We provide evidence that only in the presence of tumor cells, tetravalent (anti-TAA scFv-hIgG1-Fc-anti-CD3ε scFv)2 BiMAb studied in this work activated T cells and induced cytotoxicity in adherent cell and tumor spheroid cultures in vitro, suggesting that T cell activation strictly depended on cross-linking. Here, CD3E is linked to neoplasm.