MMP2 and neoplasm: After nanoparticle accumulation in tumors via the enhanced permeation and retention (EPR) effect, the MMP2-cleavable peptide was hydrolyzed by highly expressed MMP-2 in tumor microenvironment, then Fc fragments were exposed to activate the multiple innate immune components (complement, macrophages and dendritic cells) to attack tumor (Scheme 1B).