials Group (ACTG-218)

Study objectives were to evaluate the safety and immunogenicity of three HIV recombinant glycoproteins in HIV-infected infants and children between 1 month and 18 years of age with asymptomatic (P-1) infection. Using Chiron rgp 120 (SF-2) 15 or 50 microg; MicroGeneSys rgp 160 (IIIB) 40 or 320 microg; Genentech rgp120 (MN) 75 or 300 microg; or adjuvant control (Alum or MF-59), children were randomized to a double-blind, placebo-controlled, dose-escalating study of vaccine administered intramuscularly at entry and 1, 2, 3, 4, and 6 months later. No adverse events were attributed to study vaccines. Between 30% and 56% of volunteers exhibited a lymphoproliferative response as defined in terms of stimulation index (SI) to vaccine antigens; 65% of vaccinees but none of placebo recipients exhibited moderate or strong responses after enzyme immunoassay to HIV specific antigens. CD4 cell counts and quantitative HIV culture did not differ significantly among vaccine and control groups, nor were differences found among groups in HIV disease progression. The rgp160 and gp120 subunit vaccines were safe and immunogenic in this population.

T-tropic human immunodeficiency virus type 1 (HIV-1)-derived V3 loop peptides directly bind to CXCR-4 and inhibit T-tropic HIV-1 infection

Certain types of chemokine receptors have been identified as coreceptors for HIV-1 infection. The process of viral entry is initiated by the interaction between an envelope protein gp120 of HIV-1, CD4, and one of the relevant coreceptors. To understand the precise mechanism of the Env-mediated fusion and entry of HIV-1, we examined whether the V3 region of gp120 of T-cell line tropic (T-tropic) virus directly interacts with the coreceptor, CXCR-4, by using five synthetic V3 peptides: two cyclized V3 peptides (V3-BH10 and V3-ELI) which correspond to the V3 regions of the T-tropic HIV-1 IIIB and HIV-1 ELI strains, respectively, a linear V3 peptide (CTR36) corresponding to that of HIV-1 IIIB strain; and cyclized V3 peptides corresponding to that of the macrophage-tropic (M-tropic) HIV-1 ADA strain (V3-ADA) or the dualtropic HIV-1 89.6 strain (V3-89. 6). FACScan analysis with a CXCR-4(+) human B-cell line, JY, showed that V3-BH10, V3-ELI, and V3-89.6 but not CTR36 or V3-ADA blocked the binding of IVR7, an anti-CXCR-4 monoclonal antibody (MAb), to CXCR-4 with different magnitudes in a dose-dependent manner, while none of the V3 peptides influenced binding of an anti-CD19 MAb at all. Next, the effects of the V3 peptides on SDF-1beta-induced transient increases in intracellular Ca2+ were investigated. Three V3 peptides (V3-BH10, V3-ELI, and V3-89.6) prevented Ca2+ mobilization. Furthermore, the three peptides inhibited infection by T-tropic HIV-1 in a dose-dependent manner as revealed by an MTT assay and a reverse transcriptase assay, while the other peptides had no effects. These results present direct evidence that the V3 loop of gp120 of T-tropic HIV-1 can interact with its coreceptor CXCR-4 independently of the V1/V2 regions of gp120 or cellular CD4.

CXCR4 and CD4 mediate a rapid CD95-independent cell death in CD4(+) T cells

AIDS is characterized by a progressive decrease of CD4(+) helper T lymphocytes. Destruction of these cells may involve programmed cell death, apoptosis. It has previously been reported that apoptosis can be induced even in noninfected cells by HIV-1 gp120 and anti-gp120 antibodies. HIV-1 gp120 binds to T cells via CD4 and the chemokine coreceptor CXCR4 (fusin/LESTR). Therefore, we investigated whether CD4 and CXCR4 mediate gp120-induced apoptosis. We used human peripheral blood lymphocytes, malignant T cells, and CD4/CXCR4 transfectants, and found cell death induced by both cell surface receptors, CD4 and CXCR4. The induced cell death was rapid, independent of known caspases, and lacking oligonucleosomal DNA fragmentation. In addition, the death signals were not propagated via p56(lck) and Gialpha. However, the cells showed chromatin condensation, morphological shrinkage, membrane inversion, and reduced mitochondrial transmembrane potential indicative of apoptosis. Significantly, apoptosis was exclusively observed in CD4(+) but not in CD8(+) T cells, and apoptosis triggered via CXCR4 was inhibited by stromal cell-derived factor-1, the natural CXCR4 ligand. Thus, this mechanism of apoptosis might contribute to T cell depletion in AIDS and might have major implications for therapeutic intervention.

HIV-1 Tat Inhibits Human Natural Killer Cell Function by Blocking L-Type Calcium Channels

Herein we show that functional phenylalkylamine-sensitive L-type calcium channels are expressed by human NK cells and are involved in the killing of tumor targets. Blocking of these channels by phenylalkylamine drugs does not affect effector/target cell binding but inhibits the release of serine esterases responsible for cytotoxicity. Interestingly, treatment of NK cells with HIV-1 Tat, which is known to affect several calcium-mediated events in immune cells, impairs their cytotoxic activity. In addition, Tat inhibits the rise in intracellular free calcium concentration upon cross-linking of the adhesion molecule CD11a, engaged during effector/target cell interaction, and the activation molecule CD16. Exogenous Tat does not influence NK-target cell binding but prevents NK cell degranulation. We propose that the molecular structure(s) on NK cells mediating the inhibitory effects HIV-1 Tat belong to L-type calcium channels, based on three lines of evidence: 1) binding of phenylalkylamine derivatives to these channels is cross-inhibited by Tat; 2) L-type calcium channels from NK cell lysates bind to Tat linked to Sepharose columns; 3) the inhibitory effect of HIV-1 Tat on NK cell function is prevented by the agonist of L-type calcium channels, Bay K 8644. Altogether, these results suggest that exogenous Tat is deeply involved in the impairment of NK cell function during HIV-1 infection.

Susceptibility of human lymphoblastoid B-cell line CE to HIV1 infection

In this preliminary report, we provide evidence that the human B-lymphoblastoid cell line (LCL) CE, bone-marrow-derived, previously reported to be permissive to hepatitis C virus, is also permissive to HIV1 infection. HIV1 genomes were detectable in cell supernatants, virus RNA transcripts and proviral DNAs in cell extracts at different times post-infection. Therefore, we propose this LCL cell line as a tool for exploring the mutual interactions of the two viruses in double-infected cells.

DNA vaccination affords significant protection against feline immunodeficiency virus infection without inducing detectable antiviral antibodies

To test the potential of a multigene DNA vaccine against lentivirus infection, we generated a defective mutant provirus of feline immunodeficiency virus (FIV) with an in-frame deletion in pol (FIVDeltaRT). In a first experiment, FIVDeltaRT DNA was administered intramuscularly to 10 animals, half of which also received feline gamma interferon (IFN-gamma) DNA. The DNA was administered in four 100-microg doses at 0, 10, and 23 weeks. Immunization with FIVDeltaRT elicited cytotoxic T-cell (CTL) responses to FIV Gag and Env in the absence of a serological response. After challenge with homologous virus at week 26, all 10 of the control animals became seropositive and viremic but 4 of the 10 vaccinates remained seronegative and virus free. Furthermore, quantitative virus isolation and quantitative PCR analysis of viral DNA in peripheral blood mononuclear cells revealed significantly lower virus loads in the FIVDeltaRT vaccinates than in the controls. Immunization with FIVDeltaRT in conjunction with IFN-gamma gave the highest proportion of protected cats, with only two of five vaccinates showing evidence of infection following challenge. In a second experiment involving two groups (FIVDeltaRT plus IFN-gamma and IFN-gamma alone), the immunization schedule was reduced to 0, 4, and 8 weeks. Once again, CTL responses were seen prior to challenge in the absence of detectable antibodies. Two of five cats receiving the proviral DNA vaccine were protected against infection, with an overall reduction in virus load compared to the five infected controls. These findings demonstrate that DNA vaccination can elicit protection against lentivirus infection in the absence of a serological response and suggest the need to reconsider efficacy criteria for lentivirus vaccines.

Apoptosis induction by the binding of the carboxyl terminus of human immunodeficiency virus type 1 gp160 to calmodulin

The role of calmodulin (CaM) in apoptosis induced by gp160 of human immunodeficiency virus type 1 was investigated with cells undergoing single-cell killing. These cells were found to express, under the control of an inducible promoter, wild-type gp160 or mutant gp160 devoid of various lengths of the carboxyl terminus. Immunoprecipitation accompanied by immunoblotting revealed binding of CaM to wild-type gp160 but not to mutant gp160 bearing a carboxyl terminus with a deletion spanning more than five amino acid residues. A significant coenzyme activity was detected in the CaM bound to gp160 even in the presence of a Ca2+ chelater, EGTA. The cells forming this gp160-CaM complex exhibited an elevated intracellular Ca2+ level followed by DNA fragmentation, which is a hallmark of apoptosis, and finally cell killing, while the cells not forming this complex did not show any significant elevation in Ca2+ level or DNA fragmentation. These results thus indicated that CaM plays a key role in gp160-induced apoptosis.

Live and killed human immunodeficiency virus type-1 increases the intracellular growth of Leishmania donovani in monocyte-derived cells

We coincubated killed or live human immunodeficiency virus type-1 (HIV-1) with human monocyte-derived cells infected with Leishmania donovani and examined the effect of the virus preparations on the intracellular growth of the parasite. We found that there was significant enhancement (by a mean of 53%, p < 0.001) of intracellular L. donovani growth in the human monocytic leukaemia THP-1 cell line coincubated with killed HIV-1. Infection of peripheral blood monocyte-derived macrophages with live HIV-1 initiated after L. donovani infection led to an increase in intracellular parasites by an overall mean of 2.8% vs 4.9% (p < 0.01) at 2 and 5 d after HIV infection in L. donovani and L. donovani plus HIV-1 infected, respectively, and by an overall mean of 5.0% vs 13.3% (p < 0.001) at 5, 12 and 15 d after HIV-1 infection in L. donovani and L. donovani + HIV-1 infected, respectively. Further, L. donovani infection 2 d after infection with HIV-1 led to enhanced parasite growth (34.5%, p < 0.001) compared with cells infected with L. donovani alone (5.5%), and those where HIV-1 was added after L. donovani (18.1%). In all cases, HIV-1 from live and killed virus preparations led to decreased anti-leishmanial activity of the macrophages as evidenced by decreased control of intracellular multiplication. The findings may suggest a mechanism not requiring live virus to explain how HIV-1 coinfection may impair the control of intracellular Leishmania growth in individuals with pre-existing asymptomatic infection leading to the reactivation of the parasite. Moreover, patients with HIV-1 infection might be at increased risk of developing Leishmania infection.

Human immunodeficiency virus Tat protein induces interleukin 6 mRNA expression in human brain endothelial cells via protein kinase C- and cAMP-dependent protein kinase pathways

The intracellular signal transduction pathways utilized by the HIV-1-derived protein, Tat, in the activation of human central nervous system-derived endothelial cells (CNS-ECs) were examined using specific enzymatic assays. Tat induced an increase in interleukin 6 (IL-6) mRNA within 1 hr of treatment. This biological effect of Tat involved activation of both protein kinase C (PK-C) and cAMP-dependent protein kinase (PK-A) in CNS-ECs. Tat at 10 ng/ml induced a sharp, transient increase in membrane PK-C activity within 30 sec of incubation, and reached maximum levels at 2 min, declining to control values within 10 min. Tat also induced a sharp increase in intracellular cAMP levels and PK-A activity in these cells, with the PK-A activity reaching a maximum at 10 min and slowly declining to control values in 4 hr of incubation. Activation of PK-A was dependent on a Tat-induced increase in membrane PK-C activity as demonstrated by calphostin C (a PK-C inhibitor) abolishing this effect. Incubation of cells with the cyclooxygenase inhibitor indomethacin did not affect Tat-induced activation of PK-A, indicating that prostacyclins are not involved in this process. Tat-induced increase in IL-6 mRNA was abolished in the presence on PK-A inhibitor H-89, demonstrating that activation of PK-A is necessary and sufficient for the increase in IL-6 production by these cells. Both the Tat-induced increase in intracellular cAMP and IL-6 mRNA levels in CNS-ECs may play a role in altering the blood-brain barrier and thereby inducing pathology often observed in AIDS dementia.