ULBP1 and breast cancer: To determine if bladder tumor MHC I expression affects NK cell cytotoxicity in vitro, we examined NK cell cytotoxicity against RT4 BC cells which express relatively more MHC I than K562 cells but also express NKG2D activating ligands MICA, MICB and ULBP1, 2 and 3 (Supplementary Figure 1).