Programmed cell death 1 ligand 2 (PD-L2, B7-DC, CD273) is a member of the B7 family of cell surface ligands that regulate T-cell activation and immune responses (1,2). PD-L2 binds the PD-1 transmembrane receptor and inhibits T-cell activation. PD-L2 was discovered following a search for novel B7 protein homologs and was later shown to be expressed by activated dendritic cells, macrophages, and T-cells (1,3). Similar in structure to related B7 family members, PD-L2 protein contains extracellular IgV and IgC2 domains, a transmembrane domain, and a short, cytoplasmic region. Research studies demonstrate that PD-L2 is expressed in several tumor types, including lung cancer, renal cell carcinoma, melanoma, Hodgkin’s lymphoma and primary mediastinal large B-cell lymphoma (4-7).