Besides, considering the importance of NK cells for checkpoint immunotherapy (17), we analyzed gene expression data and overall survival information from TCGA, finding that the lower expression of NCAM1 (CD56), NKG2D, and NCR3 (three important markers of NK cells) indicated a poor prognosis of the lung adenocarcinoma (P < 0.05, Figure S4). Here, KLRK1 is linked to lung adenocarcinoma.