PDCD1LG2 and cancer: PD-L2 is the second ligand for PD-1, with a two- to six-fold affinity for PD-1 compared to PD-L1, and it can be produced by stromal, immune, or tumor cells (11).PD-L2 is a less studied PD-1 ligand, which plays an important role in cancer progression and immune regulation.