Single cell analysis of protein epitopes and chromatin accessibility using PHAGE-ATAC [Human_PBMCs]

Single cell multi-omic readouts of both the cellular transcriptome and proteome have significantly enhanced our ability to comprehensively characterize cellular states. Most approaches in this area rely on oligonucleotide barcode-conjugated antibodies that target cell surface epitopes of interest, enabling their concomitant detection with the transcriptome. However, a similar high-throughput measurement of other cellular modalities such as the epigenome in concert with protein levels have not been described. Moreover, detection of epitopes is limited to antigens for which a specific antibody is available. Here, we introduce PHAGE-ATAC, an approach that enables the scalable and simultaneous detection of protein levels and chromatin accessibility data in single cells using the assay of transposase-accessible chromatin with sequencing (ATAC-seq). Quantitative detection of proteins by PHAGE-ATAC is accomplished through the use of engineerable nanobody-displaying phages that are genetically barcoded within the nanobody-encoding phagemids. We demonstrate the utility of PHAGE-ATAC for multimodal single cell genomic analysis in both cell lines and primary human cells. Analogous to phage display approaches, we further establish a synthetic high-complexity library of nanobody-displaying phages and demonstrate its utility to select novel antigen-specific nanobodies for PHAGE-ATAC. Human PBMCs were stained with Phages displaying anti-CD4, CD8, or CD16 nanobodies to quantify protein abundances along side accessible chromatin using scATAC-seq