Development of Antibody-Based PROTACs for the Degradation of the Cell-Surface Immune Checkpoint Protein PD-L1

[Image: see text] Targeted protein degradation has emerged as a new paradigm to manipulate cellular proteostasis. Proteolysis-targeting chimeras (PROTACs) are bifunctional small molecules that recruit an E3 ligase to a target protein of interest, promoting its ubiquitination and subsequent degradation. Here, we report the development of antibody-based PROTACs (AbTACs), fully recombinant bispecific antibodies that recruit membrane-bound E3 ligases for the degradation of cell-surface proteins. We show that an AbTAC can induce the lysosomal degradation of programmed death-ligand 1 by recruitment of the membrane-bound E3 ligase RNF43. AbTACs represent a new archetype within the PROTAC field to target cell-surface proteins with fully recombinant biological molecules.