HDAC9 and mature T-cell and NK-cell non-Hodgkin lymphoma: Furthermore, our in vitro study revealed that the class I HDAC inhibitor chidamide enhances IFN-γ production and restores the cytotoxic activity of PD-1(+) cells from patients with PTCL, indicating that chidamide may exert its immunomodulatory effect by regulating the function of PD-1(+) cells (8).