Electronic Thesis and Dissertation Repository

Thesis Format



Doctor of Philosophy




Li, Shawn


The treatment of tumours remains challenge, necessitating the exploration of novel therapeutic strategies. This study aims to elucidate the mechanism of T cell immune response and tumour immune evasion, as well as the development of novel mechanism-informed therapeutic strategies. The research encompasses various aspects, including the suppression mechanisms of PD-1 on T cell signalling, investigating the role of kinases, particularly LCK, in PD-1 mediated T cell suppression, and the development of peptide-based inhibitors targeting the PD-1/PD-L1 interaction.

Central to this study is the elucidation of PD-1's role in suppressing T cell function. Employing a co-culture system with T cells and antigen presenting cells, the study integrated TMT-16plex mass spectrometry and SILAC labeling to examine the kinome and phosphoproteome dynamics of T cell signalling. The results provide a detailed perspective on the dynamic interaction of signalling pathways involved in T cell activation and inhibition, underscoring the crucial function of LCK in the PD-1 mediated suppression of T cells. Additionally, the dual role of LCK in influencing both the stimulatory and inhibitory pathways in T cells is corroborated through the examination of protein-protein interactions, using LCK knockdown cell lines and a T cell depletion mouse model. Lastly, the study explores the development of peptide-based inhibitors to block the PD-1 signalling, demonstrate favorable blocking efficiency and therapeutic potential in syngeneic mouse tumour models.

Overall, this comprehensive study promotes the understanding of T cell biology in cancer immunity, and further implies the novel immunotherapeutic strategies targeting key regulators in the PD-1 signalling pathway.

Summary for Lay Audience

This thesis project is about understanding a protein called programmed cell death protein 1 (PD-1) and how it affects our immune system to fight cancer. Think of PD-1 as a sort of “off switch” for immune cells called T cells. When PD-1 is active, it stops T cells activity from doing their job of attacking cancer cells.

Activating T cells involves T cells connecting to molecules presented by other cells. This connection is crucial for activating T cells. In this study, I utilized two cell types: Jurkat T cells and Raji cells to mimic the T cells activation in the context of immune response and the PD-1 inhibitory signalling triggered by PD-L1, a protein that be able to conjugate to PD-1. In cells, proteins post translation modification (PTM) can undergo changes that reflect what's happening inside the cell. Phosphorylation, a type of PTM, is important to mediate cell signalling pathways. I studied protein phosphorylation (phosphoproteome) using advanced methods called TMT-16plex mass spectrometry and SILAC labeling. From the result, I found a dynamic pattern of T cells activation and inhibition, and further discovered the importance of a kinase protein, LCK, in mediating T cell inhibition by PD-1. My research also looked at how PD-1, LCK, and CD28 (another protein for T cell activation) work together. I found that LCK can both activate and suppress T cell responses by interacting among TCR, PD-1, and CD28. The association between PD-1 and LCK lead to the T cell exhaustion, and help the tumour evasion. Lastly, I developed new peptide-based drugs to block how PD-1 and PD-L1 interact or to target the PD-1/LCK pathway. These peptides are designed to be effective, stable, and able to get into cells easily. They did well in lab tests in blocking these interactions and showed potential for treating tumours in mouse models.

In conclusion, my study provides new insights into how PD-1 suppresses T cells and underlines the important role of LCK. It offers new ideas about T cell regulation in cancer and lays the groundwork for developing innovative cancer treatments targeting the PD-1 pathway.

Creative Commons License

Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.

Available for download on Thursday, June 04, 2026