The role of programmed cell death-1 (PD-1) and its ligands in pediatric cancer

Programmed cell death-1 (PD-1) and its ligands, PD-L1 and PD-L2 maintain self-tolerance and modulate physiological immune responses. Recently, targeting the PD-1/PD-L1 pathway with blocking antibodies has emerged as a potentially promising approach to treat advanced cancers in adult patients. Since tumor PD-L1 expression is currently considered the most important predictive biomarker for successful checkpoint blockade, we summarize expression data for the most common tumors of childhood. Additionally, we give an introduction into PD-1 function in the immune system to then focus on PD-1 mediated tumor immune escape.