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

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.