15353-j-veluchamy

10 | Chapter 1 inhibitory ligands such as MHC class I molecules (HLA-ABC, HLA-G and HLA-E) has been associated with inhibition of NK cell activation 19-22 . Furthermore, as reported in renal cell carcinoma, increased expression of the inhibitory NKG2A receptor resulted in decreased functionality of tumor infiltrating NK cells 23 . On the other hand, down-regulation of NK activating ligands for NKG2D such as MICA and MICB, and increased shedding of tumor derived soluble MIC also impair NKG2D mediated NK cell tumor recognition 24 . Another important necessity for optimal NK cell function is the ability to home and migrate to tumor sites. Several studies have correlated increased homing of NK cells to tumor tissues with improved treatment outcomes in solid tumors 25-29 . However, the immunosuppressive tumor Figure 1: An overview of major NK cell activating and inhibitory receptors and their corresponding ligands expressed on tumor cells.