A human serum mannose-binding protein inhibits in vitro infection by the human immunodeficiency virus.

In vitro infection by the human immunodeficiency virus (HIV) of CD4+ H9 lymphoblasts is inhibited by a mannose-binding protein (MBP) purified from human serum. In addition, MBP is able to selectively bind to HIV-infected H9 cells and HIV-infected cells from the monocyte cell line U937. These results indicate MBP most likely recognizes high mannose glycans known to be present on gp120 in the domain that is recognized by CD4 and thereby inhibits viral entry to susceptible cells. In support of this contention, recombinant gp120 binds directly to MBP; the binding is saturable, mannan inhibitable, removed by N-glycanase treatment, and dependent on divalent cations.

Blocking of HIV-1 infectivity by a soluble, secreted form of the CD4 antigen.

The initial event in the infection of human T lymphocytes, macrophages, and other cells by human immunodeficiency virus (HIV-1) is the attachment of the HIV-1 envelope glycoprotein gp120 to its cellular receptor, CD4. As a step toward designing antagonists of this binding event, soluble, secreted forms of CD4 were produced by transfection of mammalian cells with vectors encoding versions of CD4 lacking its transmembrane and cytoplasmic domains. The soluble CD4 so produced binds gp120 with an affinity and specificity comparable to intact CD4 and is capable of neutralizing the infectivity of HIV-1. These studies reveal that the high-affinity CD4-gp120 interaction does not require other cell or viral components and may establish a novel basis for therapeutic intervention in the acquired immune deficiency syndrome (AIDS).

Effect of heterogeneity of carcinoembryonic antigen on liver cell membrane binding and its kinetics of removal from circulation.

Carcinoembryonic antigen (CEA) is a glycoprotein metabolized primarily by the liver. Subcellular fractions of rat liver were examined for CEA binding activity. Hepatocyte plasma membrane and microsome fractions bound CEA, and this binding shared the calcium requirement, neuraminidase sensitivity, and carbohydrate specificity of the hepatocyte asialoglycoprotein receptor. CEA had previously been shown to react with this galactose-specific receptor, in vivo, only following neuraminidase treatment. Galactose receptor binding of CEA was measured in three different purified CEA preparations. The fraction of CEA capable of binding to excess levels of galactose receptor on membranes varied (46.5%, 40.2%, and 4.7% for CEA-1, -2, and -3, respectively). These CEAs were shown to be 2.3%, 7.9%, and 0.7% as effective, respectively, as asialo-alpha 1-acid glycoprotein in inhibiting the binding of radiolabeled asialo-alpha 1-acid glycoprotein to liver cell membranes. Each of the three CEA preparations showed different clearance kinetics from the circulation of mice. Coinjection of asialo-alpha 1-acid glycoprotein with the CEAs revealed differing inhibition of the clearances. These results show that differences in the carbohydrate components of purified CEA preparations affect their rate of removal from circulation and thus possibly the relationship between CEA production and observed plasma levels in patients. The possible origin of these CEA differences is discussed with their clinical implications.

Clinical isolates of HIV-1 contain few pre-existing proteinase inhibitor resistance-conferring mutations.

Proteinase inhibitors are an important new class of antiviral agents for AIDS, however, in vitro experiments have identified proteinase mutations that confer resistance to several different families of the inhibitors. This study was undertaken to determine if these resistance-conferring amino-acid substitutions occur in HIV strains before the application of selective pressure. We determined the nucleic acid sequence of the proteinase gene from the 23 clinical isolates of HIV-1 and three laboratory-adapted strains using a method that detects the majority species present in viral populations. Analysis of minor subpopulations will require alternative strategies. The clinical isolates studied contained an average of 3 (range 1-8) amino-acid substitutions as compared to the prototypical BH10 sequence. We did not detect substitutions characteristic of reported highly proteinase-resistant strains. These results suggest significant variation occurs in the HIV-1 proteinase gene but pre-existing highly proteinase-resistant strains are uncommon.

The regulation of HIV by retinoic acid correlates with cellular expression of the retinoic acid receptors.

OBJECTIVES: To analyze the effect of retinoic acids (RA) on HIV-1 expression and correlate this effect with expression levels of RA receptors (RARs) in T-lymphoid and monocytoid cell lines. DESIGN AND METHODS: The effect of all-trans and 9-cis RA on HIV-1 production in T-lymphoid (H9, CEM) and monocytoid (U937,THP-1) cell lines was measured during acute and chronic infection. The expression levels of human RAR alpha (hRAR alpha, receptor for all-trans RA) and the human retinoid-X receptor alpha (hRXR alpha receptor for 9-cis RA) were determined by Northern blot analysis. RESULTS: Both all-trans and 9-cis RA inhibited virus replication in HIV-1 IIIB-infected monocytoid cells, in the presence and absence of the co-stimulatory agent phorbol myristate acetate (PMA). The retinoids had weak or no stimulatory effects on HIV production by T-cell lines. HIV production by PMA-stimulated T-cell lines was inhibited by these retinoids. The 9-cis RA was generally more effective than all-trans RA in inhibiting HIV production and in combination generally more effective than the single agents alone. Human RAR alpha was expressed in H9, U937 and THP-1 cells, but almost undetectable in CEM cells. Human RXR alpha was significantly expressed in U937 and THP-1 cells, weakly expressed in H9 cells and not detectable in CEM cells. After stimulation by PMA, RXR alpha expression increased in H9 and U937 cells but not in CEM cells. Human RAR alpha expression was unchanged in H9 and CEM cells, and elevated in U937 cells, after PMA stimulation. CONCLUSION: The effect of RA on HIV-1 expression was cell-type-dependent and partially correlated with cellular expression of RARs. Endogenous or exogenously administered RA may have a significant role in HIV regulation.

Comparison of the immune response to recombinant gp120 in humans and chimpanzees.

OBJECTIVE: To assess similarities and differences in antibody responses to recombinant (r) HIV-1IIIB gp120 in chimpanzees, previously protected from HIV-1 infection, and human volunteers immunized in connection with a Phase I clinical trial. METHODS: Frozen sera from humans immunized with rgp120 from HIV-1IIIB and chimpanzees immunized with the same antigen or recombinant soluble gp160 were compared in a variety of serologic assays. RESULTS: The magnitude of the antibody response to gp120 was similar in both species; however, the half-life of the antibody response to rgp120 was approximately 4.5 times longer in humans (9 weeks) than in chimpanzees (2 weeks). Antibodies to gp120 in both species were broadly cross-reactive with gp120 from diverse isolates of HIV-1 and were effective in blocking the binding of gp120 to CD4. Antibody binding to native gp120 was greater than to denatured gp120 in both species. Antibody responses to the principal neutralizing determinant (V3 domain) and virus neutralization titers were approximately 10-fold lower in humans than chimpanzees. The relative avidity of antibody binding to gp120 was higher in the sera from the immunized chimpanzees than in the immunized humans. CONCLUSIONS: While the antibody responses to rgp120 elicited in man and chimpanzees were in many ways similar, significant differences did occur. Predictions made on the basis of chimpanzee immunogenicity studies over-estimated the potency of the virus neutralizing titers and under-estimated the duration of the antibody response achieved in humans.

Inhibition of serum-enhanced HIV-1 infection of U937 monocytoid cells by recombinant soluble CD4 and anti-CD4 monoclonal antibody.

Mononuclear phagocytes can be infected with the human immunodeficiency virus type 1 (HIV-1). Although these cells express CD4 antigen, which is the recognized cellular receptor for HIV, additional cell surface proteins such as the Fc receptor, might serve as receptors for infection. In order to study this possibility we used the U937 monocytic cell line as a target for HIV infection. Flow cytometry of U937 showed that 97% of cells expressed CD4, 33% expressed the high affinity 72 kD Fc receptor (FcRI), and 74% expressed the low-affinity 40 kD Fc receptor (FcRII). Virus neutralization tests were performed by preincubating heat-inactivated human anti-HIV sera with HIV-1, IIIB strain, and then challenging U937. After 13 days in culture, productive HIV-1 infection was monitored by reverse transcriptase activity. High concentrations of certain sera (10(-1)-10(-3) dilutions) neutralized HIV-1, but at subneutralizing concentrations (10(-4)-10(-6) dilutions), five of these sera enhanced viral infection approximately two- to threefold. This enhancement of HIV-1 infection was totally blocked by 1 microgram/ml recombinant soluble CD4 (rCD4) or by 0.5 microgram/ml anti-CD4 Leu3a monoclonal antibody. These results suggest that serum enhancement of HIV-1 infection, thought to be due to binding to the monocyte Fc receptor, requires HIV-1 binding to CD4, since rCD4 or Leu3a blocked this phenomenon.

HIV type 1 protease activation of NF-kappa B within T lymphoid cells.

NF-kappa B is a nuclear protein of the rel oncogene family capable of enhancing transcription of several cellular genes, including IL-2 and the IL-2 receptor, and viral genes transcribed from the HIV-1 LTR. It has been reported that HIV-1 protease may cleave the NF-kappa B precursor to its active form in vitro. In this study the effects of HIV protease on NF-kappa B precursor activation were examined in Jurkat T cells by introducing a protease expression vector into the cells. Increased NF-kappa B activity was observed and this increased activity was blocked by a specific inhibitor of the viral protease. Viral transcription, as measured using LTR-CAT assays, was only slightly enhanced in the HIV-protease expressing cells, while secretion of IL-2 and expression of the IL-2 receptor were not affected. The limited activation of NF-kappa B by HIV protease appears unlikely to have a significant effect on virus expression or T cell function.

Stimulation of human immunodeficiency virus type 1 expression by ceramide.

Ceramide, an intracellular lipid mediator of tumor necrosis factor alpha (TNF-alpha) action, was studied for its effects on the expression of the proviral human immunodeficiency virus type 1 genome in latently infected myelomonocytic cell lines U-1IIIB and OM-10.1. Ceramide treatment resulted in a 20- to 100-fold enhancement of HIV production in these cells. Ceramide also enhanced the expression of the chloramphenicol acetyltransferase gene directed by a human immunodeficiency virus type 1 long terminal repeat in transfected U-937 cells, indicating that ceramide acts at the level of viral transcription. These observations suggest that the TNF-ceramide signaling system may be involved in the regulation of HIV expression in certain myeloid cell types.

The multiple inhibitory mechanisms of GEM 91, a gag antisense phosphorothioate oligonucleotide, for human immunodeficiency virus type 1.

GEM 91 (gene expression modulator) is a 25-mer oligonucleotide phosphorothioate complementary to the gag initiation site of HIV-1. GEM 91 has been studied in various in vitro cell culture models to examine inhibitory effects on different stages of HIV-1 replication. Experiments were focused on the binding of virions to the cell surface, inhibition of virus entry, reverse transcription (HIV DNA production), inhibition of steady state viral mRNA levels, inhibition of virus production from chronically infected cells, and inhibition of HIV genome packaging within virions. Experiments were also performed in vitro in an attempt to generate strains of HIV with reduced sensitivity to GEM 91. We observed sequence-dependent inhibition of virus entry/reverse transcription and a reduction in steady state viral RNA levels. We also observed sequence-independent inhibition of virion binding to cells and inhibition of virus production by chronically infected cells. Using in vitro methods that were successful in generating HIV strains with reduced sensitivity to AZT, we were unable to generate strains with reduced sensitivity to GEM 91.

Human immunodeficiency virus in semen arises from a genetically distinct virus reservoir.

The reservoir of human immunodeficiency virus (HIV) in semen is unknown. Several lines of evidence suggest that semen HIV may not arise from the same reservoir of infection as peripheral blood. If true, the viral burden in the two compartments could be qualitatively and quantitatively different, a scenario of potentially profound significance for the design of effective strategies of treatment, disease monitoring, and infection containment. We report here that the ratio of infected to uninfected leukocytes in ejaculated semen specimens is highly discordant with paired blood samples, demonstrating that they derive from distinct populations of infected cells. In addition, infectious HIV was isolated from semen cells, but not from blood cells, of an individual on triple antiretroviral therapy; the absence of major resistance-conferring mutations in the semen virus indicates that it was replicating in isolation from the antiviral agents. The compartmentalization of blood and semen infection was further supported by genetic analysis of several infectious HIV clones isolated from semen cells and peripheral blood cells of another donor not on antiretroviral therapy. Protease gene sequence analyses revealed significant divergence of the two viral populations. These findings confirm the distinct compartmentalization of HIV in the semen of this study cohort, and support the concept that semen HIV arises from an isolated reservoir of infection that may function independently in the pathobiology of HIV disease.

Synergistic inhibition of HIV-1 by an antisense oligonucleotide and nucleoside analog reverse transcriptase inhibitors.

We have studied the effects of the gag antisense phosphorothioate oligonucleotide GEM 91 and mismatch antisense controls on the antiviral activities of ddC and other nucleoside analogs in HIV-infected MT-4 cells using a cytoprotection based assay. Under standard assay conditions, i.e. simultaneous incubation of drugs, HIV-1 IIIB and MT-4 cells, both GEM 91 and mismatch controls interacted synergistically with ddC resulting in an approximate 40-fold decrease in the IC50 value of ddC; this suggests a potent but sequence non-specific effect of GEM 91. Under post-adsorption assay conditions, i.e. pre-incubation of virus and cells and removal of excess HIV before drug addition, GEM 91 exhibited synergism with ddC, with an approximate 5-fold decrease in ddC IC50 value. This favorable interaction was not seen with any of the mismatch oligonucleotides, suggesting the involvement of a sequence-specific mechanism of action. Similar results were seen with the thymidine analogs AZT and d4T in combination with GEM 91. These data suggest a potential role for GEM 91 and future sequence-specific antisense drugs in combination with nucleoside analogs for the treatment of HIV infection. It is essential that potential interactions between new and existing classes of anti-HIV drugs are studied extensively as antiretroviral drug combinations become increasingly more complex.

Analysis of human immunodeficiency virus in semen: indications of a genetically distinct virus reservoir.

It is well established that HIV is found in semen, either as cell-free or cell associated virus, yet many questions remain about the source of the virus. A number of factors, including anatomic features of the male reproductive tract, the restricted access of the immune system to the germ cell compartment, and the results from sexually transmitted virus studies, suggest that the source of HIV in semen may be different from that in the peripheral blood. In this study, we examine the HIV in the infected cells of semen as indicators of the virus producing reservoir. The frequency of HIV positive leukocytes in semen is compared to that of concurrent blood samples from eight donors and these values are found to be highly variable and frequently discordant. The protease gene sequences of HIV strains isolated from semen cells and blood cells were determined and phylogenetic analyses were performed which indicate the virus populations in the two sources are genetically distinct. In one patient receiving anti-HIV protease inhibitor therapy, gene sequences indicative of protease inhibitor resistance were found in the blood, but not the semen cell compartment. These results suggest that HIV in the semen and blood compartments are distinct, and further, may respond differently to antiviral therapy.

Stimulation of HIV expression by intracellular calcium pump inhibition.

We have studied the role of intracellular calcium sequestration on human immunodeficiency virus (HIV) production by latently infected T-lymphocytic cells. Inhibition of the sarco-endoplasmic reticulum-type calcium transport ATPases by thapsigargin or cyclopiazonic acid induced activation of HIV production in the CEM-derived ACH-2 cells. An approximately 50% depletion of the thapsigargin-sensitive calcium pools as measured fluorimetrically of Indo-loaded cells fully activated virus production. Viral activation was manifest by increases in soluble viral core p24 production, increases in cellular immunofluorescent staining for viral antigens, and increased viral transcription as measured by HIV long terminal repeat-directed expression of the chloramphenicol acetyltransferase reporter gene. Virus induction could be blocked in a dose-dependent manner by the calcium channel blocker econazole. Virus production by the Jurkat-derived HIV-1-inducible J1.1 cells was not significantly stimulated by thapsigargin. These data indicate that intracellular calcium pool function is involved in the control of the transcription of proviral HIV in a cell type-specific manner within the T-lymphoid lineage and that ACH-2 cells represent a useful model for the study of calcium dependent activation of the transcription of proviral HIV.

Sequence-specific RNase H cleavage of gag mRNA from HIV-1 infected cells by an antisense oligonucleotide in vitro.

We have used a ribonuclease protection assay to investigate RNase H cleavage of HIV-1 mRNA mediated by phosphorothioate antisense oligonucleotides complementary to the gag region of the HIV-1 genome in vitro. Cell lysate experiments in H9 and U937 cells chronically infected with HIV-1 IIIB showed RNase H cleavage of unspliced gag message but no cleavage of spliced message which did not contain the target gag region. RNase H cleavage products were detected at oligonucleotide concentrations as low as 0.01 microM and the RNase H activity was seen to be concentration dependent. Similar experiments with 1-, 3- and 5-mismatch oligonucleotides demonstrated sequence specificity at low concentrations, with cleavage of gag mRNA correlating with the predicted activities of the parent and mismatch oligonucleotides based on their hybridization melting temperatures. Experiments in living cells suggested that RNase H-specific antisense activity was largely determined by the amount of oligonucleotide taken up by the different cell lines studied. RNase H cleavage products were detected in antisense oligonucleotide treated MT-4 cells acutely infected with HIV-1 IIIB, but not in infected H9 cells treated with oligonucleotide under the same conditions. The data presented demonstrate potent and specific RNase H cleavage of HIV-1 mRNA mediated by an antisense oligonucleotide targeted to HIV-1 gag mRNA, and are in agreement with previous reports that the major obstacle to demonstrating antisense activity in living cells remains the lack of penetration of these agents into the desired cellular compartment.

A modified nonradioactive method for northern blot analysis.

In this report we use several previously described methods, in novel combination, to establish a sensitive and flexible nonradioactive method. First, we prepared single-stranded digoxigenin-labeled probes using a high-efficiency polymerase chain reaction (PCR) method (4). For detection of RNA, blots were hybridized with probes containing digoxigenin and then incubated with alkaline phosphatase-conjugated anti-digoxigenin antibody. Bound probe was rapidly detected with X-ray film using localized light emission from the reaction of alkaline phosphatase with lumigen-paraphenylenediamine substrate (5). This method allows flexibility in probe sequence selection, independent of restriction enzyme site location, and it works well with small probes. This approach allows sensitive differential analysis of closely related members of a gene family.

Design, biochemical, biophysical and biological properties of cooperative antisense oligonucleotides.

Short oligonucleotides that can bind to adjacent sites on target mRNA sequences are designed and evaluated for their binding affinity and biological activity. Sequence-specific binding of short tandem oligonucleotides is compared with a full-length single oligonucleotide (21mer) that binds to the same target sequence. Two short oligonucleotides that bind without a base separation between their binding sites on the target bind cooperatively, while oligonucleotides that have a one or two base separation between the binding oligonucleotides do not. The binding affinity of the tandem oligonucleotides is improved by extending the ends of the two oligonucleotides with complementary sequences. These extended sequences form a duplex stem when both oligonucleotides bind to the target, resulting in a stable ternary complex. RNase H studies reveal that the cooperative oligonucleotides bind to the target RNA with sequence specificity. A short oligonucleotide (9mer) with one or two mismatches does not bind at the intended site, while longer oligonucleotides (21mers) with one or two mismatches still bind to the same site, as does a perfectly matched 21mer, and evoke RNase H activity. HIV-1 inhibition studies reveal an increase in activity of the cooperative oligonucleotide combinations as the length of the dimerization domain increases.

Infection of nonlymphoid cells by human immunodeficiency virus type 1 or type 2.

Human epithelial cells (L132) derived from embryonic lung and human lung fibroblasts (MRC5) were infected by human immunodeficiency virus type 1 (HIV-1) or type 2 (HIV-2). Surface CD4 protein was detected on these cells, and recombinant soluble CD4 (sCD4) blocked infection, indicating that HIV infection was mediated by the cell surface CD4 protein. In contrast, infection of human primary chondrocyte cells (C23), synovial cells (HSA), and foreskin fibroblasts (F13) was apparently independent of cell CD4-mediated mechanisms. Surface CD4 protein could not be detected on these cells, and sCD4 did not block the infection. F13 cells could be infected only by HIV-2, not by HIV-1, under our experimental conditions. In cells of mesenchymal orgin, viral production could be detected only after cocultivation with the human T-lymphoid H9 cells but not by conventional viral assays, including reverse transcriptase and p24 antigen assays in cell culture supernatant and immunofluorescence of host cells. Our DNA transfection studies indicated that this lack of detectable viral production was not due to the inefficient use of the HIV long terminal repeat or the Tat protein in these cells. These mesenchymal and epithelial cells were susceptible to HIV infection but differed in mechanism of virus entry compared with hematopoietic cells such as T lymphocytes. These observations may provide insights into clinical syndromes such as lung dysfunction in HIV-infected newborns and connective tissue disorders in HIV-infected adults.

CD4+ lymphocyte function with early human immunodeficiency virus infection.

The pathogenesis of cellular immune deficiency following human immunodeficiency virus (HIV) infection could result from quantitative and/or qualitative dysfunction of the CD4+ lymphocyte population. To better characterize the T-cell response to soluble antigen with HIV infection, we have isolated peripheral blood lymphocytes and purified populations of CD4+ lymphocytes from healthy HIV antibody-positive subjects, patients with acquired immunodeficiency syndrome (AIDS)-related complex (ARC), and healthy HIV antibody-negative controls. T-lymphocyte function was determined by proliferative response to lectin (phytohemagglutinin), phorbol 12-myristate 13-acetate (PMA), calcium ionophore, purified recombinant HIV envelope gp120, tetanus toxoid antigen, and tetanus toxoid antigen in the presence of recombinant gp120 or purified recombinant soluble CD4. PBLs and CD4+ lymphocytes from asymptomatic HIV-infected subjects responded equally well to lectin, PMA, and/or calcium ionophore and to tetanus toxoid as cells from uninfected control subjects. The cells that proliferated in response to a soluble antigenic stimulus did not respond to gp120. Cells from subjects with ARC had a selective antigen recognition defect independent of the number of CD4+ lymphocytes. Recombinant gp120 inhibited CD4+ lymphocyte proliferation to antigenic stimulus by 30-40%. Recombinant soluble CD4, a proposed therapeutic for HIV, had no effect on T-cell response to antigen. A selective antigen recognition response was not compromised early in HIV infection but was compromised in subjects with ARC. Inhibition of proliferation to tetanus toxoid by gp120 suggests that HIV may affect major histocompatibility complex II restricted antigen recognition independent of CD4+ cell loss.