Mechanisms of NK cell-mediated regulation of inflammation and cancer

NK cells are an important effector lymphocyte in the resolution of viral infections and the spontaneous recognition of cancer. Their activity is governed by contact dependent receptor-ligand interactions and responses to cytokines in inflammatory responses. This thesis examined receptor-ligand interactions that govern NK cell activity in cancer and inflammation, and how to harness these therapeutically. Chapter 3 investigated the specific contexts in which the DNAX accessory molecule (DNAM)-1 receptor has most relevance in the recognition of tumours. DNAM-1 was a dominant receptor when tumours were engineered to express costimulatory molecules, but not when NKG2D ligands were expressed or were targets of antibody-dependent cellular cytotoxicity (ADCC). This data suggested that a hierarchy of NK cell activating ligands exists that may have evolved to combat the loss of certain activating ligand upregulation during viral infection and tumourigenesis. In addition to these studies, the role of DNAM-1 in mediating natural suppression of spontaneous lymphomagenesis in the Eμ-myc model was assessed. A trend of early acceleration of lymphomagenesis was seen when there was a loss of DNAM-1, but this did not affect overall survival. This may indicate that DNAM-1 is important in the early recognition of developing tumours in this model. Chapter 4 investigated the function of a DNAM-1 related receptor, CD96, utilising a novel, previously unreported gene-targeted mouse. The results in this chapter demonstrated that CD96 was not important for NK cell development or NK cell-mediated cytotoxicity. However, CD96 was important in the regulation of innate inflammation induced by the bacterial product LPS, and the mechanism was through negative modulation of NK cell-macrophage crosstalk. CD96 was also shown to be important in pathogenesis associated with Citrobacter rodentium infection and MCA-induced fibrosarcoma. Chapter 5 investigated whether the expression of NK cell ligands are important in the prognosis, progression, and clinical treatment of acute myeloid leukaemia. On patient diagnostic samples, NK cell activating ligands were heterogeneously expressed, and this expression had a strong correlation with overall survival. Possible NK cell-specific immunoselection was also observed between diagnostic and relapse samples suggesting that NK cells may actively shape AML blast immunogenicity during minimal residual disease. To capitalize on this observation therapeutically, bortezomib, a novel therapy in clinical trials for AML, was assessed for its ability to stimulate NK cell activating ligand expression on AML cell lines. These results demonstrated that bortezomib could stimulate the upregulation of NKG2D ligands on AML cell lines through a PI3K-dependent mechanism. Bortezomib treatment also rendered these cells more susceptible to NK cell-mediated cytotoxicity.