Unlocking single cell chromatin accessibility in formalin-fixed paraffin-embedded tissues by scFFPE-ATAC

Formalin-fixed paraffin-embedded (FFPE) samples are the gold standard for clinical tissue preservation. However, single-cell chromatin accessibility profiling technology, a powerful tool to understand epigenetic regulation in human disease, is not available for FFPE samples due to extensive DNA damage. To solve this technical challenge, we introduce scFFPE-ATAC by integrating uniquely designed DNA oligos on Tn5 transposase, split-and-pool ligation DNA barcoding, T7 promoter-mediated DNA damage rescue, and in vitro transcription—the first high-throughput single-cell chromatin accessibility assay for FFPE samples. scFFPE-ATAC enables the simultaneous profiling of up to 64 FFPE samples or spatial regions, with 884,736 cell barcodes in a single run. We successfully applied scFFPE-ATAC to clinical FFPE human lymph nodes stored for 8–15 years and identified distinct epigenetic regulators between tumor centers and invasive edge epithelial cells in human lung cancer. Additionally, we analyzed paired primary and relapsed follicular lymphoma (FL), as well as FL transformed into diffuse large B-cell lymphoma, from clinical samples archived for 2–7 years, revealing key epigenetic drivers of tumor progression. Overall, scFFPE-ATAC enables high-throughput, high-sensitivity chromatin accessibility profiling in long-term archived clinical specimens, paving the way for retrospective epigenetic studies and spatial epigenetic analysis. This technology provides a powerful tool for understanding tumor relapse and metastasis, with broad applications in basic research and personalized medicine.