Immunological potential of tertiary lymphoid structures surrounding the primary tumor in gastric cancer.

Tertiary lymphoid structures (TLSs), which consist of B cells, T cells, follicular dendritic cells and high endothelial venules, have recently been found to be associated with effective antitumor immune responses in patients with cancer. Tumorinfiltrating T cells and B cells have each been demonstrated to be associated with survival in patients with cancer. We hypothesized that TLSs, an assembly of immune cells, may be important for the initiation and/or maintenance of T cell and B cell responses against tumors. The aim of the present study was to examine the cellular mechanism of B cells in TLSs within gastric cancer and to understand the antitumor immune response of TLSs. Each B cell subset in a tumor was examined using flow cytometry to evaluate B cell differentiation and the functional status of B cells. In addition, B cell clonality was investigated by analyzing the B cell antigen receptor gene using PCR, and the function and formation/maintenance of TLSs were evaluated using reverse transcriptionquantitative PCR. Tumorinfiltrating B cells were more differentiated compared with that in distant nontumor tissues and tumordraining lymph nodes. The PCR results revealed specific BCR gene expression in tumorinfiltrating B cells. The expression of costimulatory factors, CD80 and CD86, was observed, in addition to the constantly expressed major histocompatibility complex molecules (HLAABC and HLADR). CD70 was expressed in addition to CD27 in both CD20+ B cells and CD8+ T cells, indicating that these factors are activated together through their interaction. The mRNA expression levels of CCL21, CXCL13, PDL1, perforin and granzyme B in TLSs was significantly higher compared with that in nonTLSs. The majority of tumorinfiltrating B cells in gastric cancer exist in the form of TLSs around the tumor and have been antigensensitized and differentiated, and proliferated in TLSs but not in the lymph nodes. In addition, B cells in TLSs might primarily function as antigenpresenting cells and be associated with the induction of cytotoxic T cells.