Mucosal immune responses in the genital tract of HIV-1-exposed uninfected women

Deciphering the Role of Mucosal Immune Responses and the Cervicovaginal Microbiome in Resistance to HIV Infection in HIV-Exposed Seronegative (HESN) Women

The female genital tract (FGT) is an important site of human immunodeficiency virus (HIV) infection. Discerning the nature of HIV-specific local immune responses is crucial for identifying correlates of protection in HIV-exposed seronegative (HESN) individuals. The present study involved a comprehensive analysis of soluble immune mediators, secretory immunoglobulins (sIg), natural killer (NK) cells, CXCR5⁺ CD8⁺ T cells, T follicular helper (Tfh) cells, and T regulatory cells (Tregs) in the vaginal mucosa as well as the nature and composition of the cervicovaginal microbiome in HESN women. We found significantly elevated antiviral cytokines, soluble immunoglobulins, and increased frequencies of activated NK cells, CXCR5⁺ CD8⁺ T cells, and Tfh cells in HESN females compared to HIV-unexposed healthy (UH) women. Analysis of the genital microbiome of HESN women revealed a greater bacterial diversity and increased abundance of Gardnerella spp. in the mucosa. The findings suggest that the female genital tract of HESN females represents a microenvironment equipped with innate immune factors, antiviral mediators, and critical T cell subsets that protect against HIV infection.

IMPORTANCE The vast majority of human immunodeficiency virus (HIV) infections across the world occur via the sexual route. The genital tract mucosa is thus the primary site of HIV replication, and discerning the nature of HIV-specific immune responses in this compartment is crucial. The role of the innate immune system at the mucosal level in exposed seronegative individuals and other HIV controllers remains largely unexplored. This understanding can provide valuable insights to improve vaccine design. We investigated mucosal T follicular helper (Tfh) cells, CXCR5⁺ CD8⁺ T cells, natural killer (NK) cells subsets, soluble immune markers, and microbiome diversity in HIV-exposed seronegative (HESN) women. We found a significantly higher level of mucosal CXCR5⁺ CD8⁺ T cells, CD4⁺ Tfh cells, activated NK cell subsets, and antiviral immune cell mediators in HESN women. We also found a higher abundance of Gardnerella spp., microbiome dysbiosis, and decreased levels of inflammatory markers to be associated with reduced susceptibility to HIV infection. Our findings indicate that increased distribution of mucosal NK cells, CXCR5⁺ CD8⁺ T cells, Tfh cells, and soluble markers in HIV controllers with a highly diverse cervicovaginal microbiome could contribute effectively to protection against HIV infection. Overall, our findings imply that future vaccine design should emphasize inducing these highly functional cell types at the mucosal sites.

Progestin-based contraception regimens modulate expression of putative HIV risk factors in the vaginal epithelium of pig-tailed Macaques

PROBLEM

In women, the use of progestin-based contraception may increase the risk of vaginal HIV acquisition. We previously showed in macaques that there is a significantly higher simian-human immunodeficiency virus (SHIV) acquisition rate in the luteal phase of the menstrual cycle, which presents a naturally high-progesterone state, and this may be attributable to altered expression of innate immune factors. We hypothesized that progestin-based contraception, especially depot medroxyprogesterone acetate (DMPA), would, in a similar way, affect mucosal immune factors that influence HIV acquisition risk.

METHOD OF STUDY

We used a pig-tailed macaque model to evaluate the effects of two progestin-based contraceptives, DMPA, and levonorgestrel (LNG)/ethinyl estradiol (EE)-based combined oral contraceptives (COCs), on innate mucosal factors. We compared the vaginal epithelial thickness data from previous studies and used cytokine profiling and microarray analysis to evaluate contraception-induced molecular changes in the vagina.

RESULTS

The administration of DMPA caused a reduction in the thickness of the vaginal epithelium relative to that of the follicular or luteal phase. DMPA also induced a significant increase in vaginal levels of the anti-inflammatory cytokine IL-10. Both DMPA- and LNG-based contraception induced a signature of gene expression similar to that of the luteal phase, only more exacerbated, including widespread downregulation of antiviral genes.

CONCLUSION

The use of progestin-based contraception might engender a milieu that poses an increased risk of HIV acquisition as compared to both the luteal and follicular phases of the menstrual cycle.

The Effect of Commonly Used Excipients on the Epithelial Integrity of Human Cervicovaginal Tissue

Pharmaceutical excipients are widely used in vaginal drug products. The epithelial integrity of the cervicovaginal tissue is important for HIV-1 prevention. However, the effects of excipients on cervicovaginal epithelium remain unknown. This study aims at assessing the effects of vaginal product excipients on the integrity of human cervicovaginal epithelium and on a lead HIV prevention antiretroviral drug, tenofovir (TFV). In the current study, nine excipients commonly used in vaginal formulations were incubated for 6 h with excised human ectocervical tissue. The effects of the excipients were examined by measuring the transepithelial electrical resistance (TEER), epithelial morphology, paracellular/transcellular permeability, and cell viability. The efficacy of TFV for preventing HIV-1 infection in the ex vivo cultured ectocervix was also tested. We found that disodium ethyl-enediaminetetraacetate (EDTA), sorbic acid, and benzoic acid had no effect on the tissue TEER. Butylated hydroxyanisole, glycerin, propylene glycol, methylparaben, and propylparaben slightly to moderately decreased tissue TEER, whereas citric acid significantly decreased the TEER in a time-dependent manner. Tissue morphology observed post-exposure strongly correlated with TEER data; however, a less strong correlation was observed between paracellular permeability and TEER data after exposure to different excipients. In addition, treatment with EDTA, methylparaben, and propylene glycol at tested levels had no effect on the efficacy of TFV in preventing tissue HIV-1 infection. In conclusion, the combined measurements of TEER, morphology, permeability, and viability using human cervicovaginal tissue represent a clinically relevant platform for safety evaluation of excipients and formulated products for HIV-1 prevention.

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.

Repeated Vaginal SHIV Challenges in Macaques Receiving Oral or Topical Preexposure Prophylaxis Induce Virus-Specific T-Cell Responses

BACKGROUND

Preexposure prophylaxis (PrEP) for HIV prevention is a novel biomedical prevention method. We have previously modeled PrEP during rectal SHIV exposures in macaques and identified that Simian/Human Immunodeficiency Virus chimera (SHIV)-specific T-cell responses were induced in the presence of antiretroviral drugs, an observation previously termed T-cell chemo-vaccination. This report expands those initial findings by examining a larger group of macaques that were given oral or topical PrEP during repeated vaginal virus exposure.

METHODS

Thirty-six female pigtail macaques received up to 20 repeat low-dose vaginal inoculations with wild-type (WT) SHIVSF162P3 (n = 24) or a clonal derivative with the tenofovir (TFV) K65R drug-resistant mutation (n = 12). PrEP consisted of oral Truvada (n = 6, WT), TFV vaginal gel (n = 6, K65R), or TFV intravaginal ring (n = 6, WT). The remaining animals were PrEP-inexperienced controls (n = 12, WT; n = 6, K65R). SHIV-specific T cells were identified and characterized using interferon γ Enzyme-Linked ImmunoSpot (ELISPOT) and multiparameter flow cytometry.

RESULTS

Of 9 animals that were on PrEP and remained uninfected during WT SHIV vaginal challenges, 8 (88.9%) developed virus-specific T-cell responses. T cells were in CD4 and CD8 compartments, reached up to 4900 interferon γ-producing cells per million peripheral blood mononuclear cells, and primarily pol directed. In contrast, the replication-impaired K65R virus did not induce detectable T-cell responses, likely reflecting the need for adequate replication.

CONCLUSIONS

Virus-specific T-cell responses occur frequently in oral or topical PrEP-protected pigtail macaques after vaginal exposure to WT SHIV virus. The contribution of such immune responses to protection from infection during and after PrEP warrants further investigation.

Acceptability and feasibility of repeated mucosal specimen collection in clinical trial participants in Kenya

BACKGROUND

Mucosal specimens are essential to evaluate compartmentalized immune responses to HIV vaccine candidates and other mucosally targeted investigational products. We studied the acceptability and feasibility of repeated mucosal sampling in East African clinical trial participants at low risk of HIV and other sexually transmitted infections.

METHODS AND FINDINGS

The Kenya AIDS Vaccine Initiative (KAVI) enrolled participants into three Phase 1 trials of preventive HIV candidate vaccines in 2011-2012 at two clinical research centers in Nairobi. After informed consent to a mucosal sub-study, participants were asked to undergo collection of mucosal secretions (saliva, oral fluids, semen, cervico-vaginal and rectal), but could opt out of any collection at any visit. Specimens were collected at baseline and two additional time points. A tolerability questionnaire was administered at the final sub-study visit. Of 105 trial participants, 27 of 34 women (79%) and 62 of 71 men (87%) enrolled in the mucosal sub-study. Nearly all sub-study participants gave saliva and oral fluids at all visits. Semen was collected from about half the participating men (47-48%) at all visits. Cervico-vaginal secretions were collected by Softcup from about two thirds of women (63%) at baseline, increasing to 78% at the following visits, with similar numbers for cervical secretion collection by Merocel sponge; about half of women (52%) gave cervico-vaginal samples at all visits. Rectal secretions were collected with Merocel sponge from about a quarter of both men and women (24%) at all 3 visits, with 16% of men and 19% of women giving rectal samples at all visits.

CONCLUSIONS

Repeated mucosal sampling in clinical trial participants in Kenya is feasible, with a good proportion of participants consenting to most sampling methods with the exception of rectal samples. Experienced staff members of both sexes and trained counselors with standardized messaging may improve acceptance of rectal sampling.

Immune responses during spontaneous control of HIV and AIDS: what is the hope for a cure?

HIV research has made rapid progress and led to remarkable achievements in recent decades, the most important of which are combination antiretroviral therapies (cART). However, in the absence of a vaccine, the pandemic continues, and additional strategies are needed. The 'towards an HIV cure' initiative aims to eradicate HIV or at least bring about a lasting remission of infection during which the host can control viral replication in the absence of cART. Cases of spontaneous and treatment-induced control of infection offer substantial hope. Here, we describe the scientific knowledge that is lacking, and the priorities that have been established for research into a cure. We discuss in detail the immunological lessons that can be learned by studying natural human and animal models of protection and spontaneous control of viraemia or of disease progression. In particular, we describe the insights we have gained into the immune mechanisms of virus control, the impact of early virus-host interactions and why chronic inflammation, a hallmark of HIV infection, is an obstacle to a cure. Finally, we enumerate current interventions aimed towards improving the host immune response.

Increased Serpin A5 levels in the cervicovaginal fluid of HIV-1 exposed seronegatives suggest that a subtle balance between serine proteases and their inhibitors may determine susceptibility to HIV-1 infection

HIV-exposed seronegative individuals (HESNs) are persons who remain seronegative despite repeated exposure to HIV, suggesting an in vivo resistance mechanism to HIV. Elucidation of endogenous factors responsible for this phenomenon may aid in the development of new classes of microbicides and therapeutics. We compared cervicovaginal protein abundance profiles between high-risk HESN and two control groups: low-risk HESN and HIV-positives. Four iTRAQ-based quantitative experiments were performed using samples classified based on presence/absence of particular gynaecological conditions. After statistical analysis, two proteins were shown to be differentially abundant between high-risk HESNs and control groups. Serpin A5, a serine proteinase inhibitor and Myeloblastin, a serine protease, were up- and downregulated, respectively. Commercially available ELISA assays were used to confirm differential Serpin A5 levels. These results suggest that HIV resistance in CVF of HESNs is the result of a delicate balance between two complementary mechanisms: downregulation of serine proteinases and upregulation of their inhibitors.

Human immunodeficiency virus antibodies and the vaccine problem

Despite the great advances made in controlling human immunodeficiency virus type 1 (HIV-1) infection with antiretroviral drug treatment, a safe and efficacious HIV vaccine has yet to be developed. Here, we discuss why clinical trials and vaccine development for HIV have so far been disappointing, with an emphasis on the lack of protective antibodies. We review approaches for developing appropriate HIV immunogens and the stimulation of long-lasting B-cell responses with antibody maturation. We conclude that candidate reagents in the pipeline for HIV vaccine development are unlikely to be particularly effective. Although the major funders of HIV vaccine research and development are placing increasing emphasis on clinical product development, a genuine breakthrough in preventing HIV infection through vaccines is more likely to come from novel immunogen research.

Distribution of immune cells in the human cervix and implications for HIV transmission

PROBLEM

Knowledge of the mucosal immune cell composition of the human female genital tract is important for understanding susceptibility to HIV-1.

METHOD OF STUDY

We developed an optimized procedure for multicolor flow cytometry analysis of immune cells from human cervix to characterize all major immune cell subsets in the endocervix and ectocervix.

RESULTS

Half of tissue hematopoietic cells were CD14(+) , many of which were macrophages and about a third were CD11c(+) , most of which were CD103(-) CD11b(+) CX3CR1(+) DC-SIGN(+) dendritic cells (DCs). The other dominant population were T cells, with more CD8 than CD4 cells. T cells (both CD8 and CD4) and B cells were more abundant in the ectocervix than endocervix of pre-menopausal women; however, CD8(+) T cell and B cell numbers declined in the ectocervix after menopause, while CD4 T cell counts remained higher. B, NK and conventional myeloid and plasmocytoid DCs each were a few percent of tissue hematopoietic cells. Although the ectocervix had more HIV-susceptible CD4(+) T cells, polarized endocervical explants supported HIV replication significantly better.

CONCLUSION

Due to their abundance in the genital tract, CX3CR1(+) DC-SIGN(+) DCs might be important in HIV transmission. Our data also suggest that the columnar epithelium of the upper genital tract might be a preferential site for HIV transmission.

Pre-exposure prophylaxis for the prevention of HIV infection in high risk populations: a meta-analysis of randomized controlled trials

BACKGROUND

Nearly ten randomized controlled trials (RCTs) of pre-exposure prophylaxis (PrEP) have been completed or are ongoing worldwide to evaluate the effectiveness of PrEP in HIV transmission among HIV-uninfected high risk populations. The purpose of this study was to evaluate the role of PrEP to prevent HIV transmission through a Mata-analysis.

METHODS

A comprehensive computerized literature search was carried out in PubMed, EMbase, Ovid, Web of Science, Science Direct, Wan Fang, CNKI and related websites to collect relevant articles (from their establishment date to August 30, 2013). The search terms were "pre-exposure prophylaxis", "high risk population", "HIV infection", "reduction", "relative risk" and "efficacy". We included any RCT assessing PrEP for the prevention of HIV infection in high risk populations. Interventions of the studies were continuously daily or intermittent doses of single or compound antiretrovirals (ARVs) before HIV exposure or during HIV exposure. A meta-analysis was conducted using Stata 10.0. A random-effects method was used to calculate the pooled relative risk (RR) and 95% confidence intervals (CI) for all studies included.

RESULTS

Seven RCTs involving 14,804 individuals in high risk populations were eligible for this study. The number of subjects in the experimental groups was 8,195, with HIV infection rate of 2.03%. The number of subjects in the control groups was 6,609, with HIV infection rate of 4.07%. The pooled RR was 0.53 (95% CI = 0.40 ∼ 0.71, P<0.001). The re-analyzed pooled RR were 0.61 (95% CI = 0.48 ∼ 0.77, P<0.001), 0.49 (95% CI = 0.38 ∼ 0.63, P<0.001), respectively, by excluding the largest study or two studies without statistical significance. Publication bias analysis revealed a symmetry funnel plot. The fail-safe number was 1,022.

CONCLUSION

These results show that PrEP is an effective strategy for reducing new HIV infections in high risk populations.

IL-22 levels are associated with Trichomonas vaginalis infection in the lower genital tract

PROBLEM

IL-22 has important functions at mucosal surfaces, including the induction of antimicrobial peptides and maintenance of epithelium. However, IL-22 has not been investigated in the genital tract during TV infection.

METHODS OF STUDY

Women who visited an STD clinic and women from a cohort with frequent Trichomoniasis were studied. IL-22, IL-17, and antimicrobial peptides were measured in cervicovaginal lavage by ELISA.

RESULTS

In women visiting the STD clinic, those without STDs (n = 10) had a median IL-22 of 0 pg/mL, while women with infections (n = 30) had 27 pg/mL (P = 0.04). In the cohort, women with Trichomoniasis (n = 19) had significantly higher IL-22 than women with no infections (n = 21, 74 versus 0 pg/mL, P = 0.0001). IL-17 was also significantly increased in Trichomoniasis, and there was a correlation between IL-22 and IL-17 (P = 0.001).

CONCLUSION

IL-22 is increased in STDs generally and in Trichomoniasis specifically suggesting an antimicrobial response of the mucosa and an epithelial repair process induced by the STDs.

Adaptive HIV-specific B cell-derived humoral immune defenses of the intestinal mucosa in children exposed to HIV via breast-feeding

Background

We evaluated whether B cell-derived immune defenses of the gastro-intestinal tract are activated to produce HIV-specific antibodies in children continuously exposed to HIV via breast-feeding.

Methods

Couples of HIV-1-infected mothers (n = 14) and their breastfed non HIV-infected (n = 8) and HIV-infected (n = 6) babies, and healthy HIV-negative mothers and breastfed babies (n = 10) as controls, were prospectively included at the Complexe Pédiatrique of Bangui, Central African Republic. Immunoglobulins (IgA, IgG and IgM) and anti-gp160 antibodies from mother’s milk and stools of breastfed children were quantified by ELISA. Immunoaffinity purified anti-gp160 antibodies were characterized functionally regarding their capacity to reduce attachment and/or infection of R5- and X4- tropic HIV-1 strains on human colorectal epithelial HT29 cells line or monocyte-derived-macrophages (MDM).

Results

The levels of total IgA and IgG were increased in milk of HIV-infected mothers and stools of HIV-exposed children, indicating the activation of B cell-derived mucosal immunity. Breast milk samples as well as stool samples from HIV-negative and HIV-infected babies exposed to HIV by breast-feeding, contained high levels of HIV-specific antibodies, mainly IgG antibodies, less frequently IgA antibodies, and rarely IgM antibodies. Relative ratios of excretion by reference to lactoferrin calculated for HIV-specific IgA, IgG and IgM in stools of HIV-exposed children were largely superior to 1, indicating active production of HIV-specific antibodies by the intestinal mucosa. Antibodies to gp160 purified from pooled stools of HIV-exposed breastfed children inhibited the attachment of HIV-1NDK on HT29 cells by 63% and on MDM by 77%, and the attachment of HIV-1JRCSF on MDM by 40%; and the infection of MDM by HIV-1JRCSF by 93%.

Conclusions

The intestinal mucosa of children exposed to HIV by breast-feeding produces HIV-specific antibodies harbouring in vitro major functional properties against HIV. These observations lay the conceptual basis for the design of a prophylactic vaccine against HIV in exposed children.

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

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

Differential innate immune responses to low or high dose oral SIV challenge in Rhesus macaques

Mucosal transmission of HIV predominately occurs during sexual intercourse or breast-feeding and generally results in a successful infection from just one or few founder virions. Here we assessed the impact of viral inoculum size on both viral and immune events within two groups of Rhesus macaques that were non-traumatically, orally inoculated with either multiple low (1000 to 4000 TCID(50)) or high (100,000 TCID(50)) doses of SIV. In agreement with previous studies, more diverse SIV variants were observed in macaques following infection with high dose oral SIV compared to a low dose challenge. In peripheral blood cells, the immune gene transcript levels of CXCL9, IFNγ, TNFα and IL10 remained similar to uninfected macaques. In contrast, OAS and CXCL10 were upregulated following SIV infection in both the high and low dosed macaques, with a more rapid kinetics (detectable by 7 days) following the high SIV dose challenge. In peripheral lymph nodes, an increase in CXCL10 was observed irrespective of viral dose while CXCL9 and OAS were differentially regulated in the two SIV dosed groups. Magnetic bead sorting of CD3+, CD14+ and CD3- /CD14- cells from peripheral blood identified the increase in OAS expression primarily within CD14+ monocytes, whereas the CXCL10 expression was primarily in CD3+ T cells. These findings provide insights into the impact of SIV challenge dose on viral and innate immune factors, which has the potential to inform future SIV/HIV vaccine efficacy trials in which vaccinated hosts have the potential to be infected with a range of viral challenge doses.

HIV vaccines: progress to date

The quest for an effective and safe HIV-1 vaccine has been and still is the aspiration of many scientists and clinicians worldwide. Until recently, the hopes for an effective vaccine were thwarted by the disappointing results and early termination in September 2007 of the STEP study, which saw a subgroup of male vaccine recipients at an increased risk of HIV-1 infection, and the failure of earlier trials of vaccines based on recombinant envelope proteins to provide any level of protection. The results of the STEP study raised important questions in the field of HIV vaccines, including the use of recombinant adenovirus vectors as immunogens, the rationale for the development of T-cell-based vaccines and the development pathway for these vaccines, in terms of assessment of immunogenicity and the challenge models used. The study of neutralizing antibodies has demonstrated that the induction of high-titre, broadly neutralizing antibodies in the majority of recipients is likely to be highly problematic. However, the results of the RV144 Thai trial released in September 2009 have brought new optimism to the field. This study employed envelope-based immunogens delivered as a priming vaccination with a recombinant poxvirus vector and boosting with recombinant proteins. This regimen provided modest protection to HIV-1 infection in a low-risk population. Although the correlates of protection are currently unknown, extensive studies are underway to try to determine these. Neutralizing antibodies were not induced in the RV144 study; however, considerable titres of binding antibodies to HIV-1 viral envelope (Env) were. It is speculated that these antibodies may have provided a means of protection by a mechanism such as antibody-dependent cell-mediated cytotoxicity. In addition, no CD8+ T-cell responses were induced, but robust CD4+ T-cell responses were, and correlates of protection are being sought by analysing the quality of this aspect of the vaccine-induced immune response. The current paradigm for an optimal HIV-1 vaccine is to design immunogens and vaccination protocols that allow the induction of both broadly neutralizing humoral and broadly reactive and effective cell-mediated immunity, to act at sites of possible infection and post-infection, respectively. However, this is challenged by the results of the RV144 trial as neither of these responses were induced but modest protection was observed. Understanding the biology and immunopathology of HIV-1 early following infection, its modes of transmission and the human immune system's response to the virus should aid in the rational design of vaccines of increased efficacy.

Coming of age: reconstruction of heterosexual HIV-1 transmission in human ex vivo organ culture systems

Heterosexual transmission of human immunodeficiency virus-1 (HIV-1), from men to women, involves exposure to infectious HIV-1 in semen. Therefore, the cellular and molecular processes that underlie HIV-1 transmission are closely interconnected with fundamental principles of human reproductive biology. Human ex vivo organ culture systems allow experimental reconstruction of HIV-1 transmission, using human semen and premenopausal cervicovaginal mucosal tissue, with specific emphasis on the progression from exposure to development of primary HIV-1 infection. Clearly, an isolated piece of human tissue cannot duplicate the full complexity of events in natural infections, but with correct observation of conventional medical and ethical standards, there is no opportunity to study HIV-1 exposure and primary infection in young women. Human mucosal organ cultures allow direct study of HIV-1 infection in a reproducible format while retaining major elements of complexity and variability that typify community-based HIV-1 transmission. Experimental manipulation of human mucosal tissue both allows and requires acquisition of new insights into basic processes of human mucosal immunology. Expanding from the current foundations, we believe that human organ cultures will become increasingly prominent in experimental studies of HIV-1 transmission and continuing efforts to prevent HIV-1 infection at human mucosal surfaces.

Scarcity or absence of humoral immune responses in the plasma and cervicovaginal lavage fluids of heavily HIV-1-exposed but persistently seronegative women

To address an existing controversy concerning the presence of HIV-1-specific antibodies of the IgA isotype in the female genital tract secretions of highly-exposed but persistently seronegative (HEPSN) women, 41 samples of plasma and cervicovaginal lavage (CVL) fluid were distributed to six laboratories for their blinded evaluation using ELISA with 10 different HIV-1 antigens, chemiluminescence-enhanced Western blots (ECL-WB), and virus neutralization. HIV-specific IgG or IgA antibodies in plasma samples from HEPSN women were absent or detectable only at low levels. In CVL, 11/41 samples displayed low levels of reactivity in ELISA against certain antigens. However, only one sample was positive in two of five laboratories. All but one CVL sample yielded negative results when analyzed by ECL-WB. Viral neutralizing activity was either absent or inconsistently detected in plasma and CVL. Plasma and CVL samples from 26 HIV-1-infected women were used as positive controls. Irrespective of the assays and antigens used, the results generated in all laboratories displayed remarkable concordance in the detection of HIV-1-specific antibodies of the IgG isotype. In contrast, IgA antibodies to HIV-1 antigens were not detected with consistency, and where present, IgA antibodies were at markedly lower levels than IgG. Although HIV-neutralizing activity was detected in plasma of all HIV-1-infected women, only a few of their CVL samples displayed such activity. In conclusion, frequent HIV-1 sexual exposure does not stimulate uniformly detectable mucosal or systemic HIV-1-specific responses, as convincingly documented in the present blindly performed study using a broad variety of immunological assays. Although HIV-1-infection leads to vigorous IgG responses in plasma and CVL, it does not stimulate sustained IgA responses in either fluid.

Evidence for the innate immune response as a correlate of protection in human immunodeficiency virus (HIV)-1 highly exposed seronegative subjects (HESN)

The description of highly exposed individuals who remain seronegative (HESN) despite repeated exposure to human immunodeficiency virus (HIV)-1 has heightened interest in identifying potential mechanisms of HIV-1 resistance. HIV-specific humoral and T cell-mediated responses have been identified routinely in HESN subjects, although it remains unknown if these responses are a definitive cause of protection or merely a marker for exposure. Approximately half of HESN lack any detectible HIV-specific adaptive immune responses, suggesting that other mechanisms of protection from HIV-1 infection also probably exist. In support of the innate immune response as a mechanism of resistance, increased natural killer (NK) cell activity has been correlated with protection from infection in several high-risk cohorts of HESN subjects, including intravenous drug users, HIV-1 discordant couples and perinatally exposed infants. Inheritance of protective NK KIR3DL1(high) and KIR3DS1 receptor alleles have also been observed to be over-represented in a high-risk cohort of HESN intravenous drug users and HESN partners of HIV-1-infected subjects. Other intrinsic mechanisms of innate immune protection correlated with resistance in HESN subjects include heightened dendritic cell responses and increased secretion of anti-viral factors such as β-chemokines, small anti-viral factors and defensins. This review will highlight the most current evidence in HESN subjects supporting the role of epithelial microenvironment and the innate immune system in sustaining resistance against HIV-1 infection. We will argue that as a front-line defence the innate immune response determines the threshold of infectivity that HIV-1 must overcome to establish a productive infection.

Pharmacological considerations for tenofovir and emtricitabine to prevent HIV infection

The use of antiretroviral medications in HIV-negative individuals as pre-exposure prophylaxis (PrEP) is a promising approach to prevent HIV infection. Tenofovir disoproxil fumarate (TDF) and emtricitabine exhibit desirable properties for PrEP including: favourable pharmacokinetics that support infrequent dosing; few major drug-drug or drug-food interactions; an excellent clinical safety record; and pre-clinical evidence for efficacy. Several large, randomized, controlled clinical trials are evaluating the safety and efficacy of TDF and emtricitabine for this new indication. A thorough understanding of variability in drug response will help determine future investigations in the field and/or implementation into clinical care. Because tenofovir and emtricitabine are nucleos(t)ide analogues, the HIV prevention and toxicity effects depend on the triphosphate analogue formed intracellularly. This review identifies important cellular pharmacology considerations for tenofovir and emtricitabine, which include drug penetration into relevant tissues and cell types, race/ethnicity/pharmacogenetics, gender, cellular activation state and appropriate episodic or alternative dosing strategies based on pharmacokinetic principles. The current state of knowledge in these areas is summarized and the future utility of intracellular pharmacokinetics/pharmacodynamics for the PrEP field is discussed.

Use of cervicovaginal fluid for the identification of biomarkers for pathologies of the female genital tract

Cervicovaginal fluid has an important function in the homeostasis and immunity of the lower female genital tract. Analysis of the cervicovaginal fluid proteome may therefore yield important information about the pathogenesis of numerous gynecological pathologies. Additionally, cervicovaginal fluid has great potential as a source of biomarkers for these conditions.

This review provides a detailed discussion about the human cervicovaginal proteome and the proteomics studies performed to characterize this biological fluid. Furthermore, infection-correlated pathological conditions of the female genital tract are discussed for which cervicovaginal fluid has been used in order to identify potential biomarkers. Recent years, numerous studies have analyzed cervicovaginal fluid samples utilizing antibody-based technologies, such as ELISA or Western blotting, to identify biomarkers for preterm birth, premature preterm rupture of membranes, bacterial vaginosis and cervical cancer. The present article will discuss the importance of proteomic technologies as alternative techniques to gain additional meaningful information about these conditions. In addition, the review focuses on recent proteomic studies on cervicovaginal fluid samples for the identification of potential biomarkers. We conclude that the use of proteomic technology for analysis of human cervicovaginal fluid samples is promising and may lead to the discovery of new biomarkers which can improve disease prevention and therapy development.

In vivo evaluation of the release of zidovudine and polystyrene sulfonate from a dual intravaginal bioadhesive polymeric device in the pig model

This study focused on determining the concentration of zidovudine (AZT) and polystyrene sulfonate (PSS) in the plasma and vaginal tissue of the large white pig from an intravaginal bioadhesive polymeric device (IBPD). Biocompatible polymers were compressed with AZT and PSS into caplet-shaped devices for insertion into the posterior fornix of the pig vagina. A total of 25 pigs were used in this study. Plasma was sampled from the jugular vein at various time points after insertion of the IBPD reaching 28 days. At day 28, the pigs were euthanized and vaginal tissue was removed and digested with subtilisin for AZT and PSS extraction. The mean concentration detected in vaginal tissue at day 28 was 1.214 ± 0.062 mg/mL for AZT and 1.400 ± 0.071 mg/mL for PSS. Plasma concentration was significantly lower for AZT (0.332 ± 0.014 mg/mL) and PSS (0.256 ± 0.013 mg/mL). This indicated higher retention of AZT and PSS within the vaginal tissue. Molecular mechanics simulations blueprinted polymer-drug-mucin force-field interactions and energies that explicated the spatial preference of AZT and PSS for the vaginal tissue. Histopathotoxicity studies revealed negative-to-mild foreign body events and results strongly suggest that the IBPD may be suitable for prolonged intravaginal drug delivery in preventing the transmission of sexually transmitted infections and HIV/AIDS.

Innovative approaches to develop prophylactic and therapeutic vaccines against HIV/AIDS

The acquired immunodeficiency syndrome (AIDS) emerged in the human population in the summer of 1981. According to the latest United Nations estimates, worldwide over 33 million people are infected with human immunodeficiency virus (HIV) and the prevalence rates continue to rise globally. To control the alarming spread of HIV, an urgent need exists for developing a safe and effective vaccine that prevents individuals from becoming infected or progressing to disease. To be effective, an HIV/AIDS vaccine should induce broad and long-lasting humoral and cellular immune responses, at both mucosal and systemic level. However, the nature of protective immune responses remains largely elusive and this represents one of the major roadblocks preventing the development of an effective vaccine. Here we summarize our present understanding of the factors responsible for resistance to infection or control of progression to disease in human and monkey that may be relevant to vaccine development and briefly review recent approaches which are currently being tested in clinical trials. Finally, the rationale and the current status of novel strategies based on nonstructural HIV-1 proteins, such as Tat, Nef and Rev, used alone or in combination with modified structural HIV-1 Env proteins are discussed.

Prime-boost vaccination using chemokine-fused gp120 DNA and HIV envelope peptides activates both immediate and long-term memory cellular responses in rhesus macaques

HIV vaccine candidates with improved immunogenicity and induction of mucosal T-cell immunity are needed. A prime-boost strategy using a novel HIV glycoprotein 120 DNA vaccine was employed to immunize rhesus macaques. The DNA vaccine encoded a chimeric gp120 protein in fusion with monocyte chemoattractant protein-3, which was hypothesized to improve the ability of antigen-presenting cells to capture viral antigen through chemokine receptor-mediated endocytosis. DNA vaccination induced virus-reactive T cells in peripheral blood, detectable by T cell proliferation, INFgamma ELISPOT and sustained IL-6 production, without humoral responses. With a peptide-cocktail vaccine containing a set of conserved polypeptides of HIV-1 envelope protein, given by nasogastric administration, primed T-cell immunity was significantly boosted. Surprisingly, long-term and peptide-specific mucosal memory T-cell immunity was detected in both vaccinated macaques after one year. Therefore, data from this investigation offer proof-of-principle for potential effectiveness of the prime-boost strategy with a chemokine-fused gp120 DNA and warrant further testing in the nonhuman primate models for developing as a potential HIV vaccine candidate in humans.

Correlates of antibody-mediated protection against HIV infection

PURPOSE OF REVIEW

The only unequivocal correlate of protection against primate immunodeficiency virus infection is the presence of neutralizing antibody at sufficient titre. This correlate has been determined experimentally using animal models, and the data are reproducible and robust. Recent advances have added further depth to this knowledge by moving us closer to understanding how antibodies neutralize HIV-1, and what effects they may have in vivo with regard to protection from infection and disease.

RECENT FINDINGS

This review will cover recent advances in our understanding of the structural basis of HIV-1 neutralization by antibody and how this understanding may relate to vaccine design, and incorporate this into the broader context of how antibodies may influence viral transmission, replication and disease.

SUMMARY

The sum of these findings provides a strong rationale for designing an HIV-1 vaccine on the principle of induction of neutralizing antibodies, although other effector functions of antibodies such as complement and antibody-mediated cellular immunity should also be borne in mind, as should CD4 and CD8 T cell responses.

Antibody-Mediated Fcγ Receptor-Based Mechanisms of HIV Inhibition: Recent Findings and New Vaccination Strategies

The HIV/AIDS pandemic is one of the most devastating pandemics worldwide. Today, the major route of infection by HIV is sexual transmission. One of the most promising strategies for vaccination against HIV sexual infection is the development of a mucosal vaccine, which should be able to induce strong local and systemic protective immunity. It is believed that both humoral and cellular immune responses are needed for inducing a sterilizing protection against HIV. Recently, passive administration of monoclonal neutralizing antibodies in macaques infected by vaginal challenge demonstrated a crucial role of FcγRs in the protection afforded by these antibodies. This questioned about the role of innate and adaptive immune functions, including ADCC, ADCVI, phagocytosis of opsonized HIV particles and the production of inflammatory cytokines and chemokines, in the mechanism of HIV inhibition in vivo. Other monoclonal antibodies - non-neutralizing inhibitory antibodies - which recognize immunogenic epitopes, have been shown to display potent FcγRs-dependent inhibition of HIV replication in vitro. The potential role of these antibodies in protection against sexual transmission of HIV and their biological relevance for the development of an HIV vaccine therefore need to be determined. This review highlights the potential role of FcγRs-mediated innate and adaptive immune functions in the mechanism of HIV protection.

Mucosal immunology of the genital and gastrointestinal tracts and HIV-1 infection

The male and female genital tracts are protected by a local immune system that displays features distinguishing them from other mucosal sites. In contrast to the intestinal tract, where locally produced IgA is the dominant Ig, secretions of the male and female genital tract contain predominantly IgG of both local and systemic origin. Genital tract tissues also lack mucosal lymphoepithelial inductive sites analogous to intestinal Peyer's patches; consequently, local immunization or infections with sexually transmitted pathogens induce low immune responses. Human immunodeficiency virus 1 (HIV-1) infection must be primarily considered as a mucosal disease with extensive involvement of the systemic immune compartment. Although the majority of infections is acquired through the genital mucosa, a high rate of virus replication and profound CD4(+) T cell depletion occurs in the intestinal mucosa and other mucosal tissues shortly after infection. Evaluation of HIV-specific antibodies in sera and external secretions, including vaginal washes and semen, unexpectedly revealed a selective lack of IgA responses. Moreover, specific antibody-secreting cells in peripheral blood were of the IgG isotype, even in mucosally infected individuals. Whether humoral responses to previously or newly encountered antigens are compromised in HIV-1-infected persons is under current investigation.

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

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

Elevated elafin/trappin-2 in the female genital tract is associated with protection against HIV acquisition

OBJECTIVES

Globally, heterosexual intercourse is the primary route of HIV-1 (HIV) transmission. It follows that mechanisms that protect against HIV infection are likely operative at the genital mucosa. In HIV-resistant Kenyan sex workers who are highly exposed to HIV infection yet remain uninfected, protection correlates with HIV-specific immune responses and genetic factors. However, these factors do not entirely explain this model of natural immunity to HIV. We hypothesized that protection may be mediated by innate immune proteins in the genital tract of HIV-resistant sex workers.

DESIGN AND METHODS

The genital proteome of mucosal secretions from HIV-resistant women was examined using surface-enhanced laser desorption/ionization time-of-flight mass spectrometry. Cervical lavage samples were collected from 315 HIV-resistant, HIV-uninfected and HIV-infected commercial sex workers.

RESULTS

Univariate analysis identified a 6 kDa biomarker of HIV resistance in genital secretions from these women. This protein was identified by tandem mass spectrometry as elafin and was found to be overexpressed in HIV-resistant women compared with HIV-uninfected (P = 0.001) and infected (P = 0.002) women. The elevated levels of elafin/trappin-2 in HIV-resistant women were confirmed using ELISA. The prospective association of elevated cervicovaginal elafin/trappin-2 levels with protection from HIV acquisition was then confirmed in an independent cohort of high-risk female sex workers.

CONCLUSION

Using a unique proteomics approach in a large scale, cross-sectional cohort study, we identified elafin/trappin-2 as a novel innate immune factor, which is highly associated with resistance. This association was confirmed within an independent, prospective cohort study. Genital tract elafin/trappin-2 levels constitute a natural correlate of HIV protection in humans.

Levels of innate immune factors in genital fluids: association of alpha defensins and LL-37 with genital infections and increased HIV acquisition

BACKGROUND

Several mucosal innate immune proteins exhibit HIV inhibitory activity and their analogues are potential microbicide candidates. However, their clinical associations and in-vivo role in cervicovaginal host defense against HIV acquisition are poorly defined.

METHODS

Cervicovaginal secretions (CVSs) were collected from HIV uninfected Kenyan sex workers at enrolment into an HIV prevention trial. After trial completion, CVS from participants acquiring HIV (cases) and matched controls were assessed for levels of innate immune factors and HIV neutralizing capacity, by blinded investigators. Cross-sectional and prospective associations of innate immune factors were examined.

RESULTS

CVS contained high levels of defensins (human neutrophil peptide-1-3 and human beta defensin-2-3), LL-37 and secretory leukocyte protease inhibitor. Regulated upon activation normal T-cell expressed and secreted levels were lower, and IFNalpha was undetectable. CVS from 20% of participants neutralized a clade A primary HIV isolate, and 12% neutralized both clade A and C isolates. HIV neutralization was correlated with human neutrophil peptide-1-3 (alpha-defensins) and LL-37 levels. However, alpha-defensin and LL-37 levels were increased in participants with bacterial sexually transmitted infections and were independently associated with increased HIV acquisition in multivariate analysis.

CONCLUSIONS

Despite significant HIV inhibitory activity, cervicovaginal levels of alpha-defensins and LL-37 were associated with increased HIV acquisition, perhaps due to their association with bacterial sexually transmitted infections.

Mucosal immunity and protection against HIV/SIV infection: strategies and challenges for vaccine design

To date, most HIV vaccine strategies have focused on parenteral immunization and systemic immunity. These approaches have not yielded the efficacious HIV vaccine urgently needed to control the AIDS pandemic. As HIV is primarily mucosally transmitted, efforts are being re-focused on mucosal vaccine strategies, in spite of complexities of immune response induction and evaluation. Here, we outline issues in mucosal vaccine design and illustrate strategies with examples from the recent literature. Development of a successful HIV vaccine will require in-depth understanding of the mucosal immune system, knowledge that ultimately will benefit vaccine design for all mucosally transmitted infectious agents.

Excretion of human immunodeficiency virus type 1 through polarized epithelium by immunoglobulin A

Human immunodeficiency virus (HIV) is transmitted primarily sexually across mucosal surfaces. After infection, HIV propagates initially in the lamina propria below the polarized epithelium and causes extensive destruction of mucosal T cells. Immunoglobulin A (IgA) antibodies, produced in the lamina propria and then transcytosed across the mucosal epithelium into the lumen, can be the first line of immune defense against HIV. Here, we used IgA monoclonal antibodies against HIV envelope proteins to investigate the abilities of polarized primate and human epithelial cells to excrete HIV virions from the basolateral to the apical surface via polymeric Ig receptor (pIgR)-mediated binding and the internalization of HIV-IgA immune complexes. African green monkey kidney cells expressing pIgR demonstrated HIV excretion that was dependent on the IgA concentration and the exposure time. Matched IgG antibodies with the same variable regions as the IgA antibodies and IgA antibodies to non-HIV antigens had no HIV excretory function. A mixture of two IgA anti-bodies against gp120 and gp41 showed a synergistic increase in the level of HIV excreted. The capacity for HIV excretion correlated with the ability of IgA antibodies to bind HIV and of the resulting immune complexes to bind pIgR. Consistent with the epithelial transcytosis of HIV-IgA immune complexes, the colocalization of HIV proteins and HIV-specific IgA was detected intracellularly by confocal microscopy. Our results suggest the potential of IgA antibodies to excrete HIV from mucosal lamina propria, thereby decreasing the viral burden, access to susceptible cells, and the chronic activation of the immune system.

Potentially exposed but uninfected individuals produce cytotoxic and polyfunctional human immunodeficiency virus type 1-specific CD8(+) T-cell responses which can be defined to the epitope level

We measured CD8(+) T-cell responses in 12 potentially exposed but uninfected men who have sex with men by using cytokine flow cytometry. Four of the individuals screened exhibited polyfunctional immune responses to human immunodeficiency virus type 1 Gag or Vif. The minimum cytotoxic T lymphocyte epitope was mapped in one Gag responder.

HIV-1 reverse transcriptase artificially targeted for proteasomal degradation induces a mixed Th1/Th2-type immune response

Targeting of a DNA vaccine encoded protein for degradation via the proteasome is attempted since it may enhance the immunogenicity of the vaccine. We have fused HIV-1 reverse transcriptase (RT) to mouse ornithine decarboxylase (ODC), a protein rapidly degraded by proteasome in an ubiquitine-independent fashion, to enhance the introduction of RT into the MHC class I pathway. We also designed a fusion of RT with two short signals from the C-terminus of ODC (ODCsig) representing a minimal proteasome-targeting moiety of ODC (PEST signal). Fusion to ODC or ODC signal domain led to a marked enhancement of RT degradation. Plasmids encoding RT-ODC and RT-ODCsig chimera were used to immunize BALB/c mice. The administration of the plasmids was not associated with autoimmune disease. Moreover, mice receiving RT-ODCsig gene mounted a mixed Th1/Th2 response characterized by the in vitro secretion of IFN-gamma, IL-2, TNF-alpha, IL-4, and IL-10 upon stimulation of splenocytes with RT protein or RT derived peptides. Serum titers of 10(2) to 10(3) were observed in more than 50% of animals in that group, whereas fewer animals mounted an anti-RT response in the RT-ODC gene immunized group. Chimeras of the type described here can, therefore, be used in vaccinations aiming to induce HIV-1 RT-specific immune response.

Immunogenetic basis of HIV-1 infection, transmission and disease progression

Susceptibility to HIV-1 infection and rate of disease progression to AIDS are complex traits modulated by environmental and genetic factors. Studies on large AIDS cohorts and their meta-analyses have identified numerous AIDS restriction genes that regulate HIV cell entry (particularly chemokine co-receptors and their ligands), acquired and innate immunity (major histocompatibility complex (MHC), killer immunoglobulin-like receptors (KIRs), and cytokines) and others that influence outcome of HIV infection. However, vast inter-individual variability is often observed and some rare individuals like 'long-term non-progressors (LTNPs) or exposed uninfected' (EUs) appear to be protected due to natural resistance. A better understanding of genetic basis of such a 'natural resistance' to infection would bear important implications in designing therapeutic vaccine designs. The genetic variants that could limit AIDS vary in different populations. We have studied genetic variations in the MHC, cytokines and CCR2-CCR5 loci in the Asian-Indian HIV-infected population and compared with other global populations.