MICA and cancer: For example, many cancer cells upregulate the stress-induced ligands MHC class I polypeptide related sequence A and B (MICA and MICB), which bind to the activating receptor NKG2D, and downregulate MHC Class I, which are then unable to bind inhibitory receptors, such as KIRs, potentiating NK cell activation and target cell killing (13–15).