Ex vivo culture of human colorectal tissue for the evaluation of candidate microbicides

Human immunodeficiency virus transmission-Mechanisms underlying the cell-to-cell spread of human immunodeficiency virus

Despite the success of combined antiretroviral therapy in controlling viral load and reducing the risk of human immunodeficiency virus (HIV) transmission, an estimated 1.5 million new infections occurred worldwide in 2021. These new infections are mainly the result of sexual intercourse and thus involve cells present on the genital mucosa, such as dendritic cells (DCs), macrophages (Mø) and CD4+ T lymphocytes. Understanding the mechanisms by which HIV interacts with these cells and how HIV exploits these interactions to establish infection in a new human host is critical to the development of strategies to prevent and control HIV transmission. In this review, we explore how HIV has evolved to manipulate some of the physiological roles of these cells, thereby gaining access to strategic cellular niches that are critical for the spread and pathogenesis of HIV infection. The interaction of HIV with DCs, Mø and CD4+ T lymphocytes, and the role of the intercellular transfer of viral particles through the establishment of the infectious or virological synapses, but also through membrane protrusions such as filopodia and tunnelling nanotubes (TNTs), and cell fusion or cell engulfment processes are presented and discussed.

Dose finding study for on-demand HIV pre-exposure prophylaxis for insertive sex in sub-Saharan Africa: results from the CHAPS open label randomised controlled trial

BACKGROUND

The efficacy of on-demand HIV pre-exposure prophylaxis (PrEP) for men in sub-Saharan Africa has not been evaluated, and the on-demand PrEP dosing requirement for insertive sex remains unknown.

METHODS

HIV-negative males 13-24 years, requesting voluntary medical male circumcision (VMMC), were enrolled into an open-label randomised controlled trial (NCT03986970), and randomised 1:1:1:1:1:1:1:1:1 to control arm or one of eight arms receiving emtricitabine-tenofovir disoproxil fumarate (F/TDF) or emtricitabine-tenofovir alafenamide (F/TAF) over one or two days, and circumcised 5 or 21 h thereafter. The primary outcome was foreskin p24 concentrations following ex vivo HIV-1BaL challenge. Secondary outcomes included peripheral blood mononuclear cell (PBMC) p24 concentration, and drug concentrations in foreskin tissue, PBMCs, plasma and foreskin CD4+/CD4-cells. In the control arm, post-exposure prophylaxis (PEP) activity of non-formulated tenofovir-emtricitabine (TFV-FTC) or TAF-FTC was assessed with ex vivo dosing 1, 24, 48 or 72 h post-HIV-1 challenge.

FINDINGS

144 participants were analysed. PrEP with F/TDF or F/TAF prevented ex vivo infection of foreskins and PBMCs both 5 and 21 h after PrEP dosing. There was no difference between F/TDF and F/TAF (p24day15 geometric mean ratio 1.06, 95% confidence interval: 0.65-1.74). Additional ex vivo dosing did not further increase inhibition. In the control arm, PEP ex vivo dosing was effective up to 48 post-exposure diminishing thereafter, with TAF-FTC showing prolonged protection compared to TFV-FTC. Participants receiving F/TAF had higher TFV-DP concentrations in foreskin tissue and PBMCs compared with F/TDF, irrespective of dose and sampling interval; but F/TAF did not confer preferential TFV-DP distribution into foreskin HIV target cells. FTC-TP concentrations with both drug regimens were equivalent and ∼1 log higher than TFV-DP in foreskin.

INTERPRETATION

A double dose of either F/TDF or F/TAF given once either 5 or 21 h before ex vivo HIV-challenge provided protection across foreskin tissue. Further clinical evaluation of pre-coital PrEP for insertive sex is warranted.

FUNDING

EDCTP2, Gilead Sciences, Vetenskapsrådet.

Ex Vivo Colonic Tissue Susceptibility to HIV-1 in Cisgender Men and Women

The biology of HIV-1 acquisition through unprotected receptive anal intercourse is understudied. Considering that sex hormones are implicated in intestinal physiology, pathology, and HIV acquisition and pathogenesis, we explored links between sex hormones, ex vivo HIV-1BaL infection of colonic mucosa, and candidate biomarkers of susceptibility to HIV-1 (CD4+ T cell frequencies and immune mediators) in cisgender women and men. No consistent significant associations between sex hormone concentrations and ex vivo tissue infection with HIV-1BaL were detected. In men, serum estradiol (E2) concentrations were positively associated with tissue proinflammatory mediators (IL17A, GM-CSF, IFNγ, TNFα, and MIG/CXCL9) and serum testosterone concentrations were negatively associated with frequencies of activated CD4+ T cells (CD4+CCR5+, CD4+HLA-DR+, and CD4+CD38+HLA-DR+). In women, the only significant interactions were positive associations between progesterone (P4)/E2 ratios and tissue ILRA concentrations and between P4/E2 ratios and frequencies of tissue CD4+α4β7high+ T cells. The study did not reveal relationships between biological sex or phase of the menstrual cycle and ex vivo tissue HIV-1BaL infection and tissue immune mediators. A comparison of CD4+ T cell frequencies between study groups revealed a higher frequency of tissue CD4+α4β7high+ T cells in women versus men. In contrast, higher frequencies of tissue CD4+CD103+ T cells were detected in men versus women in the follicular phase of the menstrual cycle. Overall, the study identified associations between systemic sex hormone concentrations, biological sex, and tissue candidate biomarkers of susceptibility to HIV-1. The significance of these results for tissue susceptibility to HIV-1 and early HIV-1 pathogenesis warrants further investigation.

Pharmacokinetics, the Immunological Impact, and the Effect on HIV Ex-Vivo Infectivity of Maraviroc, Raltegravir, and Lopinavir in Men Who Have Sex with Men Using Postexposure Prophylaxis

Most of the studies using the colorectal tissue explants challenge model have been conducted after one single dose and before reaching a steady state. We consider that longer exposure as in 28-day postexposure prophylaxis (PEP) course and in an at-risk setting, such as after a sexual risk exposure to HIV could give us valuable information about these drugs. In a substudy we assessed pharmacokinetics, changes on immune system and ex-vivo rectal mucosal susceptibility to HIV-1 infection after taking maraviroc (MVC), raltegravir (RAL), and ritonavir-boosted lopinavir (LPV/r) PEP-based regimens in 30 men who have sex with men. Participants received 28 days of twice-daily MVC (n = 11), RAL (n = 10) or LPV/r (n = 9) all with tenofovir/emtricitabine (TDF/FTC) backbone. Blood, rectal fluid, and rectal tissue samples were collected at days 7, 28, and 90 after starting PEP. The samples obtained at day 90 were considered baseline. All studied antiretrovirals were quantifiable at 7 and 28 days in all tissues. Activation markers were increased in CD4 mucosal mononuclear cells (MMCs) after 28 days of MVC: CD38 + 68.5 versus 85.1, p = .008 and CD38+DR +16.1 versus 26.7, p = .008. Exposure to MVC at both endpoints (7 and 28 days) was associated with significant suppression of HIV-1BAL (p = .005 and p = .028), but we did not observe this effect with RAL or LPV/r. Merging together changes in MMC in all arms, we found a positive correlation in the CD8 T cell lineage between the infectivity at day 7 and activation (CD38+ r = 0.43, p = .025, DR + r = 0.547, p = .003 and 38+DR+ r = 0.526, p = .05), senescence (CD57+CD28- r = 0.479, p = .012), naive cells (RA+CCR7+ r = 0.484, p = .01), and CCR5 expression (r = 0.593, p = .001). We conclude that MVC in combination with TDF/FTC was associated with viral suppression in rectal explants and that overall ex-vivo HIV infectivity correlated with activation and senescence in CD8 MMCs.

Pre-clinical evaluation of antiproteases as potential candidates for HIV-1 pre-exposure prophylaxis

Previous studies on highly HIV-1-exposed, yet persistently seronegative women from the Punwami Sex Worker cohort in Kenya, have shed light on putative protective mechanisms, suggesting that mucosal immunological factors, such as antiproteases, could be mediating resistance to HIV-1 transmission in the female reproductive tract. Nine protease inhibitors were selected for this study: serpin B4, serpin A1, serpin A3, serpin C1, cystatin A, cystatin B, serpin B13, serpin B1 and α-2-macroglobulin-like-protein 1. We assessed in a pilot study, the activity of these antiproteases with cellular assays and an ex vivo HIV-1 challenge model of human ecto-cervical tissue explants. Preliminary findings with both models, cellular and tissue explants, established an order of inhibitory potency for the mucosal proteins as candidates for pre-exposure prophylaxis when mimicking pre-coital use. Combination of all antiproteases considered in this study was more active than any of the individual mucosal proteins. Furthermore, the migration of cells out of ecto-cervical explants was blocked indicating potential prevention of viral dissemination following amplification of the founder population. These findings constitute the base for further development of these mucosal protease inhibitors for prevention strategies.

Mucosal Responses to Zika Virus Infection in Cynomolgus Macaques

Zika virus (ZIKV) cases continue to be reported, and no vaccine or specific antiviral agent has been approved for the prevention or treatment of infection. Though ZIKV is primarily transmitted by mosquitos, cases of sexual transmission and prolonged viral RNA presence in semen have been reported. In this observational study, we report the mucosal responses to sub-cutaneous and mucosal ZIKV exposure in cynomolgus macaques during acute and late chronic infection. Subcutaneous challenge induced a decrease in the growth factor VEGF in colorectal and cervicovaginal tissues 100 days post-challenge, in contrast to the observed increase in these tissues following vaginal infection. This different pattern was not observed in the uterus, where VEGF was upregulated independently of the challenge route. Vaginal challenge induced a pro-inflammatory profile in all mucosal tissues during late chronic infection. Similar responses were already observed during acute infection in a vaginal tissue explant model of ex vivo challenge. Non-productive and productive infection 100 days post-in vivo vaginal challenge induced distinct proteomic profiles which were characterized by further VEGF increase and IL-10 decrease in non-infected animals. Ex vivo challenge of mucosal explants revealed tissue-specific modulation of cytokine levels during the acute phase of infection. Mucosal cytokine profiles could represent biosignatures of persistent ZIKV infection.

Hypo-osmotic stress induces the epithelial alarmin IL-33 in the colonic barrier of ulcerative colitis

Epithelial alarmins are gaining interest as therapeutic targets for chronic inflammation. The nuclear alarmin interleukin-33 (IL-33) is upregulated in the colonic mucosa of acute ulcerative colitis (UC) and may represent an early instigator of the inflammatory cascade. However, it is not clear what signals drive the expression of IL-33 in the colonic mucosa, nor is the exact role of IL-33 elucidated. We established an ex vivo model using endoscopic colonic biopsies from healthy controls and UC patients. Colonic biopsies exposed to hypo-osmotic medium induced a strong nuclear IL-33 expression in colonic crypts in both healthy controls and UC biopsies. Mucosal IL33 mRNA was also significantly increased following hypo-osmotic stress in healthy controls compared to non-stimulated biopsies (fold change 3.9, p-value < 0.02). We observed a modest induction of IL-33 in response to TGF-beta-1 stimulation, whereas responsiveness to inflammatory cytokines TNF and IFN-gamma was negligible. In conclusion our findings indicate that epithelial IL-33 is induced by hypo-osmotic stress, rather than prototypic proinflammatory cytokines in colonic ex vivo biopsies. This is a novel finding, linking a potent cytokine and alarmin of the innate immune system with cellular stress mechanisms and mucosal inflammation.

The ex vivo pharmacology of HIV-1 antiretrovirals differs between macaques and humans

Non-human primates (NHP) are widely used for the pre-clinical assessment of antiretrovirals (ARVs) for HIV treatment and prevention. However, the utility of these models is questionable given the differences in ARV pharmacology between humans and macaques. Here, we report a model based on ex vivo ARV exposure and the challenge of mucosal tissue explants to define pharmacological differences between NHPs and humans. For colorectal and cervicovaginal explants in both species, high concentrations of tenofovir (TFV) and maraviroc were predictive of anti-viral efficacy. However, their combinations resulted in increased inhibitory potency in NHP when compared to human explants. In NHPs, higher TFV concentrations were measured in colorectal versus cervicovaginal explants (p = 0.042). In humans, this relationship was inverted with lower levels in colorectal tissue (p = 0.027). TFV-resistance caused greater loss of viral fitness for HIV-1 than SIV. This, tissue explants provide an important bridge to refine and appropriately interpret NHP studies.

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Tenofovir-maraviroc combinations show greater potency in NHP than in human tissue

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Opposite drug distribution in mucosal tissues was observed between both species

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Greater loss of viral replication fitness with RT mutations for SIV than for HIV-1

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Ex vivo tissue models are a bridge between NHP studies and human clinical trials

Pre-Clinical Evaluation of Tenofovir and Tenofovir Alafenamide for HIV-1 Pre-Exposure Prophylaxis in Foreskin Tissue

Background: HIV-1 pre-exposure prophylaxis (PrEP) has focused predominantly on protective efficacy in receptive sex, with limited research on the dosing requirements for insertive sex. We pre-clinically assessed the ex vivo pharmacokinetic–pharmacodynamic (PK–PD) profile of tenofovir (TFV) and tenofovir alafenamide (TAF) in foreskin tissue. Methods: Inner and outer foreskin explants were exposed to serial dilutions of TFV or TAF prior to addition of HIV-1_BaL at a high (HVT) or a low viral titer (LVT). Infection was assessed by measurement of p24 in foreskin culture supernatants. TFV, TAF and TFV–diphosphate (TFV–DP) concentrations were measured in tissues, culture supernatants and dosing and washing solutions. Results: Dose–response curves were obtained for both drugs, with greater potency observed against LVT. Inhibitory equivalency mimicking oral dosing was defined between 1 mg/mL of TFV and 15 µg/mL of TAF against HVT challenge. Concentrations of TFV–DP in foreskin explants were approximately six-fold higher after ex vivo dosing with TAF than with TFV. Statistically significant negative linear correlations were observed between explant levels of TFV or TFV–DP and p24 concentrations following HVT. Conclusions: Pre-clinical evaluation of TAF in foreskin explants revealed greater potency than TFV against penile HIV transmission. Clinical evaluation is underway to support this finding.

3D In Vitro Platform for Cell and Explant Culture in Liquid-like Solids

Existing 3D cell models and technologies have offered tools to elevate cell culture to a more physiologically relevant dimension. One mechanism to maintain cells cultured in 3D is by means of perfusion. However, existing perfusion technologies for cell culture require complex electronic components, intricate tubing networks, or specific laboratory protocols for each application. We have developed a cell culture platform that simply employs a pump-free suction device to enable controlled perfusion of cell culture media through a bed of granular microgels and removal of cell-secreted metabolic waste. We demonstrated the versatile application of the platform by culturing single cells and keeping tissue microexplants viable for an extended period. The human cardiomyocyte AC16 cell line cultured in our platform revealed rapid cellular spheroid formation after 48 h and ~90% viability by day 7. Notably, we were able to culture gut microexplants for more than 2 weeks as demonstrated by immunofluorescent viability assay and prolonged contractility.

Ex Vivo HIV Infection Model of Cervico-Vaginal and Rectal Tissue

Globally, the most frequent route of HIV transmission is through sexual intercourse. In women, sexual transmission of HIV involves cervical, vaginal, endometrial, and rectal mucosal exposure to the virus. Here we describe technical protocols for ex vivo cervical, vaginal, and rectal tissue infection models and cultures that can be used to assess tissue susceptibility to infection under different conditions as well as the potential antiviral efficacy of a treatment for HIV prevention or cure.

Leukocytospermia induces intraepithelial recruitment of dendritic cells and increases SIV replication in colorectal tissue explants

Mucosal exposure to infected semen accounts for the majority of HIV-1 transmission events, with rectal intercourse being the route with the highest estimated risk of transmission. Yet, the impact of semen inflammation on colorectal HIV-1 transmission has never been addressed. Here we use cynomolgus macaques colorectal tissue explants to explore the effect of leukocytospermia, indicative of male genital tract inflammation, on SIVmac251 infection. We show that leukocytospermic seminal plasma (LSP) has significantly higher concentration of a number of pro-inflammatory molecules compared to normal seminal plasma (NSP). In virus-exposed explants, LSP enhance SIV infection more efficiently than NSP, being the increased viral replication linked to the level of inflammatory and immunomodulatory cytokines. Moreover, LSP induce leukocyte accumulation on the apical side of the colorectal lamina propria and the recruitment of a higher number of intraepithelial dendritic cells than with NSP. These results suggest that the outcome of mucosal HIV-1 infection is influenced by the inflammatory state of the semen donor, and provide further insights into mucosal SIV/HIV-1 pathogenesis.

Examining the Safety, Pharmacokinetics, and Pharmacodynamics of a Rectally Administered IQP-0528 Gel for HIV Pre-Exposure Prophylaxis: A First-In-Human Study

A lubricating microbicide gel designed for rectal and vaginal use would provide a behaviorally congruent strategy to enhance pre-exposure prophylaxis adherence and reduce HIV infection risk. In this study, we report the first-in-human evaluation of such a gel containing 1% IQP-0528, an investigational antiretroviral. Seven HIV-1-negative participants received one 10 mL rectal dose of radiolabeled 1% IQP-0528 gel. We assessed safety; IQP-0528 pharmacokinetics in plasma, and rectal and vaginal tissue; ex vivo local pharmacodynamics (PD); and colorectal distribution. The 1% gel was determined to be safe with one mild event attributed to study product and no effects on rectal tissue histology. All concentrations measured in plasma and vaginal tissue were below the limit of quantitation. Median IQP-0528 concentrations in rectal tissue exceeded the in vitro EC₉₅ against HIV-1 (0.07 ng/mg) by 3-5 h of dosing and remained above this concentration for at least 24 h, despite a 3-log reduction in concentration over this duration of time. Rectal tissue PD-assessed by ex vivo HIV challenge-demonstrated significant p24 antigen reduction 3-5 h postdose compared with baseline (p = .05), but not 24-26 h postdose (p = .75). Single-photon emission computed tomography/computed tomography imaging revealed that product distribution was localized to the rectosigmoid. The IQP-0528 gel possesses desirable features for a topical microbicide including: local safety with no systemic absorption, delivery of locally high IQP-0528 concentrations, and significant reductions in ex vivo HIV infectivity. However, the gel is limited by its rapid clearance and inability to penetrate vaginal tissues following rectal dosing. Clinical Trial Registration number: NCT03082690.

Organoids and organs-on-chips: Insights into human gut-microbe interactions

The important and diverse roles of the gut microbiota in human health and disease are increasingly recognized. The difficulty of inferring causation from metagenomic microbiome sequencing studies and from mouse-human interspecies differences has prompted the development of sophisticated in vitro models of human gut-microbe interactions. Here, we review recent advances in the co-culture of microbes with intestinal and colonic epithelia, comparing the rapidly developing fields of organoids and organs-on-chips with other standard models. We describe how specific individual processes by which microbes and epithelia interact can be recapitulated in vitro. Using examples of bacterial, viral, and parasitic infections, we highlight the advantages of each culture model and discuss current trends and future possibilities to build more complex co-cultures.

Apolipoprotein A-I mimetics attenuate macrophage activation in chronic treated HIV

OBJECTIVES

Despite antiretroviral therapy (ART), there is an unmet need for therapies to mitigate immune activation in HIV infection. The goal of this study is to determine whether the apoA-I mimetics 6F and 4F attenuate macrophage activation in chronic HIV.

DESIGN

Preclinical assessment of the in-vivo impact of Tg6F and the ex-vivo impact of apoA-I mimetics on biomarkers of immune activation and gut barrier dysfunction in treated HIV.

METHODS

We used two humanized murine models of HIV infection to determine the impact of oral Tg6F with ART (HIV+ART+Tg6F+) on innate immune activation (plasma human sCD14, sCD163) and gut barrier dysfunction [murine I-FABP, endotoxin (LPS), LPS-binding protein (LBP), murine sCD14]. We also used gut explants from 10 uninfected and 10 HIV-infected men on potent ART and no morbidity, to determine the impact of ex-vivo treatment with 4F for 72 h on secretion of sCD14, sCD163, and I-FABP from gut explants.

RESULTS

When compared with mice treated with ART alone (HIV+ART+), HIV+ART+Tg6F+ mice attenuated macrophage activation (h-sCD14, h-sCD163), gut barrier dysfunction (m-IFABP, LPS, LBP, and m-sCD14), plasma and gut tissue oxidized lipoproteins. The results were consistent with independent mouse models and ART regimens. Both 4F and 6F attenuated shedding of I-FABP and sCD14 from gut explants from HIV-infected and uninfected participants.

CONCLUSION

Given that gut barrier dysfunction and macrophage activation are contributors to comorbidities like cardiovascular disease in HIV, apoA-I mimetics should be tested as therapy for morbidity in chronic treated HIV.

Early Colorectal Responses to HIV-1 and Modulation by Antiretroviral Drugs

Innate responses during acute HIV infection correlate with disease progression and pathogenesis. However, limited information is available about the events occurring during the first hours of infection in the mucosal sites of transmission. With an ex vivo HIV-1 challenge model of human colorectal tissue we assessed the mucosal responses induced by R5- and X4-tropic HIV-1 isolates in the first 24 h of exposure. Microscopy studies demonstrated virus penetration of up to 39 μm into the lamina propia within 6 h of inoculation. A rapid, 6 h post-challenge, increase in the level of secretion of inflammatory cytokines, chemokines, interferon- γ (IFN-γ), and granulocyte-macrophage colony-stimulating factor (GM-CSF) was observed following exposure to R5- or X4-tropic isolates. This profile persisted at the later time point measured of 24 h. However, exposure to the X4-tropic isolate tested induced greater changes at the proteomic and transcriptomic levels than the R5-tropic. The X4-isolate induced greater levels of CCR5 ligands (RANTES, MIP-1α and MIP-1β) secretion than R5-HIV-1. Potential drugs candidates for colorectal microbicides, including entry, fusion or reverse transcriptase inhibitors demonstrated differential capacity to modulate these responses. Our findings indicate that in colorectal tissue, inflammatory responses and a Th1 cytokine profile are induced in the first 24 h following viral exposure.

Importance of structure-based studies for the design of a novel HIV-1 inhibitor peptide

Based on the structure of an HIV-1 entry inhibitor peptide two stapled- and a retro-enantio peptides have been designed to provide novel prevention interventions against HIV transmission. The three peptides show greater inhibitory potencies in cellular and mucosal tissue pre-clinical models than the parent sequence and the retro-enantio shows a strengthened proteolytic stability. Since HIV-1 fusion inhibitor peptides need to be embedded in the membrane to properly interact with their viral target, the structural features were determined by NMR spectroscopy in micelles and solved by using restrained molecular dynamics calculations. Both parent and retro-enantio peptides demonstrate a topology compatible with a shared helix–turn–helix conformation and assemble similarly in the membrane maintaining the active conformation needed for its interaction with the viral target site. This study represents a straightforward approach to design new targeted peptides as HIV-1 fusion inhibitors and lead us to define a retro-enantio peptide as a good candidate for pre-exposure prophylaxis against HIV-1.

Complement opsonization of HIV affects primary infection of human colorectal mucosa and subsequent activation of T cells

HIV transmission via genital and colorectal mucosa are the most common routes of dissemination. Here, we explored the effects of free and complement-opsonized HIV on colorectal tissue. Initially, there was higher antiviral responses in the free HIV compared to complement-opsonized virus. The mucosal transcriptional response at 24 hr revealed the involvement of activated T cells, which was mirrored in cellular responses observed at 96 hr in isolated mucosal T cells. Further, HIV exposure led to skewing of T cell phenotypes predominantly to inflammatory CD4+ T cells, that is Th17 and Th1Th17 subsets. Of note, HIV exposure created an environment that altered the CD8+ T cell phenotype, for example expression of regulatory factors, especially when the virions were opsonized with complement factors. Our findings suggest that HIV-opsonization alters the activation and signaling pathways in the colorectal mucosa, which promotes viral establishment by creating an environment that stimulates mucosal T cell activation and inflammatory Th cells.

Topical Microbicides in HIV Prevention: State of the Promise

HIV topical microbicides are products with anti-HIV activity, generally incorporating a direct-acting antiretroviral agent, that when applied to the vagina or rectum have the potential to prevent the sexual acquisition of HIV in women and men. Topical microbicides may meet the prevention needs of individuals and groups for whom oral daily forms of pre-exposure prophylaxis (PrEP) have not been acceptable. Microbicides can provide personal control over HIV prevention and offer the possibility of discreet use, qualities that may be particularly important for receptive partners in sexual relationships such as women and transgender women and men, who together account for the clear majority of new HIV infections worldwide. Although the promise of such a product emerged nearly three decades ago, proof of concept has been demonstrated only within the last decade. A robust pipeline of microbicidal gels, films, inserts, and rings has been evaluated in multiple studies among at-risk women and men, and refinement of products for ease of use, reversibility, and high safety is the priority for the field.

The Pre-clinical Toolbox of Pharmacokinetics and Pharmacodynamics: in vitro and ex vivo Models

Prevention strategies against sexual transmission of human immunodeficiency virus (HIV) are essential to curb the rate of new infections. In the absence of a correlate of protection against HIV infection, pre-clinical evaluation is fundamental to facilitate and accelerate prioritization of prevention candidates and their formulations in a rapidly evolving clinical landscape. Characterization of pharmacokinetic (PK) and pharmacodynamic (PD) properties for candidate inhibitors is the main objective of pre-clinical evaluation. in vitro and ex vivo systems for pharmacological assessment allow experimental flexibility and adaptability at a relatively low cost without raising as significant ethical concerns as in vivo models. Applications and limitations of pre-clinical PK/PD models and future alternatives are reviewed in the context of HIV prevention.

Sustained release silk fibroin discs: Antibody and protein delivery for HIV prevention

With almost 2 million new HIV infections worldwide each year, the prevention of HIV infection is critical for stopping the pandemic. The only approved form of pre-exposure prophylaxis is a costly daily pill, and it is recognized that several options will be needed to provide protection to the various affected communities around the world. In particular, many at-risk people would benefit from a prevention method that is simple to use and does not require medical intervention or a strict daily regimen. We show that silk fibroin protein can be formulated into insertable discs that encapsulate either an antibody (IgG) or the potent HIV inhibitor 5P12-RANTES. Several formulations were studied, including silk layering, water vapor annealing and methanol treatment to stabilize the protein cargo and impact the release kinetics over weeks. In the case of IgG, high concentrations were released over a short time using methanol treatment, with more sustained results with the use of water vapor annealing and layering during device fabrication. For 5P12-RANTES, sustained release was obtained for 31 days using water vapor annealing. Further, we show that the released inhibitor 5P12-RANTES was functional both in vitro and in ex vivo colorectal tissue. This work shows that silk fibroin discs can be developed into formidable tools to prevent HIV infection.

The Use of Droplet Digital PCR to Quantify HIV-1 Replication in the Colorectal Explant Model

Ex vivo explant models are used to characterize in vitro efficacy of preexposure prophylaxis (PrEP) agents. Tissue is challenged with virus in culture and HIV-1 p24 levels are quantified with enzyme-linked immunosorbent assay (ELISA) on supernatants collected throughout a 14-21-day incubation. Due to the narrow dynamic range of HIV-1 p24 kits, we evaluated whether droplet digital PCR (ddPCR) provides an alternative method to quantify HIV-1 replication in supernatant samples. We used samples from the MWRI-01 study, which evaluated the pharmacokinetic/pharmacodynamic profile of long-acting rilpivirine using the explant model (McGowan et al. Lancet HIV 2016). HIV-1 pol RNA was measured with ddPCR, either directly with a one-step method or reverse transcribed to cDNA before ddPCR (two-step method) on supernatants from the MWRI-01 study. Previously analyzed HIV-1 p24 antigen levels (Alliance; Perkin-Elmer) were available for comparison purposes. Both ddPCR methods strongly correlated with HIV-1 p24 and displayed similar patterns of HIV-1 suppression before and after rilpivirine. Compared to the p24 ELISA, two-step and one-step ddPCR reduced the amount of hands-on time by approximately one-half and two-thirds, respectively. ddPCR also required less sample and based on p24 versus ddPCR correlation, could potentially reduce the explant culture time from 14 to 10 days (r² = 0.78, p < .001) due to the increased sensitivity of ddPCR. We demonstrate that ddPCR is a suitable alternative to HIV-1 p24 ELISA to quantify HIV-1 infection in the explant model and has the potential to decrease explant culture time.

Ranpirnase Reduces HIV-1 Infection and Associated Inflammatory Changes in a Human Colorectal Explant Model

Ranpirnase (RNP) is a low molecular weight type III endoribonuclease, which demonstrates broad antiviral and antitumor properties. We sought to characterize the antiviral activity of RNP against HIV-1 and to determine whether RNP modulates local inflammatory changes associated with HIV infection in the colorectal explant model. Colorectal explants were incubated for 2 h with HIV-1_BaL, in the presence of increasing concentrations of RNP (0-60 μg/mL). After washing, explants were cultured for 14 days, with supernatant collected at days 3, 7, 10, and 14. All samples were assayed for HIV-1 p24. Additionally, 30 soluble inflammatory biomarkers were assayed in the day 3 supernatant sample. Other biopsies were stimulated with lipopolysaccharides (LPS) (10 μg/mL) in the presence of RNP and soluble biomarkers assayed at day 3. RNP inhibited productive infection of the colorectal explants with HIV-1_BaL and induced a dose-dependent decrease in 15/30 biomarkers. Affected biomarkers included IP-10, MDC, MIP-1α, MIP-1β, TARC, IL12-p40, IL-15, IL-17, IL-1α, IL-7, IFNγ, IL12-p70, IL-1β, IL-4, IL-5, and TNF-β. Similarly, RNP dose-dependent inhibition was demonstrated in 7/30 biomarkers after LPS stimulation, all of which overlapped with HIV-1_BaL-induced biomarker changes. The ability of RNP to inhibit both colorectal explant HIV-1_BaL infection and inflammatory changes associated with HIV-1 infection makes RPN a promising agent for topical rectal pre-exposure prophylaxis.

Comparative Assessment of Small and Large Intestine Biopsies for Ex Vivo HIV-1 Pathogenesis Studies

Ex vivo mucosal explants have become a mainstay of HIV-1 studies using human tissue. In this study, we examine the baseline phenotypic and virologic differences between biopsies derived from the small intestine (SI) and large intestine (LI) for use in ex vivo explant studies. To do this, we collected endoscopic mucosal biopsies from both SI and LI from the same healthy, HIV-seronegative participants. Mucosal mononuclear cell phenotypes and quantity were compared using flow cytometry. Comparative HIV-1 infectibility of the explants was assessed using an ex vivo explant HIV-1 infection assay. We found that all biopsies had similar numbers of T cells per biopsy. While the percentage of CD4⁺ T cells from SI biopsies expressed significantly more activation markers (CD38, HLA-DR) and HIV coreceptors (CXCR4, CCR5), the absolute numbers of activated CD4⁺ T cells were similar between both sites. LI explants, however, supported more efficient HIV-1 infection, as evidenced by earlier rise in p24 accumulation and greater percent of infected explants at limiting infectious doses. These results suggest that explants from LI biopsies support more efficient HIV-1 infection than SI biopsies, despite similar numbers of available, activated HIV-1 target cells. These findings highlight important differences in LI and SI explants, which must be considered in designing and interpreting ex vivo HIV-1 infection studies, and suggest that factors within the tissue other than target cell number and activation state may play a role in regulating HIV-1 infection.

Immunological responsiveness of intestinal tissue explants and mucosal mononuclear cells to ex vivo stimulation

BACKGROUND

There are limited data on the immunological responsiveness of healthy intestinal tissue when it is cultured and stimulated ex vivo. Such an ex vivo model has the potential to be a valuable tool in understanding disease pathogenesis and as a preclinical tool for the assessment of candidate therapeutic agents used to treat inflammatory bowel disease (IBD).

AIM

We undertook a comprehensive study to evaluate ex vivo immunological responses of intestinal tissue and isolated mucosal mononuclear cells (MMC) to a broad range of stimuli.

METHODS

Colorectal biopsies (explants) were obtained from healthy participants by flexible sigmoidoscopy and were placed either directly into culture or digested to isolate MMC prior to placement in culture. Explants or MMC were treated with polyinosinic:polycytidylic acid (Poly IC), phytohemagglutinin (PHA), lipopolysacccharides from E Coli (LPS), anti-CD3/CD28 antibodies, or IL-1β/TNF-α for 24 h. Supernatants were assayed for 40 inflammatory biomarkers using multiplexed enzyme-linked immunosorbent assay (ELISA). The isolated MMCs were further characterized using twelve color flow cytometry.

RESULTS

Explants have greater weight adjusted constitutive expression of inflammatory biomarkers than MMCs. Biomarker responses varied as a function of immunogen and use of intact tissue or isolated cells. PHA applied to intact explants was the most effective agent in inducing biomarker changes. Stimulation induced activated and memory cellular phenotypes in both explants and MMCs.

CONCLUSIONS

The breadth and magnitude of responses from intact and enzymatically digested intestinal tissue explants stimulated with exogenous immunogens are complex and vary by tissue form and treatment. Overall, PHA stimulation of intact explants produced the most robust responses in normal human colorectal tissue. This system could potentially serve as a preliminary model of the disease state, suitable for small scale screening of new therapeutic agents prior to using IBD patient derived tissue.

Human Semen or Seminal Plasma Does Not Enhance HIV-1BaL Ex Vivo Infection of Human Colonic Explants

To determine whether human whole semen (WS) and seminal plasma (SP) either previously frozen or freshly acquired altered ex vivo infectibility of human colonic explants or was associated with histology or toxicity changes, which may influence mucosal HIV-1 transmission in vivo. Pooled human semen samples were freshly obtained from study volunteers (never frozen) and from commercial sources (frozen/thawed). Endoscopically acquired rectal biopsies were evaluated for toxicity following titered ex vivo WS/SP exposure by histological grading and by MTT assay. The ex vivo HIV-1 biopsy challenge model was used to evaluate effects of exposure to either previously frozen or freshly acquired WS/SP on HIVBaL infectibility at a range of viral inocula (104-100 TCID50). To evaluate the effects at lower viral inocula of HIV-1 (10-2-102), experiments in the presence or absence of WS/SP were also performed utilizing TZM-bl cells. MTT assays and histological scoring demonstrated no tissue degradation of biopsies when exposed for 2 h to concentrations of 10% or 100% of either fresh or previously frozen WS/SP. Ex vivo biopsy HIV-1 challenge experiments showed no differences in the presence of freshly acquired or previously frozen/thawed WS/SP compared with control; no differences were seen with lower infectious titers on TZM-bl cells. Within the limits of assay sensitivity and variability, these data show no toxicity or significant enhancement of HIV-1 infectibility of human rectal mucosa using the colorectal explant model with either pooled fresh or frozen/thawed nonautologous human semen.

Short Communication: Specimen Processing Impacts Tissue Tenofovir Pharmacokinetic Measurements

Antiretroviral drug concentrations at sites of HIV exposure are important drivers that influence the development of HIV pre-exposure chemoprophylaxis strategies and regimens. We assessed the effect of collection method-in the presence or absence of tissue culture medium-on tenofovir (TFV) and tenofovir diphosphate (TFV-DP) concentrations in colonic biopsies. We find significant baseline interbiopsy variation in TFV (38% CV) and TFV-DP (33% CV) concentrations. Incubation in medium leads to a fluid absorption-driven twofold increase in tissue weight with a concomitant 75% decrease in weight-adjusted tissue TFV concentrations 120 min post-incubation. In contrast, adjusted TFV-DP concentrations decrease by only 25% during the same period, with this difference not achieving statistical significance. Although colonic biopsies should be collected in the absence of medium for accurate TFV concentrations, the presence of medium does not significantly impact TFV-DP-dependent pharmacokinetic or pharmacodynamic assays. Appropriate assessment of tissue drug concentrations should account for biopsy collection method and drug mechanism of action.

Human Organotypic Models for Anti-infective Research

The use of human organotypic models for biomedical research is experiencing a significant increase due to their biological relevance, the possibility to perform high-throughput analyses, and their cost efficiency. In the field of anti-infective research, comprising the search for novel antipathogenic treatments including vaccines, efforts have been made to reduce the use of animal models. That is due to two main reasons: unreliability of data obtained with animal models and the increasing willingness to reduce the use of animals in research for ethical reasons. Human three-dimensional (3-D) models may substitute and/or complement in vivo studies, to increase the translational value of preclinical data. Here, we provide an overview of recent studies utilizing human organotypic models, resembling features of the cervix, intestine, lungs, brain, and skin in the context of anti-infective research. Furthermore, we focus on the future applications of human skin models and present methodological protocols to culture human skin equivalents and human skin explants.

Hypo-osmolar Formulation of Tenofovir (TFV) Enema Promotes Uptake and Metabolism of TFV in Tissues, Leading to Prevention of SHIV/SIV Infection

Oral preexposure prophylaxis (PrEP) has been approved for prophylaxis of HIV-1 transmission but is associated with high costs and issues of adherence. Protection from anal transmission of HIV using topical microbicides and methods congruent with sexual behavior offers the promise of improved adherence. We compared the pharmacokinetics (PK) and ex vivo efficacy of iso-osmolar (IOsm) and hypo-osmolar (HOsm) rectal enema formulations of tenofovir (TFV) in rhesus macaques. Single-dose PK of IOsm or HOsm high-dose (5.28 mg/ml) and low-dose (1.76 mg/ml) formulations of TFV enemas were evaluated for systemic uptake in blood, colorectal biopsy specimens, and rectal CD4⁺ T cells. Markedly higher TFV concentrations were observed in plasma and tissues after administration of the HOsm high-dose formulation than with all other formulations tested. TFV and TFV diphosphate (TFV-DP) concentrations in tissue correlated for the HOsm high-dose formulation, demonstrating rapid uptake and transformation of TFV to TFV-DP in tissues. TFV-DP amounts in tissues collected at 1 and 24 h were 7 times and 5 times higher, respectively (P < 0.01), than the ones collected in tissues with the IOsm formulation. The HOsm high-dose formulation prevented infection in ex vivo challenges of rectal tissues collected at 1, 24, and 72 h after the intrarectal dosing, whereas the same TFV dose formulated as an IOsm enema was less effective.

Three-dimensional (3D) culture of adult murine colon as an in vitro model of cryptosporidiosis: Proof of concept

Cryptosporidium parvum is a major cause of diarrheal illness and was recently potentially associated with digestive carcinogenesis. Despite its impact on human health, Cryptosporidium pathogenesis remains poorly known, mainly due to the lack of a long-term culture method for this parasite. Thus, the aim of the present study was to develop a three-dimensional (3D) culture model from adult murine colon allowing biological investigations of the host-parasite interactions in an in vivo-like environment and, in particular, the development of parasite-induced neoplasia. Colonic explants were cultured and preserved ex vivo for 35 days and co-culturing was performed with C. parvum. Strikingly, the resulting system allowed the reproduction of neoplastic lesions in vitro at 27 days post-infection (PI), providing new evidence of the role of the parasite in the induction of carcinogenesis. This promising model could facilitate the study of host-pathogen interactions and the investigation of the process involved in Cryptosporidium-induced cell transformation.

In vitro models for deciphering the mechanisms underlying the sexual transmission of viruses at the mucosal level

Sexually transmitted viruses infect the genital and colorectal mucosa of the partner exposed to contaminated genital secretions through a wide range of mechanisms, dictated in part by the organization of the mucosa. Because understanding the modes of entry into the organism of viruses transmitted through sexual intercourse is a necessary prerequisite to the design of treatments to block those infections, in vitro modeling of the transmission is essential. The aim of this review is to present the models and methodologies available for the in vitro study of the interactions between viruses and mucosal tissue and for the preclinical evaluation of antiviral compounds, and to point out their advantages and limitations according to the question being studied.

Targeted microbicides for preventing sexual HIV transmission

Sexual transmission remains one of the most significant hurdles in the fight against HIV infection. The use of vaginal or rectal microbicides has been proposed for topical pre-exposure prophylaxis but available results from clinical trials of candidate products have been, at best, less than optimal. While waiting for the first product to get regulatory approval, novel approaches are being explored in order to enhance efficacy, as well as to assure safety. Strategies involving specific delivery of antiviral agents to key players involved in the early steps of sexual transmission have the potential to help achieving such purposes. Engineering systems that allow targeting cells, tissues or other biological structures of interest may provide a way to modulate local pharmacokinetics of promising microbicide molecules and, thus, maximize protection. This concise review discusses the identification and use of potential targets for such purpose, while detailing on several examples of targeted systems engineered as potential microbicide candidates. Furthermore, remaining challenges and hints for future work in the field of targeted microbicides are addressed.

Unique microRNA expression in the colonic mucosa during chronic HIV-1 infection

OBJECTIVE

Chronic HIV-1 infection leads to widespread inflammation and immune dysregulation. The gastrointestinal mucosa, a primary site for HIV-1 replication, is thought to play a significant role in this response. MicroRNAs (miRs) are small noncoding RNAs that regulate gene expression, including immune activation and inflammation. Here we investigate miR expression and function in the colonic mucosa during HIV-1 infection.

DESIGN AND METHODS

Using miR profiling, we examined miR expression in the colonic mucosa of HIV-infected patients. These miRs were further parsed to identify those that most likely function in HIV-related inflammation. Using bioinformatics tools, we identified potential target genes which were confirmed using in-vitro functional testing.

RESULTS

We identified 12 miRs that were differentially expressed in the colonic mucosa of HIV-infected patients with high versus undetectable plasma viral concentrations. Of these, both miR-26a and miR-29a were downregulated in untreated HIV-1 infection, yet not in the colonic mucosa from inflammatory bowel disease. This downregulation occurs within the first hours after infection. These miRs were further shown to directly target IL-6 and STAT3, respectively, with similar changes confirmed in an ex-vivo explant infection model.

CONCLUSION

miR-26a and miR-29a levels are decreased in the colonic mucosa during chronic HIV-1 infection, and this change may be initiated during acute infection. Both miRs de-repress the IL-6/STAT3 signaling pathway, which could contribute to increased inflammation during infection. These miRs may represent novel therapeutic targets for HIV-1-associated inflammation in the colonic mucosa.

Highly Human Immunodeficiency Virus-Exposed Seronegative Men Have Lower Mucosal Innate Immune Reactivity

Risk of HIV acquisition varies, and some individuals are highly HIV-1-exposed, yet, persistently seronegative (HESN). The immunologic mechanisms contributing to this phenomenon are an area of intense interest. As immune activation and inflammation facilitate disease progression in HIV-1-infected persons and gastrointestinal-associated lymphoid tissue is a highly susceptible site for transmission, we hypothesized that reduced gut mucosal immune reactivity may contribute to reduced HIV-1 susceptibility in HESN men with a history of numerous rectal sexual exposures. To test this, we used ex vivo mucosal explants from freshly acquired colorectal biopsies from healthy control and HESN subjects who were stimulated with specific innate immune ligands and inactivated whole pathogens. Immune reactivity was then assessed via cytokine arrays and proteomic analysis. Mucosal immune cell compositions were quantified via immunohistochemistry. We found that explants from HESN subjects produced less proinflammatory cytokines compared with controls following innate immune stimulation; while noninflammatory cytokines were similar between groups. Proteomic analysis identified several immune response proteins to be differentially expressed between HIV-1-stimulated HESN and control explants. Immunohistochemical examination of colorectal mucosa showed similar amounts of T cells, macrophages, and dendritic cells between groups. The results of this pilot study suggest that mucosal innate immune reactivity is dampened in HESN versus control groups, despite presence of similar densities of immune cells in the colorectal mucosa. This observed modulation of the rectal mucosal immune response may contribute to lower risk of mucosal HIV-1 transmission in these individuals.

In Silico and in Vitro Screening for P-Glycoprotein Interaction with Tenofovir, Darunavir, and Dapivirine: An Antiretroviral Drug Combination for Topical Prevention of Colorectal HIV Transmission

The aim of the study was to use in silico and in vitro techniques to evaluate whether a triple formulation of antiretroviral drugs (tenofovir, darunavir, and dapivirine) interacted with P-glycoprotein (P-gp) or exhibited any other permeability-altering drug-drug interactions in the colorectal mucosa. Potential drug interactions with P-gp were screened initially using molecular docking, followed by molecular dynamics simulations to analyze the identified drug-transporter interaction more mechanistically. The transport of tenofovir, darunavir, and dapivirine was investigated in the Caco-2 cell models and colorectal tissue, and their apparent permeability coefficient (P_app), efflux ratio (ER), and the effect of transporter inhibitors were evaluated. In silico, dapivirine and darunavir showed strong affinity for P-gp with similar free energy of binding; dapivirine exhibiting a ΔG_PB value -38.24 kcal/mol, darunavir a ΔG_PB value -36.84 kcal/mol. The rank order of permeability of the compounds in vitro was tenofovir < darunavir < dapivirine. The P_app for tenofovir in Caco-2 cell monolayers was 0.10 ± 0.02 × 10^-6 cm/s, ER = 1. For dapivirine, P_app was 32.2 ± 3.7 × 10^-6 cm/s, but the ER = 1.3 was lower than anticipated based on the in silico findings. Neither tenofovir nor dapivirine transport was influenced by P-gp inhibitors. The absorptive permeability of darunavir (P_app = 6.4 ± 0.9 × 10^-6 cm/s) was concentration dependent with ER = 6.3, which was reduced by verapamil to 1.2. Administration of the drugs in combination did not alter their permeability compared to administration as single agents. In conclusion, in silico modeling, cell culture, and tissue-based assays showed that tenofovir does not interact with P-gp and is poorly permeable, consistent with a paracellular transport mechanism. In silico modeling predicted that darunavir and dapivirine were P-gp substrates, but only darunavir showed P-gp-dependent permeability in the biological models, illustrating that in silico modeling requires experimental validation. When administered in combination, the disposition of the proposed triple-therapy antiretroviral drugs in the colorectal mucosa will depend on their distinctly different permeability, but was not interdependent.

A novel preventive strategy against HIV-1 infection: combinatorial use of inhibitors targeting the nucleocapsid and fusion proteins

The strategy of simultaneously attacking multiple targets is worthy of exploration in the field of microbicide development to combat HIV-1 sequence diversity and minimize the transmission of resistant variants. A combination of S-acyl-2-mercaptobenzamide thioester-10 (SAMT10), an inhibitor of the HIV-1 nucleocapsid protein (NCp7), and the fusion inhibitor sifuvirtide (SFT) may exert synergistic effects, since SFT can block viral fusion at an early stage of the viral cycle and SAMT10 can disrupt viral particles at a later stage. In this study, we investigated the effect of the combination of SAMT10 and SFT on HIV-1 infection using in vitro cell culture and ex vivo mucosal explant models. A range of doses for each compound was tested at 10-fold serial dilutions based on their 50% effective concentrations (EC₅₀). We observed a synergistic effect of SAMT10 and SFT in vitro against both the laboratory-adapted HIV-1 strain HIV-1_IIIB (subtype B, X4) and three pseudotyped viruses prevalent in Chinese sexually transmitted populations (SVPB16 (subtype B, R5), SVPC12 (subtype C, R5) and SH1.81 (CRF01_AE, R5)). In the ex vivo study, the EC₅₀ values of the inhibitor combinations were reduced 1.5- to 2-fold in colorectal mucosal explants compared to treatment with SAMT10 or SFT alone by using with HIV-1_IIIB. These results may provide a novel strategy for microbicide development against HIV-1 sexual transmission.

Analytical Advances in the Ex Vivo Challenge Efficacy Assay

The ex vivo challenge assay is being increasingly used as an efficacy endpoint during early human clinical trials of HIV prevention treatments. There is no standard methodology for the ex vivo challenge assay, although the use of different data collection methods and analytical parameters may impact results and reduce the comparability of findings between trials. In this analysis, we describe the impact of data imputation methods, kit type, testing schedule and tissue type on variability, statistical power, and ex vivo HIV growth kinetics. Data were p24 antigen (pg/ml) measurements collected from clinical trials of candidate microbicides where rectal (n = 502), cervical (n = 88), and vaginal (n = 110) tissues were challenged with HIV-1BaL ex vivo. Imputation of missing data using a nonlinear mixed effect model was found to provide an improved fit compared to imputation using half the limit of detection. The rectal virus growth period was found to be earlier and of a relatively shorter duration than the growth period for cervical and vaginal tissue types. On average, only four rectal tissue challenge assays in each treatment and control group would be needed to find a one log difference in p24 to be significant (alpha = 0.05), but a larger sample size was predicted to be needed for either cervical (n = 21) or vaginal (n = 10) tissue comparisons. Overall, the results indicated that improvements could be made in the design and analysis of the ex vivo challenge assay to provide a more standardized and powerful assay to compare efficacy of microbicide products.

The culture of gut explants: A model to study the mucosal response

Various experimental model designs have been used to analyze the inflammatory pathways in human gastrointestinal illnesses. Traditionally, analytical techniques and animal models are popular experimental tools to study the inflammation process of intestinal diseases. However, the comparison of results between animal and human models is difficult for the inconsistency of outcomes. Although there are different animal models for studying the intestinal diseases, none of them fully represents the physiological and environmental conditions typical of the human species. Also, there is currently a concerted effort to decrease the experimental use of animals. On the converse, experimental protocols using the culture of gut mucosa had become popular with the advent of endoscopy which allows explanting multiple fragments from the intestine. The peculiar characteristic of this model is the ability to preserve in vitro the features that we found in vivo, thus also the response to various stimuli that differs from person to person. The aim of the present paper is to provide a review of some of the possible uses of the organ intestinal mucosa culture.

Pharmacodynamic correlations using fresh and cryopreserved tissue following use of vaginal rings containing dapivirine and/or maraviroc in a randomized, placebo controlled trial

BACKGROUND

The ex vivo challenge assay is a bio-indicator of drug efficacy and was utilized in this randomized, placebo controlled trial as one of the exploratory endpoints. Fresh and cryopreserved tissues were evaluated for human immunodeficiency virus (HIV) infection and pharmacokinetic (PK)/pharmacodynamic (PD) relationships.

METHODS

HIV-negative women used vaginal rings containing 25 mg dapivirine (DPV)/100 mg maraviroc (MVC) (n = 12), DPV only (n = 12), MVC only (n = 12), or placebo (n = 12) for 28 days. Blood plasma, cervicovaginal fluid (CVF), and cervical biopsies were collected for drug quantification and the ex vivo challenge assay; half (fresh) were exposed immediately to HIV while the other half were cryopreserved, thawed, then exposed to HIV. HIV replication was monitored by p24 enzyme-linked immunosorbent assay from culture supernatant. Data were log-transformed and analyzed by linear least squared regression, nonlinear Emax dose-response model and Satterthwaite t test.

RESULTS

HIV replication was greater in fresh compared to cryopreserved tissue (P = 0.04). DPV was detected in all compartments, while MVC was consistently detected only in CVF. Significant negative correlations between p24 and DPV levels were observed in fresh cervical tissue (P = 0.01) and CVF (P = 0.03), but not plasma. CVF MVC levels showed a significant negative correlation with p24 levels (P = 0.03); drug levels in plasma and tissue were not correlated with HIV suppression. p24 levels from cryopreserved tissue did not correlate to either drug from any compartment.

CONCLUSION

Fresh tissue replicated HIV to greater levels and defined PK/PD relationships while cryopreserved tissue did not. The ex vivo challenge assay using fresh tissue could prioritize drugs being considered for HIV prevention.

In Vitro Pre- and Post-Exposure Prophylaxis Using HIV Inhibitors as Microbicides Against Cell-Free or Cell-Associated HIV-1 Infection

Several classes of microbicides are being evaluated for the prevention of sexual HIV transmission. In vivo, the infectious dose and viral source involved in transmission remain uncertain and it is likely that women will use microbicides both before and after high-risk HIV exposure. Therefore, we evaluated HIV entry inhibitors (EIs) and reverse transcriptase inhibitors (RTIs) for their ability to block cell-free and cell-associated HIV-1 infection in co-cultures of monocyte-derived dendritic cells (MO-DC) and CD4+T-cells using settings of pre- and post-exposure prophylaxis. In the pre-exposure assay, where compound was present before, during and 24 h after infection, all tested EIs (BMS806, TAK779 and T20) and RTIs (PMPA, TMC120 and UC781) blocked infection with 10−4multiplicity of infection (MOI) of cell-free virus at a dose between 100 and 10,000 nM, dependent on the compound used. At 10−3MOI, however, only T20 and the RTIs completely blocked infection. Furthermore, in experiments with cell-associated virus, EIs were ineffective, whereas RTIs actively blocked infection with similar potency as in the experiments with cell-free virus. In the post-exposure assay, where compound was added 2 h after infection and remained present for 24 h, EIs were inactive whereas RTIs blocked cell-free and cell-associated viral infections equally efficiently. Moreover, post-exposure prophylaxis initiated 24 h after infection with cell-free or cell-associated HIV-1 was still effective with 1,000 nM of TMC120. Both EIs and RTIs were non-cytotoxic at any tested concentration for MO-DC and CD4+T-cells in co-culture. Our study shows that RTIs are potent inhibitors of cell-free and cell-associated virus used either in pre- or post-exposure settings. It highlights that parameters such as viral input, viral source, the time of compound addition and the target cells should be considered in microbicides evaluation.

Development and evaluation of a porcine in vitro colon organ culture technique

The intestinal mucosa comprises a complex assemblage of specialized tissues that interact in numerous ways. In vitro cell culture models are generally focused on recreating a specific characteristic of this organ and do not account for the many interactions between the different tissues. In vitro organ culture (IVOC) methods offer a way to overcome these limitations, but prolonging cell viability is essential. This study aimed to determine the feasibility and optimal conditions for in vitro culture of swine colonic mucosa for use as an enteric pathogen infection model. Explants (n = 168) from commercial pigs (n = 12), aged 5 to 10 wk, were used to assess the impact of various culture protocols on explant viability. Explants were cultured for up to 5 d and formalin fixed at 24-h intervals. Following establishment of the culture protocol, explants (n = 208) from 13 pigs were evaluated at Day 0 and 5 of culture. Assessment of viability was based on histological changes (tissue architecture evaluated by H&E, immunostaining of cell proliferation marker Ki-67) and expression of genes encoding IL-1α, IL-8, TNF-α, IFN-γ, and e-cadherin. After 5 d in culture, 20% of explants displayed over 80% of epithelial coverage, whereas 31% of explants had more than 50% of their surface covered by columnar epithelium, and 81% had crypts but with a decreased number of Ki-67-positive cells when compared to Day 0. Notably, large variability in explant quality was observed between donor pigs. Best possible explants were obtained from the distal colon of pigs, processed immediately after euthanasia, cultured at the liquid-tissue-gas interface in media supplemented with a mixture of antibiotics and antifungals and an oxygen-rich gas mix.

Maraviroc and reverse transcriptase inhibitors combinations as potential preexposure prophylaxis candidates

OBJECTIVE

Receptive anal intercourse in both men and women is associated with the highest probability for sexual acquisition of HIV infection. As part of a program to develop an effective prevention strategy, we performed an ex-vivo preclinical evaluation to determine the efficacy of multiple double combinations of maraviroc (MVC) and reverse transcriptase inhibitors (RTIs).

DESIGN

The entry inhibitor, MVC, a nucleotide RTI, tenofovir and two non-nucleoside RTIs, UC781 and TMC120 (dapivirine, DPV), were used in double, combinations against a panel of CCR5-using clade B and clade C HIV-1 isolates and against MVC-escape variants. A gel-formulated version of MVC-DPV combination was also tested.

METHODS

Indicator cells, cocultures of immature dendritic cells with CD4T cells, and colorectal tissue explants were used to assess antiviral activity of drug combinations.

RESULTS

All dual MVC-RTI combinations tested inhibited MVC-sensitive and resistant isolates in cellular and colorectal explants models. All the combinations were positive with no reduction in the activity of MVC. In tissue explants, the combinations against all viral isolates tested produced an increase in the activity of MVC. An initial gel-formulation of MVC-DPV combination showed greater and prolonged antiviral activity of MVC in mucosal tissue explants.

CONCLUSION

This study demonstrates that combinations based on antiretroviral drugs inhibiting HIV transmission at viral entry and reverse transcription have potential as prevention strategies against colorectal transmission of HIV-1 including MVC-resistant isolates. Preclinical evaluation with colorectal tissue explants indicates that a gel-formulation of MVC-DPV is an effective candidate colorectal microbicide.

Short Communication: Limited Anti-HIV-1 Activity of Maraviroc in Mucosal Tissues

The potential of maraviroc (MVC), a small-molecule CCR5 antagonist, as a candidate to prevent HIV-1 sexual transmission by oral or topical dosing has not yet been completely established. Using relevant cellular and mucosal tissue explant models, we show partial antiviral activity of MVC when tested in multiple preclinical dosing strategies.

Animal and human mucosal tissue models to study HIV biomedical interventions: can we predict success?

Introduction

Preclinical testing plays an integral role in the development of HIV prevention modalities. Several models are used including humanized mice, non-human primates and human mucosal tissue cultures.

Discussion

Pharmaceutical development traditionally uses preclinical models to evaluate product safety. The HIV prevention field has extended this paradigm to include models of efficacy, encompassing humanized mice, non-human primates (typically Asian macaques) and human mucosal tissue (such as cervical and colorectal). As our understanding of the biology of HIV transmission improves and includes the influence of human behaviour/biology and co-pathogens, these models have evolved as well to address more complex questions. These three models have demonstrated the effectiveness of systemic (oral) and topical use of antiretroviral drugs. Importantly, pharmacokinetic/pharmacodynamic relationships are being developed and linked to information gathered from human clinical trials. The models are incorporating co-pathogens (bacterial and viral) and the effects of coitus (mucosal fluids) on drug distribution and efficacy. Humanized mice are being tailored in their immune reconstitution to better represent humans. Importantly, human mucosal tissue cultures are now being used in early clinical trials to provide information on product efficacy to more accurately characterize efficacious products to advance to larger clinical trials. While all of these models have made advancements in product development, each has limitations and the data need to be interpreted by keeping these limitations in mind.

Conclusions

Development and refinement of each of these models has been an iterative process and linkages to data generated among each of them and from human clinical trials are needed to determine their reliability. Preclinical testing has evolved from simply identifying products that demonstrate efficacy prior to clinical trials to defining essential pharmacokinetic/pharmacodynamic relationships under a variety of conditions and has the potential to improve product selection prior to the initiation of large-scale human clinical trials. The goal is to provide researchers with ample information to make conversant decisions that guide optimized and efficient product development.

Drug transporter gene expression in human colorectal tissue and cell lines: modulation with antiretrovirals for microbicide optimization

OBJECTIVES

The objectives of this study were to comprehensively assess mRNA expression of 84 drug transporters in human colorectal biopsies and six representative cell lines, and to investigate the alteration of drug transporter gene expression after exposure to three candidate microbicidal antiretroviral (ARV) drugs (tenofovir, darunavir and dapivirine) in the colorectal epithelium. The outcome of the objectives informs development of optimal ARV-based microbicidal formulations for prevention of HIV-1 infection.

METHODS

Drug transporter mRNA expression was quantified from colorectal biopsies and cell lines by quantitative real-time PCR. Relative mRNA expression was quantified in Caco-2 cells and colorectal explants after induction with ARVs. Data were analysed using Pearson's product moment correlation (r), hierarchical clustering and principal component analysis (PCA).

RESULTS

Expression of 58 of the 84 transporters was documented in colorectal biopsies, with genes for CNT2, P-glycoprotein (P-gp) and MRP3 showing the highest expression. No difference was noted between individual subjects when analysed by age, gender or anatomical site (rectum or recto-sigmoid) (r = 0.95-0.99). High expression of P-gp and CNT2 proteins was confirmed by immunohistochemical staining. Similarity between colorectal tissue and cell-line drug transporter gene expression was variable (r = 0.64-0.84). PCA showed distinct clustering of human colorectal biopsy samples, with the Caco-2 cells defined as the best surrogate system. Induction of Caco-2 cell lines with ARV drugs suggests that darunavir-based microbicides incorporating tenofovir may result in drug-drug interactions likely to affect distribution of individual drugs to sub-epithelial target cells.

CONCLUSIONS

These findings will help optimize complex formulations of rectal microbicides to realize their full potential as an effective approach for pre-exposure prophylaxis against HIV-1 infection.

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.

The Molecular Characterization of Intestinal Explant HIV Infection Using Polymerase Chain Reaction-Based Techniques

The ex vivo mucosal explant model is frequently used to test the efficacy of microbicides that have the potential for preventing HIV-1 transmission. The conventional assessment of product efficacy has been the extent of HIV-1 p24 suppression in supernatant fluids sampled up to day 14 after HIV-1 challenge ex vivo. The purpose of this study was to determine if measurement of HIV-1 nucleic acids by real-time PCR and HIV-1 integration by Alu-gag PCR provides advantages with regard to monitoring HIV-1 infection in explants. Rectal biopsies from HIV-1-negative individuals were challenged with 1 × 10(5) virions/ml of HIV-1BaL or HIV-1CH077 ex vivo. HIV-1 RNA and HIV-1 p24 in supernatant fluids and HIV-1 nucleic acids and integrated provirus in individual biopsies were measured at days 1-14 after infection. HIV-1 RNA and proviral DNA were measured by quantitative real-time PCR (qRT-PCR) while integrated virus was detected by Alu-gag PCR. Real-time PCR assays detecting HIV-1 DNA and RNA performed similarly provided that the infecting virus sequences were a good match with the sequences of the assay primers and probes. Increased HIV-1 nucleic acid levels and DNA integration were measurable on days 11 and 14 after infection. The magnitude of explant infection was similar after challenge with HIV-1BaL and HIV-1CH077, although the trajectory of infection was delayed in the HIV-1CH077-infected biopsies. In the majority of experiments, qRT-PCR did not appreciably shorten the time necessary to detect evidence of HIV-1 infection.

Human Non-neutralizing HIV-1 Envelope Monoclonal Antibodies Limit the Number of Founder Viruses during SHIV Mucosal Infection in Rhesus Macaques

HIV-1 mucosal transmission begins with virus or virus-infected cells moving through mucus across mucosal epithelium to infect CD4+ T cells. Although broadly neutralizing antibodies (bnAbs) are the type of HIV-1 antibodies that are most likely protective, they are not induced with current vaccine candidates. In contrast, antibodies that do not neutralize primary HIV-1 strains in the TZM-bl infection assay are readily induced by current vaccine candidates and have also been implicated as secondary correlates of decreased HIV-1 risk in the RV144 vaccine efficacy trial. Here, we have studied the capacity of anti-Env monoclonal antibodies (mAbs) against either the immunodominant region of gp41 (7B2 IgG1), the first constant region of gp120 (A32 IgG1), or the third variable loop (V3) of gp120 (CH22 IgG1) to modulate in vivo rectal mucosal transmission of a high-dose simian-human immunodeficiency virus (SHIV-BaL) in rhesus macaques. 7B2 IgG1 or A32 IgG1, each containing mutations to enhance Fc function, was administered passively to rhesus macaques but afforded no protection against productive clinical infection while the positive control antibody CH22 IgG1 prevented infection in 4 of 6 animals. Enumeration of transmitted/founder (T/F) viruses revealed that passive infusion of each of the three antibodies significantly reduced the number of T/F genomes. Thus, some antibodies that bind HIV-1 Env but fail to neutralize virus in traditional neutralization assays may limit the number of T/F viruses involved in transmission without leading to enhancement of viral infection. For one of these mAbs, gp41 mAb 7B2, we provide the first co-crystal structure in complex with a common cyclical loop motif demonstrated to be critical for infection by other retroviruses.

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.