Background
Natural killer (NK) cells are a subset of innate lymphoid cells that are inherently capable of recognizing and killing infected or tumour cells. This has positioned NK cells as a promising live drug for tumour immunotherapy, but limited success suggests incomplete knowledge of their killing mechanism. NK cell-mediated killing involves a complex decision-making process based on integrating activating and inhibitory signals from various ligand-receptor repertoires. However, the relative importance of the different activating ligand-receptor interactions in triggering NK killing remains unclear.
Methods
We employed a systematic approach combining clinical, in silico, in vitro, and in vivo data analysis to quantify the impact of various activating ligands. Clinical data analysis was conducted using massive pan-cancer data (n = 10,595), where patients with high NK cell levels were stratified using CIBERSORT. Subsequently, multivariate Cox regression and Kaplan-Meier (KM) survival analysis were performed based on activating ligand expression. To examine the impact of ligand expression on NK killing at the cellular level, we assessed surface expression of five major activating ligands (B7H6, MICA/B, ULBP1, ULBP2/5/6, and ULBP3) of human tumour cell lines of diverse origins (n = 33) via flow cytometry (FACs) and their NK cell-mediated cytotoxicity on by calcein-AM assay using human primary NK cells and NK-92 cell lines. Based on this data, we quantified the contribution of each activating ligand to the NK killing activity using mathematical models and Bayesian statistics. To further validate the