Tribodies: Fab–scFv Fusion Proteins as a Platform to Create Multifunctional Pharmaceuticals

Abstract

Tribodies are multifunctional recombinant antibody derivatives, which utilize the natural in vivo heterodimerization of the heavy chain (Fd fragment) and light chain (L) of a Fab fragment, to form a scaffold, upon which additional functions can be incorporated, such as additional binders-e.g. scFv binding domains. Each chain can be extended preferably at the C-terminus with an additional scFv binder. The chains are co-produced in mammalian cells, where the host-cell BiP chaperone drives the formation of the heavy chain-light chain heterodimer (Fd:L)-this reaction does not appear to be inhibited by the chain extensions, and leads to a very specific heterodimerization, using molecules abundantly present in serum (non-immunogenic) These heterodimers are stable, with each of the binders retaining their specific affinities, with the bivalent tribody having higher affinity, and higher activatation of T-cell proliferation and cytotoxicity in vivo. This design allows easy engineering of multispecificity in a single molecule, e.g. bispecific antibodies bivalent for the target and monovalent for effector activation (e.g.