Outbreak of Corynebacterium diphtheriae among asylum seekers in Belgium in 2022: operational challenges and lessons learnt.

Since 2022, European countries have been facing an outbreak of mainly cutaneous diphtheria caused by toxigenic Corynebacterium diphtheriae among asylum seekers. In Belgium, between 1 March and 31 December 2022, 25 cases of toxigenic C. diphtheriae infection were confirmed among asylum seekers, mostly among young males from Afghanistan. Multi-locus sequence typing showed that most isolates belonged to sequence types 574 or 377, similar to the majority of cases in other European countries. The investigation and management of the outbreak, with many asylum seekers without shelter, required adjustments to case finding, contact tracing and treatment procedures. A test-and-treat centre was organised by non-governmental organisations, the duration of the antimicrobial treatment was shortened to increase compliance, and isolation and contact tracing of cases was not possible. A vaccination centre was opened, and mobile vaccination campaigns were organised to vaccinate a maximum of asylum seekers. No more cases were detected between end December 2022 and May 2023. Unfortunately, though, three cases of respiratory diphtheria, including one death, were reported at the end of June 2023. To prevent future outbreaks, specific attention and sufficient resources should be allocated to this vulnerable population, in Belgium and at international level.

Interference with glycosaminoglycan-chemokine interactions with a probe to alter leukocyte recruitment and inflammation in vivo.

In vivo leukocyte recruitment is not fully understood and may result from interactions of chemokines with glycosaminoglycans/GAGs. We previously showed that chlorite-oxidized oxyamylose/COAM binds the neutrophil chemokine GCP-2/CXCL6. Here, mouse chemokine binding by COAM was studied systematically and binding affinities of chemokines to COAM versus GAGs were compared. COAM and heparan sulphate bound the mouse CXC chemokines KC/CXCL1, MIP-2/CXCL2, IP-10/CXCL10 and I-TAC/CXCL11 and the CC chemokine RANTES/CCL5 with affinities in the nanomolar range, whereas no binding interactions were observed for mouse MCP-1/CCL2, MIP-1α/CCL3 and MIP-1ß/CCL4. The affinities of COAM-interacting chemokines were similar to or higher than those observed for heparan sulphate. Although COAM did not display chemotactic activity by itself, its co-administration with mouse GCP-2/CXCL6 and MIP-2/CXCL2 or its binding of endogenous chemokines resulted in fast and cooperative peritoneal neutrophil recruitment and in extravasation into the cremaster muscle in vivo. These local GAG mimetic features by COAM within tissues superseded systemic effects and were sufficient and applicable to reduce LPS-induced liver-specific neutrophil recruitment and activation. COAM mimics glycosaminoglycans and is a nontoxic probe for the study of leukocyte recruitment and inflammation in vivo.

Role of cations in the interaction of pradimicins with HIV-1 envelope gp120.

Pradimicins (PRM) are a unique class of nonpeptidic carbohydrate-binding agents that inhibit HIV infection by efficiently binding to the HIV-1 envelope gp120 glycans in the obligatory presence of Ca(2+). Surface plasmon resonance (SPR) data revealed that addition of EDTA dose-dependently results in lower binding signals of PRM-A to immobilized gp120. Pradimicin derivatives that lack the free carboxylic acid group on the C-18 position failed to bind gp120 and were devoid of significant antiviral activity. Ca(2+) was much more efficient for PRM-A binding to gp120 than Cd(2+), Ba(2+) or Sr(2+). Instead, calcium could not be replaced by any other mono- (i.e. K(+)), di- (i.e. Cu(2+), Mg(2+), Mn(2+), Fe(2+), Zn(2+)) or trivalent (i.e. Al,(3+), Fe(3+)) cation without complete loss of gp120 binding. However, Zn(2+), Mg(2+) and Mn(2+) added to a Ca(2+)- pradimicin mixture, prevented pradimicin from efficient binding to gp120 glycans. These data suggest that these bivalent cations may bind to pradimicins but lead to pradimicin-cation complexes that are unable to further coordinate with the glycans of gp120. Thus, in order to afford antiviral activity, only a few cations can (i) bind to pradimicin to form a dimeric complex and (ii) subsequently coordinate the pradimicin/cation interaction with gp120 glycans.

The lantibiotic peptide labyrinthopeptin A1 demonstrates broad anti-HIV and anti-HSV activity with potential for microbicidal applications.

Lantibiotics are peptides, produced by bacteria, that contain the noncanonical amino acid lanthionine and many of them exhibit antibacterial activities. The labyrinthopeptin A1 (LabyA1) is a prototype peptide of a novel class of carbacyclic lantibiotics. Here, we extensively evaluated its broad-spectrum activity against HIV and HSV in vitro, studied its mechanism of action and evaluated potential microbicidal applications. LabyA1 exhibited a consistent and broad anti-HIV activity (EC50s: 0.70-3.3 µM) and anti-HSV activity (EC50s: 0.29-2.8 µM) in cell cultures. LabyA1 also inhibited viral cell-cell transmission between persistently HIV-infected T cells and uninfected CD4(+) T cells (EC50∶2.5 µM) and inhibited the transmission of HIV captured by DC-SIGN(+)-cells to uninfected CD4(+) T cells (EC50∶4.1 µM). Time-of-drug addition studies revealed that LabyA1 acts as an entry inhibitor against HIV and HSV. Cellular and virus binding studies combined with SPR/FLIPR technology showed that LabyA1 interacted with the HIV envelope protein gp120, but not with the HIV cellular receptors. LabyA1 also demonstrated additive to synergistic effects in its anti-HIV-1 and anti-HSV-2 activity with anti(retro)viral drugs in dual combinations such as tenofovir, acyclovir, saquinavir, raltegravir and enfuvirtide. LabyA1 can be considered as a novel lead peptide as it had profound antiviral activity against HIV and HSV. Pre-treatment of PBMCs with LabyA1 neither increased the expression of the activation markers CD69 and CD25, nor enhanced HIV replication, nor significantly induced various inflammatory cytokines/chemokines. LabyA1 also did not affect the growth of vaginal Lactobacilli populations. Based on the lack of toxicity on the vaginal Lactobacillus strains and its synergistic/additive profile in combination with clinically approved anti(retro)virals, it deserves further attention as a potential microbicide candidate in the prevention of sexual transmitted diseases.

The griffithsin dimer is required for high-potency inhibition of HIV-1: evidence for manipulation of the structure of gp120 as part of the griffithsin dimer mechanism.

Griffithsin (Grft) is a protein lectin derived from red algae that tightly binds the HIV envelope protein gp120 and effectively inhibits virus infection. This inhibition is due to the binding by Grft of high-mannose saccharides on the surface of gp120. Grft has been shown to be a tight dimer, but the role of the dimer in Grft's anti-HIV function has not been fully explored. To investigate the role of the Grft dimer in anti-HIV function, an obligate dimer of Grft was designed by expressing the protein with a peptide linker between the two subunits. This "Grft-linker-Grft" is a folded protein dimer, apparently nearly identical in structural properties to the wild-type protein. A "one-armed" obligate dimer was also designed (Grft-linker-Grft OneArm), with each of the three carbohydrate binding sites of one subunit mutated while the other subunit remained intact. While both constructed dimers retained the ability to bind gp120 and the viral surface, Grft-linker-Grft OneArm was 84- to 1,010-fold less able to inhibit HIV than wild-type Grft, while Grft-linker-Grft had near-wild-type antiviral potency. Furthermore, while the wild-type protein demonstrated the ability to alter the structure of gp120 by exposing the CD4 binding site, Grft-linker-Grft OneArm largely lost this ability. In experiments to investigate gp120 shedding, it was found that Grft has different effects on gp120 shedding for strains from subtype B and subtype C, and this might correlate with Grft function. Evidence is provided that the dimer form of Grft is critical to the function of this protein in HIV inhibition.

Role of the carbohydrate-binding sites of griffithsin in the prevention of DC-SIGN-mediated capture and transmission of HIV-1.

BACKGROUND: The glycan-targeting C-type DC-SIGN lectin receptor is implicated in the transmission of the human immunodeficiency virus (HIV) by binding the virus and transferring the captured HIV-1 to CD4(+) T lymphocytes. Carbohydrate binding agents (CBAs) have been reported to block HIV-1 infection. We have now investigated the potent mannose-specific anti-HIV CBA griffithsin (GRFT) on its ability to inhibit the capture of HIV-1 to DC-SIGN, its DC-SIGN-directed transmission to CD4(+) T-lymphocytes and the role of the three carbohydrate-binding sites (CBS) of GRFT in these processes. FINDINGS: GRFT inhibited HIV-1(IIIB) infection of CEM and HIV-1(NL4.3) infection of C8166 CD4(+) T-lymphocytes at an EC50 of 0.059 and 0.444 nM, respectively. The single mutant CBS variants of GRFT (in which a key Asp in one of the CBS was mutated to Ala) were about ∼20 to 60-fold less potent to prevent HIV-1 infection and ∼20 to 90-fold less potent to inhibit syncytia formation in co-cultures of persistently HIV-1 infected HuT-78 and uninfected C8166 CD4(+) T-lymphocytes. GRFT prevents DC-SIGN-mediated virus capture and HIV-1 transmission to CD4(+) T-lymphocytes at an EC50 of 1.5 nM and 0.012 nM, respectively. Surface plasmon resonance (SPR) studies revealed that wild-type GRFT efficiently blocked the binding between DC-SIGN and immobilized gp120, whereas the point mutant CBS variants of GRFT were ∼10- to 15-fold less efficient. SPR-analysis also demonstrated that wild-type GRFT and its single mutant CBS variants have the capacity to expel bound gp120 from the gp120-DC-SIGN complex in a dose dependent manner, a property that was not observed for HHA, another mannose-specific potent anti-HIV-1 CBA. CONCLUSION: GRFT is inhibitory against HIV gp120 binding to DC-SIGN, efficiently prevents DC-SIGN-mediated transfer of HIV-1 to CD4(+) T-lymphocytes and is able to expel gp120 from the gp120-DC-SIGN complex. Functionally intact CBS of GRFT are important for the optimal action of GRFT.

HIV-1 envelope trimer has similar binding characteristics for carbohydrate-binding agents as monomeric gp120.

The native HIV-1 Env complex consists of a gp120/gp41 trimer, but surface plasmon resonance (SPR)-directed binding studies for gp120-binding agents were almost exclusively performed on monomeric gp120. SPR-directed binding kinetics of monomeric gp120 and trimeric gp140 were investigated for a broad variety of envelope (Env)-binding agents. Similar kinetics for carbohydrate-binding agents (CBAs), the antibody 2G12 and sCD4 were observed, irrespective of the oligomeric state of gp120 that either contain the native mixture of complex and high-mannose N-glycans or that contain exclusively oligomannose N-glycans. The generally comparable kinetic properties of CBA, 2G12 and sCD4 binding to monomeric gp120 and trimeric gp140 indicate that monomeric gp120 is a good surrogate molecule for native HIV-1 Env trimer to investigate the binding affinities of Env-binding compounds.

Feglymycin, a unique natural bacterial antibiotic peptide, inhibits HIV entry by targeting the viral envelope protein gp120.

Feglymycin (FGM), a natural Streptomyces-derived 13mer peptide, consistently inhibits HIV replication in the lower µM range. FGM also inhibits HIV cell-to-cell transfer between HIV-infected T cells and uninfected CD4(+) T cells and the DC-SIGN-mediated viral transfer to CD4(+) T cells. FGM potently interacts with gp120 (X4 and R5) as determined by SPR analysis and shown to act as a gp120/CD4 binding inhibitor. Alanine-scan analysis showed an important role for l-aspartic acid at position 13 for its anti-HIV activity. In vitro generated FGM-resistant HIV-1 IIIB virus (HIV-1 IIIB(FGMres)) showed two unique mutations in gp120 at positions I153L and K457I. HIV-1 IIIB(FGMres) virus was equally susceptible to other viral binding/adsorption inhibitors with the exception of dextran sulfate (9-fold resistance) and cyclotriazadisulfonamide (>15-fold), two well-described compounds that interfere with HIV entry. In conclusion, FGM is a unique prototype lead peptide with potential for further development of more potent anti-HIV derivatives.

New anti-HIV aptamers based on tetra-end-linked DNA G-quadruplexes: effect of the base sequence on anti-HIV activity.

This communication reports on the synthesis and biophysical, biological and SAR studies of a small library of new anti-HIV aptamers based on the tetra-end-linked G-quadruplex structure. The new aptamers showed EC(50) values against HIV-1 in the range of 0.04-0.15 µM as well as affinities for the HIV-1 gp120 envelope in the same order of magnitude.

The role of individual carbohydrate-binding sites in the function of the potent anti-HIV lectin griffithsin.

Griffithsin (GRFT) is a lectin that has been shown to inhibit HIV infection by binding to high mannose glycan structures on the surface of gp120, and it is among the most potent HIV entry inhibitors reported so far. However, important biochemical details on the antiviral mechanism of GRFT action remain unexplored. In order to understand the role of the three individual carbohydrate-binding sites (CBS) in GRFT, mutations were made at each site (D30A, D70A, and D112A), and the resulting mutants were investigated. NMR studies revealed that each GRFT variant was folded but showed significant peak movement on the carbohydrate-binding face of the protein. The wild-type and each point mutant protein appeared as tight dimers with a K(d) below 4.2 µM. Mutation of any individual CBS on GRFT reduced binding of the protein to mannose, and ELISA assays revealed a partial loss of ability of each GRFT point mutant to bind gp120, with a near-complete loss of binding by the triple mutant D30A/D70A/D112A GRFT. A more quantitative surface plasmon resonance (SPR) examination showed a rather small loss of binding to gp120 for the individual GRFT point mutants (K(D): 123 to 245 pM range versus 73 pM for wild-type GRFT), but dramatic loss of the triple mutant to bind gp120 derived from R5 and X4 strains (K(D) > 12 nM). In contrast to the 2- to 3-fold loss of binding to gp120, the single CBS point mutants of GRFT were significantly less able to inhibit viral infection, exhibiting a 26- to 1900-fold loss of potency, while the triple mutant was at least 875-fold less effective against HIV-1 infection. The disparity between HIV-1 gp120 binding ability and HIV inhibitory potency for these GRFT variants indicates that gp120 binding and virus neutralization do not necessarily correlate, and suggests a mechanism that is not based on simple gp120 binding.

Targeting HIV entry through interaction with envelope glycoprotein 120 (gp120): synthesis and antiviral evaluation of 1,3,5-triazines with aromatic amino acids.

On the basis of the interesting inhibitory properties that lectins show against HIV-replication through their interaction with glycoprotein 120 (gp120), we here describe the design, synthesis, and anti-HIV evaluation of three series of 1,3,5-triazine derivatives (monomers, dimers, and trimers) functionalized with aromatic amino acids meant to mimic interactions that lectins establish with gp120. While monomers were inactive against HIV replication, dimers showed limited anti-HIV activity that is, however, considerably more significant in the trimers series, with EC(50) values in the lower µM range. These findings most likely reflect the requirement of multivalency of the 1,3,5-triazine derivatives to display anti-HIV activity, as lectins do. The pronounced anti-HIV activity (EC(50) ∼ 20 µM) is accompanied by the absence of toxicity in CEM T-cell line (CC(50) > 250 µM). Moreover, SPR experiments revealed that the prototype trimers with a central core of 2,4,6-triethylbenzene and six l-Trp or six l-Tyr residues at the periphery were efficient binders of CXCR4- and CCR5-tropic HIV-1 gp120 (estimated K(D): lower micromolar range). The collected data support the interest of this novel family of anti-HIV agents and qualify them as potential novel microbicide lead compounds.

Synthesis and antiviral activity of highly water-soluble polycarboxylic derivatives of [70]fullerene.

We report here a facile preparation of highly water-soluble derivatives C(70)[p-C(6)H(4)(CH(2))(n)COOH](8) (n = 2, 3) starting from readily available chlorinated [70]fullerene precursors C(70)Cl(8) and C(70)Cl(10). The synthesized fullerene derivatives showed pronounced antiviral activity in vitro, particularly against human immunodeficiency virus (HIV) and influenza A virus (subtypes H1N1 and H3N2).

Discovery of novel anti-HIV active G-quadruplex-forming oligonucleotides.

A series of d((5')TGGGAG(3')) sequences, 5'-conjugated with a variety of aromatic groups through phosphodiester linkages, were synthesized, showing CD spectra diagnostic of parallel-stranded, tetramolecular G-quadruplex structures. When tested for anti-HIV-1 and HIV-2 activity, potent inhibition of HIV-1 infection in CEM cell cultures was found, associated with high selectivity index values. Surface Plasmon Resonance assays revealed specific binding to HIV-1 gp120 and gp41.

Differences in the mannose oligomer specificities of the closely related lectins from Galanthus nivalis and Zea mays strongly determine their eventual anti-HIV activity.

BACKGROUND: In a recent report, the carbohydrate-binding specificities of the plant lectins Galanthus nivalis (GNA) and the closely related lectin from Zea mays (GNAmaize) were determined by glycan array analysis and indicated that GNAmaize recognizes complex-type N-glycans whereas GNA has specificity towards high-mannose-type glycans. Both lectins are tetrameric proteins sharing 64% sequence similarity. RESULTS: GNAmaize appeared to be ~20- to 100-fold less inhibitory than GNA against HIV infection, syncytia formation between persistently HIV-1-infected HuT-78 cells and uninfected CD4+ T-lymphocyte SupT1 cells, HIV-1 capture by DC-SIGN and subsequent transmission of DC-SIGN-captured virions to uninfected CD4+ T-lymphocyte cells. In contrast to GNA, which preferentially selects for virus strains with deleted high-mannose-type glycans on gp120, prolonged exposure of HIV-1 to dose-escalating concentrations of GNAmaize selected for mutant virus strains in which one complex-type glycan of gp120 was deleted. Surface Plasmon Resonance (SPR) analysis revealed that GNA and GNAmaize interact with HIV IIIB gp120 with affinity constants (KD) of 0.33 nM and 34 nM, respectively. Whereas immobilized GNA specifically binds mannose oligomers, GNAmaize selectively binds complex-type GlcNAcß1,2Man oligomers. Also, epitope mapping experiments revealed that GNA and the mannose-specific mAb 2G12 can independently bind from GNAmaize to gp120, whereas GNAmaize cannot efficiently bind to gp120 that contained prebound PHA-E (GlcNAcß1,2man specific) or SNA (NeuAcα2,6X specific). CONCLUSION: The markedly reduced anti-HIV activity of GNAmaize compared to GNA can be explained by the profound shift in glycan recognition and the disappearance of carbohydrate-binding sites in GNAmaize that have high affinity for mannose oligomers. These findings underscore the need for mannose oligomer recognition of therapeutics to be endowed with anti-HIV activity and that mannose, but not complex-type glycan binding of chemotherapeutics to gp120, may result in a pronounced neutralizing activity against the virus.

Tetra-end-linked oligonucleotides forming DNA G-quadruplexes: a new class of aptamers showing anti-HIV activity.

The biophysical and biological properties of unprecedented anti-HIV aptamers are presented. The most active aptamer (1L) shows a significant affinity to the HIV protein gp120.

Actinohivin, a broadly neutralizing prokaryotic lectin, inhibits HIV-1 infection by specifically targeting high-mannose-type glycans on the gp120 envelope.

The lectin actinohivin (AH) is a monomeric carbohydrate-binding agent (CBA) with three carbohydrate-binding sites. AH strongly interacts with gp120 derived from different X4 and R5 human immunodeficiency virus (HIV) strains, simian immunodeficiency virus (SIV) gp130, and HIV type 1 (HIV-1) gp41 with affinity constants (KD) in the lower nM range. The gp120 and gp41 binding of AH is selectively reversed by (alpha1,2-mannose)3 oligosaccharide but not by alpha1,3/alpha1,6-mannose- or GlcNAc-based oligosaccharides. AH binding to gp120 prevents binding of alpha1,2-mannose-specific monoclonal antibody 2G12, and AH covers a broader epitope on gp120 than 2G12. Prolonged exposure of HIV-1-infected CEM T-cell cultures with escalating AH concentrations selects for mutant virus strains containing N-glycosylation site deletions (predominantly affecting high-mannose-type glycans) in gp120. In contrast to 2G12, AH has a high genetic barrier, since several concomitant N-glycosylation site deletions in gp120 are required to afford significant phenotypic drug resistance. AH is endowed with broadly neutralizing activity against laboratory-adapted HIV strains and a variety of X4 and/or R5 HIV-1 clinical clade isolates and blocks viral entry within a narrow concentration window of variation (approximately 5-fold). In contrast, the neutralizing activity of 2G12 varied up to 1,000-fold, depending on the virus strain. Since AH efficiently prevents syncytium formation in cocultures of persistently HIV-1-infected HuT-78 cells and uninfected CD4+ T lymphocytes, inhibits dendritic cell-specific intercellular adhesion molecule 3-grabbing nonintegrin-mediated capture of HIV-1 and subsequent virus transmission to CD4+ T lymphocytes, does not upregulate cellular activation markers, lacks mitogenic activity, and does not induce cytokines/chemokines in peripheral blood mononuclear cell cultures, it should be considered a potential candidate drug for microbicidal use.

Generation of a family-specific phage library of llama single chain antibody fragments that neutralize HIV-1.

Recently, we described llama antibody fragments (VHH) that can neutralize human immunodeficiency virus, type 1 (HIV-1). These VHH were obtained after selective elution of phages carrying an immune library raised against gp120 of HIV-1 subtype B/C CN54 with soluble CD4. We describe here a new, family-specific approach to obtain the largest possible diversity of related VHH that compete with soluble CD4 for binding to the HIV-1 envelope glycoprotein. The creation of this family-specific library of homologous VHH has enabled us to isolate phages carrying similar nucleotide sequences as the parental VHH. These VHH displayed varying binding affinities and neutralization phenotypes to a panel of different strains and subtypes of HIV-1. Sequence analysis of the homologs showed that the C-terminal three amino acids of the CDR3 loop were crucial in determining the specificity of these VHH for different subtype C HIV-1 strains. There was a positive correlation between affinity of VHH binding to gp120 of HIV-1 IIIB and the breadth of neutralization of diverse HIV-1 envelopes. The family-specific approach has therefore allowed us to better understand the interaction of the CD4-binding site antibodies with virus strain specificity and has potential use for the bioengineering of antibodies and HIV-1 vaccine development.

Pradimicin S, a highly soluble nonpeptidic small-size carbohydrate-binding antibiotic, is an anti-HIV drug lead for both microbicidal and systemic use.

Pradimicin S (PRM-S) is a highly water-soluble, negatively charged derivative of the antibiotic pradimicin A (PRM-A) in which the terminal xylose moiety has been replaced by 3-sulfated glucose. PRM-S does not prevent human immunodeficiency virus (HIV) adsorption on CD4(+) T cells, but it blocks virus entry into its target cells. It inhibits a wide variety of HIV-1 laboratory strains and clinical isolates, HIV-2, and simian immunodeficiency virus (SIV) in various cell culture systems (50% and 90% effective concentrations [EC(50)s and EC(90)s] invariably in the lower micromolar range). PRM-S inhibits syncytium formation between persistently HIV-1- and SIV-infected cells and uninfected CD4(+) T lymphocytes, and prevents dendritic cell-specific intercellular adhesion molecule-3-grabbing nonintegrin (DC-SIGN)-mediated HIV-1 and SIV capture and subsequent virus transmission to CD4(+) T cells. Surface plasmon resonance (SPR) studies revealed that PRM-S strongly binds to gp120 in a Ca(2+)-dependent manner at an affinity constant (K(D)) in the higher nanomolar range. Its anti-HIV activity and HIV-1 gp120-binding properties can be dose-dependently reversed in the presence of an (alpha-1,2)mannose trimer. Dose-escalating exposure of HIV-1-infected cells to PRM-S eventually led to the isolation of mutant virus strains that had various deleted N-glycosylation sites in the envelope gp120 with a strong preference for the deletion of the high-mannose-type glycans. Genotypic resistance development occurred slowly, and significant phenotypic resistance occurred only after the sequential appearance of up to six mutations in gp120, pointing to a high genetic barrier of PRM-S. The antibiotic is nontoxic against a variety of cell lines, is not mitogenic, and does not induce cytokines and chemokines in peripheral blood mononuclear cells as determined by the Bio-Plex human cytokine 27-plex assay. It proved stable at high temperature and low pH. Therefore, PRM-S may qualify as a potential anti-HIV drug candidate for further (pre)clinical studies, including its microbicidal use.

Llama antibody fragments with cross-subtype human immunodeficiency virus type 1 (HIV-1)-neutralizing properties and high affinity for HIV-1 gp120.

Members of the Camelidae family produce immunoglobulins devoid of light chains. We have characterized variable domains of these heavy chain antibodies, the VHH, from llamas immunized with human immunodeficiency virus type 1 (HIV-1) envelope protein gp120 in order to identify VHH that can inhibit HIV-1 infection. To increase the chances of isolating neutralizing VHH, we employed a functional selection approach, involving panning of phage libraries expressing the VHH repertoire on recombinant gp120, followed by a competitive elution with soluble CD4. By immunizing with gp120 derived from an HIV-1 subtype B'/C primary isolate, followed by panning on gp120 from HIV-1 isolates of subtypes A, B, and C, we could select for VHH with cross-subtype neutralizing activity. Three VHH able to neutralize HIV-1 primary isolates of subtypes B and C were characterized. These bound to recombinant gp120 with affinities close to the suggested affinity ceiling for in vivo-maturated antibodies and competed with soluble CD4 for this binding, indicating that their mechanism of neutralization involves interacting with the functional envelope spike prior to binding to CD4. The most potent VHH in terms of low 50% inhibitory concentration (IC(50)) and IC(90) values and cross-subtype reactivity was A12. These results indicate that camelid VHH can be potent HIV-1 entry inhibitors. Since VHH are stable and can be produced at a relatively low cost, they may be considered for applications such as HIV-1 microbicide development. Antienvelope VHH might also prove useful in defining neutralizing and nonneutralizing epitopes on HIV-1 envelope proteins, with implications for HIV-1 vaccine design.

Thermodynamic benchmark study using Biacore technology.

A total of 22 individuals participated in this benchmark study to characterize the thermodynamics of small-molecule inhibitor-enzyme interactions using Biacore instruments. Participants were provided with reagents (the enzyme carbonic anhydrase II, which was immobilized onto the sensor surface, and four sulfonamide-based inhibitors) and were instructed to collect response data from 6 to 36 degrees C. van't Hoff enthalpies and entropies were calculated from the temperature dependence of the binding constants. The equilibrium dissociation and thermodynamic constants determined from the Biacore analysis matched the values determined using isothermal titration calorimetry. These results demonstrate that immobilization of the enzyme onto the sensor surface did not alter the thermodynamics of these interactions. This benchmark study also provides insights into the opportunities and challenges in carrying out thermodynamic studies using optical biosensors.