Antibodies to HIV-1 gp41 recognize synthetic peptides of human IFN-alpha and IFN-beta

Based on our finding that a common epitope exists between HIV-1 gp41 and human type I interferons (IFN-alpha and IFN-beta), and increased levels of antibodies against human IFN-alpha and IFN-beta were observed in HIV-1-infected individuals, we tried to explain the mechanism of increased levels of antibodies. Mouse antisera recognizing HIV-1 recombinant soluble (rs) gp41 (aa 539-684) interacted with two synthetic peptides sequence-corresponding to the IFN-alpha/beta receptor binding site on human IFN-alpha and IFN-beta, while normal mouse serum (pooled normal sera) did not. The anti-rspg41 antisera after adsorption by IFN-beta sepharose column lost the activity of interaction with both synthetic peptides. In another experiment, rsgp41 could bind to sepharose column conjugated with anti-IFN-beta polyclonal antibodies (IgG). These results indicate that the common epitope on gp41 and type I interferons could induce antibodies recognizing the receptor binding site on IFN-alpha and IFN-beta, suggesting that increased levels of antibodies against IFN-alpha and IFN-beta in HIV-1-infected individuals could be induced by gp41.     

HIV-1 gp41 and type I interferon

HIV-1 gp41-like human type I interferon (IFN) could inhibit lymphocyte proliferation and up-modulate MHC class I and II and ICAM-1 molecule expression. Sequence comparison indicates that a similar epitope RILAV-YLKD exists between N-domain of gp41 and two regions in IFN-alpha(aa29-35 and 113-129), IFN-beta (aa31-37 and 125-138) and IFN-omega (aa29-35 and 123-136), which was shown to form IFN-alpha/beta-receptor binding site. Weak sequence similarity was also found to exist in both regions on gp41 and type I IFN of murine and bovine. Experimental studies indicated that a common immunological epitope exists between gp41 and IFN-alpha and -beta. Antibodies against human IFN-alpha and -beta recognized the common immunological epitope and inhibited gp41-binding to the potential cellular receptor protein p45. Moreover, the polyclonal antibody to IFN-beta completely inhibited gp41-binding to human T, B cells and monocytic cells, while IFN-alpha could only inhibit this binding incompletely. It was interestingly observed that human IFN-beta after preincubating with cells could incompletely inhibit the binding of gp41 to human B cells and monocytic cells, and very weakly inhibit the binding to human T cells, indicating that the receptor for IFN-beta-binding may be involved in gp41 binding. This potential relationship may be based on the amino acid sequence homology in the receptor binding region between gp41 and IFN-beta. It was observed that the increased levels of antibodies against human IFN-alpha and -beta exist in HIV-1-infected individuals and are associated with the common epitope on gp41. Besides, several studies provided experimental evidence that the common immunological epitope could induce protective activity against HIV-1. The IFN-alpha-based vaccine has showed a significant reduction of disease progression in IFN-alpha-vaccine-treated HIV-infected patients. Recent experimental evidence indicates that gp41 and IFN-beta were involved in downregulation of CCR5 expression and induction of cell activation or signal transduction. Whether it may be performed by a similar mechanism is still to be investigated.     

Binding behaviour of antibodies reacting specifically with an immunodominant region of the transmembrane protein gp41 of HIV-1.

A highly conserved region of the transmembrane protein gp41 of the HIV-1 was found in which the amino acid sequence 606 to 620 was characterized as an immunodominant region. The binding behaviours of a human monoclonal antibody and of polyclonal specific antibodies in sera of HIV-infected persons to this particular sequence have been studied. In two sandwich-type ELISAs with synthetic peptides as antigen representing this region, sera of 312 HIV-infected persons at all stages could be clearly discriminated against 500 anti-HIV antibody negative sera of healthy blood donors.     

Monoclonal antibodies to an HIV-1 group O envelope recombinant

Monoclonal antibodies were developed to a recombinant HIV-I group O envelope protein derived from the isolate HAM112. These monoclonal antibodies were characterized for reactivity to a series of overlapping synthetic peptides (29-30 mers) covering gp120 C-terminal and gp41 ectodomain regions of the HIV-1 group O envelope protein. Most of these monoclonal antibodies reacted with peptides spanning sequences analogous to HIV-1 group M epitopes identified from studies in mice and humans. However, several of the antibodies that were nonreactive to individual peptides did react to a mixture of longer peptides from the N-terminal and C-terminal helical regions of the gp41 ectodomain. The monoclonal antibodies described in this study are valuable tools for characterization of antigenic differences between HIV-1 group O and group M viruses.     

The immunogenic CBD1 peptide corresponding to the caveolin-1 binding domain in HIV-1 envelope gp41 has the capacity to penetrate the cell membrane and bind caveolin-1

The potential caveolin-1 binding domain (CBD), referred to as CBD1 and CBD2, is highly conserved in the transmembrane envelope glycoprotein of various HIV-1 and HIV-2 isolates, respectively. However, HIV-1 neutralizing antibodies raised against the synthetic CBD1 peptide (SLEQIWNNMTWMQWDK) do not cross-react with the CBD2 peptide (SLTPDWNNMTWQEWER) and have no effect on HIV-2 infection. Here we show that the CBD2 peptide is not immunogenic under similar immunization conditions as the CBD1 peptide. Moreover, the CBD1 but not the CBD2 peptide has the capacity to bind caveolin-1 in crude cell extracts thus suggesting the existence of structural and/or conformational differences between CBD1 and CBD2. Accordingly, circular dichroism spectroscopy and fluorimetry analysis indicated that CBD1 but not CBD2 could adopt a defined secondary structure and form a complex with a peptide corresponding to the caveolin-1 scaffolding domain, which is the site of interaction of caveolin-1 with various proteins. In line with these observations, CBD1 but not CBD2 binds cells and forms large aggregates at the plasma membrane by colocalizing with cytofacial caveolin-1. This latter is dependent on the lipid raft integrity of the plasma membrane. Supporting that the ability to penetrate into plasma membranes is sustained by folding at the interface, CBD1 but not CBD2 has the capacity to insert into lipid monolayers, penetrate into artificial membranes and adopt a beta-sheet conformation in presence of lipid vesicles. These structural determinants and membrane partitioning properties could account for the immunogenicity of the CBD1 peptide in various animals.     

Salivary detection of HIV-1 antibodies using recombinant HIV-1 peptides

Salivary antibodies may play a role in the absence of HIV-1 transmission by saliva. We evaluated the presence of salivary IgG antibodies to HIV-1 using a recombinant ELISA. Whole saliva was collected from 21 HIV-1-seropositive individuals and assayed in an ELISA, ASQ (Beckman Instruments, Brea, CA), consisting of a panel of six HIV-1 recombinant peptides. Saliva samples from 20 individuals demonstrated IgG to one or more peptides and 18 to two or more peptides. Samples from 20 seropositive individuals were reactive with the gp41 peptide, whereas only 12 were reactive with the two gp120 peptides. Nineteen of twenty salivas also had detectable IgG antibodies to HIV-1 by Western blotting. The results indicate that viral-specific IgG antibodies are present in the saliva of a high percentage of HIV-infected individuals and that a recombinant peptide ELISA for saliva might be useful for the detection of HIV-1 infection.     

Characterization of a novel human immunodeficiency virus type 1 neutralizable epitope within the immunodominant region of gp41

Previously, we generated human monoclonal antibodies using peripheral blood mononuclear cells from an asymptomatic human immunodeficiency virus type 1 (HIV-1)-seropositive donor. One of these monoclonal antibodies (designated clone 3, CL3) recognized 10 amino acids (GCSGKLICTT) within the immunodominant region (cluster I) of the transmembrane envelope glycoprotein gp41 and neutralized infection of target cells with different laboratory isolates. Because the epitope recognized by CL3 has two cysteine residues that could potentially produce a disulfide loop in gp41, we analyzed binding of our monoclonal antibody to the cyclic and linear motif of the peptide sequence IWGCSGKLICTTAVP (residues 600-614). The CL3 antibody did not bind to the synthetic cyclic peptide but did recognize the linear form. Two polyclonal rabbit sera against both the linear and cyclic peptides were then generated. Both antisera bound to viral glycoproteins gp41 and gp160, but neither sera neutralized HIV-1 laboratory isolates. Using a set of alanine-substituted IWGCSGKLICTTAV peptides, we analyzed binding of polyclonal antisera and CL3. The profile of binding of polyclonal antisera to these peptides was different from that of CL3 to the same peptides. This suggests that CL3 recognized a unique neutralizable core epitope, which was not immunogenic in either the cyclic or the linear IWGCSGKLICTTAVP peptides used as immunogens in the rabbits.     

Maternal antibodies to HIV-1 envelope domains: No correlation with HIV-1 vertical transmission in patients from Argentina

The role of the maternal antibody response in relation to vertical human immunodeficiency virus type 1 (HIV-1) transmission was investigated in HIV-1-infected mothers from Argentina. Sera from 23 transmitting and 18 nontransmitting HIV-1-infected mothers were tested for the presence of antibodies to V3 loop gp120 peptides representing both Argentinian sequences and several well-characterized viral isolates from different geographic areas. Argentinian sera from transmitting mothers had significantly higher capacity to react with four of 14 V3 loop peptides tested than sera from nontransmitting mothers. Frequency of reactivity against the other peptides did not differ between the two maternal groups. Furthermore, no differences in antibody affinity were found between transmitting and nontransmitting mothers. Sera were also tested against overlapping peptides covering a neutralizing epitope of the HIV-1 MN gp41 (amino acids 648-677). Statistical analysis indicated that no correlation between anti-gp41 antibodies and vertical transmission exists. Although we used V3 loop peptides based on local HIV-1 sequences, our data showed that maternal antibodies to these peptides, as well as to gp41 peptides, are not correlated with protection against HIV-1 vertical transmission.     

Human immunodeficiency virus type 1 gp120 C5 region mimics the HLA class I α1 peptide-binding domain

Molecular mimicry of major histocompatibility (MHC) antigens by viral glycoproteins has been suggested as one of the possible mechanisms of induction of an autoimmune response by human immunodeficiency viruses. A monoclonal antibody (M38) was previously shown to bind to both human immunodeficiency virus type 1 (HIV-1) gp120 and β-2 microglobulin-free HLA class I heavy chains encoded by an HLA C allele. Using HLA C recombinant proteins and synthetic peptides, the M38 class I binding site was mapped to a stretch of 44 amino acids of the al domain. The amino acid residues recognized are clustered in two non-contiguous regions at positions 66-69 (KYKR) and 79-82 (RKLR) shared by almost all HLA C alleles. On HIV-1 gp120, M38 binds to two non-contiguous sequences (KYK and KAKR) at positions 490-492 and 505-508 located at the edges of a large hydrophobic region that is apparently involved in binding the transmembrane glycoprotein gp41. The C-terminal gp120 M38-reactive region (KAKR) lies within the immunodominant sequence APTKAKRRVVQREKR, against which the majority of HIV-infected individuals produce antibodies. The results indicate that a functionally important region of HIV-1 gp120 shares similar amino acid sequence motifs with the antigen recognition site of most HLA class I C alleles. The molecular mimicry may be the basis for autoimmune responses in HIV infection.     

Antibody-dependent cellular cytotoxicity (ADCC) is directed against immunodominant epitopes of the envelope proteins of human immunodeficiency virus 1 (HIV-1).

In this study, epitopes of HIV envelope proteins that are involved in ADCC were identified. Peripheral blood mononuclear cells (PBMC) were obtained from adults with asymptomatic HIV infection or early symptoms of AIDS. These PBMC, which were reported to be "armed" in vivo with HIV-specific antibodies, were used as effector cells in 51Cr release assays. Target cells consisted of CD4 lymphocytes from healthy seronegative donors, coated with the IIIB strain of HIV-1 or with one of seven synthetic peptides. Cytotoxicity was detected against CD4 lymphocytes coated with HIV-1 IIIB or with the peptides env aa 507-518, corresponding to the carboxy-terminus of gp120, and env aa 597-611, corresponding to the region of the cysteine loop of gp41. The magnitude of target cell lysis was directly related to the quantity of peptide used. In contrast, target cells coated with the peptide gag aa 129-135, corresponding to the p17/p24 cleavage region of the gag precursor, were not killed. The same immunodominant regions which were involved in ADCC were recognized in enzyme-linked immunoabsorbent assays (ELISA) by the majority of 107 sera from HIV-infected adults. We conclude that the immunodominant epitopes located at the carboxy-terminus of gp120 and the cysteine loop of gp41 serve as recognition structure for antibodies, capable of mediating ADCC against HIV-infected cells.     

Potency of HIV-1 envelope glycoprotein gp120 antibodies to inhibit the interaction of DC-SIGN with HIV-1 gp120

The interaction of DC-SIGN with gp120 provides an attractive target for intervention of HIV-1 transmission. Here, we have investigated the potency of gp120 antibodies to inhibit the DC-SIGN-gp120 interaction. We demonstrate that although the V3 loop is not essential for DC-SIGN binding, antibodies against the V3 loop partially inhibit DC-SIGN binding, suggesting that these antibodies sterically hinder DC-SIGN binding to gp120. Polyclonal antibodies raised against non-glycosylated gp120 inhibited both low and high avidity DC-SIGN-gp120 interactions in contrast to polyclonal antibodies raised against glycosylated gp120. Thus, glycans present on gp120 may prevent the generation of antibodies that block the DC-SIGN-gp120 interactions. Moreover, the polyclonal antibodies against non-glycosylated gp120 efficiently inhibited HIV-1 capture by both DC-SIGN transfectants and immature dendritic cells. Therefore, non-glycosylated gp120 may be an attractive immunogen to elicit gp120 antibodies that block the binding to DC-SIGN. Furthermore, we demonstrate that DC-SIGN binding to gp120 enhanced CD4 binding, suggesting that DC-SIGN induces conformational changes in gp120, which may provide new targets for neutralizing antibodies.     

Definition of an immunodominant T cell epitope contained in the envelope gp41 sequence of HIV-1.

The majority of the immunodominant amino acid sequences of HIV-1 that have been characterized to date are coded for by hypervariable gene sequences. These variable sequences are however interspersed with sequences that are highly conserved between HIV strains. Immunogenic viral products with amino acid sequences that vary minimally between strains, and that consistently elicit both humoral and cellular immune responses, may be ideal for inclusion in a subunit vaccine. We studied HIV-seronegative and HIV-infected persons, classified as asymptomatic (AS), ARC or AIDS. Initially, we assessed the cellular immune status of each subject from results of T cell phenotype analyses, assays for serum levels of surrogate markers of disease progression, and responses to mitogens and recall antigen. In addition, we tested whether three short synthetic peptides derived from the conserved sequences of the envelope gp120 (aa 262-284) and gp41 (aa 579-601), and core p17 (aa 106-125) regions of the HTLV-IIIB isolate, could elicit B cell as well as T cell responses in HIV-infected subjects. Only the gp41-derived sequence was immunogenic at both B and T cell levels. To further characterize the gp41 epitope, we used a series of overlapping synthetic peptides derived from a conserved region of the envelope gp41 (aa 572-613). We thus identified an immunodominant 12-mer peptide sequence, gp41(8)(aa 593-604), which consistently elicited both T cell blastogenic and B cell (antibody) responses in AS HIV-seropositive individuals but not in ARC and AIDS patients. Linear regression analysis showed that in AS persons there was a strong positive correlation (P less than 0.0005) between the absolute CD8+ T cell numbers and the magnitude of blastogenic responses to the gp41(8)(aa 593-604). Furthermore, those AS subjects with T cells that proliferated in response to this gp41 analogue also had significantly greater serum levels of antibody to the same short peptide sequence than symptomatic ARC and AIDS patients. These results suggest that cellular responses to the immunodominant and highly conserved envelope sequences of HIV-1, associated with increased CD8+ T cells, may be important in the pathogenesis of HIV disease.     

Depletion in antibodies targeted to the HR2 region of HIV-1 glycoprotein gp41 in sera of HIV-1-seropositive patients treated with T20

The anti-HIV drug T20 is a synthetic peptide derived from the HR2 region of HIV-1 gp41. T20 contains the sequence ELDKWA, which binds the broadly neutralizing antibody 2F5. Using plates coated with T20 or with synthetic peptides and recombinant proteins representing gp120 or gp41 domains, this study investigated by enzyme-linked immunosorbent assay the levels of antibodies directed to the gp160 molecule in patients treated with T20. Analysis of sera obtained before and after administration of T20 indicated that the levels of antibodies directed to T20, to MBP44, a maltose binding protein representing the HR2 region, and to 4765, a synthetic peptide containing the sequence ELDKWA, fell following administration of T20, while the levels of antibodies directed to other regions of gp41 ectodomain and to gp120 remained stable. The decline observed was independent of the viral load and of the total IgG concentration. Follow-up studies with sera obtained from HIV-1-seropositive patients naive to T20 indicated no decline in the level of antibodies directed to HR2 and other regions of gp160. Analysis of sera obtained from a patient after 2 months of T20 treatment interruption showed a level of antibodies to the HR2 region similar to that measured before administration of T20. The addition of increasing amounts of T20 to sera from T20-naive patients decreased the level of serum antibodies against peptide 4765, T20, and MBP44. The observation of antibody depletion by T20 suggests that anti-gp41 antibodies may interfere with T20 treatment by forming T20-antibody complexes.     

Assessment of antibody responses against gp41 in HIV-1-infected patients using soluble gp41 fusion proteins and peptides derived from M group consensus envelope

Human immunodeficiency virus type 1 (HIV-1) transmembrane glycoprotein gp41 is targeted by broadly-reactive neutralizing antibodies 2F5 and 4E10, making it an attractive target for vaccine development. To better assess immunogenic properties of gp41, we generated five soluble glutathione S-transferase fusion proteins encompassing C-terminal 30, 64, 100, 142, or 172 (full-length) amino acids of gp41 ectodomain from M group consensus envelope sequence. Antibody responses in HIV-1-infected patients were evaluated using these proteins and overlapping peptides. We found (i) antibody responses against different regions of gp41 varied tremendously among individual patients, (ii) patients with stronger antibody responses against membrane-proximal external region exhibit broader and more potent neutralizing activity, and (iii) several patients mounted antibodies against epitopes that are near, or overlap with, those targeted by 2F5 or 4E10. These soluble gp41 fusion proteins could be an important source of antigens for future vaccine development efforts.     

Fine specificity of the humoral immune response to HIV-1 GP160 in HIV-1 infected individuals from Tanzania.

A total of 160 sera from HIV-1 infected individuals from Tanzania were examined for their fine specificity characteristics relative to 9 synthetic peptides that define HIV-1 gp160 epitopes. Immunorecessive and immunodominant epitopes were identified in both gp120 and gp41 based on serologic reactivity of these HIV-1 infected sera. A significant difference in fine specificity among HIV-1 infected individuals from Tanzania and the United States was observed for an immunodominant gp41 epitope. No significant differences in reactivity among asymptomatic vs. symptomatic HIV-1 infected individuals were detected for the selected HIV-1 gp160 epitopes defined by these peptides. The majority of sera from HIV-1 infected Tanzanians contained antibodies that recognized a peptide corresponding to the V3 region of gp120 from the HIV-1 MN isolate. These data suggest that regional isolates of HIV-1 may exist in Tanzania that differ from HIV-1 isolated in the United States. However, based on serology, HIV-1 isolates exhibiting sequences with HIV-1 MN V3 similarity may also be prevalent in Tanzania. The results of this study may be useful for the design of more effective AIDS diagnostic and therapeutic products for use worldwide.     

The effect of sCD4 on the binding and accessibility of HIV-1 gp41 MPER epitopes to human monoclonal antibodies

Two human monoclonal anti-HIV-1 antibodies, 2F5 and 4E10, were utilized to investigate the accessibility and conservation of gp41 MPER epitopes on five different clades of HIV-1 in the absence and presence of sCD4. The binding of human monoclonal antibodies (mAbs) to HIV-1 was dependent upon the virus clade. Soluble CD4 significantly increased the accessibility of gp41 MPER-binding epitopes on several isolates that previously showed little or no binding with 2F5 and 4E10 mAbs as determined by a modified ELISA-based virus capture assay and surface plasmon resonance. Studies on the relationship between virus binding and neutralization in a TZM-bl pseudovirus assay indicated that in most cases, mAbs that exhibited neutralization also bound the virus. However, neither binding per se nor the total envelope content per virion was a predictor of neutralization. The hidden or conformational gp41 MPER epitopes unmasked by sCD4 may provide additional targets for vaccine design.     

Analysis of the neutralizing antibody response elicited in rabbits by repeated inoculation with trimeric HIV-1 envelope glycoproteins

The elicitation of broadly neutralizing antibodies directed against the human immunodeficiency virus type 1 (HIV-1) envelope glycoproteins, gp120 and gp41, remains a major challenge. Attempts to utilize monomeric gp120 as an immunogen to elicit high titers of neutralizing antibodies have been disappointing. Envelope glycoprotein constructs that better reflect the trimeric structure of the functional envelope spike have exhibited improved immunogenicity compared with monomeric gp120. We have described soluble gp140 ectodomain constructs with a heterologous trimerization motif; these have previously been shown to elicit antibodies in mice that were able to neutralize a number of HIV-1 isolates, among them primary isolate viruses. Recently, solid-phase proteoliposomes retaining the envelope glycoproteins as trimeric spikes in a physiologic membrane setting have been described. Here, we compare the immunogenic properties of these two trimeric envelope glycoprotein formulations and monomeric gp120 in rabbits. Both trimeric envelope glycoprotein preparations generated neutralizing antibodies more effectively than gp120. In contrast to monomeric gp120, the trimeric envelope glycoproteins elicited neutralizing antibodies with some breadth of neutralization. Furthermore, repeated boosting with the soluble trimeric formulations resulted in an increase in potency that allowed neutralization of a subset of neutralization-resistant HIV-1 primary isolates. We demonstrate that the neutralization is concentration-dependent, is mediated by serum IgG and that the major portion of the neutralizing activity is not directed against the gp120 V3 loop. Thus, mimics of the trimeric envelope glycoprotein spike described here elicit HIV-1-neutralizing antibodies that could contribute to a protective immune response and provide platforms for further modifications to improve the efficiency of this process.     

Recombinant multi-epitope vaccine induce predefined epitope-specific antibodies against HIV-1

Monoclonal antibody 2F5 recognizing ELDKWA-epitope on HIV-1 gp41 has significant neutralization potency against 90% of the investigated viruses of African, Asia, American and European strains, but antibodies responses to ELDKWA-epitope in HIV-1 infected individuals were very low. Based on the epitope-vaccine strategy suggested by us, a recombinant glutathione S-transferase (GST) fusion protein (GST-MELDKWAGELDKWAGELDKWAVDIGPGRAFYGPGRAFYGPGRAFY) as vaccine antigen containing three repeats of neutralizing epitope ELDKWA on gp41 and GPGRAFY on gp120 was designed and expressed in Escherichia coli. After vaccination course, the recombinant multi-epitope vaccine could induce high levels of predefined multi-epitope-specific antibodies in mice. These antibodies in sera could bind to both neutralizing epitopes on gp41 peptide, V3 loop peptide and recombinant soluble gp41 (aa539-684) in ELISA assay (antisera dilution: 1:1,600-25,600), while normal sera did not. Moreover, these antibodies in sera could recognize the CHO-WT cells which expressed HIV-1 envelope glycoprotein on the cell surfaces, indicating that the predefined epitope-specific antibodies could recognize natural envelope protein of HIV-1 though these antibodies were induced by recombinant multi-epitope-vaccine. These experimental results suggested a possible way to develop recombinant multi-epitope vaccine inducing multi-antiviral activities against HIV-1.     

Utility of various commercially available human immunodeficiency virus (HIV) antibody diagnostic kits for use in conjunction with efficacy trials of HIV-1 vaccines.

There is a need for human immunodeficiency virus (HIV) screening assays which will distinguish uninfected HIV vaccine recipients from HIV-infected individuals. Commercial screening kits were used to test serum samples from low- and high-risk participants in clinical trials before and after immunization with various recombinant HIV type 1 (HIV-1) envelope glycoprotein 120 (gp120) candidate vaccines. All kits were 100% sensitive in detecting HIV infection. Both Murex Single Use Diagnostic System and United Biomedical, Inc., HIV type 1 or 2 (HIV-1/2) enzyme immunoassay (EIA) kits, which detect antibodies to HIV-1 gp41, were 98 to 100% specific when used to screen baseline or recombinant gp120-vaccinated populations as vaccine-induced antibodies to gp120 were nonreactive in these tests. The Abbott HIVAB HIV-1 EIA (lysate of whole infected cells, reactive with anti-gp120 antibodies) gave high levels of reactivity due to vaccine-induced antibodies and a high baseline rate of false positives (12 of 83) among nonvaccinated high-risk volunteers. Assays containing only gp41 and p24 solid-phase components are compatible with gp120-based vaccines but are unlikely to be useful in a similar role for vaccines containing gp160, gp41, or gp120 plus p24 antigens. Efficacy trials must be designed in concert with available diagnostic screening assays to avoid problems caused by vaccine-induced seroconversion in high-risk populations.     

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.