Anushka Dikshit, PhD: No relevant disclosure to display
Introduction/Rationale: Protein-protein interaction is one of the many mechanisms where individual cells communicate with nearby cells or extracellular matrix to modulate the environment. Visualizing these interactions using a spatial platform can validate known interactions implicated in disease pathology, especially cancer. We developed the ProximityScope™ assay that can be used with the RNAscopeTM Multiomic LS assay to visualize protein interactions, proteins, and mRNA on a single tissue section.
Methods: Antibodies were conjugated to oligonucleotides designed to bind RNAscope signal amplification complexes. The entire workflow was performed using the fully automated Leica BOND RX system. The assay detects 1 interaction with 5 RNA/protein targets and was deployed on samples from patients with localized, muscle-invasive bladder cancer who received neoadjuvant anti-PD-L1 checkpoint inhibitor therapy prior to surgery on a clinical trial (NCT02451423). To characterize tumor-immune microenvironment of these patients, PD-1/PD-L1 interactions were assessed with protein markers for immune and tumor cells (CD3, CD4, CD8, FoxP3, and PanCK) and activation markers (IFNG, GZMB, GZMK).
Results: We visualized PD-1/PD-L1 interactions, proteins and RNA targets within the tumor before and after immunotherapy treatment. The PD-1/PD-L1 interaction between CD4+ or CD8+ T cells and CK+ tumor cells, showed significant reduction in responder samples than non-responder samples. Additionally, responder samples showed a decrease in percent of tumor-infiltrating regulatory and cytotoxic T cells. These results demonstrate that while anti-PD-L1 may not induce an increase in CD8+ T cell recruitment overall, this treatment modulates PD-1/PD-L1 interaction between specific cell populations.
Conclusion: Our findings underscore the importance of spatial evaluation of PD-1/PD-L1 interaction alongside cell phenotyping protein and effector molecule encoding RNA in assessing anti-PD-L1 treatment responses.
