RESEARCH PROJECTS

NATURAL KILLER CELL-MEDIATED TUMOR IMMUNOEDITING

The term tumor immunoediting describes the dual role by which the immune system can suppress and promote tumor growth and is divided into three phases: elimination, equilibrium and escape. It elucidates the phenomenon whereby constant pressure exerted by the immune system can prompt tumors to alter their appearance to become resistant to immune cells.

Natural Killer (NK) cells are part of the innate immune response and are primarily responsible for eliminating virus-infected and transformed tumor cells. In this project, we hypothesized that NK cells play a crucial role not only during the elimination phase but in all three stages of tumor immunoediting. To address this question, we developed an in vitro model in which murine acute lymphoblastic leukemia (B-ALL) cells were co-cultivated with NK cells over an extended period.

To quantitatively assess NK cell-mediated tumor immunoediting, newly generated B-ALL cell lines were labeled with DNA barcodes. The inheritable sequence of the DNA barcode, akin to commercial products, marks each individual B-ALL cell and allows the simultaneous tracking of individual tumor clones under various experimental conditions over extended periods of time.

In summary, here we use a combination of single-cell tracking and next-generation sequencing of tumor cells to quantify the process of NK cell-mediated tumor immunoediting and uncover novel mechanisms of tumor escape. We believe that the identification of the molecular signature of NK cell-resistant tumor cell clones will provide the basis for the discovery of novel therapeutic targets to increase the immunogenicity of tumor cells.

Funding:

DOC fellowship of the Austrian Academy of Science (ÖAW) to Michelle C. Buri (2021-2024)
Grant of the Fellinger Krebsforschung to Eva M. Putz (2021-2022)
FWF stand-alone project (P32001-B) to Eva M. Putz (2019-2023)

Primary human NK cells (red, left) or NK-92 cells (purple, right) killing K562 leukemic cells (yellow) within a few minutes. NK cells form immunological synapses with tumor cells and the tumor cell dies, which is indicated by cell blebbing. Credits by Martin Distel and Eva Putz.

NON-CANONICAL STAT1 SIGNALING IN NATURAL KILLER CELLS

Individuals as well as mice lacking functional NK cells have an increased risk of developing tumors, thereby highlighting the importance of NK cells in the elimination of cancer cells. The rapid and powerful activity of NK cells against cancer cells, while efficiently sparing healthy tissue, makes them an invaluable tool in cancer therapy. Accordingly, ways to enhance NK cell numbers and functionality are manifold and a fast expanding area of current research.

The JAK/STAT signaling pathway harbors several hubs that may serve as starting points to boost NK cells’ anti-tumor potential. In the last decade, we and others found that NK cell functionality can be increased by targeting distinct family members of the JAK/STAT pathway, such as STAT3, CIS, CDK8, or by disabling STAT1-S727 phosphorylation.

As part of the JAK/STAT signaling pathway, STAT1 transports extracellular signals from the cell membrane to the nucleus mediating responses to interferons, interleukins and growth factors. Thereby, STAT1 regulates a variety of cellular processes, such as host defense to infection, cell growth and cell death. In the canonical JAK/STAT1 pathway, cytokine binding to the cell surface receptor activates Janus kinases to phosphorylate STAT1 on the amino acid tyrosine 701. Thereby activated, STAT1 proteins form complexes and migrate to the nucleus, where they bind to DNA and modulate target gene transcription. In the nucleus, STAT1 is phosphorylated on serine 727 (S727) by the cyclin-dependent kinase 8 (CDK8). In recent years, a paradigm shift took place when we found deviations from the canonical JAK/STAT pathway depending on the type of stimulation and most importantly depending on the cell origin.

In this project, we hypothesize that STAT1 participates in non-canonical signaling pathways that are activated independently of cytokine signaling in the immunological synapse of natural killer cells. We hypothesize that STAT1 is phosphorylated on S727 by a serine/threonine kinase upon target cell contact, and ultimately restrains NK cell cytotoxicity. We aim to (i) define the signals and upstream regulators responsible for non-canonical STAT1 activation and to (ii) study the general role of this serine/threonine kinase in mouse and human NK cells. In the course of this project, we aim to find a novel target to improve NK cell functionality for the potential use in immunotherapy.

Funding:

FWF stand-alone project (P34832-B) to Eva M. Putz (2022-2026)