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.