KLRK1 and neoplasm: The authors fused the extracellular domain of PD-1, transmembrane and cytoplasmic domains of NKG2D, and the cytoplasmic domain of 4-1BB to create a chimeric co-stimulatory converting receptor-NK-92 cell line that reversed the inhibitory PD-1 signaling and increased anti-tumor activity against lung cancer cells [173].