Phase 1 trial of nonoxynol-9 film among sex workers in South Africa

Advancing HIV prevention using tenofovir-based pre-exposure prophylaxis

Tenofovir-based pre-exposure prophylaxis (PrEP) revolutionized the global HIV prevention landscape. Prior to the proof-of concept trial in 2010, which demonstrated that tenofovir (TFV) could prevent sexual transmission of HIV, prevention options were largely limited to behavior change, condoms, and circumcision. Several subsequent studies evaluating oral tenofovir disoproxil fumarate (TDF) or the TDF/emtricitabine (FTC) combination as PrEP for HIV prevention provided evidence for regulatory approval and inclusion in national and international guidelines. By 2021, 1.5 million people had initiated oral tenofovir-based PrEP, contributing to declines in HIV incidence in some regions. Here we reflect on how oral tenofovir-based PrEP became an important component of combination HIV prevention programs across the globe.

Comparative in vitro study on the local tolerance and efficacy of benzalkonium chloride, myristalkonium chloride and nonoxynol-9 as active principles in vaginal contraceptives

BACKGROUND

Spermicides have been identified as a potentially attractive alternative to hormonal contraceptives and/or intrauterine devices. Thus, this study aimed evaluating the efficacy and local tolerance of benzalkonium chloride (BKC) and myristalkonium chloride (MKC) contained in Pharmatex^® vaginal formulations and compare them with nonoxynol-9 (N-9), the most common active ingredient in topical vaginal contraceptives.

METHODS

Human normozoospermic samples were assessed for motility, viability, acrosome status and penetration ability after exposure to control, N-9 or different BKC and MKC doses for 0 and 10 minutes. Local tolerance on HeLa cells was evaluated by the Trypan-blue and MTT assays.

RESULTS

Exposure to BKC and MKC reduced acrosome integrity while promoting total immobilisation and complete loss of sperm viability (p < .001, n = 15). Both compounds also compromised sperm penetration ability upon exposure (p < .001, n = 15). N-9 induced the same outcomes (p < .001, n = 15); nevertheless, it was more toxic to HeLa cells than BKC and MKC (p < .05, n = 14).

CONCLUSIONS

BKC and MKC present strong in vitro spermicidal activity at lower doses than N-9 and were better tolerated after immediate exposure than N-9. Available Pharmatex^® galenic formulations were as effective as products based on N-9.

Personal and Clinical Vaginal Lubricants: Impact on Local Vaginal Microenvironment and Implications for Epithelial Cell Host Response and Barrier Function

BACKGROUND

A majority of US women report past use of vaginal lubricants to enhance the ease and comfort of intimate sexual activities. Lubricants are also administered frequently in clinical practice. We sought to investigate if hyperosmolar lubricants are toxic to the vaginal mucosal epithelia.

METHODS

We tested a panel of commercially available lubricants across a range of osmolalities in human monolayer vaginal epithelial cell (VEC) culture and a robust 3-dimensional (3-D) VEC model. The impact of each lubricant on cellular morphology, cytotoxicity, barrier targets, and the induction of inflammatory mediators was examined. Conceptrol, containing nonoxynol-9, was used as a cytotoxicity control.

RESULTS

We observed a loss of intercellular connections, and condensation of chromatin, with increasing lubricant osmolality. EZ Jelly, K-Y Jelly, Astroglide, and Conceptrol induced cytotoxicity in both models at 24 hours. There was a strong positive correlation (r = 0.7326) between lubricant osmolality and cytotoxicity in monolayer VECs, and cell viability was reduced in VECs exposed to all the lubricants tested for 24 hours, except McKesson. Notably, select lubricants altered cell viability, barrier targets, and inflammatory mediators in 3-D VECs.

CONCLUSIONS

These findings indicate that hyperosmolar lubricants alter VEC morphology and are selectively cytotoxic, inflammatory, and barrier disrupting in the 3-D VEC model.

Evaluation of immunological markers of ovine vaginal irritation: Implications for preclinical assessment of non-vaccine HIV preventive agents

The presence of genital inflammatory responses and a compromised vaginal epithelial barrier have been linked to an increased risk of HIV acquisition. It is important to assure that application of candidate microbicides designed to limit HIV transmission will not cause these adverse events. We previously developed high resolution in vivo imaging methodologies in sheep to assess epithelial integrity following vaginal application of a model microbicide, however characterization of genital inflammation in sheep has not been previously possible. In this study, we significantly advanced the sheep model by developing approaches to detect and quantify inflammatory responses resulting from application of a nonoxynol-9-containing gel known to elicit vaginal irritation. Vaginal application of this model microbicide resulted in foci of disrupted epithelium detectable by confocal endomicroscopy. Leukocytes also infiltrated the treated mucosa and the number and composition of leukocytes obtained by cervicovaginal lavage (CVL) were determined by differential staining and flow cytometry. By 18h post-treatment, a population comprised predominantly of granulocytes and monocytes infiltrated the vagina and persisted through 44h post-treatment. The concentration of proinflammatory cytokines and chemokines in CVL was determined by quantitative ELISA. Concentrations of IL-8 and IL-1β were consistently significantly increased after microbicide application suggesting these cytokines are useful biomarkers for epithelial injury in the sheep model. Together, the results of these immunological assessments mirror those obtained in previous animal models and human trials with the same compound and greatly extend the utility of the sheep vaginal model in assessing the vaginal barrier and immune microenvironment.

Historical development of vaginal microbicides to prevent sexual transmission of HIV in women: from past failures to future hopes

Infection with human immunodeficiency virus (HIV) remains a global public health concern and is particularly serious in low- and middle-income countries. Widespread sexual violence and poverty, among other factors, increase the risk of infection in women, while currently available prevention methods are outside the control of most. This has driven the study of vaginal microbicides to prevent sexual transmission of HIV from men to women in recent decades. The first microbicides evaluated were formulated as gels for daily use and contained different substances such as surfactants, acidifiers and monoclonal antibodies, which failed to demonstrate efficacy in clinical trials. A gel containing the reverse transcriptase inhibitor tenofovir showed protective efficacy in women. However, the lack of adherence by patients led to the search for dosage forms capable of releasing the active principle for longer periods, and hence to the emergence of the vaginal ring loaded with dapivirine, which requires a monthly application and is able to reduce the sexual transmission of HIV. The future of vaginal microbicides will feature the use of alternative dosage forms, nanosystems for drug release and probiotics, which have emerged as potential microbicides but are still in the early stages of development. Protecting women with vaginal microbicide formulations would, therefore, be a valuable tool for avoiding sexual transmission of HIV.

Preferred Physical Characteristics of Vaginal Film Microbicides for HIV Prevention in Pittsburgh Women

Unprotected heterosexual intercourse is the leading cause of HIV acquisition in women. Due to the complex nature of correct and consistent condom use by both men and women, developing alternative female-controlled HIV prevention options is a global health priority. Vaginal films containing antiretroviral drugs are a potential delivery system for the prevention of HIV acquisition through sexual contact. In this study, we explored women's preferences regarding physical characteristics of microbicide vaginal films through questionnaires and focus groups. Eighty-four sexually active, ethnically diverse women 18-30 years of age from Pittsburgh, Pennsylvania, participated in the study. Women visually and manually examined a variety of vaginal films, as well as three other vaginal products undergoing evaluation for HIV prevention: tablet, ring, and gel. Means and standard deviations or frequencies and 95 % confidence intervals were calculated for questionnaire data. Focus groups were audio-recorded, transcribed verbatim, and coded for content analysis. Women most frequently preferred vaginal films to be smooth and thin (63 %), translucent (48 %), and 2″ × 2″ square size (36 %). Driving these preferences were five major themes: ease and accuracy of use, desire for efficacy, discretion, intravaginal comfort and minimal impact, and minimizing disruption of sexual mood/activities. Women's preferences for various microbicide vaginal film physical attributes represented a balance of multiple values. In general, women desired a comfortable, efficacious, easy to use, and minimally intrusive product.

Combination HIV prevention interventions: the potential of integrated behavioral and biomedical approaches

Combination HIV prevention interventions that integrate efficacious behavioral and biomedical strategies offer the potential to reduce new HIV infections. We overview the efficacy data for three biomedical HIV prevention approaches, namely microbicides, pre-exposure prophylaxis (PrEP), and HIV vaccination; review factors associated with differential acceptability and uptake of these methods; and suggest strategies to optimize the effectiveness and dissemination of combination HIV prevention approaches. A narrative review was conducted highlighting key efficacy data for microbicides, PrEP, and an HIV vaccination and summarizing acceptability data for each of the three biomedical HIV prevention approaches. Recommendations for the integration and dissemination of combined behavioral and biomedical HIV prevention approaches are provided. To date, microbicides and an HIV vaccination have demonstrated limited efficacy for the prevention of HIV. However, PrEP has demonstrated efficacy in reducing HIV incident infections. A diverse array of factors influences both hypothetical willingness and actual usage of each biomedical prevention method. Strategies to effectively integrate and evaluate combination HIV prevention interventions are urgently needed.

Unexpected Inflammatory Effects of Intravaginal Gels (Universal Placebo Gel and Nonoxynol-9) on the Upper Female Reproductive Tract: A Randomized Crossover Study

Intravaginal anti-HIV microbicides could provide women with a self-controlled means for HIV prevention, but results from clinical trials have been largely disappointing. We postulated that unrecognized effects of intravaginal gels on the upper female reproductive tract might contribute to the lower-than-expected efficacy of HIV microbicides. Our objective was to study the effects of intravaginal gels on the immune microenvironment of the cervix and uterus. In this randomized crossover study, 27 healthy female volunteers used a nightly application of intravaginal nonoxynol-9 (N9) gel as a "failed" microbicide or the universal placebo gel (UPG) as a "safe" gel (intervention cycles), or nothing (control cycle) from the end of menses to the mid-luteal phase. At a specific time-point following ovulation, all participants underwent sample collection for measurements of T-cell phenotypes, gene expression, and cytokine/chemokine protein concentrations from 3 anatomic sites above the vagina: the cervical transformation zone, the endocervix and the endometrium. We used hierarchical statistical models to estimate mean (95% CI) intervention effects, for N9 and UPG relative to control. Exposure to N9 gel and UPG generated a common "harm signal" that included transcriptional up-regulation of inflammatory genes chemokine (C-C motif) ligand 20 (macrophage inflammatory factor-3alpha) and interleukin 8 in the cervix, decreased protein concentrations of secretory leukocyte protease inhibitor, and transcriptional up-regulation of inflammatory mediators glycodelin-A and osteopontin in the endometrium. These results need to be replicated with a larger sample, but underscore the need to consider the effects of microbicide agents and gel excipients on the upper female reproductive tract in studies of vaginal microbicides.

Communication About Microbicide Use Between Couples in KwaZulu-Natal, South Africa

The ways in which couples communicate about microbicides is likely to influence microbicide uptake and usage. We collected quantitative data about whether women in a microbicide trial discussed microbicides with their partners and explored communication about microbicides during 79 in-depth-interviews with women enrolled in the trial and 17 focus-group discussions with community members. After 4 weeks in the trial, 60 % of 1092 women had discussed microbicides with their partners; in multivariate analysis, this was associated with younger age, clinic of enrolment and not living in households that owned cattle. After 52 weeks, 84 % of women had discussed microbicides; in multivariate analysis, this was associated with not living in households that owned cattle, not living in a household that relied on the cheapest water source, allocation to 0.5 % PRO2000 gel and consistent gel adherence. Qualitative findings highlighted that women in committed relationships were expected to discuss microbicides with their partners and preferred to use microbicides with their partner's knowledge. Women had different reasons for, and ways of, discussing microbicides and these were influenced by the couple's decision-making roles. Although there was tolerance for the use of microbicides without a partner's knowledge, the women who used microbicides secretly appeared to be women who were least able to discuss microbicides. In KwaZulu-Natal, socio-cultural norms informing sexual communication are amenable to microbicide introduction.

Combination HIV prevention for female sex workers: what is the evidence?

Sex work occurs in many forms and sex workers of all genders have been affected by HIV epidemics worldwide. The determinants of HIV risk associated with sex work occur at several levels, including individual biological and behavioural, dyadic and network, and community and social environmental levels. Evidence indicates that effective HIV prevention packages for sex workers should include combinations of biomedical, behavioural, and structural interventions tailored to local contexts, and be led and implemented by sex worker communities. A model simulation based on the South African heterosexual epidemic suggests that condom promotion and distribution programmes in South Africa have already reduced HIV incidence in sex workers and their clients by more than 70%. Under optimistic model assumptions, oral pre-exposure prophylaxis together with test and treat programmes could further reduce HIV incidence in South African sex workers and their clients by up to 40% over a 10-year period. Combining these biomedical approaches with a prevention package, including behavioural and structural components as part of a community-driven approach, will help to reduce HIV infection in sex workers in different settings worldwide.

Community empowerment and involvement of female sex workers in targeted sexual and reproductive health interventions in Africa: a systematic review

Background

Female sex workers (FSWs) experience high levels of sexual and reproductive health (SRH) morbidity, violence and discrimination. Successful SRH interventions for FSWs in India and elsewhere have long prioritised community mobilisation and structural interventions, yet little is known about similar approaches in African settings. We systematically reviewed community empowerment processes within FSW SRH projects in Africa, and assessed them using a framework developed by Ashodaya, an Indian sex worker organisation.

Methods

In November 2012 we searched Medline and Web of Science for studies of FSW health services in Africa, and consulted experts and websites of international organisations. Titles and abstracts were screened to identify studies describing relevant services, using a broad definition of empowerment. Data were extracted on service-delivery models and degree of FSW involvement, and analysed with reference to a four-stage framework developed by Ashodaya. This conceptualises community empowerment as progressing from (1) initial engagement with the sex worker community, to (2) community involvement in targeted activities, to (3) ownership, and finally, (4) sustainability of action beyond the community.

Results

Of 5413 articles screened, 129 were included, describing 42 projects. Targeted services in FSW ‘hotspots’ were generally isolated and limited in coverage and scope, mostly offering only free condoms and STI treatment. Many services were provided as part of research activities and offered via a clinic with associated community outreach. Empowerment processes were usually limited to peer-education (stage 2 of framework). Community mobilisation as an activity in its own right was rarely documented and while most projects successfully engaged communities, few progressed to involvement, community ownership or sustainability. Only a few interventions had evolved to facilitate collective action through formal democratic structures (stage 3). These reported improved sexual negotiating power and community solidarity, and positive behavioural and clinical outcomes. Sustainability of many projects was weakened by disunity within transient communities, variable commitment of programmers, low human resource capacity and general resource limitations.

Conclusions

Most FSW SRH projects in Africa implemented participatory processes consistent with only the earliest stages of community empowerment, although isolated projects demonstrate proof of concept for successful empowerment interventions in African settings.

Analysis of vaginal microbicide film hydration kinetics by quantitative imaging refractometry

We have developed a quantitative imaging refractometry technique, based on holographic phase microscopy, as a tool for investigating microscopic structural changes in water-soluble polymeric materials. Here we apply the approach to analyze the structural degradation of vaginal topical microbicide films due to water uptake. We implemented transmission imaging of 1-mm diameter film samples loaded into a flow chamber with a 1.5×2 mm field of view. After water was flooded into the chamber, interference images were captured and analyzed to obtain high resolution maps of the local refractive index and subsequently the volume fraction and mass density of film material at each spatial location. Here, we compare the hydration dynamics of a panel of films with varying thicknesses and polymer compositions, demonstrating that quantitative imaging refractometry can be an effective tool for evaluating and characterizing the performance of candidate microbicide film designs for anti-HIV drug delivery.

The implications of post-coital intravaginal cleansing for the introduction of vaginal microbicides in South Africa

Post-coital intravaginal cleansing (IVC) could counteract the protective effect of a vaginal microbicide. IVC less than 1 h after sex is discouraged in most microbicide trials. During a microbicide trial in KwaZulu-Natal, we collected quantitative data on post-coital IVC. We discussed IVC during in-depth-interviews (IDIs) and focus-group discussions (FGDs) with women enrolled in the trial, and during FGDs with community members. Nearly one-third (336/1,143) of women reported IVC less than an hour after sex. In multivariate analysis, post-coital IVC was associated with younger age, larger household size, greater sexual activity, consistent gel use, and clinic of enrolment. During IDIs and FGDs, respondents described post-coital IVC as a common hygiene practice motivated by the need to remove semen, vaginal fluids and sweat, although this practice may be amenable to change in the context of microbicide use. We need to consider strategies for influencing post-coital IVC practices in future microbicide trials and delivery programmes.

Quantitative assessment of altered rectal mucosal permeability due to rectally applied nonoxynol-9, biopsy, and simulated intercourse

BACKGROUND

Microbicide toxicity may reduce the efficacy of topical preexposure prophylaxis for human immunodeficiency virus (HIV) transmission. Noninvasive quantitative measures of microbicide toxicity would usefully inform microbicide development.

METHODS

Ten subjects received 3 one-time interventions: 5 mL of Normosol-R fluid alone (negative control), 5 mL of 2% nonoxynol-9 (N-9) gel, and 5 mL of Normosol-R with coital simulation and sigmoidoscopic biopsy (CS + BX). Each dose of N-9 and Normosol-R contained 500 µCi of (99m)technetium-diethylene triamine pentaacetic acid. Plasma and urine radioactivity was assessed over 24 hours.

RESULTS

The plasma radioisotope concentration peaked 1 hour after N-9 dosing. The mean maximum radioisotope concentration after N-9 receipt was 12.0 times (95% confidence interval [CI], 6.8-21.0) and 8.4 times (95% CI, 5.2-13.5) the mean concentration after Normosol-R control receipt and CS + BX receipt, respectively; paired differences persisted for 24 hours. After N-9 dosing, the urine isotope level was 3.6 times (95% CI, 1.1-11.4) the level observed 8 hours after Normosol-R control receipt and 4.0 times (95% CI, 1.4-11.4) the level observed 4 hours after CS + BX receipt. Permeability after CS + BX receipt was greater than that after Normosol-R control receipt in 0-2-hour urine specimens only (mean permeability, 2.4; 95% CI, 1.0-5.8) but was not greater in blood.

CONCLUSIONS

Plasma sampling after rectal radioisotope administration provided quantitative estimates of altered mucosal permeability after chemical and mechanical stresses. Permeability testing may provide a useful noninvasive adjunct to assess the mucosal effects of candidate microbicides. Clinical Trials Registration. NCT00389311.

Pharmacokinetics and efficacy of a vaginally administered maraviroc gel in rhesus macaques

OBJECTIVES

To investigate the pharmacokinetics (PK) of maraviroc, a CCR5-targeted HIV-1 entry inhibitor, in rhesus macaques following vaginal administration of various maraviroc-loaded aqueous hydroxyethylcellulose (HEC) gels, and to correlate the PK data with efficacy in a single high-dose vaginal SHIV-162P3 challenge model.

METHODS

Maraviroc concentrations in vaginal fluid (Weck-Cel(®) sponge), vaginal tissue (punch biopsy) and plasma were assessed over 72 h following single-dose vaginal application of various maraviroc-loaded HEC gels. The range of maraviroc gel concentrations was sufficiently broad (0.003%-3.3% w/w) that test gels included both fully solubilized and predominantly dispersed formulations. The efficacy of the HEC gels against a single high-dose vaginal SHIV-162P3 challenge was also measured, and correlated with the PK concentrations.

RESULTS

Maraviroc concentrations in vaginal fluid (range 10(4)-10(7) ng/mL), vaginal tissue (100-1200 ng/g) and plasma (<10(2) ng/mL) were highly dependent on maraviroc gel loading, irrespective of the form of the maraviroc component within the gel (solubilized versus dispersed). Fluid and plasma concentrations were generally highest 0.5 or 2 h after gel application, before declining steadily through to 72 h. Maraviroc concentrations in the various biological compartments correlated strongly with the extent of protection against vaginal SHIV-162P3 challenge. Complete protection was achieved with a 3.3% w/w maraviroc gel.

CONCLUSIONS

A high degree of correlation between PK and efficacy was observed. Based on the data obtained with the 3.3% w/w maraviroc gel, maintenance of vaginal fluid and tissue levels in the order of 10(7) ng/mL and 10(3) ng/g, respectively, are required for complete protection with this compound.

Assessing the relationship between cervical ectopy and HIV susceptibility: implications for HIV prevention in women

Cervical ectopy, which occurs when the columnar epithelium of the endocervical canal extends outwards into the ectocervix, has been suggested to increase the susceptibility to HIV infection in at-risk women. This study summarizes observational studies, primarily conducted in sub-Saharan Africa, that have assessed a possible causative association between cervical ectopy and HIV acquisition and also examines the biological plausibility as well as other cofactors that may mediate this association. Only about half of the studies reviewed found cervical ectopy to be a significant risk factor for HIV acquisition. The reasons for these divergent results still remain to be fully elucidated. Understanding biological factors that affect HIV susceptibility provide opportunities to identify prevention strategies to reduce the risk of HIV acquisition.

Vaginal microbicides to prevent human immunodeficiency virus infection in women: perspectives on the female genital tract, sexual maturity and mucosal inflammation

Topically applied vaginal microbicides to protect against human immunodeficiency (HIV) virus infection offer an important female-controlled prevention strategy. Microbicides have been in development for more than 2 decades, and have included various agents that disrupt cellular and microbial membranes (surfactants), restore the natural acidic protective pH of the vagina (acid buffers), and those that interfere with interactions between HIV envelope proteins and cellular receptors (anionic polymers). Although none of these candidate microbicides have shown significant protection against HIV in clinical trials, a topical gel, including the antiretroviral drug tenofovir (TFV) 1% was the first microbicide to be tested to show some protection against HIV infection. This review explores the effect of female genital tract biology and anatomy, mucosal inflammation, and age on the effectiveness of microbicides to prevent HIV infection.

Future strategies in microbicide development

The reduction in human immunodeficiency virus (HIV) infection in women demonstrated by pericoital use of tenofovir gel has encouraged the continued development of microbicides. Novel approaches include new ways to deliver tenofovir, as well as products that contain different antiretroviral drugs, either as single agents or as combinations of antiretroviral drugs. Indeed, emphasis has renewed on the development of multipurpose prevention technologies, products designed to address multiple sexually transmitted infections. Dual-purpose contraceptive antiretroviral products are also being designed to prevent HIV and pregnancy. Since consistent and correct use of these products will be critical to their effectiveness, the active pharmaceutical ingredients must be delivered in acceptable vaginal dosage forms, such as gels, films and sustained-release vaginal rings. The development of different dosage forms will help ensure that women can find a method to protect themselves from HIV, pregnancy, and potentially other sexually transmitted infections.

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.

Microbicides in the prevention of HIV infection: current status and future directions

More than 28 years since the first cases of HIV/AIDS, there is still no cure or vaccine. The worst affected region is sub-Saharan Africa and, increasingly, it is young women who are bearing the brunt of the epidemic. Consequently, there is an urgent need for HIV prevention options for women in developing countries. Microbicides are topical products that can be used vaginally by women to impede sexual transmission of HIV and thus represent one of the most promising prevention strategies. Efficacy trials with early nonspecific microbicide gels have so far been unsuccessful, but the field has now switched its focus to products containing highly potent and highly specific antiretroviral drugs that are easier to use, and can be formulated in a variety of dosage forms to suit individual and regional preferences. However, these products have their own challenges, with a greater likelihood of absorption, and the potential for systemic toxicities or the development of resistance in infected individuals who are unaware of their HIV status. The conduct of clinical trials is complex for all microbicides, with limited availability of trial sites, difficulties in dose selection and safety monitoring, and a lack of a truly objective measure of adherence. Once a microbicide has been shown to be safe and effective, there will need to be a clear pathway to regulatory approval, and the successful launch of a product will depend on having in place appropriate methods for distribution to the women who need it, along with a strategy for ensuring that they use it correctly. This will require substantial effort in terms of education and community engagement, and these activities need to be initiated well in advance of microbicide rollout.

In vitro and ex vivo testing of tenofovir shows it is effective as an HIV-1 microbicide

BACKGROUND

Tenofovir gel has entered into clinical trials for use as a topical microbicide to prevent HIV-1 infection but has no published data regarding pre-clinical testing using in vitro and ex vivo models. To validate our findings with on-going clinical trial results, we evaluated topical tenofovir gel for safety and efficacy. We also modeled systemic application of tenofovir for efficacy.

METHODS AND FINDINGS

Formulation assessment of tenofovir gel included osmolality, viscosity, in vitro release, and permeability testing. Safety was evaluated by measuring the effect on the viability of vaginal flora, PBMCs, epithelial cells, and ectocervical and colorectal explant tissues. For efficacy testing, PBMCs were cultured with tenofovir or vehicle control gels and HIV-1 representing subtypes A, B, and C. Additionally, polarized ectocervical and colorectal explant cultures were treated apically with either gel. Tenofovir was added basolaterally to simulate systemic application. All tissues were challenged with HIV-1 applied apically. Infection was assessed by measuring p24 by ELISA on collected supernatants and immunohistochemistry for ectocervical explants. Formulation testing showed the tenofovir and vehicle control gels were >10 times isosmolar. Permeability through ectocervical tissue was variable but in all cases the receptor compartment drug concentration reached levels that inhibit HIV-1 infection in vitro. The gels were non-toxic toward vaginal flora, PBMCs, or epithelial cells. A transient reduction in epithelial monolayer integrity and epithelial fracture for ectocervical and colorectal explants was noted and likely due to the hyperosmolar nature of the formulation. Tenofovir gel prevented HIV-1 infection of PBMCs regardless of HIV-1 subtype. Topical and systemic tenofovir were effective at preventing HIV-1 infection of explant cultures.

CONCLUSIONS

These studies provide a mechanism for pre-clinical prediction of safety and efficacy of formulated microbicides. Tenofovir was effective against HIV-1 infection in our algorithm. These data support the use of tenofovir for pre-exposure prophylaxis.

Monkeying around with HIV vaccines: using rhesus macaques to define 'gatekeepers' for clinical trials

Rhesus macaques are an important animal model for the study of human disease and the development of vaccines against HIV and AIDS. HIV vaccines have been benchmarked in rhesus macaque preclinical challenge studies using chimeric viruses made up of parts of HIV and simian immunodeficiency viruses. However, the lack of efficacy in a recent clinical trial calls for a re-evaluation of the scientific assumptions regarding the predictive value of using data generated from rhesus macaques as a 'gatekeeper' for the advancement of candidate vaccines into the clinic. In this context, there is significant consensus among HIV vaccinologists that next-generation HIV vaccines must generate 'better' immunity in rhesus macaques than clinically unsuccessful vaccines generated using validated assays. Defining better immunity is the core challenge of HIV vaccine development in this system and is the focus of this Review.

The safety of candidate vaginal microbicides since nonoxynol-9: a systematic review of published studies

OBJECTIVE

To gain a greater understanding of published safety data for candidate vaginal microbicides.

DESIGN

A systematic review of human safety trials of candidate vaginal microbicides - agents designed to protect women against HIV and other sexually transmitted infections.

METHODS

Trials were published in peer-reviewed journals, and publication cut-off was August week 4, 2008. Trials of nonoxynol-9 were excluded, as were trials without a control group, trials that enrolled only male participants or reported on the investigation of a product for the treatment of a genital infection.

RESULTS

Twenty-one trials of 11 products, involving 1465 women, satisfied review criteria. Most trials reported on genital epithelial findings and urogenital symptoms and a number reported a range of other local and systemic toxicity endpoints. Trials were generally of short duration (2 weeks or less) with small sample sizes. There were few findings of significant difference between women in active and control arms. Among the products assessed in more than one study, there were significantly more genital findings with intact epithelium in recipients of PRO2000 [relative risk (RR) 1.68, 95% confidence interval (CI) 1.08-2.60] and a lower incidence of bacterial vaginosis in dextrin sulphate recipients (RR 0.61, 95% CI 0.42-0.88). CIs were generally very wide, and most studies were unable to exclude differences of a substantial magnitude between treated and control women.

CONCLUSION

Larger and longer safety studies are necessary to detect clinically important toxicities, including those that indicate a potential increase in HIV risk, and provide assurance that agents are ready for large-scale effectiveness trials.

Managing men: women's dilemmas about overt and covert use of barrier methods for HIV prevention

Women in sub-Saharan Africa are at high risk of HIV infection and may struggle to negotiate condom use. This has led to a focus on the development of female-controlled barrier methods such as the female condom, microbicides and the diaphragm. One of the advantages of such products is their contribution to female empowerment through attributes that make covert use possible. We used focus groups to discuss covert use of barrier methods with a sample of South African women aged 18-50 years from Eastern Johannesburg. Women's attitudes towards covert use of HIV prevention methods were influenced by the overarching themes of male dislike of HIV and pregnancy prevention methods, the perceived untrustworthiness of men and social interpretations of female faithfulness. Women's discussions ranged widely from overt to covert use of barrier methods for HIV prevention and were influenced by partner characteristics and previous experience with contraception and HIV prevention. The discussions indicate that challenging gender norms for HIV prevention can be achieved in quite subtle ways, in a manner that suits individual women's relationships and previous experiences with negotiation of either HIV or pregnancy prevention.

Incomplete protection against simian immunodeficiency virus vaginal transmission in rhesus macaques by a topical antiviral agent revealed by repeat challenges

The rising prevalence of human immunodeficiency virus type 1 (HIV-1) infection in women, especially in resource-limited settings, accentuates the need for accessible, inexpensive, and female-controlled preexposure prophylaxis strategies to prevent mucosal transmission of the virus. While many compounds can inactivate HIV-1 in vitro, evaluation in animal models for mucosal transmission of virus may help identify which approaches will be effective in vivo. Macaques challenged intravaginally with pathogenic simian immunodeficiency virus (SIV(mac251)) provide a model to preclinically evaluate candidate microbicides. 2-Hydroxypropyl-beta-cyclodextrin (BCD) prevents HIV-1 and SIV infection of target cells at subtoxic doses in vitro. Consistent with these findings, intravaginal challenge of macaques with SIV(mac251) preincubated with BCD prevented mucosal transmission, as measured by plasma viremia and antiviral antibodies, through 10 weeks postchallenge. In an initial challenge, BCD applied topically prior to SIV(mac251) prevented intravaginal transmission of virus compared to controls (P < 0.0001). However, upon a second virus challenge following BCD pretreatment, the majority of the previously protected animals became infected. The mechanism through which animals become infected at a frequency similar to that of controls after prior exposure to BCD and SIV(mac251) in subsequent intravaginal virus challenges (P = 0.63), despite the potent antiviral properties of BCD, remains to be determined. These results highlight the unpredictability of antiviral compounds as topical microbicides and suggest that repeated exposures to candidate treatments should be considered for in vivo evaluation.

Cervicovaginal colposcopic lesions associated with 5 nonoxynol-9 vaginal spermicide formulations

OBJECTIVE

This study was undertaken to compare the colposcopic appearance of the cervicovaginal epithelium with spermicide use vs condom use in a low-risk population.

STUDY DESIGN

This was an ancillary study of a trial comparing the efficacy of 5 nonoxynol-9 spermicides. A cohort of women who used condoms without spermicide served as a control group. Colposcopic examinations were performed during product use to identify genital lesions.

RESULTS

One hundred fifty-one participants had 1 or more follow-up examinations. At baseline, study groups differed only by the prevalence of baseline lesions. New lesions were identified at 49% of follow-up visits. Controlling for the presence of a baseline lesion, compared with condom use none of the spermicides were associated with an increase in new lesions (overall odds ratio, 0.8; 95% CI, 0.4-1.6; P = .5); and lesions characterized by epithelial disruption were less frequent with spermicide use (overall odds ratio, 0.3; 95% CI, 0.1-0.6; P < .001).

CONCLUSION

In a low-risk population, women who used nonoxynol-9 spermicides were less likely to have lesions with epithelial disruption, and equally likely to have any new lesion compared with condom use.

Temperature and pH Sensitive Hydrogels: An Approach Towards Smart Semen-Triggered Vaginal Microbicidal Vehicles

Microbicides are drug delivery systems (DDSs) for the prevention of sexual transmission of HIV and other STDs. A topically applied vaginal microbicidal gel should provide uniform coating of vaginal tissue, retention of this gel layer prior to intercourse, and controlled release kinetics of antivirals to inactivate the viral load potentially introduced during sexual activity. Here, we describe the microbicide-oriented characterization of a DDS made with a dual pH sensitive and thermosensitive smart polymer gel composed of a random terpolymer of N-isopropyl acrylamide, butyl methacrylate, and acrylic acid. The system was engineered to coat vaginal tissue with a stable gel layer and to release entrapped model agents in a burst release profile in response to the presence of the infecting agent: semen. The gel rheology, layer erosion properties, model drug release kinetics, and cytocompatibility of the terpolymer system were studied. Negligible erosion of the gel in the presence of vaginal fluid simulant suggests prolonged retention. Burst release of molecular and macromolecular model compounds was observed when the system's pH changed from the vaginal pH to the pH of semen, and cytotoxicity studies showed that the terpolymer is equally cytocompatible as a commonly used polymeric vaginal carrier.

Nested Case–Control Study of Cervical Mucosal Lesions, Ectopy, and Incident HIV Infection Among Women in Cape Town, South Africa

OBJECTIVE

The objective of this study was to test whether cervical mucosal lesions and ectopy increase women's susceptibility to HIV infection.

STUDY DESIGN

HIV-seronegative women ages 35 to 65 years (n = 5773) enrolled into a cervical cancer screening trial were followed for up to 36 months. All HIV seroconverters (n = 86) in the cohort were compared with randomly selected controls (n = 324) who did not seroconvert. Magnified photographs of the cervix taken during speculum examination at enrollment were evaluated for cervical mucosal lesions and ectopy using standard criteria.

RESULTS

The presence of mucosal lesions (observed among 19% of controls) was associated with increased risk of HIV seroconversion (adjusted odds ratio [AOR] = 1.93; 95% confidence interval [CI] = 1.07-3.48). Ectopy extending over >20% of the cervix was also associated with HIV seroconversion (AOR = 2.18; 95% CI = 1.01-4.69).

CONCLUSIONS

Visible lesions of cervical mucosa and cervical ectopy may be markers of increased susceptibility to HIV infection among women. Protection of the mucosa of the cervix may provide an important approach for new HIV prevention technologies.

Preclinical evaluation of synthetic -2 RANTES as a candidate vaginal microbicide to target CCR5

A potential strategy that can be used to combat the worldwide AIDS epidemic is the development of a vaginal microbicide that prevents the sexual transmission of human immunodeficiency virus type 1 (HIV-1). Certain CC chemokines, including RANTES, MIP-1alpha, and MIP-1beta, might facilitate the development of such microbicides since they potently suppress HIV-1 infection by binding to CCR5, the viral coreceptor used by most sexually transmitted strains of HIV-1 to enter host cells. In this study, we evaluated whether a CCR5-specific fragment of RANTES that lacks two N-terminal residues (-2 RANTES) and possesses especially potent HIV-1 suppressive activity has toxicity profiles conducive to the advancement of testing in candidate microbicide formulations. Analyses were carried out with a synthetic version of the chemokine, which was formulated with either Novasomes 7474, a nonphospholipid liposome, or methylcellulose gel. Dialysis studies demonstrated that the formulated -2 RANTES was released from both vehicles and retained anti-HIV-1 activity. Preclinical toxicity studies carried out with Swiss Webster mouse and New Zealand White rabbit vaginal irritation models demonstrated minimal inflammation and minimal adverse changes in cervicovaginal tissue integrity after short-term (10 min) and long-term (24 h) exposure to formulations containing up to 1 mg/ml of -2 RANTES. Similarly, no toxicity was observed with formulations of bioactive murine RANTES in the Swiss Webster mouse vaginal irritation model. Overall, these preclinical studies suggest that -2 RANTES is suitable for further testing as a candidate anti-HIV-1 microbicide.

Intravaginal practices, bacterial vaginosis, and women's susceptibility to HIV infection: epidemiological evidence and biological mechanisms

Intravaginal practices such as "dry sex" and douching have been suggested as a risk factor that may increase women's susceptibility to HIV infection. These behaviours appear common in different populations across sub-Saharan Africa, where practices include the use of antiseptic preparations, traditional medicines, or the insertion of fingers or cloths into the vagina. We systematically review the evidence for the association between women's intravaginal practices and HIV infection. Although a number of cross-sectional studies have shown that prevalent HIV infection is more common among women reporting intravaginal practices, the temporal nature of this association is unclear. Current evidence suggests that bacterial vaginosis, which is a likely risk factor for HIV infection, may be a mediator of the association between intravaginal practices and HIV. Although biologically plausible mechanisms exist, there is currently little epidemiological evidence suggesting that intravaginal practices increase women's susceptibility to HIV infection. Further research into factors that increase women's susceptibility to HIV will help to inform the design of vaginal microbicides and other HIV prevention interventions.

Nonoxynol-9 100 mg gel: multi-site safety study from sub-Saharan Africa

OBJECTIVES

To evaluate the safety of 100 mg nonoxynol-9 (N-9) gel, a vaginal microbicide, on the genital mucosa of women from Malawi and Zimbabwe in preparation for a phase III efficacy study.

METHODS

HIV-uninfected women (180) were enrolled and randomized to either N-9 or placebo gel and instructed to insert gel into the vagina twice daily for 14 days. Follow up examinations were conducted at 7 and 14 days.

RESULTS

The number of adverse events in the N-9 gel group was higher than in the placebo group (40% versus 13%; P < 0.01). Reported number of any genital symptoms was significantly higher in the N-9 group (38% N-9, 13% placebo; P = 0.01). The number of total epithelial disruptions was higher in the N-9 group (20% versus 3%; P < 0.01); however, the number of genital ulcers and abrasions in the N-9 group was low (2% and 3%, respectively) and not different from that in the placebo group (1% and 2%, respectively).

CONCLUSIONS

N-9 gel 100 mg caused a significant increase in the rate of genital symptoms and epithelial disruptions compared with placebo. The clinical significance of these epithelial disruptions is unknown. Although these findings alone were not sufficient to cancel the planned phase III study, when considered together with the negative results from the COL-1492 effectiveness trial of 52.5 mg N-9 gel, the decision was made to cancel the planned phase III trial of 100 mg N-9 gel.

Water dispersible microbicidal cellulose acetate phthalate film

Background

Cellulose acetate phthalate (CAP) has been used for several decades in the pharmaceutical industry for enteric film coating of oral tablets and capsules. Micronized CAP, available commercially as "Aquateric" and containing additional ingredients required for micronization, used for tablet coating from water dispersions, was shown to adsorb and inactivate the human immunodeficiency virus (HIV-1), herpesviruses (HSV) and other sexually transmitted disease (STD) pathogens. Earlier studies indicate that a gel formulation of micronized CAP has a potential as a topical microbicide for prevention of STDs including the acquired immunodeficiency syndrome (AIDS). The objective of endeavors described here was to develop a water dispersible CAP film amenable to inexpensive industrial mass production.

Methods

CAP and hydroxypropyl cellulose (HPC) were dissolved in different organic solvent mixtures, poured into dishes, and the solvents evaporated. Graded quantities of a resulting selected film were mixed for 5 min at 37°C with HIV-1, HSV and other STD pathogens, respectively. Residual infectivity of the treated viruses and bacteria was determined.

Results

The prerequisites for producing CAP films which are soft, flexible and dispersible in water, resulting in smooth gels, are combining CAP with HPC (other cellulose derivatives are unsuitable), and casting from organic solvent mixtures containing ≈50 to ≈65% ethanol (EtOH). The films are ≈100 µ thick and have a textured surface with alternating protrusions and depressions revealed by scanning electron microscopy. The films, before complete conversion into a gel, rapidly inactivated HIV-1 and HSV and reduced the infectivity of non-viral STD pathogens >1,000-fold.

Conclusions

Soft pliable CAP-HPC composite films can be generated by casting from organic solvent mixtures containing EtOH. The films rapidly reduce the infectivity of several STD pathogens, including HIV-1. They are converted into gels and thus do not have to be removed following application and use. In addition to their potential as topical microbicides, the films have promise for mucosal delivery of pharmaceuticals other than CAP.

Development of topical microbicides for prevention of human immunodeficiency virus and herpes simplex virus

Topical microbicides, designed for vaginal or rectal administration, are needed to prevent human immunodeficiency virus (HIV) and other sexually transmitted infections (STI). Presently marketed topical microbicides are cytotoxic and damage the vaginal epithelium with frequent use. Rational development of new candidate compounds should build on knowledge of the pathways of microbial invasion. The establishment of assays and models that predict efficacy and safety is critical. Comprehensive pre-clinical evaluation of promising microbicides should include rigorous assessment of the effects of repeated application of topical agents on mucosal inflammatory cells, cytokines, and the genital tract virus population. These studies will lay the groundwork for future clinical trials.

Microbicide efficacy and toxicity tests in a mouse model for vaginal transmission of Chlamydia trachomatis

BACKGROUND

Microbicides are being developed for woman-controlled protection against sexually transmitted diseases (STDs).

GOAL

The goal of the study was to test candidate microbicides in a mouse model for preventing vaginal transmission of and for acute toxicity to columnar epithelium.

STUDY DESIGN

Progestin-sensitized CF-1 mice were treated vaginally with 50 microl of microbicide, followed either by vaginal inoculation with 10 ID(50) of serovar D or by examination of the epithelial surface for acute toxicity with a viability stain (ethidium homodimer-1).

RESULTS

Nonoxynol-9 (N9), sodium dodecyl sulfate (SDS), chlorhexidine digluconate, and BufferGel all provided significant though incomplete protection against vaginal transmission. Other candidates, all of which were effective in vitro, provided no vaginal protection: kappa-carrageenan, dextran sulfate, polystyrene sulfonate, Concanavalin A, wheat germ agglutinin, and agglutinin. The surface-active agents (N9, SDS, and chlorhexidine) caused significant acute epithelial toxicity: 3 days after chlorhexidine exposure, mice also had vaginal friability and markedly increased susceptibility to. BufferGel was the only candidate tested that was both protective and relatively nontoxic.

CONCLUSION

Microbicides can provide vaginal protection against in highly susceptible progestin-sensitized mice. Since N9 does not inactivate, it likely protects by killing target cells in the vagina. Despite the ability to both potently inactivate and kill target cells, two surface-active agents, SDS and chlorhexidine, failed to provide complete protection, a circumstance which emphasizes the importance of distributing microbicides to all susceptible surfaces.

Rectal applications of nonoxynol-9 cause tissue disruption in a monkey model

BACKGROUND

Efforts to develop topical microbicide products have all but ignored evaluation for rectal use.

GOAL

The goal of this study was to assess the effects of multiple rectal applications of Conceptrol (containing 4% nonoxynol-9) on flora and mucosal tissues in the pig-tailed macaque model.

STUDY DESIGN

Monkeys (8 per group) received daily rectal applications of Conceptrol, placebo gel, or no product, for 3 days. At each visit, a preapplication rectal lavage specimen and swab specimen for microbiology and pH determination were collected. Conceptrol or placebo gel (2.5 ml) was then administered intrarectally. Fifteen minutes after application, samples were again collected.

RESULTS

Gross observation of rectal lavage indicated sheets of epithelium 15 minutes after application of the nonoxynol-9 product. Histopathology of these samples revealed epithelial sheets with stroma attached. The presence of H(2)O(2)-producing lactobacilli remained relatively constant, whereas that of H(2)O(2)-producing viridans streptococci diminished in all nonoxynol-9-exposed animals in which these organisms were detected at baseline.

CONCLUSIONS

Repeated applications of nonoxynol-9 disrupts the rectal mucosa of the pig-tailed macaque. The disruption of these tissues could have serious implications for an increase in likelihood of acquisition of sexually transmitted infection/HIV in humans.

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.

A brief sexual barrier intervention for women living with AIDS: acceptability, use, and ethnicity

Interventions aimed at reducing sexual transmission of human immunodeficiency virus/sexually transmitted diseases (HIV/STDs) have focused primarily on male condom use among seronegative men and women. However, female-controlled sexual barriers (female condoms and vaginal microbicides) offer women living with acquired immunodeficiency syndrome (AIDS) alternative methods to protect themselves and others from disease transmission. A pilot behavioral intervention was conducted to increase sexual barrier use and enhance and assess factors related to acceptability. Participants (N = 178) were drawn from the Stress Management and Relaxation Training with Expressive Supportive Therapy (SMART/EST) Women's Project, a multisite phase III clinical trial for women living with AIDS (Miami, FL; New York City, NY; Newark, NJ). Intervention participants (n = 89) were matched for age and ethnicity with control condition participants (n = 89). Women were African American (52%), Haitian (15%), Hispanic (19%), Caucasian (10%), and other ethnicities (4%). The intervention condition received barrier products (male and female condoms and spermicides based on nonoxynol-9 in the form of vaginal gel, film, and suppositories) during three sessions held over 3 months. Data on barrier use and acceptability were analyzed at baseline and 3 and 9 months postintervention. Use of N-9 spermicides on a trial basis increased significantly by 3 months in the intervention conditions (22%-51%, P <.05). Cultural differences in acceptability were greatest between Haitian women and women in other ethnic groups. Exposure to this pilot behavioral intervention was associated with increased acceptability and use of chemical barriers without decreased use of male condoms.

Awareness and use of untested barrier methods by HIV-seropositive gay and bisexual men

Little is known about HIV-seropositive men's awareness and use of untested barrier methods during anal intercourse. A sample of 240 HIV-seropositive men (69.2% men of color) completed a self-administered survey that included items on nonoxynol-9 (N-9), female condoms, and the simultaneous use of two male condoms (double bagging). Most participants (79.6%) had heard of N-9 being used to prevent HIV transmission during anal intercourse. Of these, 20.0% rated N-9 as more effective than condoms, and 14.6% had used N-9 instead of condoms. Fewer men (35.4%) were aware of female condoms being used during anal intercourse. Overall, few respondents (5.4%) had used female condoms; 53.8% of whom rated the device as more pleasurable than male condoms. Most men (69.6%) had heard of double bagging, and 35.2% had engaged in this practice. Of these, 45.1% rated the practice as less pleasurable than using a single condom. Few associations were observed between participant characteristics and the awareness or use of these barrier methods. The widespread use of these untested methods emphasizes the urgent need to further educate HIV-seropositive men about the potential risks of N-9 use and to test the effectiveness of other strategies that may serve as alternatives to male condom use.

Microbicide research and development--where to?

PURPOSE

Against the backdrop of increasing numbers of HIV infections in women and the limitations of current safer sex messages, several calls have been made for the development of women-initiated methods of prevention as an essential component of the armamentarium to reduce women's vulnerability of acquiring infection with HIV. An effective microbicide is a critical survival tool in instances and situations where existing proven prevention strategies have failed to be adopted.

METHOD

The results of published N-9 clinical trials in terms of anti-HIV activity, safety data, and anti-sexually transmitted infection (STI) activity are discussed.

RESULTS

There is no evidence of efficacy against HIV in three clinical trials, there is scanty evidence for protection against STIs, and there is considerable evidence of dose-related adverse effects.

CONCLUSION

During this time, a vast array of potential microbicides with differing modes of action have been discovered, and some have undergone preclinical and early clinical testing. Effort, time, and resources might be better spent on advancing preclinical and clinical testing of these other candidate microbicides.

Sodium dodecyl sulfate and C31G as microbicidal alternatives to nonoxynol 9: comparative sensitivity of primary human vaginal keratinocytes

A broad-spectrum vaginal microbicide must be effective against a variety of sexually transmitted disease pathogens and be minimally toxic to the cell types found within the vaginal epithelium, including vaginal keratinocytes. We assessed the sensitivity of primary human vaginal keratinocytes to potential topical vaginal microbicides nonoxynol-9 (N-9), C31G, and sodium dodecyl sulfate (SDS). Direct immunofluorescence and fluorescence-activated cell sorting analyses demonstrated that primary vaginal keratinocytes expressed epithelial cell-specific keratin proteins. Experiments that compared vaginal keratinocyte sensitivity to each agent during a continuous, 48-h exposure demonstrated that primary vaginal keratinocytes were almost five times more sensitive to N-9 than to either C31G or SDS. To evaluate the effect of multiple microbicide exposures on cell viability, primary vaginal keratinocytes were exposed to N-9, C31G, or SDS three times during a 78-h period. In these experiments, cells were considerably more sensitive to C31G than to N-9 or SDS at lower concentrations within the range tested. When agent concentrations were chosen to result in an endpoint of 25% viability after three daily exposures, each exposure decreased cell viability at the same constant rate. When time-dependent sensitivity during a continuous 48-h exposure was examined, exposure to C31G for 18 h resulted in losses in cell viability not caused by either N-9 or SDS until at least 24 to 48 h. Cumulatively, these results reveal important variations in time- and concentration-dependent sensitivity to N-9, C31G, or SDS within populations of primary human vaginal keratinocytes cultured in vitro. These investigations represent initial steps toward both in vitro modeling of the vaginal microenvironment and studies of factors that impact the in vivo efficacy of vaginal topical microbicides.