An investigation into T cell inactivity and exhaustion in Colorectal Liver Metastasis and the role of Neutrophil Extracellular Traps

Colorectal cancer (CRC) is the 4th most common cancer diagnosed in the UK. Half of these patients will develop metastasis to the liver (CRLM), the leading cause of death in CRC patients. Although there is a myriad of options to treat CRLM, surgery is the gold standard, but with a 5-year recurrence rate of 75%. Better systemic therapies are therefore required to improve the outcome of CRLM patients. Although we are in the midst of an era of immunotherapeutic development, with significant progress demonstrated in lymphoreticular cancers and melanoma, microsatellite-stable CRC remains insensitive to immunotherapy. Proposed biological mechanisms underlying this insensitivity include impaired cancer antigen presentation, immunoinhibitory chemokine expression, extracellular matrix deposition and myeloid cell-driven immunosuppression. Central to these mechanisms is a failure of T-cell infiltration and activation within CRLM. In this research, I will utilise two cutting-edge, fully human disease models to study impaired T-cell activity in CRLM. I will perfuse human hemi-liver specimens containing CRLM with fluorescently labelled T-cells. I will study their extravasation, migration and exhaustion in real-time over multiple days to understand the factors limiting T-cell extravasation, migration and activation. In higher-throughput experiments, I will generate multiple perfused slices from resected CRLM specimens and study T-cell activity in situ, supporting findings from the hemi-liver perfusion platform. Once I have developed an enhanced understanding of T-cell activity in both models, I will use them to investigate whether Neutrophil Extracellular Traps (NETs) contribute to impaired T-cell activity in CRLM. NET formation is a form of neutrophil apoptosis that involves detangling and expansion of chromatin upon cell death. It has been implicated as a key regulator of liver metastasis development and impaired T-cell activity in various cancers. PDL-1 , a key T-cell immunosuppressant, is present within the detangled chromatin of NETs, suggesting a mechanism through which they may inhibit T-cell activation in the tumour microenvironment (TME). NETs accumulate physiologically during liver perfusion as they do in-vivo, and I will assess the effect of NET removal on CRLM T-cell biology through the use of a novel, clinically approved NET capture device acquired through collaboration with our industry partner. Showing that NET removal has a positive effect on T-cell activity in CRLM will open therapeutic approaches where NET capture is used synergistically with immunotherapeutics to overcome insensitivity. The use of fully human models where NET capture is deployed in a physiologically relevant setting will significantly reduce the time to clinical application, and de-risking trial design. The PhD project, in a surgically orientated lab within an exceptional research environment, will provide an invaluable scientific experience, enabling me to translate my already significant basic science experience into a formal research qualification. Ultimately, I will use this as a platform from which to further develop my surgical research career.