Setting the stage: host invasion by HIV

The regulation of inflammatory pathways and infectious disease of the cervix by seminal fluid

The connection between human papillomavirus (HPV) infection and the consequent sequelae which establishes cervical neoplastic transformation and invasive cervical cancer has redefined many aspects of cervical cancer research. However there is still much that we do not know. In particular, the impact of external factors, like seminal fluid in sexually active women, on pathways that regulate cervical inflammation and tumorigenesis, have yet to be fully understood. HPV infection is regarded as the initiating noninflammatory cause of the disease; however emerging evidence points to resident HPV infections as drivers of inflammatory pathways that play important roles in tumorigenesis as well as in the susceptibility to other infections such as human immunodeficiency virus (HIV) infection. Moreover there is emerging evidence to support a role for seminal fluid, in particular, the inflammatory bioactive lipids, and prostaglandins which are present in vast quantities in seminal fluid in regulating pathways that can exacerbate inflammation of the cervix, speed up tumorigenesis, and enhance susceptibility to HIV infection. This review will highlight some of our current knowledge of the role of seminal fluid as a potent driver of inflammatory and tumorigenic pathways in the cervix and will provide some evidence to propose a role for seminal plasma prostaglandins in HIV infection and AIDS-related cancer.

Combination of the CCL5-derived peptide R4.0 with different HIV-1 blockers reveals wide target compatibility and synergic cobinding to CCR5

R4.0, a synthetic CCL5/RANTES-derived peptide, exerts potent anti-HIV-1 activity via its nonactivating interaction with CCR5, the major HIV-1 coreceptor. CCR5 chronic activation may promote undesirable inflammatory effects and enhance viral infection; thus, receptor antagonism is a necessary requisite. HIV-1 gp120, CCL5, and maraviroc dock on CCR5 by sharing two receptor sites: the N terminus and the second extracellular loop. In combination studies, R4.0, CCL5, and maraviroc exhibited concomitant interactions with CCR5 and promoted synergic inhibition of HIV-1 in acute-infection assays. Furthermore, various degrees of additive/synergic HIV-1 inhibition were observed when R4.0 was tested in combination with drugs and lead compounds directed toward different viral targets (gp120, gp41, reverse transcriptase, and protease). In combination with tenofovir, R4.0 provides cross-clade synergic inhibition of primary HIV-1 isolates. Remarkably, an in vitro-generated maraviroc-resistant R5 HIV-1 strain was inhibited by R4.0 comparably to the wild-type strain, suggesting the presence of viral resistance barriers similar to those reported for CCL5. Overall, R4.0 appears to be a promising lead peptide with potential for combination in anti-HIV-1 therapy and in microbicide development to prevent sexual HIV-1 transmission.

Recent progress in HIV vaccines inducing mucosal immune responses

In spite of several attempts over many years at developing a HIV vaccine based on classical strategies, none has convincingly succeeded to date. As HIV is transmitted primarily by the mucosal route, particularly through sexual intercourse, understanding antiviral immunity at mucosal sites is of major importance. An ideal vaccine should elicit HIV-specific antibodies and mucosal CD8⁺ cytotoxic T-lymphocyte (CTL) as a first line of defense at a very early stage of HIV infection, before the virus can disseminate into the secondary lymphoid organs in mucosal and systemic tissues. A primary focus of HIV preventive vaccine research is therefore the induction of protective immune responses in these crucial early stages of HIV infection. Numerous approaches are being studied in the field, including building upon the recent RV144 clinical trial. In this article, we will review current strategies and briefly discuss the use of adjuvants in designing HIV vaccines that induce mucosal immune responses.

The semen microbiome and its relationship with local immunology and viral load in HIV infection

Semen is a major vector for HIV transmission, but the semen HIV RNA viral load (VL) only correlates moderately with the blood VL. Viral shedding can be enhanced by genital infections and associated inflammation, but it can also occur in the absence of classical pathogens. Thus, we hypothesized that a dysregulated semen microbiome correlates with local HIV shedding. We analyzed semen samples from 49 men who have sex with men (MSM), including 22 HIV-uninfected and 27 HIV-infected men, at baseline and after starting antiretroviral therapy (ART) using 16S rRNA gene-based pyrosequencing and quantitative PCR. We studied the relationship of semen bacteria with HIV infection, semen cytokine levels, and semen VL by linear regression, non-metric multidimensional scaling, and goodness-of-fit test. Streptococcus, Corynebacterium, and Staphylococcus were common semen bacteria, irrespective of HIV status. While Ureaplasma was the more abundant Mollicutes in HIV-uninfected men, Mycoplasma dominated after HIV infection. HIV infection was associated with decreased semen microbiome diversity and richness, which were restored after six months of ART. In HIV-infected men, semen bacterial load correlated with seven pro-inflammatory semen cytokines, including IL-6 (p = 0.024), TNF-α (p = 0.009), and IL-1b (p = 0.002). IL-1b in particular was associated with semen VL (r² = 0.18, p = 0.02). Semen bacterial load was also directly linked to the semen HIV VL (r² = 0.15, p = 0.02). HIV infection reshapes the relationship between semen bacteria and pro-inflammatory cytokines, and both are linked to semen VL, which supports a role of the semen microbiome in HIV sexual transmission.

The classical paradigm of HIV infectivity centers on the blood HIV RNA viral load. However, while other fluid compartments such as semen and cerebrospinal fluid can have distinct viral loads from blood, the causes of localized HIV shedding are not fully understood. Since the semen viral load is an independent predictor of HIV transmission risk, it is critical to understand the local factors that trigger increased semen viral shedding in order to develop novel preventative strategies. Here, we evaluated the semen microbiome, bacterial load, and cytokine levels in 22 HIV-uninfected men who have sex with men (MSM) and in 27 HIV-infected MSM before and after initiation of antiretroviral therapy (ART). We found that HIV infection reduces semen microbiome biodiversity, which is restored with ART and immune reconstitution. We also found that semen bacterial load in untreated, HIV-infected men is associated with the levels of seven semen cytokines, relationships not seen in the uninfected controls. In particular, the cytokine IL-1b was uniquely correlated with both semen bacterial and viral load. Our findings support the interaction between semen microbiome and local immunology, and suggest that IL-1b could be a mechanism for semen microbiome to trigger semen viral shedding.

HIV-1 specific IgA detected in vaginal secretions of HIV uninfected women participating in a microbicide trial in Southern Africa are primarily directed toward gp120 and gp140 specificities

Background

Many participants in microbicide trials remain uninfected despite ongoing exposure to HIV-1. Determining the emergence and nature of mucosal HIV-specific immune responses in such women is important, since these responses may contribute to protection and could provide insight for the rational design of HIV-1 vaccines.

Methods and Findings

We first conducted a pilot study to compare three sampling devices (Dacron swabs, flocked nylon swabs and Merocel sponges) for detection of HIV-1-specific IgG and IgA antibodies in vaginal secretions. IgG antibodies from HIV-1-positive women reacted broadly across the full panel of eight HIV-1 envelope (Env) antigens tested, whereas IgA antibodies only reacted to the gp41 subunit. No Env-reactive antibodies were detected in the HIV-negative women. The three sampling devices yielded equal HIV-1-specific antibody titers, as well as total IgG and IgA concentrations. We then tested vaginal Dacron swabs archived from 57 HIV seronegative women who participated in a microbicide efficacy trial in Southern Africa (HPTN 035). We detected vaginal IgA antibodies directed at HIV-1 Env gp120/gp140 in six of these women, and at gp41 in another three women, but did not detect Env-specific IgG antibodies in any women.

Conclusion

Vaginal secretions of HIV-1 infected women contained IgG reactivity to a broad range of Env antigens and IgA reactivity to gp41. In contrast, Env-binding antibodies in the vaginal secretions of HIV-1 uninfected women participating in the microbicide trial were restricted to the IgA subtype and were mostly directed at HIV-1 gp120/gp140.

Human immature Langerhans cells restrict CXCR4-using HIV-1 transmission

Background

Sexual transmission is the main route of HIV-1 infection and the CCR5-using (R5) HIV-1 is predominantly transmitted, even though CXCR4-using (X4) HIV-1 is often abundant in chronic HIV-1 patients. The mechanisms underlying this tropism selection are unclear. Mucosal Langerhans cells (LCs) are the first immune cells to encounter HIV-1 and here we investigated the role of LCs in selection of R5 HIV-1 using an ex vivo epidermal and vaginal transmission models.

Results

Immature LCs were productively infected by X4 as well as R5 HIV-1. However, only R5 but not X4 viruses were selectively transmitted by immature LCs to T cells. Transmission of HIV-1 was depended on de novo production of HIV-1 in LCs, since it could be inhibited by CCR5 fusion inhibitors as well as reverse transcription inhibitors. Notably, the activation state of LCs affected the restriction in X4 HIV-1 transmission; immune activation by TNF facilitated transmission of X4 as well as R5 HIV-1.

Conclusions

These data suggest that LCs play a crucial role in R5 selection and that immature LCs effectively restrict X4 at the level of transmission.

Innate and adaptive immune responses in male and female reproductive tracts in homeostasis and following HIV infection

The male and female reproductive tracts are complex microenvironments that have diverse functional demands. The immune system in the reproductive tract has the demanding task of providing a protective environment for a fetal allograft while simultaneously conferring protection against potential pathogens. As such, it has evolved a unique set of adaptations, primarily under the influence of sex hormones, which make it distinct from other mucosal sites. Here, we discuss the various components of the immune system that are present in both the male and female reproductive tracts, including innate soluble factors and cells and humoral and cell-mediated adaptive immunity under homeostatic conditions. We review the evidence showing unique phenotypic and functional characteristics of immune cells and responses in the male and female reproductive tracts that exhibit compartmentalization from systemic immunity and discuss how these features are influenced by sex hormones. We also examine the interactions among the reproductive tract, sex hormones and immune responses following HIV-1 infection. An improved understanding of the unique characteristics of the male and female reproductive tracts will provide insights into improving clinical treatments of the immunological causes of infertility and the design of prophylactic interventions for the prevention of sexually transmitted infections.

Prolonged expression of an anti-HIV-1 gp120 minibody to the female rhesus macaque lower genital tract by AAV gene transfer

Topical microbicides are a leading strategy for prevention of HIV mucosal infection to women, however, numerous pharmacokinetic limitations associated with coitally-related dosing strategy have contributed to their limited success. Here we test the hypothesis that adeno-associated virus (AAV) mediated delivery of the b12 human anti-HIV-1 gp120 minibody gene to the lower genital tract of female rhesus macaques (Rh) can provide prolonged expression of b12 minibodies in the cervical-vaginal secretions. Gene transfer studies demonstrated that, of various GFP-expressing AAV serotypes, AAV-6 most efficiently transduced freshly immortalized and primary genital epithelial cells (PGECs) of female Rh in vitro. In addition, AAV-6-b12 minibody transduction of Rh PGECs led to inhibition of SHIV162p4 transmigration and virus infectivity in vitro. AAV-6-GFP could also successfully transduce vaginal epithelial cells of Rh when applied intra-vaginally, including p63+ epithelial stem cells. Moreover, intra-vaginal application of AAV-6-b12 to female Rh resulted in prolonged minibody detection in their vaginal secretions throughout the 79 day study period. These data provide proof-of-principle that AAV-6-mediated delivery of anti-HIV broadly neutralizing antibody (BnAb) genes to the lower genital tract of female Rh results in persistent minibody detection for several months. This strategy offers promise that an anti-HIV-1 genetic microbicide strategy may be possible in which topical application of AAV vector, with periodic reapplication as needed, may provide sustained local BnAb expression and protection.

Broad anti-HIV activity of the Oscillatoria agardhii agglutinin homologue lectin family

OBJECTIVES

Oscillatoria agardhii agglutinin homologue (OAAH) proteins belong to a recently discovered lectin family. The founding member OAA and a designed hybrid OAAH (OPA) recognize similar but unique carbohydrate structures of Man-9, compared with other antiviral carbohydrate-binding agents (CBAs). These two newly described CBAs were evaluated for their inactivating properties on HIV replication and transmission and for their potential as microbicides.

METHODS

Various cellular assays were used to determine antiviral activity against wild-type and certain CBA-resistant HIV-1 strains: (i) free HIV virion infection in human T lymphoma cell lines and PBMCs; (ii) syncytium formation assay using persistently HIV-infected T cells and non-infected CD4+ T cells; (iii) DC-SIGN-mediated viral capture; and (iv) transmission to uninfected CD4+ T cells. OAA and OPA were also evaluated for their mitogenic properties and potential synergistic effects using other CBAs.

RESULTS

OAA and OPA inhibit HIV replication, syncytium formation between HIV-1-infected and uninfected T cells, DC-SIGN-mediated HIV-1 capture and transmission to CD4+ target T cells, thereby rendering a variety of HIV-1 and HIV-2 clinical isolates non-infectious, independent of their coreceptor use. Both CBAs competitively inhibit the binding of the Manα(1-2)Man-specific 2G12 monoclonal antibody (mAb) as shown by flow cytometry and surface plasmon resonance analysis. The HIV-1 NL4.3(2G12res), NL4.3(MVNres) and IIIB(GRFTres) strains were equally inhibited as the wild-type HIV-1 strains by these CBAs. Combination studies indicate that OAA and OPA act synergistically with Hippeastrum hybrid agglutinin, 2G12 mAb and griffithsin (GRFT), with the exception of OPA/GRFT.

CONCLUSIONS

OAA and OPA are unique CBAs with broad-spectrum anti-HIV activity; however, further optimization will be necessary for microbicidal application.

Vaccine-induced HIV-1 envelope gp120 constant region 1-specific antibodies expose a CD4-inducible epitope and block the interaction of HIV-1 gp140 with galactosylceramide

Mucosal epithelial cell surface galactosylceramide (Galcer) has been postulated to be a receptor for HIV-1 envelope (Env) interactions with mucosal epithelial cells. Disruption of the HIV-1 Env interaction with such alternate receptors could be one strategy to prevent HIV-1 entry through the mucosal barrier. To study antibody modulation of HIV-1 Env-Galcer interactions, we used Galcer-containing liposomes to assess whether natural- and vaccine-induced monoclonal antibodies can block HIV-1 Env binding to Galcer. HIV-1 Env gp140 proteins bound to Galcer liposomes with Kds (dissociation constants) in the nanomolar range. Several HIV-1 ALVAC/AIDSVAX vaccinee-derived monoclonal antibodies (MAbs) specific for the gp120 first constant (C1) region blocked Galcer binding of a transmitted/founder HIV-1 Env gp140. Among the C1-specific MAbs that showed Galcer blocking, the antibody-dependent cellular cytotoxicity-mediating CH38 IgG and its natural IgA isotype were the most potent blocking antibodies. C1-specific IgG monoclonal antibodies that blocked Env binding to Galcer induced upregulation of the gp120 CD4-inducible (CD4i) epitope bound by MAb 17B, demonstrating that a conformational change in gp120 may be required for Galcer blocking. However, the MAb 17B itself did not block Env-Galcer binding, suggesting that the C1 antibody-induced gp120 conformational changes resulted in alteration in a Galcer binding site distant from the CD4i 17B MAb binding site.

IMPORTANCE

Galactosyl ceramide, a glycosphingolipid, has been postulated to be a receptor for the HIV-1 envelope glycoprotein (Env) interaction with mucosal epithelial cells. Here, we have mimicked this interaction by using an artificial membrane containing synthetic Galcer and recombinant HIV-1 Env proteins to identify antibodies that would block the HIV-1 Env-Galcer interaction. Our study revealed that a class of vaccine-induced human antibodies potently blocks HIV-1 Env-Galcer binding by perturbing the HIV-1 Env conformation.

Effect of female genital schistosomiasis and anti-schistosomal treatment on monocytes, CD4+ T-cells and CCR5 expression in the female genital tract

Background

Schistosoma haematobium is a waterborne parasite that may cause female genital schistosomiasis (FGS), characterized by genital mucosal lesions. There is clinical and epidemiological evidence for a relationship between FGS and HIV. We investigated the impact of FGS on HIV target cell density and expression of the HIV co-receptor CCR5 in blood and cervical cytobrush samples. Furthermore we evaluated the effect of anti-schistosomal treatment on these cell populations.

Design

The study followed a case-control design with post treatment follow-up, nested in an on-going field study on FGS.

Methods

Blood and cervical cytobrush samples were collected from FGS negative and positive women for flow cytometry analyses. Urine samples were investigated for schistosome ova by microscopy and polymerase chain reaction (PCR).

Results

FGS was associated with a higher frequency of CD14⁺ cells (monocytes) in blood (11.5% in FGS+ vs. 2.2% in FGS-, p = 0.042). Frequencies of CD4⁺ cells expressing CCR5 were higher in blood samples from FGS+ than from FGS- women (4.7% vs. 1.5%, p = 0.018). The CD14⁺ cell population decreased significantly in both compartments after anti-schistosomal treatment (p = 0.043). Although the frequency of CD4+ cells did not change after treatment, frequencies of CCR5 expression by CD4+ cells decreased significantly in both compartments (from 3.4% to 0.5% in blood, p = 0.036; and from 42.4% to 5.6% in genital samples, p = 0.025).

Conclusions

The results support the hypothesis that FGS may increase the risk of HIV acquisition, not only through damage of the mucosal epithelial barrier, but also by affecting HIV target cell populations, and that anti-schistosomal treatment can modify this.

Interactions between HIV-1 and mucosal cells in the female reproductive tract

Worldwide, the heterosexual route is the prevalent mode of HIV-1 transmission, and the female reproductive tract accounts for approximately 40% of all HIV-1 transmissions. HIV-1 infection in the female reproductive tract involves three major events: entry through the mucosal epithelium, productive infection in subepithelial mononuclear cells, and delivery to lymph nodes to initiate systemic infection. Here, we provide a focused review of the interaction between HIV-1 and mucosal epithelial cells, lymphocytes, macrophages, and dendritic cells in female genital mucosa. Increased understanding of these interactions could illuminate new approaches for interdicting HIV-1 heterosexual transmission.

Virus particle release from glycosphingolipid-enriched microdomains is essential for dendritic cell-mediated capture and transfer of HIV-1 and henipavirus

Human immunodeficiency virus type 1 (HIV-1) exploits dendritic cells (DCs) to promote its transmission to T cells. We recently reported that the capture of HIV-1 by mature dendritic cells (MDCs) is mediated by an interaction between the glycosphingolipid (GSL) GM3 on virus particles and CD169/Siglec-1 on MDCs. Since HIV-1 preferentially buds from GSL-enriched lipid microdomains on the plasma membrane, we hypothesized that the virus assembly and budding site determines the ability of HIV-1 to interact with MDCs. In support of this hypothesis, mutations in the N-terminal basic domain (29/31KE) or deletion of the membrane-targeting domain of the HIV-1 matrix (MA) protein that altered the virus assembly and budding site to CD63(+)/Lamp-1-positive intracellular compartments resulted in lower levels of virion incorporation of GM3 and attenuation of virus capture by MDCs. Furthermore, MDC-mediated capture and transmission of MA mutant viruses to T cells were decreased, suggesting that HIV-1 acquires GSLs via budding from the plasma membrane to access the MDC-dependent trans infection pathway. Interestingly, MDC-mediated capture of Nipah and Hendra virus (recently emerged zoonotic paramyxoviruses) M (matrix) protein-derived virus-like particles that bud from GSL-enriched plasma membrane microdomains was also dependent on interactions between virion-incorporated GSLs and CD169. Moreover, capture and transfer of Nipah virus envelope glycoprotein-pseudotyped lentivirus particles by MDCs were severely attenuated upon depletion of GSLs from virus particles. These results suggest that GSL incorporation into virions is critical for the interaction of diverse enveloped RNA viruses with DCs and that the GSL-CD169 recognition nexus might be a conserved viral mechanism of parasitization of DC functions for systemic virus dissemination.

IMPORTANCE

Dendritic cells (DCs) can capture HIV-1 particles and transfer captured virus particles to T cells without establishing productive infection in DCs, a mechanism of HIV-1 trans infection. We have recently identified CD169-mediated recognition of GM3, a host-derived glycosphingolipid (GSL) incorporated into the virus particle membrane, as the receptor and ligand for the DC-HIV trans infection pathway. In this study, we have identified the matrix (MA) domain of Gag to be the viral determinant that governs incorporation of GM3 into HIV-1 particles, a previously unappreciated function of the HIV-1 MA. In addition, we demonstrate that the GSL-CD169-dependent trans infection pathway is also utilized as a dissemination mechanism by henipaviruses. GSL incorporation in henipaviruses was also dependent on the viral capsid (M) protein-directed assembly and budding from GSL-enriched lipid microdomains. These findings provide evidence of a conserved mechanism of retrovirus and henipavirus parasitization of cell-to-cell recognition pathways for systemic virus dissemination.

Oral and vaginal epithelial cell lines bind and transfer cell-free infectious HIV-1 to permissive cells but are not productively infected

The majority of HIV-1 infections worldwide are acquired via mucosal surfaces. However, unlike the vaginal mucosa, the issue of whether the oral mucosa can act as a portal of entry for HIV-1 infection remains controversial. To address potential differences with regard to the fate of HIV-1 after exposure to oral and vaginal epithelium, we utilized two epithelial cell lines representative of buccal (TR146) and pharyngeal (FaDu) sites of the oral cavity and compared them with a cell line derived from vaginal epithelium (A431) in order to determine (i) HIV-1 receptor gene and protein expression, (ii) whether HIV-1 genome integration into epithelial cells occurs, (iii) whether productive viral infection ensues, and (iv) whether infectious virus can be transferred to permissive cells. Using flow cytometry to measure captured virus by HIV-1 gp120 protein detection and western blot to detect HIV-1 p24 gag protein, we demonstrate that buccal, pharyngeal and vaginal epithelial cells capture CXCR4- and CCR5-utilising virus, probably via non-canonical receptors. Both oral and vaginal epithelial cells are able to transfer infectious virus to permissive cells either directly through cell-cell attachment or via transcytosis of HIV-1 across epithelial cells. However, HIV-1 integration, as measured by real-time PCR and presence of early gene mRNA transcripts and de novo protein production were not detected in either epithelial cell type. Importantly, both oral and vaginal epithelial cells were able to support integration and productive infection if HIV-1 entered via the endocytic pathway driven by VSV-G. Our data demonstrate that under normal conditions productive HIV-1 infection of epithelial cells leading to progeny virion production is unlikely, but that epithelial cells can act as mediators of systemic viral dissemination through attachment and transfer of HIV-1 to permissive cells.

Transcytosis of HIV-1 through vaginal epithelial cells is dependent on trafficking to the endocytic recycling pathway

Background

While it is accepted that viruses can enter epithelial cells by endocytosis, the lack of an established biological mechanism for the trafficking of infectious virions through vaginal epithelial cells and their release from the plasma membrane has contributed to ongoing controversy about whether endocytosis is a mere artifact of some cell culture systems and whether squamous vaginal epithelial cells are even relevant as it pertains to HIV-1 transmission.

Methodology/Principal Findings

In this study, we investigated the intracellular trafficking pathway that HIV-1 exploits to transcytose vaginal epithelial cells. The reduction of endosome tubulation by recycling endosome inhibitors blocked transcytosis of HIV-1 in a cell culture and transwell system. In addition, we demonstrate that although heat-inactivated virus was endocytosed as efficiently as native virus, heat-inactivated virus was trafficked exclusively to the lysosomal pathway for degradation following endocytosis. Lysosomal protease-specific inhibitors blocked the degradation of inactivated virions. Immunofluorescence analysis not only demonstrated that HIV-1 was inside the cells but the different colocalization pattern of native vs. heat inactivated virus with transferrin provided conclusive evidence that HIV-1 uses the recycling pathway to get across vaginal epithelial cells.

Conclusions/Significance

Altogether, our findings demonstrate the precise intracellular trafficking pathway utilized by HIV-1 in epithelial cells, confirms that HIV-1 transcytosis through vaginal epithelial cells is a biological phenomenon and brings to light the differential intracellular trafficking of native vs heat-inactivated HIV-1 which with further exploration could prove to provide valuable insights that could be used in the prevention of transcytosis/transmission of HIV-1 across the mucosal epithelia.

Induction of Potent and Long-Lived Antibody and Cellular Immune Responses in the Genitorectal Mucosa Could be the Critical Determinant of HIV Vaccine Efficacy

The field of HIV prevention has indeed progressed in leaps and bounds, but with major limitations of the current prevention and treatment options, the world remains desperate for an HIV vaccine. Sadly, this continues to be elusive, because more than 30 years since its discovery there is no licensed HIV vaccine. Research aiming to define immunological biomarkers to accurately predict vaccine efficacy have focused mainly on systemic immune responses, and as such, studies defining correlates of protection in the genitorectal mucosa, the primary target site for HIV entry and seeding are sparse. Clearly, difficulties in sampling and analysis of mucosal specimens, as well as their limited size have been a major deterrent in characterizing the type (mucosal antibodies, cytokines, chemokines, or CTL), threshold (magnitude, depth, and breadth) and viral inhibitory capacity of HIV-1-specific immune responses in the genitorectal mucosa, where they are needed to immediately block HIV acquisition and arrest subsequent virus dissemination. Nevertheless, a few studies document the existence of HIV-specific immune responses in the genitorectal mucosa of HIV-infected aviremic and viremic controllers, as well as in highly exposed persistently seronegative (HEPS) individuals with natural resistance to HIV-1. Some of these responses strongly correlate with protection from HIV acquisition and/or disease progression, thus providing significant clues of the ideal components of an efficacious HIV vaccine. In this study, we provide an overview of the key features of protective immune responses found in HEPS, elite and viremic controllers, and discuss how these can be achieved through mucosal immunization. Inevitably, HIV vaccine development research will have to consider strategies that elicit potent antibody and cellular immune responses within the genitorectal mucosa or induction of systemic immune cells with an inherent potential to home and persist at mucosal sites of HIV entry.

Immune correlates of HIV exposure without infection in foreskins of men from Rakai, Uganda

Human immunodeficiency virus (HIV) susceptibility is heterogenous, with some HIV-exposed but seronegative (HESN) individuals remaining uninfected despite repeated exposure. Previous studies in the cervix have shown that reduced HIV susceptibility may be mediated by immune alterations in the genital mucosa. However, immune correlates of HIV exposure without infection have not been investigated in the foreskin. We collected sub-preputial swabs and foreskin tissue from HESN (n=20) and unexposed control (n=57) men undergoing elective circumcision. Blinded investigators assayed swabs for HIV-neutralizing IgA, innate antimicrobial peptides, and cytokine levels. Functional T-cell subsets from foreskin tissue were assessed by flow cytometry. HESN foreskins had elevated α-defensins (3,027 vs. 1,795 pg ml(-1), P=0.011) and HIV-neutralizing IgA (50.0 vs. 13.5% of men, P=0.019). Foreskin tissue from HESN men contained a higher density of CD3 T cells (151.9 vs. 69.9 cells mm(-2), P=0.018), but a lower proportion of these was Th17 cells (6.12 vs. 8.04% of CD4 T cells, P=0.007), and fewer produced tumor necrosis factor α (TNFα) (34.3 vs. 41.8% of CD4 T cells, P=0.037; 36.9 vs. 45.7% of CD8 T cells, P=0.004). A decrease in the relative abundance of susceptible CD4 T cells and local TNFα production, in combination with HIV-neutralizing IgA and α-defensins, may represent a protective immune milieu at a site of HIV exposure.

Role of Fc-mediated antibody function in protective immunity against HIV-1

The importance of Fc-mediated effector function in protective immunity to HIV-1 (hereafter referred to simply as HIV) is becoming increasingly apparent. A large of number of studies in natural infection cohorts, spanning the last 26 years, have associated Fc-mediated effector function, particularly antibody-dependent cellular cytotoxicity, with a favourable clinical course. These studies strongly suggest a role for Fc-mediated effector function in the post-infection control of viraemia. More recently, studies in both humans and non-human primates (NHPs) also implicate Fc-mediated effector function in blocking HIV acquisition. Accordingly, this review will discuss the results supporting a role of Fc-mediated effector function in both blocking acquisition and post-infection control of viraemia. Parallel studies in NHPs and humans will be compared for common themes. Context for this discussion will be provided by summarizing the temporal emergence of key host and virological events over the course of an untreated HIV infection framing where, when and how Fc-mediated effector function might be protective. A hypothesis that Fc-mediated effector function protects primarily in the early stages of both acquisition and post-infection control of viraemia will be developed.

SHIV susceptibility changes during the menstrual cycle of pigtail macaques

BACKGROUND

Hormonal changes during menstrual cycling may affect susceptibility to HIV.

METHODS

We determined the simian human immunodeficiency virus (SHIV) acquisition time point in 43 cycling pigtail macaques infected by repeated vaginal virus exposures initiated randomly in the cycle.

RESULTS

SHIV infection was first detected in the follicular phase in 38 macaques (88%), and in the luteal phase in five macaques (12%), indicating a statistically significant timing difference. Assuming a 7-day eclipse phase, most infections occurred during or following a high-progesterone period associated with menstruation, vaginal epithelium thinning, and suppressed mucosal immunity.

CONCLUSIONS

This raises questions whether other high-progesterone conditions (pregnancy, hormonal contraception) similarly affect HIV risk.

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

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

Dual role of commensal bacteria in viral infections

With our abilities to culture and sequence the commensal bacteria that dwell on and within a host, we can now study the host in its entirety, as a supraorganism that must be navigated by the pathogen invader. At present, the majority of studies have focused on the interaction between the host's microbiota and bacterial pathogens. This is not unwarranted, given that bacterial pathogens must compete with commensal organisms for the limited territory afforded by the host. However, viral pathogens also enter the host through surfaces coated with microbial life and encounter an immune system shaped by this symbiotic community. Therefore, we believe that the microbiota cannot be ignored when examining the interplay between the host and viral pathogens. Here, we review work that details mechanisms by which the microbiota either promotes or inhibits viral replication and virally induced pathogenesis. The impact of the microbitota on viral infection promises to be a new and exciting avenue of investigation, which will ultimately lead to better treatments and preventions of virally induced disease.

HIV-1 infection: the role of the gastrointestinal tract

The intestinal mucosa has an important role as portal of entry during mother-to-child transmission of HIV-1 and during sexual transmission. Tissue morphology and integrity, as well as distribution of relevant cell types within the mucosa, spanning from the oropharynx to the rectum, can greatly influence viral infection, replication, presentation, and persistence. The relative contribution to transmission by cell-associated or cell-free virus is still not defined for the different routes of transmission. Although the main target cells for HIV-1 replication are the CD4+ T lymphocytes, which are rapidly depleted both in the periphery and in the mucosal tissues, dendritic cells, Langerhans' cells, and macrophages are players in each of these processes. The predominant cells involved may differ according to the tract of the gut and the route of transmission. The microenvironment of the intestinal mucosa, including mucus, antibodies, or chemo-cytokines, can as well influence infection and replication of the virus: their role is still under investigation. The understanding of these processes may help in developing efficient prevention strategies.

The rise and fall of HIV in high-prevalence countries: a challenge for mathematical modeling

Several countries with generalized, high-prevalence HIV epidemics, mostly in sub-Saharan Africa, have experienced rapid declines in transmission. These HIV epidemics, often with rapid onsets, have generally been attributed to a combination of factors related to high-risk sexual behavior. The subsequent declines in these countries began prior to widespread therapy or implementation of any other major biomedical prevention. This change has been construed as evidence of behavior change, often on the basis of mathematical models, but direct evidence for behavior changes that would explain these declines is limited. Here, we look at the structure of current models and argue that the common “fixed risk per sexual contact" assumption favors the conclusion of substantial behavior changes. We argue that this assumption ignores reported non-linearities between exposure and risk. Taking this into account, we propose that some of the decline in HIV transmission may be part of the natural dynamics of the epidemic, and that several factors that have traditionally been ignored by modelers for lack of precise quantitative estimates may well hold the key to understanding epidemiologic trends.

Influence of common mucosal co-factors on HIV infection in the female genital tract

Women constitute almost half of HIV-infected population globally, and the female genital tract (FGT) accounts for approximately 40% of all new HIV infections worldwide. The FGT is composed of upper and lower parts, distinct in their morphological and functional characteristics. Co-factors in the genital microenvironment, such as presence of hormones, semen, and other sexually transmitted infections, can facilitate or deter HIV infection and play a critical role in determining susceptibility to HIV. In this review, we examine some of these co-factors and their potential influence. Presence of physical and chemical barriers such as epithelial tight junctions, mucus, and anti-microbial peptides can actively block and inhibit viral replication, presenting a significant deterrent to HIV. Upon exposure, HIV and other pathogens first encounter the genital epithelium: cells that express a wide repertoire of pattern recognition receptors that can recognize and directly initiate innate immune responses. These and other interactions in the genital tract can lead to direct and indirect inflammation and enhance the number of local target cells, immune activation, and microbial translocation, all of which promote HIV infection and replication. Better understanding of the dynamics of HIV transmission in the female genital tract would be invaluable for improving the design of prophylactic strategies against HIV.

New directions for HIV vaccine development from animal models

PURPOSE OF REVIEW

The development of a preventive HIV vaccine remains an unresolved challenge. Animal models that can predict the results of HIV vaccine efficacy trials and identify the immune mechanisms responsible for vaccine protection would be most useful for HIV vaccine development. The purpose of the current review is to critique recent developments in the use of animal models of HIV infection in preclinical studies of AIDS vaccines and to describe how the use of improved animal models can inform the development of an HIV vaccine.

RECENT FINDINGS

The results of preclinical experiments with candidate HIV vaccines can vary with the SIV challenge virus used. It is now known that there is considerable variability in the neutralization sensitivity and that the level of viral sequence diversity within the challenge stocks varies. This has allowed more realistic preclinical vaccine studies with heterologous vaccine antigens and challenge viruses. Further, the dose of challenge virus and the route of virus challenge can modify the efficacy of candidate vaccines in preclinical studies.

SUMMARY

Recent experiments demonstrate that nonhuman primate models of AIDS can reproduce the complex biology of HIV transmission, recapitulate the results of HIV vaccine efficacy trials in humans and be used to identify correlates of protection.

Pharmacokinetic and safety analyses of tenofovir and tenofovir-emtricitabine vaginal tablets in pigtailed macaques

Vaginal rapidly disintegrating tablets (RDTs) containing tenofovir (TFV) or TFV and emtricitabine (FTC) were evaluated for safety and pharmacokinetics in pigtailed macaques. Two separate animal groups (n = 4) received TFV (10 mg) or TFV-FTC (10 mg each) RDTs, administered near the cervix. A third group (n = 4) received 1 ml TFV gel. Blood plasma, vaginal tissue biopsy specimens, and vaginal fluids were collected before and after product application at 0, 0.5, 1, 4, and 24 h. A disintegration time of <30 min following vaginal application of the RDTs was noted, with negligible effects on local inflammatory cytokines, vaginal pH, and microflora. TFV pharmacokinetics were generally similar for both RDTs and gel, with peak median concentrations in vaginal tissues and vaginal secretions being on the order of 10(4) to 10(5) ng/g (147 to 571 μM) and 10(6) ng/g (12 to 34 mM), respectively, at 1 to 4 h postdose. At 24 h, however, TFV vaginal tissue levels were more sustained after RDT dosing, with median TFV concentrations being approximately 1 log higher than those with gel dosing. FTC pharmacokinetics after combination RDT dosing were similar to those of TFV, with peak median vaginal tissue and fluid levels being on the order of 10(4) ng/g (374 μM) and 10(6) ng/g (32 mM), respectively, at 1 h postdose with levels in fluid remaining high at 24 h. RDTs are a promising alternative vaginal dosage form, delivering TFV and/or FTC at levels that would be considered inhibitory to simian-human immunodeficiency virus in the macaque vaginal microenvironment over a 24-h period.

Vaginal microbicides and their delivery platforms

INTRODUCTION

HIV type 1 infection, despite having fallen by one-third over the past decade, remains a global health concern affecting millions of individuals worldwide. A focal point in contemporary research aimed at global HIV prevention has been the development of safe and efficacious coitally dependent and coitally independent anti-HIV microbicides to curb heterosexual HIV transmission. Despite extensive research efforts to develop novel vaginal antiretroviral (ARV) formulations and intravaginal ring delivery systems, the clinical advancement of microbicides with improved safety, efficacy and tolerability has significantly lagged behind.

AREAS COVERED

This review focuses on the current status of both coitally dependent and coitally independent delivery platforms designed to increase user acceptability and clinical effectiveness of anti-HIV microbicides. The clinical failure of several vaginal microbicide candidates has propelled the field to mechanism-based ARV candidates that act more specifically on viral receptors, viral enzymes and host proteins. Consequently, improved vaginal microbicide delivery strategies that achieve uniform drug distribution with enhanced solubility, sustained drug release, improved product adherence with reduced dosing frequency and lack of effect on the vaginal mucosa and microbiota are being sought.

EXPERT OPINION

Clinical success with vaginal microbicides may best be achieved through the combined effects of ARV compounds that exhibit different mechanisms of action with potent activity against multidrug-resistant HIV and efficacious delivery systems.

Vaginal microbiota and its role in HIV transmission and infection

The urogenital tract appears to be the only niche of the human body that shows clear differences in microbiota between men and women. The female reproductive tract has special features in terms of immunological organization, an epithelial barrier, microbiota, and influence by sex hormones such as estrogen. While the upper genital tract is regarded as free of microorganisms, the vagina is colonized by bacteria dominated by Lactobacillus species, although their numbers vary considerably during life. Bacterial vaginosis is a common pathology characterized by dysbiosis, which increases the susceptibility for HIV infection and transmission. On the other hand, HIV infections are often characterized by a disturbed vaginal microbiota. The endogenous vaginal microbiota may protect against HIV by direct production of antiviral compounds, through blocking of adhesion and transmission by ligands such as lectins, and/or by stimulation of immune responses. The potential role of probiotics in the prevention of HIV infections and associated symptoms, by introducing them to the vaginal and gastrointestinal tract (GIT), is also discussed. Of note, the GIT is a site of considerable HIV replication and CD4(+) T-cell destruction, resulting in both local and systemic inflammation. Finally, genetically engineered lactobacilli show promise as new microbicidal agents against HIV.

Role of inflammation in HIV-1 disease progression and prognosis

Inflammation and immune activation have been thrust to center stage in the understanding of HIV-1 disease pathogenesis and progression. Early work demonstrated that heightened levels of immune activation correlated with the extent of CD4 + T cell death in lymphoid tissue; however, this concept was not incorporated into the general view of disease pathogenesis. Since these early studies, the extension of life for patients on combination antiretroviral therapies (cART) has heralded a new era of non-AIDS-related diseases and incomplete restoration of immune function. The common link appears to be ongoing inflammation and immune activation. Thus, despite good control of viral loads, persons living with HIV (PLWH) remain at increased risk of inflammatory-associated complications such as cardiovascular disease and certain cancers. HIV-specific mechanisms as well as non-specific generalized responses to infection contribute to ongoing activation of the immune system. An early loss of gastrointestinal (GI) tract mucosal integrity, the pro-inflammatory cytokine milieu, co-infections and marked destruction of lymph node architecture are all factors contributing to the ongoing activation of the immune system as well as impaired immune recovery. It is becoming increasingly evident that the CD4 count and viral load do not provide a complete picture of the underlying state of the immune system. Heightened levels of inflammatory markers have been shown to predict increased mortality and other adverse events. Therefore, it will be important to incorporate these markers into management algorithms as soon as possible. This is particularly relevant in resource-poor countries where difficulties in cART roll-out and access are still encountered and, therefore, a mechanism for prioritizing individuals for therapy would be of value. This review will focus on the closely inter-related concepts of immune activation and inflammation. Both are broad concepts involving the interaction of various key players in the immune system. Importantly, immune activation promotes inflammation and thrombosis and similarly, inflammation and thrombosis induce immune activation. These concepts are thus intricately linked. Studies highlighting the potentially harmful effects of ongoing inflammation/immune activation are reviewed and the contributions of the GI tract "damage" and other co-infections such as CMV are explored. The complications resulting from persistent immune activation include enhanced CD4 + T cell death, lymphoid tissue destruction, and various pathologies related to chronic inflammation. Ultimately, we envision that the long-term management of the disease will incorporate both the identification and the amelioration of the potentially harmful effects of ongoing immune activation and inflammation.

Biodistribution and pharmacokinetics of dapivirine-loaded nanoparticles after vaginal delivery in mice

PURPOSE

To assess the potential of polymeric nanoparticles (NPs) to affect the genital distribution and local and systemic pharmacokinetics (PK) of the anti-HIV microbicide drug candidate dapivirine after vaginal delivery.

METHODS

Dapivirine-loaded, poly(ethylene oxide)-coated poly(epsilon-caprolactone) (PEO-PCL) NPs were prepared by a nanoprecipitation method. Genital distribution of NPs and their ability to modify the PK of dapivirine up to 24 h was assessed after vaginal instillation in a female mouse model. Also, the safety of NPs upon daily administration for 14 days was assessed by histological analysis and chemokine/cytokine content in vaginal lavages.

RESULTS

PEO-PCL NPs (180-200 nm) were rapidly eliminated after administration but able to distribute throughout the vagina and lower uterus, and capable of tackling mucus and penetrate the epithelial lining. Nanocarriers modified the PK of dapivirine, with higher drug levels being recovered from vaginal lavages and vaginal/lower uterine tissues as compared to a drug suspension. Systemic drug exposure was reduced when NPs were used. Also, NPs were shown safe upon administration for 14 days.

CONCLUSIONS

Dapivirine-loaded PEO-PCL NPs were able to provide likely favorable genital drug levels, thus attesting the potential value of using this vaginal drug delivery nanosystem in the context of HIV prophylaxis.

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

Background

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

Methods and Findings

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

Conclusions

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

High transcript levels of vitamin D receptor are correlated with higher mRNA expression of human beta defensins and IL-10 in mucosa of HIV-1-exposed seronegative individuals

Vitamin D (VitD) is an endogenous immunomodulator that could protect from HIV-1 infection reducing immune activation and inducing the expression of anti-HIV-1 peptides. To establish a correlation between VitD and natural resistance to HIV-1 infection, a case-control study using blood and mucosa samples of 58 HIV-1-exposed but seronegative (HESN) individuals, 43 HIV-1 seropositives (SPs) and 59 non-exposed healthy controls (HCs) was carried out. The VitD concentration in plasma was determined by ELISA, and mRNA relative units (RU) of VDR, IL-10, TGF-β, TNF-α and IL-1β in peripheral blood mononuclear cells (PBMCs), oral and genital mucosa was quantified by qRT-PCR. mRNA levels of human beta-defensin (HBD) -2 and -3 were previously reported and used for correlations. Significantly higher levels of VitD were found in plasma as well as higher mRNA RU of VDR in PBMCs, and in genital mucosa from HESN compared to HCs. In addition, higher mRNA RU of TNF-α, IL-1β and IL-10, and lower mRNA RU of TGF-β were found in PBMC from HESNs compared to HCs. We also observed higher IL-10 mRNA RU in genital mucosa of HESNs compared to HCs, and the mRNA levels of TNF-α in oral and genital mucosa of SPs were higher compared to HESNs. Furthermore, positive correlations between VDR and IL-10 mRNA RU in PBMCs and genital mucosa of HESNs were found. Finally, HBD-2 and HBD-3 mRNA RU were positively correlated with VDR mRNA expression in oral mucosa from HESNs. These results suggest that high levels of VitD and its receptor are associated with natural resistance to HIV-1 infection. Up-regulation of the anti-inflammatory IL-10, and the induction of anti-HIV-1 defensins in mucosa might be part of the mechanisms involved in this association. However, further studies are required to define causal associations.

Human immunodeficiency virus and heparan sulfate: from attachment to entry inhibition

By targeting cells that provide protection against infection, HIV-1 causes acquired immunodeficiency syndrome. Infection starts when gp120, the viral envelope glycoprotein, binds to CD4 and to a chemokine receptor usually CCR5 or CXCR4. As many microorganisms, HIV-1 also interacts with heparan sulfate (HS), a complex group of cell surface associated anionic polysaccharides. It has been thought that this binding, occurring at a step prior to CD4 recognition, increases infectivity by pre-concentrating the virion particles at the cell surface. Early work, dating from before the identification of CCR5 and CXCR4, showed that a variety of HS mimetics bind to the gp120 V3 loop through electrostatic interactions, compete with cell surface associated HS to bind the virus and consequently, neutralize the infectivity of a number of T-cell line-adapted HIV-1 strains. However, progress made to better understand HIV-1 attachment and entry, coupled with the recent identification of additional gp120 regions mediating HS recognition, have considerably modified this view. Firstly, the V3 loop from CXCR4-using viruses is much more positively charged compared to those using CCR5. HS inhibition of cell attachment is thus restricted to CXCR4-using viruses (such as T-cell line-adapted HIV-1). Secondly, studies aiming at characterizing the gp120/HS complex revealed that HS binding was far more complex than previously thought: in addition to the V3 loop of CXCR4 tropic gp120, HS interacts with several other cryptic areas of the protein, which can be induced upon CD4 binding, and are conserved amongst CCR5 and CXCR4 viruses. In view of these data, this review will detail the present knowledge on HS binding to HIV-1, with regards to attachment and entry processes. It will discuss the perspective of targeting the gp120 co-receptor binding site with HS mimetic compounds, a strategy that recently gave rise to entry inhibitors that work in the low nanomolar range, independently of co-receptor usage.

An HIV-1 replication pathway utilizing reverse transcription products that fail to integrate

Integration is a central event in the replication of retroviruses, yet ≥ 90% of HIV-1 reverse transcripts fail to integrate, resulting in accumulation of unintegrated viral DNA in cells. However, understanding what role, if any, unintegrated viral DNA plays in the natural history of HIV-1 has remained elusive. Unintegrated HIV-1 DNA is reported to possess a limited capacity for gene expression restricted to early gene products and is considered a replicative dead end. Although the majority of peripheral blood CD4(+) T cells are refractory to infection, nonactivated CD4 T cells present in lymphoid and mucosal tissues are major targets for infection. Treatment with cytokine interleukin-2 (IL-2), IL-4, IL-7, or IL-15 renders CD4(+) T cells permissive to HIV-1 infection in the absence of cell activation and proliferation and provides a useful model for infection of resting CD4(+) T cells. We found that infection of cytokine-treated resting CD4(+) T cells in the presence of raltegravir or with integrase active-site mutant HIV-1 yielded de novo virus production following subsequent T cell activation. Infection with integration-competent HIV-1 naturally generated a population of cells generating virus from unintegrated DNA. Latent infection persisted for several weeks and could be activated to virus production by a combination of a histone deacetylase inhibitor and a protein kinase C activator or by T cell activation. HIV-1 Vpr was essential for unintegrated HIV-1 gene expression and de novo virus production in this system. Bypassing integration by this mechanism may allow the preservation of genetic information that otherwise would be lost.

HIV-1 gp120 induces TLR2- and TLR4-mediated innate immune activation in human female genital epithelium

Although women constitute half of all HIV-1-infected people worldwide (UNAIDS World AIDS Day Report, 2011), the earliest events in the female reproductive tract (FRT) during heterosexual HIV-1 transmission are poorly understood. Recently, we demonstrated that HIV-1 could directly impair the mucosal epithelial barrier in the FRT. This suggested that the HIV-1 envelope glycoprotein gp120 was being recognized by a membrane receptor on genital epithelial cells, leading to innate immune activation. In this study, we report that pattern-recognition receptors TLR2 and -4 bind to HIV-1 gp120 and trigger proinflammatory cytokine production via activation of NF-κB. The gp120-TLR interaction also required the presence of heparan sulfate (HS). Bead-binding assays showed that gp120 can bind to HS, TLR2, and TLR4, and studies in transfected HEK293 cells demonstrated that HS and TLR2 and -4 were necessary to mediate downstream signaling. Exposure to seminal plasma from HIV-1-infected and uninfected men with gp120 added to it induced a significant proinflammatory cytokine response from genital epithelial cells and disruption of tight junctions, indicating a role for gp120 in mucosal barrier disruption during HIV-1 heterosexual transmission. These studies provide, for the first time to our knowledge, a possible mechanism by which HIV-1 gp120 could directly initiate innate immune activation in the FRT during heterosexual transmission.

Comprehensive assessment of HIV target cells in the distal human gut suggests increasing HIV susceptibility toward the anus

BACKGROUND

Prevention of rectal HIV transmission is a high-priority goal for vaccines and topical microbicides because a large fraction of HIV transmissions occurs rectally. Yet, little is known about the specific target-cell milieu in the human rectum other than inferences made from the colon.

METHODS

We conducted a comprehensive comparative in situ fluorescence study of HIV target cells (CCR5-expressing T cells, macrophages, and putative dendritic cells) at 4 and 30 cm proximal of the anal canal in 29 healthy individuals, using computerized analysis of digitized combination stains.

RESULTS

Most strikingly, we find that more than 3 times as many CD68 macrophages express the HIV coreceptor CCR5 in the rectum than in the colon (P = 0.0001), and as such rectal macrophages seem biologically closer to the HIV-susceptible CCR5 phenotype in the vagina than the mostly HIV-resistant CCR5 phenotype in the colon. Putative CD209 dendritic cells are generally enriched in the colon compared with the rectum (P = 0.0004), though their CCR5 expression levels are similar in both compartments. CD3 T-cell densities and CCR5 expression levels are comparable in the colon and rectum.

CONCLUSIONS

Our study establishes the target-cell environment for HIV infection in the human distal gut and demonstrates in general terms that the colon and rectum are immunologically distinct anatomical compartments. Greater expression of CCR5 on rectal macrophages suggests that the most distal sections of the gut may be especially vulnerable to HIV infection. Our findings also emphasize that caution should be exercised when extrapolating data obtained from colon tissues to the rectum.

Novel intravaginal nanomedicine for the targeted delivery of saquinavir to CD4+ immune cells

The goal of this study was to develop and characterize an intravaginal nanomedicine for the active targeted delivery of saquinavir (SQV) to CD4(+) immune cells as a potential strategy to prevent or reduce HIV infection. The nanomedicine was formulated into a vaginal gel to provide ease in self-administration and to enhance retention within the vaginal tract. SQV-encapsulated nanoparticles (SQV-NPs) were prepared from poly(lactic-co-glycolic acid) (PLGA) and conjugated to antihuman anti-CD4 antibody. Antibody-conjugated SQV-NPs (Ab-SQV-NPs) had an encapsulation efficiency (EE%) of 74.4% + 3.7% and an antibody conjugation efficiency (ACE%) of 80.95% + 1.10%. Over 50% of total loaded SQV was released from NPs over 3 days. NPs were rapidly taken up by Sup-T1 cells, with more than a twofold increase in the intracellular levels of SQV when delivered by Ab-SQV-NPs in comparison to controls 1 hour post-treatment. No cytotoxicity was observed when vaginal epithelial cells were treated for 24 hours with drug-free Ab-NPs (1,000 μg/mL), 1% HEC placebo gel (200 mg/mL), or 1% HEC gel loaded with drug-free Ab-NPs (5 mg NPs/g gel, 200 mg/mL of gel mixture). Overall, we described an intravaginal nanomedicine that is nontoxic and can specifically deliver SQV into CD4(+) immune cells. This platform may demonstrate potential utility in its application as postexposure prophylaxis for the treatment or reduction of HIV infection, but further studies are required.

Uptake of tenofovir and emtricitabine into non-monocytic female genital tract cells with and without hormonal contraceptives

Background

Pre-exposure prophylaxis is becoming a strategic component used to control the human immunodeficiency virus (HIV-1) epidemic. The goal of this study was to characterize intracellular uptake of tenofovir and emtricitabine using five surrogate cell lines of the female genital tract and determine whether exogenous hormones influence their uptake.

Methods

Surrogate cell lines, ie, THP-1 (representing macrophages), BC-3 (CD8+), Ect1/E6E7 (squamous epithelial), HeLa (CD4+), and TF-1 (dendritic), were incubated for one hour with tenofovir and emtricitabine to assess uptake. In separate experiments, ethinyl estradiol (EE) and etonogestrel (ET) individually and together (EE/ET) were added prior to, simultaneously, and after incubation. Intracellular phosphorylated tenofovir and emtricitabine were quantified using validated tandem mass spectrometry methods.

Results

HeLa and Ect1/E6E7 cells showed significantly increased uptake relative to THP-1 controls for both antiretrovirals. Individually, ethinyl estradiol and etonogestrel significantly altered antiretroviral uptake across all cell lines, except Ect1/E6E7 for tenofovir and HeLa for emtricitabine. Cellular uptake of tenofovir and emtricitabine in BC-3 and TF-1 cells were significantly lower when dosed one hour prior to EE/ET administration compared with each antiretroviral administered in the absence of EE/ET (tenofovir, 80 versus 470 fmol/10⁶ for BC-3 and 77 versus 506 fmol/10⁶ cells for TF-1; emtricitabine, 36 versus 12 fmol/10⁶ for BC-3 and 75 versus 5 fmol/10⁶ cells for TF-1; P < 0.01 for each).

Conclusion

These data suggest that intracellular uptake of tenofovir and emtricitabine within the female genital tract varies by cell type and in the presence of hormonal contraceptives. The potential clinical implications of these findings should be further evaluated in vivo.

HIV-1 autologous antibody neutralization associates with mother to child transmission

The HIV-1 characteristics associated with mother to child transmission (MTCT) are still poorly understood and if known would indicate where intervention strategies should be targeted. In contrast to horizontally infected individuals, exposed infants possess inherited antibodies (Abs) from their mother with the potential to protect against infection. We investigated the HIV-1 gp160 envelope proteins from seven transmitting mothers (TM) whose children were infected either during gestation or soon after delivery and from four non-transmitting mothers (NTM) with similar viral loads and CD4 counts. Using pseudo-typed viruses we tested gp160 envelope glycoproteins for TZM-bl infectivity, CD4 and CCR5 interactions, DC-SIGN capture and transfer and neutralization with an array of common neutralizing Abs (NAbs) (2F5, 2G12, 4E10 and b12) as well as mother and infant plasma. We found no viral correlates associated with HIV-1 MTCT nor did we find differences in neutralization with the panel of NAbs. We did, however, find that TM possessed significantly higher plasma neutralization capacities than NTM (P = 0.002). Furthermore, we found that in utero (IU) TM had a higher neutralization capacity than mothers transmitting either peri-partum (PP) or via breastfeeding (BF) (P = 0.002). Plasma from children infected IU neutralized viruses carrying autologous gp160 viral envelopes as well as those from their corresponding mothers whilst plasma from children infected PP and/or BF demonstrated poor neutralizing capacity. Our results demonstrate heightened autologous NAb responses against gp120/gp41 can associate with a greater risk of HIV-1 MTCT and more specifically in those infants infected IU. Although the number of HIV-1 transmitting pairs is low our results indicate that autologous NAb responses in mothers and infants do not protect against MTCT and may in fact be detrimental when considering IU HIV-1 transmissions.

Use of human mucosal tissue to study HIV-1 pathogenesis and evaluate HIV-1 prevention modalities

The use of human mucosal tissue models is an important tool advancing our understanding of the specific mechanisms of sexual HIV transmission. Despite 30 years of study, major gaps remain, including how HIV-1 transverses the epithelium and the identity of the early immune targets (gate keepers). Because defining HIV-1 transmission in vivo is difficult, mucosal tissue is being used ex vivo to identify key steps in HIV-1 entry and early dissemination. Elucidating early events of HIV-1 infection will help us develop more potent and specific HIV-1 preventatives such as microbicides and vaccines. Mucosal tissue has been incorporated into testing regimens for antiretroviral drugs and monoclonal antibodies. The use of mucosal tissue recapitulates the epithelium and immune cells that would be exposed in vivo to virus and drug. This review will discuss the use of mucosal tissue to better understand HIV-1 pathogenesis and prevention modalities.

Preformulation studies of EFdA, a novel nucleoside reverse transcriptase inhibitor for HIV prevention

4'-Ethynyl-2-fluoro-2'-deoxyadenosine (EFdA) is a novel nucleoside analog of great interest because of its superior activity against wild-type and multidrug-resistant HIV-1 strains, and favorable safety profiles in vitro and in vivo. The aim of this work was to provide preformulation information of EFdA important for delivery system development. A simple, accurate and specific reverse-phase high performance liquid chromatographic (RP-HPLC) method with UV detection was developed for quantification of EFdA. In addition, physicochemical characterizations including pH solubility profile, octanol/water partition coefficient (Log Po/w), DSC analysis, field emission scanning electron microscopy, and stability studies under various conditions were conducted. EFdA existed in planar or flake shape, with a melting point of ∼130 °C, and had a pH dependent solubility. The log Po/w value of EFdA was -1.19. The compound was stable upon exposure to pH levels from 3 to 9 and showed good stability at elevated temperature (65 °C). In vitro cytotoxicity assessments were performed in two different epithelial cell lines. In cell-based studies, the EFdA selectivity index (50% cytotoxic concentration [CC50] values/50% effective concentration [EC50]) was found to be greater than 1 × 10(3). Permeability studies using cell- and tissue-based models showed that EFdA had an apparent permeability coefficient (Papp) <1 × 10(-6)cm/s and that the paracelluar pathway was the dominant transport route for EFdA. Overall, EFdA possesses favorable characteristics for further formulation development.

Hormonal contraception and HIV acquisition - what is the evidence? What are the policy and operational implications?

OBJECTIVES

Family planning (FP) is essential in achieving the United Nations Millennium Development Goals. We critically review the evidence on HIV acquisition among women using hormonal contraception, and discuss the policy and operational implications.

METHODS

Longitudinal studies conducted in sub-Saharan Africa published between 2008 and 2012, as well as key policy documents related to contraception and HIV were reviewed.

RESULTS

Findings on hormonal contraception and HIV acquisition conducted in sub- Saharan Africa are inconsistent. While in the large scale studies no statistically significant association between oral contraceptive use and HIV acquisition was found, results for injectables were mixed. Potential biases, such as those resulting from self-selection, related to the observational study design and main confounders such as condom use, sexual activity and contraceptive use are discussed.

CONCLUSIONS

It is currently not possible to conclude whether the use of hormonal contraceptives is associated with a greater risk of acquiring HIV, or not. The use of male or female condoms for dual protection should be promoted in FP programmes. While there is need for further research on a broader range of contraceptive methods and HIV transmission, studies documenting acceptability of currently less used/more recent contraceptive methods are also warranted.

The adult penile urethra is a novel entry site for HIV-1 that preferentially targets resident urethral macrophages

The penile urethra is routinely targeted by sexually transmitted bacterial and viral pathogens, and also represents a probable site for HIV type-1 (HIV-1) entry. Yet, the mechanisms of urethral HIV-1 transmission are unknown. To describe the initial steps of penile HIV-1 entry, we obtained whole penile tissues from individuals undergoing elective gender reassignment and developed ex vivo polarized explants of different penile epithelia, as well as in vitro immunocompetent reconstructed urethra. In penile explants, 1 h exposure to cell-associated HIV-1 results in higher HIV-1 entry into the urethra, whereas the fossa navicularis and glans are relatively resistant to HIV-1. CCR5+/CD4+ urethral macrophages are the initial cells infected by HIV-1, which exit the epithelial compartment following inoculation with cell-associated HIV-1 that induces decreased CCL2/MCP-1 production. Urethral T cells are mostly CD8+ or naive CD4+, and not infected by HIV-1 on its early entry. In urethral reconstructions, efficient translocation of cell-associated HIV-1 depends on viral tropism (R5>X4) and can be decreased by gp41-specific IgAs. Cell-free HIV-1 is inefficient at urethral penetration. Our results identify the male urethra as a novel entry site for HIV-1 that targets resident urethral macrophages. These results might explain the incomplete prophylactic efficacy of male circumcision in reducing HIV-1 transmission.

Plasma membrane signaling in HIV-1 infection

Plasma membrane is a multifunctional structure that acts as the initial barrier against infection by intracellular pathogens. The productive HIV-1 infection depends upon the initial interaction of virus and host plasma membrane. Immune cells such as CD4+ T cells and macrophages contain essential cell surface receptors and molecules such as CD4, CXCR4, CCR5 and lipid raft components that facilitate HIV-1 entry. From plasma membrane HIV-1 activates signaling pathways that prepare the grounds for viral replication. Through viral proteins HIV-1 hijacks host plasma membrane receptors such as Fas, TNFRs and DR4/DR5, which results in immune evasion and apoptosis both in infected and uninfected bystander cells. These events are hallmark in HIV-1 pathogenesis that leads towards AIDS. The interplay between HIV-1 and plasma membrane signaling has much to offer in terms of viral fitness and pathogenicity, and a better understanding of this interplay may lead to development of new therapeutic approaches. This article is part of a Special Issue entitled: Viral Membrane Proteins - Channels for Cellular Networking.

Antibody and antiretroviral preexposure prophylaxis prevent cervicovaginal HIV-1 infection in a transgenic mouse model

The development of an effective vaccine preventing HIV-1 infection remains elusive. Thus, the development of novel approaches capable of preventing HIV-1 transmission is of paramount importance. However, this is partly hindered by the lack of an easily accessible small-animal model to rapidly measure viral entry. Here, we report the generation of a human CD4- and human CCR5-expressing transgenic luciferase reporter mouse that facilitates measurement of peritoneal and genitomucosal HIV-1 pseudovirus entry in vivo. We show that antibodies and antiretrovirals mediate preexposure protection in this mouse model and that the serum antibody concentration required for protection from cervicovaginal infection is comparable to that required to protect macaques. Our results suggest that this system represents a model for the preclinical evaluation of prophylactic or vaccine candidates. It further supports the idea that broadly neutralizing antibodies should be evaluated for use as preexposure prophylaxis in clinical trials.

The lantibiotic peptide labyrinthopeptin A1 demonstrates broad anti-HIV and anti-HSV activity with potential for microbicidal applications

Lantibiotics are peptides, produced by bacteria, that contain the noncanonical amino acid lanthionine and many of them exhibit antibacterial activities. The labyrinthopeptin A1 (LabyA1) is a prototype peptide of a novel class of carbacyclic lantibiotics. Here, we extensively evaluated its broad-spectrum activity against HIV and HSV in vitro, studied its mechanism of action and evaluated potential microbicidal applications. LabyA1 exhibited a consistent and broad anti-HIV activity (EC₅₀s: 0.70–3.3 µM) and anti-HSV activity (EC₅₀s: 0.29–2.8 µM) in cell cultures. LabyA1 also inhibited viral cell-cell transmission between persistently HIV-infected T cells and uninfected CD4⁺ T cells (EC₅₀∶2.5 µM) and inhibited the transmission of HIV captured by DC-SIGN⁺-cells to uninfected CD4⁺ T cells (EC₅₀∶4.1 µM). Time-of-drug addition studies revealed that LabyA1 acts as an entry inhibitor against HIV and HSV. Cellular and virus binding studies combined with SPR/FLIPR technology showed that LabyA1 interacted with the HIV envelope protein gp120, but not with the HIV cellular receptors. LabyA1 also demonstrated additive to synergistic effects in its anti-HIV-1 and anti-HSV-2 activity with anti(retro)viral drugs in dual combinations such as tenofovir, acyclovir, saquinavir, raltegravir and enfuvirtide. LabyA1 can be considered as a novel lead peptide as it had profound antiviral activity against HIV and HSV. Pre-treatment of PBMCs with LabyA1 neither increased the expression of the activation markers CD69 and CD25, nor enhanced HIV replication, nor significantly induced various inflammatory cytokines/chemokines. LabyA1 also did not affect the growth of vaginal Lactobacilli populations. Based on the lack of toxicity on the vaginal Lactobacillus strains and its synergistic/additive profile in combination with clinically approved anti(retro)virals, it deserves further attention as a potential microbicide candidate in the prevention of sexual transmitted diseases.