Abstract 4134: Boosting anti-tumor immunity by promoting high endothelial venule and tertiary lymphoid structure formation in solid tumors via LTBR agonism

Abstract High endothelial venules (HEV) are specialized blood vessels that mediate lymphocyte trafficking to lymph nodes. Tertiary lymphoid structures (TLS) are ectopic lymphoid formations that develop in inflamed, infected or tumoral tissues. TLS contain HEV and B cell follicles surrounded by a T-cell zone and are characterized by abundant chemokine expression. The presence of TLS and HEV in solid tumors is positively correlated with patient survival in many cancer types, and may even be predictive of better response to immune-checkpoint blockade. However, the molecular mechanisms underlying the intratumoral HEV and TLS formation remain unclear. Using murine syngeneic tumor models, we found that systemic activation of lymphotoxin beta receptor (LTBR) with an agonistic antibody induced tumor-specific HEV formation, increased dendritic cell (DC) and T cell infiltration, and enhanced T cell activation in the tumor. In vitro assays revealed that LTBR agonism directly upregulated activation and maturation markers in bone marrow-derived DCs and promoted DC-mediated CD4 and CD8 T cell activation. Single agent LTBR agonist treatment attenuated Colon26 tumor growth in a CD8 T cell-dependent manner. In combination treatment studies, LTBR agonism further augmented anti-tumor efficacy of anti-PD1 and of CAR-T therapy. Notably, LTBR agonist mAb treatment upregulated the expression of TLS-related chemokines and induced TLS-like structures in approximately 20% of treated tumors. To enhance TLS induction, we generated syngeneic tumor models engineered to express several cytokines/chemokines and performed an in vivo screen for tumor-associated TLS formation. We identified some factors that in combination with LTBR agonism induced B cell enrichment and immature TLS formation, while others promoted robust TLS induction and anti-tumor effect. TLS formation induced by combined LTBR agonism and cytokine expression is associated with augmented anti-tumor responses to anti-CTLA-4 treatment. By studying anti-tumor mechanisms of LTBR agonism-mediated HEV and TLS formation, this work informs the future therapeutic strategies to boost T cell infiltration and activation in solid tumors. Citation Format: Disi An, Guoying Chen, Wei Wang, Katja Mohrs, David DiLillo, Christopher Daly, Gavin Thurston, John Lin, Namita Gupta, Mickey Atwal, Frank Kuhnert. Boosting anti-tumor immunity by promoting high endothelial venule and tertiary lymphoid structure formation in solid tumors via LTBR agonism. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4134.