CD28 and neoplasm: Using frBsAbs of diverse antigen specificities, we show that tumor antigen-specific frBsAbs specifically bind target antigen on human tumor cells and, upon co-engagement of the BsAb-IR on engineered T-cells, delivers simultaneous TCR CD3 activation and CD28 costimulation signals in a target dependent manner, resulting in the selective augmentation of activation, proliferation and antitumor activity of BsAb-IR T-cell subset.