Dependence on a variable residue limits the breadth of an HIV MPER neutralizing antibody, despite convergent evolution with broadly neutralizing antibodies

Broadly neutralizing antibodies (bNAbs) that target the membrane-proximal external region (MPER) of HIV gp41 envelope, such as 4E10, VRC42.01 and PGZL1, can neutralize >80% of viruses. These three MPER-directed monoclonal antibodies share germline antibody genes (IGHV1-69 and IGKV3-20) and form a bNAb epitope class. Furthermore, convergent evolution within these two lineages towards a ^111.2GW^111.3 motif in the CDRH3 is known to enhance neutralization potency. We have previously isolated an MPER neutralizing antibody, CAP206-CH12, that uses these same germline heavy and light chain genes but lacks breadth (neutralizing only 6% of heterologous viruses). Longitudinal sequencing of the CAP206-CH12 lineage over three years revealed similar convergent evolution towards ^111.2GW^111.3 among some lineage members. Mutagenesis of CAP206-CH12 from ^111.2GL^111.3 to ^111.2GW^111.3 and the introduction of the double GWGW motif into CAP206-CH12 modestly improved neutralization potency (2.5–3-fold) but did not reach the levels of potency of VRC42.01, 4E10 or PGZL1. To explore the lack of potency/breadth, viral mutagenesis was performed to map the CAP206-CH12 epitope. This indicated that CAP206-CH12 is dependent on D⁶⁷⁴, a highly variable residue at the solvent-exposed elbow of MPER. In contrast, VRC42.01, PGZL1 and 4E10 were dependent on highly conserved residues (W⁶⁷², F⁶⁷³, T⁶⁷⁶, and W⁶⁸⁰) facing the hydrophobic patch of the MPER. Therefore, while CAP206-CH12, VRC42.01, PGZL1 and 4E10 share germline genes and show some evidence of convergent evolution, their dependence on different amino acids, which impacts orientation of binding to the MPER, result in differences in breadth and potency. These data have implications for the design of HIV vaccines directed at the MPER epitope.

Germline-targeting immunogens are a promising HIV vaccine design strategy. This approach is reliant on the identification of broadly neutralizing antibody (bNAb) classes, which use the same germline antibody genes to target the same viral epitopes. Here, we compare four HIV Envelope MPER-directed antibodies (4E10, VRC42.01, PGZL1 and CAP206-CH12) that despite having shared antibody genes, show distinct neutralization profiles. We show that CAP206-CH12 is dependent on a highly variable residue in the MPER, which results in low neutralization breadth. In contrast, the 4E10, PGZL1 and VRC42.01 mAbs are dependent on highly conserved residues in the MPER, resulting in exceptional neutralization breadth. Our data suggest that while shared germline genes within bNAb epitope classes are required, in some cases these are not sufficient to produce neutralization breadth, and MPER immunogens will need to trigger responses to conserved sites.

A Conserved Tryptophan in the Envelope Cytoplasmic Tail Regulates HIV-1 Assembly and Spread

The HIV-1 envelope (Env) is an essential determinant of viral infectivity, tropism and spread between T cells. Lentiviral Env contain an unusually long 150 amino acid cytoplasmic tail (EnvCT), but the function of the EnvCT and many conserved domains within it remain largely uncharacterised. Here, we identified a highly conserved tryptophan motif at position 757 (W757) in the LLP-2 alpha helix of the EnvCT as a key determinant for HIV-1 replication and spread between T cells. Alanine substitution at this position potently inhibited HIV-1 cell–cell spread (the dominant mode of HIV-1 dissemination) by preventing recruitment of Env and Gag to sites of cell–cell contact, inhibiting virological synapse (VS) formation and spreading infection. Single-molecule tracking and super-resolution imaging showed that mutation of W757 dysregulates Env diffusion in the plasma membrane and increases Env mobility. Further analysis of Env function revealed that W757 is also required for Env fusion and infectivity, which together with reduced VS formation, result in a potent defect in viral spread. Notably, W757 lies within a region of the EnvCT recently shown to act as a supporting baseplate for Env. Our data support a model in which W757 plays a key role in regulating Env biology, modulating its temporal and spatial recruitment to virus assembly sites and regulating the inherent fusogenicity of the Env ectodomain, thereby supporting efficient HIV-1 replication and spread.

Cholesterol Constrains the Antigenic Configuration of the Membrane-Proximal Neutralizing HIV-1 Epitope

The envelope glycoprotein (Env) enables HIV-1 cell entry through fusion of host-cell and viral membranes induced by the transmembrane subunit gp41. Antibodies targeting the C-terminal sequence of the membrane-proximal external region (C-MPER) block the fusogenic activity of gp41 and achieve neutralization of divergent HIV-1 strains and isolates. Thus, recreating the structure that generates broadly neutralizing C-MPER antibodies during infection is a major goal in HIV vaccine development. Here, we have reconstituted a peptide termed CpreTM-TMD in a membrane environment. This peptide contains the C-MPER epitope and the minimum TMD residues required for the anchorage of the Env glycoprotein to the viral membrane. In addition, we have used antibody 10E8 variants to gauge the antigenic configuration attained by CpreTM-TMD as a function of the membrane cholesterol content, a functional determinant of the HIV envelope and liposome-based vaccines. Differential binding of the 10E8 variants and the trend of the IgG responses recovered from rabbits immunized with liposome-peptide formulations, suggested that cholesterol may restrict 10E8 accessibility to the C-MPER epitope. Our data ruled out the destabilization of the lipid bilayer architecture in CpreTM-TMD-containing membranes, and pointed to the perturbation of the helical conformation by lipid packing as the cause of the antigenic configuration loss induced by cholesterol. Overall, our results provide additional insights into the structural basis of the Env complex anchoring to membranes, and suggest new approaches to the design of effective immunogens directed against the near pan-neutralizing HIV-1 epitope C-MPER.

Massively Parallel Profiling of HIV-1 Resistance to the Fusion Inhibitor Enfuvirtide

Identifying drug resistance mutations is important for the clinical use of antivirals and can help define both a drug’s mechanism of action and the mechanistic basis of resistance. Resistance mutations are often identified one-at-a-time by studying viral evolution within treated patients or during viral growth in the presence of a drug in cell culture. Such approaches have previously mapped resistance to enfuvirtide, the only clinically approved HIV-1 fusion inhibitor, to enfuvirtide’s binding site in the N-terminal heptad repeat (NHR) of the Envelope (Env) transmembrane domain as well as a limited number of allosteric sites. Here, we sought to better delineate the genotypic determinants of resistance throughout Env. We used deep mutational scanning to quantify the effect of all single-amino-acid mutations to the subtype A BG505 Env on resistance to enfuvirtide. We identified both previously characterized and numerous novel resistance mutations in the NHR. Additional resistance mutations clustered in other regions of Env conformational intermediates, suggesting they may act during different fusion steps by altering fusion kinetics and/or exposure of the enfuvirtide binding site. This complete map of resistance sheds light on the diverse mechanisms of enfuvirtide resistance and highlights the utility of using deep mutational scanning to comprehensively map potential drug resistance mutations.

Anti-HIV double variable domain immunoglobulins binding both gp41 and gp120 for targeted delivery of immunoconjugates

Background

Anti-HIV immunoconjugates targeted to the HIV envelope protein may be used to eradicate the latent reservoir of HIV infection using activate-and-purge protocols. Previous studies have identified the two target epitopes most effective for the delivery of cytotoxic immunoconjugates the CD4-binding site of gp120, and the hairpin loop of gp41. Here we construct and test tetravalent double variable domain immunoglobulin molecules (DVD-Igs) that bind to both epitopes.

Methods

Synthetic genes that encode DVD-Igs utilizing V-domains derived from human anti-gp120 and anti-gp41 Abs were designed and expressed in 293F cells. A series of constructs tested different inter-V-linker domains and orientations of the two V domains. Antibodies were tested for binding to recombinant Ag and native Env expressed on infected cells, for neutralization of infectious HIV, and for their ability to deliver cytotoxic immunoconjugates to infected cells.

Findings

The outer V-domain was the major determinant of binding and functional activity of the DVD-Ig. Function of the inner V-domain and bifunctional binding required at least 15 AA in the inter-V-domain linker. A molecular model showing the spatial orientation of the two epitopes is consistent with this observation. Linkers that incorporated helical domains (A[EAAAK]_nA) resulted in more effective DVD-Igs than those based solely on flexible domains ([GGGGS]_n). In general, the DVD-Igs outperformed the less effective parental antibody and equaled the activity of the more effective. The ability of the DVD-Igs to deliver cytotoxic immunoconjugates in the absence of soluble CD4 was improved over that of either parent.

Conclusions

DVD-Igs can be designed that bind to both gp120 and gp41 on the HIV envelope. DVD-Igs are effective in delivering cytotoxic immunoconjugates. The optimal design of these DVD-Igs, in which both domains are fully functional, has not yet been achieved.

[Development of a rapid test kit for antibody to HIV by nano immunomagnetic lateral flow method]

OBJECTIVE

To develop a rapid test kit for antibody to HIV by nano immunomagnetic lateral flow method.

METHODS

A rapid test kit was developed by conjugation of the HIV antigen gp41 and gp36 to 200nm super paramagnetic particles by carbodiimide (EDC) and coating of the HIV antigen gp41 and gp36 to nitrocellulose membrane. Then the kit was evaluated with serials of experiments.

RESULTS

The kit was qualified with examination of national reference panel of anti-HIV antibody for colloidal gold diagnostic kit. The sensitivity was 100% by tested with 20 HIV antibody positive sera, the specificity was 98.5% by tested with 600 HIV antibody negative sera, respectively. The stability of the kit was over 12 month by storage at room temperature.

CONCLUSION

A diagnostic kit for antibody to HIV was developed with the advantages of convenience, rapid test, good stability and point of care.

Cryoelectron tomography of HIV-1 envelope spikes: further evidence for tripod-like legs

A detailed understanding of the morphology of the HIV-1 envelope (Env) spike is key to understanding viral pathogenesis and for informed vaccine design. We have previously presented a cryoelectron microscopic tomogram (cryoET) of the Env spikes on SIV virions. Several structural features were noted in the gp120 head and gp41 stalk regions. Perhaps most notable was the presence of three splayed legs projecting obliquely from the base of the spike head toward the viral membrane. Subsequently, a second 3D image of SIV spikes, also obtained by cryoET, was published by another group which featured a compact vertical stalk. We now report the cryoET analysis of HIV-1 virion-associated Env spikes using enhanced analytical cryoET procedures. More than 2,000 Env spike volumes were initially selected, aligned, and sorted into structural classes using algorithms that compensate for the "missing wedge" and do not impose any symmetry. The results show varying morphologies between structural classes: some classes showed trimers in the head domains; nearly all showed two or three legs, though unambiguous three-fold symmetry was not observed either in the heads or the legs. Subsequently, clearer evidence of trimeric head domains and three splayed legs emerged when head and leg volumes were independently aligned and classified. These data show that HIV-1, like SIV, also displays the tripod-like leg configuration, and, unexpectedly, shows considerable gp41 leg flexibility/heteromorphology. The tripod-like model for gp41 is consistent with, and helps explain, many of the unique biophysical and immunological features of this region.

Preferential use of the VH5-51 gene segment by the human immune response to code for antibodies against the V3 domain of HIV-1

Human anti-V3 monoclonal antibodies (mAbs) generated from HIV-1 infected individuals display diversity in the range of their cross-neutralization that may be related to their immunogenetic background. The study of the immunoglobulin (Ig) variable region gene usage of heavy chains have shown a preferential usage of the VH5-51 gene segment which was detected in 35% of 51 human anti-V3 mAbs. In contrast, human mAbs against other envelope regions of HIV-1 (anti-Env), including the CD4-binding domain, the CD4-induced epitope, and gp41 preferentially used the VH1-69 gene segment, and none of them used the VH5-51 gene. Furthermore, the usage of the VH4 family by anti-V3 mAbs was restricted to only one gene segment, VH4-59, while the VH3 gene family was used at a significantly lower frequency by all of the analyzed anti-HIV-1 mAbs. Multivariate analysis showed that usage of VH gene segments was significantly different between anti-V3 and anti-Env mAbs, and compared to antibodies from healthy subjects. In addition, the anti-V3 mAbs preferentially used the JH3 and D2-15 gene segments. The preferential usage of selected Ig gene segments and the characteristic pattern of Ig gene usage by anti-V3 mAbs can be related to the conserved structure of the V3 region.

Pharmacokinetics of enfuvirtide in patients treated in typical routine clinical settings

Therapeutic drug monitoring (TDM) is gaining importance for improving the success of antiretroviral treatment in human immunodeficiency virus-infected patients. However, enfuvirtide (ENF) concentrations are not regularly determined. The objective of this work was to study the pharmacokinetics (PK) of ENF in patients treated in routine clinical settings, to develop a population PK model describing the concentration-time profile, and to establish PK reference values. A liquid chromatography-tandem mass spectrometry method was developed and applied to serum samples submitted for TDM. A two-compartment model with linear absorption and elimination was fitted to 329 concentrations from 131 patients. The PK model was used for simulations resulting in percentile curves for ENF levels for the full dosing interval. The model predicted that a median concentration of 1,968 ng/ml would be reached 12 h after administration of 90 mg of ENF, and 23% and 58% of patients are expected to have concentrations below 1,000 ng/ml and 2,200 ng/ml, respectively. Both values have been proposed as cutoffs for virological efficacy. The median maximum concentration of drug in serum (Cmax) of 3,943 ng/ml, predicted for 3 h after drug administration, is lower than the Cmax reported previously. We found an enormous interpatient variability at every time point, with concentration spectrums covering >1 log and 52% and 123% interindividual variabilities in the typical clearance and volume of distribution, respectively, in contrast to preexisting PK data. In summary, ENF levels are lower and more variable than expected. Many patients may achieve insufficient concentrations. Further covariate analysis in the population PK model might help to identify factors influencing the variability in ENF concentrations.

[HIV entry into the cells--mechanisms and therapeutic possibilities]

Human immunodeficiency virus (HIV) entry into cells is the first step in the viral replication cycle, which has been explored as a new therapeutic target. A better knowledge of the mechanisms involved in the entry process has led to the development of agents, which may inhibit each of the different steps of the viral entry process: attachment of the gp120 to the CD4 cell receptor; binding of the gp120 to CCR5 or CXCR4 coreceptors; and the fusion of viral and cell membranes. Entry inhibitors are the latest family of antiretroviral compounds, being enfuvirtide, a fusion inhibitor, the first approved. Several other entry inhibitors are currently in clinical development and hopefully soon will be part of the therapeutic armamentarium against HIV.

[Progress in antiretroviral drugs]

HIV-1, causative agent of acquired immunodeficiency syndrome, was identified in the early 1980s . The plague quickly spread throughout the world and today 40 million people are living with HIV/AIDS. The first anti-HIV drug "zidovudine", was discovered in 1985, and many other inhibitory compounds have been developed successfully in the last decade. Today, three classes 17 antiretroviral drugs are available in Japan. This article overviews the history of anti-HIV drug discovery, present HIV-1 treatment, and on-going drug discovery.

Pharmacokinetics of Enfuvirtide in a Patient with Impaired Renal Function

Enfuvirtide is the first member of the fourth class of antiretroviral drugs to become available. We present a case report of a human immunodeficiency virus (HIV)-positive patient with mild renal impairment who developed severe renal impairment secondary to tenofovir therapy while receiving enfuvirtide. Because the patient's pharmacokinetic profile was not significantly altered, compared with that of HIV-infected patients with normal renal function, no dose modifications were required.

Penetration of enfuvirtide, tenofovir, efavirenz, and protease inhibitors in the genital tract of HIV-1-infected men

One likely mechanism of virological failure is poor antiretroviral drug diffusion in sites of viral replication such as the genital tract. We measured antiretroviral drug concentrations in blood and semen in 13 HIV-infected men failing treatment. Enfuvirtide did not cross the blood-testis barrier, whereas tenofovir accumulated in semen. Unlike indinavir, semen concentrations of lopinavir, amprenavir, saquinavir and efavirenz were ineffective. These are worrying findings, because suboptimal semen drug concentrations may enhance the risk of sexually transmitted drug-resistant HIV variants.

Long term tolerability and safety of enfuvirtide for human immunodeficiency virus 1-infected children

BACKGROUND

Enfuvirtide, a peptide inhibitor of human immunodeficiency virus (HIV)-1-host cell membrane fusion, is the first of a new class of antiretroviral agents, the entry inhibitors. The safety and antiretroviral activity of enfuvirtide treatment of 24 weeks in HIV-1-infected children has been previously documented. Here we present the long term tolerability and safety of enfuvirtide.

METHODS

Fourteen children, 4 to 12 years of age, with incompletely suppressed HIV-1 infection were evaluated. Enfuvirtide was administered twice daily by subcutaneous injection. After the first 24 weeks of enfuvirtide dosing, subjects were evaluated every 8 weeks up to 96 weeks of therapy. At each visit, each subject had a physical examination and an assessment for adverse events with particular attention to evaluation of injection site reactions. Laboratory studies obtained at each visit included hematology and blood chemistry values, plasma HIV-1 RNA concentrations and CD4+ T cell counts.

RESULTS

Of 14 subjects, 6 completed at least 96 weeks of treatment. One child discontinued enfuvirtide after 22 days of treatment because of an aversion to injections, and 1 child electively discontinued after week 24 because of surgical complications unrelated to study drug. Four subjects discontinued study because of virologic failure, defined as an increase or persistence of plasma HIV-1 RNA 1.0 copies/mL above baseline, which occurred between >or =log10 weeks 40 and 63. Two children experienced grade 3 adverse events resulting in discontinuation of the study drug; 1 subject developed grade 3 thrombocytopenia and 1 developed grade 3 edema at weeks 65 and 77, respectively. Eleven of 14 children had local injection site reactions during the first 24 weeks of treatment, 4 of the 12 subjects who continued treatment beyond week 24 reported local reactions. Generally, these local reactions were 1- to 3-cm tender nodules that developed after the injections and lasted for 1-2 days. Twelve children developed new diagnoses during treatment with enfuvirtide. None was judged to be definitively related to the study drug. Thirty-six percent of children starting enfuvirtide had HIV-1 RNA levels > 1 log10 copies/mL below baseline levels at week 96. Children remaining on enfuvirtide for the entire 96 weeks had a median of 65 cells/mm and 9% increase in CD4+ T cells.

CONCLUSIONS

Enfuvirtide was generally safe and, except for a high rate of injection site reactions, well-tolerated in HIV-1-infected children for as long as 96 weeks.

Large-scale manufacture of peptide therapeutics by chemical synthesis

The large-scale commercial production of a 36-amino-acid peptide by chemical synthesis has been demonstrated in the development of enfuvirtide (T-20 or Fuzeon), a first-in-class membrane fusion inhibitor for the treatment of HIV. The rationale behind route selection and the scale-up of the process used to manufacture enfuvirtide are discussed.

Automatic quantitation of HIV-1 mediated cell-to-cell fusion with a digital image analysis system (DIAS): application for rapid screening of HIV-1 fusion inhibitors

Human immunodeficiency viruses type 1 (HIV-1) mediated cell-to-cell fusion plays an important role in HIV-1 spread from infected cells to uninfected cells and in HIV-1 cytopathogenesis. In the present study, we developed a convenient cell fusion assay using a computer-controlled digital image analysis system (DIAS) for automatic quantitation. Compared with a manual quantitative method, DIAS automatic method is less laborious, and more rapid. Furthermore, it is more objective and less dependent on the researchers' experience. This method has great potential to be developed further as a high-throughput screening assay for rapid screening of HIV-1 fusion inhibitors, for evaluating the activity of HIV-1 entry inhibitors and for studying the mechanism of action of anti-HIV-1 agents.

[Coreceptors of HIV infection and the development of HIV entry inhibitors: overview and targets]

In 1996 CXCR4 was identified as a coreceptor for HIV-1. This finding has lead to further identification of more than ten G-protein-coupled receptors (GPCRs) as coreceptors for HIV/SIV. Cell tropisms and coreceptor uses of HIV during the course of HIV infection are summarized. Promiscuous properties of correlations between chemokines and their chemokine receptor uses and also between variable amino acid sequences in the V3 region of HIV gp120 Env and HIV coreceptor uses are discussed. This promiscuous property of HIV-1 is claimed to be a possible cause of a difficulty in developing highly effective entry inhibitors and in addition to allow rapid appearance of immune escape HIV mutants. Representative agents that inhibit HIV entry with a special reference to inhibitors of coreceptor use and gp41 function are summarized. gp41 is discussed as a promising target for the development of effective entry inhibitors.

HIV type 1 non-B subtype prevalence in Spain, 1997-1998

We have evaluated the prevalence of HIV-1 non-B subtypes in Spain by means of an enzyme immunoassay (EIA) for discrimination between B and non-B subtypes. Samples were obtained from newly diagnosed patients attended at internal medicine outpatient clinics between October 1997 and October 1998. Discrimination between HIV-1 B and non-B subtypes was carried out by means of the EIA, with V3 synthetic peptides specific to the different subtypes. Non-B-serotyped samples were genetically analyzed in the gp41 region from the original sera. During the study period, 909 samples were collected from 21 medical units located in various Spanish geographical regions. Serotyping was possible in 885 cases, of which 791 were assigned as B serotype (89.38%), 70 showed no reactivity to any of the peptides (7.91%), and the remaining samples displayed other reaction patterns (2.72%). Of the 94 non-B-assigned samples, 65 were genetically characterized in the gp41 region of the env gene: 55 were B subtype, 5 were A subtype (4 clustered with CRF02AG reference strains), 3 were C subtype, and 2 were G subtype. The prevalence rate for non-B subtypes in Spain was established at 1.13% (95% CI, 0.59-2.21). Although the B subtype is predominant in the Spanish population, other subtypes have been detected.

Synthetic peptide strategy for the detection of and discrimination among highly divergent primate lentiviruses

We developed a simple, rapid, inexpensive, and highly sensitive and specific strategy for the detection and lineage differentiation of primate lentiviruses (PIV-ELISA). It is based on the use of two indirect ELISA methods using synthetic peptides mapping the gp41/36 region (detection component) and the V3 region (differentiation component) of four lentivirus lineages, namely SIVcpz/HIV-1 (groups M, O, N, and SIVcpz-gab), SIVmnd, SIVagm, and SIVsm/SIVmac/HIV-2. This strategy was evaluated with panels of sera originating from both humans and nonhuman primates. The human reference panel consisted of 144 HIV Western blot (WB)-positive sera in which the corresponding virus had been genotyped (HIV-1: 72 group M, 28 group O, and 6 group N; HIV-2: 21 subtype A and 10 subtype B; and 7 HIV-1+2) and 105 HIV WB-negative samples. The nonhuman primate reference panel consisted of 24 sera from monkeys infected by viruses belonging to the four lineages included in the PIV-ELISA strategy (5 chimpanzees, 5 macaques, 8 mandrills, and 6 vervets) and 42 samples from seronegative animals. Additional field evaluation panels consisted of 815 human sera from Gabon, Cameroon, and France and 537 samples from 25 nonhuman primate species. All the samples from the two reference panels were correctly detected and discriminated by PIV-ELISA. In the human field evaluation panel, the gp41/36 component correctly identified all the test samples, with 98% specificity. The V3 component discriminated 206 HIV-1 group M, 98 group O, 12 group M+O, and 128 HIV-2 sera. In the primate field evaluation panel, both gp41/36 and V3 detected and discriminated all the WB-positive samples originating from monkeys infected with SIVcpz, SIVagm-ver, SIVmnd-1, SIVmnd-2, SIVdrl, or SIVsun. These results were confirmed by genotyping in every case. Four SIV-infected red-capped mangabeys (confirmed by PCR) were correctly identified by gp41/36, but only two reacted with the V3 peptides in the absence of a specific SIVrcm V3 peptide. Addition of a V3 SIVrcm peptide discriminated all the SIVrcm-positive samples. Fourteen Papio papio samples were positive for SIVsm gp 36 and by WB, but negative by PCR, whereas three Papio cynocephalus samples were positive by gp41/36 but indeterminate by WB and negative by PCR. This combined ELISA system is thus highly sensitive and specific for antibodies directed against HIV and SIV. In addition, the V3-based serotyping results always agreed with genotyping results. This method should prove useful for studies of lentivirus prevalence and diversity in human and nonhuman primates, and may also have the potential to detect previously undescribed SIVs.

Interference with complement regulatory molecules as a possible therapeutic strategy in HIV infection

Drugs which inhibit different stages of the HIV infection process, such as cell entry through CD4 and chemokine receptors, production of double stranded DNA from the HIV genome and maturation of newly produced viruses, are now proposed for AIDS therapy. None of these treatments, however, solve the problem of complete HIV eradication and the frequent appearance of mutants displaying drug resistance. We have recently detailed a strategy describing how HIV protects itself from the human complement and propose that interference of this resistance could be a possible target for therapy.

Gamete interactions in Xenopus laevis: identification of sperm binding glycoproteins in the egg vitelline envelope

A quantitative assay was developed to study the interaction of Xenopus laevis sperm and eggs. Using this assay it was found that sperm bound in approximately equal numbers to the surface of both hemispheres of the unfertilized egg, but not to the surface of the fertilized egg. To understand the molecular basis of sperm binding to the egg vitelline envelope (VE), a competition assay was used and it was found that solubilized total VE proteins inhibited sperm-egg binding in a concentration-dependent manner. Individual VE proteins were then isolated and tested for their ability to inhibit sperm binding. Of the seven proteins in the VE, two related glycoproteins, gp69 and gp64, inhibited sperm-egg binding. Polyclonal antibody was prepared that specifically recognized gp69 and gp64. This gp69/64 specific antibody bound to the VE surface and blocked sperm binding, as well as fertilization. Moreover, agarose beads coated with gp69/64 showed high sperm binding activity, while beads coated with other VE proteins bound few sperm. Treatment of unfertilized eggs with crude collagenase resulted in proteolytic modification of only the gp69/64 components of the VE, and this modification abolished sperm-egg binding. Small glycopeptides generated by Pronase digestion of gp69/64 also inhibited sperm-egg binding and this inhibition was abolished by treatment of the glycopeptides with periodate. Based on these observations, we conclude that the gp69/64 glycoproteins in the egg vitelline envelope mediate sperm-egg binding, an initial step in Xenopus fertilization, and that the oligosaccharide chains of these glycoproteins may play a critical role in this process.

Advantage of dimeric peptide antigens in serodiagnosis of HIV-1 infection

The reactivity of antibodies with dimeric and monomeric peptide antigens was compared by ELISA. A panel of highly purified synthetic peptides of HIV-1 representing defined regions, 598-609 and 524-533 (fusion domain) of gp41 and 306-320 of gp120, were used as antigens in the ELISA. These peptides were selected and synthesized taking into account the level of sequence conservation of various strains and hydrophilicity. The analysis included sera from 52 HIV-1 infected individuals and 53 HIV-1 negative controls. Both peptides from gp41 were found to be particularly immunoreactive with sera from HIV-1 infected individuals. The frequency of reactivity to the selected peptide from gp120 (V3 loop) in infected individuals was 82%. An interesting observation was that the dimeric peptide antigens had a detection rate more than 4-fold higher than the monomeric antigens. We found that lower levels of antibodies could be detected with dimeric antigens. The peptides reacted with few sera other than HIV-1 positive sera. These results implicate the potential dimeric peptide antigens to be utilized in the serodiagnosis of HIV-1 infection.

[Biochemical changes in cerebrospinal fluid associated with the neurotoxic action of HIV-1]

The aim of this study is to evaluate the usefulness of different markers to diagnose neurologic and psychiatric diseases due to HIV-1 infection Increased concentration of quinolenic acid has been implicated in the neurologic deficits and brain atrophy that may accompany infection with the HIV-1 virus. CFS concentrations of quinolenic acid have been implicated in the pathogenesis of the AIDS dementia complex. Cytokines liberation are very altered and this factor may be correlated with direct toxicity about central nervous system cells. Also are increased the values of neopterin. In the different stages of AIDS, the highest values are obtained in dementia complex. Neopterin, tryptofan and kinorenina, in blood and CFS are directly correlated with neurologic and psychiatry sintomatology. The highest values of soluble intercellular adhesion molecule 1 are found in HIV encephalopathy As well as are important the values, in CSF and blood of beta-2-M, Ag HIV, Ac41, tumor necrosis factor-alpha in the neurologic disease in HIV-1 infection

The most highly amphiphilic alpha-helices include two amino acid segments in human immunodeficiency virus glycoprotein 41

A search for highly amphiphilic alpha-helices has been made in a data base of protein sequences, using the helical hydrophobic moment as a criterion of amphiphilicity. The protein segments of largest hydrophobic moment have been analyzed. For the segments whose structures are known, they are in fact alpha-helices. Two of the segments having very large hydrophobic moments are from the smaller C-terminal portion of the human immunodeficiency virus (HIV) envelope glycoprotein gp41. Also, among segments having large hydrophobic moments, but not among the most extreme, are lytic peptides such as melittin. Melittin seeks surfaces between polar and apolar phases, including the membrane-water interface. It is conceivable that the gp41 segments of extreme hydrophobic moment may participate in one of the membrane-related functions of the HIV virus.

Role of the carboxy-terminal portion of the HIV-1 transmembrane protein in viral transmission and cytopathogenicity

The transmembrane glycoprotein (gp41) of human immunodeficiency virus type-1 (HIV-1) has a long cytoplasmic domain of unknown functional significance. To investigate the role of the carboxy-terminal (C-terminal) portion of the HIV-1 envelope protein in viral replication, infectivity, and cytopathogenicity, we examined the properties of a panel of mutants with variable deletions in the 3'-env region. Deletion of the C-terminal 76 amino acids did not abolish production of reverse transcriptase upon transfection of COS-1 cells. Deletion of the C-terminal 6-14 amino acids appeared sufficient to alter the replication pattern, infectivity, and cytopathogenicity of some clones. The data suggest that conformational determinants or specific sequences are responsible for the observed changes, rather than simply the length of the gp41 cytoplasmic tail.

Mapping of IgG subclass and T-cell epitopes on HIV proteins by synthetic peptides

Fifteen amino acid peptides, sequentially overlapping by 10 amino acids, were synthesized on the basis of the HTLV-III sequences of the gag and env proteins. They were used as antigens in IgG subclass ELISAs and T-cell stimulation assays. Sera and cells were obtained from 30 asymptomatic, HIV-infected homosexuals. In all subclasses reactivity was found to parts of the gag protein, while IgG1 dominated anti-env peptide responses. It was possible to delineate peptides showing restricted IgG subclass responses that were dominated by either IgG1, 2, 3 or 4. A negative correlation was generally observed between B-cell and T-cell reactivity, but a T-cell and B-cell co-operation was suggested by the response to two IgG1-restricted peptides. The IgG3-dominated epitopes were present in peptides previously known to be amphipathic and capable of T-cell stimulation. The analysis of subclass-restricted responses on the peptide level will assist the understanding of the subclass expression in vivo, since the peptide mapping approximates the delineation of a subclass-restricted response at the level of single epitopes.

Fine mapping of an immunodominant region of the transmembrane protein of the human immunodeficiency virus (HIV-1)

Peptides of HIV sequences are significant for antibody screening systems, and because of the limited number of amino acids they have to represent immunodominant regions of the virus proteins in order to maintain sensitivity. We detected, in a region of the outside loop of the transmembrane protein gp41 of the human immunodeficiency virus HIV-1 (amino acid 586-620), two immunodominant sequences which are distinct from each other. Whereas in the first immunodominant region the sensitivity and specificity of ELISA were inadequate, a neighbouring region is well suited for use as antigen for an anti-HIV screening ELISA.

A general model for the transmembrane proteins of HIV and other retroviruses

A hypothetical model of the transmembrane (TM) protein of human immunodeficiency virus (HIV) is proposed that is derived from the known structure of the influenza TM protein HA2. This model is consistent with computer algorithms of predicted protein structure and with known properties of TM proteins determined by sequence homology, site-directed mutations, peptide analogs, immunochemistry, or other biologic means. It is applicable to a wide variety of retroviral TM proteins differing widely in overall molecular weight.

Inhibition of lymphoproliferation by a synthetic peptide with sequence identity to gp41 of human immunodeficiency virus type 1

Peptides were synthesized that contained sequences from two regions (env amino acids [aa] 581 to 597 and 655 to 671) of the transmembrane protein gp41 and one region of the external envelope glycoprotein gp120 (aa 457 to 464) of human immunodeficiency virus type 1. Selection of these sequences was based on their homology to the highly conserved and immunosuppressive sequence contained within the transmembrane proteins p15E and gp21 of animal and human retroviruses, respectively. Peptide aa581-597 was found to specifically inhibit human and murine lymphoproliferation, whereas peptides aa655-671 and aa457-464 had no activity. These results suggest a mechanism by which human immunodeficiency virus type 1 gp41 exerts a direct immunosuppressive effect in vivo, analogous to that postulated for p15E and gp21, which could contribute to the immune dysfunction observed in patients suffering from acquired immunodeficiency syndrome. It is of particular interest that the sequence aa 584 to 609, shown to contain B- and T-helper-cell epitopes, overlaps with the sequence aa 581 to 597 that is shown here to inhibit lymphoproliferation. The potential implications of this overlap of immunologic activities are discussed.

Oligomeric structure of gp41, the transmembrane protein of human immunodeficiency virus type 1

We characterized the structural forms of the human immunodeficiency virus env-encoded proteins with a panel of monoclonal and polyclonal antibodies. Western blot (immunoblot) assays with antibodies specific for gp41 invariably recognized a major component of 160 kilodaltons and a less intense component of 120 kilodaltons in viral lysates. We demonstrated that these species are noncovalently associated tetramers and trimers of gp41 which represent the native form of this protein in virions. These complexes were stable when boiled in the presence of low concentrations of sodium dodecyl sulfate but were dissociated to gp41 monomers at high sodium dodecyl sulfate concentrations. Moreover, two human monoclonal antibodies preferentially recognized the oligomeric complexes over monomeric gp41 in Western blots, indicating the presence of epitopes recognized by the human immune system on the gp41 multimers which are not efficiently expressed by the dissociated monomers. The demonstration of the existence of multimeric env complexes and the enhanced and altered antigenicity of such multimers may be relevant to the design of subunit and recombinant human immunodeficiency virus env vaccines.

A syncytia assay for human immunodeficiency virus type I (HIV-I) envelope protein and its use in studying HIV-I mutations

We describe a syncytia assay that utilizes a noninfectious plasmid (pEVd1443) derived from human immunodeficiency virus type I (HIV-I). This plasmid carries a large deletion of gag-pol sequences but expresses HIV-I envelope proteins and induces syncytia following transfection into HeLa-CD4 cells. This plasmid was used to study the effects of mutations in the gp 120 and gp41 portions of the envelope gene of HIV-I.

IgG subclass responses to a transmembrane protein (gp41) peptide in HIV infection

The IgG subclass distribution to the E34/E32 peptides, derived from the HIV-1 glycoprotein 41 transmembrane protein, was analyzed in ELISA. Sera from individuals at different stages of the disease were assayed. A restricted subclass response of mainly IgG1 and IgG2 was found. The subclass response was of a different type than the one observed to HIV whole Ag and to a synthetic peptide from the C'-terminal part of the HIV-1 p24 core protein. An increased subclass restriction was observed in progressed stages of the disease.

Biosynthesis and processing of human immunodeficiency virus type 1 envelope glycoproteins: effects of monensin on glycosylation and transport

When human immunodeficiency virus type 1 envelope glycoproteins were expressed in 293 cells by using a recombinant adenovirus expression vector, the envelope precursor (gp160) was initially glycosylated by cotranslational addition of N-linked high-mannose oligosaccharide units to the protein backbone and then cleaved to gp120 and gp41. The subunits gp120 and gp41 were then further modified by the addition of fucose, galactose, and sialic acid, resulting in glycoproteins containing a mixture of hybrid and complex oligosaccharide side chains. A fraction of glycosylated gp160 that escaped cleavage was further modified by the terminal addition of fucose and galactose, but the addition of sialic acid did not occur, consistent with the notion that it is compartmentalized separately from the gp120 envelope protein. Processing and transport of gp160 were blocked by the monovalent ionophore monensin, which at high concentrations (25 microM and above) was a potent inhibitor of the endoproteolytic cleavage of gp160; at lower concentrations (1 to 10 microM), it selectively blocked the secondary glycosylation steps so that smaller products were produced. Monensin (1 microM) treatment also resulted in a reduction in syncytium formation, which was observed when recombinant infected cells were cocultivated with CD4-bearing HeLa cells. The infectivity of human immunodeficiency virus type 1 was also reduced by monensin treatment, a decrease that may be due to incompletely glycosylated forms of gp120 that have a lower affinity for the CD4 receptor.

Discrimination of HIV-1 and HIV-2 infection based on recombinant immunoblots

Recombinant polypeptides representing various parts of structural proteins of HIV-1 and HIV-2 were expressed in E. coli. Fragments of the transmembrane proteins gp41 of HIV-1 (HTLV-IIIB) and gp38 of HIV-2 (LAV-2 ROD) proved to be highly antigenic in the immunoblot test system. Each protein was found to be suitable for detection and differentiation of antibodies in sera of patients infected with HIV-1 or HIV-2. Sera of 100 patients from West-Germany, which were confirmed as positive for HIV-1 antibodies, reacted clearly with the HIV-1 recombinant antigen (fpOE-6); no or only weak immune reactions were seen when the analogous recombinant HIV-2 antigen (fpOE-T) was used in the same immunoblot test. An inverse reaction pattern was found with 7 sera from Africa which, by conventional means, were proved to be HIV-2 antibody positive. These sera specifically reacted with the homologous HIV-2 fusion protein and no or only weakly stained bands were identified on the analogous strip with the HIV-1 antigen (fpOE-6).

Early detection of antibodies against rDNA-produced HIV proteins with a flow cytometric assay

There is evidence that some human immunodeficiency virus (HIV)-infected individuals have prolonged periods of seronegativity. A flow cytometric immunoreactive bead (IRB) assay is described for quantitative, simultaneous, and early detection of antibodies to HIV. Polystyrene beads of four diameters, each size coated with a different HIV recombinant DNA-produced protein (p24, p31, gp41, or gp120), bound anti-HIV antibodies detected with fluorescent antiglobulin. The IRB assay was performed on a panel of blood donor samples, many giving consistently false-positive enzyme immunoassay (EIA) and indeterminant Western blot (WB) results. The IRB assay proved as sensitive and more specific than currently licensed EIA and WB tests. Results on serial samples from eight HIV-infected individuals indicated that quantitation of anti-p24 by IRB assay may be useful in monitoring disease progression. Sequential pre- and post-EIA seroconversion sera from 35 HIV-infected homosexual men were tested by the IRB assay using IgM- and IgG-specific fluorescent probes. All 35 cases were IRB assay positive for at least one rDNA-p either before (17 of 35, 49%) or at the time of EIA positivity. Eleven cases (31%) initially had only IgM anti-HIV, primarily to gp41 (17%). In two individuals, the IgM response was detected at least 18 months before EIA seroconversion. The IRB assay is a widely applicable analytic procedure, potentially useful in pretransfusion anti-HIV screening of blood.

Identification of the fusion peptide of primate immunodeficiency viruses

Membrane fusion induced by the envelope glycoproteins of human and simian immunodeficiency viruses (HIV and SIVmac) is a necessary step for the infection of CD4 cells and for the formation of syncytia after infection. Identification of the region in these molecules that mediates the fusion events is important for understanding and possibly interfering with HIV/SIVmac infection and pathogenesis. Amino acid substitutions were made in the 15 NH2-terminal residues of the SIVmac gp32 transmembrane glycoprotein, and the mutants were expressed in recombinant vaccinia viruses, which were then used to infect CD4-expressing T cell lines. Mutations that increased the overall hydrophobicity of the gp32 NH2-terminus increased the ability of the viral envelope to induce syncytia formation, whereas introduction of polar or charged amino acids in the same region abolished the fusogenic function of the viral envelope. Hydrophobicity in the NH2-terminal region of gp32 may therefore be an important correlate of viral virulence in vivo and could perhaps be exploited to generate a more effective animal model for the study of acquired immunodeficiency syndrome.