A topical microbicide gel formulation of CCR5 antagonist maraviroc prevents HIV-1 vaginal transmission in humanized RAG-hu mice

The menstrual cycle regulates migratory CD4 T-cell surveillance in the female reproductive tract via CCR5 signaling

Despite their importance for immunity against sexually transmitted infections, the composition of female reproductive tract (FRT) memory T-cell populations in response to changes within the local tissue environment under the regulation of the menstrual cycle remains poorly defined. Here, we show that in humans and pig-tailed macaques, the cycle determines distinct clusters of differentiation 4 T-cell surveillance behaviors by subsets corresponding to migratory memory (TMM) and resident memory T cells. TMM displays tissue-itinerant trafficking characteristics, restricted distribution within the FRT microenvironment, and distinct effector responses to infection. Gene pathway analysis by RNA sequencing identified TMM-specific enrichment of genes involved in hormonal regulation and inflammatory responses. FRT T-cell subset fluctuations were discovered that synchronized to cycle-driven CCR5 signaling. Notably, oral administration of a CCR5 antagonist drug blocked TMM trafficking. Taken together, this study provides novel insights into the dynamic nature of FRT memory CD4 T cells and identifies the menstrual cycle as a key regulator of immune surveillance at the site of STI pathogen exposure.

Translational Models to Predict Target Concentrations for Pre-Exposure Prophylaxis in Women

The HIV epidemic remains a significant public health burden. Women represent half of the global HIV epidemic, yet there is an urgent need for a variety of prevention options to meet the needs of more women. Pre-exposure prophylaxis (PrEP) is a valuable prevention tool that uses antiretrovirals before a potential HIV exposure to prevent virus transmission. Development of effective preventive drug regimens for women is dependent on convenient dosing schedules and routes of administration, and on identifying defined target concentrations in mucosal tissues that provide complete protection against HIV transmission. There is a critical need for a translational model that can accurately predict in vivo target concentrations that are completely protective against HIV infection. There is no gold-standard preclinical model to predict PrEP efficacy. In this study, we review the strengths and limitations of three different preclinical models and their utility in predicting target concentrations in the female genital tract: humanized mice, non-human primates, and the ex vivo tissue model.

Synthetic Mucin Gels with Self-Healing Properties Augment Lubricity and Inhibit HIV-1 and HSV-2 Transmission

Mucus is a self-healing gel that lubricates the moist epithelium and provides protection against viruses by binding to viruses smaller than the gel's mesh size and removing them from the mucosal surface by active mucus turnover. As the primary nonaqueous components of mucus (≈0.2%-5%, wt/v), mucins are critical to this function because the dense arrangement of mucin glycans allows multivalence of binding. Following nature's example, bovine submaxillary mucins (BSMs) are assembled into "mucus-like" gels (5%, wt/v) by dynamic covalent crosslinking reactions. The gels exhibit transient liquefaction under high shear strain and immediate self-healing behavior. This study shows that these material properties are essential to provide lubricity. The gels efficiently reduce human immunodeficiency virus type 1 (HIV-1) and genital herpes virus type 2 (HSV-2) infectivity for various types of cells. In contrast, simple mucin solutions, which lack the structural makeup, inhibit HIV-1 significantly less and do not inhibit HSV-2. Mechanistically, the prophylaxis of HIV-1 infection by BSM gels is found to be that the gels trap HIV-1 by binding to the envelope glycoprotein gp120 and suppress cytokine production during viral exposure. Therefore, the authors believe the gels are promising for further development as personal lubricants that can limit viral transmission.

A Randomized, Open-Label, Crossover Phase 1 Safety and Pharmacokinetic Study of Oral Maraviroc and Maraviroc 1% Gel (the CHARM-03 Study)

The Combination HIV Antiretroviral Rectal Microbicide-3 (CHARM-03) study was a randomized, open-label, crossover Phase 1 safety and pharmacokinetic (PK) study of oral maraviroc (MVC) and MVC 1% gel. At a single site, healthy HIV-uninfected men and women were enrolled and randomized to an open label crossover sequence of eight consecutive daily exposures to MVC 300 mg dosed orally, MCV 1% gel dosed rectally, and MVC 1% gel dosed vaginally. Male participants received oral and rectal dosing and female participants received oral, rectal, and vaginal dosing. Assessments were undertaken at baseline and following each 8-day period and included collection of plasma, rectal/cervical tissue (CT), and rectal/endocervical/vaginal fluids. Eleven men and nine women were enrolled. Two participants withdrew from the study before receiving study product. There were 25 adverse events, of which 24 were Grade 1 (G1) and one was G2 (unrelated). After eight doses, MVC was quantifiable in all samples following oral, rectal, or vaginal product administration. The highest drug concentrations in plasma, rectal tissue (RT), and CT were associated with oral, rectal, and vaginal drug delivery, respectively. There were significant reductions in tissue drug concentrations when rectal and cervical biopsies were incubated in media before tissue processing for PK (p < .0001). Only oral MVC was associated with limited protection in the rectal explant HIV challenge model (p < .05). There were no immunological changes in RT, and all products were acceptable to participants. In conclusion, all products were found to be safe and acceptable and did not induce local inflammation. The lack of ex vivo efficacy demonstrated in study samples may be due to rapid disassociation of MVC from the explant tissue. ClinicalTrials.gov Identifier: NCT02346084.

Expression, Activity, and Regulation of Phosphorylating Enzymes in Tissues and Cells Relevant to HIV-1 Sexual Transmission

Phosphorylating enzymes (PEs) are responsible for activating nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs) such as tenofovir (TFV) and are critical for their conversion to obtain intracellular antiviral activity. However, there are limited data available regarding the expression of PEs and their activity in the female genital tract. This work compared the messenger RNA (mRNA) expression levels of PEs in human female genital tissue, immune cells, and animal models that are commonly used in human immunodeficiency virus (HIV) research. Furthermore, the effect of contraceptive hormones and proinflammatory cytokines on tenofovir diphosphate (TFV-DP) formation and efficacy in human vaginal, epithelial, and immune cells was also evaluated. We found that human vaginal and ectocervical tissues had similar mRNA expression for seven PEs tested. Polymerase chain reaction results revealed that creatine kinase brain (CKB), mitochondrial creatine kinase 1 (CKMT1), mitochondrial creatine kinase 2 (CKMT2), adenylate kinase AK3L1 (AK4), and nucleoside diphosphate kinase 1 (NME1) exhibited a 10- to 10,000-fold higher expression level in a vaginal epithelial cell line, VK2, compared with CD4⁺ T cells (p < .05). Medroxyprogesterone acetate (MPA)/progesterone (P4) and IL-1β/IL-8 treatment resulted in altered TFV-DP levels in VK2 and PM1 cells. MPA and P4 at concentrations above 0.1 μM, as well as IL-1β and IL-8 at concentrations above 10 ng/mL, significantly decreased HIV-1_BaL inhibition in PM1 cells when 1 μM TFV was added. However, this observed effect of hormones and cytokines was abrogated when TFV concentration was raised to 1 mM. These in vitro results elucidate the role of PEs in TFV metabolism and provide information regarding differences in PE tissue expression for animal models commonly used in HIV testing. This information can be applied to better understand and interpret data obtained using these models.

Advances in Humanized Mouse Models to Improve Understanding of HIV-1 Pathogenesis and Immune Responses

Although antiretroviral therapy has transformed human immunodeficiency virus-type 1 (HIV-1) from a deadly infection into a chronic disease, it does not clear the viral reservoir, leaving HIV-1 as an uncurable infection. Currently, 1.2 million new HIV-1 infections occur globally each year, with little decrease over many years. Therefore, additional research is required to advance the current state of HIV management, find potential therapeutic strategies, and further understand the mechanisms of HIV pathogenesis and prevention strategies. Non-human primates (NHP) have been used extensively in HIV research and have provided critical advances within the field, but there are several issues that limit their use. Humanized mouse (Hu-mouse) models, or immunodeficient mice engrafted with human immune cells and/or tissues, provide a cost-effective and practical approach to create models for HIV research. Hu-mice closely parallel multiple aspects of human HIV infection and disease progression. Here, we highlight how innovations in Hu-mouse models have advanced HIV-1 research in the past decade. We discuss the effect of different background strains of mice, of modifications on the reconstitution of the immune cells, and the pros and cons of different human cells and/or tissue engraftment methods, on the ability to examine HIV-1 infection and immune response. Finally, we consider the newest advances in the Hu-mouse models and their potential to advance research in emerging areas of mucosal infections, understand the role of microbiota and the complex issues in HIV-TB co-infection. These innovations in Hu-mouse models hold the potential to significantly enhance mechanistic research to develop novel strategies for HIV prevention and therapeutics.

CD34T+ Humanized Mouse Model to Study Mucosal HIV-1 Transmission and Prevention

Humanized mice are critical for HIV-1 research, but humanized mice generated from cord blood are inefficient at mucosal HIV-1 transmission. Most mucosal HIV-1 transmission studies in mice require fetal tissue-engraftment, the use of which is highly restricted or prohibited. We present a fetal tissue-independent model called CD34T+ with enhanced human leukocyte levels in the blood and improved T cell homing to the gut-associated lymphoid tissue. CD34T+ mice are highly permissive to intra-rectal HIV-1 infection and also show normal env diversification in vivo despite high viral replication. Moreover, mucosal infection in CD34T+ mice can be prevented by infusion of broadly neutralizing antibodies. CD34T+ mice can be rapidly and easily generated using only cord blood cells and do not require any complicated surgical procedures for the humanization process. Therefore, CD34T+ mice provide a novel platform for mucosal HIV-1 transmission studies as well as rapid in vivo testing of novel prevention molecules against HIV-1.

Development and evaluation of mucoadhesive bigel containing tenofovir and maraviroc for HIV prophylaxis

BACKGROUND

Sexual transmission of HIV is the most common means of acquiring the disease. Topical microbicides have been investigated to prevent transmission. This study will use a specific entry inhibitor, maraviroc, and a nucleotide reverse transcriptase inhibitor (NRTI), tenofovir, a dual combination which will provide a synergist effect that can enhance the efficacy of HIV microbicides via a mucoadhesive dual compartment bigel. Bigel formulation via hydrogel organogel linkages were developed and evaluated for their physicochemical characteristics, safety, and anti-HIV efficacy. In vitro diffusion studies were performed with Franz diffusion cells having effective diffusion surface area of 1.76cm2 and receiver chamber volume of 15mL.

RESULT

The bigel formulations showed a viscosity ranging from 14179 to 14560 cPs and had a good spreadability and acidic pH in the range of 4.0 ± 0.34 to 5.2 ± 0.18. The bigel formulations showed good anti-HIV activity at a concentration of 0.1 μg/mL. The in vitro release study of maraviroc from the bigel formulations showed a release rate ranging from 2.675 to 3.838 μg/cm2/min½ while the release rate for tenofovir ranged from 3.475 to 3.825 μg/cm2/min½. The bigel formulations were non-toxic to the human vagina as there was < 1 log10 change in Lactobacilli crispatus viability.

CONCLUSION

This study successfully developed a dual compartment bigel containing maraviroc and tenofovir. BG C was found to be stable and safe towards vaginal and rectal epithelium, and it actively prevented HIV transmission. This bigel has the potential for long-term pre-exposure prophylaxis prevention of HIV transmission.

Evaluation of the fusion inhibitor P3 peptide as a potential microbicide to prevent HIV transmission in women

Microbicides are an important strategy for preventing the sexual transmission of HIV but, so far, the most advanced tenofovir-based microbicides have had modest efficacy. This has been related to adherence problems and high prevalence of tenofovir-resistant HIV-1 strains. P3 is a new peptide with potent activity against HIV that may be a good microbicide candidate. In this work P3 was formulated in a gel of hydroxyethyl cellulose and its activity, stability and safety profile in Balb/c mice were evaluated. HIV infection was fully blocked by a 1.5% gel containing P3 at the IC90 (366.4 nM) concentration. The antiviral activity did not change at 4°C during 4 months and at 25, 37 and 65°C for 1 week. P3 was stable and fully functional at acidic pH up to 24h, under different concentrations of hydrogen peroxide and in the presence of genital fluids up to 48h. P3 had no antibacterial activity and did not affect sperm motility and vitality. Finally, P3 didn't cause significant alterations in the vaginal epithelium of Balb/c mice at 0.06 (456.8 μM) and 0.2 mg/day (1522.7 μM) doses. These findings indicate that P3 is an excellent candidate for further development as a microbicide gel for the prevention of HIV transmission in women.

G2-S16 dendrimer as a candidate for a microbicide to prevent HIV-1 infection in women

Unprotected heterosexual intercourse is the first route for sustaining the global spread of human immunodeficiency virus type 1 (HIV-1), being responsible for 80% of new HIV-1 infections in the world. The presence of inflammation in the female reproductive tract and the presence of semen increases the risk of heterosexual HIV-1 transmission. This state-of-the-art research based on an innovative nanotechnology design was focused on a toxicological study of the limitation of the activity of the novel H₂O-soluble anionic carbosilane dendrimer G2-S16 in the adult cervical and foreskin epithelia. The G2-S16 dendrimer did not cause any irritation or inflammation in the vaginal epithelium, proving that this dendrimer is a safe nanocompound for vaginal application to control viral transmission. It was shown that no significant differences were found in mortality, sublethal or teratogenic effects when the zebra fish embryos were treated with G2-S16. In short, G2-S16 seems to be an ideal candidate for the development of a topical microbicide against HIV-1 infection and the next step is try in clinical trials, because of its great in vivo biocompatibility, as well as its ability to halt HIV-1 infection in the presence of semen.

Induction of a Tier-1-Like Phenotype in Diverse Tier-2 Isolates by Agents That Guide HIV-1 Env to Perturbation-Sensitive, Nonnative States

The envelope glycoproteins (Envs) on the surfaces of HIV-1 particles are targeted by host antibodies. Primary HIV-1 isolates demonstrate different global sensitivities to antibody neutralization; tier-1 isolates are sensitive, whereas tier-2 isolates are more resistant. Single-site mutations in Env can convert tier-2 into tier-1-like viruses. We hypothesized that such global change in neutralization sensitivity results from weakening of intramolecular interactions that maintain Env integrity. Three strategies commonly applied to perturb protein structure were tested for their effects on global neutralization sensitivity: exposure to low temperature, Env-activating ligands, and a chaotropic agent. A large panel of diverse tier-2 isolates from clades B and C was analyzed. Incubation at 0°C, which globally weakens hydrophobic interactions, causes gradual and reversible exposure of the coreceptor-binding site. In the cold-induced state, Envs progress at isolate-specific rates to unstable forms that are sensitive to antibody neutralization and then gradually lose function. Agents that mimic the effects of CD4 (CD4Ms) also induce reversible structural changes to states that exhibit isolate-specific stabilities. The chaotropic agent urea (at low concentrations) does not affect the structure or function of native Env. However, urea efficiently perturbs metastable states induced by cold and CD4Ms and increases their sensitivity to antibody neutralization and their inactivation rates Therefore, chemical and physical agents can guide Env from the stable native state to perturbation-sensitive forms and modulate their stability to bestow tier-1-like properties on primary tier-2 strains. These concepts can be applied to enhance the potency of vaccine-elicited antibodies and microbicides at mucosal sites of HIV-1 transmission.IMPORTANCE An effective vaccine to prevent transmission of HIV-1 is a primary goal of the scientific and health care communities. Vaccine-elicited antibodies target the viral envelope glycoproteins (Envs) and can potentially inhibit infection. However, the potency of such antibodies is generally low. Single-site mutations in Env can enhance the global sensitivity of HIV-1 to neutralization by antibodies. We found that such a hypersensitivity phenotype can also be induced by agents that destabilize protein structure. Exposure to 0°C or low concentrations of Env-activating ligands gradually guides Env to metastable forms that expose cryptic epitopes and that are highly sensitive to neutralization. Low concentrations of the chaotropic agent urea do not affect native Env but destabilize perturbed states induced by cold or CD4Ms and increase their neutralization. The concept of enhancing antibody sensitivity by chemical agents that affect the structural stability of proteins can be applied to increase the potency of topical microbicides and vaccine-elicited antibodies.

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.

The future of pre-exposure prophylaxis (PrEP) for human immunodeficiency virus (HIV) infection

INTRODUCTION

People at high risk for HIV acquisition should be offered pre-exposure prophylaxis (PrEP). Tenofovir disoproxil fumarate (TDF)/emtricitabine (FTC) is currently the only medication recommended for pre-exposure prophylaxis (PrEP) by the Centers for Disease Control and Prevention (CDC) in people at high risk for HIV acquisition. This article will review medications currently under investigation and the future landscape of PrEP therapy. Areas covered: This article will review clinical trials that have investigated nontraditional regimens of TDF/FTC, antiretroviral agents from different drug classes such as integrase strand transfer inhibitors (INSTI), nucleoside reverse transcriptase inhibitors (NRTI), and non-nucleoside reverse transcriptase inhibitors (NNRTI) as potential PrEP therapies. Expert commentary: Currently, there are several investigational drugs in the pipeline for PrEP against HIV infection. Increased utilization of PrEP therapy depends on provider identification of people at high risk for HIV transmission. Advances in PrEP development will expand options and access for people and reduce the risk of HIV acquisition.

Mucosal Topical Microbicide Candidates Exert Influence on the Subsequent SIV Infection and Survival by Regulating SIV-Specific T-Cell Immune Responses

OBJECTIVE

To determine whether mucosal topical microbicides have any influence on disease progression during subsequent simian immunodeficiency virus (SIV) infection.

DESIGN

A 2-phase study was performed in primate monkeys. The first phase mimicked microbicide efficacy studies; the second phase served to determine the disease progression in a productive infection model.

METHODS

During the first phase, monkeys were intrarectally pretreated with tenofovir, sifuvirtide (SFT), or maraviroc-formulated microbicides and then challenged with low-dose SHIV-1157ipd3N4. Second, all monkeys were rechallenged with a single high dose of SIVmac239 to generate productive infections. The survival rate, viral loads, CD4(+) T-cell counts, and SIV-specific T-cell responses were determined during the 104-week following up.

RESULTS

Repeated rectal challenges did not result in productive infection in all groups, evidenced by undetectable viral loads with occasional viral blips during the first phase of this study. All monkeys were productively infected after the high-dose rechallenge with SIVmac239. Two groups, including maraviroc-treated and tenofovir-treated groups, experienced 100% mortality during the 104-week following up. In contrast, the SFT-treated group showed significantly higher survival, and only 25% died at week 95. Interestingly, SIV-specific T-cell responses were also significantly higher in the SFT group. Transcriptomic analyses evidenced immune imprint in immune system among different microbicide-treated groups.

CONCLUSIONS

This study provides preliminary but important evidence for the influence of prophylactically applied microbicides on disease progression of subsequent SIV infection and suggests that the long-term immune safety concern for microbicides should be also considered in the effort to develop effective microbicides.

Perceptions among Dutch men who have sex with men and their willingness to use rectal microbicides and oral pre-exposure prophylaxis to reduce HIV risk--a preliminary study

Oral pre-exposure prophylaxis (PrEP) with antiretroviral (ARV) tablets and topical PrEP or microbicides containing ARV drugs could help to reduce HIV incidence. These methods hold promise for men who have sex with men (MSM) who are at higher risk of acquiring HIV. This mixed-methods study in the Netherlands explored perceptions of MSM and their willingness to use oral PrEP and rectal microbicides (RM) if made available. Recruited through social media (Facebook and Twitter), 108 MSM completed online questionnaires. Seven of them consented to discuss the survey results in semi-structured interviews. Survey participants preferred a RM that could be applied before and after anal intercourse (60.8%) to daily oral PrEP (20.3%). This preference was based on anticipated user friendliness, hypothetically fewer expected adverse events, and perceptions that RM would be less likely to be confused with ARVs for treatment. Those who preferred oral PrEP had stronger beliefs in the effectiveness of pills, perceived its use as easy, and viewed not requiring sexual partner awareness as advantages. No predictive factors were found for the choice of one prevention method over the other. Although Dutch MSM perceive both oral and topical PrEP positively, many barriers exist to the introduction of these products in the Netherlands. These include lack of regulatory approval of oral PrEP, no proven efficacy as yet for RM, and strong HIV stigma within the MSM population. In-depth qualitative research is needed to further explore the perceptions of MSM to inform implementation of programmes should these HIV prevention methods become available.

Chemokine receptor CCR5 antagonist maraviroc: medicinal chemistry and clinical applications

The human immunodeficiency virus (HIV) causes acquired immumodeficiency syndrome (AIDS), one of the worst global pandemic. The virus infects human CD4 T cells and macrophages, and causes CD4 depletion. HIV enters target cells through the binding of the viral envelope glycoprotein to CD4 and the chemokine coreceptor, CXCR4 or CCR5. In particular, the CCR5-utilizing viruses predominate in the blood during the disease course. CCR5 is expressed on the surface of various immune cells including macrophages, monocytes, microglia, dendric cells, and active memory CD4 T cells. In the human population, the CCR5 genomic mutation, CCR5Δ32, is associated with relative resistance to HIV. These findings paved the way for the discovery and development of CCR5 inhibitors to block HIV transmission and replication. Maraviroc, discovered as a CCR5 antagonist, is the only CCR5 inhibitor that has been approved by both US FDA and the European Medicines Agency (EMA) for treating HIV/AIDS patients. In this review, we summarize the medicinal chemistry and clinical studies of Maraviroc.

Improvements and Limitations of Humanized Mouse Models for HIV Research: NIH/NIAID "Meet the Experts" 2015 Workshop Summary

The number of humanized mouse models for the human immunodeficiency virus (HIV)/acquired immunodeficiency syndrome (AIDS) and other infectious diseases has expanded rapidly over the past 8 years. Highly immunodeficient mouse strains, such as NOD/SCID/gamma chain(null) (NSG, NOG), support better human hematopoietic cell engraftment. Another improvement is the derivation of highly immunodeficient mice, transgenic with human leukocyte antigens (HLAs) and cytokines that supported development of HLA-restricted human T cells and heightened human myeloid cell engraftment. Humanized mice are also used to study the HIV reservoir using new imaging techniques. Despite these advances, there are still limitations in HIV immune responses and deficits in lymphoid structures in these models in addition to xenogeneic graft-versus-host responses. To understand and disseminate the improvements and limitations of humanized mouse models to the scientific community, the NIH sponsored and convened a meeting on April 15, 2015 to discuss the state of knowledge concerning these questions and best practices for selecting a humanized mouse model for a particular scientific investigation. This report summarizes the findings of the NIH meeting.

Mucosal tissue pharmacokinetics of the integrase inhibitor raltegravir in a humanized mouse model: Implications for HIV pre-exposure prophylaxis

Orally administered anti-retroviral drugs show considerable promise for HIV/AIDS pre-exposure prophylaxis (PrEP). For the success of these strategies, pharmacokinetic (PK) data defining the optimal concentration of the drug needed for protection in relevant mucosal exposure sites is essential. Here we employed a humanized mouse model to derive comprehensive PK data on the HIV integrase inhibitor raltegravir (RAL), a leading PrEP drug candidate. Under steady state conditions following oral dosing, plasma and multiple mucosal tissues were sampled simultaneously. RAL exhibited higher drug exposure in mucosal tissues relative to that in plasma with one log higher exposure in vaginal and rectal tissue and two logs higher exposure in intestinal mucosa reflecting the trends seen in the human studies. These data demonstrate the suitability of RAL for HIV PrEP and validate the utility of humanized mouse models for deriving important preclinical PK-PD data.

Modeling HIV-1 Mucosal Transmission and Prevention in Humanized Mice

The new generation humanized mice (hu-mice) that permit continuous de novo generation of human hematopoietic cells have led to novel strategies in studying HIV-1 pathogenesis, prevention and therapies. HIV-1 infection of hu-mice results in chronic viremia and CD4+ T cell loss, thus mimicking key aspects of the disease progression. In addition, the new generation hu-mice are permissive for HIV-1 sexual transmission by vaginal and rectal routes thus allowing in vivo efficacy testing of new anti-HIV-1 drugs for prevention. Two leading models are currently being used, namely the hu-HSC mice and the BLT mice. Here we describe the methodology for generating both hu-HSC and BLT mice and their use in the study of HIV-1 transmission and prevention of infection by topical and oral administration of anti-retroviral drugs. Practical aspects of the methodologies are emphasized.

Single oral dose of maraviroc does not prevent ex-vivo HIV infection of rectal mucosa in HIV-1 negative human volunteers

OBJECTIVE

Maraviroc (MVC) is a potential candidate for 'on demand' preexposure prophylaxis. In the present study, we evaluated the efficacy of a single oral dose of MVC to prevent ex-vivo HIV-1 infection of rectal tissue in humans.

DESIGN AND METHODS

Eight HIV-1-negative healthy volunteers received a single oral dose of MVC (300 or 600 mg), and two additional volunteers received tenofovir disoproxil fumarate/emtricitabine (TDF/FTC, 300/200 mg) for 10 days. Rectal biopsies were performed prior to the ex-vivo challenge (day 0), at day 7 (4 h after MVC) or after 10 days with TDF/FTC. Rectal biopsies were infected ex-vivo, and viral inhibition and CCR5 occupancy was analyzed. MVC concentration in plasma and rectal tissue was measured just after biopsy and after viral incubation.

RESULTS

Ex-vivo rectal tissue protection with MVC was incomplete in all but two participants, whereas TDF/FTC avoided ex-vivo infection in the two controls. Median dose-normalized concentration of MVC was significantly higher in rectal tissue than in plasma (561.1 and 155.1 ng/ml, respectively). A significant loss of MVC during the virus incubation (about 60%) and a low CCR5 occupancy (approximately 45%) were detected in rectal cells.

CONCLUSIONS

An ex-vivo challenge with a single oral dose of MVC does not prevent ex-vivo infection of human rectal mucosa. The lack of prophylactic efficacy observed suggests that 'on demand' MVC preexposure prophylaxis would not prevent rectal HIV-1 transmission.

Maraviroc: a review of its use in HIV infection and beyond

The human immunodeficiency virus-1 (HIV-1) enters target cells by binding its envelope glycoprotein gp120 to the CD4 receptor and/or coreceptors such as C-C chemokine receptor type 5 (CCR5; R5) and C-X-C chemokine receptor type 4 (CXCR4; X4), and R5-tropic viruses predominate during the early stages of infection. CCR5 antagonists bind to CCR5 to prevent viral entry. Maraviroc (MVC) is the only CCR5 antagonist currently approved by the United States Food and Drug Administration, the European Commission, Health Canada, and several other countries for the treatment of patients infected with R5-tropic HIV-1. MVC has been shown to be effective at inhibiting HIV-1 entry into cells and is well tolerated. With expanding MVC use by HIV-1-infected humans, different clinical outcomes post-approval have been observed with MVC monotherapy or combination therapy with other antiretroviral drugs, with MVC use in humans infected with dual-R5- and X4-tropic HIV-1, infected with different HIV-1 genotype or infected with HIV-2. This review discuss the role of CCR5 in HIV-1 infection, the development of the CCR5 antagonist MVC, its pharmacokinetics, pharmacodynamics, drug–drug interactions, and the implications of these interactions on treatment outcomes, including viral mutations and drug resistance, and the mechanisms associated with the development of resistance to MVC. This review also discusses available studies investigating the use of MVC in the treatment of other diseases such as cancer, graft-versus-host disease, and inflammatory diseases.

Role of Semen on Vaginal HIV-1 Transmission and Maraviroc Protection

We used bone marrow/liver/thymus (BLT) humanized mice to establish the effect of semen on vaginal HIV infection and on the efficacy of topically applied maraviroc. Our results demonstrate that vaginal transmission of cell-free HIV occurs efficiently in the presence of semen and that topically applied maraviroc efficiently prevents HIV transmission in the presence of semen. We also show that semen has no significant effect on the transmission of transmitted/founder viruses or cell-associated viruses.

Development of water-soluble polyanionic carbosilane dendrimers as novel and highly potent topical anti-HIV-2 microbicides

The development of topical microbicide formulations for vaginal delivery to prevent HIV-2 sexual transmission is urgently needed. Second- and third-generation polyanionic carbosilane dendrimers with a silicon atom core and 16 sulfonate (G2-S16), napthylsulfonate (G2-NS16) and sulphate (G3-Sh16) end-groups have shown potent and broad-spectrum anti-HIV-1 activity. However, their antiviral activity against HIV-2 and mode of action have not been probed. Cytotoxicity, anti-HIV-2, anti-sperm and antimicrobial activities of dendrimers were determined. Analysis of combined effects of triple combinations with tenofovir and raltegravir was performed by using CalcuSyn software. We also assessed the mode of antiviral action on the inhibition of HIV-2 infection through a panel of different in vitro antiviral assays: attachment, internalization in PBMCs, inactivation and cell-based fusion. Vaginal irritation and histological analysis in female BALB/c mice were evaluated. Our results suggest that G2-S16, G2-NS16 and G3-Sh16 exert anti-HIV-2 activity at an early stage of viral replication inactivating the virus, inhibiting cell-to-cell HIV-2 transmission, and blocking the binding of gp120 to CD4, and the HIV-2 entry. Triple combinations with tenofovir and raltegravir increased the anti-HIV-2 activity, consistent with synergistic interactions (CIwt: 0.33-0.66). No vaginal irritation was detected in BALB/c mice after two consecutive applications for 2 days with 3% G2-S16. Our results have clearly shown that G2-S16, G2-NS16 and G3-Sh16 have high potency against HIV-2 infection. The modes of action confirm their multifactorial and non-specific ability, suggesting that these dendrimers deserve further studies as potential candidate microbicides to prevent vaginal/rectal HIV-1/HIV-2 transmission in humans.

Recent advances on anti-HIV vaginal delivery systems development

A review of the recent outcomes regarding technologies to prevent vaginal transmission of HIV, mainly by using antiretroviral (ARV) drugs formulated as microbicides. An introduction about the HIV transmission mechanisms by the vaginal route is included, together with the recent challenges faced for development of successful microbicide products. The outcomes of clinical evaluations are mentioned, and the different formulation strategies studied to-date, with the requirements, advantages, disadvantages and limitations of each dosage-form type, are presented. Finally, the recent attempts to apply various types of nanotechnologies in order to develop advanced microbicide-products and overcome existing limitations, are discussed.

Application of Humanized Mice in Immunological Research

During the past decade, the development of humanized mouse models and their general applications in biomedical research greatly accelerated the translation of outcomes obtained from basic research into potential diagnostic and therapeutic strategies in clinic. In this chapter, we firstly present an overview on the history and current progress of diverse humanized mouse models and then focus on those equipped with reconstituted human immune system. The update advancement in the establishment of humanized immune system mice and their applications in the studies of the development of human immune system and the pathogenesis of multiple human immune-related diseases are intensively reviewed here, while the shortcoming and perspective of these potent tools are discussed as well. As a valuable bridge across the gap between bench work and clinical trial, progressive humanized mouse models will undoubtedly continue to play an indispensable role in the wide area of biomedical research.

Models for predicting effective HIV chemoprevention in women

OBJECTIVE

Model systems that rapidly identify tissue drug concentrations protective of HIV infection could streamline the development of chemoprevention strategies. Tissue models are promising, but limited concentration targets exist, and no systematic comparison to cell models or clinical studies has been performed.

DESIGN

We explored the efficacy of maraviroc (MVC) and tenofovir (TFV) for HIV prevention by comparing Emax models from TZM-bl cells to vaginal tissue explants and evaluated their predictive capabilities with a dose-challenge clinical study.

METHODS

HIV-1JR-CSF was used for viral challenge. Drug efficacy was assessed using a luciferase reporter assay in TZM-bl cells and real-time PCR to quantify spliced RNA in a tissue explant model. Cell and tissue concentrations of MVC, TFV, and the active metabolite tenofovir diphosphate were measured by liquid chromatography with tandem mass spectrometry and used to create Emax models of efficacy. Efficacy after a single oral dose of 600 mg MVC and 600 mg tenofovir disoproxil fumarate was predicted from cell and tissue models and confirmed in a clinical study with viral biopsy challenge postdose.

RESULTS

TFV was >10-fold and MVC >1000-fold, more potent in TZM-bl cells compared with vaginal explant tissue. In the dose-challenge study, tissues from 3 of 6 women were protected from HIV infection, which was 49% lower than predicted by TZM-bl data and 36% higher than predicted by tissue explant data.

CONCLUSIONS

Comparative effective concentration data were generated for TFV and MVC in 3 HIV chemoprophylaxis models. These results provide a framework for future early investigations of antiretroviral efficacy in HIV prevention to optimize dosing strategies in clinical investigations.

Expression of chimeric receptor CD4ζ by natural killer cells derived from human pluripotent stem cells improves in vitro activity but does not enhance suppression of HIV infection in vivo

Cell-based immunotherapy has been gaining interest as an improved means to treat human immunodeficiency virus (HIV)/AIDS. Human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) could become a potential resource. Our previous studies have shown hESC and iPSC-derived natural killer (NK) cells can inhibit HIV-infected targets in vitro. Here, we advance those studies by expressing a HIV chimeric receptor combining the extracellular portion of CD4 to the CD3ζ intracellular signaling chain. We hypothesized that expression of this CD4ζ receptor would more efficiently direct hESC- and iPSC-derived NK cells to target HIV-infected cells. In vitro studies showed the CD4ζ expressing hESC- and iPSC-NK cells inhibited HIV replication in CD4+ T-cells more efficiently than their unmodified counterparts. We then evaluated CD4ζ expressing hESC (CD4ζ-hESC)- and iPSC-NK cells in vivo anti-HIV activity using a humanized mouse model. We demonstrated significant suppression of HIV replication in mice treated with both CD4ζ-modified and -unmodified hESC-/iPSC-NK cells compared with control mice. However, we did not observe significantly increased efficacy of CD4ζ expression in suppression of HIV infection. These studies indicate that hESC/iPSC-based immunotherapy can be used as a unique resource to target HIV/AIDS.

Cell-associated transmission of HIV type 1 and other lentiviruses in small-animal models

Small-animal models of lentivirus transmission have repeatedly demonstrated transmission by cell-associated virus via vaginal, rectal, and oral routes. The earliest experiments were in the cat/feline immunodeficiency virus model, followed a decade later by successful vaginal transmission of cell-associated human immunodeficiency virus (HIV) in mice bearing transplanted human immune cells. After early unsuccessful attempts at cell-associated transmission in nonhuman primates, renewed investigation in diverse primate models has now confirmed the findings from the cat and humanized mouse models. Improvements in humanized mouse models have made them the preferred small-animal models to study HIV mucosal transmission. They provide complementary systems to nonhuman primate models to aid in the elucidation of the many remaining questions on the mechanism of and means to prevent both cell-associated and cell-free HIV transmission across mucosal barriers.

Nanotech-derived topical microbicides for HIV prevention: the road to clinical development

More than three decades since its discovery, HIV infection remains one of the most aggressive epidemics worldwide, with more than 35 million people infected. In sub-Saharan Africa, heterosexual transmissions represent nearly 80% of new infections, with 50% of these occurring in women. In an effort to stop the dramatic spread of the HIV epidemic, new preventive treatments, such as microbicides, have been developed. Nanotechnology has revolutionized this field by designing and engineering novel highly effective nano-sized materials as microbicide candidates. This review illustrates the most recent advances in nanotech-derived HIV prevention strategies, as well as the main steps required to translate promising in vitro results into clinical trials.

Formulation and delivery of anti-HIV rectal microbicides: advances and challenges

Men and women engaged in unprotected receptive anal intercourse (RAI) are at higher risk of acquiring HIV from infected partners. The implementation of preventive strategies is urgent and rectal microbicides may be a useful tool in reducing the sexual transmission of HIV. However, pre-clinical and first clinical trials have been able to identify limitations of candidate products, mostly related with safety issues, which can in turn enhance viral infection. Indeed, the development of suitable formulations for the rectal delivery of promising antiretroviral drugs is not an easy task, and has been mostly based on products specifically intended for vaginal delivery, but these have been shown to provide sub-optimal outcomes when administered rectally. Research and development in the rectal microbicide field are now charting their own path and important information is now available. In particular, specific formulation requirements of rectal microbicide products that need to be met have just recently been acknowledged despite additional work being still required. Desirable rectal microbicide product features regarding characteristics such as pH, osmolality, excipients, dosage forms, volume to be administered and the need for applicator use have been studied and defined in recent years, and specific guidance is now possible. This review provides a synopsis of the field of rectal microbicides, namely past and ongoing clinical studies, and details on formulation and drug delivery issues regarding the specific development of rectal microbicide products. Also, future work, as required for the advancement of the field, is discussed.

HIV pre-exposure prophylaxis: mucosal tissue drug distribution of RT inhibitor Tenofovir and entry inhibitor Maraviroc in a humanized mouse model

Pre-exposure prophylaxis (PrEP) strategies utilizing anti-retroviral drugs show considerable promise for HIV prevention. However there is insufficient pharmacokinetic (PK) data on drug concentrations required for protection at the relevant mucosal tissues where the infection is initiated. Here we evaluated the utility of a humanized mouse model to derive PK data on two leading drugs, the RT inhibitor Tenofovir (TFV) and CCR5 inhibitor Maraviroc (MVC). Following oral dosing, both the drugs and the intracellular active TFV-diphosphate could be detected in vaginal, rectal and intestinal tissues. The drug exposures (AUC₂₄ h) were found to be higher in vaginal tissue compared to plasma with even higher levels detected in rectal and intestinal tissues. The overall trends of drug concentrations seen in humanized mice reflect those seen in the human thus establishing the utility of this model complementing the present non-human primate (NHP) models for future pre-clinical evaluations of promising HIV PrEP drug candidates.

Formulation and characterization of polymeric films containing combinations of antiretrovirals (ARVs) for HIV prevention

PURPOSE

To develop polymeric films containing dual combinations of anti-HIV drug candidate tenofovir, maraviroc and dapivirine for vaginal application as topical microbicides.

METHODS

A solvent casting method was used to manufacture the films. Solid phase solubility was used to identify potential polymers for use in the film formulation. Physical and chemical properties (such as water content, puncture strength and in vitro release) and product stability were determined. The bioactivity of the film products against HIV was assessed using the TZM-bl assay and a cervical explant model.

RESULTS

Polymers identified from the solid phase solubility study maintained tenofovir and maraviroc in an amorphous state and prevented drug crystallization. Three combination film products were developed using cellulose polymers and polyvinyl alcohol. The residual water content in all films was <10% (w/w). All films delivered the active agents with release of >50% of film drug content within 30 min. Stability testing confirmed that the combination film products were stable for 12 months at ambient temperature and 6 months under stressed conditions. Antiviral activity was confirmed in TZM-bl and cervical explant models.

CONCLUSIONS

Polymeric films can be used as a stable dosage form for the delivery of antiretroviral combinations as microbicides.

Enhanced activity of carbosilane dendrimers against HIV when combined with reverse transcriptase inhibitor drugs: searching for more potent microbicides

Self-administered topical microbicides or oral preexposure prophylaxis could be very helpful tools for all risk groups to decrease the human immunodeficiency virus (HIV)-1 infection rates. Up until now, antiretrovirals (ARVs) have been the most advanced microbicide candidates. Nevertheless, the majority of clinical trials has failed in HIV-1 patients. Nanotechnology offers suitable approaches to develop novel antiviral agents. Thereby, new nanosystems, such as carbosilane dendrimers, have been shown to be safe and effective compounds against HIV with great potential as topical microbicides. In addition, because most of the attempts to develop effective topical microbicides were unsuccessful, combinatorial strategies could be a valid approach when designing new microbicides. We evaluated various combinations of anionic carbosilane dendrimers with sulfated (G3-S16) and naphthyl sulfonated (G2-NF16) ended groups with different ARVs against HIV-1 infection. The G3-S16 and G2-NF16 dendrimers showed a synergistic or additive activity profile with zidovudine, efavirenz, and tenofovir in the majority of the combinations tested against the X4 and R5 tropic HIV-1 in cell lines, as well as in human primary cells. Therefore, the combination of ARVs and polyanionic carbosilane dendrimers enhances the antiviral potency of the individual compounds, and our findings support further clinical research on combinational approaches as potential microbicides to block the sexual transmission of HIV-1.

Development and bioanalytical validation of a liquid chromatographic-tandem mass spectrometric (LC-MS/MS) method for the quantification of the CCR5 antagonist maraviroc in human plasma

BACKGROUND

Maraviroc is a CCR5 antagonist that has been utilized as a viral entry inhibitor in the management of HIV-1. Current clinical trials are pursuing maraviroc drug efficacy in both oral and topical formulations. Therefore, in order to fully understand drug pharmacokinetics, a sensitive method is required to quantify plasma drug concentrations.

METHODS

Maraviroc-spiked plasma was combined with acetonitrile containing an isotopically-labeled internal standard, and following protein precipitation, samples were evaporated to dryness and reconstituted for liquid chromatographic-tandem mass spectrometric (LC-MS/MS) analysis. Chromatographic separation was achieved on a Waters BEH C8, 50×2.1 mm UPLC column, with a 1.7 μm particle size and the eluent was analyzed using an API 4000 mass analyzer in selected reaction monitoring mode. The method was validated as per FDA Bioanalytical Method Validation guidelines.

RESULTS

The analytical measuring range of the LC-MS/MS method is 0.5-1000 ng/ml. Calibration curves were generated using weighted 1/x(2) quadratic regression. Inter-and intra-assay precision was ≤5.38% and ≤5.98%, respectively; inter-and intra-assay accuracy (%DEV) was ≤10.2% and ≤8.44%, respectively. Additional studies illustrated similar matrix effects between maraviroc and its internal standard, and that maraviroc is stable under a variety of conditions. Method comparison studies with a reference LC-MS/MS method show a slope of 0.948 with a Spearman coefficient of 0.98.

CONCLUSIONS

Based on the validation metrics, we have generated a sensitive and automated LC-MS/MS method for maraviroc quantification in human plasma.

Targeting the C-type lectins-mediated host-pathogen interactions with dextran

Dextran, the α-1,6-linked glucose polymer widely used in biology and medicine, promises new applications. Linear dextran applied as a blood plasma substitute demonstrates a high rate of biocompatibility. Dextran is present in foods, drugs, and vaccines and in most cases is applied as a biologically inert substance. In this review we analyze dextran's cellular uptake principles, receptor specificity and, therefore, its ability to interfere with pathogen-lectin interactions: a promising basis for new antimicrobial strategies. Dextran-binding receptors in humans include the DC-SIGN (dendritic cell-specific intercellular adhesion molecule 3-grabbing nonintegrin) family receptors: DC-SIGN (CD209) and L-SIGN (the liver and lymphatic endothelium homologue of DC-SIGN), the mannose receptor (CD206), and langerin. These receptors take part in the uptake of pathogens by dendritic cells and macrophages and may also participate in the modulation of immune responses, mostly shown to be beneficial for pathogens per se rather than host(s). It is logical to predict that owing to receptor-specific interactions, dextran or its derivatives can interfere with these immune responses and improve infection outcome. Recent data support this hypothesis. We consider dextran a promising molecule for the development of lectin-glycan interaction-blocking molecules (such as DC-SIGN inhibitors) that could be applied in the treatment of diseases including tuberculosis, influenza, hepatitis B and C, human immunodeficiency virus infection and AIDS, etc. Dextran derivatives indeed change the pathology of infections dependent on DC-SIGN and mannose receptors. Complete knowledge of specific dextran-lectin interactions may also be important for development of future dextran applications in biological research and medicine.

Evaluation of PD 404,182 as an anti-HIV and anti-herpes simplex virus microbicide

PD 404,182 (PD) is a synthetic compound that was found to compromise HIV integrity via interaction with a nonenvelope protein viral structural component (A. M. Chamoun et al., Antimicrob. Agents Chemother. 56:672-681, 2012). The present study evaluates the potential of PD as an anti-HIV microbicide and establishes PD's virucidal activity toward another pathogen, herpes simplex virus (HSV). We show that the anti-HIV-1 50% inhibitory concentration (IC50) of PD, when diluted in seminal plasma, is ∼1 μM, similar to the IC50 determined in cell culture growth medium, and that PD retains full anti-HIV-1 activity after incubation in cervical fluid at 37°C for at least 24 h. In addition, PD is nontoxic toward vaginal commensal Lactobacillus species (50% cytotoxic concentration [CC50], >300 μM), freshly activated human peripheral blood mononuclear cells (CC50, ∼200 μM), and primary CD4(+) T cells, macrophages, and dendritic cells (CC50, >300 μM). PD also exhibited high stability in pH-adjusted Dulbecco's phosphate-buffered saline with little to no activity loss after 8 weeks at pH 4 and 42°C, indicating suitability for formulation for transportation and storage in developing countries. Finally, for the first time, we show that PD inactivates herpes simplex virus 1 (HSV-1) and HSV-2 at submicromolar concentrations. Due to the prevalence of HSV infection, the ability of PD to inactivate HSV may provide an additional incentive for use as a microbicide. The ability of PD to inactivate both HIV-1 and HSV, combined with its low toxicity and high stability, warrants additional studies for the evaluation of PD's microbicidal candidacy in animals and humans.

Pharmacokinetics and pharmacodynamics in HIV prevention; current status and future directions: a summary of the DAIDS and BMGF sponsored think tank on pharmacokinetics (PK)/pharmacodynamics (PD) in HIV prevention

Thirty years after its beginning, the HIV/AIDS epidemic is still raging around the world. According to UNAIDS, in 2011 alone 1.7M deaths were attributable to AIDS, and 2.5M people were newly infected by the virus. Despite the success in treating HIV-infected people with potent antiretroviral drugs, preventing HIV infection is the key to ending the epidemic. Recently, the efficacy of topical and systemic antiviral chemoprophylaxis (i.e., preexposure prophylaxis or "PrEP"), using the same drugs used for HIV treatment, has been demonstrated in a number of clinical trials. However, results from other trials have been inconsistent, especially those evaluating PrEP in women. These inconsistencies may result from our incomplete understanding of pharmacokinetics (PK)/pharmacodynamics (PD) at the mucosal sites of sexual transmission: the male and female gastrointestinal and reproductive tracts. The drug concentrations used in these trials were derived from those used for treatment; however, we still do not know the relationship between the therapeutic and the preventive dose. This article presents the first comprehensive review of the available data in the HIV pharmacology field from animal models to human studies, and outlines gaps, challenges, and future directions. Addressing these pharmacological gaps and challenges will be critical in selecting and advancing future PrEP candidates and strategies with the greatest impact on the HIV epidemic.

Lack of prophylactic efficacy of oral maraviroc in macaques despite high drug concentrations in rectal tissues

Maraviroc (MVC) is a potent CCR5 coreceptor antagonist that is in clinical testing for daily oral pre-exposure prophylaxis (PrEP) for HIV prevention. We used a macaque model consisting of weekly SHIV162p3 exposures to evaluate the efficacy of oral MVC in preventing rectal SHIV transmission. MVC dosing was informed by the pharmacokinetic profile seen in blood and rectal tissues and consisted of a human-equivalent dose given 24 h before virus exposure, followed by a booster postexposure dose. In rectal secretions, MVC peaked at 24 h (10,242 ng/ml) with concentrations at 48 h that were about 40 times those required to block SHIV infection of peripheral blood mononuclear cells (PBMCs) in vitro. Median MVC concentrations in rectal tissues at 24 h (1,404 ng/g) were 30 and 10 times those achieved in vaginal or lymphoid tissues, respectively. MVC significantly reduced macrophage inflammatory protein 1β-induced CCR5 internalization in rectal mononuclear cells, an indication of efficient binding to CCR5 in rectal lymphocytes. The half-life of CCR5-bound MVC in PBMCs was 2.6 days. Despite this favorable profile, 5/6 treated macaques were infected during five rectal SHIV exposures as were 3/4 controls. MVC treatment was associated with a significant increase in the percentage of CD3(+)/CCR5(+) cells in blood. We show that high and durable MVC concentrations in rectal tissues are not sufficient to prevent SHIV infection in macaques. The increases in CD3(+)/CCR5(+) cells seen during MVC treatment point to unique immunological effects of CCR5 inhibition by MVC. The implications of these immunological effects on PrEP with MVC require further evaluation.

Efficient single tobamoviral vector-based bioproduction of broadly neutralizing anti-HIV-1 monoclonal antibody VRC01 in Nicotiana benthamiana plants and utility of VRC01 in combination microbicides

Broadly neutralizing monoclonal antibodies (bnMAbs) may offer powerful tools for HIV-1 preexposure prophylaxis, such as topical microbicides. However, this option is hampered due to expensive MAb biomanufacturing based on mammalian cell culture. To address this issue, we developed a new production system for bnMAb VRC01 in Nicotiana benthamiana plants using a tobamovirus replicon vector. Unlike conventional two-vector-based expression, this system was designed to overexpress full-length IgG1 from a single polypeptide by means of kex2p-like enzyme recognition sites introduced between the heavy and light chains. An enzyme-linked immunosorbent assay (ELISA) revealed that gp120-binding VRC01 IgG1 was maximally accumulated on 5 to 7 days following vector inoculation, yielding ~150 mg of the bnMAb per kg of fresh leaf material. The plant-made VRC01 (VRC01p) was efficiently purified by protein A affinity followed by hydrophobic-interaction chromatography. ELISA, surface plasmon resonance, and an HIV-1 neutralization assay demonstrated that VRC01p has gp120-binding affinity and HIV-1-neutralization capacity virtually identical to the human-cell-produced counterpart. To advance VRC01p's use in topical microbicides, we analyzed combinations of the bnMAb with other microbicide candidates holding distinct antiviral mechanisms in an HIV-1 neutralization assay. VRC01p exhibited clear synergy with the antiviral lectin griffithsin, the CCR5 antagonist maraviroc, and the reverse transcriptase inhibitor tenofovir in multiple CCR5-tropic HIV-1 strains from clades A, B, and C. In summary, VRC01p is amenable to robust, rapid, and large-scale production and may be developed as an active component in combination microbicides with other anti-HIV agents such as antiviral lectins, CCR5 antagonists, and reverse transcriptase inhibitors.

Durable knockdown and protection from HIV transmission in humanized mice treated with gel-formulated CD4 aptamer-siRNA chimeras

The continued spread of HIV underscores the need to interrupt transmission. One attractive strategy, in the absence of an effective vaccine, is a topical microbicide, but the need for application around the time of sexual intercourse leads to poor patient compliance. Intravaginal (IVAG) application of CD4 aptamer-siRNA chimeras (CD4-AsiCs) targeting the HIV coreceptor CCR5, gag, and vif protected humanized mice from sexual transmission. In non-dividing cells and tissue, RNAi-mediated gene knockdown lasts for several weeks, providing an opportunity for infrequent dosing not temporally linked to sexual intercourse, when compliance is challenging. Here, we investigate the durability of gene knockdown and viral inhibition, protection afforded by CCR5 or HIV gene knockdown on their own, and effectiveness of CD4-AsiCs formulated in a gel in polarized human cervicovaginal explants and in humanized mice. CD4-AsiC-mediated gene knockdown persisted for several weeks. Cell-specific gene knockdown and protection were comparable in a hydroxyethylcellulose gel formulation. CD4-AsiCs against CCR5 or gag/vif performed as well as a cocktail in humanized mice. Transmission was completely blocked by CCR5 CD4-AsiCs applied 2 days before challenge. Significant, but incomplete, protection also occurred when exposure was delayed for 4 or 6 days. CD4-AsiCs targeting gag/vif provided some protection when administered only after exposure. These data suggest that CD4-AsiCs are a promising approach for developing an HIV microbicide.

New generation humanized mice for virus research: comparative aspects and future prospects

Work with human specific viruses will greatly benefit from the use of an in vivo system that provides human target cells and tissues in a physiological setting. In this regard humanized mice (hu-Mice) have played an important role in our understanding of viral pathogenesis and testing of therapeutic strategies. Limitations with earlier versions of hu-Mice that lacked a functioning human immune system are currently being overcome. The new generation hu-Mouse models are capable of multilineage human hematopoiesis and generate T cells, B cells, macrophages and dendritic cells required for an adaptive human immune response. Now any human specific pathogen that can infect humanized mice can be studied in the context of ongoing infection and immune responses. Two leading humanized mouse models are currently employed: the hu-HSC model is created by transplantation of human hematopoietic stem cells (HSC), whereas the BLT mouse model is prepared by transplantation of human fetal liver, thymus and HSC. A number of human specific viruses such as HIV-1, dengue, EBV and HCV are being studied intensively in these systems. Both models permit infection by mucosal routes with viruses such as HIV-1 thus allowing transmission prevention studies. Cellular and humoral immune responses are seen in both the models. While there is efficient antigen specific IgM production, IgG responses are suboptimal due to inefficient immunoglobulin class switching. With the maturation of T cells occurring in the autologous human thymus, BLT mice permit human HLA restricted T cell responses in contrast to hu-HSC mice. However, the strength of the immune responses needs further improvement in both models to reach the levels seen in humans. The scope of hu-Mice use is further broadened by transplantation of additional tissues like human liver thus permitting immunopathogenesis studies on hepatotropic viruses such as HCV. Numerous studies that encompass antivirals, gene therapy, viral evolution, and the generation of human monoclonal antibodies have been conducted with promising results in these mice. For further improvement of the new hu-Mouse models, ongoing work is focused on generating new strains of immunodeficient mice transgenic for human HLA molecules to strengthen immune responses and human cytokines and growth factors to improve human cell reconstitution and their homeostatic maintenance.

Engineering HIV-1-resistant T-cells from short-hairpin RNA-expressing hematopoietic stem/progenitor cells in humanized BLT mice

Down-regulation of the HIV-1 coreceptor CCR5 holds significant potential for long-term protection against HIV-1 in patients. Using the humanized bone marrow/liver/thymus (hu-BLT) mouse model which allows investigation of human hematopoietic stem/progenitor cell (HSPC) transplant and immune system reconstitution as well as HIV-1 infection, we previously demonstrated stable inhibition of CCR5 expression in systemic lymphoid tissues via transplantation of HSPCs genetically modified by lentiviral vector transduction to express short hairpin RNA (shRNA). However, CCR5 down-regulation will not be effective against existing CXCR4-tropic HIV-1 and emergence of resistant viral strains. As such, combination approaches targeting additional steps in the virus lifecycle are required. We screened a panel of previously published shRNAs targeting highly conserved regions and identified a potent shRNA targeting the R-region of the HIV-1 long terminal repeat (LTR). Here, we report that human CD4⁺ T-cells derived from transplanted HSPC engineered to co-express shRNAs targeting CCR5 and HIV-1 LTR are resistant to CCR5- and CXCR4- tropic HIV-1-mediated depletion in vivo. Transduction with the combination vector suppressed CXCR4- and CCR5- tropic viral replication in cell lines and peripheral blood mononuclear cells in vitro. No obvious cytotoxicity or interferon response was observed. Transplantation of combination vector-transduced HSPC into hu-BLT mice resulted in efficient engraftment and subsequent stable gene marking and CCR5 down-regulation in human CD4⁺ T-cells within peripheral blood and systemic lymphoid tissues, including gut-associated lymphoid tissue, a major site of robust viral replication, for over twelve weeks. CXCR4- and CCR5- tropic HIV-1 infection was effectively inhibited in hu-BLT mouse spleen-derived human CD4⁺ T-cells ex vivo. Furthermore, levels of gene-marked CD4⁺ T-cells in peripheral blood increased despite systemic infection with either CXCR4- or CCR5- tropic HIV-1 in vivo. These results demonstrate that transplantation of HSPCs engineered with our combination shRNA vector may be a potential therapy against HIV disease.

A silicone elastomer vaginal ring for HIV prevention containing two microbicides with different mechanisms of action

Vaginal rings are currently being developed for the long-term (at least 30 days) continuous delivery of microbicides against human immunodeficiency virus (HIV). Research to date has mostly focused on devices containing a single antiretroviral compound, exemplified by the 25mg dapivirine ring currently being evaluated in a Phase III clinical study. However, there is a strong clinical rationale for combining antiretrovirals with different mechanisms of action in a bid to increase breadth of protection and limit the emergence of resistant strains. Here we report the development of a combination antiretroviral silicone elastomer matrix-type vaginal ring for simultaneous controlled release of dapivirine, a non-nucleoside reverse transcriptase inhibitor, and maraviroc, a CCR5-targeted HIV-1 entry inhibitor. Vaginal rings loaded with 25mg dapivirine and various quantities of maraviroc (50-400mg) were manufactured and in vitro release assessed. The 25mg dapivirine and 100mg maraviroc formulation was selected for further study. A 24-month pharmaceutical stability evaluation was conducted, indicating good product stability in terms of in vitro release, content assay, mechanical properties and related substances. This combination ring product has now progressed to Phase I clinical testing.

In vivo blockade of the PD-1 receptor suppresses HIV-1 viral loads and improves CD4+ T cell levels in humanized mice

The programmed death-1 (PD-1) pathway limits the function of virus-specific T cells during chronic infection. We previously showed that blockade of the PD-1 pathway increases HIV-1-associated T cell function in vitro. However, the effect of PD-1 blockade on HIV-1 disease progression in vivo has not been examined. As in humans, HIV-1-infected humanized BALB/c-Rag2(-/-)γc(-/-) (Rag-hu) mice express elevated levels of PD-1 on T cells during chronic infection. To examine the effect of PD-1 blockade on disease progression, Rag-hu mice with chronic HIV-1 infection were treated with a blocking mAb directed against programmed cell death-1 ligand-1, the ligand for PD-1. Programmed cell death-1 ligand-1-treated Rag-hu mice exhibited a progressive decrease in the HIV-1 plasma viral load, with a 7-fold decrease by day 7, a 20-fold decrease by day 14, a 178-fold decrease by day 21, and a 269-fold decrease by day 28 postinitiation of treatment. By day 7, the percentage of CD4(+) T cells was statistically higher in the treated compared with the untreated group, and this trend was sustained throughout the 28-d treatment period. Moreover, there was a strong inverse correlation between plasma viral load and the percentage of both CD4(+) (r = -0.66; p < 0.0001) and CD8(+) (r = -0.64; p < 0.0001) T cells in the treated mice but not the untreated mice. This study provides "proof of concept" that humanized mice can be used to examine the effects of immunotherapeutic interventions on HIV-1 infection. Furthermore, to our knowledge, these data demonstrate for the first time that blockade of the PD-1 pathway reduces HIV-1 viral loads.

Premature activation of the HIV RNase H drives the virus into suicide: a novel microbicide?

Sexual transmission of HIV is the major cause of spread of HIV in Africa and the Third World and is an unmet medical need. Recently, microbicides have attracted attention because they allow females to protect themselves and their offspring. We are exploiting one of the four retroviral enzymes, the ribonuclease H, RNase H, as a novel approach for a microbicide. It is the only enzyme of HIV not yet targeted by antiretroviral therapy. The enzyme is linked to the reverse transcriptase (RT) and hydrolyzes the RNA moiety of RNA-DNA hybrids. The RNase H is located inside virus particles and normally functions during viral replication inside cells. Here we show that activating the RNase H prematurely inside the virus particles destroys the viral genome and abrogates viral infectivity. The antiviral compound consists of a synthetic oligodeoxynucleotide (ODN), which creates an artificial RNA-DNA hybrid substrate for the RNase H inside the particle. The compound was analyzed in mouse models including humanized SCID mice and the vagina of mice. Infection was reduced up to 1000-fold or could be completely prevented. The compound is suitable as microbicide or to prevent mother-to-child transmission.

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.

Microbicides: still a long road to success

The development of efficient microbicides, the topically applied compounds that protect uninfected individuals from acquiring HIV-1, is a promising strategy to contain HIV-1 epidemics. Such microbicides should of course possess anti-HIV-1 activity, but they should also act against other genital pathogens, which facilitate HIV-1 transmission. The new trend in microbicide strategy is to use drugs currently used in HIV-1 therapy. The success of this strategy is mixed so far and is impaired by our limited knowledge of the basic mechanisms of HIV-1 transmission as well as by the inadequacy of the systems in which microbicides are tested in preclinical studies.

Topical gel formulation of broadly neutralizing anti-HIV-1 monoclonal antibody VRC01 confers protection against HIV-1 vaginal challenge in a humanized mouse model

The new generation broadly neutralizing antibody VRC01 against HIV-1 shows great potential as a topically administered microbicide to prevent sexual transmission. We evaluated its efficacy in a RAG-hu humanized mouse model of vaginal HIV-1 transmission. Mice were challenged vaginally with R5 tropic HIV-1 BaL an hour after intravaginal application of the VRC01 (1 mg/ml concentration) gel. A combination of four first generation bNAbs, namely b12, 2F5, 4E10 and 2G12, was used as a positive efficacy control whereas a non-specific dengue MAb 4G2 was used as negative control. Our results showed that seven out of nine VRC01 antibody administered mice and all of the mice receiving the four bNAb antibody combination were protected against HIV-1 challenge. These findings demonstrate the efficacy of the new bNAb VRC01 as a topical microbicide to protect against HIV-1 vaginal transmission and highlight the use of the RAG-hu mouse model for testing HIV prevention strategies.