PDCD1 and classic Hodgkin lymphoma: Classic Hodgkin’s lymphoma (cHL) is a typical inflamed lymphoma with upregulated programmed cell death protein 1 (PD-1) expression in the TME, which binds to programmed cell death ligand 1 (PD-L1) on tumour cells to inhibit the effector function of CD8+ T cells (Liu and Shipp, 2017).