The rules of different B cell subtypes in colorectal cancer: friends or foes?

Tumor-infiltrating B cells (TIBs) are the most important cell type involved in the immune response. TIBs display considerable intratumor heterogeneity due to genetic variation, epigenetic differences and transcriptional plasticity in the tumor microenvironment (TME). Owing to the unique anatomical location of CRC, the B cell subpopulation exhibits more extensive heterogeneity. Many studies have shown that TIBs have gradually become a key predictor of immunotherapy for malignant cancers, including CRC. TIBs have essential functions, including antigen presentation and antibody secretion, and they promote T-cell activation and myeloid chemotaxis. However, owing to the complex TME, TIBs not only promote the antitumor immune response but also inhibit the immune response. With the in-depth study of tumor-infiltrating T cells, tumor-associated myeloid cells and the interactions among these cells in the TME, the special role of immune cells in the TME has gradually become clear. However, the influence of TIBs in the TME and their interactions with nonimmune cells in the TME remain unclear. Here, we summarize the current progress in TIBs based on single-cell RNA sequencing in CRC in recent years, focusing on specific effector or regulatory characteristics of different B cell subclusters in the CRC TME.