Immunosuppressive contribution of tumour-infiltrating B cells in human intrahepatic cholangiocarcinoma and their role in chemoimmunotherapy outcome

Background: Intrahepatic cholangiocarcinoma (iCCA) is a highly aggressive biliary tract cancer with a poor prognosis and a complex tumour microenvironment (TME) that remains poorly understood. Objective: This study aimed to investigate the phenotypic and molecular characteristics of B lymphocytes, their interactions with the TME and their prognostic implications. Design: B-cell compartments in the tumour, peritumour, and peripheral blood of iCCA patients were analysed using multimodal single-cell technologies. The B-cell interactome with the iCCA TME was explored in silico, and ex vivo assays assessed the impact of interactions with cancer-associated fibroblasts (CAFs) and tumour cells on B-cell biology. B-cell modulation during chemoimmunotherapy in advanced iCCA was also evaluated. Results: B cells were enriched in adjacent tumour-free tissues and formed mature tertiary lymphoid structures (TLS), correlating with better prognosis. Conversely, tumour-infiltrating B cells were scarce, immature and displayed reduced effector function with increased immunosuppressive features. Coculture with tumour cells or CAFs impaired B-cell differentiation and function, including downregulation of BAFFR in peripheral B cells. IL-6 and TGF-β emerged as major drivers of B-cell dysfunction; dual blockade restored B-cell activation and differentiation. Elevated frequencies of circulating BAFFR+ B cells and hyperexpanded clonotypes were linked to improved chemoimmunotherapy response. Conclusions: iCCA is characterised by a profoundly immunosuppressive TME that impairs B-cell function through soluble factors and cellular interactions. Our findings identify B cells as biomarkers and therapeutic targets, supporting strategies to restore B-cell function and promote mature TLS to enhance immunotherapy responsiveness in iCCA.