Natascha Teufert

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B1 STAT-Activation in T-cell growth transformation

Principal investigator
Armin Ensser

Mentor
Andrea Kress

Virus transformed human natural killer (NK) cell lines – a model for functional analysis

Natural killer (NK) cells

NK cells are effector lymphocytes and part of the innate immunity. They have important functions in limiting the spread and subsequent tissue damage of several tumors and microbial infections. NK cells represent about 2-18% of total lymphocytes in normal human peripheral blood and could be distinguished from B and T lymphocytes by a CD3-/CD56+phenotype. Via secretion of IFN-γ and TNF they communicate with dendritic cells (DCs), T cells, macrophages and endothelial cells. The natural life span of NK cells in the human body is about two weeks and their potential to kill tumor or viral or bacterial infected cells without further stimulation is tightly controlled by an interaction of activating and inhibitory cell surface receptors. NK cell activation is induced by stress-induced self-ligands (e.g. UL-16 binding proteins (ULBPs) or MHC class I chain-related (MIC) molecules), Toll-like receptor (TLR) ligands and infectious non-self-ligands. There are two different mechanisms to kill specific target cells: granule-dependent killing and killing by death ligands (Fig.1). Furthermore, NK cell activity and cytotoxicity can be achieved through interferons and macrophage derived cytokines, which leads to a secretion of IFNγ and TNFα. NK cell inactivity is mediated by MHC class I-specific inhibitory receptors. Every normal single cell expresses activating as well as inhibitory ligands on their cell surface, maintained in a healthy balance. Processes like oncogenesis, missing-self recognition or bacterial or viral infections lead to an imbalance and down regulation of inhibitory ligands and thus to NK cell activation and target cell lysis.

Natural killer (NK) cells and Herpesvirus saimiri (HVS)

Herpesvirussaimiri is a T lymphotropic g2-herpesvirus (rhadinovirus) and due to its oncogenic potential is further be divided into the subgroups A, B and C. Viruses of substrain C, in particular strain C488, are able to transform human T lymphocytes in vitro into an interleukin (IL)-2-independent growth. Our group discovered that also NK cells are infected and transformed by HVS. These NK cell lines proliferate under high doses of IL-2 over months and show specific cytotoxicity comparable to untransformed NKs.
Currently, the hardest problem in NK cell research is the very short lifespan of these cells. There are only a few permanent NK-like cell lines available. All but one of these lines derived from NK cell leukemia or lymphoma patients and lack important features of normal NK cells. Moreover, they are very difficult to cultivate and require several specific interleukins such as IL-7, IL-12 and IL-2. By transforming the cells with HVS it is possible to overcome these obstacles.
In this project we will investigate the cytotoxicity of our transformed human NK cell lines against established tumor cells from acute myeloid leukemias and solid tumors as well as against freshly isolated tumor cells from patients. Furthermore, the anti-neoplastic activity and the cytotoxic potential of the NK lines are examined in vivo in a mouse xenotransplantation model. Another part of this project is the generation of patient specific autologous NK cell lines in order to test their activity against homologous tumor cells and thereby get information about functional NK cell-defects in tumor patients.

Figure: Mechanisms of NK cell cytotoxicity. There are two main strategies of NK cell cytotoxicity. The first mechanism is the granule-dependent cytotoxicity. After activation of the NK cell by (a) activating receptors or (b) the Fcγ receptor (CD16), the cytotoxic granules in the cytosol of the NK cell form an immunological synapse and the contents (mostly perforin and granzyme B) are released upon the target cell by exocytosis. The second mechanism is the killing by death ligands. In this case apoptosis pathways are triggered in the target cell via stimulation of death receptors on the target cell by (c) TRAIL or (d) Fas ligand expressed on the NK cell surface or (e) the secretion of TNF-α (modified after Sutlu&Alici, 2009).

 

Publications

 

 

Presentations

July 2015 7th Annual Retreat, Erlangen School of Molecular Communication, Schloss Hirschberg, Beilngries, Germany
”Efficient generation of human natural killer cell lines by viral transformation”
Poster