Table 1.

NK cell resistance mechanisms against solid tumors.

Mechanism	References
Abnormal NK cell trafficking to the tumor location	(4, 41)
Poor NK cell infiltration into the tumor	(6–8)
Abnormal NK cell function/activity in patients with malignancy	(37)
Lack of unique targetable tumor antigens	(13, 42)
Antigen escape/downregulation following targeted therapies	(16)
Increased angiogenesis and upregulation of tumor growth factors by hypoxic microenvironment	(11, 12)
Hypoxia induced shedding of MHC class I chain-related (MIC) on tumor cells and downregulation of NKG2D on effector cells	(43)
Chronic immunosuppressive signals in the tumor microenvironment inhibiting NK cell function and activity	(4)