Chemocatalytic Cell Tagging Platform for Recording Cell‐Cell Interactions via Engineered Palladium‐Based Artificial Metalloenzymes

Abstract Proximity labeling platforms (PLPs) have become a powerful tool for studying spatial cell‐cell interactions (CCIs) in living organisms. However, their effectiveness often relies on membranal catalytic modules of bait cells, such as natural enzymes or small‐molecule photocatalysts, which are typically constrained by complex genetic modifications or the limited applicability of visible light. Here, we present a novel chemocatalytic approach, ArM‐Tag, which utilizes an engineered artificial metalloenzyme (ArM) for cell surface‐localized tagging. The ArM‐Tag system combines a palladium (Pd) cofactor, a lipid anchor, and a streptavidin (SAV) scaffold to catalyze the O ‐deallylation reaction on the surface of target cells, generating short‐lived electrophilic intermediates that label neighboring cells within a micrometer‐scale range. By integrating Biotin‐SAV technology with directed evolution, we engineered a series of biotinylated Pd complexes and optimized the ArM for efficient catalysis. We demonstrate the power of this approach by applying the ArM‐Tag system to selectively record antigen‐specific CCIs, specifically showing how CAR−T cells interact with tumor cells through the mesothelin/anti‐mesothelin axis. This versatile, non‐genetic system provides a powerful tool for probing CCIs and offers exciting prospects for advancing immunotherapy, particularly in targeted cancer treatments and immune cell‐based therapies.