The cytotoxicity of diabodies derived from the anti-CD28 Fv (Fig. 4A, bottom panels) was lower than that of diabodies with anti-CD3 domains; however, both the HL-type and LH-type diabodies with anti-CD28 domains showed cytotoxicity against tumor cells and they had little difference in cytotoxicity between HL-type and LH-type. Here, CD28 is linked to neoplasm.