CD28 and neoplasm: Our previous work showed that full T cell activation by bispecific anti-tumor antigen/anti-CD3ε antibodies strongly benefited from the presence of costimulatory bispecific antibodies engaging CD28 on T cells and targeting a second tumor-associated antigen due to the use of a functionally attenuated anti-CD3ε single-chain variable fragment (scFv) antibody format [20].