The lectins griffithsin, cyanovirin-N and scytovirin inhibit HIV-1 binding to the DC-SIGN receptor and transfer to CD4(+) cells

From exploring cancer and virus targets to discovering active peptides through mRNA display

During carcinogenesis, neoplastic cells accumulate mutations in genes important for cellular homeostasis, producing defective proteins. Viral infections occur when viral capsid proteins bind to the host cell receptor, allowing the virus to enter the cells. In both cases, proteins play important roles in cancer development and viral infection, so these targets can be exploited to develop alternative treatments. mRNA display technology is a very powerful tool for the development of peptides capable of acting on specific targets in neoplastic cells or on viral capsid proteins. mRNA display technology allows the selection and evolution of peptides with desired functional properties from libraries of many nucleic acid variants. Among other advantages of this technology, the use of flexizymes allows the production of peptides with unnatural amino acid residues, which can enhance the activity of these molecules. From target immobilization, peptides with greater specificity for the targets of interest are generated during the selection rounds. Herein, we will explore the use of mRNA display technology for the development of active peptides after successive rounds of selection, using proteins present in neoplastic cells and viral particles as targets.

Lectins and lectibodies: potential promising antiviral agents

In nature, lectins are widely dispersed proteins that selectively recognize and bind to carbohydrates and glycoconjugates via reversible bonds at specific binding sites. Many viral diseases have been treated with lectins due to their wide range of structures, specificity for carbohydrates, and ability to bind carbohydrates. Through hemagglutination assays, these proteins can be detected interacting with various carbohydrates on the surface of cells and viral envelopes. This review discusses the most robust lectins and their rationally engineered versions, such as lectibodies, as antiviral proteins. Fusion of lectin and antibody’s crystallizable fragment (Fc) of immunoglobulin G (IgG) produces a molecule called a “lectibody” that can act as a carbohydrate-targeting antibody. Lectibodies can not only bind to the surface glycoproteins via their lectins and neutralize and clear viruses or infected cells by viruses but also perform Fc-mediated antibody effector functions. These functions include complement-dependent cytotoxicity (CDC), antibody-dependent cell-mediated cytotoxicity (ADCC), and antibody-dependent cell-mediated phagocytosis (ADCP). In addition to entering host cells, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein S1 binds to angiotensin-converting enzyme 2 (ACE2) and downregulates it and type I interferons in a way that may lead to lung disease. The SARS-CoV-2 spike protein S1 and human immunodeficiency virus (HIV) envelope are heavily glycosylated, which could make them a major target for developing vaccines, diagnostic tests, and therapeutic drugs. Lectibodies can lead to neutralization and clearance of viruses and cells infected by viruses by binding to glycans located on the envelope surface (e.g., the heavily glycosylated SARS-CoV-2 spike protein).

Plant lectins as prospective antiviral biomolecules in the search for COVID-19 eradication strategies

Lectins or clusters of carbohydrate-binding proteins of non-immune origin are distributed chiefly in the Plantae. Lectins have potent anti-infectivity properties for several RNA viruses including SARS-CoV-2. The primary purpose of this review is to review the ability of lectins mediated potential biotherapeutic and bioprophylactic strategy against coronavirus causing COVID-19. Lectins have binding affinity to the glycans of SARS-COV-2 Spike glycoprotein that has N-glycosylation sites. Apart from this, the complement lectin pathway is a "first line host defense" against the viral infection that is activated by mannose-binding lectins. Mannose-binding lectins deficiency in serum influences innate immunity of the host and facilitates infectious diseases including COVID-19. Our accumulated evidence obtained from scientific databases particularly PubMed and Google Scholar databases indicate that mannose-specific/mannose-binding lectins (MBL) have potent efficacies like anti-infectivity, complement cascade induction, immunoadjuvants, DC-SIGN antagonists, or glycomimetic approach, which can prove useful in the strategy of COVID-19 combat along with the glycobiological aspects of SARS-CoV-2 infections and antiviral immunity. For example, plant-derived mannose-specific lectins BanLac, FRIL, Lentil, and GRFT from red algae can inhibit and neutralize SARS-CoV-2 infectivity, as confirmed with in-vitro, in-vivo, and in-silico assessments. Furthermore, Bangladesh has a noteworthy resource of antiviral medicinal plants as well as plant lectins. Intensifying research on the antiviral plant lectins, adopting a glyco-biotechnological approach, and with deeper insights into the "glycovirological" aspects may result in the designing of alternative and potent blueprints against the 21st century's biological pandemic of SARS-CoV-2 causing COVID-19.

Synthesis of fluorescence labelled aptamers for use as low-cost reagents in HIV/AIDS research and diagnostics

Aptamers are nucleic acids selected by systematic evolution of ligands by exponential enrichment. They have potential as alternatives to antibodies in medical research and diagnostics, with the advantages of being non-immunogenic and relatively inexpensive to produce. In the present study, gp120 aptamers conjugated with fluorescein isothiocyanate (FITC) were generated, which could interact with HIV-1 gp120. A previously isolated gp120 aptamer, CSIR 1.1, was conjugated with FITC by incubation with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and imidazole. The conjugation and binding to the glycoprotein were confirmed by flow cytometry. FITC conjugated aptamers showed an increase in fluorescence emission 24-fold higher than baseline, and this difference was statistically significant (P=0.0016). Compared with a commercially available biotinylated anti-gp120 antibody, detected using FITC conjugated streptavidin, the emission of fluorescence obtained from the FITC-conjugated aptamer was 8-fold higher, suggesting a stronger interaction with gp120. In addition, the FITC conjugated aptamer neutralized HIV-1 pseudoviruses with an average IC₅₀ of 21.3 nM, similar to the parent aptamer that had an IC₅₀ of 19.2 nM. However, the difference in inhibition between the two aptamers was not statistically significant (P=0.784). These results indicate that the FITC-conjugated aptamer generated in the present study could potentially be used as a low-cost reagent in HIV/AIDS research and diagnostics.

Algal and Cyanobacterial Lectins and Their Antimicrobial Properties

Lectins are proteins with a remarkably high affinity and specificity for carbohydrates. Many organisms naturally produce them, including animals, plants, fungi, protists, bacteria, archaea, and viruses. The present report focuses on lectins produced by marine or freshwater organisms, in particular algae and cyanobacteria. We explore their structure, function, classification, and antimicrobial properties. Furthermore, we look at the expression of lectins in heterologous systems and the current research on the preclinical and clinical evaluation of these fascinating molecules. The further development of these molecules might positively impact human health, particularly the prevention or treatment of diseases caused by pathogens such as human immunodeficiency virus, influenza, and severe acute respiratory coronaviruses, among others.

Lobostemon trigonus (Thunb.) H. Buek, a medicinal plant from South Africa as a potential natural microbicide against HIV-1

ETHNOPHARMACOLOGICAL RELEVANCE

There have been different methods proposed to prevent the sexual transmission of HIV-1 and many of them have centered on the use of anti-retrovirals as microbicides. Given that a large section of the African population still relies on herbal medicine, Lobostemon trigonus (L. trigonus), a traditionally used medicinal plant in South Africa to treat HIV-1 was further investigated for its potential as a natural microbicide to prevent the sexual transmission of HIV-1.

METHODS

The aerial parts of L. trigonus were oven-dried at 80 °C, ground, extracted with boiling water for 30 min and then filtered. The aqueous extract produced was then bioassayed using different HIV-1 inhibition assays. The active components were purified and chemically profiled using ultra-performance liquid chromatography/quadrupole time-of flight mass spectrometry (UPLC-qTOF-MS). The mechanism of HIV-1 inhibition was determined by fusion arrest assay and time of addition assay. Molecular modelling and molecular dynamic simulations, using Schrödinger, were used to better understand the molecule's mechanism of entry inhibition by evaluating their docking affinity and stability against the gp120 of HIV-1.

RESULTS

The aqueous extract of this plant had a broad spectrum of activity against different subtypes of the virus; neutralizing subtype A, B and C in the TZM-bl cells, with IC₅₀ values ranging from 0.10 to 7.21 μg/mL. The extract was also inhibitory to the virus induced cytopathic effects in CEM-SS cells with an EC₅₀ of 8.9 μg/mL. In addition, it inhibited infection in peripheral blood mononuclear cells (PBMC) and macrophages with IC₅₀ values of 0.97 and 4.4 μg/mL, respectively. In the presence of vaginal and seminal simulants, and in human semen it retained its inhibitory activity albeit with a decrease in efficiency, by about 3-fold. Studies of the mode of action suggested that the extract blocked HIV-1 attachment to target cells. No toxicity was observed when the Lactobacilli strains, L. acidophilus, L. jensenii, and L. crispatus that populate the female genital tract were cultured in the presence of L. trigonus extract. UPLC-qTOF-MS analyses of the purified fraction of the extract, confirmed the presence of six compounds of which four were identified as rosmarinic acid, salvianolic acids B and C and lithospermic acid. The additional molecular dynamic simulations provided further insight into the entry inhibitory characteristics of salvianolic acid B against the HIV-1 gp120, with a stable pose being found within the CD4 binding site.

CONCLUSION

The data suggests that the inhibitory effect of L. trigonus may be due to the presence of organic acids which are known to possess anti-HIV-1 properties. The molecules salvianolic acids B and C have been identified for the first time in L. trigonus species. Our study also showed that the L. trigonus extract blocked HIV-1 attachment to target cells, and that it has a broad spectrum of activity against different subtypes of the virus; thus, justifying further investigation as a HIV-1 microbicide.

Antiviral Potential of Algal Metabolites-A Comprehensive Review

Historically, algae have stimulated significant economic interest particularly as a source of fertilizers, feeds, foods and pharmaceutical precursors. However, there is increasing interest in exploiting algal diversity for their antiviral potential. Here, we present an overview of 50-years of scientific and technological developments in the field of algae antivirals. After bibliometric analysis of 999 scientific references, a survey of 16 clinical trials and analysis of 84 patents, it was possible to identify the dominant algae, molecules and viruses that have been shaping and driving this promising field of research. A description of the most promising discoveries is presented according to molecule class. We observed a diverse range of algae and respective molecules displaying significant antiviral effects against an equally diverse range of viruses. Some natural algae molecules, like carrageenan, cyanovirin or griffithsin, are now considered prime reference molecules for their outstanding antiviral capacity. Crucially, while many algae antiviral applications have already reached successful commercialization, the large spectrum of algae antiviral capacities already identified suggests a strong potential for future expansion of this field.

The Potential of Algal Biotechnology to Produce Antiviral Compounds and Biopharmaceuticals

The emergence of the Coronavirus Disease 2019 (COVID-19) caused by the SARS-CoV-2 virus has led to an unprecedented pandemic, which demands urgent development of antiviral drugs and antibodies; as well as prophylactic approaches, namely vaccines. Algae biotechnology has much to offer in this scenario given the diversity of such organisms, which are a valuable source of antiviral and anti-inflammatory compounds that can also be used to produce vaccines and antibodies. Antivirals with possible activity against SARS-CoV-2 are summarized, based on previously reported activity against Coronaviruses or other enveloped or respiratory viruses. Moreover, the potential of algae-derived anti-inflammatory compounds to treat severe cases of COVID-19 is contemplated. The scenario of producing biopharmaceuticals in recombinant algae is presented and the cases of algae-made vaccines targeting viral diseases is highlighted as valuable references for the development of anti-SARS-CoV-2 vaccines. Successful cases in the production of functional antibodies are described. Perspectives on how specific algae species and genetic engineering techniques can be applied for the production of anti-viral compounds antibodies and vaccines against SARS-CoV-2 are provided.

Modification and optimization of the inhibition of HIV-1 cell-to-cell transmission assay

HIV-1 infection is caused by cell-free and cell-associated viruses. Currently most of the assays used to screen potential HIV-1 entry inhibitors focus on the inhibition of cell-free viruses. One assay that is widely employed is the TZM-bl neutralization assay that uses pseudotyped viruses. However, a study by Abela et al. showed that many inhibitors that potently inhibit cell-free HIV-1 in this assay can be less effective against the cell-to-cell transmission of the virus. These researchers then designed a method to screen entry inhibitors for activity against cell-associated HIV-1, using pseudotyped viruses. The main limitation of this method, however, was that it can only be reliably employed against viruses that cannot infect target cells as cell-free virion in the absence of a polycation supplement such as DEAE (diethylaminoethyl). Thus, in the current study we provide modifications to this method that solves the problem and makes it possible to study entry inhibitors against cell-to-cell infection of both polycation depend and independent viruses. The main modification involves the introduction of the relative light unit (RLU) vs. virus producing 293-T cells / corresponding supernatants graph. This graph is used to select a virus input that only allows for the detection of cell-associated viruses infection.•The method is a modification of the cell-to-cell transmission assay published by Abela et al.•The method allows for the study of the inhibition of cell-to-cell transmission of both polycation dependent and independent HIV-1 pseudoviruses.

Rapid-Release Griffithsin Fibers for Dual Prevention of HSV-2 and HIV-1 Infections

The biologic griffithsin (GRFT) has recently emerged as a candidate to safely prevent sexually transmitted infections (STIs), including human immunodeficiency virus type 1 (HIV-1) and herpes simplex virus 2 (HSV-2). However, to date, there are few delivery platforms that are available to effectively deliver biologics to the female reproductive tract (FRT). The goal of this work was to evaluate rapid-release polyethylene oxide (PEO), polyvinyl alcohol (PVA), and polyvinylpyrrolidone (PVP) fibers that incorporate GRFT in in vitro (HIV-1 and HSV-2) and in vivo (HSV-2) infection models. GRFT loading was determined via enzyme-linked immunosorbent assay (ELISA), and the bioactivity of GRFT fibers was assessed using in vitro HIV-1 pseudovirus and HSV-2 plaque assays. Afterwards, the efficacy of GRFT fibers was assessed in a murine model of lethal HSV-2 infection. Finally, murine reproductive tracts and vaginal lavage samples were evaluated for histology and cytokine expression, 24 and 72 h after fiber administration, to determine safety. All rapid-release formulations achieved high levels of GRFT incorporation and were completely efficacious against in vitro HIV-1 and HSV-2 infections. Importantly, all rapid-release GRFT fibers provided potent protection in a murine model of HSV-2 infection. Moreover, histology and cytokine levels, evaluated from collected murine reproductive tissues and vaginal lavage samples treated with blank fibers, showed no increased cytokine production or histological aberrations, demonstrating the preliminary safety of rapid-release GRFT fibers in vaginal tissue.

Comparison of the antiviral activity of the microbicide candidate griffithsin and its tandemers derivatives against different modes of HIV-1 transmission

Tandemers 2MG, 2MG3, 3MG and 4MG are derivatives of the potent anti-HIV-1 microbicide candidate griffithsin (GRFT). We compared these compounds anti-HIV-1 activity to GRFT using the viruses CAP206.08 and CAAN5342.A2 that have decreased sensitivity to this lectin. The 2MG and 2MG3 tandemers had similar activity to GRFT against cell-free and cell-associated viruses, while 3MG and 4MG were significantly more potent. Furthermore, the restoration of the 234N or 295N glycan in these viruses, known to increase sensitivity to GRFT, also increased sensitivity to 2MG and 2MG3, and not to 3MG and 4MG. In addition, GRFT resistant viruses generated in-vitro were equally resistant to 2MG and 2MG3 while they had considerably low resistance to 3MG and 4MG. Lastly, all five compounds showed increased inhibitory activity in seminal and vaginal simulants although the effect was more pronounced in the former. These data support further studies of tandemers as potential microbicides.

Selective transmission of some HIV-1 subtype C variants might depend on Envelope stimulating dendritic cells to secrete IL-10

Envelope (Env) phenotype(s) that provide transmitted founders (TF) with a selective advantage during HIV-1 transmission would be the ideal target for preventative therapy. We generated Env clones from four individuals infected with a single virus and one participant infected with multiple variants at transmission and compared phenotype with matched Envs from chronic infection (CI). When we determined whether pseudovirus (PSV) of the five TF and thirteen matched CI Env clones differed in their ability to 1) enter TZM-bl cells, 2) bind DC-SIGN, and 3) trans-infect CD4+ cells there was no association between time post-infection and variation in Env phenotype. However, when we compared the ability of PSV to induce monocyte-derived dendritic cells (MDDCs) to secrete Interleukin-10 (IL-10), we found that only TF Envs from single variant transmission cases induced MDDCs to secrete either higher or similar levels of IL-10 as the CI clones. Furthermore, interaction between MDDC DC-SIGN and Env was required for secretion of IL-10. When variants were grouped according to time post-infection, TF PSV induced the release of higher levels of IL-10 than their CI counterparts although this relationship varied across MDDC donors. The selection of variants during transmission is therefore likely a complex event dependent on both virus and host genetics. Our findings suggest that, potentially due to overall variation in N-glycosylation across variants, nuanced differences in binding of TF Env to DC-SIGN might trigger alternative DC immune responses (IRs) in the female genital tract (FGT) that favour HIV-1 survival and facilitate transmission.

Griffithsin, a Highly Potent Broad-Spectrum Antiviral Lectin from Red Algae: From Discovery to Clinical Application

Virus entry into a susceptible host cell is the first step in the formation of all viral diseases. Controlling viral infections by disrupting viral entry is advantageous for antibody-mediated neutralization by the host’s immune system and as a preventive and therapeutic antiviral strategy. Recently, several plant-derived carbohydrate-binding proteins (lectins) have emerged as a new class of antiviral biologics by taking advantage of a unique glycosylation pattern only found on the surface of viruses. In particular, a red algae-derived griffithsin (GRFT) protein has demonstrated superior in vitro and in vivo antiviral activity with minimum host toxicity against a variety of clinically relevant, enveloped viruses. This review examines the structural characteristics of GRFT, focusing on its carbohydrate-binding capability. Its in vitro antiviral profiles against human immunodeficiency virus (HIV) are also discussed followed by a description of the results from a combination study using anti-HIV drugs. The results of several studies regarding its novel antiviral mechanism of action are provided in conjunction with an explanation of viral resistance profiles to GRFT. In addition, its in vitro and in vivo host toxicity profiles are summarized with its pharmacokinetic behavior using in vivo efficacy study results. Also, a large-scale production and formulation strategy, as well as a drug delivery strategy, for GRFT as a new class of broad-spectrum microbicides is discussed. Finally, results from two ongoing clinical studies examining GRFT’s effects on viruses are presented.

Mannose-Specific Lectins from Marine Algae: Diverse Structural Scaffolds Associated to Common Virucidal and Anti-Cancer Properties

To date, a number of mannose-specific lectins have been isolated and characterized from seaweeds, especially from red algae. In fact, man-specific seaweed lectins consist of different structural scaffolds harboring a single or a few carbohydrate-binding sites which specifically recognize mannose-containing glycans. Depending on the structural scaffold, man-specific seaweed lectins belong to five distinct structurally-related lectin families, namely (1) the griffithsin lectin family (β-prism I scaffold); (2) the Oscillatoria agardhii agglutinin homolog (OAAH) lectin family (β-barrel scaffold); (3) the legume lectin-like lectin family (β-sandwich scaffold); (4) the Galanthus nivalis agglutinin (GNA)-like lectin family (β-prism II scaffold); and, (5) the MFP2-like lectin family (MFP2-like scaffold). Another algal lectin from Ulva pertusa, has been inferred to the methanol dehydrogenase related lectin family, because it displays a rather different GlcNAc-specificity. In spite of these structural discrepancies, all members from the five lectin families share a common ability to specifically recognize man-containing glycans and, especially, high-mannose type glycans. Because of their mannose-binding specificity, these lectins have been used as valuable tools for deciphering and characterizing the complex mannose-containing glycans from the glycocalyx covering both normal and transformed cells, and as diagnostic tools and therapeutic drugs that specifically recognize the altered high-mannose N-glycans occurring at the surface of various cancer cells. In addition to these anti-cancer properties, man-specific seaweed lectins have been widely used as potent human immunodeficiency virus (HIV-1)-inactivating proteins, due to their capacity to specifically interact with the envelope glycoprotein gp120 and prevent the virion infectivity of HIV-1 towards the host CD4+ T-lymphocyte cells in vitro.

Marine Algae Metabolites as Promising Therapeutics for the Prevention and Treatment of HIV/AIDS

This review presents an analysis of works devoted to the anti-human immunodeficiency virus (HIV) activity of algae metabolites-sulfated polysaccharides (fucoidans, carrageenans), lectins, laminarans, and polyphenols. Despite the presence of a significant number of antiretroviral drugs, the development of new therapeutic and prophylactic agents against this infection remains very urgent problem. This is due to the variability of HIV, the absence of an animal model (except monkeys) and natural immunity to this virus and the toxicity of therapeutic agents and their high cost. In this regard, the need for new therapeutic approaches and broad-spectrum drugs, which in addition to antiviral effects can have anti-inflammatory, antioxidant, and immunomodulatory effects, and to which the minimum resistance of HIV strains would be formed. These requirements meet the biologically active substances of marine algae. The results of experimental and clinical studies conducted in vitro and in vivo are presented, and the issues of the anti-HIV activity of these compounds are considered depending on their structural features. On the whole, the presented data prove the high efficiency of seaweed metabolites and justify the possibility of their use as a potential basis for the development of new drugs with a wide spectrum of activity.

Overview of the Structure⁻Function Relationships of Mannose-Specific Lectins from Plants, Algae and Fungi

To date, a number of mannose-binding lectins have been isolated and characterized from plants and fungi. These proteins are composed of different structural scaffold structures which harbor a single or multiple carbohydrate-binding sites involved in the specific recognition of mannose-containing glycans. Generally, the mannose-binding site consists of a small, central, carbohydrate-binding pocket responsible for the "broad sugar-binding specificity" toward a single mannose molecule, surrounded by a more extended binding area responsible for the specific recognition of larger mannose-containing N-glycan chains. Accordingly, the mannose-binding specificity of the so-called mannose-binding lectins towards complex mannose-containing N-glycans depends largely on the topography of their mannose-binding site(s). This structure⁻function relationship introduces a high degree of specificity in the apparently homogeneous group of mannose-binding lectins, with respect to the specific recognition of high-mannose and complex N-glycans. Because of the high specificity towards mannose these lectins are valuable tools for deciphering and characterizing the complex mannose-containing glycans that decorate both normal and transformed cells, e.g., the altered high-mannose N-glycans that often occur at the surface of various cancer cells.

Vaginal Product Formulation Alters the Innate Antiviral Activity and Glycome of Cervicovaginal Fluids with Implications for Viral Susceptibility

Glycosylated proteins (i.e., mucins, IgG) are important mediators of innate antiviral immunity in the vagina; however, our current knowledge of the role that glycan themselves play in genital immunity is relatively low. Herein, we evaluate the relationship between innate antiviral immunity and glycomic composition in cervicovaginal lavage fluid (CVL) collected as part of a Phase I clinical trial testing the impact of two distinct formulations of the antiretroviral drug dapivirine. Using lectin microarray technology, we discovered that formulation (hydrogel- versus film-based delivery) impacted the CVL glycome, with hydrogel formulations inducing more changes, including a loss of high-mannose. The loss of this epitope correlated to a loss of anti-HIV-1 activity. Glycoproteomic identification of high-mannose proteins revealed a cohort of antiproteases shown to be important in HIV-1 resistance, whose expression covaried with the high-mannose signature. Our data strongly suggests high-mannose as a marker for secreted proteins mediating innate antiviral immunity in vaginal fluids and that drug formulation may impact this activity as reflected in the glycome.

Griffithsin carrageenan fast dissolving inserts prevent SHIV HSV-2 and HPV infections in vivo

Human immunodeficiency virus (HIV) pre-exposure prophylaxis (PrEP) strategies with proven in vivo efficacy rely on antiretroviral drugs, creating the potential for drug resistance and complicated treatment options in individuals who become infected. Moreover, on-demand products are currently missing from the PrEP development portfolio. Griffithsin (GRFT) is a non-antiretroviral HIV entry inhibitor derived from red algae with an excellent safety profile and potent activity in vitro. When combined with carrageenan (CG), GRFT has strong activity against herpes simplex virus-2 (HSV-2) and human papillomavirus (HPV) in vitro and in vivo. Here, we report that GRFT/CG in a freeze-dried fast dissolving insert (FDI) formulation for on-demand use protects rhesus macaques from a high dose vaginal SHIV SF162P3 challenge 4 h after FDI insertion. Furthermore, the GRFT/CG FDI also protects mice vaginally against HSV-2 and HPV pseudovirus. As a safe, potent, broad-spectrum, on-demand non-antiretroviral product, the GRFT/CG FDI warrants clinical development.

Unexpected synergistic HIV neutralization by a triple microbicide produced in rice endosperm

Our paper provides an approach for the durable deployment of anti-HIV agents in the developing world. We developed a transgenic rice line expressing three microbicidal proteins (the HIV-neutralizing antibody 2G12 and the lectins griffithsin and cyanovirin-N). Simultaneous expression in the same plant allows the crude seed extract to be used directly as a topical microbicide cocktail, avoiding the costs of multiple downstream processes. This groundbreaking strategy is realistically the only way that microbicidal cocktails can be manufactured at a cost low enough for the developing world, where HIV prophylaxis is most in demand.

The transmission of HIV can be prevented by the application of neutralizing monoclonal antibodies and lectins. Traditional recombinant protein manufacturing platforms lack sufficient capacity and are too expensive for developing countries, which suffer the greatest disease burden. Plants offer an inexpensive and scalable alternative manufacturing platform that can produce multiple components in a single plant, which is important because multiple components are required to avoid the rapid emergence of HIV-1 strains resistant to single microbicides. Furthermore, crude extracts can be used directly for prophylaxis to avoid the massive costs of downstream processing and purification. We investigated whether rice could simultaneously produce three functional HIV-neutralizing proteins (the monoclonal antibody 2G12, and the lectins griffithsin and cyanovirin-N). Preliminary in vitro tests showed that the cocktail of three proteins bound to gp120 and achieved HIV-1 neutralization. Remarkably, when we mixed the components with crude extracts of wild-type rice endosperm, we observed enhanced binding to gp120 in vitro and synergistic neutralization when all three components were present. Extracts of transgenic plants expressing all three proteins also showed enhanced in vitro binding to gp120 and synergistic HIV-1 neutralization. Fractionation of the rice extracts suggested that the enhanced gp120 binding was dependent on rice proteins, primarily the globulin fraction. Therefore, the production of HIV-1 microbicides in rice may not only reduce costs compared to traditional platforms but may also provide functional benefits in terms of microbicidal potency.

Viral glycoproteomes: technologies for characterization and outlook for vaccine design

It has long been known that surface proteins of most enveloped viruses are covered with glycans. It has furthermore been demonstrated that glycosylation is essential for propagation and immune evasion for many viruses. The recent development of high-resolution mass spectrometry techniques has enabled identification not only of the precise structures but also the positions of such post-translational modifications on viruses, revealing substantial differences in extent of glycosylation and glycan maturation for different classes of viruses. In-depth characterization of glycosylation and other post-translational modifications of viral envelope glycoproteins is essential for rational design of vaccines and antivirals. In this Review, we provide an overview of techniques used to address viral glycosylation and summarize information on glycosylation of enveloped viruses representing ongoing public health challenges. Furthermore, we discuss how knowledge on glycosylation can be translated to means to prevent and combat viral infections.

Pharmacokinetics of the Protein Microbicide 5P12-RANTES in Sheep following Single-Dose Vaginal Gel Administration

5P12-RANTES, a chemokine analogue that potently blocks the HIV CCR5 coreceptor, is being developed as both a vaginal and rectal microbicide for prevention of sexual transmission of HIV. Here, we report the first pharmacokinetic data for 5P12-RANTES following single-dose vaginal gel administration in sheep. Aqueous gel formulations containing low (1.24-mg/ml), intermediate (6.18-mg/ml), and high (32.0-mg/ml; suspension-type gel) concentrations of 5P12-RANTES were assessed via rheology, syringeability, and in vitro release testing. Following vaginal gel administration to sheep, 5P12-RANTES concentrations were measured in vaginal fluid, vaginal tissue, and serum over a 96-h period. All gels showed non-Newtonian pseudoplastic behavior, with the high-concentration gels exhibiting a greater viscosity and cohesive structure than the intermediate- and low-concentration gels. In in vitro release testing, >90% 5P12-RANTES was released from the low- and intermediate-concentration gels after 72 h. For the high-concentration gel, ∼50% 5P12-RANTES was detected, attributed to protein denaturation during lyophilization and/or subsequent solvation of the protein within the gel matrix. In sheep, 5P12-RANTES concentrations in vaginal fluid, vaginal tissue, and serum increased in a dose-dependent manner. The highest concentrations were measured in vaginal fluid (10⁵ to 10⁷ ng/ml), followed by vaginal tissue (10⁴ to 10⁶ ng/ml). Both of these concentration ranges are several orders of magnitude above the reported half-maximal inhibitory concentrations. The lowest concentration was measured in serum (<10² ng/ml). The 5P12-RANTES pharmacokinetic data are similar to those reported previously for other candidate microbicides. These data, coupled with 5P12-RANTES's potency at picomolar concentrations, its strong barrier to resistance, and the full protection that it was observed to provide in a rhesus macaque vaginal challenge model, support the continued development of 5P12-RANTES as a microbicide.

Cyanobacterial lectins characteristics and their role as antiviral agents

Lectins are ubiquitous proteins/glycoproteins of non-immune origin that bind reversibly to carbohydrates in non-covalent and highly specific manner. These lectin-glycan interactions could be exploited for establishment of novel therapeutics, targeting the adherence stage of viruses and thus helpful in eliminating wide spread viral infections. Here the review focuses on the haemagglutination activity, carbohydrate specificity and characteristics of cyanobacterial lectins. Cyanobacterial lectins exhibiting high specificity towards mannose or complex glycans have potential role as anti-viral agents. Prospective role of cyanobacterial lectins in targeting various diseases of worldwide concern such as HIV, hepatitis, herpes, influenza and ebola viruses has been discussed extensively. The review also lays emphasis on recent studies involving structural analysis of glycan-lectin interactions which in turn influence their mechanism of action. Altogether, the promising approach of these cyanobacterial lectins provides insight into their use as antiviral agents.

Pharmacokinetics of the Antiviral Lectin Griffithsin Administered by Different Routes Indicates Multiple Potential Uses

Griffithsin (GRFT) is a red alga-derived lectin with demonstrated broad spectrum antiviral activity against enveloped viruses, including severe acute respiratory syndrome-Coronavirus (SARS-CoV), Japanese encephalitis virus (JEV), hepatitis C virus (HCV), and herpes simplex virus-2 (HSV-2). However, its pharmacokinetic profile remains largely undefined. Here, Sprague Dawley rats were administered a single dose of GRFT at 10 or 20 mg/kg by intravenous, oral, and subcutaneous routes, respectively, and serum GRFT levels were measured at select time points. In addition, the potential for systemic accumulation after oral dosing was assessed in rats after 10 daily treatments with GRFT (20 or 40 mg/kg). We found that parenterally-administered GRFT in rats displayed a complex elimination profile, which varied according to administration routes. However, GRFT was not orally bioavailable, even after chronic treatment. Nonetheless, active GRFT capable of neutralizing HIV-Env pseudoviruses was detected in rat fecal extracts after chronic oral dosing. These findings support further evaluation of GRFT for pre-exposure prophylaxis against emerging epidemics for which specific therapeutics are not available, including systemic and enteric infections caused by susceptible enveloped viruses. In addition, GRFT should be considered for antiviral therapy and the prevention of rectal transmission of HIV-1 and other susceptible viruses.

Griffithsin: An Antiviral Lectin with Outstanding Therapeutic Potential

Griffithsin (GRFT), an algae-derived lectin, is one of the most potent viral entry inhibitors discovered to date. It is currently being developed as a microbicide with broad-spectrum activity against several enveloped viruses. GRFT can inhibit human immunodeficiency virus (HIV) infection at picomolar concentrations, surpassing the ability of most anti-HIV agents. The potential to inhibit other viruses as well as parasites has also been demonstrated. Griffithsin's antiviral activity stems from its ability to bind terminal mannoses present in high-mannose oligosaccharides and crosslink these glycans on the surface of the viral envelope glycoproteins. Here, we review structural and biochemical studies that established mode of action and facilitated construction of GRFT analogs, mechanisms that may lead to resistance, and in vitro and pre-clinical results that support the therapeutic potential of this lectin.

Cyanovirin-N produced in rice endosperm offers effective pre-exposure prophylaxis against HIV-1BaL infection in vitro

Cyanovirin-N produced in rice endosperm provides efficient pre-exposure prophylaxis against HIV-1 BaL infection in vitro. Cyanovirin-N (CV-N) is a lectin with potent antiviral activity that has been proposed as a component of microbicides for the prevention of infection with Human immunodeficiency virus (HIV). The production of protein-based microbicide components requires a platform that is sufficiently economical and scalable to meet the demands of the large at-risk population, particularly in resource poor developing countries. We, therefore, expressed CV-N in rice endosperm, because the dried seed is ideal for storage and transport and crude extracts could be prepared locally and used as a microbicide component without further purification. We found that crude extracts from rice seeds expressing up to 10 µg CV-N per gram dry seed weight showed dose-dependent gp120 binding activity, confirming that the protein was soluble, correctly folded and active. The recombinant lectin ((OS)CV-N) reduced the infectivity of HIV-1BaL (an R5 virus strain representing the majority of transmitted infections) by ~90 % but showed only weak neutralization activity against HIV-1RF (representative of X4 virus, rarely associated with transmission), suggesting it would be highly effective for pre-exposure prophylaxis against the vast majority of transmitted strains. Crude extracts expressing (OS)CV-N showed no toxicity towards human cells at working dilutions indicating that microbicide components produced in rice endosperm are safe for direct application as topical microbicides in humans.

Short Communication: Inhibition of DC-SIGN-Mediated HIV-1 Infection by Complementary Actions of Dendritic Cell Receptor Antagonists and Env-Targeting Virus Inactivators

The DC-SIGN receptor on human dendritic cells interacts with HIV gp120 to promote both infection of antigen-presenting cells and transinfection of T cells. We hypothesized that in DC-SIGN-expressing cells, both DC-SIGN ligands such as dextrans and gp120 antagonists such as peptide triazoles would inhibit HIV infection with potential complementary antagonist effects. To test this hypothesis, we evaluated the effects of dextran (D66), isomaltooligosaccharides (D06), and several peptide triazoles (HNG156, K13, and UM15) on HIV infection of B-THP-1/DC-SIGN cells. In surface plasmon resonance competition assays, D66 (IC50 = 35.4 μM) and D06 (IC50 = 3.4 mM) prevented binding of soluble DC-SIGN to immobilized mannosylated bovine serum albumin (BSA). An efficacious dose-dependent inhibition of DC-SIGN-mediated HIV infection in both pretreatment and posttreatment settings was observed, as indicated by inhibitory potentials (EC50) [D66 (8 μM), D06 (48 mM), HNG156 (40 μM), UM15 (100 nM), and K13 (25 nM)]. Importantly, both dextrans and peptide triazoles significantly decreased HIV gag RNA levels [D66 (7-fold), D06 (13-fold), HNG156 (7-fold), K-13 (3-fold), and UM15 (6-fold)]. Interestingly, D06 at the highest effective concentration showed a 14-fold decrease of infection, while its combination with 50 μM HNG156 showed a 26-fold decrease. Hence, these compounds can combine to inactivate the viruses and suppress DC-SIGN-mediated virus-cell interaction that as shown earlier leads to dendritic cell HIV infection and transinfection dependent on the DC-SIGN receptor.

Human lectins and their roles in viral infections

Innate recognition of virus proteins is an important component of the immune response to viral pathogens. A component of this immune recognition is the family of lectins; pattern recognition receptors (PRRs) that recognise viral pathogen-associated molecular patterns (PAMPs) including viral glycoproteins. In this review we discuss the contribution of soluble and membrane-associated PRRs to immunity against virus pathogens, and the potential role of these molecules in facilitating virus replication. These processes are illustrated with examples of viruses including human immunodeficiency virus (HIV), hepatitis C virus (HCV) and Ebola virus (EBOV). We focus on the structure, function and genetics of the well-characterised C-type lectin mannose-binding lectin, the ficolins, and the membrane-bound CD209 proteins expressed on dendritic cells. The potential for lectin-based antiviral therapies is also discussed.

The evolution of HIV-1 interactions with coreceptors and mannose C-type lectin receptors

The phenotype of human immunodeficiency virus type 1 (HIV-1) commonly evolves between and within infected individuals, at virus transmission, and during disease progression. This evolution includes altered interactions between the virus and its coreceptors, i.e., chemokine receptors, as well as mannose C-type lectin receptors (CLRs). Transmitted/founder viruses are predominantly restricted to CCR5, whereas the subsequent intrapatient evolution of HIV-1 coreceptor use during progressive disease can be subdivided into two distinct pathways. Accordingly, the CCR5-restricted virus population is either gradually replaced by virus variants able to use CXCR4 or evolves toward an altered, more flexible use of CCR5. Despite a strong dependency on these coreceptors for host cell entry, HIV-1 also interacts with other cell surface molecules during target cell attachment, including the CLRs. The virus interaction with the CLRs may result either in the efficient transfer of virus to CD4(+) T cells or in the degradation of the virus in endosomal compartments. The determinants of the diverse outcomes depend on which CLR is engaged and also on the glycan makeup of the envelope glycoproteins, which may evolve with the strength of the immune pressure during the disease course. With the current clinical introduction of CCR5 antagonists and the development of additional entry inhibitors, knowledge on the evolution and baseline characteristics of HIV-1 interactions with coreceptor and CLR interactions may play important roles for individualized and optimized treatment strategies. This review summarizes our current understanding of the evolution of HIV-1 interactions with these receptors.

Bitter-sweet symphony: glycan-lectin interactions in virus biology

Glycans are carbohydrate modifications typically found on proteins or lipids, and can act as ligands for glycan-binding proteins called lectins. Glycans and lectins play crucial roles in the function of cells and organs, and in the immune system of animals and humans. Viral pathogens use glycans and lectins that are encoded by their own or the host genome for their replication and spread. Recent advances in glycobiological research indicate that glycans and lectins mediate key interactions at the virus-host interface, controlling viral spread and/or activation of the immune system. This review reflects on glycan-lectin interactions in the context of viral infection and antiviral immunity. A short introduction illustrates the nature of glycans and lectins, and conveys the basic principles of their interactions. Subsequently, examples are discussed highlighting specific glycan-lectin interactions and how they affect the progress of viral infections, either benefiting the host or the virus. Moreover, glycan and lectin variability and their potential biological consequences are discussed. Finally, the review outlines how recent advances in the glycan-lectin field might be transformed into promising new approaches to antiviral therapy.

The lectin pathway of complement: advantage or disadvantage in HIV pathogenesis?

The pattern recognition molecules of the lectin complement pathway are important components of the innate immune system with known functions in host-virus interactions. This paper summarizes current knowledge of how these intriguing molecules, including mannose-binding lectin (MBL), Ficolin-1, -2 and -3, and collectin-11 (CL-11) may influence HIV-pathogenesis. It has been demonstrated that MBL is capable of binding and neutralizing HIV and may affect host susceptibility to HIV infection and disease progression. In addition, MBL may cause variations in the host immune response against HIV. Ficolin-1, -2 and -3 and CL-11 could have similar functions in HIV infection as the ficolins have been shown to play a role in other viral infections, and CL-11 resembles MBL and the ficolins in structure and binding capacity.

The antiviral lectin cyanovirin-N: probing multivalency and glycan recognition through experimental and computational approaches

CVN (cyanovirin-N), a small lectin isolated from cyanobacteria, exemplifies a novel class of anti-HIV agents that act by binding to the highly glycosylated envelope protein gp120 (glycoprotein 120), resulting in inhibition of the crucial viral entry step. In the present review, we summarize recent work in our laboratory and others towards determining the crucial role of multivalency in the antiviral activity, and we discuss features that contribute to the high specificity and affinity for the glycan ligand observed in CVN. An integrated approach that encompasses structural determination, mutagenesis analysis and computational work holds particular promise to clarify aspects of the interactions between CVN and glycans.

Characterizing carbohydrate-protein interactions by nuclear magnetic resonance spectroscopy

Interactions between proteins and soluble carbohydrates and/or surface displayed glycans are central to countless recognition, attachment and signaling events in biology. The physical chemical features associated with these binding events vary considerably, depending on the biological system of interest. For example, carbohydrate-protein interactions can be stoichiometric or multivalent, the protein receptors can be monomeric or oligomeric, and the specificity of recognition can be highly stringent or rather promiscuous. Equilibrium dissociation constants for carbohydrate binding are known to vary from micromolar to millimolar, with weak interactions being far more prevalent; and individual carbohydrate-binding sites can be truly symmetrical or merely homologous, and hence, the affinities of individual sites within a single protein can vary, as can the order of binding. Several factors, including the weak affinities with which glycans bind their protein receptors, the dynamic nature of the glycans themselves, and the nonequivalent interactions among oligomeric carbohydrate receptors, have made nuclear magnetic resonance (NMR) an especially powerful tool for studying and defining carbohydrate-protein interactions. Here, we describe those NMR approaches that have proven to be the most robust in characterizing these systems, and explain what type of information can (or cannot) be obtained from each. Our goal is to provide the reader the information necessary for selecting the correct experiment or sets of experiments to characterize their carbohydrate-protein interaction of interest.

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.

Binding sugars: from natural lectins to synthetic receptors and engineered neolectins

The large diversity and complexity of glycan structures together with their crucial role in many biological or pathological processes require the development of new high-throughput techniques for analyses. Lectins are classically used for characterising, imaging or targeting glycoconjugates and, when printed on microarrays, they are very useful tools for profiling glycomes. Development of recombinant lectins gives access to reliable and reproducible material, while engineering of new binding sites on existing scaffolds allows tuning of specificity. From the accumulated knowledge on protein-carbohydrate interactions, it is now possible to use nucleotide and peptide (bio)synthesis for producing new carbohydrate-binding molecules. Such a biomimetic approach can also be addressed by boron chemistry and supra-molecular chemistry for the design of fully artificial glycosensors.

Combinations of griffithsin with other carbohydrate-binding agents demonstrate superior activity against HIV Type 1, HIV Type 2, and selected carbohydrate-binding agent-resistant HIV Type 1 strains

Carbohydrate-binding agents (CBAs) are potential HIV microbicidal agents with a high genetic barrier to resistance. We wanted to evaluate whether two mannose-specific CBAs, recognizing multiple and often distinct glycan structures on the HIV envelope gp120, can interact synergistically against HIV-1, HIV-2, and HIV-1 strains that were selected for resistance against particular CBAs [i.e., 2G12 mAb and microvirin (MVN)]. Paired CBA/CBA combinations mainly showed synergistic activity against both wild-type HIV-1 and HIV-2 but also 2G12 mAb- and MVN-resistant HIV-1 strains as based on the median effect principle with combination indices (CIs) ranging between 0.29 and 0.97. Upon combination, an increase in antiviral potency of griffithsin (GRFT) up to ∼12-fold (against HIV-1), ∼8-fold (against HIV-2), and ∼6-fold (against CBA-resistant HIV-1) was observed. In contrast, HHA/GNA combinations showed additive activity against wild-type HIV-1 and HIV-2 strains, but remarkable synergy with HHA and GNA was observed against 2G12 mAb- and MVN-resistant HIV-1 strains (CI, 0.64 and 0.49, respectively). Overall, combinations of GRFT and other CBAs showed synergistic activity against HIV-1, HIV-2, and even against certain CBA-resistant HIV-1 strains. The CBAs tested appear to have distinct binding patterns on the gp120 envelope and therefore do not necessarily compete with each other's glycan binding sites on gp120. As a result, there might be no steric hindrance between two different CBAs in their competition for glycan binding (except for the HHA/GNA combination). These data are encouraging for the use of paired CBA combinations in topical microbicide applications (e.g., creams, gels, or intravaginal rings) to prevent HIV transmission.

HIV-1 gp120 impairs the induction of B cell responses by TLR9-activated plasmacytoid dendritic cells

Plasmacytoid dendritic cells (pDCs) play a central role in innate and adaptive immune responses to viral infections, including HIV type 1 (HIV-1). pDCs produce substantial quantities of type I IFN and proinflammatory cytokines upon stimulation via TLRs, specifically TLR7 or TLR9. The HIV-1 envelope glycoproteins, exemplified by the gp120 monomer, are the focus of vaccines aimed at inducing B cell responses. We have studied how the interactions of gp120 with various receptors on human pDCs affect the activation of these cells via TLR9 and their subsequent ability to stimulate B cells. We observed that IFN-α production by pDCs in response to TLR9, but not TLR7, stimulation was reduced by exposure to gp120. Specifically, gp120 inhibited the CpG-induced maturation of pDCs and their expression of TNF-α, IL-6, TLR9, IFN regulatory factor 7, and BAFF. Receptor-blocking and cross-linking studies showed that these inhibitory effects of gp120 were mediated by interactions with CD4 and mannose-binding C-type lectin receptors, but not with the chemokine receptors CCR5 and CXCR4. Of note is that gp120 inhibited the activation of B cells by TLR9-stimulated pDCs. Taken together, our data show that HIV-1 gp120 impairs pDC functions, including activation of B cell responses, and imply that TLR9 ligands may not be good adjuvants to use in combination with envelope glycoprotein vaccines.

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.

Algal lectins as potential HIV microbicide candidates

The development and use of topical microbicides potentially offers an additional strategy to reduce the spread of the Human Immunodeficiency Virus (HIV). Carbohydrate-binding agents (CBAs) that show specificity for high mannose carbohydrates on the surface of the heavily glycosylated envelope of HIV are endowed with potent anti-HIV activity. In fact, a number of algal lectins such as cyanovirin-N, microvirin, microcystis viridis lectin, scytovirin, Oscillatoria agardhii agglutinin and griffithsin are considered as potential microbicide candidates to prevent the sexual transmission of HIV through topical applications. They not only inhibit infection of cells by cell-free virus but they can also efficiently prevent virus transmission from virus-infected cells to uninfected CD4⁺ target T-lymphocytes and DC-SIGN-directed capture of HIV-1 and transmission to CD4⁺ T lymphocytes. This review focuses on the structural properties and carbohydrate specificity of these algal lectins, their antiviral activity against HIV and several other enveloped viruses, their safety profile and viral resistance patterns.