Unravelling the triad of neuroinvasion, neurodissemination, and neuroinflammation of human immunodeficiency virus type 1 in the central nervous system.

Since the identification of human immunodeficiency virus type 1 (HIV-1) in 1983, many improvements have been made to control viral replication in the peripheral blood and to treat opportunistic infections. This has increased life expectancy but also the incidence of age-related central nervous system (CNS) disorders and HIV-associated neurodegeneration/neurocognitive impairment and depression collectively referred to as HIV-associated neurocognitive disorders (HAND). HAND encompasses a spectrum of different clinical presentations ranging from milder forms such as asymptomatic neurocognitive impairment or mild neurocognitive disorder to a severe HIV-associated dementia (HAD). Although control of viral replication and suppression of plasma viral load with combination antiretroviral therapy has reduced the incidence of HAD, it has not reversed milder forms of HAND. The objective of this review, is to describe the mechanisms by which HIV-1 invades and disseminates in the CNS, a crucial event leading to HAND. The review will present the evidence that underlies the relationship between HIV infection and HAND. Additionally, recent findings explaining the role of neuroinflammation in the pathogenesis of HAND will be discussed, along with prospects for treatment and control.

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

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

Cell-to-Cell Transmission of HIV-1 and HIV-2 from Infected Macrophages and Dendritic Cells to CD4+ T Lymphocytes.

Macrophages (Mø) and dendritic cells (DCs) are key players in human immunodeficiency virus (HIV) infection and pathogenesis. They are essential for the spread of HIV to CD4+ T lymphocytes (TCD4+) during acute infection. In addition, they constitute a persistently infected reservoir in which viral production is maintained for long periods of time during chronic infection. Defining how HIV interacts with these cells remains a critical area of research to elucidate the pathogenic mechanisms of acute spread and sustained chronic infection and transmission. To address this issue, we analyzed a panel of phenotypically distinct HIV-1 and HIV-2 primary isolates for the efficiency with which they are transferred from infected DCs or Mø to TCD4+. Our results show that infected Mø and DCs spread the virus to TCD4+ via cell-free viral particles in addition to other alternative pathways. We demonstrate that the production of infectious viral particles is induced by the co-culture of different cell populations, indicating that the contribution of cell signaling driven by cell-to-cell contact is a trigger for viral replication. The results obtained do not correlate with the phenotypic characteristics of the HIV isolates, namely their co-receptor usage, nor do we find significant differences between HIV-1 and HIV-2 in terms of cis- or trans-infection. The data presented here may help to further elucidate the cell-to-cell spread of HIV and its importance in HIV pathogenesis. Ultimately, this knowledge is critical for new therapeutic and vaccine approaches.

HIV/Mtb Co-Infection: From the Amplification of Disease Pathogenesis to an "Emerging Syndemic".

Human immunodeficiency virus (HIV) and Mycobacterium tuberculosis (Mtb) are pathogens responsible for millions of new infections each year; together, they cause high morbidity and mortality worldwide. In addition, late-stage HIV infection increases the risk of developing tuberculosis (TB) by a factor of 20 in latently infected people, and even patients with controlled HIV infection on antiretroviral therapy (ART) have a fourfold increased risk of developing TB. Conversely, Mtb infection exacerbates HIV pathogenesis and increases the rate of AIDS progression. In this review, we discuss this reciprocal amplification of HIV/Mtb coinfection and how they influence each other's pathogenesis. Elucidating the infectious cofactors that impact on pathogenesis may open doors for the design of new potential therapeutic strategies to control disease progression, especially in contexts where vaccines or the sterile clearance of pathogens are not effectively available.

Characterization of Envelope Surface Glycoprotein from HIV-2 Primary Isolates with Different Coreceptor Usage Profile.

The main goal of this work was to identify molecular signatures in envelope surface glycoprotein that may be correlated with coreceptor usage by different human immunodeficiency virus (HIV)-2 strains. From inspection of aligned HIV-2 sequences, we verified that V1/V2 region showed the highest degree of amino acid sequence heterogeneity, including polymorphisms in N-linked glycosylation sites, sequence, and length. Furthermore, we did not find any correlation between the net charge and specific amino acid positions in V3 region with any particular coreceptor usage pattern. In conclusion, we showed that for HIV-2, the genetic determinants for coreceptor usage are distinct from those of HIV-1. More specifically, we did not identify any molecular signature, based on discrete amino acid positions either in V1/V2 or in V3 regions, which could be assigned to the preferential usage of a specific coreceptor.

Development of synthetic light-chain antibodies as novel and potent HIV fusion inhibitors.

OBJECTIVE: To develop a novel and potent fusion inhibitor of HIV infection based on a rational strategy for synthetic antibody library construction. DESIGN: The reduced molecular weight of single-domain antibodies (sdAbs) allows targeting of cryptic epitopes, the most conserved and critical ones in the context of HIV entry. Heavy-chain sdAbs from camelids are particularly suited for this type of epitope recognition because of the presence of long and flexible antigen-binding regions [complementary-determining regions (CDRs)]. METHODS: We translated camelid CDR features to a rabbit light-chain variable domain (VL) and constructed a library of minimal antibody fragments with elongated CDRs. Additionally to elongation, CDRs' variability was restricted to binding favorable amino acids to potentiate the selection of high-affinity sdAbs. The synthetic library was screened against a conserved, hidden, and crucial-to-fusion sequence on the heptad-repeat 1 (HR1) region of the HIV-1 envelope glycoprotein. RESULTS: Two anti-HR1 VLs, named F63 and D104, strongly inhibited laboratory-adapted HIV-1 infectivity. F63 also inhibited infectivity of HIV-1 and HIV-2 primary isolates similarly to the Food and Drug Administration-approved fusion inhibitor T-20 and HIV-1 strains resistant to T-20. Moreover, epitope mapping of F63 revealed a novel target sequence within the highly conserved hydrophobic pocket of HR1. F63 was also capable of interacting with viral and cell lipid membrane models, a property previously associated with T-20's inhibitory mechanism. CONCLUSION: In summary, to our best knowledge, we developed the first potent and broad VL sdAb fusion inhibitor of HIV infection. Our study also gives insights into engineering strategies that could be explored to enhance the development of antiviral drugs.

HIV Interaction With Human Host: HIV-2 As a Model of a Less Virulent Infection.

HIV-1 and HIV-2 are the causal agents of AIDS. While similar in many ways, a significant amount of data suggests that HIV-2 is less virulent than HIV-1. In fact, HIV-2 infection is characterized by a longer asymptomatic stage and lower transmission rate, and the majority of HIV-2-infected patients can be classified as long-term non-progressors or elite controllers. The mechanisms underlying the ability of human host to naturally control HIV-2 infection are far from being completely understood. The identification of the differences between HIV-1 and HIV-2 interactions with human host cells could provide important insights into several aspects of retroviral pathogenesis that remain elusive, with significant implications for HIV vaccine development and therapy. In this review, we delve into some of the differences that notably distinguish HIV-2 from HIV-1, highlighting possible consequences in the pathogenesis and natural history of both infections.

HIV-2 interaction with cell coreceptors: amino acids within the V1/V2 region of viral envelope are determinant for CCR8, CCR5 and CXCR4 usage.

BACKGROUND: Human immunodeficiency virus 1 and 2 (HIV-1 and HIV-2) use cellular receptors in distinct ways. Besides a more promiscuous usage of coreceptors by HIV-2 and a more frequent detection of CD4-independent HIV-2 isolates, we have previously identified two HIV-2 isolates (HIV-2MIC97 and HIV-2MJC97) that do not use the two major HIV coreceptors: CCR5 and CXCR4. All these features suggest that in HIV-2 the Env glycoprotein subunits may have a different structural organization enabling distinct - although probably less efficient - interactions with cellular receptors. RESULTS: By infectivity assays using GHOST cell line expressing CD4 and CCR8 and blocking experiments using CCR8-specific ligand, I-309, we show that efficient replication of HIV-2MIC97 and HIV-2MJC97 requires the presence of CCR8 at plasma cell membrane. Additionally, we disclosed the determinants of chemokine receptor usage at the molecular level, and deciphered the amino acids involved in the usage of CCR8 (R8 phenotype) and in the switch from CCR8 to CCR5 or to CCR5/CXCR4 usage (R5 or R5X4 phenotype). The data obtained from site-directed mutagenesis clearly indicates that the main genetic determinants of coreceptor tropism are located within the V1/V2 region of Env surface glycoprotein of these two viruses. CONCLUSIONS: We conclude that a viral population able to use CCR8 and unable to infect CCR5 or CXCR4-positive cells, may exist in some HIV-2 infected individuals during an undefined time period, in the course of the asymptomatic stage of infection. This suggests that in vivo alternate molecules might contribute to HIV infection of natural target cells, at least under certain circumstances. Furthermore we provide direct and unequivocal evidence that the usage of CCR8 and the switch from R8 to R5 or R5X4 phenotype is determined by amino acids located in the base and tip of V1 and V2 loops of HIV-2 Env surface glycoprotein.

Susceptibility of HIV type 2 primary isolates to CCR5 and CXCR4 monoclonal antibodies, ligands, and small molecule inhibitors.

Human immunodeficiency virus (HIV) entry into susceptible cells involves the interaction between viral envelope glycoproteins with CD4 and a chemokine receptor (coreceptor), namely CCR5 and CXCR4. This interaction has been studied to enable the discovery of a new class of antiretroviral drugs that targets the envelope glycoprotein-coreceptor interaction. However, very few data exist regarding HIV-2 susceptibility to these coreceptor inhibitors. With this work we aimed to identify this susceptibility in order to assess the potential use of these molecules to treat HIV-2-infected patients and to further understand the molecular basis of HIV-2 envelope glycoprotein interactions with CCR5 and CXCR4. We found that CCR5-using HIV-2 isolates are readily inhibited by maraviroc, TAK-779, and PF-227153, while monoclonal antibody 2D7 shows only residual or no inhibitory effects. The anti-HIV-2 activity of CXCR4-targeted molecules reveals that SDF-1α/CXCL12 inhibited all HIV-2 tested except one, while mAb 12G5 inhibited the replication of only two isolates, showing residual inhibitory effects with all the other CXCR4-using viruses. A major conclusion from our results is that infection by HIV-2 primary isolates is readily blocked in vitro by maraviroc, at concentrations similar to those required for HIV-1. The susceptibility to maraviroc was independent of CD4(+) T cell counts or clinical stage of the patient from which the virus was obtained. These findings indicate that maraviroc could constitute a reliable therapeutic alternative for HIV-2-infected patients, as long as they are infected with CCR5-using variants, and this may have direct implications for the clinical management of HIV-2-infected patients.

[The chemokines and their receptors: characteristics and physiological functions]. / As quimiocinas e os seus receptores: características e funções fisiológicas.

Chemokines are members of a large family of small soluble proteins, which were discovered by their adhesion control, chemotaxis and leukocyte activation abilities. Nevertheless, it is now known they are involved in other equally important functions, namely, angiogenesis, haematopoiesis, embryologic development, B and T cell development, dendritic cell maturation, inflammation, infection, tumour growth and metastasis. Hence, the increasing interest on chemokines and their receptors is due not only to chemokine chemoattractant properties but also to their contribution to immune processes that do not directly involve leukocyte migration. According to the number and spacing of the first two conserved cysteine residues in the N-terminal, chemokines have been divided into four subfamilies (CXC, CC, CX3C and C) and mediate their functions by binding to G-protein coupled receptors. This interaction may result in multiple signal transduction pathways, depending on the player subunit and the effector protein activated. It triggers a cascade of intracellular events that promote from gene transcription to cytoskeleton rearrangement and chemotaxis. The pattern of migration of cell populations and of leukocytes in particular is closely related to chemokine receptors expression. One of the characteristics associated with the chemokine system is an apparent redundancy: several chemokine receptors bind multiple ligands and in turn, a single ligand binds multiple receptors. Another overall classification of chemokines is based on functional criteria that group them into homeostatic and inflammatory chemokines. Homeostatic chemokines are constitutively expressed and regulate the migration of leukocytes and their precursors. The inflammatory chemokines are inducible and regulate the leukocyte migration into tissues in response to an inflammatory stimulus, such as tissue damage, inflammation or infection. Many of the inflammatory chemokines have wide target-cell selectivity, acting both on the cells of the innate and adaptive immunity. The purpose of this review is to collect all the research that has been done so far concerning chemokines and their receptors through analysing their expression patterns, in order to define their cellular localisation with the aim of understanding their role in human physiology.

Molecular characterization of the env gene of two CCR5/CXCR4-independent human immunodeficiency 2 primary isolates.

Human immunodeficiency virus 2 (HIV-2) infection is characterized by a slower disease progression and lower transmission rates. The molecular features that could be assigned as directly involved in this in vivo phenotype remain essentially unknown, and the importance of HIV-2 as a model to understand pathogenicity of HIV infection has been frequently underestimated. The early events of the HIV replication cycle involve the interaction between viral envelope glycoproteins and cellular receptors: the CD4 molecule and a chemokine receptor, usually CCR5 or CXCR4. Despite the importance of these two chemokine receptors in human immunodeficiency virus 1 (HIV-1) entry into cells, we have previously shown that in some HIV-2 asymptomatic individuals, a viral population exists that is unable to use both CCR5 and CXCR4. The goal of the present study was to investigate whether possible regions in the env gene of these viruses might account for this phenotype. From the molecular characterization of these env genes we could not detect any correlation between V3 loop sequence and viral phenotype. In contrast, it reveals the existence of remarkable differences in the V1/V2 and C5 regions of the surface glycoprotein, including the loss of a putative glycosilation site. Moreover, in the transmembrane glycoprotein some unique sequence signatures could be detected in the central ectodomain and second heptad repeat (HR2). Some of the mutations affect well-conserved residues, and may affect the conformation and/or the dynamics of envelope glycoproteins complex, including the SU-TM association and the modulation of viral entry function.

HIV-2 infection and chemokine receptors usage - clues to reduced virulence of HIV-2.

Human immunodeficiency virus type 1 (HIV-1) and type 2 (HIV-2) are the causative agents of Acquired Immunodeficiency Syndrome (AIDS). Without therapeutic intervention, HIV-1 or HIV-2 infections in humans are characterized by a gradual and irreversible immunologic failure that ultimately leads to the onset of a severe immunodeficiency that constitutes the hallmark of AIDS. In the last two decades AIDS has evolved into a global epidemic affecting millions of persons worldwide. Although sharing several identical properties, HIV-1 and HIV-2 have shown some important differences in vivo. In fact, a significant amount of epidemiologic, clinical and virologic data suggest that HIV-2 is in general less virulent than HIV-1. This reduced virulence is revealed by the longer asymptomatic period and the smaller transmission rate that characteristically are observed in HIV-2 infection. In this context, studies using HIV-2 as a model of a naturally less pathogenic infection could bring important new insights to HIV pathogenesis opening to new strategies to vaccines or therapeutic design. The reasons underlying the reduced pathogenicity of HIV-2 are still essentially unknown and surely are the outcome of a combination of distinct factors. In this review we will discuss the importance and the possible implications in HIV-2 pathogenesis, particularly during the asymptomatic period, of a less fitted interaction between viral envelope glycoproteins and cellular receptors that have been described in the way HIV-2 and HIV-1 use these receptors.