MMP2 and neoplasm: For example, the enzyme and pH dual‐responsive nanosystem PMVL, which is camouflaged with tumor cell membranes modified with programmed death ligand 1 (PD‐L1) inhibitory peptide (PPA) and coupled with matrix metalloproteinase‐2 (MMP‐2) sensitive peptide(Figure 7B).[125] In response to the overexpression of matrix metalloproteinase‐2 (MMP‐2) in cancer cells, first, PPA is released to block the PD‐1/PD‐L1 recognition between cytotoxic T lymphocytes (CTLs) and tumor cells.