This includes several bispecific antibodies, with one arm targeting 4-1BB and the other targeting either tumor-specific antigens or PD-L1, ɑ4-1BB antibodies that bind only in tumor-specific niches, such as high ATP concentrations, or pro-drug ɑ4-1BB antibodies where the binding domain of the antibody is shielded by a peptide “mask” that is cleaved by tumor specific proteases22–26. Here, CD274 is linked to neoplasm.