Detection of Cell-Cell Interactions via Photocatalytic Cell Tagging

The growing appreciation of immune cell-cell interactions within disease environments has led to significant efforts to develop highly effective protein- and cell-based immunotherapies. However, characterizing these complex cell-cell interfaces in high resolution remains challenging. Thus, technologies that can leverage therapeutic-based modalities to profile intercellular environments offer the opportunity to study cell-cell interactions with molecular-level insight. To address this, we introduce Photocatalytic Cell Tagging (PhoTag), a platform for profiling cell-cell interactions utilizing a single domain antibody (VHH) conjugated to a photoactivatable flavin-based cofactor. Upon irradiation with visible light, the tethered flavin photocatalyst generates phenoxy radical tags for targeted labeling within cell-cell contact regions. Using anti-PD-1 or anti-PD-L1 VHH flavin conjugates, we demonstrate that PhoTag achieves highly selective synaptic labeling in antigen presenting cell-T cell co-culture systems. By combining the high resolution transcellular biotinylation capability of PhoTag with multi-omics single cell sequencing, we interrogated transient interactions between peripheral blood mononuclear cell (PBMC) populations and Raji PD-L1 B cells and discovered that specific T cell subtypes can transiently interact more efficiently than others. We envision that the spatiotemporal and modular nature of PhoTag will enable its broad utilization for detailed profiling of intercellular interactions across different biological systems.