Single-Cell Atlas of Infiltrating B Cells and Their Clinical Outcomes in Colorectal Cancer

Background: B cells constitute a major component of infiltrating immune cells in colorectal cancer (CRC). However, the characterization of B cells and their clinical significance remain unclear. Methods: We performed single-cell RNA sequencing to identify the features of B cells in the CRC tumor microenvironment (TME), and validated these findings using flow cytometry and multicolor immunofluorescence staining experiments. B cell-related cellular interactions within the TME were estimated using CellChat and in vitro chemotaxis assay. We then derived gene signatures to construct TME compositions for The Cancer Genome Atlas Colon Adenocarcinoma (TCGA-COAD) dataset using the single sample gene set enrichment analysis (ssGSEA) method and unsupervised consensus clustering analysis was employed to identify four colon immune classes (CICs). Finally, we reviewed the landscape of gene mutations across these four CICs. Findings: We identified five distinct subtypes of B cells with their marker genes, distribution patterns, and functional properties in the CRC TME. We found an increased ratio of IgG/IgA plasma cells in tumor sites compared with adjacent normal mucosal tissue. In addition, the CXCL13-producing CD8+ T cells in the tumor tissue could recruit tertiary lymphoid structure (TLS) B cells and CCL28-CCR10 axis are pivotal for IgG plasma cell migration to the intratumor tissue. Finally, we identified four distinct CICs (CIC: A–D) and found that CD20+ B cells within TLS were enriched in one immune-inflamed or hot tumor group (CIC-D). This B cell-rich group, characterized by strong antigen presentation, IgG plasma cell accumulation, microsatellite instability-high (MSI-H) and high tumor mutation burden (TMB-H), as well as immunosuppressive property in particular, might become a potential predictive biomarker for future immunotherapy. Interpretation: Our analysis provides deep insight into infiltrating B cells and their potential clinical implications for immunotherapy in colorectal cancer. Funding Information: This study was financially supported by project grants from the Medical System of Shanghai Minhang District (grant number 2020MWDXK02). Declaration of Interests: The authors declare no competing interests. Ethics Approval Statement: This study was approved by the Ethical Committee of The Fifth People’s Hospital of Shanghai, Fudan University. All animal experiment were conducted under the approved protocol Guidelines for the Care and Use of Laboratory Animals.