PDCD1 and cancer: Recent studies have shown that targeting the PD-1 and PD-L1 pathways and PD-1/PD-L1 checkpoints with monoclonal antibodies are promising to reverse the exhausted T-cell response in chronic viral infections and in the treatment of various types of cancer (Blackburn et al., 2009; Nakamoto et al., 2009; Brahmer et al., 2012; Topalian et al., 2012).