HIV Fusion in Dendritic Cells Occurs Mainly at the Surface and Is Limited by Low CD4 Levels

HIV-1-induced nuclear invaginations mediated by VAP-A, ORP3, and Rab7 complex explain infection of activated T cells

The mechanism of human immunodeficiency virus 1 (HIV-1) nuclear entry, required for productive infection, is not fully understood. Here, we report that in HeLa cells and activated CD4+ T cells infected with HIV-1 pseudotyped with VSV-G and native Env protein, respectively, Rab7+ late endosomes containing endocytosed HIV-1 promote the formation of nuclear envelope invaginations (NEIs) by a molecular mechanism involving the VOR complex, composed of the outer nuclear membrane protein VAP-A, hyperphosphorylated ORP3 and Rab7. Silencing VAP-A or ORP3 and drug-mediated impairment of Rab7 binding to ORP3-VAP-A inhibited the nuclear transfer of the HIV-1 components and productive infection. In HIV-1-resistant quiescent CD4+ T cells, ORP3 was not hyperphosphorylated and neither VOR complex nor NEIs were formed. This new cellular pathway and its molecular players are potential therapeutic targets, perhaps shared by other viruses that require nuclear entry to complete their life cycle.

Human Claudin-Derived Peptides Block the Membrane Fusion Process of Zika Virus and Are Broad Flavivirus Inhibitors

Zika virus (ZIKV) is a mosquito-borne flavivirus that emerged in the Pacific islands in 2007 and spread to the Americas in 2015. The infection remains asymptomatic in most cases but can be associated with severe neurological disorders. Despite massive efforts, no specific drug or vaccine against ZIKV infection is available to date. Claudins are tight-junction proteins that favor the entry of several flaviviruses, including ZIKV. In this study, we identified two peptides derived from the N-terminal sequences of claudin-7 and claudin-1, named CL7.1 and CL1.1, respectively, that inhibited ZIKV infection in a panel of human cell lines. Using cell-to-cell fusion assays, we demonstrated that these peptides blocked the ZIKV E-mediated membrane fusion. A comparison of the antiviral efficacy of CL1.1 and CL7.1 pointed to the importance of the peptide amphipathicity. Electron microscopic analysis revealed that CL1.1 altered the ultrastructure of the viral particles likely by binding the virus lipid envelope. However, amphipathicity could not fully explain the antiviral activity of CL1.1. In silico docking simulations suggested that CL1.1 may also interact with the E protein, near its stem region. Overall, our data suggested that claudin-derived peptides inhibition may be linked to simultaneous interaction with the E protein and the viral lipid envelope. Finally, we found that CL1.1 also blocked infection by yellow fever and Japanese encephalitis viruses but not by HIV-1 or SARS-CoV-2. Our results provide a basis for the future development of therapeutics against a wide range of endemic and emerging flaviviruses. IMPORTANCE Zika virus (ZIKV) is a flavivirus transmitted by mosquito bites that have spread to the Pacific Islands and the Americas over the past decade. The infection remains asymptomatic in most cases but can cause severe neurological disorders. ZIKV is a major public health threat in areas of endemicity, and there is currently no specific antiviral drug or vaccine available. We identified two antiviral peptides deriving from the N-terminal sequences of claudin-7 and claudin-1 with the latter being the most effective. These peptides block the envelope-mediated membrane fusion. Our data suggested that the inhibition was likely achieved by simultaneously interacting with the viral lipid envelope and the E protein. The peptides also inhibited other flaviviruses. These results could provide the basis for the development of therapies that might target a wide array of flaviviruses from current epidemics and possibly future emergences.

How dendritic cells sense and respond to viral infections

The ability of dendritic cells (DCs) to sense viral pathogens and orchestrate a proper immune response makes them one of the key players in antiviral immunity. Different DC subsets have complementing functions during viral infections, some specialize in antigen presentation and cross-presentation and others in the production of cytokines with antiviral activity, such as type I interferons. In this review, we summarize the latest updates concerning the role of DCs in viral infections, with particular focus on the complex interplay between DC subsets and severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Despite being initiated by a vast array of immune receptors, DC-mediated antiviral responses often converge towards the same endpoint, that is the production of proinflammatory cytokines and the activation of an adaptive immune response. Nonetheless, the inherent migratory properties of DCs make them a double-edged sword and often viral recognition by DCs results in further viral dissemination. Here we illustrate these various aspects of the antiviral functions of DCs and also provide a brief overview of novel antiviral vaccination strategies based on DCs targeting.

How Influenza Virus Uses Host Cell Pathways during Uncoating

Influenza is a zoonotic respiratory disease of major public health interest due to its pandemic potential, and a threat to animals and the human population. The influenza A virus genome consists of eight single-stranded RNA segments sequestered within a protein capsid and a lipid bilayer envelope. During host cell entry, cellular cues contribute to viral conformational changes that promote critical events such as fusion with late endosomes, capsid uncoating and viral genome release into the cytosol. In this focused review, we concisely describe the virus infection cycle and highlight the recent findings of host cell pathways and cytosolic proteins that assist influenza uncoating during host cell entry.

Mucosal Immunity and HIV Acquisition in Women

Women acquire HIV through sexual transmission. Women worldwide represent half of the people living with HIV, but young women in endemic areas are disproportionally affected. Low transmission rates per sexual act in women suggest that local immune protective mechanisms in the genital tract have the potential to prevent infection. However, conditions that induce genital inflammation are known to increase the risk of HIV acquisition. The female genital tract (FGT) is divided into different anatomical compartments with distinct reproductive functions. The immune cells present in each of these compartments are specialized in balancing reproduction and protection against infections, and are the same cells that can encounter and respond to HIV. Understanding the physiological and pathological factors that influence mucosal immune cell presence, susceptibility to HIV-infection and anti-HIV immune responses in the FGT is necessary to develop preventive strategies. Here we review recent advances in our understanding of HIV infection in the human female genital tract, with an emphasis on the characterization of the mucosal cells susceptible to HIV-infection, innate immune responses and mucosal factors that increase genital inflammation and influence susceptibility to HIV acquisition in women.

HIV-2-Infected Macrophages Produce and Accumulate Poorly Infectious Viral Particles

A significant proportion of HIV-2-infected patients exhibit natural virological control that is generally absent from HIV-1-infected patients. Along with CD4⁺ T cells, HIV-1 targets macrophages which may contribute to viral spreading and the latent reservoir. We have studied the relationship between macrophages and HIV-2, focusing on post-entry steps. HIV-2-infected monocyte-derived macrophages (MDMs) produced substantial amounts of viral particles that were largely harbored intracellularly. New viruses assembled at the limiting membrane of internal compartments similar to virus-containing compartments (VCCs) described for HIV-1. VCCs from MDMs infected with either virus shared protein composition and morphology. Strikingly, HIV-2 Gag was mostly absent from the cytosol and almost exclusively localized to the VCCs, whereas HIV-1 Gag was distributed in both locations. Ultrastructural analyses of HIV-2-infected MDMs revealed the presence of numerous VCCs containing both immature and mature particles in the lumen. HIV-2 particles produced de novo by MDMs were poorly infectious in reporter cells and in transmission to activated T cells through a process that appeared independent of BST2 restriction. Rather than being involved in viral spreading, HIV-2-infected macrophages may represent a cell-associated source of viral antigens that can participate in the immune control of HIV-2 infection.

Nanoparticle-Based Immunoengineered Approaches for Combating HIV

Highly active antiretroviral therapy (HAART) serves as an effective strategy to combat HIV infections by suppressing viral replication in patients with HIV/AIDS. However, HAART does not provide HIV/AIDS patients with a sterilizing or functional cure, and introduces several deleterious comorbidities. Moreover, the virus is able to persist within latent reservoirs, both undetected by the immune system and unaffected by HAART, increasing the risk of a viral rebound. The field of immunoengineering, which utilizes varied bioengineering approaches to interact with the immune system and potentiate its therapeutic effects against HIV, is being increasingly investigated in HIV cure research. In particular, nanoparticle-based immunoengineered approaches are especially attractive because they offer advantages including the improved delivery and functionality of classical HIV drugs such as antiretrovirals and experimental drugs such as latency-reversing agents (LRAs), among others. Here, we present and discuss the current state of the field in nanoparticle-based immunoengineering approaches for an HIV cure. Specifically, we discuss nanoparticle-based methods for improving HAART as well as latency reversal, developing vaccines, targeting viral fusion, enhancing gene editing approaches, improving adoptively transferred immune-cell mediated reservoir clearance, and other therapeutic and prevention approaches. Although nanoparticle-based immunoengineered approaches are currently at the stage of preclinical testing, the promising findings obtained in these studies demonstrate the potential of this emerging field for developing an HIV cure.

Dendritic Cells, the Double Agent in the War Against HIV-1

Human Immunodeficiency Virus (HIV) infects cells from the immune system and has thus developed tools to circumvent the host immunity and use it in its advance. Dendritic cells (DCs) are the first immune cells to encounter the HIV, and being the main antigen (Ag) presenting cells, they link the innate and the adaptive immune responses. While DCs work to promote an efficient immune response and halt the infection, HIV-1 has ways to take advantage of their role and uses DCs to gain faster and more efficient access to CD4⁺ T cells. Due to their ability to activate a specific immune response, DCs are promising candidates to achieve the functional cure of HIV-1 infection, but knowing the molecular partakers that determine the relationship between virus and cell is the key for the rational and successful design of a DC-based therapy. In this review, we summarize the current state of knowledge on how both DC subsets (myeloid and plasmacytoid DCs) act in presence of HIV-1, and focus on different pathways that the virus can take after binding to DC. First, we explore the consequences of HIV-1 recognition by each receptor on DCs, including CD4 and DC-SIGN. Second, we look at cellular mechanisms that prevent productive infection and weapons that turn cellular defense into a Trojan horse that hides the virus all the way to T cell. Finally, we discuss the possible outcomes of DC-T cell contact.

Antigen processing and presentation in HIV infection

The presentation of virus-derived peptides by MHC molecules constitutes the earliest signals for immune recognition by T cells. In HIV infection, immune responses elicited during infection do not enable to clear infection and correlates of immune protection are not well defined. Here we review features of antigen processing and presentation specific to HIV, analyze how HIV has adapted to the antigen processing machinery and discuss how advances in biochemical and computational protein degradation analyses and in immunopeptidome definition may help identify targets for efficient immune clearance and vaccine immunogen design.

Negative and Positive Selection Pressure During Sexual Transmission of Transmitted Founder HIV-1

Sexual transmission of HIV-1 consists of processes that exert either positive or negative selection pressure on the virus. The sum of these selection pressures lead to the transmission of only one specific HIV-1 strain, termed the transmitted founder virus. Different dendritic cell subsets are abundantly present at mucosal sites and, interestingly, these DC subsets exert opposite pressure on viral selection during sexual transmission. In this review we describe receptors and cellular compartments in DCs that are involved in HIV-1 communication leading to either viral restriction by the host or further dissemination to establish a long-lived reservoir. We discuss the current understanding of host antiretroviral restriction factors against HIV-1 and specifically against the HIV-1 transmitted founder virus. We will also discuss potential clinical implications for exploiting these intrinsic restriction factors in developing novel therapeutic targets. A better understanding of these processes might help in developing strategies against HIV-1 infections by targeting dendritic cells.

HIV-1 Fusion with CD4+ T cells Is Promoted by Proteins Involved in Endocytosis and Intracellular Membrane Trafficking

The HIV-1 entry pathway into permissive cells has been a subject of debate. Accumulating evidence, including our previous single virus tracking results, suggests that HIV-1 can enter different cell types via endocytosis and CD4/coreceptor-dependent fusion with endosomes. However, recent studies that employed indirect techniques to infer the sites of HIV-1 entry into CD4+ T cells have concluded that endocytosis does not contribute to infection. To assess whether HIV-1 enters these cells via endocytosis, we probed the role of intracellular trafficking in HIV-1 entry/fusion by a targeted shRNA screen in a CD4+ T cell line. We performed a screen utilizing a direct virus-cell fusion assay as readout and identified several host proteins involved in endosomal trafficking/maturation, including Rab5A and sorting nexins, as factors regulating HIV-1 fusion and infection. Knockdown of these proteins inhibited HIV-1 fusion irrespective of coreceptor tropism, without altering the CD4 or coreceptor expression, or compromising the virus’ ability to mediate fusion of two adjacent cells initiated by virus-plasma membrane fusion. Ectopic expression of Rab5A in non-permissive cells harboring Rab5A shRNAs partially restored the HIV-cell fusion. Together, these results implicate endocytic machinery in productive HIV-1 entry into CD4+ T cells.

HIV-1 cell-to-cell transmission and broadly neutralizing antibodies

HIV-1 spreads through contacts between infected and target cells. Polarized viral budding at the contact site forms the virological synapse. Additional cellular processes, such as nanotubes, filopodia, virus accumulation in endocytic or phagocytic compartments promote efficient viral propagation. Cell-to-cell transmission allows immune evasion and likely contributes to HIV-1 spread in vivo. Anti-HIV-1 broadly neutralizing antibodies (bNAbs) defeat the majority of circulating viral strains by binding to the viral envelope glycoprotein (Env). Several bNAbs have entered clinical evaluation during the last years. It is thus important to understand their mechanism of action and to determine how they interact with infected cells. In experimental models, HIV-1 cell-to-cell transmission is sensitive to neutralization, but the effect of antibodies is often less marked than during cell-free infection. This may be due to differences in the conformation or accessibility of Env at the surface of virions and cells. In this review, we summarize the current knowledge on HIV-1 cell-to-cell transmission and discuss the role of bNAbs during this process.

Regulation of CD4 Receptor and HIV-1 Entry by MicroRNAs-221 and -222 during Differentiation of THP-1 Cells

Human immunodeficiency virus type-1 (HIV-1) infection of monocyte/macrophages is modulated by the levels of entry receptors cluster of differentiation 4 (CD4) and C-C chemokine receptor type 5 (CCR5), as well as by host antiviral restriction factors, which mediate several post-entry blocks. We recently identified two microRNAs, miR-221 and miR-222, which limit HIV-1 entry during infection of monocyte-derived macrophages (MDMs) by down-regulating CD4 expression. Interestingly, CD4 is also down-regulated during the differentiation of monocytes into macrophages. In this study, we compared microRNA expression profiles in primary monocytes and macrophages by RNAseq and found that miR-221/miR-222 are enhanced in macrophages. We took advantage of the monocytic THP-1 cell line that, once differentiated, is poorly susceptible to HIV-1. Accordingly, we found that CD4 levels are very low in THP-1 differentiated cells and that this down-regulation of the virus receptor is the result of miR-221/miR-222 up-regulation during differentiation. We thus established a THP-1 cell line stably expressing a modified CD4 (THP-1-CD4^R) that is not modulated by miR-221/miR-222. We show that in contrast to parental THP-1, this line is productively infected by HIV-1 following differentiation, sustaining efficient HIV-1 CD4-dependent replication and spread. This new THP-1-CD4^R cell line represents a useful tool for the study of HIV-1-macrophage interactions particularly in contexts where spreading of viral infection is necessary.