Integrative analysis of T cell activation

T cell activation relies on the recognition by the TCR of pMHC complexes, present at the surface of antigen presenting cells (APC), which initiates the formation of a contact zone named immune synapse (IS). Upon IS formation, signaling molecules traffic actively from and to the IS. We were among the firsts to show that the traffic of LAT, one of the key proteins of TCR-signaling, regulates T cell response to TCR triggering. This led us to postulate that signalosomes’ location is essential for T cell activation.

We are analyzing the signaling complexes in time and space to infer their relative role in T cell activation. To do so, we use biochemical tools, high-resolution microscopy and genetically modified mice and cellular models and collaborate with experts in molecular pharmacology and cell biology.

Upon T cell receptor (TCR) stimulation, excessive T cell activation is dampened by inhibitory receptors, also called immune checkpoints, such as PD-1. These “breaks” to T cell activation prevent autoimmunity. Yet, these inhibitory signals also dampen desired anti-tumor responses in patients. Targeting the inhibitory pathways with blocking antibodies has been used with success to treat cancers. Unfortunately, these checkpoint therapies are not efficient in all cancer patients. In spite of the compelling studies on the inhibitory effects of PD-1 on T cell activation and the many studies on the clinical effects of PD-1 targeted immunotherapy, the mechanisms at the root of PD-1 inhibition of T cell activation are still only partially understood.

Our goal is to characterize the effect(s) of PD-1 engagement on the formation of the immune synapse, i.e. the structure formed between T lymphocytes and antigen presenting cells (APC). We are concentrating on how PD-1 engagement modifies - the cytoskeleton and thus morphology of the T lymphocytes; the forces developed by T lymphocytes on the APC. Our study should reveal new mechanisms by which PD-1 inhibits T cells and potential targets to enhance the PD-1 based immunotherapy.

T cell activation must be controlled over time and the failure to regulate an immune response can lead to a breakdown in self-tolerance and the development of autoimmune diseases. There is emerging evidence that intracellular traffic plays an important role in regulating T cell receptor (TCR) signaling. Our lab identified the polarity kinase Par1b/Mark2 as associated with the trafficking of intracellular signaling molecules in T cells and related to T cell activation. Par1b/Mark2 was shown to be important for the establishment and maintenance of cell polarity by phosphorylating microtubule-associated proteins (MAPs) that regulate microtubule stability. However, the role of Par1b/Mark2 in T lymphocytes is still unknown.

The goal of our research is to decipher the role of Mark2 in the regulation of T cell response. To do so we developed in vivo and in vitro models and are using different approaches proteomic analysis, flow cytometry, in vivo analysis of immune responses.