Recent studies also noted that chidamide, a histone deacetylase (HDAC) inhibitor, seemed to leverage upon anti-tumor effects provided within PD-1+ cells to enhance the expression of genes associated with chemokine and chemotaxis activity, exposing the possibility of synergistic effects when combined with standard PD-1 blockade therapy (125, 126). This evidence concerns the gene PDCD1 and neoplasm.