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Single Cell and Spatial Transcriptomics Studies of Fibrosis in Prospective Registry in IBD Study at MGH and GI Disease and Endoscopy Registry

Stricturing disease or fibrosis is a common complication of inflammatory bowel disease (IBD), often requiring surgical intervention. This process is caused by the abnormal deposition of extracellular matrix in the context of inflammation, and thus involves crosstalk between multiple cell types including fibroblasts and immune cells. To understand the cellular interactions involved in fibrosis, we performed single cell and spatial transcriptomic analyses of biopsy or resection samples from IBD patients, diverticulitis patients or controls.

For single cell analyses, intestinal samples were processed within three hours of collection by first stripping the epithelial layer with EDTA and then enzymatically digesting the underlying tissue. Cells from both the epithelial and tissue fractions were separately loaded in two channels on a 10x Chromium controller and libraries were generated with the 3'v3 Chemistry pipeline before sequencing on an Illumina sequencer. The resulting sequence data was demultiplexed and analyzed with the CellRanger pipeline to generate raw fastq files and processed gene-count matrices for each sample.

For spatial transcriptomic analyses, intestinal resection samples were snap frozen in OCT (optimal cutting temperature embedding medium). Blocks were cut into 10μm sections in a cryostat and transferred to a 10x Genomics Visium slide v1. Spatially barcoded libraries were prepared according to manufacturer's instructions and sequencing on an Illumina sequencer. The resulting sequence data was processed with the SpaceRanger pipeline to generate fastq files and processed barcode-count matrices.

Using the samples deposited here, we defined 68 fine-grained cell types across the ileum and colon of control and fibrotic intestinal tissues. We show that intestinal strictures were characterized by increased immune cells - including IgG+ plasma cells and CCR7hiCD4+ T cells - and inflammatory fibroblasts. We also define the transcriptional differences associated with fibrosis, with inflammatory fibroblasts in particular showing broad changes in gene expression. Spatial transcriptomics showed that key subsets colocalize within diseased tissues and identified additional populations such as interstitial cells of Cajal and enteric neurons. Further, we mapped gene expression onto intestinal biogeography, finding that known genetic risk loci are enriched within discrete spatial modules, defined by the presence of inflammatory fibroblasts and lymphoid follicles. Altogether, our datasets chart the key transcriptomic and cellular networks in stricturing CD and highlight the spatial organization of multicellular genetic risk factors.