MMP2 and neoplasm: Herein, Gao’s group established a matrix metalloproteinase-2 (MMP-2) sensitive hyaluronic acid-PLGLAGG-doxorubicin prodrug (HA-Psi-DOX) combined with anti-PD-1 to simultaneously provoke antitumor immune response and neutralize immunosuppression function, which can accumulate at the tumor foci by EPR effect and has low systemic toxicity [143, 148].