FAP and neoplasm: Extending reports on αFAP–B7.1 and αFAP–4-1BBL fusion proteins (16–19) we show here that a tetravalent bispecific αFAP–αCD28 antibody can provide efficient co-stimulation in our mixed MCF-7/HT-1080-FAP tumor cell spheroids for T cell activation that is delivered through e.g., αEpCAM–αCD3 or αHER2–αCD3 BiMAb.