Migration of foreign lymphocytes from the mouse vagina into the cervicovaginal mucosa and to the iliac lymph nodes

Flt3-L enhances trans-epithelial migration and antigen presentation of dendritic cells adoptively transferred to genital mucosa

Dendritic cells (DCs) play a critical role in shaping adaptive immunity. Systemic transfer of DCs by intravenous injection has been widely investigated to inform the development of immunogenic DCs for use as cellular therapies. Adoptive transfer of DCs to mucosal sites has been limited but serves as a valuable tool to understand the role of the microenvironment on mucosal DC activation, maturation and antigen presentation. Here, we show that chitosan facilitates transmigration of DCs across the vaginal epithelium in the mouse female reproductive tract (FRT). In addition, ex vivo programming of DCs with fms-related tyrosine kinase 3 ligand (Flt3-L) was found to enhance translocation of intravaginally administered DCs to draining lymph nodes (dLNs) and stimulate in vivo proliferation of both antigen-specific CD4+ and CD8+ T cells (cross-presentation). Mucosal priming with chitosan and DC programming may hold great promise to enhance efficacy of DC-based vaccination to the female genital mucosa.

Cell-to-Cell Spread of HIV and Viral Pathogenesis

Human immunodeficiency virus type 1 (HIV-1) gives rise to a chronic infection that progressively depletes CD4(+) T lymphocytes. CD4(+) T lymphocytes play a central coordinating role in adaptive cellular and humoral immune responses, and to do so they migrate and interact within lymphoid compartments and at effector sites to mount immune responses. While cell-free virus serves as an excellent prognostic indicator for patient survival, interactions of infected T cells or virus-scavenging immune cells with uninfected T cells can greatly enhance viral spread. HIV can induce interactions between infected and uninfected T cells that are triggered by cell surface expression of viral Env, which serves as a cell adhesion molecule that interacts with CD4 on the target cell, before it acts as the viral membrane fusion protein. These interactions are called virological synapses and promote replication in the face of selective pressure of humoral immune responses and antiretroviral therapy. Other infection-enhancing cell-cell interactions occur between virus-concentrating antigen-presenting cells and recipient T cells, called infectious synapses. The exact roles that these cell-cell interactions play in each stage of infection, from viral acquisition, systemic dissemination, to chronic persistence are still being determined. Infection-promoting immune cell interactions are likely to contribute to viral persistence and enhance the ability of HIV-1 to evade adaptive immune responses.

Cell-to-cell transfer of HIV infection: implications for HIV viral persistence

A major research priority for HIV eradication is the elucidation of the events involved in HIV reservoir establishment and persistence. Cell-to-cell transmission of HIV represents an important area of study as it allows for the infection of cell types which are not easily infected by HIV, leading to the establishment of long-lived viral reservoirs. This phenomenon enables HIV to escape elimination by the immune system. This process may also enable HIV to escape suppressive effects of anti-retroviral drugs. During cell-to-cell transmission of HIV, a dynamic series of events ensues at the virological synapse that promotes viral dissemination. Cell-to-cell transmission involves various types of cells of the immune system and this mode of transmission has been shown to have an important role in sexual and mother-to-child transmission of HIV and spread of HIV within the central nervous system and gut-associated lymphoid tissues. There is also evidence that cell-to-cell transmission of HIV occurs between thymocytes and renal tubular cells. Herein, following a brief review of the processes involved at the virological synapse, evidence supporting the role for cell-to-cell transmission of HIV in the maintenance of the HIV reservoir will be highlighted. Therapeutic considerations and future directions for this area of research will also be discussed.

Recent progress in HIV vaccines inducing mucosal immune responses

In spite of several attempts over many years at developing a HIV vaccine based on classical strategies, none has convincingly succeeded to date. As HIV is transmitted primarily by the mucosal route, particularly through sexual intercourse, understanding antiviral immunity at mucosal sites is of major importance. An ideal vaccine should elicit HIV-specific antibodies and mucosal CD8⁺ cytotoxic T-lymphocyte (CTL) as a first line of defense at a very early stage of HIV infection, before the virus can disseminate into the secondary lymphoid organs in mucosal and systemic tissues. A primary focus of HIV preventive vaccine research is therefore the induction of protective immune responses in these crucial early stages of HIV infection. Numerous approaches are being studied in the field, including building upon the recent RV144 clinical trial. In this article, we will review current strategies and briefly discuss the use of adjuvants in designing HIV vaccines that induce mucosal immune responses.

HIV-1 vaginal transmission: cell-free or cell-associated virus?

The vast majority of new HIV infections in male-to-female transmission occurs through semen, where HIV-1 is present in two different forms: as free and as cell-associated virus. In the female lower genital tract, semen mixes with female genital secretions that contain various factors, some of which facilitate or inhibit HIV-1 transmission. Next, HIV-1 crosses the genital epithelia, reaches the regional lymph nodes, and disseminates through the female host. Cervico-vaginal mucosa contains multiple barriers, resulting in a low probability of vaginal transmission. However, in some cases, HIV-1 is able to break these barriers. Although the exact mechanisms of how these barriers function remain unclear, their levels of efficiency against cell-free and cell-associated HIV-1 are different, and both cell-free and cell-associated virions seem to use different strategies to overcome these barriers. Understanding the basic mechanisms of HIV-1 vaginal transmission is required for the development of new antiviral strategies to contain HIV-1 epidemics.

Efficiency of cell-free and cell-associated virus in mucosal transmission of human immunodeficiency virus type 1 and simian immunodeficiency virus

Effective strategies are needed to block mucosal transmission of human immunodeficiency virus type 1 (HIV-1). Here, we address a crucial question in HIV-1 pathogenesis: whether infected donor mononuclear cells or cell-free virus plays the more important role in initiating mucosal infection by HIV-1. This distinction is critical, as effective strategies for blocking cell-free and cell-associated virus transmission may be different. We describe a novel ex vivo model system that utilizes sealed human colonic mucosa explants and demonstrate in both the ex vivo model and in vivo using the rectal challenge model in rhesus monkeys that HIV-1-infected lymphocytes can transmit infection across the mucosa more efficiently than cell-free virus. These findings may have significant implications for our understanding of the pathogenesis of mucosal transmission of HIV-1 and for the development of strategies to prevent HIV-1 transmission.

M48U1 CD4 mimetic has a sustained inhibitory effect on cell-associated HIV-1 by attenuating virion infectivity through gp120 shedding

BACKGROUND

HIV-1 infected cells can establish new infections by crossing the vaginal epithelia and subsequently producing virus in a milieu that avoids the high microbicide concentrations of the vaginal lumen.

FINDINGS

To address this problem, here, we report that pretreatment of HIV-infected peripheral blood mononuclear cells (PBMCs) with a 27 amino acid CD4-mimetic, M48U1, causes dramatic and prolonged reduction of infectious virus output, due to its induction of gp120 shedding.

CONCLUSIONS

M48U1 may, therefore, be valuable for prophylaxis of mucosal HIV-1 transmission.

Nanoparticle transport from mouse vagina to adjacent lymph nodes

To test the feasibility of localized intravaginal therapy directed to neighboring lymph nodes, the transport of quantum dots across the vaginal wall was investigated. Quantum dots instilled into the mouse vagina were transported across the vaginal mucosa into draining lymph nodes, but not into distant nodes. Most of the particles were transported to the lumbar nodes; far fewer were transported to the inguinal nodes. A low level of transport was evident at 4 hr after intravaginal instillation, and transport peaked at about 36 hr after instillation. Transport was greatly enhanced by prior vaginal instillation of Nonoxynol-9. Hundreds of micrograms of nanoparticles/kg tissue (ppb) were found in the lumbar lymph nodes at 36 hr post-instillation. Our results imply that targeted transport of microbicides or immunogens from the vagina to local lymph organs is feasible. They also offer an in vivo model for assessing the toxicity of compounds intended for intravaginal use.

Selective transmigration of monocyte-associated HIV-1 across a human cervical monolayer and its modulation by seminal plasma

OBJECTIVE

To analyse the transmigration of immune cells infected by HIV-1 across the epithelial monolayer using the endometrial human endometrial carcinoma (HEC)-1A cell line and to study the influence of seminal plasma in this process.

DESIGN

After sexual intercourse involving a male partner infected by HIV-1, a selection process has been shown to lead to a predominant transmission of the R5 phenotype despite the presence of X4 and R5 strains in semen. Transmigration of HIV-infected monocytes present in semen may represent a pertinent mechanism that could explain this tropism selection.

METHODS

Epithelial monolayer crossing was studied by using HEC-1A epithelial cells cultured on permeable support and monocyte-enriched or lymphocyte-enriched populations of cells infected or not by HIV R5 or X4 strains. Transmigrating cells were quantified and analysed for their ability to transmit HIV infection to immune target cells. The effect of HIV-negative seminal plasma on cell transmigration was analysed.

RESULTS

A preferential passage of the R5 strain associated with monocyte-enriched populations was observed together with the ability of this strain to transmit infection. Seminal plasma was found able to decrease the epithelial crossing of immune cells by enhancing transepithelial resistance and by increasing the adherence of immune cells to the monolayer.

CONCLUSION

The preferential transmigration of HIV R5 strains associated with monocytes across the endocervical monolayer may explain the predominant transmission of the R5 strains after sexual intercourse. By its capacity to modulate the tightness of the epithelial structure, seminal plasma reinforces this selection process.

In vivo evaluation of the release of zidovudine and polystyrene sulfonate from a dual intravaginal bioadhesive polymeric device in the pig model

This study focused on determining the concentration of zidovudine (AZT) and polystyrene sulfonate (PSS) in the plasma and vaginal tissue of the large white pig from an intravaginal bioadhesive polymeric device (IBPD). Biocompatible polymers were compressed with AZT and PSS into caplet-shaped devices for insertion into the posterior fornix of the pig vagina. A total of 25 pigs were used in this study. Plasma was sampled from the jugular vein at various time points after insertion of the IBPD reaching 28 days. At day 28, the pigs were euthanized and vaginal tissue was removed and digested with subtilisin for AZT and PSS extraction. The mean concentration detected in vaginal tissue at day 28 was 1.214 ± 0.062 mg/mL for AZT and 1.400 ± 0.071 mg/mL for PSS. Plasma concentration was significantly lower for AZT (0.332 ± 0.014 mg/mL) and PSS (0.256 ± 0.013 mg/mL). This indicated higher retention of AZT and PSS within the vaginal tissue. Molecular mechanics simulations blueprinted polymer-drug-mucin force-field interactions and energies that explicated the spatial preference of AZT and PSS for the vaginal tissue. Histopathotoxicity studies revealed negative-to-mild foreign body events and results strongly suggest that the IBPD may be suitable for prolonged intravaginal drug delivery in preventing the transmission of sexually transmitted infections and HIV/AIDS.

Development of topical microbicides to prevent the sexual transmission of HIV

Women comprise almost 50% of the population of people living with HIV and the majority of these women contracted the virus through sexual transmission in monogamous relationships in the developing world. In these environments, where women are not empowered to protect themselves through the negotiation of condom use, effective means of preventing HIV transmission are urgently needed. In the absence of an approved and effective vaccine, microbicides have become the strategy of choice to provide women with the ability to prevent HIV transmission from their infected partners. Topical microbicides are agents specifically developed and formulated for use in either the vaginal or rectal environment that prevent infection by sexually transmitted infectious organisms, including pathogenic viruses, bacteria and fungi. Although a microbicidal product will have many of the same properties as other anti-infective agents and would be similarly developed through human clinical trials, microbicide development bears its own challenges related to formulation and delivery and the unique environment in which the product must act, as well as the requirement to develop a product that is acceptable to the user. Herein, perspectives based on preclinical and clinical microbicide development experience, which have led to an evolving microbicide development algorithm, will be discussed. This article forms part of a special issue of Antiviral Research marking the 25th anniversary of anti-retroviral drug discovery and development, Vol 85, issue 1, 2010.

HIV infection of the genital mucosa in women

The vast majority of new HIV infections are acquired via the genital and rectal mucosa. Here, we provide an overview of our current knowledge of how HIV establishes local infection, with an emphasis on viral invasion through the female genital tract. Studies using human explant tissues and in vivo animal studies have improved our understanding of the cellular and molecular pathways of infection; this information could be harnessed to design effective HIV vaccines and microbicides.

Early events in HIV transmission through a human reconstructed vaginal mucosa

OBJECTIVE

The early steps of HIV entry into intact vaginal mucosa still need to be clarified. Here we investigated how HIV translocated across the vaginal pluristratified epithelium, either by transcytosis or by uptake in Langerhans cells.

METHODS

Using human primary fibroblasts and vaginal epithelial cells, we developed an in-vitro model of vaginal mucosa in which Langerhans cells could also be integrated. Owing to the absence of T lymphocytes and macrophages, we specifically studied the role of Langerhans cells in HIV transmission and the transcytosis of cell-associated HIV.

RESULTS

Our model has a normal mucosal tissue architecture and Langerhans cells were efficiently integrated within the pluristratified epithelium. In addition, tight junction proteins' expression, high transepithelium resistance and low fluorescein isothiocyanate-BSA passage confirmed the integrity and impermeability of the reconstruction. Furthermore, we showed that human Langerhans cells also expressed tight junction proteins. Then, we demonstrated that neither transcellular nor intercellular transport of free infectious virus released by R5-infected or X4-infected peripheral blood mononuclear cells inoculated apically occured in the vaginal mucosa, irrespective to the presence of Langerhans cells.

CONCLUSION

For the first time, we documented that, within 4 h following contact with HIV-infected cells, translocation of free HIV particles across a pluristratified mucosa is not detectable and that, in this context, it seemed that Langerhans cells do not increase HIV transmission. Moreover, we provided a useful model for the development of strategies preventing HIV entry into the female genital tract, especially for testing the efficiency of various microbicides.

Setting the stage: host invasion by HIV

For more than two decades, HIV has infected millions of people worldwide each year through mucosal transmission. Our knowledge of how HIV secures a foothold at both the molecular and cellular levels has been expanded by recent investigations that have applied new technologies and used improved techniques to isolate ex vivo human tissue and generate in vitro cellular models, as well as more relevant in vivo animal challenge systems. Here, we review the current concepts of the immediate events that follow viral exposure at genital mucosal sites where most documented transmissions occur. Furthermore, we discuss the gaps in our knowledge that are relevant to future studies, which will shape strategies for effective HIV prevention.

Carrageenan/MIV-150 (PC-815), a combination microbicide

OBJECTIVE

The objective of this article is to study the effect of PC-815, a novel combination microbicide containing carrageenan and the nonnucleoside reverse transcriptase inhibitor (NNRTI) MIV-150, in blocking HIV-1 and HIV-2 infections in vitro as compared with Carraguard alone.

GOAL

The goal of this study was to develop a combination microbicide that is more efficacious than Carraguard against HIV-1 and HIV-2.

STUDY DESIGN

The microtiter syncytial assay was used to evaluate: 1) the antiviral and virucidal activity of MIV-150 against HIV-1MN; 2) the additive effect of MIV-150 when combined with carrageenan; and 3) a possible interference of seminal fluid in the antiviral activity of these compounds.

RESULTS

MIV-150 effectively inactivated free virus. Combination of MIV-150 and Carraguard demonstrated an additive antiviral effect. Seminal fluid had no effect on the antiviral activity of MIV-150 or Carraguard. The average concentration that blocks 50% of infection (EC50) for PC-815 was approximately 10 times stronger than Carraguard for the different clinical isolates used in the study.

CONCLUSION

Theoretically, PC-815 is likely to be a more efficacious microbicide than Carraguard.

Paternal Antigen-Bearing Cells Transferred during Insemination Do Not Stimulate Anti-Paternal CD8+T Cells: Role of Estradiol in Locally Inhibiting CD8+T Cell Responses

Maternal immunological tolerance of the semiallogeneic fetus involves several overlapping mechanisms to balance maternal immunity and fetal development. Anti-paternal CD8+ T cells are suppressed during pregnancy in some but not all mouse models. Since semen has been shown to mediate immune modulation, we tested whether exposure to paternal Ag during insemination activated or tolerized anti-paternal CD8+ T cells. The uterine lumen of mated female mice contained male MHC I+ cells that stimulated effector, but not naive, CD8+ T cells ex vivo. Maternal MHC class I+ myeloid cells fluxed into the uterine lumen in response to mating and cross-presented male H-Y Ag to effector, but not naive, CD8+ T cells ex vivo. However, neither unprimed nor previously primed TCR-transgenic CD8+ T cells specific for either paternal MHC I or H-Y Ag proliferated in vivo after mating. These T cells subsequently responded normally to i.p. challenge, implicating ignorance rather than anergy as the main reason for the lack of response. CD8+ T cells responded to either peptide Ag or male cells delivered intravaginally in ovariectomized mice, but this response was inhibited by systemic estradiol (inducing an estrus-like state). Subcutaneous Ag induced responses in both cases. Allogeneic dendritic cells did not induce responses intravaginally even in ovariectomized mice in the absence of estradiol. These results suggest that inhibition of antiallogeneic responses is restricted both locally to the reproductive tract and temporally to the estrous phase of the menstrual cycle, potentially decreasing the risk of maternal immunization against paternal Ags during insemination.

Low pH immobilizes and kills human leukocytes and prevents transmission of cell-associated HIV in a mouse model

Background

Both cell-associated and cell-free HIV virions are present in semen and cervical secretions of HIV-infected individuals. Thus, topical microbicides may need to inactivate both cell-associated and cell-free HIV to prevent sexual transmission of HIV/AIDS. To determine if the mild acidity of the healthy vagina and acid buffering microbicides would prevent transmission by HIV-infected leukocytes, we measured the effect of pH on leukocyte motility, viability and intracellular pH and tested the ability of an acidic buffering microbicide (BufferGel^®) to prevent the transmission of cell-associated HIV in a HuPBL-SCID mouse model.

Methods

Human lymphocyte, monocyte, and macrophage motilities were measured as a function of time and pH using various acidifying agents. Lymphocyte and macrophage motilities were measured using video microscopy. Monocyte motility was measured using video microscopy and chemotactic chambers. Peripheral blood mononuclear cell (PBMC) viability and intracellular pH were determined as a function of time and pH using fluorescent dyes. HuPBL-SCID mice were pretreated with BufferGel, saline, or a control gel and challenged with HIV-1-infected human PBMCs.

Results

Progressive motility was completely abolished in all cell types between pH 5.5 and 6.0. Concomitantly, at and below pH 5.5, the intracellular pH of PBMCs dropped precipitously to match the extracellular medium and did not recover. After acidification with hydrochloric acid to pH 4.5 for 60 min, although completely immotile, 58% of PBMCs excluded ethidium homodimer-1 (dead-cell dye). In contrast, when acidified to this pH with BufferGel, a microbicide designed to maintain vaginal acidity in the presence of semen, only 4% excluded dye at 10 min and none excluded dye after 30 min. BufferGel significantly reduced transmission of HIV-1 in HuPBL-SCID mice (1 of 12 infected) compared to saline (12 of 12 infected) and a control gel (5 of 7 infected).

Conclusion

These results suggest that physiologic or microbicide-induced acid immobilization and killing of infected white blood cells may be effective in preventing sexual transmission of cell-associated HIV.

A PNA-transportan conjugate targeted to the TAR region of the HIV-1 genome exhibits both antiviral and virucidal properties

We have earlier reported that anti-TAR PNA conjugated with the membrane-transducing peptide transportan inhibits transactivation of the HIV-1 LTR resulting in decreased production of HIV-1 virions by chronically infected H9 cells (N., Kaushik, A., Basu, P., Palumbo, R.L., Myers, V.N., Pandey, 2002. Anti-TAR polyamide nucleotide analog conjugated with a membrane permeating peptide inhibits HIV-1 production. J. Virol. 76, 3881-3891). In this study, we have found that the PNA(TAR)-transportan conjugate is efficiently internalized by cells and kinetics analysis reveals a sigmoidal curve with a cooperativity index of 6, indicating very rapid cellular uptake. Additionally, analysis of uptake at varying temperatures or in the presence of phenylarsine oxide revealed that the mechanism of uptake is neither receptor-dependent nor occurs via endocytosis. We also found that the PNA(TAR)-transportan conjugate exhibits potent virucidal activity as HIV-1 virions pretreated with the conjugate were rendered noninfectious, suggesting that the conjugate may also permeate the virus envelope. The anti-HIV-1 virucidal activity of the conjugate may be useful either in topical formulations designed to block HIV-1 infection or as a prophylactic agent for inactivation of HIV-1 in the circulating plasma prior to attachment and entry.

The effect of synthetic polymers on the migration of monocytes through human cervical mucus

The integrity of the vaginal mucosa is critical to protecting women from infection, particularly sexually transmitted diseases. For example, breakdown of the mucosa, including the cell lining and/or mucus layer, due to vaginal infections has been shown to increase the risk of HIV infection. There is considerable interest in the development of new topical microbicides for women; many of these topical agents contain polymers. One potential mechanism for altering the barrier properties of a three-dimensional fibrous gel, such as cervical mucus, to cell penetration is to alter the fiber structure. In previous studies, we have shown that addition of synthetic polymers, such as polyvinyl pyridine (PVP) and polyethylene glycol (PEG), modify the fiber structure and mechanical properties of human cervical mucus. Here we investigated the ability of peripheral blood monocytes to migrate through structurally altered mucus gels. Adding PVP to mucus increased both the average fiber spacing and the rate of random migration of monocytes; addition of PEG to mucus also caused an increased random migration rate, although changes in overall fiber spacing were not obvious. In both cases, the addition of small amounts of polymer to cervical mucus decreased the barrier property of mucus with respect to cell migration. This result raises questions about the safety of polymeric agents as ingredients in topical microbicides.

Carrageenan formulation prevents macrophage trafficking from vagina: implications for microbicide development

Considerable evidence suggests that human immunodeficiency virus (HIV)-infected macrophages and/or lymphocytes may mediate sexual transmission of HIV. We and others have previously demonstrated that when vitally stained donor mouse lymphocytes or macrophages are placed in the vaginas of mice, some of the stained cells can later be found in the iliac lymph nodes. The aim of this study was to assess the extent of mononuclear cell trafficking from the vagina and to test the possibility that carrageenan formulation, a sulfated polysaccharide formulation containing 3% PDR98-15 carrageenan (PC-515; FMC Biopolymer, Rockland, ME), a vaginal microbicide, would prevent vaginal transmigration of macrophages. When supravitally stained mouse macrophages and T cells were inoculated into the vagina of recipient mice, discrete numbers of donor cells migrated to the recipient iliac and inguinal lymph nodes and spleen. When recipient mice were preinoculated with the carrageenan formulation, the number of macrophages in lymph nodes and spleen was reduced by >90%. In contrast, a methylcellulose formulation, which is believed to be inactive, did not significantly reduce migration to the lymphoid organs. Our findings suggest that the carrageenan formulation blocks cell trafficking of macrophages from vagina and that blocking does not result from cytotoxicity. Blocking cell trafficking may help to prevent sexual transmission of HIV.

Target cells in vaginal HIV transmission

Understanding the mechanisms of HIV transmission to women will be crucial to the development of effective strategies to curb this epidemic. Current data suggest that HIV has at least two routes to penetrate the vaginal epithelium and reach lymphoid tissues, trans-epithelial migration of infected Langerhans cells or virus penetration into the lamina propria through loss of epithelial integrity resulting in direct infection of lymphocytes, dendritic cells and macrophages.

Considerations and development of topical microbicides to inhibit the sexual transmission of HIV

The increased incidence of HIV/AIDS disease in women aged 15 - 49 years has identified the urgent need for a female-controlled, efficacious and safe vaginal topical microbicide. To meet this challenge, new topical microbicide candidates consisting of molecules or formulations that modify the genital environment (BufferGel, engineered Lactobacillus, over-the-counter lubricants), surfactants (C31D/Savvy, sodium dodecyl sulfate, sodium lauryl sulfate), polyanionic polymers (PRO 2000, beta-cyclodextrin, Carraguard, CAP, D2S, SPL-7013), proteins (cyanovirin-N, monoclonal antibodies, thromspondin-1 peptides, Pokeweed antiviral protein and others), reverse transcription inhibitors (PMPA [Tenofovir ]), UC-781, SJ-3366, DABO and thiourea) and other molecules (NCp7-specific virucides, chemokine receptor agonists/antagonists, WHI-05 and WHI-07) are currently being investigated for activity, safety and efficacy. This review will assess the development of these molecules in the context of cervicovaginal defences and the clinical failure of nonoxynol-9.

The Development of Microbicides for Clinical Use to Prevent Sexually Transmitted Diseases

Approximately 60 vaginal microbicides are under development for the prevention of HIV/AIDS and other sexually transmitted pathogens. The history and current status of the field are discussed with emphasis on the lessons learned from recent clinical trials, along with an emphasis on the mechanisms involved in the sexual transmission of HIV and how this information influences microbicide development. Additionally, the current status of in vitro and animal systems used for evaluating microbicide efficacy, as well as the challenges involved in developing more appropriate and practical assays, are discussed. Also discussed are the challenges that face the microbicide product development field in meeting US Food and Drug Administration requirements regarding product safety and stability.

Vaginal transmission of cell-associated HIV-1 in the mouse is blocked by a topical, membrane-modifying agent

Because both HIV-1 virions and HIV-infected cells are present in the semen and cervical mucus of infected individuals, HIV-1 prevention strategies must consider both cell-free and cell-associated virus. Antibodies that target HIV-1 virions have been shown to prevent vaginal transmission of cell-free virus in macaques, but since cell-associated transmission has not been reliably demonstrated in this model system, no strategies to prevent such transmission have been tested. We have employed a mouse model in which SCID mice carry human peripheral blood leukocytes (HuPBLs). In these mice, vaginal transmission of cell-associated, but not cell-free, HIV-1 transmission occurs, mediated by transepithelial migration of HIV-infected cells. Topical application of beta-cyclodextrin (beta-CD), a cholesterol-sequestering agent that interferes with cell migration and budding of virus from lipid rafts, blocks transmission of cell-associated HIV-1. The HuPBL-SCID model of vaginal HIV-1 transmission should prove useful for investigating cell-associated HIV-1 transmucosal HIV-1 transmission, as well as for screening reagents for their potential efficacy in preventing sexual HIV-1 transmission.

Vaginal transmission of HIV-1 in hu-SCID mice: a new model for the evaluation of vaginal microbicides

OBJECTIVE

To develop an animal model of vaginal transmission of HIV-1 for the evaluation of vaginal microbicides.

DESIGN

Vaginal infection was performed in SCID mice reconstituted with 4 x 107 human peripheral blood lymphocytes (hu-PBL) by non-invasive vaginal administration. The hu-PBL were previously infected in vitro with a non-syncytium (NSI) strain of HIV-1 (SF162) (hu-PBL-SCID). Lymphocyte migration in vivo was examined using fluorescently labelled human lymphocytes.

METHODS

The percentage of CD4 T cells, plasma viral load and p24 antigen were evaluated using fluorescent activated cell sorting (FACS), the Amplicor HIV-1 monitor kit and enzyme-linked immunosorbent assay, respectively. Polymerase chain reaction (PCR) analysis was performed on DNA extracted from spleen and lymph nodes. For in vivo migration of labelled lymphocytes, the mice were sacrificed after 4, 24 and 48 h; vaginae and local lymph nodes were removed, snap frozen with OCT, sectioned and examined by fluorescent microscopy and FACS.

RESULTS

HIV transmission was established using virus-infected cells inoculated vaginally, as shown by FACS, HIV viral load, p24 and PCR results. Labelled cells were easily located within the vaginal tissues after 4 h. However, few or no cells could be identified after 24 or 48 h at the vaginal level, whereas labelled cells could be detected at the level of regional lymph nodes.

CONCLUSIONS

Because of its simplicity and practical features compared with other animal models, the vaginal HIV-infected hu-SCID mouse model may prove useful to test the activity of compounds against cell-associated HIV and, possibly, other sexually transmitted diseases.

Parameters of human immunodeficiency virus infection of human cervical tissue and inhibition by vaginal virucides

Heterosexual transmission of human immunodeficiency virus (HIV) is the most frequent mode of infection worldwide. However, the immediate events between exposure to infectious virus and establishment of infection are still poorly understood. This study investigates parameters of HIV infection of human female genital tissue in vitro using an explant culture model. In particular, we investigated the role of the epithelium and virucidal agents in protection against HIV infection. We have demonstrated that the major target cells of infection reside below the genital epithelium, and thus HIV must cross this barrier to establish infection. Immune activation enhanced HIV infection of such subepithelial cells. Furthermore, our data suggest that genital epithelial cells were not susceptible to HIV infection, appear to play no part in the transfer of infectious virus across the epithelium, and thus may provide a barrier to infection. In addition, experiments using a panel of virucidal agents demonstrated differential efficiency to block HIV infection of subepithelial cells from partial to complete inhibition. This is the first demonstration that virucidal agents designed for topical vaginal use block HIV infection of genital tissue. Such agents have major implications for world health, as they will provide women with a mechanism of personal and covert protection from HIV infection.

Prostaglandins in primate semen: biasing the immune system to benefit spermatozoa and virus?

The levels of prostaglandins in human semen are many orders of magnitude higher than those found elsewhere in the body and semen contains 19-hydroxy PGE which has not been found in other tissues. The reason for the presence of these prostaglandins is now becoming apparent with the demonstration of powerful effects of PGE and 19-hydroxy PGE on the balance of cytokines (stimulating IL-10 and inhibiting IL-12) released by antigen presenting cells. The effects of the seminal prostaglandins will be two-fold. First, there will be cAMP mediated direct effect on T cells, inhibiting clonal proliferation, inhibiting natural killer cell function and biasing the CD4 cells to a T-helper-2 pattern of cytokine production away from one that would favour a cell-mediated response. Second, and perhaps the major effect, is at the level of the antigen presenting cell that will reinforce the direct effects and induce a tolerance of antigens that are presented together with the IL-10, or PGE. Such tolerance might be necessary for the survival of the spermatozoa under adverse conditions, for instance, in the presence of infection Viruses and other invading organisms would also benefit from this switch in cytokines and the inhibition of the cell-mediated defences. Particular concerns are human immunodeficiency virus (HIV) and human papilloma virus (HPV) which can be transmitted in semen. Not only will the initial immune response be affected, but also repeated exposure to semen will reduce immunesurveillance and the removal of virally infected cells.