Regulation of PD-1 expression in T cells of the DLBCL microenvironment. (A) Direct and indirect antigen presentation by lymphoma cells and nonmalignant cells, respectively, in the absence of PD-L1 results in activation of TILs inducing expression of activation markers including PD-1 and expansion of PD-1⁺ TILs. (B-C) In the presence of PD-L1 on either DLBCL or nonmalignant cells, activation of TIL and expression of PD-1 are diminished, and expansion of PD-1⁺ TIL is inhibited. Ag, antigen; MHC, major histocompatibility complex; MΦ, macrophage; SC, stroma cell; TCR, T-cell receptor.