PDCD1 and diffuse large B-cell lymphoma: MFI of PD‐1 on the surface of CD4+ T cells in low‐risk and medium/high‐risk DLBCL patients were 425 (range: 254–579.25) and 570 (range 365.5–796.75), respectively, significantly higher than 250 (range: 211–326) in healthy controls (P = 0.003 and P < 0.001, respectively).