Our work mainly focuses on cellular and molecular aspects
of the replication of HIV and Zika virus,
and on the interplay between viruses and the host.
We are investigating how pathogenic viruses, mainly HIV and Zika virus, spread and interact with the host immune system. We are also studying the mechanisms of cell fusion, induced by viruses, or occurring during physiological processes such as the formation of the placenta.
Three close and complementary axes of research characterize our scientific activities. We are currently studying:
An artistic view of cells and viruses drawings by Fabrice HYBER
When scientists meet artists: http://www.organoide-pasteur.fr
Virus and Immunity Unit
June 2019 Lab meeting with Alumni
About 40 years after its appearance, the HIV/AIDS epidemic represents more than ever a public health threat worldwide. About 38 million people are living with HIV/AIDS as of the end of 2018, most of them originating from emerging countries. Our work focuses on cellular and molecular aspects of HIV-1 replication, and on the mechanisms of the interaction of HIV-infected cells with the immune system.
We are studying viral cell-to-cell spread. Direct cell-to-cell transfer represents a potent and rapid mode of viral propagation, which involves the formation of virological synapses between infected donor cells and uninfected recipients. We are examining the role of cellular and viral proteins which facilitate viral spread. We are deciphering the underlying mechanisms.
HIV cell-to-cell transfer in lymphocytes (HIV in green, target cell in blue)
HIV budding at the contact zone between one infected and one target cell
We are also studying the role of the viral protein Nef, which facilitates viral replication by interfering with the antiviral activity of cellular proteins (SERINC proteins), and which also modulates the trafficking of proteins, such as MHC-I that are involved in immune responses.
MHC-I intracellular localization in non-infected (right) and Nef-expressing lymphocytes
We are also examining how cellular proteins may inhibit viral spread. These proteins are called restriction factors and are often induced by type-I Interferons. We are studying for instance the role of IFITMs (Interferon induced Transmembrane proteins), which impair viral fusion and then access of incoming virions to the cytoplasm. Our aim is to understand how IFITM proteins inhibit HIV-1 replication and how the virus counteracts this effect.
Movie: Real time imaging of HIV-1 cell-to-cell transmission (from https://www.ncbi.nlm.nih.gov/pubmed/19369333).
Strategies to eliminate the HIV-1 reservoir
In collaboration with the teams of Hugo Mouquet (Institut Pasteur), and Olivier Lambotte (Bicêtre Hospital), we have demonstrated that bNAbs act in complementary ways. Firstly, they neutralize both cell-free virions and direct cell to cell viral spread. Secondly, the most potent bNAbs bind infected cells and trigger so called effector functions mediate by the Fc domain of the antibody.
We have shown that some bNAbs trigger the destruction of infected cells by Natural Killer (NK) cells through a process termed antibody-dependent cellular cytotoxicity (ADCC). We are currently studying how bNAbs activate the complement pathway at the surface of infected cells.
The complement is a network of proteins initially described for its ability to induce cell toxicity. Due to its ancestral origin, the complement is highly intricated within innate and adaptive immune systems. Complement deposition at the plasma membrane triggers intrinsic signaling pathways impacting cell fate or activation.
Our current aims are to study the mechanisms of ADCC and complement deposition by bNAbs and to further assess the ability of bNAbs to clear the HIV-1 reservoir, in cells from patients under successful antiretroviral treatment.
Overall, this project should provide new insights into the activity of antibodies during HIV-1 infection. More generally, it will also help define the mechanisms of antibody-based therapeutic strategies.
Example of HIV-1-infected cell killing by NK cells: An HIV-1 infected cell (green) and NK (smaller dark cells) are incubated with a bNAb and trapped in a microwells. A picture is taken every 5 minutes. A blue dye reveals the dying cell (Bruel et al. 2016)
The Zika virus (ZIKV) epidemics in South East Asia, French Polynesia, the Caribbean islands and the Americas, and its association with neurological disorders including Guillain-Barré syndrome and microcephaly and other defects in newborns have triggered a global public health response. ZIKV infection mainly occurs after a bite by infected Aedes mosquitoes, through maternal–fetal transmission, and less frequently by sexual transmission. In 2017, evidence of vector-borne ZIKV transmission have been reported in about 85 countries or territories.
The innate immune response controls viral spread and disease development in most of infected individuals, through mechanisms that are not clearly understood. We are studying the cytopathic effect of the virus, that is to say the morphological changes of the cell, to understand what happens once the virus replicates. We recently observed that the infected cell reacts by forming massive intracellular vacuoles which leads to the death of the cell. This phenomenon of cellular destruction is mainly visible in the absence of the protein IFITM3. These observations are made in the cells naturally targeted by the virus, including epithelial cells, fibroblasts of the skin and brain astrocytes.
These observations are made in the cells naturally targeted by the virus, including epithelial cells, fibroblasts of the skin and brain astrocytes.
Our aim is to understand how Zika virus replicates despite this massive cytopathic effect, and to further describe the protective innate response of the host.
We are using video microscopy electron microscopy and other techniques to address these questions.
Zika Virus particles accumulating in infected cells, visualized by electron microscopy. Scientific image by Université François Rabelais, Tours and Institut Pasteur, Paris, France
Cell infected with Zika virus (cytopathic effect), with massive vacuoles (holes). In red: viral protein. In green: cell. In blue: nucleus. Immunofluorescence microscopy (Institut Pasteur).
ZIKV modifies the morphology of the cells and makes them implode. Example of HeLa cells.
ZIKV modifies the morphology of the cells and makes them implode. Example of primary human skin fibroblasts.
High-risk pregnancies occur frequently and may be caused by various factors. It is estimated that 10 to 20% of pregnant women miscarry during their first trimester of pregnancy, and 10% will experience pre-term birth. Slow fetal growth may also arise as a result of maternal infection with certain microbes, parasites or viruses (such as toxoplasmosis or infection with rubella virus, cytomegalovirus, herpes or Zika) or because of genetic or autoimmune diseases. We have identified a new cellular mechanism that alters placental development, potentially causing serious complications during pregnancy. The mechanism is linked with interferon, a molecule produced in response to infection, especially viral infection. The placenta is both a surface for exchange and a barrier between mother and fetus – it delivers nutrients needed for fetal growth, produces hormones and protects the fetus from microbes and the maternal immune system. The external layer of the placenta, the syncytiotrophoblast is composed of cells which fuse together, forming giant cells that are optimized for the placenta’s barrier and exchange functions. If the syncytiotrophoblast fails to form correctly, it can cause placental insufficiency and hinder fetal development.
Interferon is a substance produced by immune cells during infection to combat viruses and other intracellular microbes. High levels of interferon are also observed in autoimmune or inflammatory diseases such as lupus. Exaggerated levels of interferon are responsible for placental abnormality. We demonstrated that interferon induces the production of a family of cellular proteins known as IFITMs (interferon-induced transmembrane proteins), which block cell fusion. Our aim is to understand the mechanism of formation of the placenta under normal or pathological conditions, the mechanism of action of IFN and IFITM, and to study means to prevent placental defects.
Human cells fusing and forming syncytia (green area) when the Syncytin protein is expressed (left). This process is inhibited by IFITM2 (right). (Buchrieser et al, 2019)
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