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Projects

Research in my laboratory addresses the cell biology, immunology and pathogenesis of HIV-1 infection. One focus of our studies is on the molecular mechanisms of action by which the HIV-1 pathogenicity factor Nef reprograms host cell vesicular transport, signal transduction and motility. Another emphasis is on the impact of the host innate immune system in HIV infection and on viral evasion mechanisms. This includes dissecting how the intrinsic immunity factor CD317/BST-2/tetherin impairs HIV-1 particle release and how this activity is antagonized by the viral protein Vpu, but also studies to elucidate which barriers prevent productive HIV-1 infection of resting CD4+ T lymphocytes. Finally, we are also addressing cell biology problems related to actin dynamics with a focus on the molecular biology and physiological role of the actin-nucleating diaphanous-related formins (DRFs). In this context we particularly focus on the DRF FHOD1 and its role in cell motility and polarization.

 

 

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1) Molecular mechanisms of the HIV-1 pathogenicity factor Nef

The Nef protein of HIV and SIV is critical for high virus load and full pathogenicity in the infected host. This pathogenic potential is underscored by a transgenic mouse model in which the expression of Nef alone causes an AIDS-like disease. This activity renders Nef an attractive target for antiviral strategies to complement existing treatment. Nef does not possess detectable enzymatic activity and mediates all its functions via interactions with host cell or other viral proteins. While a multitude of activities have been ascribed to Nef, the biological properties and protein-interactions that govern its pathogenic potential have still not been unambiguously identified. Nef`s activities can be divided into immune evasion functions and effects that directly boost viral spread in the absence of host immune attacks. Both these general Nef activities are achieved by manipulation of host cell signal transduction and intracellular transport processes. Our work focusses on visualizing and dissecting the independent molecular mechanisms employed by which Nef disrupts host cell vesicular transport, actin remodeling, and motility. This increasingly involves the use of complex primary cell culture models and in vivo analyses in mice.

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Fig. 1: Nef interferes with transendothelial migration of T lymphocytes ex vivo and in vivo. A: Transmigration of control (red) or Nef-expressing (blue) T lymphocytes across an endothelium under shear flow ex vivo. B: Migration of T lymphocytes in or near high endothelial venules as visualized by intravital 2-photon microcscopy in popliteal lymph nodes of mice following adoptive transfer of control (orange) or Nef-expressing (blue) T lymphocytes (Stolp et al., 2012, PNAS 109:18541-18546).
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2) The intrinsic immunity factor CD317 and antagonism by HIV-1 Vpu

Mammals have evolved a set of cellular defense mechanisms that, often upon induction by type-I interferons (INF), are capable of inhibiting the replication of viral pathogens. These restriction factors impose particularly effective barriers in the context of cross-species transmission of viruses and are thought to act as “intrinsic” immunity defense in an immunologically naïve host. As an important characteristic of such factors, fine-tuned evolution gave raise to highly species-specific adaptation between host and pathogen. CD317 (also referred to as BST-2/HM1.24/tetherin) represents such a host cell innate immunity factor that potently blocks the release of mature HIV-1 particles but also that of other retroviruses as well as Ebola, Marburg, and Lassa virus from productively infected cells. To circumvent this antiviral defense, viral pathogens acquired antagonists that counteract the replication block imposed by CD317, an activity that is exerted by the protein Vpu in the case of HIV-1. We and others have shown that Vpu alters intracellular transport routes of CD317 to antagonize its antiviral activity and we currently investigate the underlying molecular mechanisms. Additional efforts address evolutionary aspects of CD317 restriction and antagonism.

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Fig.2: Model of action of CD317 restriction to HIV-1 particle release and Vpu antagonism.
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3) HIV infection of resting CD4+ T lymphocytes

HIV-1 infects CD4+ T lymphocytes and cells of the monocytes/macrophage lineage. In the case of primary human CD4+ T lymphocytes, the permissivity to HIV-1 infection ex vivo depends on the cellular activation state: while activated, proliferating CD4+ T lymphocytes are highly susceptible to infection and support efficient virus replication, resting CD4+ T cells are largely non-permissive for HIV-1 replication but can be infected in vivo and serve as a latent viral reservoir. Since physiologically the vast majority of all CD4+ T lymphocytes are in a resting state, this phenomenon provides one explanation as to why the frequency of productively infected CD4+ T lymphocytes in AIDS patients is very low. In collaboration with Prof. Dr. Oliver T. Keppler (Goethe Universität Frankfurt/Main) we identified the deoxynucleoside triphosphate (dNTP) triphosphohydrolase SAMHD1 (sterile alpha motif (SAM) and histidine/aspartic acid (HD) domain-containing protein 1) as an essential host cell factor for this restriction that can be overcome by the Vpx protein encoded by HIV-2 and SIV (Baldauf, Pan et al., 2012, Nat. Med. 18: 1682-1687). Our current efforts focus on the mechanisms of restriction and antagonism and on the dissection of additional blocks to HIV-1 replication in resting CD4+ T cells.

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Fig. 3: Schematic model of HIV-1 replication and restrictions thereof in activated and resting CD4+ T lymphocytes (Pan et al., 2013 Cell Research 23:876-885).
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4) Cellular mechanisms of actin dynamics

The astonishing dynamics of the actin cytoskeleton provides the basis for fundamental processes in mammalian cells such as motility, kinesis, vesicular transport and signal transduction. Celluar actin polymerization depends on the coordinated action of molecular machines that drive formation of actin filaments. Diaphanous-related formins (DRFs) constitute a family of Rho GTPase-regulated proteins that typically stimulate nucleation and/or elongation of linear actin filaments required for structures such as filopodia, lamellipodia and contractile rings. Despite similar domain organization and sequence homology to other formins, the DRF FHOD1 does not nucleate or elongate actin filaments, but rather bundles them. The goal of our research is to define physiological roles and regulation of FHOD1. In collaboration with Prof. Gregg Gundersen (Columbia University New York) we recently identified FHOD1 as an essential component of the actin-based machinery that drives movement of the cell nucleus and positions the centrosome in migrating fibroblasts (Kutscheidt et al., 2014, Nat. Cell Biol. 16: 708-715). Our current studies focus on dissecting the mechanisms underlying this phenomenon.  

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Selected Publications

Complete Publication List (PubMed)

 

 

Kluge, S.F., Mack, K., Iyer, S.S., Pujol, F.M., Heigele, A., Learn, G.H., Usmani, S.H., Sauter, D., Joas, S., Hotter, D., Bibollet-Ruche, F., Plenderleith, L.J., Peeters, M., Geyer, M., Sharp, P.M., Fackler, O.T., Hahn, B.H. and Kirchhoff, F. (2014). Nef proteins of epidemic HIV-1 group O strains antagonize human tetherin. Cell Host Microbe, 5: 639–650.

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Haller, C., Müller, B., Fritz, J.V., Lamas-Murua, M., Stolp, B., Pujol, F., Keppler, O.T. and Fackler, O.T. (2014). HIV-1 Nef and Vpu are Functionally Redundant Broad-Spectrum Modulators of Cell Surface Receptors Including Tetraspanins. J. Virol., 88: 14241-14257.

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Fackler, O.T. *, Murooka, T.T., Imle, A. and Mempel, T.R.*(2014) Adding new dimensions: Towards an integrative understanding of HIV-1 spread. (* corresponding authors). Nat. Rev. Microbiol., 12:563-574.

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Kutscheidt, S+., Zhu, R. +, Antoku, S. +, Luxton, G.G.W., Stagljar, I., Fackler, O.T. * and Gundersen, G. * (2014). FHOD1 interaction with nesprin-2G mediates TAN line formation and nuclear movement (+ first authors, * corresponding authors). Nat. Cell Biol. 16: 708-715.

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Geist, M.M., Pan, X., Bender, S., Bartenschlager, R., Nickel, W and Fackler, O.T. (2014). Heterologous Src Homology 4 Domains Support Membrane Anchoring and Biological Activity of HIV-1 Nef. J. Biol. Chem. 289:14030-44.

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Fackler, O.T. and Keppler, O.T. (2013). MxB/Mx2: The latest piece in HIV’s interferon puzzle. Embo Rep. 14: 1030 – 1031.

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Pan, X., Baldauf, H.M., Keppler, O.T. and Fackler, O.T. (2013). Restrictions to HIV-1 Replication in Resting CD4+ T Lymphocytes. Cell Research, 23: 876-885.

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Floyd, S., Whiffin, N., Gavilan, M.P., Kutscheidt, S., De Luca, M., Watkins, J., Chung, K., Fackler, O.T. and Lindon, C. (2013). Spatiotemporal organization of Aurora-B by APC/C-Cdh1 coordinates cell spreading via FHOD1 after mitosis. J. Cell Sci., 126: 2845-2856.

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Pan, X., Geist, M., Rudolph, J.M., Nickel, W. and Fackler, O.T. (2013). HIV-1 Nef Disrupts Membrane-Microdomain-associated Anterograde Transport for Plasma Membrane Delivery of Selected Src Family Kinases. Cell. Microbiol., 15:1605-1621.

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Baldauf, H-M.+, Pan, X.+, Erikson, E., Schmidt, S., Daddacha, W., Burggraf, M., Schenkova, K., Ambiel, I., Wabnitz G., Gramberg, T., Panitz, S., Flory, E., Landau, N.R., Sertel, S., Rutsch, F., Lasitschka, F., Kim, B., König, R., Fackler, O.T.* and Keppler, O.T.* (2012). The deoxynucleoside triphosphate triphosphohydrolase SAMHD1 restricts HIV-1 infection in resting CD4+ T cells. Nat. Med., 18: 1682-1687 (* corresponding authors, + first authors).

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Stolp, B., Imle, A., Coelho, F.M., Hons, M., Mendiz, R.G., Lyck, R., Stein, J.V. and Fackler, O.T. (2012). HIV-1 Nef Interferes With T Lymphocyte Circulation Through Confined Environments in vivo. Proc. Natl. Acad. Sci. USA, 109: 18541–18546.

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Abraham, L. and Fackler, O.T. (2012). HIV-1 Nef: a multifaceted modulator of TCR signaling. Cell Communication and Signaling, 10:39.

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Sauter, D., Unterweger, D., Vogl, M., Usmani, S.M., Heigele, A., Kluge, S.F., Hermkes, E., Moll, M., Barker, E., Peeters, M., Learn, G.H., Fritz, J.V., Fackler, O.T., Hahn, B.H. and Kirchhoff, F. (2012). Human Tetherin Exerts Strong Selection Pressure on the HIV-1 Group N Vpu Protein. PLoS Pathogens, 8: e1003093.

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Götz, N., Sauter, D., Usmani, S.M., Fritz, J.V., Goffinet, C., Heigele, A., Geyer, M., Bibollet-Ruche, F., Learn, G.H., Fackler, O.T., Hahn, B.H. and Kirchhoff, F. (2012). Reacquisition of Nef-Mediated Tetherin Antagonism in a Single In Vivo Passage of HIV-1 Through Its Original Chimpanzee Host. Cell Host Microbe, 12: 373-380.

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Abraham, A., Bankhead, P., Pan, X., Engel, U. and Fackler, O.T. (2012). HIV-1 Nef Limits Communication Between LAT and SLP-76 to Reduce Formation of SLP-76 Signaling Microclusters Following TCR Stimulation. J. Immunol., 189: 1898–1910.

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Meuwissen, P. J., Stolp, B., Ianucci, V., Vermeire, J., Naessens, E., Saksela, K., Geyer, M., Vanham, G., Arien, K., Fackler, O.T. and Verhasselt, B. (2012). Identification of a highly conserved valine-glycine-phenylalanine amino acid triplet required for HIV-1 Nef function. Retrovirology, 9: 34.

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Fritz, J.V., Tibroni, N., Keppler, O.T. and Fackler, O.T. (2012). Membrane Microdomain Association of HIV-1 Vpu is Dispensable for Counteracting the Particle Release Restriction Imposed by CD317/BST-2/Tetherin. Virology, 424: 33–44.

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Pan, X., Rudolph, J.M., Abraham, L., Habermann, A., Haller,C., Krijnse-Locker, J. and Fackler, O.T. (2012). HIV-1 Nef Compensates Disorganization of the Immunological Synapse by Assembly of an Intracellular Lck Signalosome. Blood; 119: 786-797.

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Stastna, J., Pan, X.Y., Wang, H., Kollmannsperger, A., Kutscheid, S., Lohmann, V., Grosse, R. and Fackler, O.T. (2012). Differing and isoform specific roles for the formin DIAPH3 in plasma membrane blebbing and filopodia formation. Cell Research, 22: 728–745.

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Schmidt, S., Fritz, J.V., Bitzegeio, J., Fackler, O.T. *, and Keppler, O.T*. (2011). HIV-1 Vpu Blocks Recycling and Biosynthetic Transport of the Intrinsic Immunity Factor CD317/Tetherin to Overcome the Virion Release Restriction. (* corresponding authors). mBio, 2: e00036-11.

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Breuer, S., Schievink, S.I., Schulte, A., Blankenfeldt, W., Fackler, O.T. * and Geyer, M.* (2011). Molecular design, functional characterization, and structural basis of a protein inhibitor against the HIV-1 pathogenicity factor Nef. (* corresponding authors). PlosOne, 6: e20033.

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Stolp, B. and Fackler, O.T. (2011). How HIV takes advantage of the cytoskeleton in entry and replication. Viruses, 3: 293-311.

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Tervo, H.M., Homann, S., Ambiel, I., Fritz, J.V., Fackler, O.T. * and Keppler, O.T. * (2011). ß-TrCP is Dispensable for Vpu’s Ability to overcome the CD317/Tetherin-imposed restriction to HIV-1 release. (* corresponding authors). Retrovirology, 8:9.

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Goffinet, C., Homann, S., Ambiel, I., Tibroni, N., Rupp, D., Keppler O.T. and Fackler, O.T. (2010). Antagonism of CD317 restriction of HIV-1 particle release and depletion of CD317 are separable activities of HIV-1 Vpu. J. Virol., 84: 4089-4094.

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Stolp, B., Abraham, L., Rudolph, J.M. and Fackler, O.T. (2010). Lentiviral Nef Proteins Utilize PAK2-mediated Deregulation of Cofilin as a General Strategy to Interfere with Actin Remodeling. J. Virol., 84: 3935-3948.

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Stolp, B., Abraham, L., Rudolph, J.M. and Fackler, O.T. (2010). Lentiviral Nef Proteins Utilize PAK2-mediated Deregulation of Cofilin as a General Strategy to Interfere with Actin Remodeling. J. Virol., 84: 3935-3948.

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Rudolph, J.M.; Eickel, N., Haller, C., Schindler, M. and Fackler, O.T. (2009). Inhibition of T cell receptor induced actin remodeling and relocalization of Lck are evolutionarily conserved activities of lentiviral Nef proteins. J. Virol., 83: 11528-11539.

Stolp, B., Raichman-Fried, M., Abraham. L., Pan, X., Giese, S.I., Hannemann, S., Goulimari, P., Raz, E., Grosse, R. and Fackler, O.T. (2009). HIV-1 Nef interferes with host cell motility by deregulation of cofilin. Cell Host and Microbe 6:174-186

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Goffinet, C., Allespach, A, Homann, S., Tervo, H-M., Habermann, A., Rupp, D., Oberbremer, L., Kern, C., Tibroni, N., Welsch, S., Krijnse-Locker, J., Banting, G., Kräusslich, H.G., Fackler, O.T. and Keppler, O.T. (2009). HIV-1 Antagonism of CD317 is Species-Specific and Involves Vpu-Mediated Proteasomal Degradation of the Restriction Factor. Cell Host and Microbe, 5: 285-297.

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Homann, S., Tibroni, N., Baumann, I., Sertel, S., Keppler, O.T. and Fackler, O.T. (2009). Determinants in HIV-1 Nef for enhancement of viral replication and depletion of CD4+ T-lymphocytes in human lymphoid tissue ex vivo. Retrovirology, 6: 6.

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Schulte, A., Stolp, B., Schönichen, A., Pylypenko, O., Rak, A., Fackler, O.T. and Geyer, M. (2008). Structure of the N-terminal region of the formin FHOD1 reveals a bipartite organization of FH3 and GTPase-binding domains. Structure, 16:1313-1323.

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Hannemann, S., Madrid, R., Stastna, J., Kitzing, T., Gasteier, J., Schönichen, A., Bouchet, J., Jimenez, A., Geyer, M., Grosse, R., Benichou, S. and Fackler, O.T. The Diaphanous Related Formin FHOD1 Associates with ROCK1 and Promotes Src-dependent Plasma Membrane Blebbing. J. Biol. Chem., 283: 27891-27903.

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Haller, C. and Fackler, O.T. (2008). HIV-1 at the immunological and T lymphocytic virological synapse. Biol. Chem., 389: 1253-1260

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Fackler, O.T. and Grosse, R. (2008). Cell motility through plasma membrane blebbing. J. Cell Biol. 181: 879 

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Rauch, S., Pulkkinen, K., Saksela, K., and Fackler, O.T. (2008). HIV-1 Nef Recruits the Guanine Exchange Factor Vav1 via an Unexpected Interface into Plasma Membrane Microdomains for Association with Pak2 Activity. J. Virol., 82: 2918-2929.

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Haller, C., Rauch, S. and Fackler, O.T. (2007). HIV-1 Nef employs two distinct mechanisms to modulate Lck subcellular localization and TCR induced actin remodeling. PLoSONE, 2: e1212

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Tournaviti, S., Hannemann, S., Terjung, S., Kitzing, T.M., Stegmayer, C., Ritzerfeld, J., Walther, P., Grosse, R., Nickel, W. and Fackler, O.T. (2007). SH4 Domain-induced Plasma Membrane Dynamization Promotes bleb-associated Cell Motility. J. Cell Sci. 120: 3820-3829.

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Brügger, B., Krautkrämer, E., Tibroni, N., Munte, C.E., Rauch, S., Leibrecht, I., Glass, B., Breuer, S., Geyer, M., Kräusslich, H.G., Kalbitzer, H.R., Wieland, F.T. and Fackler, O.T. (2007). Human Immunodeficiency Virus Type 1 Nef Protein Modulates the Lipid Composition of Virions and Host Cell Membrane Microdomains. Retrovirology, 4: 70.

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Fackler, O.T.*, Alcover, A. and Schwartz, O.* (2007). Modulation of the Immunological Synapse: A key to HIV-1 pathogenesis? (* corresponding authors). Nat. Rev. Immunol. 7: 310-317.

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Haller, C., Rauch, S., Michel, N., Hannemann, S., Keppler, O.T. and Fackler, O.T. (2006). The HIV-1 pathogenicity factor Nef interferes with maturation of stimulatory T-lymphocyte contacts by modulation of N-Wasp activity. J. Biol. Chem. 281: 19618-19630.

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Fackler, O.T.*, Moris, A., Tibroni, N., Giese, S.I., Glass, B., Schwartz, O. and Kräusslich, H.G. (2006). Functional characterization of HIV-1 Nef mutants in the context of viral infection. (* corresponding author). Virology 351: 332-339.

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Gasteier J.E., Madrid R., Krautkrämer E., Schröder S., Muranyi W., Benichou S. and Fackler O.T. (2003). Activation of the Rac interaction partner formin homology 2 domain containing 1 (FHOD1) induces actin stress fibers via a ROCK dependent mechanism. J. Biol. Chem. 278: 38902-38912.

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Fackler O.T. and Baur A.S. (2002). Live and let die: Functions of Nef beyond HIV replication. Immunity 16: 493-497.

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Geyer M., Fackler O.T., and Peterlin B.M. (2001). Structure-Function Relationship in HIV-1 Nef. EMBO Rep. 2: 580-585.

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Fackler O.T., Luo W., Geyer M., Alberts A.S. and Peterlin B.M. (1999). Activation of Vav by Nef induces cytoskeletal rearrangements and downstream effector functions. Mol. Cell 3: 729-739.

 

 

 

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Group members

Oliver T. Fackler, Ph.D., Prof.

Email: oliver.fackler@med.uni-heidelberg.de

Phone: ++49-(0)6221-56-1322

Fax: ++49-(0)6221-56-5003

 


Claudia Haller, project coordinator Email: claudia.haller@med.uni-heidelberg.de Phone: ++49-(0)6221-56-5006


Amanda Chase, postdoc Email: amanda.chase@med.uni-heidelberg.de Phone: ++49-(0)6221-56-1321

Johanna Galaski, MD student Email: johanna.galaski@med.uni-heidelberg.de Phone ++49-(0)6221-56-1327

Miriam Geist, postdoc Email: miriam.geist@med.uni-heidelberg.de Phone: ++49-(0)6221-56-1327 

Andrea Imle, PhD student Email: andrea.imle@med.uni-heidelberg.de Phone: ++49-(0)6221-56-1327 

Stefan Kutscheidt, postdoc Email: stefan.kutscheidt@med.uni-heidelberg.de Phone: ++49-(0)6221-56-1321 

Miguel Lamas, PhD student Email: miguel.lamas@med.uni-heidelberg.de Phone: ++49-(0)6221-56-1327    

Birthe Müller, PhD student Email: Birthe.Mueller@med.uni-heidelberg.de Phone: ++49-(0)6221-56-1327 

Francois Pujol, postdoc Email: Francois.Pujol@med.uni-heidelberg.de Phone: ++49-(0)6221-56-1327

Tatjana Reif, PhD student Email: tatjana.reif@med.uni-heidelberg.de Phone: ++49-(0)6221-56-1321 

Bettina Stolp, postdoc Email: bettina.stolp@med.uni-heidelberg.de Phone: ++49-(0)6221-56-1327

Nadine Tibroni, research associate Email: nadine.tibroni@med.uni-heidelberg.de Phone: ++49-(0)6221-56-1327 

Maud Trotard, postdoc Email: Maud.Trotard@med.uni-heidelberg.de Phone: ++49-(0)6221-56-1321 

Nikolaos Tsopoulidis, PhD student Email: Nikolaos.Tsopoulidis@med.uni-heidelberg.de Phone: ++49-(0)6221-56-1321 

Rebecka Wombacher, PhD student Email: rebecka.wombacher@med.uni-heidelberg.de Phone: ++49-(0)6221-56-1327

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Former lab members: 

Libin Abraham (postdoc, University of British Colombia, Vancouver)

Jingyan Chen

Judith Gasteier (technical leader, Abbot)

Simone Giese 

Sebastian Hannemann (postdoc, Yale University)

Stefanie Homann (postdoc, University of California, San Diego)

Ellen Krautkrämer (postdoc, University Hospital Heidelberg)

Joelle Fritz (postdoc, University of Luxembourg)

Xiao-Yu Pan (senior scientist, manager, Boehringer Ingelheim, Shanghai)

Susanne Rauch (postdoc, King's College, London)

Jochen Rudolph  (postdoc, Universität Magdeburg)

Jana Stastna

Ilka Wörz 

Yaz Woo

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