DC biophysical parameters regulate immunity and tolerance

The immune system defends our bodies against external threats like bacteria or viruses, and against internal threats like tumour cells. At the same time, it is vital that the immune system does not overreact but instead ignores the vast majority of healthy cells and signals that come from our own body. Balancing these two processes, termed immunity and tolerance, is one of the major challenges to our immune system. Too little immunity might lead to the development of cancer while too much of it leads to auto-immune diseases like multiple-sclerosis where our body attacks itself. The decision between these two processes is made by a particular cell type called dendritic cell. These cells come in two different flavours, immunogenic and tolerogenic, and instruct other immune cell types, mainly so-called T cells, to either challenge or to ignore a given threat. These instructions are given by proteins that swim in a sea of lipids, termed the cell membrane, that together make up the surface of the cell. Immunogenic and tolerogenic dendritic cells differ in the kind and number of proteins that are present on their surface. However, our current understanding of how these proteins and combinations thereof contribute to immunity and tolerance is very limited. Moreover, the complexity of cells, tissues and ultimately whole organisms makes it very difficult to determine the effect of each protein and their combination. Therefore, this project aims to: 1.) identify the proteins on the surface of immunogenic and tolerogenic dendritic cells and 2.) to mimic the surface of dendritic cells in an artificial system with a defined set and combination of proteins. Dendritic cell surface proteins will be identified by a technique called mass spectrometry that allows to identify the type and abundance of proteins based on their mass and charge. Identified proteins and lipids will then be deposited on glass slides in order to mimic the surface of dendritic cells and their effect on the immunogenic or tolerogenic instruction of other immune cell types in a controlled environment The project will lead to a deeper understanding of the mechanisms that lead to immunity and tolerance and guide the way towards targeted therapies against cancer and auto-immune diseases.

Project 1: Bispecific T-cell engagers (TcEs) Our first project explored how the architectural design of cancer-fighting molecules called bispecific T-cell engagers (TcEs) influences their effectiveness. TcEs are engineered to act as bridges: one end connects to a T cell of the immune system, the other to a cancer cell. This connection allows the T cell to recognize and kill the tumour. We compared four TcE formats that differed in how closely they brought cells together and how flexible they were. TcEs that created shorter distances between T cells and cancer cells were more efficient, because they kept interfering molecules away from the contact site. Flexibility also played a role: depending on whether a TcE was rigid or bendable, the strength of the immune response changed. The most effective design brought cells into close contact and had an optimal balance of stability and flexibility. These results highlight that not only the molecular target matters in drug design, but also its physical architecture. This knowledge could help create next-generation immunotherapies that are more precise, powerful and potentially safer for patients. Project 2: ICAM1 mobility and T-cell activation In the second project, we focused on a molecule called ICAM1, which acts like a "molecular Velcro" between T cells and other cells. ICAM1 is normally anchored in cells, and we developed a specific laboratory setup to study this aspect by comparing mobile ICAM1 with versions that were firmly fixed and immobile. We discovered that immobilized ICAM1 had a striking effect: it strengthened T-cell activation, reorganized the contact site (the immune synapse), and enhanced the release of toxic molecules that kill target cells. In tumour-like models, cells with immobilized ICAM1 were destroyed much more efficiently by T cells. This shows that the mobility of molecules, not only their presence, is a critical factor in immune defence. The findings suggest that by engineering how molecules are anchored, we may boost the effectiveness of cancer immunotherapies and design artificial systems that better mimic natural immune responses. Overall impact: Together, these two projects demonstrate that the physical properties of immune molecules-distance, flexibility, and mobility-are key to controlling the strength of immune reactions. This perspective opens new avenues for designing therapies that harness the immune system with greater precision.