Similar to normal lymph nodes, PD-L1 is expressed by myeloid ICs in DLBCL, with different prevalence and intensity depending on the staining procedure. (A) Membranous immunohistochemical stain for PD-L1 protein (with hematoxylin counterstain) on cells with myeloid/dendritic morphology in normal lymph nodes (original magnification ×400). (B) Representative images of PD-L1 protein staining (SP263; original magnification ×400) among DLBCL patients treated in MAIN using a simplified IHC scoring system capturing PD-L1⁺ ICs or TCs (IHC 1, 1%-5%; IHC 2, 5%-10%; IHC 3, >10%). Yellow arrows represent PD-L1 staining on myeloid cells, and red arrows represent PD-L1 staining on malignant B cells. (C) PD-L1 prevalence and staining intensity among de novo DLBCL patients treated in 2 phase 3 clinical trials (MAIN, GOYA) using 2 different PD-L1 IHC reagents (SP142, SP263). (D) PD-L1 messenger RNA (mRNA) is higher in the ABC DLBCL subset (P = .004; MAIN). Freq, frequency; nRPKM, normalized reads per kilobase million.