Representative immunohistochemical analysis of PD-L1 expression in ATLL. (A) nPD-L1-positive ATLL. The plasma membranes of neoplastic cells were positive for PD-L1 (brown staining). (B) miPD-L1-positive ATLL. Neoplastic cells were negative for PD-L1. PD-L1-positive nonmalignant stromal cells were observed. Those stromal cells with PD-L1 expression were morphologically consistent with monocyte-derived cells, including macrophage or dendritic cells. (C) PD-L1-negative ATLL. PD-L1 was negative for both neoplastic cells and nonmalignant stromal cells. Original magnification ×600 for all panels.