The ability to recognize and destroy degenerative cells forms an inherent part of the human immune system. A person is therefore more likely to develop cancer if their immune system is impaired. Cancer can, however, also emerge in people whose immune systems are fully intact. One cause of this is the development of so-called immune-escape mechanisms, whereby the cancer cells employ various immune suppression mechanisms, for instance, to evade an immune response. One of these mechanisms blocks so-called immune checkpoints, which in turn inhibits the activation of T-cells. Modern immunotherapies therefore look at counteracting these protection measures or stimulating the body’s immune system to fight cancer cells. Most of the immunotherapeutic agents used here are based on proteins (e.g. antibodies) or cells (e.g. cancer vaccines). The BITCAT project pursues the development of a completely new type of immunotherapy based on oligonucleotides, i.e. short DNA or RNA molecules. These oligonucleotides are expected to modulate the expression of receptor genes (e.g. PD-L1, CTLA4) in order to prevent immune checkpoints from being blocked. This in turn facilitates T-cell activation, enabling the immune system to attack the cancer cells once more. This project will see a number of different drug candidates being investigated and optimized in vitro, i.e. in cell culture, to begin with. The most promising candidates will then be investigated in vivo, i.e. as part of an animal experiment, with an eye to functionality, efficacy and toxicity. Liposomal or polycationic nanoparticles are being used here to ensure the oligonucleotides reach the target cells in the body. Respective studies have already shown they are tolerated and demonstrate good bioavailability in the tissue. This new method has the advantage that it can also be applied ex vivo, e.g. in the case of stem cell or organ transplants. This improves cell-based cancer therapy while avoiding systemic administration. The collaboration project overseen by Fraunhofer IZI and McMaster University (Hamilton, Canada) is conducive to developing a new key technology in the field of cancer therapy.