In one embodiment, a masked monoclonal antibody (mAb) is provided, the mAb, encoded by a nucleic acid sequence or an amino acid sequence molecule comprising a signal sequence, a masking epitope sequence, a linker sequence that is cleavable by a protease specific to a target tissue; and an antibody or a functional fragment thereof. In another embodiment, a cross-masked mAb heterodimer complex is provided, comprising a first masked mAb, comprising a first signal sequence, a first masking epitope sequence, a first linker that is cleavable by a protease specific to a target tissue, and a first antibody or fragment thereof; and a second masked mAb, comprising a second signal sequence, a second masking epitope sequence, a second linker that is cleavable by a protease specific to a target tissue, and a second antibody or fragment thereof.