Oligoclonal expansion of IgG+ B cells along with Tfh cell response is associated with a better outcome in endometrial cancer.

B cells play a critical role in tumor immunity, with their presence associated with improved prognosis in various cancers, including endometrial cancer (EC). However, the nature of the B cell response within the tumor microenvironment (TME) remains incompletely understood. In this study, we conducted single-cell analyses of B cells and CD4+ T cells in the TME of EC. We found that the TME of EC harbored abundant plasmablasts and plasma cells (PCs), which were rare in normal endometria. PCs primarily expressed either IgG or IgA, and a high abundance of IgG in TME was associated with better overall survival. B cell receptor (BCR) repertoire analysis revealed a clonal expansion of IgG+ B cells, coinciding with an increased presence of T follicular helper (Tfh) cells in the TME. Notably, Tfh cells shared T cell receptor clones with cycling CD4+ T cells, indicating local proliferation. BCR repertoire analysis also suggested that IgG+ PCs differentiate from IFN-responding B cells and double-negative B cells in the TME. Additionally, recombinant oligoclonal IgG antibodies were found to recognize antigens expressed by tumor cells as well as normal endometrial cells. Collectively, our study shows that the clonal expansion of IgG+ B cells, along with the Tfh cell response, is associated with a better outcome in EC.