Ligand-induced assembly of antibody variable fragments for the chemical regulation of biological processes.

Precise control of biological processes by the application of small molecules can increase the safety and efficiency of therapies. Adverse side effects of small molecule signals and/or immunogenicity of regulatory domains hinder their biomedical utility. Here, we designed small molecule-responsive switches, based on the conditional reassembly of human antibody variable fragments, called Fv-CID switches. The principle was validated using high-affinity antibodies against nicotine and β-estradiol to construct chemically responsive transcription factors. Further, we developed an Fv-CID switch responsive to bio-inert, clinically approved compound fluorescein, which was used to control the activity of chimeric antigen receptor (CAR) T cells and bispecific T cell engagers (BiTEs) in vivo. This study provides a framework to regulate the expression of endogenous genes, combine multiple chemical signals, and regulate T cell-based immunotherapy in an animal cancer model using a clinically approved small molecule regulator that could be customized for regulating therapeutic proteins or cells.