IDO1 and diffuse large B-cell lymphoma: In addition, in a recent report which analyzed a series of DLBCL that included a small subset of DLBCL-NOS, it was observed that EBV-positive cases in young patients evidenced dysregulation of immune checkpoints, indoleamine 2,3-dioxygenase (IDO), and PD-1/PD-L1 axis with promotion of an inhibitory, tolerogenic immune environment16.