NK cell function is triggered by the loss inhibitory receptor-mediated signaling when tumor cells downregulate the expression of MHC Class I. These NK cell inhibitory receptors are the killer-cell immunoglobulin-like receptors (KIRs) in humans, and include CD158a/h, CD158b, CD158e1, and the killer cell lectin-like receptor subfamily C, member 1 (CD94/NKG2A) [7]. The gene discussed is KLRD1; the disease is neoplasm.