IDO1 and classic Hodgkin lymphoma: Regardless of their prognostic role, CD8+ T cells seem to have an important role in shaping the TME of cHL, since they express immune checkpoint molecules such as PD-1, indoleamine 2,3-Dioxygenase 1 (IDO)-1 and TIM-3 more frequently than CD4+ T cells [32] (Figure 1).