HDAC inhibitors mediated tumor cell apoptosis, decreased the expression of FOXP3 and HELIOS in Tregs, upregulated PD‐L1 expression and Class I/II human leukocyte antigen (HLA), decreased Tregs and MDSCs, and increased CD8+ TILs in tumor, which indicate that the combination of HDAC inhibitors and immunotherapy maybe an efficacy strategy for solid tumor [462, 463, 464]. The gene discussed is HDAC9; the disease is neoplasm.