**2.1 Anti-PD-1 checkpoint inhibitors**

In classical HL (cHL), malignant Reed-Sternberg cells harbor a recurrent chromosome 9p24.1 amplification. Such genetic abnormality encodes *PD-L1* and *PD-L2*, as well as *JAK2*, which further upregulates PD-1 ligand via the JAK-STAT pathway [29]. This upregulated PD-1 signaling allows cHL to suppress surrounding immune cells and survive from immune surveillance. Therefore, blocking PD-1 is likely to restore anti-tumor immunity and eradicate HL cells.
