Interactions between tumour and natural killer cells in primary and secondary liver cancer

Natural killer (NK) cells are implicated in tumour surveillance and control in a number of settings. The liver contains large numbers of NK cells and hepatocellular carcinoma (HCC) has been shown to express various ligands that permit interactions with NK cells, some of which have been shown to have prognostic significance. Similar prognostic associations have been shown for colorectal cancer, a tumour which commonly metastasizes to the liver. However the mechanistic underpinning of these effects is unclear. This thesis describes a survey of soluble NKG2D ligand expression in patients with HCC caused by chronic hepatitis B (CHB), patients with CHB without cancer, and healthy controls. ULBP1 was found to be raised in HCC patients; where it was associated with poor survival, and in active CHB; where it was associated with hepatitis B viral load. ULBP1 was not seen in secondary liver tumours, suggesting that this protein may be useful as a biomarker of severe disease or to monitor treatment response. The other NKG2D ligands MICA, MICB, ULBP2 and ULBP3 were not found to be elevated in patient serum. Soluble NKG2D ligands did not affect NKG2D expression by circulating NK cells. Tumour infiltrating NK cells have the potential to be important effector cells, but are functionally defective. This work builds on recent advances in the understanding of liver-resident NK cells to characterise the functional defect in primary and secondary liver cancers, using human ex vivo intrahepatic and tumour-infiltrating NK cells. Using an in vitro model of HCC we have investigated the mechanisms for this defect and examine the potential for IL- 15 to restore NK cell cytotoxicity and cytokine production. Ex-vivo tumourinfiltrating NK cells had reduced NKG2D expression, IFNγ production and degranulation potential compared with paired intrahepatic NK cells, but maintained expression of NKp46. We were able to recapitulate this phenotype by co-culture with an HCC cell line, but were not able to protect NK cells from NKG2D downregulation and functional inhibition by NKG2D blockade. However, IL-15 was able to restore function after HCC exposure. This model may serve as an in-vitro assay for future therapeutics targeting tumour-infiltrating NK cells