Natural Killer cells in cirrhosis and hepatocellular carcinoma and the role of LLT1 in the Liver and in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a major complication of cirrhosis and liver disease secondary to alcohol related and non-alcohol related fatty liver disease (NAFLD) is a growing concern. Work identifying cancer specific or immunomodulatory antigens is key to rapidly advancing immunotherapeutic options. Natural Killer (NK) cells provide potent anti-pathogen and tumour surveillance responses. Harnessing NK cells is an exciting prospect as they are capable of direct cytotoxicity and mediate antibody-dependent cellular cytotoxicity. However, understanding pre-existing modifications to NK cells in cirrhosis is key to understanding the role of NK cells in disease and how they can be modified. Peripheral blood and intrahepatic NK cells from patients with liver disease of a non-viral aetiology were characterised using flow cytometry, Nanostring technology and tissue culture techniques and compared to healthy controls. NK cells were hypofunctional, with reduced expression of key activating receptors NKp46, DNAM-1, and CD16 and an upregulation in inhibitory receptor CD161 in disease. NKp30 was associated with reduced cytotoxicity in NAFLD. The expansion of a CD56dimNK cell subpopulation in cirrhosis and HCC was identified, with reduced expression of CD16, increased expression of liver-homing CXCR6 and CCR5, preserved cytotoxic function but impaired cytokine production. Furthermore, having identified an increased proportion of CD161+ NK cells in cirrhosis, I demonstrated the increased expression of the ligand LLT1 on liver tissue in cirrhosis using immunohistochemistry and real-time quantitative PCR. By generating LLT1 overexpressing Huh7 cells, I demonstrated that LLT1 inhibits NK cell degranulation. Lastly, I demonstrated that tumour growth factor beta (TGFβ), a key cytokine in the pathogenesis of fibrosis, may result in the upregulation of LLT1 in the liver. Overall the data describes an inhibitory profile of NK cells in cirrhosis with impaired function, identifies a novel dysfunctional CD56dimCD16+/-NK cell subpopulation in cirrhosis and HCC and identifies an inhibitory pathway important in cirrhosis.