Tumor spheroids were grown from HNSCC (FaDu, CAL27, and Detroit562) and SiHa (39) cell lines, which show characteristic NKG2DL expression patterns and are highly susceptible to NKG2D-dependent killing (Figures S3 and S4A,B in Supplementary Material). Here, KLRK1 is linked to head and neck squamous cell carcinoma.