A Suicide Switch Directly Eliminates Intracellular scFv Oligomers in the Cytoplasm of Mammalian Cells

As intracellular antibodies (intrabodies) are highly promising tools for drug discovery, an innovative antibody screening platform in mammalian cells was previously developed by a single‐chain Fv (scFv)‐c‐kit growth sensor, which successfully selected rabies nucleoprotein and phosphoprotein‐specific intrabodies from a synthetic scFv library. Since the scFv‐c‐kit growth sensor releases a growth signal after forming oligomers due to binding to an oligomeric antigen, it is critical to use a library which does not contain self‐oligomeric scFvs to avoid the off‐target signal of the growth sensor. Here, a novel method to eliminate self‐oligomeric scFvs directly in the cytoplasm of mammalian cells is presented. A suicide switch by fusing an scFv with a cell‐death signaling domain to eliminate scFv oligomers is developed. It is found that among four cell‐death signaling domains, a suicide switch by fusing scFv with Fas‐associated death domain (FADD) can selectively reduce oligomeric scFvs. Furthermore, the library after eliminating scFv oligomers results in higher efficiency in the intrabody selection platform with a growth sensor. Collectively, the scFv‐FADD suicide switch can be applied to eliminate oligomeric scFvs from a library, which can consequently improve the quality of intracellular scFv libraries and accelerate the discovery of intrabodies in the future.