A workflow for combined detection of protein interactions and cell types for translational studies

Multiplexed imaging approaches of various molecular modalities in tissues are becoming increasingly adopted in discovery and translational studies. For clinical implementation, novel instrumentation, complex analysis workflows and high costs per sample are bottlenecks that hinders broader introduction in the clinical setting. Here, we demonstrate a cost efficient integrated workflow that combines multiplexed immunofluorescence of a handful of protein markers, with in situ proximity ligation assay, to detect direct protein interactions between neighboring cells. As a proof of concept case of relevance for clinical adaptation, we target the major immunotherapy signalling axis of programmed death receptor 1 (PD-1) and its ligand PD-L1, to demonstrate the interaction between immune cells in germinal centers of tonsil tissue and in a tertiary lymphoid structure in bladder cancer tissue, respectively, from a patient treated with immunotherapy.