HDAC9 and neoplasm: This is based on the fact that (i) HDAC is overexpressed in tumors, (ii) inhibition of HDAC negatively interferes with the expansion of MDSCs, (iii) tumor antigens (TA) are often methylated and thus not presented via HLA class I and class II molecules, and (iv) hypomethylating agents as well as HDACi have diverse immune modulating effects by e.g., upregulating HLA class I and components of the IFN-γ signal pathway (84).