Schematic diagram of the lymphoma tumor microenvironment and treatment modalities currently being evaluated to target aspects of the tumor microenvironment. D, dendritic cell; IDO, indoleamine 2,3-dioxygenase; M2 TAM, M2 tumor-associated macrophage; T4, intratumoral CD4⁺ cell; T8, intratumoral CD8⁺ cell; Treg, regulatory T cell.