On TCR clustering and serial binding in T-cell activation

Our immune system continuously protects us from a myriad of germs: phagocytes and T-cells play a particularly important role here. Phagocytes patrol our body, surround invaders, such as viruses or bacteria, and break them down into tiny fragments (antigens) to present them on their cell surface. With highly sensitive receptors, T-cells recognize these antigens and launch an immune response. Exactly how antigen recognition occurs at the molecular level is not yet fully understood. A complete understanding of this process would not only shed light on how the immune system works, but is also essential for biomedical progress, such as the development of modern, tailored therapies against cancer. The project hypothesis is that a single antigen can "turn on" multiple T-cell receptors in rapid succession, creating a hot spot for signal transduction. In this scenario, the duration of receptor- antigen binding and the spacing of individual receptors and antigens play an important role. To better study such complex recognition mechanisms, we will recreate the process of antigen recognition in a model system. Here, the antigen-presenting cell will be replaced by an artificial cell membrane. This will allow us to control the type and number of antigens and then study the T-cell response. In order to precisely set the spatial distance between the individual antigens, as well as other proteins involved, we will use tools in the nanometer range. The material and construction principle for this comes from nature itself: DNA, the carrier of genetic information in our body, consists of two precisely matching individual strands that self-assemble to form a DNA double helix. This property is exploited in DNA nanotechnology: By cleverly designing short single strands that partially fit to a long single strand, it is possible to join several double helices together. This technique is called DNA origami - instead of paper, DNA strands are folded to create complicated structures. In this way, DNA platforms will be produced on which one or more antigens and auxiliary proteins can be specifically placed. These DNA platforms will then be placed on the artificial membrane and move there like rafts. The DNA origami structures thus allow direct intervention in the antigen recognition process by manipulating the organization of the antigens. The DNA origami structures can be observed using high-resolution microscopy methods. In collaboration with the research group of Johannes Huppa (Medical University of Vienna) we will also develop new experimental approaches to detect the binding of multiple T-cell receptors by a single antigen using advanced microscopy techniques.