Rapid Prescreening for Antiviral Agents against HIV-1 Based on Their Inhibitory Activity in Site-Directed Immunoassays. Approaches Applicable to Epidemic HIV-1 Strains

Several compounds, including the triphenylmethane derivative aurintricarboxylic acid (ATA) and porphyrins, were reported to inhibit the binding of anti-V3 loop-specific antibodies to the V3 loop of gp120 from HIV-1 III-B and to have antiviral activity, probably due to interference with the biological function of the V3 loop. However, these compounds can be applied to antiviral chemotherapy only if they interact with envelope glycoproteins from a multitude of epidemic HIV-1 strains and inhibit their replication. Since recombinant envelope glycoproteins, synthetic peptides and anti-V3 monoclonal antibodies may not be available for these HIV-1 strains, alternative assays are needed to prescreen different compounds for potential antiviral activity against these viruses. Results presented here indicate that: (1) virions of HIV-1 MN, most closely related to primary HIV-1 isolates from European and North American countries, and human anti-HIV-1 antibodies, can also be used for rapid prescreening of antiviral agents, (2) compounds with antiviral activity against HIV-1 MN, discerned by site-directed immunoassays, inhibited the reaction of human anti-HIV-1 with a V3 loop consensus peptide corresponding to European/North American HIV-1 isolates, and (3) meso-tetra (4-carboxyphenyl) porphine (MTCPP), one of the most potent inhibitors of HIV-1 replication selected on the basis of site-directed immunoassays, preferentially attached to the V3 loop of gp120.

Tin Protoporphyrin IX Used in Control of Heme Metabolism in Humans Effectively Inhibits HIV-1 Infection

Recent observations indicated that several porphyrins bound to the V3 loop of the envelope glycoprotein gp120 of the human immunodeficiency virus type 1 (HIV-1) and inhibited infection of cells by HIV-1. The tin derivative of protoporphyrin IX (Sn-PTP-IX) has already been used clinically in humans to suppress hyperbilirubinemia. It was therefore of interest to determine whether Sn-PTP-IX has anti-HIV-1 activity. It is demonstrated here that Sn-PTP-IX effectively inhibited infection by several HIV-1 isolates (HIB, MN, RF, SF-2 and two isolates resistant to azidothymidine). This was surprising, since earlier studies indicated that incorporation of other metals into porphyrins markedly decreased their antiviral activity. Sn-PTP-IX blocked the binding to gp120 of anti-V3-loop-specific antibodies and of monoclonal antibodies specific for the CD4 binding site on gp120. The latter effect appeared to be allosteric and was not observed with a deletion mutant of gp 120 lacking the V3 loop sequence. This suggests that Sn-PTP-IX binds to the V3 loop and distorts the native conformation of the HIV-1 envelope, thereby preventing infection. These results merit the consideration of Sn-PTP-IX as a prophylactic and chemotherapeutic agent against HIV-1.

Rapid Prescreening for Antiviral Agents against HIV-1 Based on Their Inhibitory Activity in Site-Directed Immunoassays. I. The V3 Loop of gp 120 as Target

The anionic triphenylmethane derivative aurintricarboxylic acid (ATA) was reported to inhibit the replication and cytopathogenicity of human immunodeficiency virus type 1 (HIV-1). This antiviral effect, ascribed to the inhibitory activity of ATA on the virus reverse transcriptase, was subsequently also explained by binding of ATA to the HIV-1 envelope glycoprotein gp120 and/or to the CD4 receptor for the virus. Results presented here show: (1) the effectiveness of ATA as a potential antiviral drug by demonstrating that HIV-1 replication in vitro can be completely aborted in the presence of ATA as measured by the polymerase chain reaction; (2) that ATA inhibited the reaction between gp120 and antibodies specific for the V3 hypervariable loop of gp120; (3) that additional compounds with anti-HIV-1 activity can be rapidly identified based on their inhibitory effects measured by radioimmunoassays and/or enzyme-linked immunoadsorbent assays; and (4) that ATA also bound to synthetic peptides representing V3 loops of several HIV-1 isolates, suggesting the possibility that selected chemicals would interfere with the biological function of V3 loops of most HIV-1 isolates and would be effective for chemotherapy, and possibly for prophylaxis, of HIV-1 infections.

Rapid Prescreening for Antiviral Agents against HIV-1 Based on Their Inhibitory Activity in Site-Directed Immunoassays. II. Porphyrins Reacting with the V3 Loop of gp120

Recent observations that haernin inhibited the replication of the human immunodeficiency virus (HIV-1) and the reaction between the HIV-1 envelope glycoprotein gp120 and antibodies specific for the V3 hypervariable loop of this glycoprotein were an enticement to determine whether or not additional porphyrins had similar activities. Several porphyrin derivatives, particularly meso-tetra (4-carboxyphenyl) porphine, were more potent inhibitors of HIV-1 replication than haernin. They blocked the binding of homologous antibodies to synthetic peptides corresponding to V3 hypervariable loops of 21 distinct HIV-1 isolates, and inhibited the replication in lymphocytic (MT-2) and promonocyte (U937) cell lines of several HIV-1 isolates, tested (IIIB, RF, SF-2, and MN). Compounds with inhibitory activity had a tetrapyrrole ring and, carboxyl or sulphonate groups. However, antiviral activity depended on minor structural difference's between distinct derivatives endowed with these two features. Metalloporphyrins had a drastically reduced antiviral activity in comparison with the corresponding porphyrins. An understanding of the relationship between the structure of porphyrins and their antiviral effects, perceptible from the results presented, is expected to lead to the design of additional derivatives with more potent antiviral activity and to unravelling of molecular details involved in the association between the V3 loop of gp120 and antiviral compounds targeted to this loop.

3-Hydroxyphthaloyl-β-Lactoglobulin. II. Anti-Human Immunodeficiency Virus Type 1 Activity in in Vitro Environments Relevant to Prevention of Sexual Transmission of the Virus

It is anticipated that the rate of sexual transmission of viruses could be substantially decreased by the use of topical chemical barrier methods. Chemical modification of bovine (β-lactoglobulin (β-LG), the major protein of whey, led to the generation of a potent inhibitor (designated 3HP-β-LG) of human immunodeficiency virus type 1 (HIV-1) infection which was also active against herpesviruses. Compounds intended for topical application to prevent sexual transmission of viruses need to maintain their antiviral activity at pH <<7, corresponding to an acidic vaginal environment, and in the presence of seminal fluid. Results presented here show that the binding of 3HP-β-LG to the CD4 receptor for HIV, involved in the anti-HIV-1 activity of this compound, decreases with decreasing pH. The presence of seminal fluid also decreased the binding of 3HP-β-LG to CD4 and diminished the inhibitory effect of the compound on CD4-gp120 binding. 3HP-β-LG was shown to bind Zn++, and the inhibitory effect of seminal fluid could be substantially diminished by chelating Zn++ with ethylenediaminetetraacetate. Saliva had no effect on 3HP-β-LG binding to CD4 or on its interference with gp120-CD4 binding. The decreased 3HP-β-LG-CD4 binding and the concomitant reduction of gp120-CD4 binding inhibition by 3HP-β-LG at low pH and in the presence of seminal fluid could be compensated for by an increase of the 3HP-β-LG concentration and by adding Zn++ chelators to 3HP-β-LG. These results provide a background for the design of 3HP-β-LG formulations for topical use.

3-Hydroxyphthaloyl-β-Lactoglobulin. I. Optimization of Production and Comparison with other Compounds Considered for Chemoprophylaxis of Mucosally Transmitted Human Immunodeficiency Virus Type 1

Modification of the major bovine whey protein, β-lactoglobulin (β-LG) by 3-hydroxyphthalic anhydride (3HP) leads to the generation of a potent inhibitor of infection by human immunodeficiency virus (HIV) types 1 and 2, designated 3HP-β-LG. 3HP-β-LG also has antiviral activity against herpesviruses, albeit at concentrations exceeding those required for inhibition of HIV-1 infection. The topical application of 3HP-β-LG to decrease the rate of sexual transmission of HIV and other sexually transmitted viruses worldwide is being considered. Results presented here: (i) define the conditions for chemical modification of β-LG by 3HP, resulting in 3HP-β-LG with optimum anti-HIV-1 activity; (ii) show that β-LG, prior to chemical modification, or 3HP-β-LG can be exposed to the elevated temperatures used to pasteurize milk without adversely affecting anti-HIV-1 activity; (iii) provide evidence that 3HP-β-LG is a more potent anti-HIV-1 compound than sulphated polysaccharides, other candidate compounds considered as prophylactic agents to prevent sexual transmission of HIV-1; and (iv) confirm that the primary target for 3HP-β-LG is CD4, although binding to the HIV-1 envelope protein gp120 was also observed and contributed to the antiviral activity of 3HP-β-LG.

Anti-human immunodeficiency virus type 1 microbicide cellulose acetate 1,2-benzenedicarboxylate in a human in vitro model of vaginal inflammation

The sexual transmission of human immunodeficiency virus type 1 (HIV-1) is facilitated by inflammation and related epithelial barrier perturbation. Microbicides for vaginal applications are currently being developed to reduce the risk of HIV-1 transmission. However, little is known about their interference with epithelial immune function. In recent clinical trials, nonoxynol-9 (N-9), a virucide with a long history of intravaginal use as a contraceptive, failed to protect against HIV-1 possibly due to mucosal inflammatory damage. Cellulose acetate 1,2-benzenedicarboxylate, also named CAP (for "controls AIDS pandemic"), is an anti-HIV-1 microbicide selected from pharmaceutical excipients that are regarded as safe for oral administration but have not been assessed for potential effects on inflammatory factors in the vaginal environment. Here we use a sensitive human cell culture system to evaluate proinflammatory profiles of soluble CAP in reference to N-9 and known epithelial activators such as tumor necrosis factor alpha (TNF-alpha) and bacterial lysates. Within 6 h of exposure, TNF-alpha and N-9 triggered NF-kappaB and AP-1/cFos activation and upregulated interleukins and an array of chemokines by vaginal and polarized cervical epithelial cells. The induced proinflammatory status continued after removal of stimuli and was confirmed by enhanced transepithelial neutrophil migration. While sustaining stability and anti-HIV-1 activity in the epithelial environment, CAP did not increase the production of proinflammatory mediators during or after exposure, nor did it modify the epithelial resistance to leukocyte traffic. CAP attenuated some TNF-alpha-induced responses but did not interfere with epithelial cytokine responsiveness to gonococcal determinants. The described system may be useful for predicting proinflammatory side effects of other microbicide candidates for vaginal application.

Design of a "microbicide" for prevention of sexually transmitted diseases using "inactive" pharmaceutical excipients

The human immunodeficiency virus (HIV-1) pandemic has been driven primarily by the sexual transmission of the virus, and facilitated by prior infections with other sexually transmitted disease (STD) pathogens. Although treatment of these STDs has been proposed as a means to decrease the rate of HIV-1 sexual transmission, preventive measures effective against both HIV-1 and other STD pathogens are expected to have a larger impact. These measures include topically applied mechanical and chemical (i.e. microbicidal) barriers. Microbicides of preference should have a broad specificity against diverse STD pathogens and a well established safety record, considering their repeated use over decades. Here, we report that cellulose acetate phthalate (CAP), an "inactive" pharmaceutical excipient, commonly used in the production of enteric tablets and capsules: (1) has antiviral activity against HIV-1 and several herpesviruses (HSV); and (2) when appropriately formulated, in micronized form, inactivates HIV-1, HSV-1, HSV-2, cytomegalovirus, Neisseria gonorrhoeae, Trichomonas vaginalis, Haemophilus ducreyi and Chlamydia trachomatis but does not affect Lactobacilli, components of the natural vaginal flora contributing to resistance against STDs. Thus, the CAP formulations meet the criteria for preferred microbicides and warrant further evaluation in vivo in humans.

3-Hydroxyphthaloyl beta-lactoglobulin. III. Antiviral activity against herpesviruses

The spread of sexually transmitted diseases, including human immunodeficiency virus type 1 (HIV-1) and herpesvirus infections, has continued unabated despite educational efforts spearheaded as a response to the HIV-1 epidemic. This suggests the need for prophylactic measures, including the application of topical antiviral agents. Chemical modification of bovine beta-lactoglobulin (beta-LG), the major protein of whey, by hydroxyphthalic anhydride (3HP) led to the generation of a potent HIV-1 inhibitor (designated 3HP-beta-LG) shown to also have activity against herpes simplex virus types 1 and 2 (HSV-1, HSV-2). This report provides more detailed results concerning the anti-herpesvirus activity of 3HP-beta-LG, indicating that this compound: (i) inhibited infection by human cytomegalovirus (HCMV), which is known to be sexually transmitted; (ii) inactivated the infectivity of both HSV-1 and HSV-2; (iii) inhibited cell-to-cell transmission of HSV-1 and HSV-2; and (iv) bound to HSV-1, HSV-2 and HCMV virus particles and partially inhibited the binding of anti-glycoprotein E (gE) and anti-gC monoclonal antibodies to HSV-1 and HSV-2. The binding of 3HP-beta-LG to the herpesviruses under study was inhibited by aggregated human IgG, suggesting that the respective viral Fc receptor is one of the target sites for 3HP-beta-LG. In agreement with results on inhibition of HIV-1 infection, 3HP-beta-LG appears to be the acid anhydride-modified protein of choice as an antiviral agent against herpesviruses.

Glycodelins GdA and GdS modified by 3-hydroxyphthalic anhydride inhibit gp120-CD4 binding and HIV-1 infection in vitro

Bovine beta-lactoglobulin chemically modified with 3-hydroxyphthalic anhydride (3HP) was recently shown, at nanomolar concentrations, to block the binding site on CD4 for the HIV surface glycoprotein (gp120), potentially inhibiting HIV transmission. Human glycodelin has sequence homology with bovine beta-lactoglobulin and appears as different glycoforms in endometrium (GdA) and seminal plasma (GdS). We studied the anti-HIV effects of chemically modified GdA and GdS on both the infection of MT-2 cells by HIV-1IIIB, and the infection of peripheral blood mononuclear cells by the primary HIV isolate THA/93/051 belonging to subtype E. Whereas the native proteins were inactive when tested at physiologic concentrations, nanomolar concentrations of either 3HP-GdA or 3HP-GdS inhibited the production of HIV nucleocapsid p24, cytopathic effects of HIV-1IIIB, and infection of peripheral blood mononuclear cells by the primary HIV isolate THA/93/051. Moreover, both modified proteins inhibited gp120-CD4 binding, 3HP-GdS being more potent than 3HP-GdA (p = 0.0042). Because GdA and GdS have the same major protein core, the observed difference in gp120-CD4 binding must depend on the specific glycoform. In view of the previously reported contraceptive activity of GdA, the observed anti-HIV activity induced by its chemical modification should be of special interest in the development of antiviral strategies that may also have contraceptive effects.

Bovine beta-lactoglobulin modified by 3-hydroxyphthalic anhydride blocks the CD4 cell receptor for HIV

Sexual transmission is the most frequent (86%) route of adult HIV-1 transmission worldwide. In the absence of a prophylactic anti-HIV vaccine, other methods of preventing infection should be implemented. Virucidal spermicides have been considered for this purpose, but their application is contraindicated by adverse effects. Anti-HIV drugs or virus-neutralizing monoclonal antibodies are expensive, suggesting that their wide use in topical chemoprophylaxis is unlikely. This emphasizes the importance of developing other methods for preventing HIV transmission. The target cells for sexual and mucosal HIV transmission include T lymphocytes, monocytes/macrophages and dendritic cells. Therefore, compounds blocking HIV-CD4 binding are expected to inhibit virus transmission. In exploring the possibility that chemical modification of food proteins might lead to compounds with anti-HIV-1 activity, we found that bovine beta-lactoglobulin (beta-LG) modified by 3-hydroxyphthalic anhydride (3HP-beta-LG) (1) blocked at nanomolar concentrations the binding to CD4 of human (HIV) and simian (SIV) immunodeficiency virus surface glycoproteins and monoclonal antibodies specific for the HIV binding site on CD4 and (2) inhibited infection by HIV-1, including primary virus isolates, by HIV-2 and by SIV. The inexpensive and widely available source (whey) for production of 3HP-beta-LG suggests its potential application (nonparenteral) for diminishing the frequency of HIV transmission.

Structural requirements for and consequences of an antiviral porphyrin binding to the V3 loop of the human immunodeficiency virus (HIV-1) envelope glycoprotein gp120

Several porphyrin derivatives were reported to have anti-HIV-1 activity. Among them, meso-teta(4-carboxyphenyl)porphine (MTCPP) and other carboxyphenyl derivatives were the most potent inhibitors (EC50 <0.7 mu M). MTCPP bound to the HIV-1 envelope glycoprotein gp120 and to full-length V3 loop peptides corresponding to several HIV-1 isolates but not to other peptides from gp120 + gp41. However, it remained possible that MTCPP bound to regions on gp120 which cannot be mimicked by peptides. Further characterization of the binding domain for MTCPP is important for understanding the antiviral activity of porphyrins and for the design of anti-HIV-1 drugs interfering with functions of the virus envelope. Results presented here show that: (i) deletion of the V3 loop from the gp120 sequence resulted in drastically diminished MTCPP binding, suggesting that the V3 loop is the dominant if not the only target site on gp120; (ii) this site was only partially mimicked by full-length V3 loop peptides; (iii) MTCPP binding to the gp120 V3 loop elicited allosteric effects resulting in decreased accessibility of the CD4 receptor binding site; (iv) the binding site for MTCPP lies within the central portion of the V3 loop (KSIHIGPGRAFY for the HIV-1 subtype B consensus sequence) and does not involve directly the GPG apex of the loop. These results may help in designing antiviral compounds with improved activity.

Blocking of CD4 cell receptors for the human immunodeficiency virus type 1 (HIV-1) by chemically modified bovine milk proteins: potential for AIDS prophylaxis

The chemical transformation of synthetic combinatorial libraries to increase the diversity of compounds of medicinal interest was reported recently. Chemical modification of natural products represents a complementary approach to accomplish this aim. Modification of lysines by aromatic acid anhydrides, preferentially by 3-hydroxyphthalic and trimellitic anhydrides and trimellitic anhydride chloride, converted commonly available proteins (human and bovine serum albumin and casein) into potent inhibitors of (i) binding between the HIV-1 gp 120 envelope glycoprotein and the CD4 cell receptor, probably owing to their binding to CD4, and (ii) infection by HIV-1. Modified bovine milk proteins are also potent HIV-1 inhibitors and may have potential for anti-HIV-1 prophylaxis.

Multifaceted consequences of anti-gp41 monoclonal antibody 2F5 binding to HIV type 1 virions

A human monoclonal antibody (MAb) (2F5) neutralizing a variety of laboratory strains and clinical isolates of the human immunodeficiency virus type 1 (HIV-1) and binding to an epitope of the envelope glycoprotein gp41 encompassing the amino acid sequence ELDKWA has been described (Muster T et al., J Virol 1993;67:6642-6647). It was suggested that an immunogen eliciting virus-neutralizing antibodies having a specificity similar to that of MAb 2F5 should be considered as a component of HIV-1 vaccines. Efforts in this direction would benefit from understanding the mechanism whereby MAb 2F5 neutralizes the infectivity of HIV-1. The segment of gp41 encompassing residues ELDKWA has so far not been directly implicated in initiation of infection by HIV-1, suggesting that MAb 2F5 might affect other sites on HIV-1 envelope glycoproteins playing a role in virus entry into target cells. We provide here evidence that MAb 2F5 binding to HIV-1 virus particles decreases the accessibility or conformation of the gp41 fusion domain and of gp120 domains, including the binding site for the CD4 cell receptor. These apparently indirect consequences of MAb 2F5 binding to HIV-1 are likely to account for or contribute to the virus-neutralizing activity of this MAb.

The putative cell receptors for hepatitis B virus (HBV), annexin V, and apolipoprotein H, bind to lipid components of HBV

Annexin V and apolipoprotein H, reported to bind hepatitis B surface antigen (HBsAg) and presumed to react specifically with the HBsAg S protein and to play an important role in initiation of infection by hepatitis B virus, did not bind to delipidated HBsAg (dlHBsAg). Binding activity was restored by adding lipids to dlHBsAg. These results are consistent with the established affinity of annexin V and apolipoprotein H for lipids.

Three-dimensional structure-activity analysis of a series of porphyrin derivatives with anti-HIV-1 activity targeted to the V3 loop of the gp120 envelope glycoprotein of the human immunodeficiency virus type 1

Using comparative molecular field analysis (CoMFA), a 3D-QSAR model was developed for 21 porphyrin derivatives which have anti-HIV-1 activity and bind to the V3 loop of the envelope glycoprotein gp120 of the human immunodeficiency virus type 1. A significant PLS cross-validated r2cv (0.590) was obtained, indicating that the model could be used as a predictive tool for further design of porphyrin analogs. The model revealed at least three important sites for favorable electrostatic interactions and indicated favorable and unfavorable steric interaction sites. It was found that the occurrence of at least three positively charged and several hydrophobic amino acid residues is highly conserved at fixed positions of gp120 V3 loop sequences. This may support the validity of the proposed model and the hypothesis that porphyrins containing anionic and hydrophobic groups may interact with some of the highly conserved positively charged and hydrophobic sites, respectively, of the V3 loop. These interactions may induce conformational changes in the gp120 envelope glycoprotein leading to inhibition of virus entry into cells and of syncytium formation (cell-to-cell fusion) and thus to inhibition of virus replication.

Improbability of harmful autoimmune responses resulting from immunization with HIV-1 envelope glycoproteins

Autoimmunity mediated by cross-reactive antibodies, elicited by HIV-1 envelope glycoproteins gp120/gp160, has been postulated to contribute to the pathogenesis of AIDS. Partial amino acid sequence homology between gp120/gp160 and several human host proteins, including MHC antigens and immunoglobulins, has been perceived as the basis for immunological cross-reactivity. Binding of antibodies from sera of HIV-1-infected individuals to selected host proteins and/or to synthetic peptides derived from them and the inhibitory activity of such sera in assays measuring the functional activity of T cells provided apparent support for the autoimmunity hypothesis, which is also relevant to the issue of safety of anti-HIV-1 vaccines. Considering the possibility that the detected autoantibodies may arise for reasons other than antibody responses to gp120/gp160, the immunological cross-reactivity between gp120/gp160 and the relevant host proteins was investigated using hyperimmune rabbit anti-gp120/gp160 and monoclonal antibodies. As determined from dilution end-point comparisons for polyclonal anti-gp120, the cross-reactivity of anti-gp120 with CD4 was undetectable (< 10(-5)%). The cross-reactivity of anti-gp120/gp160 with HLA-I and HLA-II antigens was also undetectable (< 4 x 10(-4)%) and that with other human proteins reported to have partial sequence homology with gp120/gp41 was < or = 0.013%. Anti-gp120/gp160 did not have detectable inhibitory effects in functional assays measuring proliferative T cell responses. Therefore, immunization with gp120/gp160 is unlikely to elicit harmful autoimmune responses.

Inhibition of HIV-1 infection by a fusion domain binding peptide from the HIV-1 envelope glycoprotein GP41

A synthetic peptide, corresponding to the sequence (637-666) of the HIV-1 glycoprotein gp41, inhibited the replication of an array of HIV-1 strains. The peptide (637-666) selectively binds to the fusion domain at the N-terminus of gp41, suggesting that inhibition of HIV-1 infection is caused by blocking fusion of HIV-1 with cells or of infected cells with uninfected cells. Since this peptide has antiviral activity against both homologous and heterologous HIV-1 isolates and has no detectable cytotoxicity, it offers a novel approach to chemotherapy and prophylaxis of AIDS.

Cells transfected with human interleukin 6 cDNA acquire binding sites for the hepatitis B virus envelope protein

Earlier studies revealed that human interleukin 6 (IL-6) contains recognition sites for the hepatitis B virus (HBV) envelope (env) protein, and that IL-6 and anti-IL-6 antibodies, respectively, inhibited the interaction of cells expressing a receptor for HBV with the preS(21-47) segment of the HBV env protein, encompassing the complementary attachment site for IL-6. This suggested that IL-6 mediates HBV-cell interactions. We report that: (a) Chinese hamster ovary cells transfected with human IL-6 cDNA and Spodoptera frugiperda ovarian insect cells infected with recombinant baculovirus carrying human IL-6 cDNA expressed receptors for the preS(21-47) region of the HBV env protein, indicating that expression of IL-6 on the surface of cells is sufficient to endow them with receptors for HBV. (b) Among peptides covering the entire sequence of human IL-6 and the corresponding antipeptide antibodies, the peptide IL-6[35-66] and anti-IL-6[35-66] most effectively inhibited the interaction between human hepatoma HepG2 cells and the preS(21-47) ligand, suggesting that this region of the human IL-6 sequence encompasses a binding site for the HBV env protein. (c) Studies with replacement set peptides from the preS(21-47) sequence indicated that residues 21-25, 28, 31, 33-35, 39, and 43-45 can be replaced by alanine (serine) residues, while all the other residues are essential for maintaining the cell receptor/IL-6 binding activity. Further delineation of complementary sites on IL-6 and on the HBV env protein may contribute to the design of compounds inhibiting HBV replication.

Synthetic peptides and anti-peptide antibodies as probes to study interdomain interactions involved in virus assembly: the envelope of the human immunodeficiency virus (HIV-1)

Synthetic peptides and anti-peptide antibodies have been widely used as probes to map B- and T-cell epitopes on proteins. Such probes also have the potential to delineate contact sites involved generally in protein-protein interactions or in association of domains within a protein. We applied peptide/anti-peptide probes to define: (1) regions on the human immunodeficiency virus type 1 (HIV-1) envelope glycoproteins gp120 and gp41 involved in the association between these two glycoproteins; and (2) sites on gp120/gp41, essential for the association of HIV-1 with the CD4 cell receptor. Results of this examination suggested the following: (1) two segments on gp120, encompassing residues (102-126) and (425-452), contribute to the binding site for CD4 and are expected to be juxtaposed in the folded gp120 chain; (2) portions of immunodominant gp120 and gp41 epitopes, encompassing residues (303-338) and (579-611), respectively, appeared to be involved in the gp120-gp41 association, as suggested by direct binding studies and by the limited accessibility of these epitopes on HIV-1 virions: other portions of gp120 also appeared to contribute to the association between these two glycoproteins; (3) there is a partial overlap between gp41 and CD4 binding sites on gp120; (4) the fusion domain and a segment (637-666) of gp41 are not accessible to antibodies after oligomerization of gp41; and 5) the gp120-gp41 association was blocked by aurintricarboxylic acid, suggesting the possibility of developing antiviral compounds interfering with HIV-1 assembly.

Search for hepatitis B virus cell receptors reveals binding sites for interleukin 6 on the virus envelope protein

The major target organ for hepatitis B virus (HBV) is the liver. However, cells other than hepatocytes, including peripheral blood lymphocytes and monocytes, may become infected with HBV. The cell receptor binding site was assigned to the preS(21-47) segment of the HBV envelope protein. HBV receptors were detected on human liver and hepatoma cells, on B lymphocytes, and, as shown here, on monocytes, and T cell lines, activated by Escherichia coli lipopolysaccharide and concanavalin A, respectively. The cell receptors for HBV have not been characterized until now. The detection of HBV receptors and their "activation antigen" characteristic on distinct cells suggested paths for identification of the receptors with already defined cell surface proteins. This search revealed that interleukin 6 contains recognition sites for the preS(21-47) sequence and mediates HBV-cell interactions. Thus, HBV belongs to a group of viruses utilizing cytokines or cytokine receptors for replication and interference with the host immune system.

Antibody responses of chimpanzees immunized with synthetic peptides corresponding to full-length V3 hypervariable loops of HIV-1 envelope glycoproteins

Immunization of primates or humans with human immunodeficiency virus type 1 (HIV-1) glycoproteins usually elicited moderate immune responses to the principal neutralizing determinant (PND) located within the V3 hypervariable loop of gp120. Since an antibody response to the PND appears to be protective, experiments were carried out to determine the responsiveness of chimpanzees to immunization with synthetic peptides corresponding to the full-length V3 loop. Seven chimpanzees (4 preimmunized with gp160, 2 preimmunized with HIV-1 antigens unrelated to gp160, and 1 unimmunized) were vaccinated with a mixture of full-length V3 loop peptides from 21 distinct HIV-1 isolates (clones) either in unconjugated form or linked to carrier proteins from HIV-1 nef and gag P18, respectively. Six chimpanzees developed high levels of antibodies to the peptides (dilution endpoints 1: greater than 25,000), and 5 had high levels of antibodies to gp120 from HIV-1IIIB (endpoint titers 1: greater than 500,000). Chimpanzees immunized with peptide-carrier conjugates (4) had antibodies to the carrier proteins nef and gag P18, respectively (endpoint titers 1: greater than or equal to 35,000). Virus-neutralizing (VN) antibodies were detected in sera of 5 of 7 chimpanzees, but were present at titers of 1: greater than or equal to 400 only in sera of 2 chimpanzees. One of these was challenged with HIV-1 and was protected against infection, as reported elsewhere. The antibodies were primarily specific for the HIV-1 isolate used for primary immunization before boosting with peptides. The relatively low dilution endpoints of VN antibodies as compared with endpoints determined by site-specific immunoassays probably can be ascribed to imperfect mimicry of conformational epitopes by synthetic peptides. Nevertheless, sequential or simultaneous immunization with recombinant envelope glycoproteins of HIV-1 and selected synthetic peptides offers an approach for eliciting protective immunity against HIV-1.

Confronting the hypervariability of an immunodominant epitope eliciting virus neutralizing antibodies from the envelope glycoprotein of the human immunodeficiency virus type 1 (HIV-1)--II. Synthetic peptides linked to HIV-1 carrier proteins gag and nef

Combining of subtype specific peptides from the hypervariable loop of the envelope glycoprotein gp120 of divergent HIV-1 isolates may help in designing a broadly protective immunogen against HIV-1 infection. To enhance the immunogenicity of such a polyvalent antigen, in the absence of oil-containing adjuvants, it is necessary to link the peptides to a protein carrier. It is preferable to use as carriers those proteins from HIV-1 itself which may contribute to eliciting protective immunity. The structural and non-structural proteins, gag P18 and nef, respectively, which can be prepared in high yields by recombinant DNA techniques in Escherichia coli, were selected for this purpose. The corresponding peptide-protein conjugates, each containing 21 distinct peptides, were prepared using the cross-linking reagents N-succinimidyl-3-(2-pyridyldithio)-propionate (SPDP) or m-maleimidobenzoyl-N-hydroxysulfosuccinimide ester (sulfo-MBS). Conjugates prepared by the second method elicited approximately 10-100 times higher levels of antibodies recognizing the homologous peptides and the HIV-1 envelope glycoproteins. The sulfo-MBS conjugation procedure preserved the antigenicity of both gag P18 and nef and the respective conjugates elicited an immune response to these proteins. Despite the low immunization dose of single peptides (10 micrograms) present in the mixture of peptides collectively linked to the carriers, antibody responses to most of the individual peptides were high (dilution endpoints 1: greater than 16,000, 1: greater than 80,000 for the nef and gag P18 conjugates, respectively). Conjugates consisting of a multitude of HIV-1 envelope-derived peptides in combination with gag P18 and nef carriers are expected to elicit broadly protective immunity against distinct HIV-1 subtypes.

Peptides mimicking selected disulfide loops in HIV-1 gp120, other than V3, do not elicit virus-neutralizing antibodies

The positions of all 9 intrachain disulfide bonds within the envelope glycoprotein gp120 of the human immunodeficiency virus (HIV-1) have been established recently. Peptides expected to mimic some of the disulfide-bonded domains [(120-133)-(203-221); (133-138)-(164-203); (224-254); (391-425) and (385-392)-(425-452)] were synthesized. All peptides, except (120-133)-(203-221), elicited in immunized rabbits relatively high levels of antibodies reacting with gp120 in enzyme-linked immunosorbent assay (ELISA) and/or Western immunoblot assays. However, these antibodies failed to neutralize the infectivity of HIV-1. Combined with earlier reports concerning other gp120 loop peptides, these results confirm the uniqueness of the V3 (303-338) loop in encompassing a principal determinant(s) involved in virus neutralization.

Inhibitory activity of monoclonal antibody F35.25 on the interaction between hepatocytes (HepG2 cells) and preS1-specific ligands

The capacity of a preS1-specific monoclonal antibody (McAb) F35.25 to block the attachment of preS1-specific ligands to human hepatoma HepG2 cells was studied. In order to define more precisely the fine epitope specificity of McAb F35.25, its reaction with synthetic peptides derived from the preS1 sequence (12-53) was investigated. McAb F35.25 was found to recognize better synthetic peptide preS(21-47) from the adw 2 and ayw sequences than the synthetic peptide preS(32-53) adw 2. The shortest sequence recognized by McAb F35.25 among the peptide sequence studied was preS(32-47). The corresponding amino acid sequence (for HBV subtype adw 2) is PAFGANSNNPDWDFNP. As expected, it was found that McAb F35.25 inhibited the attachment of HepG2 cells to HBsAg-cellulose, as well as to preS(21-47)-cellulose, corresponding to two HBV subtypes adw 2 and ayw. Finally, the inhibitory effect of different peptides on the interaction of McAb F35.25 with HBsAg particles containing the preS1 sequence was also studied. The peptide preS(12-47) appeared to be the most effective inhibitor. Therefore, the McAb F35.25 is specific for the sequence preS1(X to 47), where (12 less than or equal to X less than 32). These results indicate that McAb F35.25 is probably virus-neutralizing and represents a reagent of great value to study the interaction between HBV and hepatocytes independently of d/y subtype changes.

Antigenic mimicry of an immunoglobulin A epitope by a hepatitis B virus cell attachment site

The preS(21-47) sequence of the hepatitis B virus (HBV) envelope protein is involved in binding of the virus to cell receptors. A protein similarity search revealed a partial homology between this sequence and a segment of the human immunoglobulin A (IgA) heavy chain constant region, suggesting that the cell attachment site for HBV might be located on secretory component representing a receptor for polymeric IgA. Data presented herein do not support this hypothesis but provide evidence for immunological cross-reactivity between IgA and the preS(21-47) region of the HBV env protein.

Search for epitope-specific antibody responses to the human immunodeficiency virus (HIV-1) envelope glycoproteins signifying resistance to disease development

It is essential for the development of strategies for prevention and therapy of human immunodeficiency virus (HIV-1) infections to define host factors playing a dominant role in determining the clinical outcome of infection. Antibodies directed against restricted regions of the HIV-1 glycoproteins gp120 and gp41 are likely to represent important factors involved in host defense against HIV-1. Definition of qualitative and quantitative differences in the spectrum of anti-gp120 and anti-gp41 antibodies between two vastly different groups of HIV-1-infected individuals, long-term asymptomatic carriers, and individuals with acquired immunodeficiency syndrome (AIDS) who died, might reveal the epitope specificity of antibodies contributing to prevention of clinical disease. To accomplish this goal, sera from both groups were assayed for antibodies recognizing synthetic peptides from gp120/gp41 which were shown in earlier experiments to mimic epitopes on the two HIV-1 glycoproteins. None of the sera recognized all of the distinct 27 peptides from gp120 and gp41. The spectrum of antibodies was distinct for each of the sera from both groups of HIV-1-infected individuals. Nevertheless, antibody responses distinguishing the two groups from each other were discerned. In particular, it was possible to predict the unfavorable outcome of disease by comparative measurements of levels of antibodies to a peptide (303-338), corresponding to the entire V3 hypervariable loop of gp120 and/or by providing evidence for declining levels of these antibodies during the course of infection. Antibodies recognizing additional peptides [(219-245), (280-306), (425-452), (658-682), (729-758), (808-845), and (845-862)] were significantly less prevalent in AIDS patients than in asymptomatic carriers. It appears possible that maintenance of high levels of the respective antibodies would contribute to preventing AIDS in HIV-1-infected individuals. Active immunization with antigens containing epitopes defined by the respective peptides and/or administration of the corresponding antibodies may be considered as a modality for therapy of HIV-1 infections.

Confronting the hypervariability of an immunodominant epitope eliciting virus neutralizing antibodies from the envelope glycoprotein of the human immunodeficiency virus type 1 (HIV-1)

Antibody mediated and cell mediated immune responses to the envelope glycoproteins gp120 and gp41 of the human immunodeficiency virus (HIV-1) are considered important for protection against infection and for attenuation of disease symptoms after infection. Virus neutralizing antibodies are mostly subtype specific and primarily directed against epitopes on a hypervariable loop from the V3 region of HIV-1 gp120. Such epitopes are recognized by helper and cytotoxic T-cells suggesting that all protective immune responses to HIV-1 are predominantly subtype specific. The extraordinary primary sequence variability of gp120 indicates that a combination of subtype specific components will be required to design a broadly effective protective immunogen against HIV-1. Peptides from hypervariable loops of the V3 region of 21 distinct HIV-1 isolates (clones) were synthesized and used to raise rabbit antisera. The antisera contained high levels of antibodies recognizing the homologous peptides and the parent gp120 sequence. The serological cross-reactivity between the distinct peptides was evaluated and related to amino acid divergence. The corresponding relationship approximated a linear regression with a correlation coefficient r = 0.718. The 21 peptides were combined into a single immunogen which elicited broadly reactive antibodies recognizing all 21 peptides as well as gp120 from the only isolate tested, HIV-1 IIIB. The results suggest the possibility of developing broadly protective HIV-1 immunogens by combining judiciously selected subtype specific peptides derived from envelope glycoproteins of divergent virus isolates.

Detection of receptors for hepatitis B virus on cells of extrahepatic origin

Receptors for hepatitis B virus (HBV; subtype adw) were identified on the surface of human hepatoma HepG2 cells in earlier studies. The cell receptor binding site on HBV was assigned to the preS(21-47) region of the preS1 sequence of the envelope protein. Studies presented here show that (1) amino acid residue replacements within the preS(21-47) sequence distinguishing HBV subtypes adw and ayw, preserve the binding capacity of the HBV env protein for HepG2 cell receptors; (2) the inhibition of binding between HepG2 cells and preS1-specific ligands by antibodies is effective only if the subtype specificity of anti-preS1-specific antibodies and of the preS1-specific ligands are matched; (3) receptors for HBV were present on the surface of human cells of nonhepatic origin, including peripheral blood B-lymphocytes, some hematopoietic cell lines of the B-cell lineage, neuroblastoma, amnion, and embryonic carcinoma cell lines. Receptors for HBV on these cells appeared similar to the receptor on HepG2 cells by the following criteria: (a) recognition by antibodies raised against the receptor on HepG2 cells; (b) inhibitory activity of lysates prepared from these cells on the interaction between HepG2 cells and preS1-specific ligands; and (c) the inhibitory effect of lysates from HepG2 cells on the reaction of these cells with HBsAg- and preS(21-47)-cellulose. The presence of receptors for HBV on some cells of extrahepatic origin is in accordance with earlier observations indicating that hepadnaviruses are not strictly hepatotropic.

Toleration of amino acid substitutions within hepatitis B virus envelope protein epitopes established by peptide replacement set analysis. I. Region S(139-147)

B and T cell epitopes expressed on the surface of S-protein, a major constituent of the envelope of hepatitis B virus (HBV), are essential for eliciting protective immunity against HBV infection. A segment of the S-protein sequence encompassing residues S(139-147) is a portion of overlapping B and T cell epitopes. This sequence is conserved among distinct serological subtypes of HBV and has a 77.8% homology with an analogous sequence in S-proteins of nonhuman mammalian hepadnaviruses. Rare subtypes and variants of HBV having amino acid replacements within the S(139-147) sequence were discerned recently. The impact of amino acid replacements within this sequence on its immunological recognition at both the B and T cell levels was explored by peptide replacement set analysis. Results of the analysis permit discrimination between tolerated and forbidden amino acid replacements and provide a background for the development of reagents and immunogens specific for emerging HBV variants.

B cell epitope mapping of human immunodeficiency virus envelope glycoproteins with long (19- to 36-residue) synthetic peptides

Envelope glycoproteins, gp 120 and gp41, of the human immunodeficiency virus type 1 (HIV-1) elicit immune responses, including virus-neutralizing antibodies, which are expected to play a role in the defence against HIV-1 infection. Subregions of the gp120/gp41 sequence have immunosuppressive effects or may be implicated in autoimmune responses. Some of the immunodominant epitopes of gp120/gp41 do not contribute to protective immunity and act as immunological decoys. These circumstances emphasize the need to select from gp120/gp41 regions inducing protective responses. Towards this goal, 30 peptides covering approximately 87% of the HIV-1 strain BH10 gp120/gp41 sequence were synthesized. Antibodies in rabbit and human anti-HIV-1 sera recognized 28 and nine of the peptides, respectively, indicating that most of the gp120/gp41 sequence is immunogenic and secondly, that the antibody response to HIV-1 is restricted in infected humans. Most of the peptides, without conjugation to carriers, elicited high levels of anti-peptide (endpoints 1: greater than 10(4] and anti-gp120/gp41 (endpoints 1: greater than or equal to 10(3] antibodies. The highest levels of virus-neutralizing antibodies were elicited by peptide 306 to 338 from a hypervariable loop of gp120. Additional peptides from the full-length hypervariable loop (303 to 338) of HIV-1 BH10 and from 20 additional HIV-1 isolates were recognized differentially by human anti-HIV, suggesting that success of passive immunization may depend on a match between administered antibodies and the challenging HIV-1 strain, and also that active immunization with selected peptides from a hypervariable region of distinct HIV-1 isolates should be explored further as a method for prophylaxis against infection.

Antibodies to synthetic peptides from the preS1 region of the hepatitis B virus (HBV) envelope (env) protein are virus-neutralizing and protective

Hepatitis B virus (HBV) envelope (env) proteins contain three antigenic domains designated S, preS2 and preS1. Studies with synthetic peptide immunogens demonstrated the role of preS2 epitopes in protection against HBV infection. The preS1 domain is implicated in virus-cell receptor interactions suggesting that anti-preS1-specific antibodies should neutralize the infectivity of HBV by blocking virus attachment to cells. We present here evidence that an antiserum to a peptide from the preS1 sequence, anti-preS(21-47), is virus-neutralizing and that active immunization of chimpanzees with a longer peptide derived from the preS1 sequence, preS(12-47), elicits antibodies protective against HBV infection. These results establish the role of the preS1 domain in the process of virus neutralization and the potential of synthetic preS1 analogues for hepatitis B vaccination.

Hepatitis B virus surface antigen (HBsAg) as carrier for synthetic peptides having an attached hydrophobic tail

B- and T-cell epitopes from three distinct regions of the hepatitis B virus (HBV) envelope (env) protein (preS1, preS2 and S) are involved in eliciting protective immunity. Since preS1 sequences inhibit the secretion of HBV env proteins from eukaryotic cells, it is difficult to prepare immunogens rich in preS1 sequences. This problem can be overcome by linking synthetic peptides from the preS1 region to particles containing both S and preS2 sequences. We describe here a novel approach for binding of synthetic peptides to exposed hydrophobic domains on HBV env proteins. Long chain fatty acids or mercaptans are covalently linked to synthetic peptides. Peptides with the attached hydrophobic tails interact strongly with HBV env proteins (S + preS2), whereby hybrid immunogens are generated. Such immunogens can be used in combination with alum, the only adjuvant approved for human use. The combination of the preS1 peptide [preS(12-47)] with particles containing the S and preS2 regions resulted in an immunogen which: (1) elicits a broad spectrum of protective antibodies; (2) circumvents the nonresponsiveness to: (a) preS1 epitopes in preS1-nonresponder strains of mice; and (b) S-protein in S-protein-nonresponder strains of mice; and (3) augments the immune response to S-protein. The combination of HBV env proteins with a synthetic peptide from the envelope of the human immunodeficiency virus (HIV-1) resulted in an immunogen eliciting anti-HIV-1. Hybrid immunogens consisting of viral proteins and of synthetic peptides represent a feasible approach for the design of future vaccines.

Antibodies recognizing human serum albumin are not elicited by immunization with preS2 sequences of the hepatitis B virus envelope protein

Antibodies to the preS2 region of the hepatitis B virus (HBV) envelope protein and to human serum albumin (HSA) were allegedly detected at about the same level in sera of humans with acute or chronic hepatitis B [Hellström et al., 1986]. It was claimed that anti-HSA arises as a result of an immune response to the preS2 sequence and that it was involved in hepatocellular damage. Over 100 sera from animals and humans immunized with HBsAg containing preS2 sequences, or with synthetic peptides from the preS1, preS2, and S regions of the HBV env protein were assayed for anti-HSA. The results revealed the following: 1) Immunization with the native preS2 sequence or with unconjugated synthetic peptides derived from that sequence does not result in elicitation of anti-HSA. Therefore the alleged appearance of anti-HSA during hepatitis B cannot be directly related to an anti-preS2-specific immune response. 2) Some synthetic peptides, whether or not they were derived from the preS2 sequence, when linked to certain carriers, but not to others, elicited in rabbits an anti-HSA response, which was markedly lower than the response to the homologous peptide. These anti-HSA antibodies could be separated from anti-preS2-specific antibodies by affinity chromatography and did not recognize the synthetic peptide used for immunization. The use in active immunoprophylaxis of hepatitis B of unconjugated peptides from the preS2 sequence with proven high immunogenicity will avoid carrier/linker-mediated induction of antibodies not relevant to protection against HBV.

Delineation of contiguous determinants essential for biological functions of the pre-S sequence of the hepatitis B virus envelope protein: its antigenicity, immunogenicity and cell-receptor recognition

The preS region of the hepatitis B virus (HBV) envelope protein has the following properties: (1) exposure on the surface of the virus; (2) high immunogenicity; (3) involvement in the reaction of the virus with cell receptors and (4) elicitation of antibodies protective against infection. Attempts to mimic B- and T-cell epitopes on the native protein by synthetic peptides were highly successful. This success depended on identification of those regions within the preS sequences which are the most important for biological function of the virus and for immunity, and on the synthesis of long peptides (20-40 residues) containing both B- and T-cell epitopes. Results presented here highlight those subregions of the preS sequence which are the most essential for the antigenicity and immunogenicity of HBV.

Antibodies to synthetic peptides from the pre-S1 and pre-S2 regions of one subtype of the hepatitis B virus (HBV) envelope protein recognize all HBV subtypes

Immunodominant B and T cell epitopes have been demonstrated recently on the preS1 and PreS2 regions of the hepatitis B virus (HBV) envelope protein. Synthetic peptide analogs corresponding to the preS2 region elicit virus-neutralizing antibodies and protect chimpanzees against HBV infection. Antibodies raised by immunization with peptides derived from the preS1 sequence block the site involved in HBV attachment to cell receptors, and are expected to be virus-neutralizing. Results presented here show that antisera raised against synthetic peptide analogs carrying the immunodominant epitope of the preS1 and preS2 sequence, respectively, and corresponding to two HBV subtypes, adw2 and ayw, each recognized preS1 and preS2 specific epitopes on all serological subtypes of the HBV envelope protein. Thus, the sequence variability within the preS1 and preS2 regions does not represent an impediment to the development of synthetic peptide or genetically engineered hepatitis B preS immunogens for worldwide immunization.

Immunological cross-reactivity between preS2 sequences of the hepatitis B virus envelope proteins corresponding to serological subtypes adw2 and ayw

An immune response to epitopes localized on the preS region of the hepatitis B virus (HBV) envelope (env) is elicited during recovery from HBV infection and appears to play a role in virus clearance. Anti-preS antibodies (Ab) are expected to be protective against HBV infection as indicated by the virus-neutralizing capacity of Ab to a preS2-specific synthetic peptide preS(120-145). However, there is considerable amino acid variability between preS regions corresponding to distinct serological subtypes of HBV, raising the question whether the preS sequences are sufficiently related immunologically to have the potential of inducing cross-protective immunity. To answer this question concerning the preS2 region, antisera to synthetic peptides preS(120-153) and preS(128-153) corresponding to subtypes adw2 and ayw, as well as to the native env [ayw] protein were raised. Using the resulting polyclonal Ab, an immunological relatedness between preS2 sequences of subtypes adw2 and ayw was demonstrated. On the other hand, Ab selected by affinity chromatography or by cloning hybridoma cells may recognize with strong preference subtype-specific determinants within the preS2 region when the compared antigens are in solution rather than on the solid phase. These findings have implication for the design of: (1) preS2-specific immunogens and (2) immunoassays for quantitation of preS2 sequences in HBV env proteins.

Characterization of monoclonal antibodies specific for the pre-S2 region of the hepatitis B virus envelope protein

Monoclonal antibodies (McAb) specific for the pre-S region of the hepatitis B virus (HBV) envelope protein were prepared using HBV particles of hepatitis B surface antigens (HBsAg) as immunogens. The antibodies reacted in Western blot analyses and in ELISA with pre-S2 sequences of the HBV envelope protein. Pepsin or protease V8 treatment of the antigen abolished reactivity. The fine specificity of one of the McAb (F376) was established by immunoassays using synthetic peptides and a pre-S2-beta-galactosidase fusion protein expressed in E. coli. The shortest peptide recognized by F376 is demarcated by residues pre-S(132) at the N-terminal and pre-S(140)-pre-S(145) at the C-terminal. The corresponding amino acid sequence (for HBV subtype adw2) is: QDPRVRGLY(LPAGG). Additional amino acid residues at the N-terminal, and possibly at the C-terminal ends contribute to the binding of McAb, probably due to conformational influences. The McAb was applied to immunoassays of pre-S2 sequences in purified HBsAg and in human sera containing HBsAg.

Identification and chemical synthesis of a host cell receptor binding site on hepatitis B virus

Hepatitis B virus (HBV) has not yet been propagated in vitro, and knowledge concerning its reaction with receptors on target cells remained scant. We have located within the HBV envelope proteins a sequence mediating the attachment of HBV to human hepatoma HepG2 cells. A synthetic peptide analog (PLGFFPDHQLDPAFGANSNNPDWDFNP) is recognized by both cell receptors and anti-HBV antibodies and elicits antibodies reacting with native HBV. The synthetic peptide is a promising immunogen expected to elicit protective antibodies based on the concept of the attachment blockade pathway of virus neutralization. The approach described here, based on anti-peptide antisera and the binding of peptide analogs to cell receptors is generally applicable for the delineation of cell receptor binding sites on viruses with known gene sequences.

Antibodies to a synthetic peptide from the preS 120-145 region of the hepatitis B virus envelope are virus neutralizing

Studies with synthetic peptides have provided evidence for the presence of preS coded sequences in the envelope (env) proteins of hepatitis B virus (HBV) and indicated that these sequences are involved in the specific attachment of HBV to liver cells. Scanning of the preS sequence for immunodominant continuous epitopes identifies the sequence within residues preS (120-145) as the most immunogenic in eliciting antibodies recognizing HBV and as the most efficiently binding antibodies from sera of rabbits and humans immunized with HBV env proteins. To assess the potential of preS (120-145) as a synthetic vaccine against hepatitis B, in vitro neutralization of the virus by rabbit antiserum to the peptide was assayed in chimpanzees. The animals, subsequently proven to be susceptible to HBV infection, did not develop hepatitis B as judged by negative serological tests for HBV-associated antigens and antibodies and by normal serum alanine aminotransferase levels and normal liver biopsies. These results establish the role of preS domains in the process of virus neutralization and the potential of synthetic preS analogues for hepatitis B vaccination.

Detection of antiviral antibodies with predetermined specificity using synthetic peptide--beta-lactamase conjugates: application to antibodies specific for the preS region of the hepatitis B virus envelope proteins

Amino acid sequences coded for by the preS region of the hepatitis B virus (HBV) envelope gene are present both in HBV and in subviral hepatitis B surface antigen (HBsAg) particles. Consequently, anti-preS-specific antibodies are elicited during the course of HBV infection. Such antibodies are virus-neutralizing. Therefore, it is important to determine whether or not vaccination with HBsAg also induces an anti-preS-specific immune response. We describe here an enzyme-linked immunosorbent assay applicable for the screening of sera from vaccinated individuals for anti-preS antibodies. IgG from serum specimens was adsorbed to staphylococcal Protein A on a superparamagnetic support and subsequently mixed with a synthetic peptide analogue [preS(120-145)] covalently linked to beta-lactamase. The presence of anti-preS in serum specimens resulted in binding of the conjugated beta-lactamase to the magnetic support. The adsorbed enzyme was quantified colorimetrically.

Enzyme-linked immunoassay of pre-S gene-coded sequences in hepatitis B vaccines

Pre-S gene coded domains of the hepatitis B virus (HBV) envelope protein are highly immunogenic in experimental animals and humans. Their presence in HBV and hepatitis B surface antigen (HBsAg) particles leads to production of anti-pre-S-specific antibodies during the course of HBV infection. Since antibodies specific for pre-S domains are capable of preventing the attachment of HBV to hepatocytes and are virus neutralizing, it would seem desirable to produce HBV vaccines with a standardized level of pre-S determinants to ensure their potential for eliciting the same repertoire of protective antibodies as found after recovery from natural infection. However, a test with appropriate sensitivity for detecting pre-S determinants to ensure their potential for eliciting the same repertoire of protective antibodies as found after (ELISA) for detecting pre-S determinants in vaccines containing less than or equal to 20 micrograms of HBsAg. The components of this assay are (1) antibodies to a synthetic peptide pre-S (120-145) adsorbed to polystyrene beads, and (2) beta-lactamase-labelled antibodies purified from anti-HBV serum on the basis of their affinity for a pre-S (120-174) beta-galactosidase fusion protein produced in Escherichia coli. Results of an evaluation of the pre-S content of HBV vaccines from two different commercial sources are discussed.

Radioimmunoassay and enzyme-linked immunoassay of antibodies directed against lymphadenopathy-associated virus (LAV) proteins larger than the core protein (P24)

The acquired immunodeficiency syndrome (AIDS) may be transmitted by blood transfusions and by blood products from donors who have been infected with the lymphadenopathy-associated virus (LAV). Such donors may generally be identified on the basis of a positive test for antibodies-against LAV proteins. We have already described an anti-LAV assay based on the use of crude virus-infected tissue culture medium, which avoids elaborate, expensive and potentially hazardous virus purification steps. This test was operationally specific for antibodies to the approximately 24 kD core protein of the virus (P24; Neurath et al. J. Virol. Methods 11, 75, 1985). Molecular exclusion chromatography of crude LAV antigen preparations allows separation of most of P24 from larger proteins of LAV (PL). PL and 125I- or beta-lactamase-labeled anti-LAV were used as reagents for radioimmunoassay (RIA)--or enzyme-linked immunoassay (ELISA)--inhibition tests to detect antibodies directed predominantly against PL (anti-PL). Among 257 individuals belonging to groups at high risk of developing AIDS, 117 (45.5%) were positive for anti-PL and 108 (42%) for anti-P24, respectively. The 2 individuals among 600 random blood donors found to be anti-P24-positive in the preceding study also had anti-PL in their serum. Sera from 500 additional blood donors were screened for anti-PL and 1 of these was positive. The implication of these findings for screening of blood donors is discussed.

Genetic restriction of immune responsiveness to synthetic peptides corresponding to sequences in the pre-S region of the hepatitis B virus (HBV) envelope gene

Proteins of the HBV envelope (env) are coded for by two adjacent regions of the HBV env gene: the pre-S and S regions. Antigenic determinants corresponding to amino acid sequences of both regions are recognized by human antibodies and are important in virus-neutralizing responses. Protective immune responses to HBV appear to be linked to the major HLA histocompatibility complex. Inbred and congenic strains of mice represent a model system relevant for studies on the genetic control of immune responsiveness of humans to HBV envelope proteins. Such mouse strains were ranked according to their antibody response to the S protein and divided into high [d,q], intermediate [a,k,b], and low [s] responders (letters in brackets indicate H-2 haplotype.) Selected pre-S antigenic determinants can be mimicked with high fidelity by synthetic peptide analogues that are immunogenic without any carriers. Thus it is possible to study directly the genetic control of immune responsiveness to pre-S epitopes mimicked by these peptides without having to consider the influence of carriers or of S protein. The results presented here show that inbred mouse strains can be ranked according to their antibody responses to the synthetic peptide pre-S(120-145) as follows: A/J[a] approximately equal to SWR/J[q] greater than C57BL/6J[b] approximately equal to AKR/J[k] approximately equal to SJL/J[s] much greater than DBA/2J[d] greater than BALB/cJ[d]. Only SJL/J[s] mice responded well to another synthetic peptide pre-S (12-32). Thus, H-2-linked genes regulating the immune response to S protein and to epitopes on pre-S-coded sequences are distinct. Anti-pre-S(120-145) responses in S protein-nonresponders circumvent this nonresponsiveness. This should be considered in the design of hepatitis B vaccines.