The expression of PD-1 ligands and IDO1 by macrophage/microglia in primary central nervous system lymphoma

Recent progress in anti-tumor immunotherapy has focused on the significance of the tumor microenvironment in tumor progression and resistance to chemo/radio-therapy. Myeloid cells such as macrophages are predominant stromal components in hematological malignancies. In the present study, we investigated the regulation of programmed death-1 (PD-1) ligand expression in primary central nervous system lymphoma (PCNSL) using PCNSL cell lines and human monocyte-derived macrophages. TK PCNSL cell line-derived soluble factors induced overexpression of PD-1 ligands, indoleamine 2,3-dioxygenase (IDO1), and several other cytokines in macrophages. The expression of PD-1 ligands was dependent on the activation of signal transducer and activator of transcription 3. PD-L1 and IDO1 were overexpressed by macrophage/microglia in PCNSL tissues, and gene expression profiling indicated that IDO1 expression was positively correlated with the expression of macrophage and lymphocyte markers. Macrophage-derived factors did not influence the proliferation or chemo-sensitivity of cell lines. These data suggest that the expression of immunosuppressive molecules, including PD-1 ligands and IDO1, by macrophage/microglia may be involved in immune evasion of lymphoma cells.