The paradoxical effects of using antiretroviral-based microbicides to control HIV epidemics

Population-level mathematical modeling of antimicrobial resistance: a systematic review

BACKGROUND

Mathematical transmission models are increasingly used to guide public health interventions for infectious diseases, particularly in the context of emerging pathogens; however, the contribution of modeling to the growing issue of antimicrobial resistance (AMR) remains unclear. Here, we systematically evaluate publications on population-level transmission models of AMR over a recent period (2006-2016) to gauge the state of research and identify gaps warranting further work.

METHODS

We performed a systematic literature search of relevant databases to identify transmission studies of AMR in viral, bacterial, and parasitic disease systems. We analyzed the temporal, geographic, and subject matter trends, described the predominant medical and behavioral interventions studied, and identified central findings relating to key pathogens.

RESULTS

We identified 273 modeling studies; the majority of which (> 70%) focused on 5 infectious diseases (human immunodeficiency virus (HIV), influenza virus, Plasmodium falciparum (malaria), Mycobacterium tuberculosis (TB), and methicillin-resistant Staphylococcus aureus (MRSA)). AMR studies of influenza and nosocomial pathogens were mainly set in industrialized nations, while HIV, TB, and malaria studies were heavily skewed towards developing countries. The majority of articles focused on AMR exclusively in humans (89%), either in community (58%) or healthcare (27%) settings. Model systems were largely compartmental (76%) and deterministic (66%). Only 43% of models were calibrated against epidemiological data, and few were validated against out-of-sample datasets (14%). The interventions considered were primarily the impact of different drug regimens, hygiene and infection control measures, screening, and diagnostics, while few studies addressed de novo resistance, vaccination strategies, economic, or behavioral changes to reduce antibiotic use in humans and animals.

CONCLUSIONS

The AMR modeling literature concentrates on disease systems where resistance has been long-established, while few studies pro-actively address recent rise in resistance in new pathogens or explore upstream strategies to reduce overall antibiotic consumption. Notable gaps include research on emerging resistance in Enterobacteriaceae and Neisseria gonorrhoeae; AMR transmission at the animal-human interface, particularly in agricultural and veterinary settings; transmission between hospitals and the community; the role of environmental factors in AMR transmission; and the potential of vaccines to combat AMR.

Degradable bioadhesive nanoparticles for prolonged intravaginal delivery and retention of elvitegravir

New methods for long-lasting protection against sexually transmitted disease, such as the human immunodeficiency virus (HIV), are needed to help reduce the severity of STD epidemics, especially in developing countries. Intravaginal delivery of therapeutics has emerged as a promising strategy to provide women with local protection, but residence times of such agents are greatly reduced by the protective mucus layer, fluctuating hormone cycle, and complex anatomical structure of the reproductive tract. Polymeric nanoparticles (NPs) capable of encapsulating the desired cargo, penetrating through the mucosal surfaces, and delivering agents to the site of action have been explored. However, prolonged retention of polymer carriers and their enclosed materials may also be needed to ease adherence and confer longer-lasting protection against STDs. Here, we examined the fate of two poly (lactic acid)-hyperbranched polyglycerols (PLA-HPG) NP formulations - 1) nonadhesive PLA-HPG NPs (NNPs) and 2) surface-modified bioadhesive NPs (BNPs) - loaded with the antiretroviral elvitegravir (EVG) after intravaginal administration. BNP distribution was widespread throughout the reproductive tract, and retention was nearly 5 times higher than NNPs after 24 h. Moreover, BNPs were found to be highly associated with submucosal leukocytes and epithelial cell populations for up to 48 h after topical application, and EVG was retained significantly better in the vaginal lumen when delivered with BNPs as opposed to NNPs over a 24 h period. Our results suggest that bioadhesive PLA-HPG NPs can greatly improve and prolong intravaginal delivery of agents, which may hold potential in providing sustained protection over longer durations.

Impact of Population Recruitment on the HIV Epidemics and the Effectiveness of HIV Prevention Interventions

Mechanistic mathematical models are increasingly used to evaluate the effectiveness of different interventions for HIV prevention and to inform public health decisions. By focusing exclusively on the impact of the interventions, the importance of the demographic processes in these studies is often underestimated. In this paper, we use simple deterministic models to assess the effectiveness of pre-exposure prophylaxis in reducing the HIV transmission and to explore the influence of the recruitment mechanisms on the epidemic and effectiveness projections. We employ three commonly used formulas that correspond to constant, proportional and logistic recruitment and compare the dynamical properties of the resulting models. Our analysis exposes substantial differences in the transient and asymptotic behavior of the models which result in 47 % variation in population size and more than 6 percentage points variation in HIV prevalence over 40 years between models using different recruitment mechanisms. We outline the strong influence of recruitment assumptions on the impact of HIV prevention interventions and conclude that detailed demographic data should be used to inform the integration of recruitment processes in the models before HIV prevention is considered.

Nanomedicine in the development of anti-HIV microbicides

Prevention plays an invaluable role in the fight against HIV/AIDS. The use of microbicides is considered an interesting potential approach for topical pre-exposure prophylaxis of HIV sexual transmission. The prospects of having an effective product available are expected to be fulfilled in the near future as driven by recent and forthcoming results of clinical trials. Different dosage forms and delivery strategies have been proposed and tested for multiple microbicide drug candidates presently at different stages of the development pipeline. One particularly interesting approach comprises the application of nanomedicine principles to the development of novel anti-HIV microbicides, but its implications to efficacy and safety are not yet fully understood. Nanotechnology-based systems, either presenting inherent anti-HIV activity or acting as drug nanocarriers, may significantly influence features such as drug solubility, stability of active payloads, drug release, interactions between active moieties and virus/cells, intracellular drug delivery, drug targeting, safety, antiviral activity, mucoadhesive behavior, drug distribution and tissue penetration, and pharmacokinetics. The present manuscript provides a comprehensive and holistic overview of these topics as relevant to the development of vaginal and rectal microbicides. In particular, recent advances pertaining inherently active microbicide nanosystems and microbicide drug nanocarriers are discussed.

How Much Do We Know about Drug Resistance Due to PrEP Use? Analysis of Experts' Opinion and Its Influence on the Projected Public Health Impact

BACKGROUND

Randomized controlled trials reported that pre-exposure prophylaxis (PrEP) with tenofovir and emtricitabine rarely selects for drug resistance. However, drug resistance due to PrEP is not completely understood. In daily practice, PrEP will not be used under the well-controlled conditions available in the trials, suggesting that widespread use of PrEP can result in increased drug resistance.

METHODS

We surveyed expert virologists with questions about biological assumptions regarding drug resistance due to PrEP use. The influence of these assumptions on the prevalence of drug resistance and the fraction of HIV transmitted resistance was studied with a mathematical model. For comparability, 50% PrEP-coverage of and 90% per-act efficacy of PrEP in preventing HIV acquisition are assumed in all simulations.

RESULTS

Virologists disagreed on the following: the time until resistance emergence (range: 20-180 days) in infected PrEP users with breakthrough HIV infections; the efficacy of PrEP against drug-resistant HIV (25%-90%); and the likelihood of resistance acquisition upon transmission (10%-75%). These differences translate into projections of 0.6%- 1% and 3.5%-6% infected individuals with detectable resistance 10 years after introducing PrEP, assuming 100% and 50% adherence, respectively. The rate of resistance emergence following breakthrough HIV infection and the rate of resistance reversion after PrEP use is discontinued, were the factors identified as most influential on the expected resistance associated with PrEP. Importantly, 17-23% infected individuals could virologically fail treatment as a result of past PrEP use or transmitted resistance to PrEP with moderate adherence.

CONCLUSIONS

There is no broad consensus on quantification of key biological processes that underpin the emergence of PrEP-associated drug resistance. Despite this, the contribution of PrEP use to the prevalence of the detectable drug resistance is expected to be small. However, individuals who become infected despite the use of PrEP should be closely monitored due to higher risk of virological failure when initiating antiretroviral treatment in the future.

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.

Comparing the cost effectiveness of harm reduction strategies: a case study of the Ukraine

Background

Harm reduction strategies commonly include needle and syringe programmes (NSP), opioid substitution therapy (OST) and interventions combining these two strategies. Despite the proven effectiveness of harm-reduction strategies in reducing human immunodeficiency virus (HIV) infection among injecting drug users (IDUs), no study has compared the cost-effectiveness of these interventions, nor the incremental cost effectiveness of combined therapy. Using data from the Global Fund, this study compares the cost-effectiveness of harm reduction strategies in Eastern Europe and Central Asia, using the Ukraine as a case study.

Methods

A Markov Monte Carlo simulation is carried out using parameters from the literature and cost data from the Global Fund. Effectiveness is presented as both QALYs and infections averted. Costs are measured in 2011 US dollars.

Results

The Markov Monte Carlo simulation estimates the cost-effectiveness ratio per infection averted as $487.4 [95% CI: 488.47-486.35] in NSP and $1145.9 [95% CI: 1143.39-1148.43] in OST. Combined intervention is more costly but more effective than the alternative strategies with a cost effectiveness ratio of $851.6[95% CI: 849.82-853.55].

The ICER of the combined strategy is $1086.9/QALY [95% CI: 1077.76:1096.24] compared with NSP, and $461.0/infection averted [95% CI: 452.98:469.04] compared with OST. These results are consistent with previous studies.

Conclusions

Despite the inherent limitations of retrospective data, this study provides evidence that harm-reduction interventions are a cost-effective way to reduce HIV prevalence. More research on into cost effectiveness in different settings, and the availability of fiscal space for government uptake of programmes, is required.

Network effects of risk behavior change following prophylactic interventions

We formulated a network-based model to understand how risk behavior change in conjunction with failure of prophylactic interventions can lead to unintended outcomes where "less (intervention) is more (effective)." Our model captures the distinction between one- and two-sided risk behavior change. In one-sided situations (e.g. influenza/H1N1) it is sufficient for either individual in an interaction to exhibit risk behavior change whereas in two-sided situations (e.g. AIDS/HIV) it is necessary for both individuals in the interaction to exhibit risk behavior change, for a potential transmission of the disease. A central discovery is that this phenomenon occurs at differing levels of intervention coverage depending upon the "sidedness" of the interaction. We find that for one-sided interactions, sufficiently high vaccination coverage is necessary for mitigating the effects of risk behavior; for two-sided interactions, it is essential to combine prophylactic treatments with programs aimed at reducing risky behavior. Furthermore, again dependent on the "sidedness," targeting highly connected nodes can be strictly worse than uniformly random interventions at the same level of coverage.

Microbicides: topical prevention against HIV

Microbicides represent a potential intervention strategy for preventing HIV transmission. Vaginal microbicides would meet the need for a discreet method that women could use to protect themselves against HIV. Although early-generation microbicides failed to demonstrate efficacy, newer candidates are based on more potent antiretroviral (ARV) products. Positive data from the CAPRISA 004 trial of tenofovir gel support use in women and represent a turning point for the field. This article reviews current progress in development of ARV-based microbicides. We discuss the consensus on selection criteria, the potential for drug resistance, rationale for drug combinations, and the use of pharmacokinetic (PK)/pharmacodynamic (PD) assessment in product development. The urgent need for continued progress in development of formulations for sustained delivery is emphasized. Finally, as the boundaries between different prevention technologies become increasingly blurred, consideration is given to the potential synergy of diverse approaches across the prevention landscape.

Beating the placebo in HIV prevention efficacy trials: the role of the minimal efficacy bound

OBJECTIVES

To produce an effect on the HIV epidemic, preventive interventions need to achieve a minimum level of efficacy to offset potential indirect effects such as an increase in risky behavior. The current generation of HIV prevention trials on oral preexposure prophylaxis and on vaginal microbicides were designed using different set points for minimum individual-level efficacy (MIE). Some trials were designed not only to show superiority over placebo but also to rule out lower efficacies. The MIE has a substantial impact on the size and cost of a trial. Ideally, the MIE should be chosen to reduce uncertainty in the estimation of population-level effects. In this article, we investigate the effect of MIE on estimates of population-level impact to better inform trial design.

METHODS

We used mathematical model simulations assuming various rates of efficacy obtained from trials and different MIEs to study the impact of wide-scale interventions on 2 public health indicators.

RESULTS

Implementation factors were the main drivers of uncertainty in public health indicators for an intervention, although MIE also contributed. The level of uncertainty introduced by the MIE was substantially lower than that of the other factors.

CONCLUSIONS

Investigators in clinical trials have set the MIE solely on the basis of potential public health impact. However, the substantial increase in trial costs associated with a large MIE is unlikely to be justified. These additional funds would be better spent in evaluating more critical implementation factors that cannot be assessed in clinical trials.

Mathematical insights in evaluating state dependent effectiveness of HIV prevention interventions

Mathematical models have been used to simulate HIV transmission and to study the use of preexposure prophylaxis (PrEP) for HIV prevention. Often a single intervention outcome over 10 years has been used to evaluate the effectiveness of PrEP interventions. However, different metrics express a wide variation over time and often disagree in their forecast on the success of the intervention. We develop a deterministic mathematical model of HIV transmission and use it to evaluate the public-health impact of oral PrEP interventions. We study PrEP effectiveness with respect to different evaluation methods and analyze its dynamics over time. We compare four traditional indicators, based on cumulative number or fractions of infections prevented, on reduction in HIV prevalence or incidence and propose two additional methods, which estimate the burden of the epidemic to the public-health system. We investigate the short and long term behavior of these indicators and the effects of key parameters on the expected benefits from PrEP use. Our findings suggest that public-health officials considering adopting PrEP in HIV prevention programs can make better informed decisions by employing a set of complementing quantitative metrics.

Impact of Pill Sharing on Drug Resistance Due to a Wide-Scale Oral Prep Intervention in Generalized Epidemics

BACKGROUND

The first antiretroviral drug (Truvada) to be used as a pre-exposure prophylaxis (PrEP) in preventing HIV transmission is about to be approved. Behavioral studies suggest that a portion of users may share anti-retroviral drugs with sex partners, family, or friends. Pill sharing will decrease PrEP efficacy and adherence level, and potentially create an environment favorable for the development of drug resistance. We aim to evaluate the potential impact of pill sharing on the PrEP effectiveness and on the rates of drug-resistance development in heterosexual populations.

METHODS

A transmission dynamic model was used to assess the population-level impact of oral PrEP. The fractions of new HIV infections prevented (CPF), drug resistance prevalence and the proportion of new infections in which drug-resistant HIV is transmitted (TDR) are evaluated over fixed time periods. The influence of different factors on CPF and TDR is studied through simulations, using epidemic parameters representative of the countries in Sub-Saharan Africa.

RESULTS

Without pill sharing, a 70% efficacious PrEP used consistently by 60% of uninfected individuals prevents 52.8% (95% CI 49.4%-56.4%) of all new HIV infections over ten years with drug-resistant HIV transmitted in 2.2% of the new infections. Absolute CPF may vary by 9% if up to 20% of the users share PrEP while the level of TDR and total resistance prevalence may increase by up to 6-fold due to pill sharing in some intervention scenarios.

CONCLUSION

Pill sharing may increase the PrEP coverage level achieved in the population but it also affects the PrEP efficacy for the users who do not follow the prescribed schedule. More importantly, it creates a pool of untracked users who remain unreached by the effort to avoid sub-optimal PrEP usage by infected people. This increases substantially the potential risk of drug resistance in the population.

A perspective on progress and gaps in HIV prevention science

In the past few years, the transdisciplinary field of HIV prevention has reached several milestones. Topically applied tenofovir gel provided significant protection from sexual transmission of HIV in a large-scale clinical trial and oral Truvada (emtricitabine/tenofovir disoproxil fumarate) was recently approved for preexposure prophylaxis (PrEP) following two successful clinical trials in men and women. These achievements are tempered by the disappointing results of other clinical trials, which highlight the complexities of prevention research. In this perspective, we discuss scientific and developmental gaps for topical chemoprophylaxis of the sexual transmission of HIV, which depends on the complex interactions between the pharmacokinetics and pharmacodynamics of drugs, formulation and delivery systems, anatomic site of transmission, and host mucosal immune defenses. Despite the considerable time and resources devoted to unraveling the initial steps in sexual transmission of HIV, current knowledge is based on animal models and human explanted tissue, which may not fully recapitulate what happens clinically. Understanding these events, including the role that sex hormones, semen, and mucosal secretions play in transmission, and the interplay between innate immunity, the mucosal environment, and drug efficacy is paramount. This drives some of the most pressing questions in the field.

Intravaginal practices and microbicide acceptability in Papua New Guinea: implications for HIV prevention in a moderate-prevalence setting

BACKGROUND

The acceptability of female-controlled biomedical prevention technologies has not been established in Papua New Guinea, the only country in the Pacific region experiencing a generalised, moderate-prevalence HIV epidemic. Socio-cultural factors likely to impact on future product uptake and effectiveness, such as women's ability to negotiate safer sexual choices, and intravaginal hygiene and menstrual practices (IVP), remain unclear in this setting.

METHODS

A mixed-method qualitative study was conducted among women and men attending a sexual health clinic in Port Moresby. During in-depth interviews, participants used copies of a hand-drawn template to indicate how they wash/clean the vulva and/or vagina. Interviewers pre-filled commercially available vaginal applicators with 2-3mL KY Jelly® to create a surrogate vaginal microbicide product, which was demonstrated to study participants.

RESULTS

A total of 28 IDIs were conducted (women=16; men=12). A diverse range of IVP were reported. The majority of women described washing the vulva only with soap and water as part of their daily routine; in preparation for sex; and following sexual intercourse. Several women described cleaning inside the vagina using fingers and soap at these same times. Others reported cleaning inside the vagina using a hose connected to a tap; using vaginal inserts, such as crushed garlic; customary menstrual 'steaming' practices; and the use of material fragments, cloth and newspaper to absorb menstrual blood. Unprotected sex during menstruation was common. The majority of both women and men said that they would use a vaginal microbicide gel for HIV/STI protection, should a safe and effective product become available. Microbicide use was considered most appropriate in 'high-risk' situations, such as sex with non-regular, transactional or commercial partners. Most women felt confident that they would be able to negotiate vaginal microbicide use with male sexual partners but if necessary would be prepared to use product covertly.

CONCLUSIONS

Notional acceptability of a vaginal microbicide gel for HIV/STI prevention was high among both women and men. IVP were diverse in nature, socio-cultural dimensions and motivators. These factors are likely to impact on the future acceptability and uptake of vaginal microbicides and other biomedical HIV prevention technologies in this setting.

Modelling the epidemiological impact of scaling up HIV testing and antiretroviral treatment in China

BACKGROUND

The HIV epidemic in China has been increasing. In response, a 5-year action plan in China has prioritised the scale-up of HIV testing and treatment.

METHODS

We use a mathematical model to reproduce HIV epidemic trends in China and to forecast epidemic trends according to current conditions or increases in the rate of HIV testing or roll-out of antiretroviral therapy.

RESULTS

We show that the epidemic in China could be expected to experience a 2.5-fold expansion over the next 5 years such that ~1.8 million people will be infected with HIV in China by 2015. However, increasing testing and treatment rates can have substantial epidemiological benefits. For example, a four-fold increase in testing rates may avert more than 42000 HIV infections and 11000 deaths over the next 5 years. A 10-fold increase in the treatment rate could decrease the number of HIV-related deaths by 58% and the number of new infections by one-quarter by 2015.

CONCLUSIONS

Increasing HIV testing and treatment are important public health strategies for prevention.

LIPOSOMAL GELS FOR VAGINAL DELIVERY OF THE MICROBICIDE MC-1220: PREPARATION AND IN VIVO VAGINAL TOXICITY AND PHARMACOKINETICS

MC-1220 is a highly potent and selective non-nucleoside reverse transcriptase inhibitor (NNRTI) of HIV. The objective is to develop formulations for the vaginal delivery of MC-1220 and characterize them in vitro and in vivo (drug uptake, pharmacokinetics, toxicokinetics and vaginal irritation/inflammation). Due to the low aqueous solubility of MC-1220, emulsion-type and liposomal formulations of MC-1220 were developed. After rheological property adjustment (by gelling agents), the toxicity of two types of vaginal formulations of MC-1220 (emulsion [E] and liposomal [LIP] formulations) at 0.1% (E and LIP) and 0.5% (LIP) drug concentration, towards the vaginal mucosa as well as the absorption of the drug through the vaginal epithelium were investigated, after single and multiple administrations in New Zealand white NZW rabbits, for 10 days. Vaginal irritation was found to be within the acceptable range and always lower compared to the irritation caused by positive control formulation (nonoxynol-9), for all the formulation types (and concentrations evaluated). Pharmacokinetic values measured showed that the 0.1% LIP formulation was faster and better absorbed compared to the similar concentration E formulation, although most differences were not significant due to high variations. In conclusion, both types of formulations can be considered as safe for prolonged vaginal administration of MC-1220 or other drugs.

HIV treatment as prevention: principles of good HIV epidemiology modelling for public health decision-making in all modes of prevention and evaluation

Public health responses to HIV epidemics have long relied on epidemiological modelling analyses to help prospectively project and retrospectively estimate the impact, cost-effectiveness, affordability, and investment returns of interventions, and to help plan the design of evaluations. But translating model output into policy decisions and implementation on the ground is challenged by the differences in background and expectations of modellers and decision-makers. As part of the PLoS Medicine Collection "Investigating the Impact of Treatment on New HIV Infections"--which focuses on the contribution of modelling to current issues in HIV prevention--we present here principles of "best practice" for the construction, reporting, and interpretation of HIV epidemiological models for public health decision-making on all aspects of HIV. Aimed at both those who conduct modelling research and those who use modelling results, we hope that the principles described here will become a shared resource that facilitates constructive discussions about the policy implications that emerge from HIV epidemiology modelling results, and that promotes joint understanding between modellers and decision-makers about when modelling is useful as a tool in quantifying HIV epidemiological outcomes and improving prevention programming.

Sex-specific immunization for sexually transmitted infections such as human papillomavirus: insights from mathematical models

BACKGROUND

Sex-specific differences regarding the transmissibility and the course of infection are the rule rather than the exception in the epidemiology of sexually transmitted infections (STIs). Human papillomavirus (HPV) provides an example: disease outcomes differ between men and women, as does the potential for transmission to the opposite sex. HPV vaccination of preadolescent girls was recently introduced in many countries, and inclusion of boys in the vaccination programs is being discussed. Here, we address the question of whether vaccinating females only, males only, or both sexes is the most effective strategy to reduce the population prevalence of an STI like HPV.

METHODS AND FINDINGS

We use a range of two-sex transmission models with varying detail to identify general criteria for allocating a prophylactic vaccine between both sexes. The most effective reduction in the population prevalence of infection is always achieved by single-sex vaccination; vaccinating the sex with the highest prevaccine prevalence is the preferred strategy in most circumstances. Exceptions arise only when the higher prevaccine prevalence is due to a substantially lower rate of natural immunity, or when natural immunity is lifelong, and a prolonged duration of infectiousness coincides with increased transmissibility. Predictions from simple models were confirmed in simulations based on an elaborate HPV transmission model. Our analysis suggests that relatively inefficient genital transmission from males to females might render male vaccination more effective in reducing overall infection levels. However, most existing HPV vaccination programs have achieved sufficient coverage to continue with female-only vaccination.

CONCLUSIONS

Increasing vaccine uptake among preadolescent girls is more effective in reducing HPV infection than including boys in existing vaccination programs. As a rule, directing prophylactic immunization at the sex with the highest prevaccine prevalence results in the largest reduction of the population prevalence.

Topical nonnucleoside reverse transcriptase inhibitor MC 1220 partially prevents vaginal RT-SHIV infection of macaques

The availability of an effective vaginal microbicide would be a major step toward containment of HIV transmission as well as allowing women self-protection against HIV infection. Here we evaluated the efficacy of vaginal application of the potent nonnucleoside reverse transcriptase inhibitor (NNRTI) MC 1220 against vaginal challenge of macaques with RT-SHIV, a chimeric simian immunodeficiency virus (SIV) containing the reverse transcriptase (RT) gene of HIV-1. Challenge infection of monkeys with RT-SHIV currently represents the only nonhuman primate model available to test the anti-HIV-1 effects of NNRTIs. Two different gel formulations containing different MC 1220 concentrations were evaluated for efficacy in female rhesus macaques exposed to RT-SHIV. Five groups of five animals each were treated with two different gel compositions containing no drug, 0.1% or 0.5% MC 1220, followed by vaginal RT-SHIV challenge 30 min later. One animal in each group treated with the low concentration of MC 1220 as well as one control animal remained uninfected after vaginal challenge. By contrast, three of the animals receiving 0.5% MC 1220 remained uninfected, suggesting a threshold of the drug. Despite being negative for plasma viral RNA and absence of seroconversion, almost all uninfected animals exhibited SIV-specific T cells, either in the periphery or in lymph nodes draining the portal of virus entry. Our results make MC 1220 a promising compound for further development as a topical microbicide and warrant additional testing with improved formulation, long-lasting vaginal delivery systems, or even combinations with other inhibitors.

Modelling the impact of antiretroviral therapy on the epidemic of HIV

Thirty years after HIV first appeared it has killed close to 30 million people but transmission continues unchecked. In 2009, an estimated 1.8 million lives were lost and 2.6 million more people were infected with HIV [1]. To cut transmission, many social, behavioural and biomedical interventions have been developed, tested and tried but have had little impact on the epidemic in most countries. One substantial success has been the development of combination antiretroviral therapy (ART) that reduces viral load and restores immune function. This raises the possibility of using ART not only to treat people but also to prevent new HIV infections. Here we consider the impact of ART on the transmission of HIV and show how it could help to control the epidemic. Much needs to be known and understood concerning the impact of early treatment with ART on the prognosis for individual patients and on transmission. We review the current literature on factors associated with modelling treatment for prevention and illustrate the potential impact using existing models. We focus on generalized epidemics in sub- Saharan Africa, with an emphasis on South Africa, where transmission is mainly heterosexual and which account for an estimated 17% of all people living with HIV. We also make reference to epidemics among men who have sex with men and injection drug users where appropriate. We discuss ways in which using treatment as prevention can be taken forward knowing that this can only be the beginning of what must become an inclusive dialogue among all of those concerned to stop acquired immune deficiency syndrome (AIDS).

Estimates of human immunodeficiency virus incidence among female sex workers in north central Nigeria: implications for HIV clinical trials

We estimated the HIV incidence among commercial female sex workers (FSWs) in north central Nigeria using bimodal methodology. Using a cross-sectional study design, a total of 900 active FSWs between the ages of 18 and 35 years were recruited from 52 brothels within Nasarawa State, Nigeria. A rapid test algorithm was used to determine their HIV status. The BED IgG-Capture enzyme immunoassay (CEIA) was applied on the HIV-seropositive samples to detect recent HIV-1 infection for the estimation of incidence among those with HIV infection. Of the 900 FSWs tested, 335 (37.2%) were found to be positive for HIV. Of these, 63 showed evidence of recent infection. Using two third-generation BED analysis approaches that account for false-recent rate, an annualized adjusted HIV incidence of 11.97% (95% CI: 8.51-15.43%) and 12.36% (95% CI: 8.18-16.34%) was observed; difference P>0.05. In addition, 875 (97.2%) of the FSWs readily agreed to participate in HIV clinical trials. We have developed the expertise and infrastructure necessary for clinical trial investigations in sub-Saharan Africa. We have recorded a high proportion of recent HIV infections among FSWs in Nigeria and also provided an enabling environment for future studies of HIV prevention methods.

Modeling the gender-specific impact of vaginal microbicides on HIV transmission

Vaginal microbicides (VMB) are currently among the few women-initiated biomedical interventions for preventing heterosexual transmission of HIV. In this paper we use a deterministic model of HIV transmission to assess the public-health benefits of a VMB intervention and evaluate its gender-specific impact over short (initial) and extended periods of time. We define two distinct quantitative benefit ratios (QBRs) based on infections prevented in men and women to create and study regions of male advantage in different parameter spaces. Our analysis exposes complicated temporal correlations between the QBRs and series of pre-intervention (e.g., HIV acquisition risks per act) and intervention parameters (e.g., VMB efficacy mechanisms, rates of resistance development and reversion) and indicates that different QBRs may often disagree on the gender distribution of the benefits from a VMB intervention. We also outline the strong influence of some modeling assumptions on the reported results and conclude that the assessment of VMB and other biomedical interventions must be based on more comprehensive analyses than calculations of infections prevented over a fixed period of time.

HIV transmission: time for translational studies to bridge the gap

More than 7000 new HIV infections are documented each day worldwide. In this Perspective, we dissect new results from a large clinical trial showing that genital and plasma HIV-1 RNA loads predict the risk of heterosexual transmission and that genital tract viral RNA load does so independently of plasma viral load. Furthermore, beyond its defined study end points, this well-conducted trial identified new research directions that should be pursued in smaller intensive basic and translational studies.

The future of microbicides

There is an urgent need to develop vaginal microbicides to empower women to better control their own sexual life and to protect themselves against HIV and other sexually transmitted infections (STIs). Prevention of STIs with its 330 million cases a year would have a great global health impact. Because of their anatomy, women are up to 8 times more susceptible than men to STIs including HIV. Women who can't negotiate condom use with their male partners have no means of protecting themselves from these infections. In the last few years, especially after the recent failures of several microbicides in Phase III trials, there was increasing pressure from those favoring the use of a more targeted approach to introduce marketed antiretroviral drugs (ARVs) into microbicides. This Pre-Exposure Prophylaxis (PrEP) concept which targets only HIV using specific ARVs contrasts with the primary approach of broad spectrum microbicides which aimed at offering universal protection against several sexually transmitted pathogens. However, before using ARVs as PrEP for HIV prevention, there are still many important issues to consider. In this article, we compare both strategies, while reviewing the last 15 years of microbicide research and its future.

In vitro surfactant structure-toxicity relationships: implications for surfactant use in sexually transmitted infection prophylaxis and contraception

BACKGROUND

The need for woman-controlled, cheap, safe, effective, easy-to-use and easy-to-store topical applications for prophylaxis against sexually transmitted infections (STIs) makes surfactant-containing formulations an interesting option that requires a more fundamental knowledge concerning surfactant toxicology and structure-activity relationships.

METHODOLOGY/PRINCIPAL FINDINGS

We report in vitro effects of surfactant concentration, exposure time and structure on the viability of mammalian cell types typically encountered in the vagina, namely, fully polarized and confluent epithelial cells, confluent but non-polarized epithelial-like cells, dendritic cells, and human sperm. Representatives of the different families of commercially available surfactants--nonionic (Triton X-100 and monolaurin), zwitterionic (DDPS), anionic (SDS), and cationic (C(n)TAB (n = 10 to 16), C(12)PB, and C(12)BZK)--were examined. Triton X-100, monolaurin, DDPS and SDS were toxic to all cell types at concentrations around their critical micelle concentration (CMC) suggesting a non-selective mode of action involving cell membrane destabilization and/or destruction. All cationic surfactants were toxic at concentrations far below their CMC and showed significant differences in their toxicity toward polarized as compared with non-polarized cells. Their toxicity was also dependent on the chemical nature of the polar head group. Our results suggest an intracellular locus of action for cationic surfactants and show that their structure-activity relationships could be profitably exploited for STI prophylaxis in vaginal gel formulations. The therapeutic indices comparing polarized epithelial cell toxicity to sperm toxicity for all surfactants examined, except C(12)PB and C(12)BZK, does not justify their use as contraceptive agents. C(12)PB and C(12)BZK are shown to have a narrow therapeutic index recommending caution in their use in contraceptive formulations.

CONCLUSIONS/SIGNIFICANCE

Our results contribute to understanding the mechanisms involved in surfactant toxicity, have a predictive value with regard to their safety, and may be used to design more effective and less harmful surfactants for use in topical applications for STI prophylaxis.

Human immunodeficiency virus type 1 resistance or cross-resistance to nonnucleoside reverse transcriptase inhibitors currently under development as microbicides

Microbicides based on nonnucleoside reverse transcriptase inhibitors (NNRTIs) are currently being developed to protect women from HIV acquisition through sexual contact. However, the large-scale introduction of these products raises two major concerns. First, when these microbicides are used by undiagnosed HIV-positive women, they could potentially select for viral resistance, which may compromise subsequent therapeutic options. Second, NNRTI-based microbicides that are inactive against NNRTI-resistant strains might promote the selective transmission of these viruses. In order to address these concerns, drug resistance was selected in vitro by the serial passage of three viral isolates from subtypes B and C and CRF02_AG (a circulating recombinant form) in activated peripheral blood mononuclear cells (PBMCs) under conditions of increasing concentrations of three NNRTIs (i.e., TMC120, UC781, and MIV-160) that are currently being developed as candidate microbicides. TMC120 and MIV-160 displayed a high genetic barrier to resistance development, whereas resistance to UC781 emerged rapidly, similarly to efavirenz and nevirapine. Phenotypically, the selected viruses appeared to be highly cross-resistant to current first-line therapeutic NNRTIs (i.e., delavirdine, nevirapine, and efavirenz), although they retained some susceptibility to the more recently developed NNRTIs lersivirine and etravirine. The ability of UC781, TMC120, and MIV-160 to inhibit the in vitro-selected NNRTI-resistant viruses was also limited, although residual activity could be observed for the candidate microbicide NNRTI MIV-170. Interestingly, only four p2/p7/p1/p6/PR/RT/INT recombinant NNRTI-resistant viruses (i.e., TMC120-resistant VI829, EFV-resistant VI829, MIV-160-resistant VI829, and EFV-resistant MP568) showed impairments in replicative fitness. Overall, these in vitro analyses demonstrate that due to potential cross-resistance, the large-scale introduction of single-NNRTI-based microbicides should be considered with caution.

What do mathematical models tell us about the emergence and spread of drug-resistant HIV?

PURPOSE OF REVIEW

To discuss recent HIV epidemic models examining the transmission of antiretroviral (ARV) drug resistance.

RECENT FINDINGS

A relatively small number of recent transmission models have investigated ARV resistance in the context of therapeutic, combined ART (cART); ARV-vaginal microbicides (ARV-VMB); and oral pre-exposure prophylaxis (PrEP). Models of cART use have highlighted potential concerns about future resistance transmission, particularly in resource-constrained settings, and have emphasized the benefits of viral load monitoring in limiting resistance spread. PrEP models have concluded that inadvertent use by HIV-infected individuals could increase resistance prevalence, and that risk compensation by PrEP users could limit their beneficial effects on HIV transmission. ARV-VMB models have demonstrated that whereas resistance can reduce prophylactic effectiveness in preventing HIV acquisition of female ARV-VMB users, it may concomitantly benefit users' male partners if the resistant strains that female users acquire are less transmissible than wild-type strains. The models have examined the balance between these two factors at the population level.

SUMMARY

Recent HIV transmission models have adopted a wide assortment of structures and assumptions to explore drug resistance in the context of different ARV interventions in various settings. There is a need for future work emphasizing the simultaneous effects of multiple ARV interventions, as well as the public health impact of resistance, not just its prevalence.

Vaginal microbicide gel for delivery of IQP-0528, a pyrimidinedione analog with a dual mechanism of action against HIV-1

Pyrimidinediones, a novel class of compounds, have previously been shown to possess antiviral activity at nanomolar concentrations. One member of this class of compounds, IQP-0528, was selected as the lead molecule for formulation development owing to its stability at physiologically relevant conditions, wide therapeutic window, and antiviral activity in the nanomolar range. Here, we report the development of two vaginal gels--3.0% hydroxyethyl cellulose (HEC) formulation and a 0.65% Carbopol formulation--for the sustained delivery of IQP-0528. Stability studies under accelerated conditions confirmed the chemical stability of IQP-0528 and mechanical stability of the gel formulation for 3 months. In vitro release studies revealed that diffusion-controlled release of IQP-0528 occurred over 6 h, with an initial lag time of approximately 1 h. Based on the drug release profile, the 3.0% HEC gel was selected as the lead formulation for safety and activity evaluations. The in vitro and ex vivo safety evaluations showed no significant loss in cell viability or significant inflammatory response after treatment with a 3.0% HEC gel containing 0.25% IQP-0528. In an in vitro HIV-1 entry inhibition assay, the lead formulation showed an 50% effective concentration of 0.14 μg/ml for gel in culture media, which corresponds to ∼0.001 μM IQP-0528. The antiviral activity was further confirmed by using polarized cervical explants, in which the formulation showed complete protection against HIV infection. In summary, these results are encouraging and warrant further evaluation of IQP-0528 gel formulations in in vivo models, as well as the development of alternative formulations for the delivery of IQP-0528 as a microbicide.

Mapping the architecture of the HIV-1 Tat circuit: A decision-making circuit that lacks bistability and exploits stochastic noise

Upon infection of a CD4(+) T cell, HIV-1 appears to 'choose' between two alternate fates: active replication or a long-lived dormant state termed proviral latency. A transcriptional positive-feedback loop generated by the HIV-1 Tat protein appears sufficient to mediate this decision. Here, we describe a coupled wet-lab and computational approach that uses mathematical modeling and live-cell time-lapse microscopy to map the architecture of the HIV-1 Tat transcriptional regulatory circuit and generate predictive models of HIV-1 latency. This approach provided the first characterization of a 'decision-making' circuit that lacks bistability and instead exploits stochastic fluctuations in cellular molecules (i.e. noise) to generate a decision between an on or off transcriptional state.

Should microbicides be controlled by women or by physicians?

In 2007, nearly 7000 new cases of HIV infection occurred each day. There is a constant increase in the proportion of women newly infected with HIV in the global population; this increase is particularly high in some areas of the world such as sub-Saharan Africa. Microbicides are products that are being developed to empower women against HIV. First- and second-generation microbicides are broad-spectrum products that include surface active agents, vaginal defense enhancers, and blocking agents. Third-generation microbicides are HIV-specific and include replication and entry inhibitors formulated as gels or as vaginal rings. However, there is a concern that antiretroviral-based microbicides could lead to drug resistance if they are used by HIV-positive women who are unaware of their HIV status. To reach the highest number of women possible, microbicides should be available over-the-counter, which might not be the case with antiretroviral-based formulations. In contrast, non-antiretroviral-based microbicides will have the advantage of being initiated and controlled by women themselves and they will not jeopardize the use of life-saving drugs.

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.

The last decade of microbicide clinical trials in Africa: from hypothesis to facts

Microbicide clinical trials have dominated biomedical HIV prevention research in the past decade. Two generations of microbicides have gone through large-scale human clinical trials. Candidate microbicides assessed in clinical trials in Africa have fallen into the categories of surfactants, polyanionic entry inhibitors, or vaginal milieu protectors. These include compounds such as nonoxynol-9, SAVVY, cellulose sulphate, Carraguard, PRO 2000, and BufferGel. Disappointingly, none of the products have shown efficacy against HIV. Each successive trial has benefited from the lessons learned in preceding trials. The trials have provided important lessons in basic, clinical, social, and behavioural science. More importantly, we have learned that the concept of a vaginally inserted product for HIV prevention is acceptable by women. We have now reached an end of an era of clinical testing with non-HIV-specific microbicides and move forward to testing novel strategies of antiretroviral therapeutic products such as preexposure prophylaxis (PrEP) for HIV prevention. PrEP for vaginal administration in various formulations is being tested to continue our commitment to providing more HIV prevention options to millions of women worldwide.

Microbicide research: current and future directions

PURPOSE OF REVIEW

Microbicide research has been in the forefront of scientific literature in recent months. Results of large-scale clinical trials have been announced with resultant investigations into the factors that may have contributed to the disappointing outcomes of the most promising candidates. This review takes into consideration clinical, basic scientific and behavioural research published on microbicides in the past 12-18 months.

RECENT FINDINGS

Two trials testing PRO 2000, a sulphated polymer, suggested that it has no effect on HIV. Basic science research revealed several facts such as the loss of antiviral activity of microbicides in the presence of seminal plasma. Methodological models suggested that dilution factors might impact on measures of efficacy. Advancement into safety testing of highly specific antiretroviral products such as tenofovir and UC781 for both rectal and vaginal use shows promise. Development of drug delivery systems such as intravaginal rings may alleviate some of the adherence challenges faced when using coitally dependant products.

SUMMARY

In the recent past, microbicide research has had disappointing outcomes. However, it has also provided a better understanding of factors that may reduce effectiveness of promising products, enabling the field to be better equipped to select and test new products.

Candidate vaginal microbicides with activity against Chlamydia trachomatis and Neisseriagonorrhoeae

Vaginal microbicides with activity towards organisms that cause sexually transmitted infections have been proposed as a strategy to reduce transmission. Small-molecule inhibitors of Chlamydia trachomatis serovar D belonging to the class of salicylidene acylhydrazides (INPs) have been shown to work through a mechanism that involves iron restriction. Expanding on this work, ten INPs were tested against a lymphogranuloma venereum strain of C. trachomatis (serovar L2), Neisseria gonorrhoeae, and hydrogen peroxide-producing Lactobacillus crispatus and Lactobacillus jensenii. Seven INPs had minimal inhibitory concentrations (MICs) and minimal bactericidal concentrations of <50 microM towards C. trachomatis L2. Three INPs had a MIC <12.5 microM against N. gonorrhoeae. Inhibition was reversed by iron, holo-transferrin and holo-lactoferrin but not by the iron-poor forms of these compounds. The compounds exhibited no bactericidal activity toward Lactobacillus. The INPs were not cytotoxic to HeLa 229 cells. When INP 0341 was tested in a mouse model of a Chlamydia vaginal infection there was a significant reduction in the number of mice shedding C. trachomatis up to 4 days after infection (P<0.01). In summary, select INPs are promising vaginal microbicide candidates as they inhibit the growth of two common sexually transmitted organisms in vitro, are active in a mouse model against C. trachomatis, are not cytotoxic and do not inhibit organisms that compose the normal vaginal flora.

Potential impact of vaginal microbicides on HIV risk among women with primary heterosexual partners

This article explores the potential public health consequences of anti-HIV microbicide adoption among women in high-risk communities, using data from an exploratory study to illustrate key points. A brief quantitative survey was administered to 71 drug-using women with primary heterosexual partners in New York City. Only 37% of women reported recent condom use with a primary male partner. A total of 86% expressed willingness to use a microbicide with a primary partner. Among women using condoms, 50% believed they would decrease condom use if they started using a vaginal microbicide. Although overall condom use and intended condom migration was low among women with HIV-infected partners, universal promotion of microbicides could nonetheless lead to an increase in HIV risk among specific subgroups of women, indicating the importance of promoting continued condom use. Further research is needed to inform public policy decisions before the availability of the first commercial microbicide.

Who will Benefit from a Wide-Scale Introduction of Vaginal Microbicides in Developing Countries?

Vaginal microbicides (VMB) are currently among the few biomedical interventions designed to help women reduce their risk of acquiring HIV infection. However, the microbicide containing antiretroviral (ARV-VMB) may lead to the development of antiretroviral resistance and could paradoxically become more beneficial to men at the population level. We developed a mathematical model to study the impact of a wide-scale population usage of VMB in a heterosexual population. Gender ratios of prevented infections and prevalence reduction are evaluated in 63 different intervention schedules including continuous and interrupted ARV-VMB use by HIV-positive women. The influence of different factors on population-level benefits is also studied through Monte Carlo simulations using parameters sampled from primary ranges representative of developing countries. Our analysis indicates that women are more likely than men to benefit from ARV-VMB use since 78-80% of the total 63,000 simulations investigated (under different parameter sets) showed a female advantage whether benefit is measured as cumulative number of infections prevented, the percentage of cumulative infections prevented, or the expected reduction in prevalence. Stratified analysis by scenarios indicates that the likelihood of a male advantage with respect to the fractions of prevented infections varies from 6% to 49% among the scenarios. It is substantial only if the risk of systemic absorption and development of resistance to ARV-VMB is high and the HIV-positive women use VMB indefinitely without interruption. Therefore, the use of ARV-VMB, with successful control measures restricting usage by HIV-positive women, is still very much a female prevention tool.

Pharmaceutical development of microbicide drug products

HIV infection rates in the developing world remain a serious problem. One potential approach to reduce infection rates is to use products known as microbicides, referred to herein as microbicide drug products (MDPs). These are drugs capable of, when administered topically to the vagina (or rectum), interfering with infection by one or more mechanisms. This review article covers the latest pharmaceutical developments in the area of microbicides dosage forms and delivery systems. These products are principally designed for use in the developing world and must therefore address cultural and societal issues generally unknown in the developed world. The first-generation microbicides evaluated clinically were principally polyanions. These drugs, administered intravaginally as gels, were found to be ineffective in preventing transmission of HIV from men to women. Second-generation drugs such as tenofovir, dapivirine, and UC781 are reverse transcriptase inhibitors developed as gels formulations and intravaginal rings (IVRs). Gels are considered coitally-related products while IVRs are coitally-independent systems designed to release the drug over a four-week period or possibly longer (up to 3 or 4 months). Other dosage forms under development include fast dissolving films, tablets/capsules, and possibly vaginal sponges. Dual protection systems are also under development. These systems include formulations capable of preventing HIV infection along with a second drug capable of preventing conception or other viral infections such as HSV.

Segmented polyurethane intravaginal rings for the sustained combined delivery of antiretroviral agents dapivirine and tenofovir

Dual segment polyurethane intravaginal rings (IVRs) were fabricated to enable sustained release of antiretroviral agents dapivirine and tenofovir to prevent the male to female sexual transmission of the human immunodeficiency virus. Due to the contrasting hydrophilicity of the two drugs, dapivirine and tenofovir were separately formulated into polymers with matching hydrophilicity via solvent casting and hot melt extrusion. The resultant drug loaded rods were then joined together to form dual segment IVRs. Compression testing of the IVRs revealed that they are mechanically comparable to the widely accepted NuvaRing IVR. Physical characterization of the individual IVR segments using wide angle X-ray scattering and differential scanning calorimetry determined that dapivirine and tenofovir are amorphous and crystalline within their polymeric segments, respectively. In vitro release of tenofovir from the dual segment IVR was sustained over 30 days while dapivirine exhibited linear release over the time period. A 90 day accelerated stability study confirmed that dapivirine and tenofovir are stable in the IVR formulation. Altogether, these results suggest that multisegment polyurethane IVRs are an attractive formulation for the sustained vaginal delivery of drugs with contrasting hydrophilicity such as dapivirine and tenofovir.

HIV-1 gp41-specific monoclonal mucosal IgAs derived from highly exposed but IgG-seronegative individuals block HIV-1 epithelial transcytosis and neutralize CD4(+) cell infection: an IgA gene and functional analysis

AIDS is mainly a sexually transmitted disease, and accordingly, mucosal tissues are the primary sites of natural human immunodeficiency virus type-1 (HIV-1) transmission. Mucosal immunoglobulin A (IgA) antibody specific for HIV-1 envelope gp41 subunit is one correlate of protection in individuals who are highly sexually exposed to HIV-1 but remain persistently IgG seronegative (HEPS). Understanding these peculiar IgAs at the gene and functional level is possible only with monoclonal IgAs. We have constructed a mucosal Fab IgA library from HEPS and have characterized a series of HIV-1 IgAs specific for gp41 that, in vitro, are transcytosis-blocking and infection-neutralizing. Characterization of their IgA genes shows that Fab specific for the gp41 membrane-proximal region harbors a long heavy-chain CDR3 loop (CDRH3) similar to the two broadly neutralizing IgG monoclonal antibodies, 2F5 and 4E10. Furthermore, the selected Fab IgA shows extensive somatic mutations that cluster in the CDR regions, indicating that affinity maturation due to an antigen-driven process had occurred in HEPS individuals, presumably upon multiple exposures to HIV. This analysis of HEPS monoclonal IgA gives a unique opportunity to correlate an antibody function (resistance to a pathogen in vivo) with an antibody gene. Such neutralizing monoclonal IgAs could be used in microbicide formulation.

The past, present, and future of HIV prevention: integrating behavioral, biomedical, and structural intervention strategies for the next generation of HIV prevention

In the past 25 years, the field of HIV prevention research has been transformed repeatedly. Today, effective HIV prevention requires a combination of behavioral, biomedical, and structural intervention strategies. Risk of transmitting or acquiring HIV is reduced by consistent male- and female-condom use, reductions in concurrent and/or sequential sexual and needle-sharing partners, male circumcision, and treatment with antiretroviral medications. At least 144 behavioral prevention programs have been found effective in reducing HIV transmission acts; however, scale up of these programs has not occurred outside of the United States. A series of recent failures of HIV-prevention efficacy trials for biomedical innovations such as HIV vaccines, treating herpes simplex 2 and other sexually transmitted infections, and diaphragm and microbicide barriers highlights the need for behavioral strategies to accompany biomedical strategies. This challenges prevention researchers to reconceptualize how cost-effective, useful, realistic, and sustainable prevention programs will be designed, delivered, tested, and diffused. The next generation of HIV prevention science must draw from the successes of existing evidence-based interventions and the expertise of the market sector to integrate preventive innovations and behaviors into everyday routines.

Intravaginal gene silencing using biodegradable polymer nanoparticles densely loaded with small-interfering RNA

Vaginal instillation of small-interfering RNA (siRNA) using liposomes has led to silencing of endogenous genes in the genital tract and protection against challenge from infectious disease. Although siRNA lipoplexes are easily formulated, several of the most effective transfection agents available commercially may be toxic to the mucosal epithelia and none are able to provide controlled or sustained release. Here, we demonstrate an alternative approach using nanoparticles composed entirely of FDA-approved materials. To render these materials effective for gene silencing, we developed novel approaches to load them with high amounts of siRNA. A single dose of siRNA-loaded nanoparticles to the mouse female reproductive tract caused efficient and sustained gene silencing. Knockdown of gene expression was observed proximal (in the vaginal lumen) and distal (in the uterine horns) to the site of topical delivery. In addition, nanoparticles penetrated deep into the epithelial tissue. This is the first report demonstrating that biodegradable polymer nanoparticles are effective delivery vehicles for siRNA to the vaginal mucosa.

Selection of a simian-human immunodeficiency virus strain resistant to a vaginal microbicide in macaques

PSC-RANTES binds to CCR5, inhibits human immunodeficiency virus type 1 (HIV-1) entry, and has been shown as a vaginal microbicide to protect rhesus macaques from a simian-human immunodeficiency virus chimera (SHIV(SF162-p3)) infection in a dose-dependent manner. In this study, env gene sequences from SHIV(SF162-p3)-infected rhesus macaques treated with PSC-RANTES were analyzed for possible drug escape variants. Two specific mutations located in the V3 region of gp120 (K315R) and C-helical domain of gp41 (N640D) were identified in a macaque (m584) pretreated with a 100 microM dose of PSC-RANTES. These two env mutations were found throughout infection (through week 77) but were found at only low frequencies in the inoculating SHIV(SF162-p3) stock and in the other SHIV(SF162-p3)-infected macaques. HIV-1 env genes from macaque m584 (env(m584)) and from inoculating SHIV(SF162-p3) (env(p3)) were cloned into an HIV-1 backbone. Increases in 50% inhibitory concentrations to PSC-RANTES with env(m584) were modest (sevenfold) and most pronounced in cells expressing rhesus macaque CCR5 as compared to human CCR5. Nonetheless, virus harboring env(m584), unlike inoculating virus env(p3), could replicate even at the highest tissue culture PSC-RANTES concentrations (100 nM). Dual-virus competitions revealed a dramatic increase in fitness of chimeric virus containing env(m584) (K315R/N640D) over that containing env(p3), but again, only in rhesus CCR5-expressing cells. This study is the first to describe the immediate selection and infection of a drug-resistant SHIV variant in the face of a protective vaginal microbicide, PSC-RANTES. This rhesus CCR5-specific/PSC- RANTES resistance selection is particularly alarming given the relative homogeneity of the SHIV(SF162-p3) stock compared to the potential exposure to a heterogeneous HIV-1 population in human transmission.

Vaccines, virucides and drugs against HIV/AIDS: hopes and optimisms for the future

More than 25 million lives have been claimed by AIDS and 33.2 million people are estimated to have HIV, the majority of which are living in the underdeveloped countries. Failed tests on vaccines, virucides and complete virus eradication have caused scientists to refocus on the basic questions of what makes an effective HIV immune response. The "gloom" over disappointing research results on vaccine development and virucides "threatens to overshadow more positive" HIV/AIDS-related news, such as findings that male circumcision might reduce the likelihood of HIV transmission and that giving antiretroviral drugs to "high-risk" HIV-negative people (pre-exposure prophylaxis) could help protect them from infection. Something like pre-exposure prophylaxis has a good chance of becoming available before we have a 100% efficacious vaccine. The future in the field of HIV/AIDS will be much brighter if global research is appropriately coordinated and sufficient funds are available.

Perspectives on antiviral drug development

The 21st International Conference on Antiviral Research provided novel insights and approaches to drug discovery across a wide array of virologic fields. Topics ranged from the chemical synthesis of new compounds against the human immunodeficiency virus (HIV) to the long-term use of established drugs against influenza. A session on novel targets for HIV therapy focused on the importance of Apobec3G, LEDGF/p75 and other cellular factors as innovative ways to control infection. New targets for hepatitis B and C viruses were surveyed. There were also discussions as to how the development of new antiviral compounds might lead to novel mechanisms of drug resistance by HIV, herpesviruses and hepatitis viruses. These covered such issues as transmission dynamics, viral fitness, the acquisition of differential resistance patterns depending on viral subtype, and clinical outcomes. Drug efficacy, toxicity, patient adherence, treatment interruption and the importance of generic drugs in resource-poor settings were also extensively discussed. These topics will all play a pivotal role in drug development and the management of viral infections in the years to come.

Relation between HIV viral load and infectiousness: a model-based analysis

BACKGROUND

A consensus statement released on behalf of the Swiss Federal Commission for HIV/AIDS suggests that people receiving effective antiretroviral therapy-ie, those with undetectable plasma HIV RNA (<40 copies per mL)-are sexually non-infectious. We analysed the implications of this statement at a population level.

METHODS

We used a simple mathematical model to estimate the cumulative risk of HIV transmission from effectively treated HIV-infected patients (HIV RNA <10 copies per mL) over a prolonged period. We investigated the risk of unprotected sexual transmission per act and cumulatively over many exposures, within couples initially discordant for HIV status.

FINDINGS

Assuming that each couple had 100 sexual encounters per year, the cumulative probability of transmission to the serodiscordant partner each year is 0.0022 (uncertainty bounds 0.0008-0.0058) for female-to-male transmission, 0.0043 (0.0016-0.0115) for male-to-female transmission, and 0.043 (0.0159-0.1097) for male-to-male transmission. In a population of 10 000 serodiscordant partnerships, over 10 years the expected number of seroconversions would be 215 (80-564) for female-to-male transmission, 425 (159-1096) for male-to-female transmission, and 3524 (1477-6871) for male-to-male transmission, corresponding to an increase in incidence of four times compared with incidence under current rates of condom use.

INTERPRETATION

Our analyses suggest that the risk of HIV transmission in heterosexual partnerships in the presence of effective treatment is low but non-zero and that the transmission risk in male homosexual partnerships is high over repeated exposures. If the claim of non-infectiousness in effectively treated patients was widely accepted, and condom use subsequently declined, then there is the potential for substantial increases in HIV incidence.

FUNDING

Australian Research Council.