The half maximal inhibitory concentrations (IC50) values of 48 h HDACis exposure in the tested cells were shown in Supplementary Figure 3a. To explore the impact of HDACis on BC cell immunogenicity, we exposed BCap37 cells to different concentrations of SAHA or VPA. HDACis dose-dependently increased MICA/B and ULBP2 expression (Figures 6a and b), whereas ULBP1/3 was not affected (data not shown). SAHA and VPA effectively increased MICA/B and ULBP2 expression, even at concentrations lower than 1/10 of the IC50 (100 nM for SAHA and 400 μM for VPA), relative to control treatment (rMFI, mean±S.D. SAHA: 249.6±32.7% for MICA/B and 113.4±4.1% for ULBP2; VPA: 247.7±25.5% for MICA/B and 180.5±8.7% for ULBP2, Figure 6b). The results were then verified using another human BC cell line (MDA-MB-231) (Supplementary Figure 3b). Interestingly, the MICA/B and ULBP2 expression levels of the human normal breast cell line HBL-100 could not be effectively increased by HDACis, even at a concentration as high as the IC50 (rMFI, SAHA: 128.2±14.2% for MICA/B and 113.9±9.3% for ULBP2; VPA: 127.6±8.3% for MICA/B and 113.9±9.4% for ULBP2, Figure 6c). We found that this upregulation of NKG2DL expression was accompanied by the decreased expression of pri-miR-17-92, miR-20a, miR-20b, miR-93 and miR-106b in a dose-dependent manner (Figure 6d). The result indicated that HDACis might elevate the NKG2DLs expression in BC cell lines by inhibiting NKG2DL-targeting miRNAs. Moreover, a miR-20a mimic reversed HDACi-mediated MICA/B and ULBP2 upregulation in BCap37 cells (Figure 6e). To evaluate the effects of HDACi-mediated NKG2DL upregulation on NK cell recognition, we treated BCap37 or MDA-MB-231 cells with low concentrations of SAHA (50 nM or 100 nM) or VPA (200 μM or 400 μM) (Supplementary Figure 3a, c and d). Cells treated with HDACi became more sensitive to NK cell-specific cytotoxicity than cells cultured under standard conditions. In addition, these upregulation effects were reversed when cells were exposed to HDACis together with miR-20a mimics (Figure 6f left and Supplementary Figure 3e). Importantly, these differences between various treatments were abolished after NKG2Ds in NK cells was blocked with an anti-NKG2D mAb (Figure 6f right). Thus, by increasing NKG2DLs expression on BC cells, low concentrations of HDACis sensitized BC cells to NK cell-mediated cytotoxicity.