Tumor infiltrating B-cells signal functional humoral immune responses in breast cancer

Tumor-infiltrating B-cells (TIL-B) in breast cancer (BC) have previously been associated with improved clinical outcomes; however, their role(s) in tumor immunity is not currently well known. This study confirms and extends the correlation between higher TIL-B densities and positive outcomes through an analysis of HER2-positive and triple-negative BC patients from the BIG 02-98 clinical trial (10yr mean follow-up). Fresh tissue analyses identify an increase in TIL-B density in untreated primary BC compared to normal breast tissues, which is associated with global, CD4⁺ and CD8⁺ TIL, higher tumor grades, higher proliferation and hormone receptor negativity. All B-cell differentiation stages are detectable but significant increases in memory TIL-B are consistently present. BC with higher infiltrates are specifically characterized by germinal center TIL-B, which in turn are correlated with T_FH TIL and antibody-secreting TIL-B principally located in tertiary lymphoid structures. Some TIL-B also interact directly with tumor cells. Functional analyses reveal TIL-B are responsive to BCR stimulation ex vivo, express activation markers and produce cytokines and immunoglobulins despite reduced expression of the antigen-presenting molecules HLA-DR and CD40. Overall, these data support the concept that ongoing humoral immune responses are generated by TIL-B and help to generate effective anti-tumor immunity at the tumor site.

View Supplementary information include: Supplementary figure: Figure S1: Gating strategies for lymphocyte subpopulations. Figure S2: Phenotypic characterization of B-cells in blood, lymph nodes, and breast cancer tissues. Figure S3: B-cell organization in tonsil. Figure S4: Spatial distribution of TIL-B in human breast cancer. Figure S5: Cytokine profile in plasma and fresh breast tissue supernatants. Supplementary table: Table S1: Association between clinicopathological parameters and TIL-B of patients from the BIG 02-98 clinical trial. Table S2: Added value of infiltrating B and T cells, stromal TIL scores as continuous variables predicting DFS and OS. Table S3A: Correlation between B cell TIL and other TIL subsets in BC. Table S3B: TIL subset correlations between FACS and IHC in IDC. Table S4: TIL subsets correlations by FACS. Table S5: The antibodies used for flow cytometry.