TCR/LFA-1 Axis as Rheostat of Cytotoxic T Cell Responses

Our immune system relies on specialized cells to fight against infections and tumors. Cytotoxic T lymphocytes (CTLs) are particularly important actors of immune defense since they have the capacity to directly kill infected cells and tumor cells. Understanding how CTL recognize target cells and regulate their killing activity is key to develop vaccines and cell therapy strategies in the context of infectious diseases and cancer. We know since many years that CTL recognize foreign determinants on target cells via their T cell receptor (TCR) and that they also need to activate the attachment molecule LFA-1 to form stable contacts with the cells to be killed. However we still have very limited understanding about the coordination of the steps of recognition and attachment to ensure optimal regulation of the killing activity. This is particularly important to elucidate why CTL are not always efficacious to control certain viral infections and cancers. Our preliminary data indicate that upon recognition of target cells, CTL activate hundreds of nanoscopic attachment points that form an adhesive belt that guarantees stable interaction with the target cell and allows for the kiss of death. Our working hypothesis is that depending on how well the target cell is recognized by the TCR, the quality of the attachment via the attachment points and the ensuing killing activity will vary. Our project will therefore aim at quantifying very precisely the recognition and attachment properties of human CTL. For that purpose, we will study CTL derived from the blood of donors that we can keep in culture and amplify in order to run multiple in vitro experiments. We will first mimic the encounter with target cells by seeding the CTL on reconstituted membranes presenting controlled quantities of stimulatory molecules to activate the TCR and LFA- 1. We will employ very sophisticated microscopes to monitor the organization of molecules at the surface of the CTL as well as signals that connect recognition and attachment. We will also develop automated microscopy approaches to monitor real-time killing under multiple conditions in which we will adjust target recognition and attachment properties. Finally, we will apply our measurements to CTL isolated from patients with immune defects of genetic origin to better understand which genes might control the CTLs decision to kill target cells.

The RheoCyT project has uncovered how the body's "killer" immune cells make highly precise decisions about when and how strongly to attack. These discoveries provide important new knowledge that could help improve treatments for cancer, infectious diseases, autoimmune disorders and organ transplant rejection. Cytotoxic T cells are a specialized type of white blood cell that destroy virus-infected and cancerous cells. To do this safely, they must strike a delicate balance: they need to react powerfully to dangerous targets while avoiding attacks on the body's own healthy tissues. Understanding how these cells achieve such precision was the central goal of the RheoCyT project. The project showed that T cells do not make simple on/off decisions. Instead, they continuously adjust their response according to the strength of the signals they receive. Tiny adhesive structures on the cell surface act like a finely tuned "volume control", allowing T cells to increase or decrease their ability to stick to and kill target cells. This finding reveals an important mechanism that helps immune cells calibrate their actions. Another major finding concerns how T cells distinguish between harmful invaders and the body's own molecules. Using advanced imaging techniques capable of observing interactions at the level of individual molecules, we found that T cells recognize virus-derived targets much more efficiently than self-derived targets. Self-molecules produce weaker and shorter signals and therefore require far stronger stimulation to activate the cells. These findings help explain how the immune system normally avoids attacking the body while remaining highly sensitive to infections. The project also uncovered an unexpected link between immune-cell activity and energy production. The search behavior of T cells and their ability to form stable contacts with target cells, require substantial amounts of energy. Our work shows that specific energy-producing pathways directly support the internal machinery that allows these cells to move and function effectively. This work highlights how cellular metabolism and immune activity are tightly connected. In addition, the project identified previously unknown molecules involved in the final step of the killing process, when toxic molecules are released to destroy a target cell. Special lipids composing the external membrane of T cells were found to play a key role in controlling this process. Finally, the researchers involved in the RheoCyT project developed new methods to replace the recognition machinery of human T cells with engineered receptors. This technology will facilitate the development of T cell-based therapies. By revealing the molecular mechanisms that fine-tune the activity of killer T cells, the RheoCyT project provides a foundation for developing safer and more effective immune-based therapies. The findings may contribute to improved cancer immunotherapies, better treatments for autoimmune diseases and transplant rejection, and new strategies to fight infectious diseases.