Distribution of cell-free and cell-associated HIV surrogates in the female genital tract after simulated vaginal intercourse

Mapping Colorectal Distribution of Cell-free and Cell-associated HIV Surrogates Following Simulated Anal Intercourse to Aid Rectal Microbicide Development

BACKGROUND

Anal sex remains the greatest HIV transmission risk for men who have sex with men and carries substantial population attributable risk among women. Despite a growing array of HIV pre-exposure prophylaxis (PrEP) options, rectal microbicides remain desirable as on demand, non-systemic PrEP. Rectal microbicide product development for PrEP requires understanding the spatiotemporal distribution of HIV infectious elements in the rectosigmoid to optimize formulation development.

SETTING

Outpatient setting with healthy research participants.

METHODS

Six healthy men underwent simulated receptive anal sex with an artificial phallus fitted with a triple lumen catheter in the urethral position. To simulate ejaculation of HIV-infected semen, autologous seminal plasma laden with autologous blood lymphocytes from apheresis labeled with 111Indium-oxine (cell-associated) and 99mTechnetium-sulfur colloid (cell-free) as HIV surrogates were injected into the rectal lumen through the phallic urethra. Spatiotemporal distribution of each radioisotope was assessed using SPECT/CT over eight hours. Analysis of radiolabel distribution used a flexible principal curve algorithm to quantitatively estimate rectal lumen distribution.

RESULTS

Cell-free and cell-associated HIV surrogates distributed to a maximal distance of 15 and 16 cm, respectively, from the anorectal junction (∼19 and ∼20 cm from the anal verge), with a maximal signal intensity located 6 and 7 cm, respectively. There were no significant differences in any distribution parameters between cell-free and cell-associated HIV surrogate.

CONCLUSIONS

Cell-free and cell-associated HIV surrogate distribution in the rectosigmoid can be quantified with spatiotemporal pharmacokinetic methods. These results describe the ideal luminal target distribution to guide rectal microbicide development.

Women-specific routes of administration for drugs: A critical overview

The woman's body presents a number of unique anatomical features that can constitute valuable routes for the administration of drugs, either for local or systemic action. These are associated with genitalia (vaginal, endocervical, intrauterine, intrafallopian and intraovarian routes), changes occurring during pregnancy (extra-amniotic, intra-amniotic and intraplacental routes) and the female breast (breast intraductal route). While the vaginal administration of drug products is common, other routes have limited clinical application and are fairly unknown even for scientists involved in drug delivery science. Understanding the possibilities and limitations of women-specific routes is of key importance for the development of new preventative, diagnostic and therapeutic strategies that will ultimately contribute to the advancement of women's health. This article provides an overview on women-specific routes for the administration of drugs, focusing on aspects such as biological features pertaining to drug delivery, relevance in current clinical practice, available drug dosage forms/delivery systems and administration techniques, as well as recent trends in the field.

PET/CT targeted tissue sampling reveals virus specific dIgA can alter the distribution and localization of HIV after rectal exposure

Human immunodeficiency virus (HIV) vaccines have not been successful in clinical trials. Dimeric IgA (dIgA) in the form of secretory IgA is the most abundant antibody class in mucosal tissues, making dIgA a prime candidate for potential HIV vaccines. We coupled Positron Emission Tomography (PET) imaging and fluorescent microscopy of 64Cu-labeled, photoactivatable-GFP HIV (PA-GFP-BaL) and fluorescently labeled dIgA to determine how dIgA antibodies influence virus interaction with mucosal barriers and viral penetration in colorectal tissue. Our results show that HIV virions rapidly disseminate throughout the colon two hours after exposure. The presence of dIgA resulted in an increase in virions and penetration depth in the transverse colon. Moreover, virions were found in the mesenteric lymph nodes two hours after viral exposure, and the presence of dIgA led to an increase in virions in mesenteric lymph nodes. Taken together, these technologies enable in vivo and in situ visualization of antibody-virus interactions and detailed investigations of early events in HIV infection.

Molecular and cellular cues governing nanomaterial-mucosae interactions: from nanomedicine to nanotoxicology

Mucosal tissues constitute the largest interface between the body and the surrounding environment and they regulate the access of molecules, supramolecular structures, particulate matter, and pathogens into it. All mucosae are characterized by an outer mucus layer that protects the underlying cells from physicochemical, biological and mechanical insults, a mono-layered or stratified epithelium that forms tight junctions and controls the selective transport of solutes across it and associated lymphoid tissues that play a sentinel role. Mucus is a gel-like material comprised mainly of the glycoprotein mucin and water and it displays both hydrophilic and hydrophobic domains, a net negative charge, and high porosity and pore interconnectivity, providing an efficient barrier for the absorption of therapeutic agents. To prolong the residence time, absorption and bioavailability of a broad spectrum of active compounds upon mucosal administration, mucus-penetrating and mucoadhesive particles have been designed by tuning the chemical composition, the size, the density, and the surface properties. The benefits of utilizing nanomaterials that interact intimately with mucosae by different mechanisms in the nanomedicine field have been extensively reported. To ensure the safety of these nanosystems, their compatibility is evaluated in vitro and in vivo in preclinical and clinical trials. Conversely, there is a growing concern about the toxicity of nanomaterials dispersed in air and water effluents that unintentionally come into contact with the airways and the gastrointestinal tract. Thus, deep understanding of the key nanomaterial properties that govern the interplay with mucus and tissues is crucial for the rational design of more efficient drug delivery nanosystems (nanomedicine) and to anticipate the fate and side-effects of nanoparticulate matter upon acute or chronic exposure (nanotoxicology). This review initially overviews the complex structural features of mucosal tissues, including the structure of mucus, the epithelial barrier, the mucosal-associated lymphatic tissues and microbiota. Then, the most relevant investigations attempting to identify and validate the key particle features that govern nanomaterial-mucosa interactions and that are relevant in both nanomedicine and nanotoxicology are discussed in a holistic manner. Finally, the most popular experimental techniques and the incipient use of mathematical and computational models to characterize these interactions are described.

Mucosal Immunity in HIV/SIV Infection: T Cells, B Cells and Beyond

As our understanding of mucosal immunity increases, it is becoming clear that the host response to HIV-1 is more complex and nuanced than originally believed. The mucosal landscape is populated with a variety of specialized cell types whose functions include combating infectious agents while preserving commensal microbiota, maintaining barrier integrity, and ensuring immune homeostasis. Advances in multiparameter flow cytometry, gene expression analysis and bioinformatics have allowed more detailed characterization of these cell types and their roles in host defense than was previously possible. This review provides an overview of existing literature on immunity to HIV-1 and SIVmac in mucosal tissues of the female reproductive tract and the gastrointestinal tract, focusing on major effector cell populations and briefly summarizing new information on tissue resident memory T cells, T_reg, Th17, Th22 and innate lymphocytes (ILC), subsets that have been studied primarily in the gastrointestinal mucosa.

HIV Antiretroviral Pre-Exposure Prophylaxis: Development Challenges and Pipeline Promise

The US Food and Drug Administration (FDA) approved oral daily tenofovir/emtricitabine (Truvada) for pre-exposure prophylaxis of human immunodeficiency virus (HIV) infection in 2012 on the basis of two randomized controlled trials (RCTs), one in men who have sex with men (MSM) and another in HIV serodiscordant heterosexual couples. Subsequently, even greater efficacy has been demonstrated in MSM with rapid population-level incidence reductions in some locations. In contrast, studies of antiretroviral pre-exposure prophylaxis (PrEP) in heterosexual women showed only modest or no efficacy, largely attributed to low adherence. The mixed results of antiretroviral-based PrEP bear witness to unique drug development challenges at this complicated intersection of sexual behavior, public health, and drug development. Multiple innovative methods and formulation strategies followed to address unmet medical needs of persons struggling with daily oral PrEP adherence or preference for nonsystemic PrEP options. Clinical pharmacology plays essential roles throughout this PrEP development process, especially in early product development and through pharmacologically informed enhancement and interpretation of clinical trials.

Pharmacology of Antiretrovirals in the Female Genital Tract for HIV Prevention

Preexposure prophylaxis (PrEP) is a powerful tool that, as part of a comprehensive prevention package, has potential to significantly impact the HIV epidemic. PrEP effectiveness is believed to be dependent on the exposure and efficacy of antiretrovirals at the site of HIV transmission. Clinical trial results as well as modeling and simulation indicate the threshold of adherence required for PrEP efficacy of emtricitabine/tenofovir disoproxil fumarate may differ between sites of HIV transmission with less forgiveness for missed doses in women exposed through genital tissue compared to people exposed through colorectal tissue. This suggests a role for local and host factors to influence mucosal pharmacology. Here we review the mucosal pharmacology of antiretrovirals in the female genital tract and explore potential determinants of PrEP efficacy. Host factors such as inflammation, coinfections, hormonal status, and the vaginal microbiome will be explored as well as the role of drug-metabolizing enzymes and transporters in regulating local drug exposure. The use of preclinical and early clinical models to predict clinical effectiveness is also discussed.

Early phase dynamics of traceable mCherry fluorescent protein-carrying HIV-1 infection in human peripheral blood mononuclear cells-transplanted NOD/SCID/Jak3-/- mice

We attempted to elucidate early-phase dynamics of HIV-1 infection using replication-competent, red-fluorescent-protein (mCherry)-labeled HIV-1JR-FL (HIVJR-FLmC) and NOD/SCID/Jak3-/- mice transplanted with Individual-A's human peripheral blood mononuclear cells (hPBMC)(hNOJ mice). On day 7 following HIVJR-FLmC inoculation, mCherry-signal-emitting infection foci were readily identified in the subserosa of 10 of 10 HIVJR-FLmC-inoculated hNOJ mice, although infection foci were not located without the mCherry signal in unlabeled HIV-1JR-FL-inoculated mice (n = 6). Even on day 14, infection foci were hardly located in the unlabeled HIV-1JR-FL-inoculated mice, while in all of 7 HIVJR-FLmC-inoculated hNOJ mice examined, mCherry-signal-emitting lymph nodes were easily identified, in which active viral replication was present. On day 14, a significantly larger number of mesenteric lymph nodes were seen in HIVJR-FLmC-exposed hNOJ mice than in HIVJR-FLmC-unexposed mice (P = 0.0025). The weights of mesenteric lymph nodes of those HIVJR-FLmC-exposed hNOJ mice were also greater than those of HIVJR-FLmC-unexposed mice (P = 0.0005). When hNOJ mice were inoculated with HIVJR-FLmC-exposed hPBMC from Individual-B, significantly greater viremia was seen than in cell-free HIVJR-FLmC-inoculated hNOJ mice as examined on day 7. In the lymph nodes of those mice inoculated with HIVJR-FLmC-exposed hPBMC from Individual-B, a substantial number of Individual-B's HIVJR-FLmC-infected cells were identified together with Individual-A's cells as examined on day 14. The present HIVJR-FLmC-infected mouse model represents the first system reported using traceable HIVJR-FLmC and human target cells, not using SIV or simian cells, which should be of utility in studies of early-phases of HIV-1 transmission and in evaluating the effects of potential agents for post-exposure and pre-exposure prophylaxis.

A Comparative Pre-Phase I Study of the Impact of Gel Vehicle Volume on Distal Colon Distribution, User Experience, and Acceptability

For persons at risk of HIV infection who practice receptive anal intercourse (RAI), topical rectal microbicides represent a promising option for coitally dependent protection. The study compared colorectal distribution and user sensory experiences of two different volumes of rectal gel for suitability as rectal microbicide. Eight HIV-negative men with a history of recent RAI were enrolled into a two-period, sequence-randomized dosing study comparing 3.5 and 10 ml of radiolabeled (1 mCi ^99mTc-DTPA) universal placebo, hydroxyethyl cellulose gel. Each participant received two doses in the research unit, one of each volume, separated by a washout period of at least 2 weeks. Each research unit dose was followed by a self-administered take-home dose in the context of preparing for RAI. Safety and gastrointestinal distribution were assessed after the research unit doses, safety, perceptibility, and acceptability, were assessed after take-home doses. There were no adverse effects of Grade 2 or higher and all resolved spontaneously. Both volumes were well tolerated and received high acceptability scores. Perceptibility scores showed meaningful effect size differences ranging from Cohen's d = 0.5 to d = 1.2. The 3.5 and 10 ml gel volumes distributed similarly (p > .2) within the rectosigmoid, ranging from 0.69 to 18.84 cm and 1.21 to 19.01 cm from the anorectal junction, respectively. Both volumes covered the typical gastrointestinal distribution of ejaculate following simulated intercourse based on other studies. Either of these gel volumes could reasonably be pursued for the next phase of development of rectal microbicides.

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.

Simultaneous Evaluation of Safety, Acceptability, Pericoital Kinetics, and Ex Vivo Pharmacodynamics Comparing Four Rectal Microbicide Vehicle Candidates

Preexposure prophylaxis (PrEP) of HIV infection with tenofovir-containing regimens is effective, but plagued by poor adherence in some studies. Options for safe, effective, and acceptable PrEP products, especially for men and women at risk of HIV via receptive anal intercourse (RAI), are needed. We performed a randomized, partially blinded, first-in-human evaluation of four candidate rectal microbicide vehicles-aqueous gel, aqueous fluid, lipid gel, and lipid fluid-to select a prototype for further clinical development. Eight seronegative participants received three doses of each product with each dose separated by at least 2 weeks: one dose was given alone without simulated RAI in clinic, another dose was followed by simulated RAI in clinic, and another dose was self-administered at home in the context of RAI with a partner. Assessments included safety, acceptability, colon histology, ex vivo HIV infectivity of colon tissue explants, and colonic luminal distribution of vehicle and HIV surrogates. Adverse events were all mild and mainly sigmoidoscopy associated. There were minor differences in colon distribution of products and little effect of RAI. Vehicle distribution covered 95% (±7% standard deviation) of the distribution of an HIV surrogate in the colonic lumen. The lipid fluid vehicle increased HIV colon tissue infectability 5-fold [log10 p24 0.68 (95% confidence interval 0.08, 1.28)] and aqueous gel provided 6-fold protection [log10 p24 0.80 (95% confidence interval 0.20, 1.41)] compared to no product baseline. Colon permeability of lipid vehicles was more than 10-fold greater than aqueous vehicles. All products received similar acceptability ratings, though trends favored the gel products. Intensive simultaneous assessment of safety and toxicity, luminal and tissue distribution, ex vivo HIV infectivity, and product acceptability in relevant sexual contexts provided clear differentiation among candidate gels very early in product development. We selected the aqueous gel for further development as a rectal microbicide vehicle.

A Pilot Study Measuring the Distribution and Permeability of a Vaginal HIV Microbicide Gel Vehicle Using Magnetic Resonance Imaging, Single Photon Emission Computed Tomography/Computed Tomography, and a Radiolabeled Small Molecule

Vaginal microbicide gels containing tenofovir have proven effective in HIV prevention, offering the advantage of reduced systemic toxicity. We studied the vaginal distribution and effect on mucosal permeability of a gel vehicle. Six premenopausal women were enrolled. In Phase 1, a spreading gel containing (99m)technetium-DTPA ((99m)Tc) radiolabel and gadolinium contrast for magnetic resonance imaging (MRI) was dosed intravaginally. MRI was obtained at 0.5, 4, and 24 h, and single photon emission computed tomography with conventional computed tomography (SPECT/CT) at 1.5, 5, and 25 h postdosing. Pads and tissues were measured for activity to determine gel loss. In Phase 2, nonoxynol-9 (N-9), containing (99m)Tc-DTPA, was dosed as a permeability control; permeability was measured in blood and urine for both phases. SPECT/CT showed the distribution of spreading gel throughout the vagina with the highest concentration of radiosignal in the fornices and ectocervix; signal intensity diminished over 25 h. MRI showed the greatest signal accumulation in the fornices, most notably 1-4 h postdosing. The median (interquartile range) isotope signal loss from the vagina through 6 h was 29.1% (15.8-39.9%). Mucosal permeability to (99m)Tc-DTPA following spreading gel was negligible, in contrast to N-9, with detectable radiosignal in plasma, peaking at 8 h (5-12). Following spreading gel dosing, 0.004% (0.001-2.04%) of the radiosignal accumulated in urine over 12 h compared to 8.31% (7.07-11.01%) with N-9, (p=0.043). Spreading gel distributed variably throughout the vagina, persisting for 24 h, with signal concentrating in the fornices and ectocervix. The spreading gel had no significant effect on vaginal mucosal permeability.

Polymer-based nanocarriers for vaginal drug delivery

The vaginal delivery of various drugs is well described and its relevance established in current medical practice. Alongside recent advances and achievements in the fields of pharmaceutical nanotechnology and nanomedicine, there is an increasing interest in the potential use of different nanocarriers for the delivery of old and new pharmacologically active molecules with either therapeutic or prophylactic purposes. Nanosystems of polymeric nature in particular have been investigated over the last years and their interactions with mucosal fluids and tissues, as well as genital tract biodistribution upon vaginal administration, are now better understood. While different applications have been envisioned, most of the current research is focusing in the development of nano-formulations with the potential to inhibit the vaginal transmission of HIV upon sexual intercourse. The present work focuses its discussion on the potential and perils of polymer-based nanocarriers for the vaginal administration of different pharmacologically active molecules.

Role of Seminal Plasma in Human Female Reproductive Failure: Immunomodulation, Inflammation, and Infections

Human seminal plasma contains factors that can regulate the female immune system and potentially promote reproductive fitness. Adverse effects on fertility and pregnancy may occur when seminal plasma provides insufficient, excessive, or altered signals or when the female partner is incapable of receiving these signals.

A multi-compartment single and multiple dose pharmacokinetic comparison of rectally applied tenofovir 1% gel and oral tenofovir disoproxil fumarate

This Phase 1, randomized, two-site (United States), double-blind, placebo-controlled study enrolled 18 sexually abstinent men and women. All received a single 300-mg dose of oral tenofovir disoproxil fumarate (TDF) and were then randomized 2∶1 to receive single and then seven daily rectal exposures of vaginally-formulated tenofovir (TFV) 1% gel or a hydroxyethyl cellulose (HEC) placebo gel. Blood, colonic biopsies and rectal and vaginal mucosal fluids were collected after the single oral TDF, the single topical TFV gel dose, and after 7 days of topical TFV gel dosing for extracellular analysis of TFV and intracellular analysis of the active metabolite tenofovir diphosphate (TFVdp) in peripheral blood mononuclear cells (PBMCs) and isolated mucosal mononuclear cells (MMC), including CD4+ and CD4- cell subsets. With a single rectal dose, TFV plasma concentrations were 24–33 fold lower and half-life was 5 h shorter compared to a single oral dose (p = 0.02). TFVdp concentrations were also undetectable in PBMCs with rectal dosing. Rectal tissue exposure to both TFV and TFVdp was 2 to 4-log₁₀ higher after a single rectal dose compared to a single oral dose, and after 7 daily doses, TFVdp accumulated 4.5 fold in tissue. TFVdp in rectal tissue homogenate was predictive (residual standard error, RSE  = 0.47) of tissue MMC intracellular TFVdp concentration, with the CD4+ cells having a 2-fold higher TFVdp concentration than CD4- cells. TFV concentrations from rectal sponges was a modest surrogate indicator for both rectal tissue TFV and TFVdp (RSE  = 0.67, 0.66, respectively) and plasma TFV (RSE  = 0.38). TFV penetrates into the vaginal cavity after oral and rectal dosing, with rectal dosing leading to higher vaginal TFV concentrations (p<0.01).

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

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

Optimizing viable leukocyte sampling from the female genital tract for clinical trials: an international multi-site study

Background

Functional analysis of mononuclear leukocytes in the female genital mucosa is essential for understanding the immunologic effects of HIV vaccines and microbicides at the site of HIV exposure. However, the best female genital tract sampling technique is unclear.

Methods and Findings

We enrolled women from four sites in Africa and the US to compare three genital leukocyte sampling methods: cervicovaginal lavages (CVL), endocervical cytobrushes, and ectocervical biopsies. Absolute yields of mononuclear leukocyte subpopulations were determined by flow cytometric bead-based cell counting. Of the non-invasive sampling types, two combined sequential cytobrushes yielded significantly more viable mononuclear leukocytes than a CVL (p<0.0001). In a subsequent comparison, two cytobrushes yielded as many leukocytes (∼10,000) as one biopsy, with macrophages/monocytes being more prominent in cytobrushes and T lymphocytes in biopsies. Sample yields were consistent between sites. In a subgroup analysis, we observed significant reproducibility between replicate same-day biopsies (r = 0.89, p = 0.0123). Visible red blood cells in cytobrushes increased leukocyte yields more than three-fold (p = 0.0078), but did not change their subpopulation profile, indicating that these leukocytes were still largely derived from the mucosa and not peripheral blood. We also confirmed that many CD4⁺ T cells in the female genital tract express the α4β7 integrin, an HIV envelope-binding mucosal homing receptor.

Conclusions

CVL sampling recovered the lowest number of viable mononuclear leukocytes. Two cervical cytobrushes yielded comparable total numbers of viable leukocytes to one biopsy, but cytobrushes and biopsies were biased toward macrophages and T lymphocytes, respectively. Our study also established the feasibility of obtaining consistent flow cytometric analyses of isolated genital cells from four study sites in the US and Africa. These data represent an important step towards implementing mucosal cell sampling in international clinical trials of HIV prevention.

Association of sex work with reduced activation of the mucosal immune system

BACKGROUND

Unprotected intercourse and seminal discharge are powerful activators of the mucosal immune system and are important risk factors for transmission of human immunodeficiency virus (HIV). This study was designed to determine if female sex work is associated with changes in the mucosal immunity.

METHODS

Cervicovaginal lavage and plasma from 122 HIV-uninfected female sex workers (FSW) and 44 HIV-uninfected low-risk non-FSW from the same socioeconomic district of Nairobi were analyzed for evidence of immune activation (IA). The cervico-mononuclear cells (CMC) were analyzed for cellular activation by flow cytometry.

RESULTS

Lower IA was observed in FSW compared to the low-risk women as demonstrated by the lower level of MIP-3α (P < .001), ITAC (P < .001), MIG (p.0001), IL-1α (P < .001), IL-1β (P < .001), IL-1Rα (P = .0002), IL-6 (P < .001), IL-8 (P < .001), IL-10 (P = .01), IP-10 (P = .0001), MDC (P < .001), MIP-1α, (P < .001), MIP-1β (P = .005), MCP-1 (P = .03), and TNF-α (P = .006). Significant differences were noted as early as 1 year following initiation of sex work and increased with duration of sex work.

CONCLUSION

This study showed that sex work is associated with important changes in the mucosal immune system. By analyzing chemokine/cytokine levels and CMC activation, we observed a lower mucosal IA in HIV-uninfected FSW compared to low-risk women.

Single dose pharmacokinetics of oral tenofovir in plasma, peripheral blood mononuclear cells, colonic tissue, and vaginal tissue

HIV seroconversion outcomes in preexposure prophylaxis (PrEP) trials of oral tenofovir (TFV)-containing regimens are highly sensitive to drug concentration, yet less-than-daily dosing regimens are under study. Description of TFV and its active moiety, TFV diphosphate (TFV-DP), in blood, vaginal tissue, and colon tissue may guide the design and interpretation of PrEP clinical trials. Six healthy women were administered a single oral dose of 300 mg tenofovir disoproxil fumarate (TDF) and 4.3 mg (12.31 MBq, 333 μCi) (14)C-TDF slurry. Blood was collected every 4 h for the first 24 h, then at 4, 8, 11, and 15 days postdosing. Colonic and vaginal samples (tissue, total and CD4(+) cells, luminal fluid and cells) were collected 1, 8 and 15 days postdose. Samples were analyzed for TFV and TFV-DP. Plasma TFV demonstrated triphasic decay with terminal elimination half-life median [interquartile range (IQR)] 69 h (58-77). Peripheral blood mononuclear cell (PBMC) TFV-DP demonstrated biphasic peaks (median 12 h and 96 h) followed by a terminal 48 h (38-76) half-life; Cmax was 20 fmol/million cells (2-63). One day postdose, the TFV-DP paired colon:vaginal tissue concentration ratio was 1 or greater in all subjects' tissue homogenates, median 124 (range 1-281), but was not sustained. The ratio was lower and more variable in cells extracted from tissue. Among all sample types, TFV and TFV-DP half-life ranged from 23 to 139 h. PBMC TFV-DP rose slowly in the hours after dosing indicating that success with exposure-driven dosing regimens may be sensitive to timing of the dose prior to exposure. Colonic tissue homogenate TFV-DP concentrations were greater than in vaginal homogenate at 24 h, but not in cells extracted from tissue. These and the other pharmacokinetic findings will guide the interpretation and design of future PrEP trials.

Pre-exposure prophylaxis for HIV infection: how antiretroviral pharmacology helps to monitor and improve adherence

INTRODUCTION

Pre-exposure prophylaxis (PrEP) with antiretroviral drugs is a novel biomedical intervention that can prevent HIV transmission among high-risk populations. As findings from multiple PrEP studies have suggested that adherence is vital to achieve the full prevention benefits of PrEP, it is important to understand the clinical pharmacology and pharmacokinetic (PK) properties of PrEP antiretrovirals, the association of PK and PrEP efficacy, and the potential for drug concentration measurement to be used as a tool to monitor PrEP adherence.

AREAS COVERED

This review examines studies related to PrEP adherence with attention to the clinical pharmacology and PK of current and novel PrEP agents. Studies of animal models, PK, and clinical trials related to PrEP and adherence were reviewed.

EXPERT OPINION

In summary, when combined as part of a comprehensive prevention strategy that includes use of condoms and risk-reduction counseling, PrEP has tremendous promise as an adjunctive biomedical HIV prevention intervention, providing that adherence is maintained.

Ex vivo characterization of particle transport in mucus secretions coating freshly excised mucosal tissues

Sustained drug delivery to mucosal surfaces has the potential to improve the effectiveness of prophylactic and therapeutic treatments for numerous diseases and conditions, including inflammatory bowel disease, sexually transmitted diseases, cystic fibrosis, glaucoma, dry eye, and various cancers. Sustained delivery systems such as nanoparticles can be useful for mucosal delivery, but recent work suggests they must penetrate the rapidly cleared mucus barrier that overlies all mucosal epithelia to achieve uniform distribution on epithelial surfaces and enhanced residence time. Thus, it is important to evaluate the mucus-penetrating ability of nanosized delivery systems in preclinical animal studies, and for administration to humans. We describe a simple ex vivo method to visualize and quantify nanoparticle transport in mucus on fresh mucosal tissues. Using this method in murine models, we observed variations in the mucus mesh at different anatomical locations, as well as cyclical variations that may have implications for mucosal delivery.

Quantification of the spatial distribution of rectally applied surrogates for microbicide and semen in colon with SPECT and magnetic resonance imaging

AIMS

We sought to describe quantitatively the distribution of rectally administered gels and seminal fluid surrogates using novel concentration-distance parameters that could be repeated over time. These methods are needed to develop rationally rectal microbicides to target and prevent HIV infection.

METHODS

Eight subjects were dosed rectally with radiolabelled and gadolinium-labelled gels to simulate microbicide gel and seminal fluid. Rectal doses were given with and without simulated receptive anal intercourse. Twenty-four hour distribution was assessed with indirect single photon emission computed tomography (SPECT)/computed tomography (CT) and magnetic resonance imaging (MRI), and direct assessment via sigmoidoscopic brushes. Concentration-distance curves were generated using an algorithm for fitting SPECT data in three dimensions. Three novel concentration-distance parameters were defined to describe quantitatively the distribution of radiolabels: maximal distance (D(max) ), distance at maximal concentration (D(Cmax) ) and mean residence distance (D(ave) ).

RESULTS

The SPECT/CT distribution of microbicide and semen surrogates was similar. Between 1 h and 24 h post dose, the surrogates migrated retrograde in all three parameters (relative to coccygeal level; geometric mean [95% confidence interval]): maximal distance (D(max) ), 10 cm (8.6-12) to 18 cm (13-26), distance at maximal concentration (D(Cmax) ), 3.8 cm (2.7-5.3) to 4.2 cm (2.8-6.3) and mean residence distance (D(ave) ), 4.3 cm (3.5-5.1) to 7.6 cm (5.3-11). Sigmoidoscopy and MRI correlated only roughly with SPECT/CT.

CONCLUSIONS

Rectal microbicide surrogates migrated retrograde during the 24 h following dosing. Spatial kinetic parameters estimated using three dimensional curve fitting of distribution data should prove useful for evaluating rectal formulations of drugs for HIV prevention and other indications.

Genital immunology and HIV susceptibility in young women

Women account for a substantial majority of HIV infections in endemic regions, where women are also infected at a much younger age than men. Part of this epidemiological skewing is due to socio-cultural factors, but it is clear that biological factors enhance the susceptibility of women--particularly young women--to HIV acquisition after sexual exposure. These factors, including important differences in mucosal immunology at the site of genital HIV exposure, are the focus of this concise review. Compared to heterosexual men, women have an increased surface area of mucosal HIV exposure, increased mucosal expression of the HIV co-receptor CCR5 and a greater probability of virus exposure on the rectal mucosa. Differences that are specific to young women include a pro-inflammatory immune environment and a proportionate increase in single-cell, columnar genital epithelium. These important biological reasons for enhanced HIV susceptibility in young women highlight the need for targeted HIV prevention within this vulnerable population.

The clinical pharmacology of antiretrovirals for HIV prevention

PURPOSE OF REVIEW

Pre-exposure prophylaxis (PrEP) clinical trial results using antiretrovirals can seem confusing, if not conflicting. We review recent antiretroviral pharmacokinetic studies to help explain PrEP trial results.

RECENT FINDINGS

Pharmacokinetic studies indicate that topical dosing, compared with oral dosing, achieves far higher colon and vaginal tissue drug concentrations, and far lower drug concentrations in blood. After oral dosing, higher tenofovir diphosphate concentrations are found in colon tissue than cervico-vaginal tissue, but the reverse is the case for emtricitabine triphosphate, although it does not persist as long. Vaginal dosing achieves measurable tenofovir concentrations in the rectum and vice versa. Within and among oral PrEP trials, increased drug concentration is associated with increased HIV protection, with drug concentration differences best explained by adherence, rather than pharmacokinetics. The poor level of protection in topical studies is not consistent with concentration-response in oral studies indicating unknown variables in need of further investigation.

SUMMARY

Sparse pharmacokinetic sampling in large trials combined with more intensive sampling in smaller pharmacokinetic-focused studies help explain trial outcome differences due largely to differences in adherence, tissue pharmacokinetics, and type of HIV exposure. Pharmacokinetic analysis can identify protective drug concentration targets, guide dose optimization, and inform future trials.

Understanding factors that modulate HIV infection at the female genital tract mucosae for the rationale design of microbicides

Women are now becoming the pivot of the epidemiological spread of HIV infection worldwide, especially in developing countries. Therefore, research to develop an efficient microbicide is now a priority for the prevention of HIV-1 acquisition in exposed women. However, recent disappointing failures in microbicide clinical trials revealed major gaps in basic and applied knowledge that hinder the development of effective microbicide formulations. Indeed, the inhibitory power of microbicide molecules may be affected by several physiological and immunological factors present in male and female genital tracts. Furthermore, mucosal crossing of HIV-1 to increase the ability to reach the submucosal target cells (macrophages, lymphocytes, and dendritic cells) may be modulated by supraepithelial factors such as seminal complement components (opsonized HIV-1), by epithelial factors released in the submucosal microenvironment such as antimicrobial soluble factors, cytokines, and chemokines, and by potent intraepithelial and submucosal innate immunity. The design of vaginal microbicide formulations should take into account an understanding of the intimate mechanisms involved in the crossing of HIV through the female genital mucosae, in the context of a mixture of both male and female genital fluids.

Factors Important to the Prioritization and Development of Successful Topical Microbicides for HIV-1

Significant advancements in topical microbicide development have occurred since the prevention strategy was first described as a means to inhibit the sexual transmission of HIV-1. The lack of clinical efficacy of the first generation microbicide products has focused development attention on specific antiretroviral agents, and these agents have proven partially successful in human clinical trials. With greater understanding of vaginal and rectal virus infection, replication, and dissemination, better microbicide products and delivery strategies should result in products with enhanced potency. However, a variety of development gaps exist which relate to product dosing, formulation and delivery, and pharmacokinetics and pharmacodynamics which must be better understood in order to prioritize microbicide products for clinical development. In vitro, ex vivo, and in vivo models must be optimized with regard to these development gaps in order to put the right product at the right place, at the right time, and at the right concentration for effective inhibition of virus transmission. As the microbicide field continues to evolve, we must harness the knowledge gained from unsuccessful and successful clinical trials and development programs to continuously enhance our preclinical development algorithms.

Clinical evaluation of microbicide formulations

The clinical evaluation of microbicide formulations presents variable and interacting challenges. Specific domains of acceptability, pharmacokinetics, and toxicity interact with each other to potentially inhibit or enhance a microbicide's efficacy. Each of these is further influenced by application and use parameters in the relative presence (or absence) of vaginal and/or seminal fluids, ultimately impacting effectiveness. Historically, acceptability of formulation and use parameters, and their concomitant behavioral influences, have been considered separately from pharmacokinetics and toxicity. While independent evaluation of these elements is necessary in some respects, we must acknowledge that this approach is not sufficient for the successful development of microbicides. Each needs to be considered in an integrated clinical evaluation strategy. This article presents the rationale for such an approach. This article forms part of a special supplement covering two presentations on clinical evaluation of microbicides from the symposium on "Recent Trends in Microbicide Formulations" held on 25 and 26 January 2010, Arlington, VA.