PDCD1 and melanoma: In addition to targeting CD279, there are ongoing phase 1 clinical trials investigating the role of CD279 ligands: CD274/programmed death ligand (PD-L)-1 in patients with solid tumors [ClinicalTrials.gov:NCT00729664] and CD273/PD-L2 in stage IV melanoma patients [ClinicalTrials.gov:NCT00658892].