However, as discussed next, NK cells activity can be dampened by secreted products from tumor cells such as prostaglandin E2 (PGE2).43 Proteolytic shedding of NKG2D ligands such as MHC class I-related chain A (MICA) and B (MICB) by tumors can also enable their escape from NK cell-mediated killing by functioning as decoys and driving NK cell exhaustion.46 47. The gene discussed is MICA; the disease is neoplasm.