KLRK1 and cancer: Knockdown of IDO in cancer cells increased their sensitivity to NK cells in vitro and promoted their accumulation in the tumors in vivo.458 L-Kynuenie, generated through IDO, depletes tryptophan, starves immune cells, impairs NK cell viability, and inhibits the upregulation of NKp46 and NKG2D under IL-2 stimulation.