Toll-like receptors (TLRs) are transmembrane proteins involved in innate immune response. They can also be expressed on cancer cells where their role is still unresolved. TLR3 activation is triggered by dsRNA of viral origin or its synthetic analogue poly(I:C). TLR3 has a dual role in cancer; its activation triggers apoptosis as well as stimulates cancer progression. In this project we will explore the role of TLR3 activation in cancer development by focusing on the role of its endogenous ligands. These ligands originate from necrotic cancer cells and may stimulate cancer progression. We will study this on several models: a) TLR3 reporter cell line HEK-Blue to validate the in vivo and in vitro existence of TLR3 endogenous ligands derived from necrotic cells and tissue, b) head and neck cancer cell lines stably transfected with shRNA for TLR3 and c) cancer tissue specimens isolated from head and neck cancer patients. Second approach will include studying the role of TLR3 and its endogenous ligands in cancer stem cells (CSC) development and self-renewal. Lastly, we will seek to develop a novel anti-cancer therapy against CSC. These cells show resistance to classical therapy and may trigger recurrence thus targeting them is a reasonable strategy in cancer therapy development. Our approach will include combining proton or gamma-ray irradiation with the treatment with poly (I:C) and pharmacological inhibitors of endogenous ligands. TLR3 agonists are currently being investigated as potential novel cancer therapy adjuvants and apoptosis inducers. This project will focus on the delivery of new knowledge on the dual role of TLR3 in cancer and resolve the conditions in which TLR3 activation is either pro-tumorigenic or pro-apoptotic. It is of great importance to elucidate this before the introduction of TLR3 agonists into clinical practice.