PD-1 blockade in solid tumors with defects in polymerase epsilon

Abstract Missense mutations in the polymerase epsilon (POLE) gene have been reported to generate proofreading defects resulting in an ultramutated genome and sensitize tumors to checkpoint blockade immunotherapy. However, many POLE mutated tumors do not respond to such treatment. To better understand the link between POLE mutation variants and response to immunotherapy, we. prospectively assessed the efficacy of nivolumab in a multicenter clinical trial in patients bearing advanced mismatch repair proficient POLE-mutated solid tumors. We found that only tumors harboring selective POLE pathogenic mutations in the DNA binding or catalytic site of the exonuclease domain presented high mutational burden with specific single base substitution signature, high T-cell infiltrates, and high response rate to anti-PD1 monotherapy. This study illustrates how specific DNA repair defects can sensitize to immunotherapy, POLE proofreading deficiency representing a novel tumor agnostic biomarker for response to PD-1 checkpoint blockade therapy.