MMP2 and neoplasm: A tumor-targeting linear peptide sequence (LyP-1) was designed with a PD-L1 antagonist (DPPA-1) through an MMP-2 switch, which could trigger PD-L1 antagonist peptide release inside the tumor and expose the LyP-1 peptide on the nanoparticle surface, targeting P32 overexpressed protein on the tumor cell surface.