An atlas of infiltrated B-lymphocytes in breast cancer revealed by paired single-cell RNA-sequencing and antigen receptor profiling

While it has been well-recognized that T-cell mediated adaptive cellular immunity plays important roles in cancer immune response and tumor control, the roles of B lymphocytes in tumor development and therapy have only been proposed until recently, and are still mostly controversial. To gain mechanistic insights into the origin and dynamics of tumor infiltrated immune cells, especially B lymphocytes, we combine single-cell RNA-sequencing and antigen receptor lineage analysis to characterize a large number of triple-negative breast cancer (TNBC) infiltrated immune cells and present a comprehensive atlas of infiltrated B-lymphocytes in TNBC, the most aggressive breast cancer subtype. We demonstrate that TNBC infiltrated B cells showed more mature and memory B cell characteristics, as well as high clonality and extensive IgH class switching recombination and somatic hypermutations. The B cell signatures based on single-cell RNA-seq results are significantly associated with improved survival for TNBC patients and provide better prognostication than classic single B cell markers (CD19 or CD20). Further dissection of the mechanisms regulating the functions and dynamic distribution of tumor infiltrated B cell populations will provide new clues for tumor immunotherapy.