PSC-RANTES blocks R5 human immunodeficiency virus infection of Langerhans cells isolated from individuals with a variety of CCR5 diplotypes

Novel small synthetic HIV-1 V3 crown variants: CCR5 targeting ligands

The CC chemokine receptor 5 (CCR5) antagonism represents a promising pharmacological strategy for therapeutic intervention as it plays a significant role in reducing the severity and progression of a wide range of pathological conditions. Here we designed and generated peptide ligands targeting the chemokine receptor, CCR5, that were derived from the critical interaction sites of the V3 crown domain of envelope protein glycoprotein gp120 (TRKSIHIGPGRAFYTTGEI) of HIV-1 using computational biology approach and the peptide sequence corresponding to this region was taken as the template peptide, designated as TMP-1. The peptide variants were synthesized by employing Fmoc chemistry using polymer support and were labelled with rhodamine B to study their interaction with the CCR5 receptor expressed on various cells. TMP-1 and TMP-2 were selected as the high-affinity ligands from in vitro receptor-binding assays. Specific receptor-binding experiments in activated peripheral blood mononuclear cells and HOS.CCR5 cells indicated that TMP-1 and TMP-2 had significant CCR5 specificity. Further, the functional analysis of TMP peptides using chemotactic migration assay showed that both peptides did not mediate the migration of responsive cells. Thus, template TMP-1 and TMP-2 represent promising CCR5 targeting peptide candidates.

Anti-α4β7 monoclonal antibody-conjugated nanoparticles block integrin α4β7 on intravaginal T cells in rhesus macaques

Intravenous administration of anti-α₄β₇ monoclonal antibody in macaques decreases simian immunodeficiency virus (SIV) vaginal infection and reduces gut SIV loads. Because of potential side effects of systemic administration, a prophylactic strategy based on mucosal administration of anti-α₄β₇ antibody may be safer and more effective. With this in mind, we developed a novel intravaginal formulation consisting of anti-α₄β₇ monoclonal antibody-conjugated nanoparticles (NPs) loaded in a 1% hydroxyethylcellulose (HEC) gel (NP-α₄β₇ gel). When intravaginally administered as a single dose in a rhesus macaque model, the formulation preferentially bound to CD4⁺ or CD3⁺ T cells expressing high levels of α₄β₇, and occupied ~40% of α₄β₇ expressed by these subsets and ~25% of all cells expressing α₄β₇ Blocking of the α₄β₇ was restricted to the vaginal tract without any changes detected systemically.

Selective Allosteric Modulation of N-Terminally Cleaved, but Not Full Length CCL3 in CCR1

Chemokines undergo post-translational modification such as N-terminal truncations. Here, we describe how N-terminal truncation of full length CCL3^(1-70) affects its activity at CCR1. Truncated CCL3^(5-70) has 10-fold higher potency and enhanced efficacy in β-arrestin recruitment, but less than 2-fold increased potencies in G protein signaling determined by calcium release, cAMP and IP₃ formation. Small positive ago-allosteric ligands modulate the two CCL3 variants differently as the metal ion chelator bipyridine in complex with zinc (ZnBip) enhances the binding of truncated, but not full length CCL3, while a size-increase of the chelator to a chloro-substituted terpyridine (ZnClTerp), eliminates its allosteric, but not agonistic action. By employing a series of receptor mutants and in silico modeling we describe residues of importance for chemokine and small molecule binding. Notably, the chemokine receptor-conserved Glu287^7.39 interacts with the N-terminal amine of truncated CCL3^(5-70) and with Zn²⁺ of ZnBip, thereby bridging their binding sites and enabling the positive allosteric effect. Our study emphasizes that small allosteric molecules may act differently toward chemokine variants and thus selectively modulate interactions of specific chemokine subsets with their cognate receptors.

(C3) The Oral Epithelial Cell and First Encounters with HIV-1

The oral epithelium is the site of first exposure of HIV-1 to host tissues during oral sex with an infected partner or through breast-feeding by an infected mother. Although the oral epithelium is distinguishable by its apparent resistance, the mucosal surfaces represent a primary target of HIV-1. After oral exposure and swallowing, infection is detected prominently in the gastrointestinal tract, which becomes depleted of CD4+ T-cells. The oral cavity and palatine tonsils appear to resist infection and transfer to susceptible lymphoid cells in the lamina propria by local anti-HIV-1 mechanisms. In some cases, expression of these antiviral mechanisms increases after exposure to HIV-1. During primary exposure and before seroconversion, based on limited in vitro and primate data, a window of opportunity for capture of HIV-1 by the oral epithelium may exist. After seroconversion, the risk of infectious HIV-1 appearing in saliva is negligible. This report considers evidence that oral epithelium has the potential both to enable and to resist infection by HIV-1.

HIV-1 border patrols: Langerhans cells control antiviral responses and viral transmission

Langerhans cells (LCs) reside in the mucosal epithelia and are refractory to HIV-1 infection; HIV-1 capture by C-type lectin receptor langerin and subsequent targeting to Birbeck granules prevents infection. Furthermore, LCs restrict transmission of CXCR4-using HIV-1 variants, which underscores the role of immature LCs as gatekeepers in the selection of HIV-1 variants. Interaction of langerin on LCs with hyaluronic acid on dendritic cells facilitates cross-presentation of HIV-1 to CD8+ T cells. Activation of LCs upon inflammation bypasses the langerin-dependent barrier, which favors cross-presentation and increases susceptibility of LCs to HIV-1 infection. These recent developments not only highlight the plasticity of LCs but also define an important role for LC-dendritic cell crosstalk at the periphery in directing adaptive immune responses to viruses.

Herpes simplex virus type 2-infected dendritic cells produce TNF-α, which enhances CCR5 expression and stimulates HIV production from adjacent infected cells

Prior HSV-2 infection enhances the acquisition of HIV-1 >3-fold. In genital herpes lesions, the superficial layers of stratified squamous epithelium are disrupted, allowing easier access of HIV-1 to Langerhans cells (LC) in the epidermis and perhaps even dendritic cells (DCs) in the outer dermis, as well as to lesion infiltrating activated T lymphocytes and macrophages. Therefore, we examined the effects of coinfection with HIV-1 and HSV-2 on monocyte-derived DCs (MDDC). With simultaneous coinfection, HSV-2 significantly stimulated HIV-1 DNA production 5-fold compared with HIV-1 infection alone. Because <1% of cells were dually infected, this was a field effect. Virus-stripped supernatants from HSV-2-infected MDDCs were shown to enhance HIV-1 infection, as measured by HIV-1-DNA and p24 Ag in MDDCs. Furthermore these supernatants markedly stimulated CCR5 expression on both MDDCs and LCs. TNF-α was by far the most prominent cytokine in the supernatant and also within HSV-2-infected MDDCs. HSV-2 infection of isolated immature epidermal LCs, but not keratinocytes, also produced TNF-α (and low levels of IFN-β). Neutralizing Ab to TNF-α and its receptor, TNF-R1, on MDDCs markedly inhibited the CCR5-stimulating effect of the supernatant. Therefore, these results suggest that HSV-2 infection of DCs in the skin during primary or recurrent genital herpes may enhance HIV-1 infection of adjacent DCs, thus contributing to acquisition of HIV-1 through herpetic lesions.

Inhibition of two temporal phases of HIV-1 transfer from primary Langerhans cells to T cells: the role of langerin

Epidermal Langerhans cells (eLCs) uniquely express the C-type lectin receptor langerin in addition to the HIV entry receptors CD4 and CCR5. They are among the first target cells to encounter HIV in the anogenital stratified squamous mucosa during sexual transmission. Previous reports on the mechanism of HIV transfer to T cells and the role of langerin have been contradictory. In this study, we examined HIV replication and langerin-mediated viral transfer by authentic immature eLCs and model Mutz-3 LCs. eLCs were productively infected with HIV, whereas Mutz-3 LCs were not susceptible because of a lack of CCR5 expression. Two successive phases of HIV viral transfer to T cells via cave/vesicular trafficking and de novo replication were observed with eLCs as previously described in monocyte-derived or blood dendritic cells, but only first phase transfer was observed with Mutz-3 LCs. Langerin was expressed as trimers after cross-linking on the cell surface of Mutz-3 LCs and in this form preferentially bound HIV envelope protein gp140 and whole HIV particles via the carbohydrate recognition domain (CRD). Both phases of HIV transfer from eLCs to T cells were inhibited when eLCs were pretreated with a mAb to langerin CRD or when HIV was pretreated with a soluble langerin trimeric extracellular domain or by a CRD homolog. However, the langerin homolog did not inhibit direct HIV infection of T cells. These two novel soluble langerin inhibitors could be developed to prevent HIV uptake, infection, and subsequent transfer to T cells during early stages of infection.

Human immature Langerhans cells restrict CXCR4-using HIV-1 transmission

Background

Sexual transmission is the main route of HIV-1 infection and the CCR5-using (R5) HIV-1 is predominantly transmitted, even though CXCR4-using (X4) HIV-1 is often abundant in chronic HIV-1 patients. The mechanisms underlying this tropism selection are unclear. Mucosal Langerhans cells (LCs) are the first immune cells to encounter HIV-1 and here we investigated the role of LCs in selection of R5 HIV-1 using an ex vivo epidermal and vaginal transmission models.

Results

Immature LCs were productively infected by X4 as well as R5 HIV-1. However, only R5 but not X4 viruses were selectively transmitted by immature LCs to T cells. Transmission of HIV-1 was depended on de novo production of HIV-1 in LCs, since it could be inhibited by CCR5 fusion inhibitors as well as reverse transcription inhibitors. Notably, the activation state of LCs affected the restriction in X4 HIV-1 transmission; immune activation by TNF facilitated transmission of X4 as well as R5 HIV-1.

Conclusions

These data suggest that LCs play a crucial role in R5 selection and that immature LCs effectively restrict X4 at the level of transmission.

New insights into viral structure and virus–cell interactions through proteomics

Although genomics techniques such as DNA microarrays have been widely used in virology, much more limited use has been made of proteomics. Although difficult, proteomics can greatly contribute to an understanding of virus-cell interactions, including the ternary structure of viral receptors at the cell surface, post-translational modifications and isoforms of critical viral and cellular proteins and even to the structure of viruses. Proteomics techniques also offer the potential for discovering markers for diagnostic and prognostic tests of viral infections in vivo. This review describes the use of several proteomic approaches for the analysis of HIV-cellular receptor interactions, the molecular mechanisms of transport of herpes simplex virus within neurons, and the structure of the tegument of herpes simplex virus.

HIV-1 envelope replication and α4β7 utilization among newly infected subjects and their corresponding heterosexual partners

BACKGROUND

Previous studies suggest that active selection limits the number of HIV-1 variants acquired by a newly infected individual from the diverse variants circulating in the transmitting partner. We compared HIV-1 envelopes from 9 newly infected subjects and their linked transmitting partner to explore potential mechanisms for selection.

RESULTS

Recipient virus envelopes had significant genotypic differences compared to those present in the transmitting partner. Recombinant viruses incorporating pools of recipient and transmitter envelopes showed no significant difference in their sensitivity to receptor and fusion inhibitors, suggesting they had relatively similar entry capacity in the presence of low CD4 and CCR5 levels. Aggregate results in primary cells from up to 4 different blood or skin donors showed that viruses with envelopes from the transmitting partner as compared to recipient envelopes replicated more efficiently in CD4+ T cells, monocyte derived dendritic cell (MDDC) - CD4+ T cell co-cultures, Langerhans cells (LCs) - CD4+ T cell co-cultures and CD4+ T cells expressing high levels of the gut homing receptor, α4β7, and demonstrated greater binding to α4β7 high / CD8+ T cells. These transmitter versus recipient envelope virus phenotypic differences, however, were not always consistent among the primary cells from all the different blood or skin donation volunteers.

CONCLUSION

Although genotypically unique variants are present in newly infected individuals compared to the diverse swarm circulating in the chronically infected transmitting partner, replication in potential early target cells and receptor utilization either do not completely dictate this genetic selection, or these potential transmission phenotypes are lost very soon after HIV-1 acquisition.

Peptide and protein-based inhibitors of HIV-1 co-receptors

Human immunodeficiency virus (HIV) afflicts an estimated 30 million people globally, making it a continuing pandemic. Despite major research efforts, the rate of new infections has remained relatively static over time. This article reviews an emerging strategy for the treatment of HIV, the inhibition of the co-receptors necessary for HIV entry, CCR5 and CXCR4. The aim of this article is to highlight potential therapeutics derived from peptides and proteins that show particular promise in HIV treatment. Molecules that act on CCR5, CXCR4 or on both receptors will be discussed herein.

Tissue dendritic cells as portals for HIV entry

Dendritic cells (DCs) are found at the portals of pathogen entry such as the mucosal surfaces of the respiratory, gastrointestinal and genital tracts where they represent the first line of contact between the immune system and the foreign invaders. They are found throughout the body in multiple subsets where they express unique combinations of C-type lectin receptors to best aid them in detection of pathogens associated with their anatomical location. DCs are important in the establishment in HIV infection for two reasons. Firstly, they are one of the first cells to encounter the virus, and the specific interaction that occurs between these cells and HIV is critical to HIV establishing a foothold infection. Secondly and most importantly, HIV is able to efficiently transfer the virus to its primary target cell, the CD4(+) T lymphocyte, in which it replicates explosively. Infection of CD4(+) T lymphocytes via DCs is far more efficient than direct infection. This review surveys the various DCs subsets found within the human sexual mucosa and their interactions with HIV. Mechanisms of HIV uptake are discussed as well as how the virus then traffics through the DC and is transferred to T cells. Until recently, most research has focussed on vaginal transmission despite the increased transmission rate associated with anal intercourse. Here, we also discuss recent advances in our understanding of HIV transmission in the colon.

HIV-1 Trans Infection of CD4(+) T Cells by Professional Antigen Presenting Cells

Since the 1990s we have known of the fascinating ability of a complex set of professional antigen presenting cells (APCs; dendritic cells, monocytes/macrophages, and B lymphocytes) to mediate HIV-1 trans infection of CD4(+) T cells. This results in a burst of virus replication in the T cells that is much greater than that resulting from direct, cis infection of either APC or T cells, or trans infection between T cells. Such APC-to-T cell trans infection first involves a complex set of virus subtype, attachment, entry, and replication patterns that have many similarities among APC, as well as distinct differences related to virus receptors, intracellular trafficking, and productive and nonproductive replication pathways. The end result is that HIV-1 can sequester within the APC for several days and be transmitted via membrane extensions intracellularly and extracellularly to T cells across the virologic synapse. Virus replication requires activated T cells that can develop concurrently with the events of virus transmission. Further research is essential to fill the many gaps in our understanding of these trans infection processes and their role in natural HIV-1 infection.

Study on CCR5 analogs and affinity peptides

The G protein-coupled receptor of human chemokine receptor 5 (CCR5) is a key target in the human immunodeficiency virus (HIV) infection process due to its major involvement in binding to the HIV type 1 (HIV-1) envelope glycoprotein gp120 and facilitating virus entry into the cells. The identification of naturally occurring CCR5 mutations (especially CCR5 delta-32) has allowed us to address the CCR5 molecule as a promising target to prevent or resist HIV infection in vivo. To obtain high-affinity peptides that can be used to block CCR5, CCR5 analogs with high conformational similarity are required. In this study, two recombinant proteins named CCR5 N-Linker-E2 and CCR5 mN-E1-E2 containing the fragments of the CCR5 N-terminal, the first extracellular loop or the second extracellular loop are cloned from a full-length human CCR5 cDNA. The recombinant human CCR5 analogs with self-cleavage activity of the intein Mxe or Ssp in the vector pTwinI were then produced with a high-yield expression and purification system in Escherichia coli. Experiments of extracellular epitope-activity identification (such as immunoprecipitation and indirective/competitive enzyme-linked immunosorbent assay) confirmed the close similarity between the epitope activity of the CCR5 analogs and that of the natural CCR5, suggesting the applicability of the recombinant CCR5 analogs as antagonists of the chemokine ligands. Subsequent screening of high-affinity peptides from the phage random-peptides library acquired nine polypeptides, which could be used as CCR5 peptide antagonists. The CCR5 analogs and affinity peptides elucidated in this paper provide us with a basis for further study of the mechanism of inhibition of HIV-1 infection.

[Mechanism for HIV invasion via skin or mucosa]

Sexual transmission of HIV is the most common mode of infection in the global HIV epidemic. In the absence of an effective vaccine, there is an urgent need for additional strategies to prevent new HIV infections. An emerging body of evidence now indicates that Langerhans cells (LC) are initial cellular targets in the sexual transmission of HIV, and CD4- and CCR5-mediated infection of LC plays a crucial role in virus dissemination. I focus on the recent advances regarding the cellular events that may occur during heterosexual transmission of HIV.

Highly potent chimeric inhibitors targeting two steps of HIV cell entry

Blocking HIV-1 cell entry has long been a major goal of anti-HIV drug development. Here, we report a successful design of two highly potent chimeric HIV entry inhibitors composed of one CCR5-targeting RANTES (regulated on activation normal T cell expressed and secreted) variant (5P12-RANTES or 5P14-RANTES (Gaertner, H., Cerini, F., Escola, J. M., Kuenzi, G., Melotti, A., Offord, R., Rossitto-Borlat, I., Nedellec, R., Salkowitz, J., Gorochov, G., Mosier, D., and Hartley, O. (2008) Proc. Natl. Acad. Sci. U.S.A. 105, 17706-17711)) linked to a gp41 fusion inhibitor, C37. Chimeric inhibitors 5P12-linker-C37 and 5P14-linker-C37 showed extremely high antiviral potency in single cycle and replication-competent viral assays against R5-tropic viruses, with IC(50) values as low as 0.004 nm. This inhibition was somewhat strain-dependent and was up to 100-fold better than the RANTES variant alone or in combination with unlinked C37. The chimeric inhibitors also fully retained the antiviral activity of C37 against X4-tropic viruses, and this inhibition can be further enhanced significantly if the target cell co-expresses CCR5 receptor. On human peripheral blood mononuclear cells, the inhibitors showed very strong inhibition against R5-tropic Ba-L strain and X4-tropic IIIB strain, with IC(50) values as low as 0.015 and 0.44 nm, which are 45- and 16-fold better than the parent inhibitors, respectively. A clear delivery mechanism requiring a covalent linkage between the two segments of the chimera was observed and characterized. Furthermore, the two chimeric inhibitors are fully recombinant and are easily produced at low cost. These attributes make them excellent candidates for anti-HIV microbicides. The results of this study also suggest a potent approach for optimizing existing HIV entry inhibitors or designing new inhibitors.

[Langerhans cell and HIV]

Heterosexual transmission of HIV is the most common mode of infection in the global HIV epidemic. In the absence of an effective vaccine, there is an urgent need for additional strategies to prevent new HIV infections. Evidence from a variety of investigations, including epidemiologic studies on sexual transmission, in vivo studies in rhesus monkey, and ex vivo studies using human explant models, indicate that CD4/CCR5-mediated de novo infection of Langerhans cells (LCs) is a major pathway involved in sexual transmission of HIV (LCs primary gate keeper model). However, it has been recently revealed that Langerin (a C-type lectin receptor) expressed on LC inactivate HIV. Thus, there may be multiple ways by which HIV interacts with LCs in the genital mucosa. In light of the current HIV infection rates in heterosexuals and the absence of a prophylactic vaccine, prevention strategies, such as topical microbicides that block sexual transmission of HIV, are urgently needed. This review focuses on the recent advances regarding the role of LCs in heterosexual transmission of HIV, and the relationship between the LCs primary gate keeper model and current prevention strategies worldwide.

HIV sexual transmission and microbicides

Pathogens often rely on the contacts between hosts for transmission. Most viruses have adapted their transmission mechanisms to defined behaviours of their host(s) and have learned to exploit these for their own propagation. Some viruses, such as HIV, the human papillomavirus (HPV), HSV-2 and HCV, cause sexually transmitted infections (STIs). Understanding the transmission of particular viral variants and comprehending the early adaptation and evolution is fundamental to eventually inhibiting sexual transmission of HIV. Here, we review the current understanding of the mechanisms of sexual transmission and the biology of the transmitted HIV. Next, we present a timely overview of candidate microbicides, including past, ongoing and future clinical trials of HIV topical microbicides.

Potent and broad neutralizing activity of a single chain antibody fragment against cell-free and cell-associated HIV-1

Several human monoclonal antibodies (hmAbs) exhibit relatively potent and broad neutralizing activity against HIV-1, but there has not been much success in using them as potential therapeutics. We have previously hypothesized and demonstrated that small engineered antibodies can target highly conserved epitopes that are not accessible by full-size antibodies. However, their potency has not been comparatively evaluated with known HIV-1-neutralizing hmAbs against large panels of primary isolates. We report here the inhibitory activity of an engineered single chain antibody fragment (scFv), m9, against several panels of primary HIV-1 isolates from group M (clades A-G) using cell-free and cell-associated virus in cell line-based assays. M9 was much more potent than scFv 17b, and more potent than or comparable to the best-characterized broadly neutralizing hmAbs IgG(1) b12, 2G12, 2F5 and 4E10. It also inhibited cell-to-cell transmission of HIV-1 with higher potency than enfuvirtide (T-20, Fuzeon). M9 competed with a sulfated CCR5 N-terminal peptide for binding to gp120-CD4 complex, suggesting an overlapping epitope with the coreceptor binding site. M9 did not react with phosphatidylserine (PS) and cardiolipin (CL), nor did it react with a panel of autoantigens in an antinuclear autoantibody (ANA) assay. We further found that escape mutants resistant to m9 did not emerge in an immune selection assay. These results suggest that m9 is a novel anti-HIV-1 candidate with potential therapeutic or prophylactic properties, and its epitope is a new target for drug or vaccine development.

HIV-1 sexual transmission: early events of HIV-1 infection of human cervico-vaginal tissue in an optimized ex vivo model

Infection and dissemination of human immunodeficiency virus (HIV)-1 through the female body after vaginal intercourse depends on the activation/differentiation status of mucosal CD4 T cells. In this study, we investigated this status and the susceptibility to HIV-1 infection of human cervico-vaginal tissue ex vivo. We found that virtually all T cells are of the effector memory phenotype with broad CC chemokine receptor 5 (CCR5) expression. As it does in vivo, human cervico-vaginal tissue ex vivo preferentially supports the productive infection of R5 HIV-1 rather than that of X4 HIV-1 in spite of the broad expression of CXC chemokine receptor 4 (CXCR4). X4 HIV-1 replicated only in the few tissues that were enriched in CD27(+)CD28(+) effector memory CD4 T cells. Productive infection of R5 HIV-1 occurred preferentially in activated CD38(+)CD4 T cells and was followed by a similar activation of HIV-1-uninfected (bystander) CD4 T cells that may amplify viral infection. These results provide new insights into the dependence of HIV-1 infection and dissemination on the activation/differentiation of cervico-vaginal lymphocytes.

Structural and functional studies of the potent anti-HIV chemokine variant P2-RANTES

The N-terminal region of the chemokine RANTES is critical for its function. A synthesized N-terminally modified analog of RANTES, P2-RANTES, was discovered using a phage display selection against living CCR5-expressing cells, and has been reported to inhibit HIV-1 env-mediated cell-cell fusion at subnanomolar levels (Hartley et al. J Virol 2003;77:6637-6644). In the present study we produced this protein using E. coli overexpression and extensively studied its structure and function. The x-ray crystal structure of P2-RANTES was solved and refined at 1.7 A resolution. This protein was found to be predominantly a monomer in solution by analytical ultracentrifugation, but a tetramer in the crystal. In studies of glycosaminoglycan binding, P2-RANTES was found to be significantly less able to bind heparin than wild type RANTES. We also tested this protein for receptor internalization where it was shown to be functional, in cell-cell fusion assays where recombinant P2-RANTES was a potent fusion inhibitor (IC(50) = 2.4 +/- 0.8 nM), and in single round infection assays where P2-RANTES inhibited at subnanomolar levels. Further, in a modified fusion assay designed to test specificity of inhibition, P2-RANTES was also highly effective, with a 65-fold improvement over the fusion inhibitor C37, which is closely related to the clinically approved inhibitor T-20. These studies provide detailed structural and functional information for this novel N-terminally modified chemokine mutant. This information will be very useful in the development of more potent anti-HIV agents. PDB Accession Number: 2vxw.

Dual action microbicides: reappraisal of their roles in contraceptive research

Of the variety of contraceptive options available for women, very few provide dual protection against sexually transmitted diseases. Due to increased incidence of human immunodeficiency virus type 1 (HIV-1), genital herpes, hepatitis B and human papilloma virus, development of novel contraceptive strategies that incorporate antiviral activity has become the top priority in contraceptive research. Topical microbicides are now considered to be the last ray of hope, as they would ideally provide protection against unwanted pregnancy, proper lubrication during sexual activity, and preclude the vaginal/rectal transmission of sexually transmitted diseases. A large number of vaginal microbicides are in the preclinical or clinical stages of evaluation for their safety, efficacy and acceptability. However, a major bottleneck in the development of novel mechanism-based dual microbicides has been their detergent-like effects, along with debilitating action on the vaginal microflora. Hence the search is still on for the ideal dual microbicide/s that may obliterate these disadvantages and provide an invincible shield to women in their crusade against unintended pregnancy as well as sexually transmitted diseases. The present review highlights the current scenario towards the development of novel contraceptive strategies to counteract the rampant spread of sexually transmitted diseases, with special reference to HIV/AIDS.

TNF-alpha and TLR agonists increase susceptibility to HIV-1 transmission by human Langerhans cells ex vivo

Genital coinfections increase an individual's risk of becoming infected with HIV-1 by sexual contact. Several mechanisms have been proposed to explain this, such as the presence of ulceration and bleeding caused by the coinfecting pathogen. Here we demonstrate that Langerhans cells (LCs) are involved in the increased susceptibility to HIV-1 in the presence of genital coinfections. Although LCs are a target for HIV-1 infection in genital tissues, we found that immature LCs did not efficiently mediate HIV-1 transmission in an ex vivo human skin explant model. However, the inflammatory stimuli TNF-alpha and Pam3CysSerLys4 (Pam3CSK4), the ligand for the TLR1/TLR2 heterodimer, strongly increased HIV-1 transmission by LCs through distinct mechanisms. TNF-alpha enhanced transmission by increasing HIV-1 replication in LCs, whereas Pam3CSK4 acted by increasing LC capture of HIV-1 and subsequent trans-infection of T cells. Genital infections such as Candida albicans and Neisseria gonorrhea not only triggered TLRs but also induced TNF-alpha production in vaginal and skin explants. Thus, during coinfection, LCs could be directly activated by pathogenic structures and indirectly activated by inflammatory factors, thereby increasing the risk of acquiring HIV-1. Our data demonstrate a decisive role for LCs in HIV-1 transmission during genital coinfections and suggest antiinflammatory therapies as potential strategies to prevent HIV-1 transmission.

Highly potent, fully recombinant anti-HIV chemokines: reengineering a low-cost microbicide

New prevention strategies for use in developing countries are urgently needed to curb the worldwide HIV/AIDS epidemic. The N-terminally modified chemokine PSC-RANTES is a highly potent entry inhibitor against R5-tropic HIV-1 strains, with an inhibitory mechanism involving long-term intracellular sequestration of the HIV coreceptor, CCR5. PSC-RANTES is fully protective when applied topically in a macaque model of vaginal HIV transmission, but it has 2 potential disadvantages related to further development: the requirement for chemical synthesis adds to production costs, and its strong CCR5 agonist activity might induce local inflammation. It would thus be preferable to find a recombinant analogue that retained the high potency of PSC-RANTES but lacked its agonist activity. Using a strategy based on phage display, we set out to discover PSC-RANTES analogs that contain only natural amino acids. We sought molecules that retain the potency and inhibitory mechanism of PSC-RANTES, while trying to reduce CCR5 signaling to as low a level as possible. We identified 3 analogues, all of which exhibit in vitro potency against HIV-1 comparable to that of PSC-RANTES. The first, 6P4-RANTES, resembles PSC-RANTES in that it is a strong agonist that induces prolonged intracellular sequestration of CCR5. The second, 5P12-RANTES, has no detectable G protein-linked signaling activity and does not bring about receptor sequestration. The third, 5P14-RANTES, induces significant levels of CCR5 internalization without detectable G protein-linked signaling activity. These 3 molecules represent promising candidates for further development as topical HIV prevention strategies.

Targeted delivery of PSC-RANTES for HIV-1 prevention using biodegradable nanoparticles

PURPOSE

Nanoparticles formulated from the biodegradable co-polymer poly(lactic-co-glycolic acid) (PLGA), were investigated as a drug delivery system to enhance tissue uptake, permeation, and targeting for PSC-RANTES anti-HIV-1 activity.

MATERIALS AND METHODS

PSC-RANTES nanoparticles formulated via a double emulsion process and characterized in both in vitro and ex vivo systems to determine PSC-RANTES release rate, nanoparticle tissue permeation, and anti-HIV bioactivity.

RESULTS

Spherical, monodisperse (PDI = 0.098 +/- 0.054) PSC-RANTES nanoparticles (d = 256.58 +/- 19.57 nm) with an encapsulation efficiency of 82.23 +/- 8.35% were manufactured. In vitro release studies demonstrated a controlled release profile of PSC-RANTES (71.48 +/- 5.25% release). PSC-RANTES nanoparticle maintained comparable anti-HIV activity with unformulated PSC-RANTES in a HeLa cell-based system with an IC(50) of approximately 1pM. In an ex vivo cervical tissue model, PSC-RANTES nanoparticles displayed a fivefold increase in tissue uptake, enhanced tissue permeation, and significant localization at the basal layers of the epithelium over unformulated PSC-RANTES.

CONCLUSIONS

These results indicate that PSC-RANTES can readily be encapsulated into a PLGA nanoparticle drug delivery system, retain its anti-HIV-1 activity, and deliver PSC-RANTES to the target tissue. This is crucial for the success of this drug candidate as a topical microbicide product.

Vaginal microbicides and the prevention of HIV transmission

Worldwide, nearly half of all individuals living with HIV are now women, who acquire the virus largely by heterosexual exposure. With an HIV vaccine likely to be years away, topical microbicide formulations applied vaginally or rectally are being investigated as another strategy for HIV prevention. A review of preclinical and clinical research on the development of microbicides formulated to prevent vaginal HIV transmission yielded 118 studies: 73 preclinical and 45 clinical. Preclinical research included in-vitro assays and cervical explant models, as well as animal models. Clinical research included phase I and II/IIb safety studies, and phase III efficacy studies. Whereas most phase I and phase II clinical trials have found microbicide compounds to be safe and well tolerated, phase III trials completed to date have not demonstrated efficacy in preventing HIV transmission. Topical microbicides are grouped into five classes of agents, based on where they disrupt the pathway of sexual transmission of HIV. These classes include surfactants/membrane disruptors, vaginal milieu protectors, viral entry inhibitors, reverse transcriptase inhibitors, and a fifth group whose mechanism is unknown. The trajectory of microbicide development has been toward agents that block more specific virus-host cell interactions. Microbicide clinical trials face scientifically and ethically complex issues, such as the choice of placebo gel, the potential for viral resistance, and the inclusion of HIV-infected participants. Assessment of combination agents will most likely advance this field of research.

Significant virus replication in Langerhans cells following application of HIV to abraded skin: relevance to occupational transmission of HIV

The cellular events that occur following occupational percutaneous exposure to HIV have not been defined. In this study, we studied relevant host cellular and molecular targets used for acquisition of HIV infection using split-thickness human skin explants. Blockade of CD4 or CCR5 before R5 HIV application to the epithelial surface of skin explants completely blocked subsequent HIV transmission from skin emigrants to allogeneic T cells, whereas preincubation with C-type lectin receptor inhibitors did not. Immunomagnetic bead depletion studies demonstrated that epithelial Langerhans cells (LC) accounted for >95% of HIV dissemination. When skin explants were exposed to HIV variants engineered to express GFP during productive infection, GFP+ T cells were found adjacent to GFP+ LC. In three distinct dendritic cell (DC) subsets identified among skin emigrants (CD1a+langerin+DC-specific intercellular adhesion molecule grabbing non-integrin (SIGN)- LC, CD1a+langerin-DC-SIGN- dermal DC, and CD1a-langerin-DC-SIGN+ dermal macrophages), HIV infection was detected only in LC. These results suggest that productive HIV infection of LC plays a critical role in virus dissemination from epithelium to cells located within subepithelial tissue. Thus, initiation of antiretroviral drugs soon after percutaneous HIV exposure may not prevent infection of LC, which is likely to occur rapidly, but may prevent or limit subsequent LC-mediated infection of T cells.

Infection of macrophages and dendritic cells with primary R5-tropic human immunodeficiency virus type 1 inhibited by natural polyreactive anti-CCR5 antibodies purified from cervicovaginal secretions

Heterosexual contact is the primary mode of human immunodeficiency virus (HIV) type 1 (HIV-1) transmission worldwide. The chemokine receptor CCR5 is the major coreceptor that is associated with the mucosal transmission of R5-tropic HIV-1 during sexual intercourse. The CCR5 molecule is thus a target for antibody-based therapeutic strategies aimed at blocking HIV-1 entry into cells. We have previously demonstrated that polyreactive natural antibodies (NAbs) from therapeutic preparations of immunoglobulin G and from human breast milk contain NAbs directed against CCR5. Such antibodies inhibit the infection of human macrophages and T lymphocytes by R5-tropic isolates of HIV in vitro. In the present study, we demonstrate that human immunoglobulins from the cervicovaginal secretions of HIV-seronegative or HIV-seropositive women contain NAbs directed against the HIV-1 coreceptor CCR5. Natural affinity-purified anti-CCR5 antibodies bound to CCR5 expressed on macrophages and dendritic cells and further inhibited the infection of macrophages and dendritic cells with primary and laboratory-adapted R5-tropic HIV but not with X4-tropic HIV. Natural anti-CCR5 antibodies moderately inhibited R5-tropic HIV transfer from monocyte-derived dendritic cells to autologous T cells. Our results suggest that mucosal anti-CCR5 antibodies from healthy immunocompetent donors may hamper the penetration of HIV and may be suitable for use in the development of novel passive immunotherapy regimens in specific clinical settings of HIV infection.

C34, a membrane fusion inhibitor, blocks HIV infection of langerhans cells and viral transmission to T cells

Development of topical microbicides that prevent sexual transmission of HIV is an active area of investigation. The purpose of this study was to test the ability of the potent membrane fusion inhibitor C34, an HIV gp41 antagonist, to block HIV infection of human Langerhans cells (LCs) in an epithelial environment that mimics a major route of HIV infection. We incubated freshly isolated epidermal explants containing LCs with various doses of C34 before, during, and after exposing explants to HIV. Although C34 only partially blocked HIV infection of LCs when pre-incubated with skin, it displayed full, dose-dependent inhibition when present during and after viral exposure. The poor protection from HIV infectivity in pre-incubated samples is consistent with mechanism of C34 inhibition and starkly contrasts to the full protection provided by PSC-RANTES, an entry inhibitor that prevents HIV gp120 interaction with its co-receptor CCR5. Real-time PCR confirmed that C34 blocked HIV infection of LCs before reverse transcription and inhibited LC-mediated transfer of virus to T cells. We conclude that C34, if used topically at susceptible mucosal sites, and if continually present, has the potential to block sexual transmission of HIV.

Microbicides: a new frontier in HIV prevention

Microbicides are products that can be applied to vaginal or rectal mucosal surfaces with the goal of preventing, or at least significantly reducing, the transmission of sexually transmitted infections (STIs) including HIV-1. Despite more than two decades of HIV-1 vaccine research, there is still no efficacious HIV-1 vaccine, and the scientific community appears skeptical about the short or long-term feasibility of developing a vaccine that has the ability to induce sterilizing immunity against HIV-1. In this setting, microbicide research has gathered momentum. Currently, 16 candidate microbicides are in clinical development and five products are being evaluated in large-scale Phase 2B/3 effectiveness studies. Initial data from these trials will be available within the next 2-3 years, and it is feasible that there could be one or more licensed microbicides by the end of the decade. The first generation of surfactant microbicides had a non-specific mechanism of action. However, subsequent candidate microbicides have been developed to target specific steps in the process of viral transmission. The purpose of this article is to provide an overview of microbicide development and an update on the candidate pipeline.

N-terminal proteolytic processing by cathepsin G converts RANTES/CCL5 and related analogs into a truncated 4-68 variant

N-terminal proteolytic processing modulates the biological activity and receptor specificity of RANTES/CCL5. Previously, we showed that an unidentified protease associated with monocytes and neutrophils digests RANTES into a variant lacking three N-terminal residues (4-68 RANTES). This variant binds CCR5 but exhibits lower chemotactic and antiviral activities than unprocessed RANTES. In this study, we characterize cathepsin G as the enzyme responsible for this processing. Cell-mediated production of the 4-68 variant was abrogated by Eglin C, a leukocyte elastase and cathepsin G inhibitor, but not by the elastase inhibitor elastatinal. Further, anti-cathepsin G antibodies abrogated RANTES digestion in neutrophil cultures. In accordance, reagent cathepsin G specifically digested recombinant RANTES into the 4-68 variant. AOP-RANTES and Met-RANTES were also converted into the 4-68 variant upon exposure to cathepsin G or neutrophils, while PSC-RANTES was resistant to such cleavage. Similarly, macaque cervicovaginal lavage samples digested Met-RANTES and AOP-RANTES, but not PSC-RANTES, into the 4-68 variant and this processing was also inhibited by anti-cathepsin G antibodies. These findings suggest that cathepsin G mediates a novel pathway for regulating RANTES activity and may be relevant to the role of RANTES and its analogs in preventing HIV infection.

HIV interactions with dendritic cells: has our focus been too narrow?

Although few in number, dendritic cells (DCs) are heterogeneous, ubiquitous, and are crucial for protection against pathogens. In this review, the different DC subpopulations have been described and aspects of DC biology are discussed. DCs are important, not only in the pathogenesis of HIV, but also in the generation of anti-HIV immune responses. This review describes the roles that DC are thought to play in HIV pathogenesis, including uptake and transport of virus. We have also discussed the effects that the virus exerts on DCs such as infection and dysfunction. Then we proceed to focus on DC subsets in different organs and show how widespread the effects of HIV are on DC populations. It is clear that the small number of studies on tissue-derived DCs limits current research into the pathogenesis of HIV.

TLR activation of Langerhans cell-like dendritic cells triggers an antiviral immune response

Langerhans cells (LC) are a unique subset of dendritic cells (DC), present in the epidermis and serving as the first line of defense against pathogens invading the skin. To investigate the role of human LCs in innate immune responses, we examined TLR expression and function of LC-like DCs derived from CD34+ progenitor cells and compared them to DCs derived from peripheral blood monocytes (monocyte-derived DC; Mo-DC). LC-like DCs and Mo-DCs expressed TLR1-10 mRNAs at comparable levels. Although many of the TLR-induced cytokine patterns were similar between the two cell types, stimulation with the TLR3 agonist poly(I:C) triggered significantly higher amounts of the IFN-inducible chemokines CXCL9 (monokine induced by IFN-gamma) and CXCL11 (IFN-gamma-inducible T cell alpha chemoattractant) in LC-like DCs as compared with Mo-DCs. Supernatants from TLR3-activated LC-like DCs reduced intracellular replication of vesicular stomatitis virus in a type I IFN-dependent manner. Finally, CXCL9 colocalized with LCs in skin biopsy specimens from viral infections. Together, our data suggest that LCs exhibit a direct antiviral activity that is dependent on type I IFN as part of the innate immune system.

Peptide, Peptidomimetic and Small-molecule Drug Discovery Targeting HIV-1 Host-cell Attachment and Entry through gp120, gp41, CCR5 and CXCR4+

This review highlights selected examples of peptide, peptidomimetic and small-molecule drug discovery targeting HIV-1 to advance novel anti-HIV pharmaceuticals that inhibit initial stages of the viral cycle; namely, attachment and entry. Some of these approaches have culminated in the development of peptide-based drugs, while other have exploited peptides as enabling tools toward the identification of small-molecule lead compounds. Both of these conceptually different approaches have facilitated lead optimization of molecules with complementary and often surprising anti-HIV pharmacological properties, supporting their role in pharmaceutical development. Furthermore, such molecules enabled mechanistic elucidation of viral attachment and entry and provided additional insights toward achieving the desired drug profile.

Inhibition of human immunodeficiency virus-1 (HIV-1) by beta-chemokine analogues in mononuclear cells from HIV-1-infected patients with active tuberculosis

Tuberculosis (TB) enhances human immunodeficiency virus-1 (HIV-1) activity in patients with dual HIV-1/TB infection. Therapies that control augmentations of HIV-1 activity at sites of Mycobacterium tuberculosis (MTB) infection may be useful in inhibition of viral expansion. Regulated upon activation, normal T-cell expressed and secreted (RANTES) analogues (AOP and NNY) are potent in inhibiting the entry of primary HIV-1 isolates into host mononuclear cells. These analogues were used to inhibit MTB-induced HIV-1 entry in blood monunuclear cells (PBMC) from patients with pulmonary TB, and pleural fluid mononuclear cells (PFMC) from patients with pleural TB. PBMC or PFMC were cultured with and without MTB in presence and absence of RANTES analogues. HIV-1 strong stop DNA was assessed by real-time polymerase chain reaction (PCR) as a measure of infection. CCR5 mRNA was assessed by real-time reverse transcription (RT)-PCR and by immunostaining and FACS analysis. HIV-1 infection was induced by MTB in vitro in PBMC from the majority (14 of 20) of HIV-1/TB subjects, and new infection was inhibited by AOP- or NNY-RANTES. HIV-1 infection was also inhibited by these reagents in MTB-induced PFMC from three of three patients with pleural TB. Expression of CCR5 mRNA was significantly induced by MTB in PBMC from patients with pulmonary TB. Further, expression of CCR5 was higher in PFMC compared to PBMC from patients with pleural TB. Also, CCR5 was fourfold higher on CD14(+) pleural mononuclear cells than on CD4(+) lymphocytes. Blocking new HIV-1 infection of mononuclear cells may be useful in control of HIV-1 during dual HIV-1/TB infection.

The role of Langerhans cells in the sexual transmission of HIV

Sexual transmission of HIV is the most common mode of infection in the global HIV epidemic. In the absence of an effective vaccine, there is an urgent need for additional strategies to prevent new HIV infections. An emerging body of evidence now indicates that Langerhans cells (LC) are initial cellular targets in the sexual transmission of HIV, and CD4- and CCR5-mediated infection of LC plays a crucial role in virus dissemination. However, interactions between HIV and LC are complex. For example, it is evident that HIV can interact concomitantly with non-LC dendritic cells in two separate and distinct ways: a CD4- and CCR5-dependent infection pathway and a CD4- and CCR5-independent capture pathway mediated by DC-SIGN, a C-type lectin molecule. Thus, there may be multiple ways by which HIV interacts with target cells in the genital mucosa. This review focuses on the recent advances regarding the cellular events that may occur during heterosexual transmission of HIV.

Differential susceptibility to human immunodeficiency virus type 1 infection of myeloid and plasmacytoid dendritic cells

Human immunodeficiency virus type 1 (HIV-1) infection of dendritic cells (DCs) plays an important role in HIV-1 transmission and pathogenesis. Here, we studied the susceptibility of ex vivo-isolated CD11c+ myeloid DCs (MDCs) and CD123+ plasmacytoid DCs (PDCs) to HIV-1 infection and the function of these cells early after infection. Both DC subsets were susceptible to CCR5- and CXCR4-using HIV-1 isolates (BaL and IIIB, respectively). However, MDCs were more susceptible to HIV-1(BaL) infection than donor-matched PDCs. In addition, HIV-1(BaL) infected MDCs more efficiently than HIV-1(IIIB), whereas PDCs were equally susceptible to both isolates. While exposure to HIV-1 alone resulted in only weak maturation of DCs, Toll-like receptor 7/8 ligation induced full maturation in both infected and uninfected DCs. Maturation did not increase HIV-1 replication in infected DCs, and infected DCs retained their ability to produce tumor necrosis factor alpha after stimulation. Both HIV-1 isolates induced alpha interferon production exclusively in PDCs, irrespective of productive infection. In conclusion, PDCs and MDCs were susceptible to HIV-1 infection, but neither displayed functional defects as a consequence of infection. The difference in susceptibility of PDCs and MDCs to HIV-1 may have implications for HIV-1 transmission and DC-mediated transfer of HIV-1 to T cells.

Generation and properties of a human immunodeficiency virus type 1 isolate resistant to the small molecule CCR5 inhibitor, SCH-417690 (SCH-D)

We describe the generation of two genetically related human immunodeficiency virus type 1 (HIV-1) isolates highly (>20,000-fold) resistant to the small molecule CCR5 inhibitor, SCH-417690 (formerly SCH-D). Both viruses were cross-resistant to other small molecules targeting entry via CCR5, but they were inhibited by some MAbs against the same coreceptor on primary CD4+ T-cells. The resistant isolates remained sensitive to inhibitors of other stages of virus entry, and to replication inhibitors acting post-entry. Neither escape mutant could replicate detectably in peripheral blood mononuclear cells (PBMC) from two donors homozygous for the CCR5-Delta32 allele and both were insensitive to the CXCR4-specific inhibitor, AMD3100. Hence, the SCH-D escape mutants retained the R5 phenotype. One of the resistant isolates was, however, capable of replication in U87.CD4.CXCR4 cells and, after expansion in those cells, was sensitive to AMD3100 in primary CD4+ T-cells. Hence, some X4 variants may be present in this escape mutant swarm. A notable observation was that the SCH-D escape mutants were also cross-resistant to PSC-RANTES and AOP-RANTES, chemokine derivatives that are reported to down-regulate cell surface CCR5 almost completely. However, the extent to which CCR5 is down-regulated was dependent upon the detection MAb. Hence, the escape mutants may be using a CCR5 configuration that is only detected by some anti-CCR5 MAbs. Finally, two SCH-D-resistant clonal viruses revealed no amino acid changes in the gp120 V3 region relative to the parental viruses, in marked contrast to clones resistant to the AD101 small molecule CCR5 inhibitor that possess 4 such sequence changes. Several sequence changes elsewhere in gp120 (V2, C3 and V4) were present in the SCH-D-resistant clones. Their influence on the resistant phenotype remains to be determined.

Medicinal chemistry applied to a synthetic protein: development of highly potent HIV entry inhibitors

We have used total chemical synthesis to perform high-resolution dissection of the pharmacophore of a potent anti-HIV protein, the aminooxypentane oxime of [glyoxylyl1]RANTES(2-68), known as AOP-RANTES, of which we designed and made 37 analogs. All involved incorporation of one or more rationally chosen nonnatural noncoded structures, for which we found a clear comparative advantage over coded ones. We investigated structure-activity relationships in the pharmacophore by screening the analogs for their ability to block the HIV entry process and produced a derivative, PSC-RANTES [N-nonanoyl, des-Ser1[L-thioproline2, L-cyclohexylglycine3]-RANTES(2-68)], which is 50 times more potent than AOP-RANTES. This promising group of compounds might be optimized yet further as potential prophylactic and therapeutic anti-HIV agents. The remarkable potency of our RANTES analogs probably involves the unusual mechanism of intracellular sequestration of CC-chemokine receptor 5 (CCR5), and it has been suggested that this arises from enhanced affinity for the receptor. We found that inhibitory potency and capacity to induce CCR5 down-modulation do appear to be correlated, but that unexpectedly, inhibitory potency and affinity for CCR5 do not. We believe this study represents the proof of principle for the use of a medicinal chemistry approach, above all one showing the advantage of noncoded structures, to the optimization of the pharmacological properties of a protein. Medicinal chemistry of small molecules is the foundation of modern pharmaceutical practice, and we believe we have shown that techniques have now reached the point at which the approach could also be applied to the many macromolecular drugs now in common use.