Although fatal toxicities are uncommon (approximately 0.4% for single-agent anti-PD-1/PD-L1 and 1.2% for combination ipilimumab and nivolumab), pneumonitis likely comprises the most frequent fatal event, accounting for 35% of fatal toxicities from anti-PD-1/PD-L1 (Wang et al., 2018). Here, PDCD1 is linked to pneumonitis.