These data indicate that DuoBody-CD3x5T4 does not only induce kill via the classical perforin-GZMB pathway but that the death receptor pathway (Fas up-regulated via IFNγ) and/or the IFNγ signaling pathway also play a direct role in DuoBody-CD3x5T4–induced tumor cell kill. Here, PRF1 is linked to neoplasm.