Hyperprogression of gastric cancer observed in some patients after PD-1 blockade was attributed to activation and expansion of PD-1+ Tregs (Kamada et al. 2019), and in a trial of grade III/IV melanoma, high-PD-1+ Treg expansion was associated with melanoma recurrence and poor disease-free survival (Huang et al. 2019). Here, PDCD1 is linked to melanoma.