Regulation of HIV production by blood mononuclear cells from HIV-infected donors: II. HIV-1 production depends on T cell-monocyte interaction

ICAM-1 in HIV infection and underlying mechanisms

Intercellular adhesion molecule 1 (ICAM-1) is a glycoprotein that participates in inflammatory and immune responses. Both cell surface and soluble ICAM-1 are significantly increased during human immunodeficiency virus (HIV) infection, and ICAM-1 has important functions in promoting inflammatory responses and enhancing HIV infectivity; however, a comprehensive summary these roles has yet to be elaborated. In this review we describe the general biological characteristics of ICAM-1, its association with HIV disease progression and promotion of HIV production, mechanisms inducing upregulation of ICAM-1, and possible intervention strategies, representing important insights in the context of HIV treatment.

THE IMPACT OF THE CD8+ CELL NON-CYTOTOXIC ANTIVIRAL RESPONSE (CNAR) AND CYTOTOXIC T LYMPHOCYTE (CTL) ACTIVITY IN A CELL-TO-CELL SPREAD MODEL FOR HIV-1 WITH A TIME DELAY

In this paper, neglecting the effects of free virus, we consider a simple model of cell-to-cell spread of HIV-1. We discuss the impact of the CD8+ cell non-cytotoxic anti-viral response (CNAR) and cytotoxic T lymphocyte (CTL) activity on infection by HIV-1. Two types of models are considered: the ordinary differential equation (ODE) model and the discrete time delay differential equation (DDE) system. The steady states of the ODE model are globally asymptotically stable respectively under two threshold criteria. In the DDE model, the global stability of the infected steady state of the ODE model becomes only ultimately stable. Moreover, at a certain interval of the time delay, the DDE model will produce Hopf bifurcation or periodic solutions. The introduction of CTL and CNAR will change the values of these steady states and induce fluctuations in the cell concentration. It also affects the critical value of the time delay and is of utility in the interpretation of typical HIV-dynamics data resulting from clinical trials. The DDE model produces sustained infective oscillations in some real parameter values, which is different from the result of the similar cell-free viral spread model with delay.

Inducible-costimulator-mediated suppression of human immunodeficiency virus type 1 replication in CD4(+) T lymphocytes

We investigated the effects of signaling through CD28 family molecules on human immunodeficiency virus type 1 (HIV-1) replication in vitro. A monoclonal antibody (mAb) specific for inducible costimulator (ICOS) suppressed both X4 and R5 HIV-1 replication in CD4(+) peripheral blood mononuclear cells (PBMC). This suppression was not attributable to reduced cell growth or viability. CD28 mAb showed variable effects and also suppressed HIV-1 replication when immobilized. Replication of pseudotype viruses with HIV-1-but not with vesicular stomatitis virus G-envelope was efficiently suppressed in CD4(+) PBMC treated with ICOS or CD28 mAbs. However, CD4, CXCR4, and CCR5 expression on the surface was not down-regulated. Moreover, HIV-1 replication in CD4(+) PBMC was suppressed by a soluble form of human B7-H2, a ligand of ICOS, but was enhanced by soluble B7-1, a ligand for CD28. These findings suggest that natural or artificial ligands for ICOS potentially suppress HIV-1 replication mainly at the entry stages.

In vivo administration of 15-deoxyspergulin inhibits antigen-presenting cell stimulation of T cells and NF-kappaB activation

15-Deoxyspergulin (DSG), a synthetic derivative of spergulin, was initially characterized for its antibiotic and antitumor effects. Recent studies have described the immunosuppressive properties of this molecule, but its mechanism of action is not clearly understood. In the study reported here, mice were treated in vivo with DSG prior to the measurement of IL-2 production and proliferation in an in vitro antigen presentation assay. At suboptimal antigen concentrations, elicited peritoneal macrophages or percoll isolated B cells from DSG-treated mice showed a 50-96% reduction in their ability to present chicken ovalbumin (cOva), cOva peptide, or superantigen (SAg) to MHC class II-matched antigen-specific primary T cells. No significant changes could be found in the cell surface expression of CD80, CD86, MHC I, MHC II, CD18, CD11b, CD40, CD25, and CD54 in antigen-presenting cells (APC) from control or DSG-treated animals. Activation with SAg of macrophages or splenocytes from DSG-treated mice revealed that there was a significant reduction in nuclear NF-kappaB levels compared to cells from untreated animals. Additionally, analysis of cytokines showed that production of TNF-alpha and IL-1beta was inhibited in cultures where macrophages from DSG-mice were used to present cOva to T cells. These results indicate that the effects of DSG in mice are not simply due to altered antigen processing or from any marked changes in cell surface antigen expression. Rather, the immunosuppression may arise from alterations in the release of one or more soluble factor from DSG-treated APC, which prevents effective antigen presentation and T cell activation.

Differential Effects of CD28 Costimulation on HIV Production by CD4+ Cells

We have observed that CD28 costimulation of CD4+ cells can have differential effects on HIV replication. Triggering the CD28 molecule on peripheral blood CD4+ cells during stimulation with anti-CD3 Abs enhances virus production following acute infection with HIV. Endogenous virus production in CD4+ cells from HIV-infected individuals is also increased by this procedure. The enhanced virus production occurs equally when anti-CD28 Abs and soluble forms of the natural ligands for CD28, CD80Ig, and CD86Ig are used to trigger CD28 on CD4+ cells during stimulation. This increased virus replication is observed only when the source of CD28 costimulation is removed immediately after stimulation and before infection. Continual exposure of CD4+ cells to anti-CD3 and CD28 Ab beads following acute infection prevents virus production. These findings may have relevance to therapeutic approaches aimed at inhibiting HIV replication by CD28 costimulation.

Sperm as infection-potentiating cofactors in HIV transmission

In this paper I will discuss the possible role of sperm as cofactors in the genital-mucosal transmission of HIV. The ideas involved arose from my laboratory's discovery that sperm bind to HLA-DR molecules expressed on somatic cells, and from our subsequent findings that lymphocytes are activated by these interactions. Sperm binding to HLA-DR mimics one of the two ligand binding characteristics of superantigens, which also bind to T-cell receptors in a V-beta-specific fashion. This property of sperm may be significant in HIV transmission because: (a) HLA-DR plays a central role in immune recognition and response; and (b) cell interactions involving HLA-DR are involved in HIV infection and disease development. After sexual contact, sperm elicit a transient leukocytic infiltration of the mammalian cervix (Thompson, L.A., Barratt, C.L., Bolton, A.E., Cooke, I.D., 1992. The leukocytic reaction of the human cervix. Am. J. Reprod. Immunol. 28, 85; Pandya, I.J., Cohen, J., 1985. The leukocytic reaction of the human uterine cervix to sperm. Fertil. Steril. 43, 417), and human cervical cells are bound and penetrated by sperm at this time (Sievers-Altermann, R., Engelbrecht, D.V., 1990. Entry of spermatozoa into the cervical mucosa and transmission of the AIDS virus. S. Afr. Med. J. 77, 319). At present, little is known about these in vivo events, but sperm-somatic cell interactions in vitro are also followed by sperm entry into the target cell cytoplasm and target cell activation. When the target cells are leukocytes, sperm interactions increase their susceptibility to HIV infection. If similar interactions occur in the cervicovaginal environment after sexual contact, they are likely to enhance the genital-mucosal transfer of HIV from semen.

CNI-H0294, a nuclear importation inhibitor of the human immunodeficiency virus type 1 genome, abrogates virus replication in infected activated peripheral blood mononuclear cells

Active nuclear importation of the human immunodeficiency virus (HIV) type 1 (HIV-1) preintegration complex (PIC) is required for the productive infection of nondividing cells, but it is believed to be dispensable for the infection of proliferating cells, such as activated T lymphocytes. To investigate this question, we exploited the properties of the small arylene bis (methyl ketone) compound CNI-H0294. We have previously shown that this compound associated with the HIV-1 matrix protein nuclear localization sequence and blocked binding of the HIV-1 PIC to yeast karyopherin alpha. CNI-H0294 abrogated nuclear importation of the HIV-1 genome in macrophages and effectively inhibited infection of nondividing cells. In this study we demonstrate that CNI-H0294 inhibits binding of the HIV-1 PIC to human karyopherin alpha and reduces nuclear importation of the viral genome in primary peripheral blood mononuclear cells (PBMCs). We also demonstrate that CNI-H0294 inhibits acute infection of PBMC cultures in vitro with a primary isolate of HIV-1 and reduces virus replication and virus load in cultures of endogenously infected PBMCs from seropositive individuals. Thus, as for infection of nondividing, terminally differentiated macrophages, HIV-1 uses active nuclear importation of the virus genome to infect activated CD4+ T cells. These results support nuclear importation as a novel target and CNI-H0294 and its derivatives as novel compounds for therapeutic intervention in HIV infection and AIDS.

Efficient virus transmission from dendritic cells to CD4+ T cells in response to antigen depends on close contact through adhesion molecules

Monocyte-derived cultured dendritic cells (DCs) are potent antigen-presenting cells (APCs) and are susceptible to HIV-1Lai infection. Compared to the low level of virus production by HIV-1-infected DCs alone, a level of virus two to three orders of magnitude higher was produced by cocultivation of HIV-1-infected DCs with autologous resting CD4+ T cells in the presence of a nominal antigen. In this coculture system, direct contact of HIV-1-infected DCs with T cells was crucial for efficient virus transmission and subsequent virus production. Blocking of the LFA-1/ICAM-1 or LFA-3/CD2 interaction between these cells substantially reduced virus production, without influence or IL-2 production by activated T cells. In contrast, cell-cell transmission of HIV between non-APCs and activated T cells was not blocked by an antibody against LFA-3. Since a low level of virus production by HIV-infected DCs was upregulated by cross-linking of CD40, it was suggested that not only focal adhesion, but also mutual activation of HIV-infected DCs and T cells through adhesion molecules, may potentiate virus transmission and production and that such activation signals to HIV may be distinct from signals responsible for IL-2 production in activated T cells.

TCR-independent CD28-mediated gene expression in peripheral blood lymphocytes from donors chronically infected with HIV-1

Complete activation of peripheral blood T cells requires both T-cell receptor (TCR) stimulation and CD28 costimulation. Signalling pathways associated specifically with CD28 are not well understood, however, because ligation of CD28 in the absence of TCR stimulation does not give rise to cellular responses in normal cells. In peripheral blood lymphocytes (PBL) from donors chronically infected with human immunodeficiency virus-1 (HIV-1), CD28 can induce viral replication through an alternative pathway that does not require TCR ligation. We have exploited this observation to study CD28-mediated signal transduction using reverse transcriptase-mediated polymerase chain reaction (RT-PCR) to amplify viral RNA. Independent ligation of CD28 on donor PBL induced expression of the HIV-1 tat gene but not the interleukin-2 (IL-2) gene. Viral induction did not occur following pretreatment of cells with actinomycin D, suggesting it was mediated through transcriptional activation of the viral long terminal repeat (LTR). tat was induced in the presence of the protein kinase C inhibitor H-7, but was inhibited by cyclosporin A. Our results demonstrate that CD28 is linked directly to specific signalling pathways leading to de novo induction of genes in PBL.

Pitfalls in the use of surrogate markers for human immunodeficiency virus disease: further evidence on pathogenesis

The administration of drugs to human immunodeficiency virus patients with a pronounced CD4+ T lymphocytopenia may cause non-specific binding of the murine antibodies used in flow cytometry. This has produced spurious reports of early thymocytes in the circulating blood of human immunodeficiency virus-infected individuals following treatment with an anti-adhesion monoclonal mouse antibody (Cytolin+). Recent clinical experience with Cytolin+ confirms the pathogenic role of leukocyte adhesion pathways in human immunodeficiency virus infection. However, this experience also illustrates how comparisons of viral burden can be misleading. For nine patients with low CD4 counts, Cytolin+ alone reduced the mean ribonucleic acid-polymerase chain reaction by 0.45 log to 39 800 particles per mL. Ten patients with more advanced disease added Cytolin+ to an established regimen of standard antiretroviral drugs. Their mean polymerase chain reaction was only reduced by 0.2 log to 91 501. Yet, 67% of the former patients experienced a major clinical event within seven months, whereas the latter patients remained stable during this time.

Interleukin-2 and human immunodeficiency virus infection: pathogenic mechanisms and potential for immunologic enhancement

A hallmark of human immunodeficiency virus (HIV) infection is the progressive loss of CD4+ T lymphocytes; however, qualitative defects in immune responses occur prior to the precipitous drop CD4+ T cell numbers. One of the first immunologic defects to be described in HIV-infected individuals is a deficiency in interleukin (IL)-2 production. The addition of IL-2 in vitro to cultures of mononuclear cells from HIV-infected individuals partially or completely restored certain defective cellular immune responses. However, production of or addition of IL-2 has also been associated with increased viral replication in infected T cells. These observations underscore the pernicious correlation between immune activation and HIV replication. However, recent in vitro and in vivo studies have provided promising preliminary results suggesting that, at least at certain stages of disease, the benefits of IL-2 mediated immune enhancement may outweigh or override the inductive effects of this cytokine on HIV production.

Rapid and reliable cloning of antibody variable regions and generation of recombinant single chain antibody fragments

Single chain antibody variable region fragments (sFv), by virtue of their size and method of construction are potentially useful as therapeutic reagents and as tools for exploring cell surface receptor function. sFv offer several advantages over the intact immunoglobulin molecule. For instance, they are expressed from a single transcript and can be molecularly linked to other proteins to generate bispecific sFv molecules or single-chain immunotoxins. The relatively small size of sFv is an advantage in allowing for easier penetrance into tissue spaces, and their clearance rate is exceedingly rapid. sFv are useful for gene therapy since they can be directed to a specific cellular localization and can be fused to retroviral env genes to control viral host range. To prepare sFv to murine and human leukocyte CD antigens, we devised a method for rapid cloning and expression that can yield functional protein within 2-3 weeks of RNA isolation from hybridoma cells. The variable regions were cloned by poly-G tailing the first strand cDNA followed by anchor PCR with a forward poly-C anchor primer and a reverse primer specific for constant region sequence. Both primers contain flanking restriction sites for insertion into PUC19. Sets of PCR primers for isolation of murine, hamster and rat VL and VH genes were generated. Following determination of consensus sequences for a specific VL and VH pair, the VL and VH genes were linked by DNA encoding an intervening peptide linker [usually (Gly4Ser)3] and the VL-link-VH gene cassettes were transferred into the pCDM8 mammalian expression vector. The constructs were transfected into COS cells and sFvs were recovered from spent culture supernatant. We have used this method to generate functional sFv to human CD2, CD3, CD4, CD8, CD28, CD40, CD45 and to murine CD3 and gp39, from hybridomas producing murine, rat, or hamster antibodies. Initially, the sFvs were expressed as fusion proteins with the hinge-CH2-CH3 domains of human IgG1 to facilitate rapid characterization and purification using goat anti-human IgG reagents or protein A. We also found that active sFv could be expressed with a small peptide > or = tag > or = or in a tail-less form. Expression of CD3 (G19-4) sFv tail-less or Ig tailed forms demonstrated increased cellular signalling activity and suggested that sFv have potential for activating receptors.

Costimulation of CD4+ T cells via CD28 modulates human immunodeficiency virus type 1 infection and replication in vitro

Stimulation of human immunodeficiency virus type 1 (HIV-1)-infected donor peripheral blood mononuclear cells (PBMCs) via the TCR-CD3 complex induces HIV-1 production in vitro (Zarling JM, et al.: Nature [London] 1990;347:92; Haffar OK, et al.: J Virol 1992;66:4279; Moran PM, et al.: AIDS Res Hum Retroviruses 1993;9:455). However, in addition to the primary stimulatory signal delivered through the TCR-CD3 complex, optimal T cell activation requires secondary or costimulatory signals delivered via various T cell accessory proteins (Alton A, et al.: Adv Immunol 1990;48:227). In this article we explore the role of costimulation of T cells via CD28 in HIV-1 replication. Ligation of CD28 with either a CD28-specific MAb or by coculture of PBMCs with Chinese hamster ovary (CHO) cell lines stably expressing either of the CD28 counterreceptors, B7-1 (CD80) or B7-2 (CD86), concomitant with stimulation via CD3, results in increased virus replication compared to stimulation via CD3 alone. CD28 ligation also augments de novo infection of CD3-stimulated seronegative donor PBMCs with cell-free virus. Increased virus replication following CD28 ligation is not solely attributed to increased levels of endogenous IL-2, because addition of an anti-IL-2-neutralizing antibody only partially inhibits the response. In contrast, interfering with the interaction between CD28 and its counterreceptors on antigen-presenting cells (APCs) using CTLA4Ig effectively inhibits virus replication. At high concentrations CTLA4Ig also reduces cell proliferation. These in vitro results suggest that CD28 plays a central role in HIV-1 replication and that interfering with the CD28 costimulatory pathway may modify the course of HIV-1 infection.

Leukocyte adhesion molecules as a cofactor in AIDS: basic science and pilot study

It is well known that the AIDS pandemic is a consequence of pandemic HIV infection. However, Koch's postulates are not satisfied for two reasons: 1) AIDS cannot be experimentally produced in animals susceptible to HIV infection and 2) some people have AIDS (idiopathic CD4+ T lymphocytopenia) in the absence of HIV infection. It follows that there is a human immunologic cofactor (HIC) that causes AIDS when certain other conditions are satisfied, and the most common of these other conditions (but not the only one) is HIV infection. Results from microbiology make leukocyte adhesion molecules a good candidate for the HIC. We have tested this hypothesis with a pilot study in which a small number of patients with HIV disease were infused with a monoclonal mouse antibody (MmAb) directed against an LFA-1 adhesion epitope, and then with F(ab) and F(ab)2' fragments that bind to the same epitope but are nonimmunogenic. Both agents reduced peripheral viral burden significantly but fragments were more effective in this respect than the MmAb due to the mitogenic properties of the latter. For the same reason, only the MmAb were highly effective in raising circulating levels of single and double-marked CD4+ T lymphocytes, with a correlated resolution of cutaneous anergy.

Cell surface phenotypic changes induced in H9 T cells chronically infected with HTLV type I or HIV type 1 or coinfected with the two viruses

To investigate whether HTLV-I infection, HIV-I infection, or HIV-I infection of HTLV-I-infected cells affect the expression of cellular surface molecules, an HTLV-I-infected T cell line derived from the H9 T cell line was established (H36). H9 cells uninfected or infected with HTLV-I were then infected with HIV-1. We have compared the density of different surface markers on these three infected H9 T cell lines. These markers consist of T cell-specific antigens (CD2, CD3, CD4, and CD8), activated T cell antigens (CD25 and CD71), major histocompatibility complex (MHC) antigens (class I and II), and adhesion molecules (LFA-1 and ICAM-1). The experiments reported in this article show that chronic HTLV-I infection, HIV-1 infection, and HIV-1 infection of HTLV-I-infected T cells modulate the expression of several immunologically important cell surface antigens. The nature and the extent of T lymphoid cell phenotypic modulation depend on the infecting virus. Furthermore, HTLV-I and HIV-1 interact with each other in the phenotypic modulation of coinfected cells.

Expression patterns of Fc gamma receptors, HLA-DR and selected adhesion molecules on monocytes from normal and HIV-infected individuals

The expression and co-expression profiles of functionally important monocyte surface markers were compared between control and HIV+ individuals using combined physical gating and dim CD4 expression to delineate the monocytes. The Fc gamma RII (CD32), the MHC class II antigen HLA-DR and the adhesion molecules CD11a (LFA-1 alpha), CD18 and CD54 (ICAM-1) showed an unimodal distribution. Of these markers, CD11a and HLA-DR were up-regulated in the HIV+ subjects compared with controls. The expression levels of the adhesion molecules correlated with each other in both patients and controls. The CD11b (CR3-alpha), CD14, Fc gamma RI, and Fc gamma RIII markers were bimodally distributed. Compared with controls, monocytes from seropositives contained fewer CD14bright+ cells, an equal proportion of Fc gamma RIbright+ cells, but twice as many Fc gamma RIII+ cells. The expression level of Fc gamma RI and CD11b within their brightly positive subset increased as CD4 T cells decreased. Both in patients and controls, co-expression of bright CD11b, CD14 and Fc gamma RI was shown, whereas the Fc gamma RIII+ cells were negative or dim positive for the former triad. We conclude that the expression of two Fc gamma R (I and III), of the adhesion molecules CD11a and CD11b and of HLA-DR showed particular alterations on monocytes from HIV+ subjects. The relationship of these phenotypic observations with altered cytokine profiles and altered monocyte function is discussed.

The role of CD40 and CD80 accessory cell molecules in dendritic cell-dependent HIV-1 infection

We investigated the role of blood dendritic cells (DCs) in transmission of HIV-1 from infected to uninfected CD4+ T cells, and the accessory molecules involved. DCs promoted transmission from infected to uninfected CD4+ cells, but DCs themselves were not infectable. DC-mediated transmission was blocked by MAb to CD4 and MHC class II, but strongly increased by MAb to CD40 on DCs or CD28 on T cells. The DC-dependent infection was inhibitable by anti-CD80 and a soluble fusion protein of the CD80 ligand, CTLA4; soluble CTLA4 immunoglobulin also blocked infection augmented by cross-linking CD40. These data suggest a linkage between CD40-CD40L and CD28-CD80 counterreceptors on DCs and T cells, and spread of HIV infection in vivo.

Costimulation of T-cell activation and virus production by B7 antigen on activated CD4+ T cells from human immunodeficiency virus type 1-infected donors

Infection with the human immunodeficiency virus type 1 (HIV-1) requires T-cell activation. Recent studies have shown that interactions of the T-lymphocyte receptors CD28 and CTLA-4 with their counter receptor, B7, on antigen-presenting cells are required for optimal T-cell activation. Here we show that HIV-1 infection is associated with decreased expression of CD28 and increased expression of B7 on CD4+ T-cell lines generated from seropositive donors by alloantigen stimulation. Loss of CD28 expression was not seen on CD4+ T-cell lines from seronegative donors, but up-regulation of B7 expression was observed upon more prolonged culture. Both T-cell proliferation and interleukin 2 mRNA accumulation in HIV-1-infected cultures required costimulation with exogenous B7 because these events were blocked by CTLA4Ig, a soluble form of CTLA-4 that binds B7 with high avidity. In contrast, levels of HIV-1 RNA were not affected by CTLA4Ig, indicating that regulation of virus transcription in these cultures did not depend upon CD28-B7 engagement. Infected T cells could present alloantigen to fresh, uninfected CD4+ T cells, leading to increased proliferation and virus spread to the activated cells. Both of these events were blocked by CTLA4Ig. Thus, chronic activation of HIV-1-infected CD4+ T cells reduces expression of CD28 and increases expression of B7, thereby enabling these T cells to become antigen-presenting cells for uninfected CD4+ T cells; this might be another mechanism for HIV-1 transmission via T-cell-T-cell contact.

Regulation of HIV production by blood mononuclear cells from HIV-infected donors: I. Lack of correlation between HIV-1 production and T cell activation

The relationship between production of HIV-1 by peripheral blood mononuclear cells (PBMCs) from HIV-1-infected donors and the level of T cell activation by various stimuli was examined. Stimulation of PBMCs with soluble anti-CD3 antibody or staphylococcal enterotoxin/superantigen (SAg) was found to be 100-1000 times more effective at inducing production of HIV-1 than was stimulation with immobilized anti-CD3 or various other T cell activating agents. However, proliferation of CD4+ T cells and lymphokine production following stimulation with soluble anti-CD3 were less than with immobilized anti-CD3. To determine whether immobilized anti-CD3 stimulated cells may produce a factor(s) that suppresses HIV production, dual-chamber coculture experiments were performed in which soluble and immobilized anti-CD3-stimulated CD8-depleted PBMCs were separated by porous membranes. Stimulation of cells by immobilized anti-CD3 suppressed HIV-1 production by soluble anti-CD3-stimulated cells in the inner chamber, suggesting that diffusible factor(s) are involved in suppressing HIV-1 production. Experiments in which exogenous cytokines were added to cells stimulated with soluble anti-CD3 did not reveal the suppressive factor(s) produced; however, IL-7 was found to markedly increase HIV-1 production. Both T cells and monocytes were found to be required for soluble anti-CD3 to induce high levels of HIV-1 production, suggesting a role for adhesion molecules. Our results thus show that (1) soluble anti-CD3 is a powerful stimulus for HIV production, (2) there is not an absolute correlation between the level of HIV-1 production and T cell activation following stimulation of PBMCs with T cell activating agents, (3) immobilized anti-CD3 stimulation produces a factor that decreases HIV replication, and (4) T cell monocyte interactions are important for production of HIV-1 following stimulation with soluble anti-CD3.