KLRK1 and ovarian cancer: To assess the immunosuppressive capacity of sULBP6, we cocultured NKG2D-expressing PBMCs (Supplementary Fig. S3A and S3B) with COV644, a human ovarian cancer cell line that endogenously expresses membranous MICA/B and ULBP6 and produces sULBP6 (Supplementary Fig. S3C–S3F) in the presence of recombinant sULBP6 or sMICA, the latter of which has the third highest binding affinity to NKG2D of all NKG2DLs (Fig. 3A).