Movements of HIV-virions in human cervical mucus

Time-resolved confocal microscopy and fluorescence correlation spectroscopy were used to examine the movements of fluorescently labeled HIV-virions (approximately 100 nm) added to samples of human cervical mucus. Particle-tracking analysis indicates that the motion of most virions is decreased 200-fold compared to that in aqueous solution and is not driven by typical diffusion. Rather, the time-dependence of their ensemble-averaged mean-square displacements is proportional to tau(alpha) + v(2)tau(2), describing a combination of anomalous diffusion (alpha approximately 0.3) and flow-like behavior, with tau being the lag time. We attribute the flow-like behavior to slowly relaxing mucus matrix that follows mechanical perturbations such as stretching and twisting of the sample. Further analysis of the tracks and displacements of individual virions indicates differences in the local movements among the virions, including constrained motion and infrequent jumps, perhaps due to abrupt changes in matrix structure. Changes in the microenvironments due to slow structural changes may facilitate movement of the virions, allowing them to reach the epithelial layer.

Mechanisms associated with HIV-1 resistance to acyclovir by the V75I mutation in reverse transcriptase

It has recently been demonstrated that the anti-herpetic drug acyclovir (ACV) also displays antiviral activity against the human immunodeficiency virus type 1 (HIV-1). The triphosphate form of ACV is accepted by HIV-1 reverse transcriptase (RT), and subsequent incorporation leads to classical chain termination. Like all approved nucleoside analogue RT inhibitors (NRTIs), the selective pressure of ACV is associated with the emergence of resistance. The V75I mutation in HIV-1 RT appears to be dominant in this regard. By itself, this mutation is usually not associated with resistance to currently approved NRTIs. Here we studied the underlying biochemical mechanism. We demonstrate that V75I is also selected under the selective pressure of a monophosphorylated prodrug that was designed to bypass the bottleneck in drug activation to the triphosphate form (ACV-TP). Pre-steady-state kinetics reveal that V75I discriminates against the inhibitor at the level of catalysis, whereas binding of the inhibitor remains largely unaffected. The incorporated ACV-monophosphate (ACV-MP) is vulnerable to excision in the presence of the pyrophosphate donor ATP. V75I compromises binding of the next nucleotide that can otherwise provide a certain degree of protection from excision. Collectively, the results of this study suggest that ACV is sensitive to two different resistance pathways, which warrants further investigation regarding the detailed resistance profile of ACV. Such studies will be crucial in assessing the potential clinical utility of ACV and its derivatives in combination with established NRTIs.

Coinfecting viruses as determinants of HIV disease

The human body constitutes a balanced ecosystem of its own cells together with various microbes ("host-microbe ecosystem"). The transmission of HIV-1 and the progression of HIV disease in such an ecosystem are accompanied by de novo infection by other microbes or by activation of microbes that were present in the host in homeostatic equilibrium before HIV-1 infection. In recent years, data have accumulated on the interactions of these coinfecting microbes-viruses in particular-with HIV. Coinfecting viruses generate negative and positive signals that suppress or upregulate HIV-1. We suggest that the signals generated by these viruses may largely affect HIV transmission, pathogenesis, and evolution. The study of the mechanisms of HIV interaction with coinfecting viruses may indicate strategies to suppress positive signals, enhance negative signals, and lead to the development of new and original anti-HIV therapies.

A highly sensitive and dynamic immunofluorescent cytometric bead assay for the detection of HIV-1 p24

Nucleic acid measurements are used to follow HIV-1 viral load in clinical applications while p24 ELISA is commonly used to monitor HIV-1 replication in research settings. Current ELISA assays are expensive and offer a narrow dynamic measurement range. This report describes a simple, sensitive and inexpensive bead-based assay offering a wide dynamic measurement range. This cytometric bead assay allows the detection of p24 concentrations over 4 orders of magnitude from less than 0.4pg to up to 20,000pgml(-1) in a volume of 50microl and can be combined with other measurements.

Acyclovir is activated into a HIV-1 reverse transcriptase inhibitor in herpesvirus-infected human tissues

For most viruses, there is a need for antimicrobials that target unique viral molecular properties. Acyclovir (ACV) is one such drug. It is activated into a human herpesvirus (HHV) DNA polymerase inhibitor exclusively by HHV kinases and, thus, does not suppress other viruses. Here, we show that ACV suppresses HIV-1 in HHV-coinfected human tissues, but not in HHV-free tissue or cell cultures. However, addition of HHV-6-infected cells renders these cultures sensitive to anti-HIV ACV activity. We hypothesized that such HIV suppression requires ACV phosphorylation by HHV kinases. Indeed, an ACV monophosphorylated prodrug bypasses the HHV requirement for HIV suppression. Furthermore, phosphorylated ACV directly inhibits HIV-1 reverse transcriptase (RT), terminating DNA chain elongation, and can trap RT at the termination site. These data suggest that ACV anti-HIV-1 activity may contribute to the response of HIV/HHV-coinfected patients to ACV treatment and could guide strategies for the development of new HIV-1 RT inhibitors.

The lymph node in HIV pathogenesis

Since the earliest days of the AIDS epidemic, clinicians and researchers have recognized the importance of lymphoid tissue both in the clinical manifestations of disease and in its pathogenesis. Generalized lymphadenopathy was one of the earliest harbingers of AIDS in the United States and over the past 27 years an increasing body of evidence has implicated the lymphoid organs as central to the pathogenesis of immune deficiency in chronic HIV-1 infection. In this essay, we will review some of the data that have been accumulated and propose a testable model that may reconcile them.

Biological and technical variables affecting immunoassay recovery of cytokines from human serum and simulated vaginal fluid: a multicenter study

The increase of proinflammatory cytokines in vaginal secretions may serve as a surrogate marker of unwanted inflammatory reaction to microbicide products topically applied for the prevention of sexually transmitted diseases, including HIV-1. Interleukin (IL)-1beta and IL-6 have been proposed as indicators of inflammation and increased risk of HIV-1 transmission; however, the lack of information regarding detection platforms optimal for vaginal fluids and interlaboratory variation limit their use for microbicide evaluation and other clinical applications. This study examines fluid matrix variants relevant to vaginal sampling techniques and proposes a model for interlaboratory comparisons across current cytokine detection technologies. IL-1beta and IL-6 standards were measured by 12 laboratories in four countries, using 14 immunoassays and four detection platforms based on absorbance, chemiluminescence, electrochemiluminescence, and fluorescence. International reference preparations of cytokines with defined biological activity were spiked into (1) a defined medium simulating the composition of human vaginal fluid at pH 4.5 and 7.2, (2) physiologic salt solutions (phosphate-buffered saline and saline) commonly used for vaginal lavage sampling in clinical studies of cytokines, and (3) human blood serum. Assays were assessed for reproducibility, linearity, accuracy, and significantly detectable fold difference in cytokine level. Factors with significant impact on cytokine recovery were determined by Kruskal-Wallis analysis of variance with Dunn's multiple comparison test and multiple regression models. All assays showed acceptable intra-assay reproducibility; however, most were associated with significant interlaboratory variation. The smallest reliably detectable cytokine differences ( P < 0.05) derived from pooled interlaboratory data varied from 1.5- to 26-fold depending on assay, cytokine, and matrix type. IL-6 but not IL-1beta determinations were lower in both saline and phosphate-buffered saline as compared to vaginal fluid matrix, with no significant effect of pH. The (electro)chemiluminescence-based assays were most discriminative and consistently detected <2-fold differences within each matrix type. The Luminex-based assays were less discriminative with lower reproducibility between laboratories. These results suggest the need for uniform vaginal sampling techniques and a better understanding of immunoassay platform differences and cross-validation before the biological significance of cytokine variations can be validated in clinical trials. This investigation provides the first standardized analytic approach for assessing differences in mucosal cytokine levels and may improve strategies for monitoring immune responses at the vaginal mucosal interface.

Semen-derived amyloid fibrils drastically enhance HIV infection

Sexual intercourse is the major route of HIV transmission. To identify endogenous factors that affect the efficiency of sexual viral transmission, we screened a complex peptide/protein library derived from human semen. We show that naturally occurring fragments of the abundant semen marker prostatic acidic phosphatase (PAP) form amyloid fibrils. These fibrils, termed Semen-derived Enhancer of Virus Infection (SEVI), capture HIV virions and promote their attachment to target cells, thereby enhancing the infectious virus titer by several orders of magnitude. Physiological concentrations of SEVI amplified HIV infection of T cells, macrophages, ex vivo human tonsillar tissues, and transgenic rats in vivo, as well as trans-HIV infection of T cells by dendritic or epithelial cells. Amyloidogenic PAP fragments are abundant in seminal fluid and boost semen-mediated enhancement of HIV infection. Thus, they may play an important role in sexual transmission of HIV and could represent new targets for its prevention.

Sustained secretion of immunoglobulin by long-lived human tonsil plasma cells

Immunoglobulin-secreting cells comprise both short-lived proliferating plasmablasts and long-lived nonproliferating plasma cells. To determine the phenotype and functional activity of Ig-secreting cells in human lymphoid tissue, we used a tonsillar organ culture model. A significant proportion of IgA and IgG secretion was shown to be mediated by long-lived, nonproliferating plasma cells that coexpressed high levels of CD27 and CD38. The presence of such cells was further corroborated by the finding of enhanced expression in the CD19(+) B-cell population of XBP-1, IRF-4, and particularly Blimp-1 genes involved in the differentiation of plasma cells. Intact tissue seemed to be necessary for optimal functional activity of plasma cells. A strong correlation was found between concentrations of interleukin-6 and IgA or IgG, but not IgM, in culture supernatants suggesting a role for interleukin-6 in the survival of long-lived plasma cells. Taken together, the present study demonstrates that human lymphoid tissue harbors a population of nonproliferating plasma cells that are dependent on an intact microenvironment for ongoing Ig secretion.

Measles virus vaccine attenuation: suboptimal infection of lymphatic tissue and tropism alteration

The mechanisms of measles virus (MV) vaccine attenuation are insufficiently characterized. Because the Edmonston vaccine strain can enter cells through CD46 in addition to the primary MV receptor signaling lymphocyte activation molecule (SLAM or CD150), we asked whether and how its tropism is altered. In human tonsillar tissue, this vaccine strain infects naive (CD45RA(+)CD62L(+)) T lymphocytes, which express SLAM very infrequently, with much higher efficiency than do wild-type strains. By contrast, it infects B lymphocytes, macrophages, and NK cells with significantly lower efficiencies than those of wild-type strains. Infection levels by wild-type strains correlate with the frequency of SLAM expression and are highest in B cells, which are 40%-55% infected. SLAM-expressing T cells are more readily infected by all MV strains than are SLAM-expressing B cells. Thus, vaccine attenuation may be caused by tropism alteration in combination with suboptimal replication.

HIV-1 pathogenesis differs in rectosigmoid and tonsillar tissues infected ex vivo with CCR5- and CXCR4-tropic HIV-1

Gut-associated lymphoid tissue (GALT) has been identified as the primary target of HIV-1 infection. To investigate why GALT is especially vulnerable to HIV-1, and to determine whether the selective transmission of CCR5-using viral variants (R5) in vivo is the result of a greater susceptibility of GALT to this viral variant, we performed comparative studies of CXCR4-using (X4) and R5 HIV-1 infections of human lymphoid (tonsillar) and rectosigmoid tissues ex vivo under controlled laboratory conditions. We found that the relative level of R5 replication in rectosigmoid tissue is much greater than in tonsillar tissue. This difference is associated with the expression of the CCR5 co-receptor on approximately 70% of CD4 T cells in rectosigmoid tissue, whereas in tonsillar tissue it is expressed on fewer than 15% of CD4 T cells. Furthermore, tonsillar tissue responds to X4 HIV-1 infection by upregulating the secretion of CC-chemokines, providing a potential CCR5 blockade and further resistance to R5 infection, whereas gut tissue failed to increase such innate immune responses. Our results show that rectosigmoid tissue is more prone than tonsillar lymphoid tissue to R5 HIV-1 infection, primarily because of the high prevalence and availability of R5 cell targets and reduced chemokine blockade. The majority of CD4 T cells express CXCR4, however, and X4 HIV-1 readily replicates in both tissues, suggesting that although the differential expression of co-receptors contributes to the GALT vulnerability to R5 HIV-1, it alone cannot account for the selective R5 infection of the rectal mucosa in vivo.

Cell-cell and cell-extracellular matrix interactions regulate embryonic stem cell differentiation

Cell interactions with the extracellular matrix (ECM) play a critical role in their physiology. Here, we sought to determine the role of exogenous and endogenous ECM in the differentiation of nonhuman primate ESCs. We evaluated cell differentiation from expression of lineage gene mRNA and proteins using real-time polymerase chain reaction and immunohistochemistry. We found that ESCs that attached to and spread upon highly adhesive collagen do not differentiate efficiently, whereas on the less adhesive Matrigel, ESCs form aggregates and differentiate along mesoderm and especially endoderm lineages. To further decrease ESC attachment to the substrate, we cultured them either on nonadhesive agarose or in suspension. In both cases, ESCs formed aggregates and efficiently differentiated along endoderm and mesoderm lineages, most strikingly into cardiomyocytes. Aggregates formed by thus-differentiated ESCs started to beat with a frequency of 50-100 beats per minute and continued to beat for approximately a month. In spite of the presence of exogenous ECM, ESCs were dependent on endogenous ECM for their survival and differentiation, as the inhibition of endogenous collagen induced a gradual loss of ESCs and neither a simple matrix, such as type I collagen, nor the complex matrix Matrigel was able to rescue these cells. In conclusion, adhesiveness to various ECM and nonbiological substrates determines the differentiation of ESCs in such a way that efficient cell-cell aggregation, together with less efficient cell attachment and spreading, results in more efficient cell differentiation.

Design and cellular kinetics of dansyl-labeled CADA derivatives with anti-HIV and CD4 receptor down-modulating activity

A new class of anti-retrovirals, cyclotriazadisulfonamide (CADA) and its derivatives, specifically down-regulate CD4, the main receptor of HIV, and prevent HIV infection in vitro. In this work, several CADA derivatives, chemically labeled with a fluorescent dansyl group, were evaluated for their biological features and cellular uptake kinetics. We identified a derivative KKD-016 with antiviral and CD4 down-modulating capabilities similar to those of the parental compound CADA. By using flow cytometry, we demonstrated that the dose-dependent cellular uptake of this derivative correlated with CD4 down-modulation. The uptake and activity of the dansyl-labeled compounds were not dependent on the level of expression of CD4 at the cell surface. Removal of the CADA compounds from the cell culture medium resulted in their release from the cells followed by a complete restoration of CD4 expression. The inability of several fluorescent CADA derivatives to down-modulate CD4 was not associated with their lower cellular uptake and was not reversed by facilitating their cell penetration by a surfactant. These results prove the successful integration of the dansyl fluorophore into the chemical structure of a CD4 down-modulating anti-HIV compound, and show the feasibility of tracking a receptor and its down-modulator simultaneously. These fluorescent CADA analogs with reversible CD4 down-regulating potency can now be applied in further studies on receptor modulation, and in the exploration of their potentials as preventive and therapeutic anti-HIV drugs.

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

OBJECTIVES

Establishment of an in vitro model to evaluate rectal safety and the efficacy of microbicide candidates.

DESIGN

An investigation and characterization of human colorectal explant culture for screening candidate microbicides to prevent rectal transmission of HIV-1 infection.

METHODS

Human colorectal explants were cultured at the liquid-air interface on gelfoam rafts. Phenotypic characterization of HIV-1 target cells was performed by fluorescence-activated cell sorter analysis. HIV-1 infection was determined by the measurement of p24 antigen release, viral RNA, and proviral DNA accumulation.

RESULTS

Colorectal explant CD4 T cells expressed higher CCR5 and CXCR4 levels compared with blood. Minor differences between the rectal and sigmoid colon were observed with a trend for slightly higher CCR5 and HLA-DR expression in cells from the sigmoid colon. Favourable culture conditions were established for colorectal tissue. Although tissue structure degenerated with time, CD4: CD8 cell ratios remained constant, and tissue supported productive HIV-1 infection. The ability of candidate microbicides to inhibit R5 HIV-1 infection was evaluated. Polyanion candidates, PRO2000 and dextrin sulphate, provided 99% protection at 1 microg/ml and 1 mg/ml, respectively, equivalent to 1/5000 and 1/40 of the vaginal formulations. The nucleotide reverse transcriptase inhibitor (NRTI) 9-[2-(phosphonomethoxy)propyl]adenine (PMPA) provided protection at concentrations 1000-fold lower (10 microg/ml) than the proposed vaginal formulation (1%). Furthermore, non-NRTI UC-781 and TMC-120 provided greater than 99% inhibition at 3.3 or 0.33 microg/ml, respectively. No products demonstrated toxicity to rectal mucosa at inhibitory concentrations.

CONCLUSION

Colorectal explant culture was shown to be a useful tool for the preclinical evaluation of potential microbicides. The data suggest that rectally applied microbicides might provide protection from HIV-1 transmission.

Primate embryonic stem cells create their own niche while differentiating in three-dimensional culture systems

Rhesus monkey embryonic stem cells (ESCs) (R366.4), cultured on a three-dimensional (3D) collagen matrix with or without human neonatal foreskin fibroblasts (HPI.1) as feeder cells, or embedded in the collagen matrix, formed complex tubular or spherical gland-like structures and differentiated into phenotypes characteristic of neural, epithelial and endothelial lineages. Here, we analysed the production of endogenous extracellular matrix (ECM) proteins, cell-cell adhesion molecules, cell-surface receptors, lectins and their glycoligands, by differentiating ESCs, forming a micro-environment, a niche, able to positively influence cell behaviour. The expression of some of these molecules was modulated by HPI.1 cells while others were unaffected. We hypothesized that both soluble factors and the niche itself were critical in directing growth and/or differentiation of ESCs in this 3D environment. Creating such an appropriate experimental 3D micro-environment, further modified by ESCs and modulated by exogenous soluble factors, may constitute a template for adequate culture systems in developmental biology studies concerning differentiation of stem cells.

Selective transmission of CCR5-utilizing HIV-1: the 'gatekeeper' problem resolved?

Understanding the mechanisms of HIV-1 transmission is crucial for the development of effective preventive microbicides and vaccine strategies, and remains one of the main goals of HIV research. Over the past decade, many studies have focused on trying to identify the 'gatekeeping' mechanism that restricts the transmission of CXCR4-utilizing HIV-1 more efficiently than CCR5-utilizing HIV-1. However, to date, no study has explained the almost perfect negative selection of the former in vivo. Here, we propose that there is no single gatekeeper and that, instead, the selective transmission of R5 HIV-1 depends on the superimposition of multiple imperfect gatekeepers.

Differentiation of rhesus monkey embryonic stem cells in three-dimensional collagen matrix

During normal embryogenesis, embryonic stem cells (ESCs) reside in the context of complex three-dimensional tissue structures, in particular of extracellular matrices (ECMs), which determine cell migration, proliferation, and differentiation. Therefore, to study ESC differentiation in an in vivo-like microenvironment, three-dimensional culture systems are necessary. Here, we developed protocols for ESC cultures in three-dimensional systems consisting of collagen matrices (collagen gels and porous collagen sponges) to investigate the mechanisms of ESC differentiation as well as the formation of tissue-like structures. In collagen matrices, ESCs differentiate into neural, epithelial, and endothelial lineages. In this system, ESCs form various tissue-like structures. The abilities of ESCs to form such structures in two chemically similar but topologically different matrices are different. In particular, in collagen gels ESCs form gland-like circular structures, whereas in collagen sponges ESCs are scattered through the matrix and form aggregates. To mimic the in vivo situation further, we developed a protocol for co-cultures of ESCs with human dermal fibroblasts or keratinocytes in collagen matrixes. Co-culture with fibroblasts in collagen gel facilitates ESC differentiation into cells of a neural lineage expressing nestin, neural cell adhesion molecule (NCAM), and class III beta-tubulin. In collagen sponges, keratinocytes facilitated ESC differentiation into cells of an endothelial lineage expressing factor VIII. Thus, the developed protocols promote ESC differentiation into a particular lineage, accompanied by the formation of tissue-like structures. Three-dimensional culture systems are a valuable tool for directing ESC differentiation and the formation of organs and tissues.

The nonnucleoside reverse transcriptase inhibitor UC-781 inhibits human immunodeficiency virus type 1 infection of human cervical tissue and dissemination by migratory cells

Heterosexual transmission of human immunodeficiency virus remains the major route of transmission worldwide; thus, there is an urgent need for additional prevention strategies, particularly those that could be controlled by women. Using cellular and tissue explant models, we have evaluated the potential activity of thiocarboxanilide nonnucleoside analogue reverse transcriptase inhibitor UC-781 as a vaginal microbicide. We were able to demonstrate a potent dose-dependent effect against R5 and X4 infections of T cells. In human cervical explant cultures, UC-781 was not only able to inhibit direct infection of mucosal tissue but was able to prevent dissemination of virus by migratory cells. UC-781 formulated into a carbopol gel (0.1%) retained significant activity against both direct tissue infection and transinfection mediated by migratory cells. Furthermore, UC-781 demonstrated prolonged inhibitory effects able to prevent both localized and disseminated infections up to 6 days post compound treatment. Additional studies were carried out to determine the concentration of compound that might be required to block a primary infection within draining lymph nodes. While a greater dose of compound was required to inhibit both X4 and R5 infections of lymphoid versus cervical explants, this was equivalent to a 1:3,000 dilution of the 0.1% formulation. Furthermore, a 2-h exposure to the compound prevented infection of lymphoid tissue when challenged up to 2 days later. The prolonged protection observed following pretreatment of both genital and lymphoid tissues with UC-781 suggests that this class of inhibitors may have unique advantages over other classes of potential microbicide candidates.

Pertussis toxin B-oligomer dissociates T cell activation and HIV replication in CD4 T cells released from infected lymphoid tissue

OBJECTIVE

To investigate, in human lymphoid tissue infected with HIV-1 ex vivo, the immunostimulatory and HIV inhibitory properties of pertussis toxin B oligomer (PTX-B) and of the genetically modified non-toxic PT-9K/129G.

METHODS

Human tonsils from uninfected donors were infected ex vivo with R5 or X4 HIV-1 in the presence or absence of PTX-B. Virus replication was evaluated in culture supernatants; cells emigrated from tissue blocks were immunostained for lymphocytic and activation markers. HIV DNA and cell proliferation were evaluated with real-time PCR and [H]thymidine incorporation, respectively.

RESULTS

Both PTX-B and PT-9K/129G inhibited HIV-1 replication. These compounds activated and stimulated the proliferation of emigrated cells, most of which were CD4 T lymphocytes. Cells emigrated from infected tissues did not produce detectable virus in unstimulated or in PTX-B- or PT-9K/129G-stimulated cultures whereas robust virus production was triggered by phytohemagglutinin (PHA) or interleukin-2 (IL-2). Analysis of HIV DNA content indicated that infected cells were present among emigrated cells and that their number greatly increased following IL-2 stimulation, whereas it remained constant in the presence of PTX-B or PT-9K/129G.

CONCLUSIONS

PTX-B and PT-9K/129G inhibit both R5 and X4 HIV-1 replication in human lymphoid tissue ex vivo. In contrast to PHA and IL-2, they promote the proliferation of CD4 T lymphocytes emigrated from tissue, including HIV-infected cells, without triggering virus replication. Therefore, these emigrated CD4 T cells represent a novel model of a latent inducible HIV reservoir. Thus, PTX-B and the clinically approved PT-9K/129G are potential antiretroviral agents endowed with immunostimulatory capacity.