Abstract 168: Harnessing TLS-derived B cells through STING and LTβR activation reveals a novel opportunity to antibody-mediated immunotherapy in pancreatic cancer.

Abstract B cells are increasingly recognized as key orchestrators of anti-tumor immunity, yet their therapeutic potential remains far less developed than T cell-based strategies. Tumor-infiltrating B cells often assemble into tertiary lymphoid structures (TLS), which associate with improved immune activation and favorable clinical outcomes across multiple malignancies. However, whether TLS-resident B cells directly mediate tumor control has remained unresolved. We recently demonstrated that concurrent activation of STING and lymphotoxin β receptor (LTβR) signaling reliably induces mature, germinal center-like B cell-rich TLS across diverse tumor models. Here, we investigated the functional requirement for TLS formation using CD79a-deficient mice, which lack B cells and therefore cannot generate TLS. In parallel, we used hybridoma technology to isolate monoclonal antibodies secreted by TLS-derived B cells. In wild-type pancreatic tumor models, dual STING+LTβR activation induced high endothelial venules, promoted robust TLS maturation, and drove the development of class-switched IgG+ memory B cells and long-lived plasma cells. This intervention constrained tumor growth, improved responsiveness to anti-PD-1 therapy, and when deployed as neoadjuvant treatment, prevented recurrence and conferred complete protection upon tumor rechallenge. TLS induction was observed across distinct tumor types and anatomical locations. Hybridoma clones derived from intratumoral TLS-B cells secreted tumor-reactive IgG that activated NK cells and stimulated the release of cytotoxic effector molecules, including Granzyme B, TNF-α, IFN-γ, and Perforin, consistent with potent antibody-dependent cellular cytotoxicity. In contrast, CD79a-deficient mice, despite maintaining T cell infiltration and forming high endothelial venules, failed to develop TLS and exhibited significantly reduced survival following rechallenge, underscoring the essential contribution of B cells and TLS-derived humoral immunity to durable anti-tumor effect. We are now leveraging the TLS-derived IgG for antibody therapy and antigen discovery. Using immunoprecipitation pull-down assays followed by mass spectrometry, we aim to identify novel tumor-associated antigens in pancreatic cancer as candidate therapeutic targets. Together, these findings show that therapeutically induced TLS function as in situ factories for generating potent, tumor-specific antibodies and reveal a promising B cell-centered strategy to overcome the resistance of immune-cold pancreatic tumors. Citation Format: Maxwell Duah, Yasuhiro Kikuchi, Fumiaki Kanamori, Tomoko Stansel, Gabrielle Brown, Masanobu Komatsu. Harnessing TLS-derived B cells through STING and LTβR activation reveals a novel opportunity to antibody-mediated immunotherapy in pancreatic cancer abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 168.