Immune-checkpoint engagement as predictive biomarkers in clear cell renal cell carcinoma and melanoma

Many cancers are termed immuno-evasive due to expression of immuno-modulatory ligands. Programmed death ligand-1 (PD-L1) and cluster of differentiation 80/86 (CD80/86) interact with their receptors, programmed death receptor-1 (PD-1) and cytotoxic T-lymphocyte associated protein-4 (CTLA-4), on tumour infiltrating leukocytes, thus eliciting immunosuppression. Immunotherapies aimed at blocking these interactions are revolutionising cancer treatments, albeit in an inadequately described patient subset. Our prognostic assay, utilising amplified two-site time-resolved Förster resonance energy transfer (iFRET), quantifies PD-1/ PD-L1 and CTLA-4/ CD80 cell-cell interactions in single cell assays and tumour biopsies. iFRET efficiencies demonstrate, in cell-cell engagement models, that receptor-ligand interactions are significantly lower with anti-PD-1 or anti-CTLA-4 blocking antibodies. In patient samples, iFRET detects immune-cell/tumour-cell interaction variance in different cancers. These results revealed inter-cancer, inter-patient and intra-tumoural heterogeneity of engaged immune-checkpoints, contradicting their ligand expression patterns. Exploiting spatio-temporal interactions of immune-checkpoint proteins defined biomarker functionality for determining whether checkpoint inhibitors are appropriate treatments. Statement of Significance Quantitative photophysics exploitation in determining immune-checkpoint engagement, as predictive biomarkers in cancers led to revealing inter-cancer, inter-patient and intra-tumoural heterogeneity of the engaged immune-checkpoints. This receptor-ligand interaction did not reflect simple expression patterns of these immuno-modulatory proteins. Our findings may affect immunotherapies aimed at blocking these intercellular interactions in patients.