B-1a cells occupy a distinctive niche within the B cell lineage, characterized by early-life development, self-renewal, and potent immunoregulatory functions. Their presence in humans has long been debated, yet emerging evidence points to a population with phenotypic and functional similarity to murine B-1 cells. In a recent study, Shen, Q., Wang, H., Roco, J.A. et al. delineate a transcriptional program driven by TCF1 and LEF1 that underpins both the maintenance and regulatory capacity of B-1a cells.
Using genetic ablation models, the authors demonstrate that TCF1 and LEF1 are essential for sustaining B-1a cell numbers and function. LEF1 is predominantly expressed in fetal and bone marrow B-1 progenitors, while TCF1 expression is enriched in mature splenic and peritoneal B-1 cells. Loss of both factors results in a collapse of the B-1a pool, accompanied by aberrant proliferation, metabolic insufficiency, and acquisition of an exhausted phenotype marked by diminished IL-10 and PDL1. Mechanistically, TCF1 and LEF1 activate MYC-dependent metabolic pathways and foster a stem-like state upon activation, ensuring long-term persistence and immunoregulatory output.
The functional consequences of this transcriptional program are highlighted in an adoptive transfer model of neuroinflammation, B-1 cells deficient in TCF1 and LEF1 fail to restrain CNS pathology, emphasizing their contribution to immune homeostasis. Moreover, the detection of TCF1/LEF1-expressing B-1-like cells in human pleural fluid and in chronic lymphocytic leukemia suggests a conserved program with clinical relevance.
By linking transcriptional regulation to metabolic fitness and immunosuppressive function, this work positions TCF1 and LEF1 as central determinants of B-1a cell biology, providing a framework for investigating human B-1-like cells in health and disease.