In vitro study revealed decreased level of IFN‐γ secretion and impaired cytotoxic activity of PD‐1 (+) cells compared with PD‐1 (−) cells, while chidamide could recover the deficiencies and upregulate adaptive immune‐associated genes in PD‐1 (+) cells of PTCL patients. The gene discussed is PDCD1; the disease is mature T-cell and NK-cell non-Hodgkin lymphoma.