PDCD1 and cancer: recently constructed M‐αPD‐L1 NVs expressing a matrix metallopeptidase‐2 (MMP‐2)‐activating lock masking on αPD‐L1 (M‐αPD‐L1) through genetic engineering, which can avoid αPD‐L1 binding with normal tissues.[114] Furthermore, high MMP‐2 expression in tumors cleaves the curling peptides of the MMP‐2‐activating lock, exposing αPD‐L1 and blocking the PD‐1–PD‐L1 signaling axis at the cancer site, providing a promising strategy to enhance cancer immunotherapy.