KIR3DL1 and neoplasm: Early observations showed that NK cell cytotoxicity was triggered by tumor cells that lacked expression of some or all self-MHC class I molecules, referred to as ‘missing-self’ recognition.8 Therefore, it was postulated that NK cells might be particularly effective when transferred across HLA barriers,9 10 where NK cell alloreactivity would be unleashed through mismatch between donor NK clones bearing inhibitory killer immunoglobulin-like receptor (KIR) specific for self-HLA class I molecules (‘self-KIR’) and recipient cells lacking the cognate HLA class I ligands.