To address this, we first tested whether VPA affected the expression of activating NK ligands on human melanoma cells; VPA has been reported previously to upregulate NK ligand expression on acute myeloid leukemia cells in vivo.29, 30 We observed upregulation of the NKG2D ligands MICA/B on MEL888 cells and MICA/B and ULBP2/5/6 on less permissive A375 cells upon treatment with VPA (Figure 4A); similar results were also observed using primary melanoma cells (Figure S6A and data not shown). Here, ULBP2 is linked to acute myeloid leukemia.