HDAC9 and acute myeloid leukemia: We and others also demonstrated that different histone deacetylase (HDAC) inhibitors like the FDA-approved drugs romidepsin or valproic acid upregulate NKG2D ligands (MICA/MICB) on the surface of AML cells, thus providing further immunoregulatory signals and sensitizing them to NKG2DL-based immunotherapy [50,51] (Table 1).