Deepening the knowledge of the immune checkpoint PD-L1 in anti-tumor immunity

Details

Supervisors

Zhu, Jingjing

Faculty

Faculté de pharmacie et des sciences biomédicales

Degree label

Master [120] en sciences biomédicales, à finalité approfondie

Abstract

Programmed death ligand 1 (PD-L1) is a critical immune checkpoint molecule that plays a piv- otal role in regulating anti-tumor immunity. Expressed on tumor cells and antigen-presenting cells (APCs), PD-L1 interacts with the programmed death protein 1 (PD-1) on T cells, inhibiting T cell activation and proliferation. This immunosuppressive mechanism has been a major focus in cancer immunotherapy, leading to the development of PD-1/PD-L1 targeting antibodies that have shown substantial efficacy in various cancers by reactivating T cell-mediated anti- tumor responses. Recent discoveries have shown that, beyond its canonical interaction with PD-1, PD-L1 also binds to CD80, indicating a more complex role in immune regulation and necessitating consideration of its binding partners in therapeutic strategies. In the host labor- atory, flow cytometry experiments have revealed the presence of PD-L1 on T cells following interactions with PD-L1-expressing tumor cells. Further investigations have shown that T cells acquire PD-L1 through trogocytosis — a process by which membrane fragments, along with associated proteins, are transferred from donor to recipient cells during cell-to-cell contact. Notably, this transfer of PD-L1 from tumor cells to T cells is mediated by PD-1. This master's thesis seeks to decipher the mechanism behind this PD-1-mediated transfer of its ligand from tumor cells to T cells. To begin, we examined the cellular mechanisms involved in the transfer of PD-L1 to PD-1-expressing T cells. To further visualize the transfer, we generated plasmids that fused eGFP to PD-1 and mRFP to PD-L1. We first validated the transfer of PD-L1 from tumor cells to T cells by detecting the appearance of mRFP on T cells following co-culture with tumor cells. This observation was subsequently confirmed and visualized using confocal mi- croscopy. The second objective of this project is to explore whether PD-L2, the other PD-1 ligand, undergoes a similar transfer as PD-L1. We demonstrated that PD-L2 is also transferred to PD-1-expressing cells in a PD-1-dependent manner. Additionally, we observed that the ex- pression levels of PD-L1 and PD-L2 on the same donor cells influence each other's transfer efficiency. In conclusion, our results provide new insights into the mechanisms regulating im- mune checkpoint molecules and offer perspectives for investigating the functional conse- quences of PD-L1 and PD-L2 transfer to PD-1-expressing T cells.