An additional marker expressed by cancer cells, programmed cell death-2 ligand 2 (PD-L2) has been shown to have a two- to six-fold higher affinity for PD-1 than does PD-L1, but because high quality antibody reagents for PD-L2 are unavailable, IHC analysis is not a good indicator of PD-L2 abundance 67. Here, PDCD1 is linked to cancer.