Projects Innate Immunity and Viral Evasion

Projects Innate Immunity and Viral Evasion

Cellular Restriction factors of HIV-1 Infection

DFG Collaborative Research Centre 900 Chronic Infections: "Microbial Persistence and its Control", project C8

After recognition of pathogen-associated molecular patterns (PAMPs) by infected cells, interferons are synthesized, secreted and bind the interferon receptor on neighboring cells to „alarm“ them from an upcoming virus invasion. Binding induces a signaling cascade that ultimately results in synthesis of several interferon-stimulated genes, so-called ISGs (“interferon-stimulated genes”). ISGs comprise many antiviral genes, including those encoding APOBEC3G, a cellular deaminase which hypermutates the viral genome, or Tetherin, which prevents release of mature virions from the producer cell´s surface. Another ISG is lgals3bp, which encodes for the cellular glycoprotein 90K. Previous work of our group demonstrated the antiviral potency of 90K against HIV. Specifically, 90K reduces the infectivity of newly assembled virions by interfering with the viral incorporation of HIV Envelope proteins (Lodermeyer et al., Retrovirology 2013).  Using truncated versions of 90K, we plan to define which domains/regions within 90K are essential and sufficient for its antiviral function. In parallel, 90K orthologs from non-human species, which share a high degree of homology with human 90K, but differ in their antiviral capability, are useful tools for the elucidation of the antiviral mechanism. Further, they shed light on the evolutionary conservation of 90K´s antiviral function. (Lodermeyer et al., Journal of Virology 2018) The long-term perspective is to pave avenues towards a new antiviral treatment strategy.
SERINC5 reduces the infectivity of HIV-1 particles by interfering with the fusogenicity of HIV-1 Env glycoproteins. The accessory protein HIV-1 Nef counteracts the antiviral effect of SERINC5. Via CRISPR/Cas9-mediated gene editing, we created T-cell lines expressing serinc5 alleles bearing a knocked-in HA-coding sequence. Using this unique tool, we study basic characteristics of endogenous SERINC5 expression and modes of Nef-mediated antagonism. A better understanding of SERINC5 restriction helps to identify vulnerable steps of the HIV-1 replication cycle, which may be targeted therapeutically.

A novel approach for eradicating HIV

Gilead Infectiology Programme 2016 (Cooperation with Prof. Georg Behrens, MHH)

Latently infected cells produce no viral products and remain invisible to the immune system. A “shock and kill” strategy of transcription induction (“shock”) with subsequent cell elimination (“kill”) has been proposed to reduce or even eradicate the HIV-1 reservoir. While reactivation of HIV-1 from the reservoir (shock) is mostly pursued by pharmacological interventions such as histone deacytelase inhibitors (HDACi), the elimination of cells which are in the process of reactivation (kill) is believed to be best achieved by immune-mediated mechanisms. Our proposed experiments are crucial to confirm autophagy as novel therapeutic targets in cells with incomplete reactivation of provirus. Our project provides an alternative to the predominantly immune-based strategies. The project has the potential to identify novel cellular pathways for efficient reduction of the HIV reservoir. An important translational aspect is that we focus on available and licensed compounds for rapid evaluation in patients/animal models if proven effective in the preclinical evaluation.

Characterisation of the cGAS-mediated DNA-sensing signaling in HIV infected T-cells

DFG Priority Programme 1923, "Innate Sensing and Restriction of Retroviruses"

Upon HIV-1 infection of T-cells, viral DNA can be sensed by the cytosolic DNA sensor cGAS. In cocultures with macrophages, HIV-1 Env-mediated membrane fusion pores allow the horizontal transfer of the cGAS product and cyclic dinucleotide cGAMP to macrophages, where it activates STING-dependent expression of antiviral cytokines and effector molecules (Xu und Ducroux et al., Cell Host & Microbe 2016). In monocultures of T-cells and macrophages, HIV-1 prevents or counteracts activation of this cellular defense mechanism. In contrast to the situation in macrophages, our understanding of the reasons for the lack of a detectable type I IFN response in HIV-1-infected T-cells is limited. In this project, we address the effectiveness of the cGAS-mediated DNA sensing pathway in primary T-cells and try to unravel potential explanations for the lack of IFN induction in this important HIV-1 target cell type.

Fluorescent dye-labelled, HIV-1 Env-expressing T-cells (green) and primary macrophages (red) exchange dye at distinct contact sites (white signal), presumably via HIV-1 Env-CD4/coreceptor-mediated fusion pores.

The interplay of Mycobacterium tuberculosis and HIV-1 in co-infected human macrophages and its impact on cell-intrinsic innate immunity

Boehringer Ingelheim Foundation Exploration Grant

Human co-infection by Mycobacterium tuberculosis (M.tb) and HIV-1 occur at unprecedented scale and pose tremendous health care challenges. While the immune responses to infection by each individual pathogen have been extensively studied, the functional interplay of M.tb and HIV-1 in a co-infect host has remained largely ignored. In this project, we are aiming at solving the complex interplay of these two co-existing human pathogenic infections in the context of the cell-intrinsic innate immunity raised in co-infected human macrophages. How do these two pathogens perform in a co-infected cell? Are they friends or foes? Results of this project may pave new avenues towards new therapeutic and/or protective strategies specifically tailored to combatting HIV-1/M.tb-coinfection in vivo.

Cell Entry and Immunological Restriction of Chikungunya Virus

Chikungunya virus is an emerging pathogen which has been spreading from Africa to other tropical and subtropical regions worldwide, but also to colder areas such as southern Europe and North America. Due to its ability to cause acute symptoms such as high fever, but also chronic suffering such as severe arthritic joint pain, specific treatments and prophylactic options need to be established. Therefore, we aim to study the cell attachment and entry process as well as cellular restriction by antiviral proteins and interferon stimulated genes. Using a range of different reporter viruses and pseudotyped lentiviral particles, we can dissect the steps of the infection from the binding to the host cell to the production of new viral particles and study its cell type and tissue tropism. Together with Dr. Eduardo Samo Gudo, NIH Maputo, Mozambique, we are investigating the genetic variability of this rapidly mutating virus and searching for immunological and genetic correlates of chronicity and reconvalescence in infected patients.  Finally, in cooperation with Prof. Eike Steinmann (TWINCORE and University of Bochum) we are investigating the stability of CHIKV and testing disinfection methods for inactivation of this virus (Franz et al., Journal of Infectious Diseases, 2018).