Abstract LB125: Increased expression of tertiary lymphoid structure related genes contributes the strong anti-tumor activity of 5DEX-0509R that is dextran conjugated TLR7 agonist targeting TAM

Abstract Introduction: Toll-like Receptors (TLRs) are a class of Pattern Recognition Receptors (PRRs) capable of recognizing pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs). Since TLR activation in the tumor initiates anti-tumor immune responses, TLR agonists are an attractive target and are still actively studied in cancer immunotherapy. We have reported that 5DEX-0509R, a TLR7 agonist targeting Tumor-Associated Macrophages (TAMs), demonstrates selective delivery to TAMs and strongly shifts their phenotype from M2-like to M1-like, resulting in anti-tumor efficacy in various mouse models. Tertiary Lymphoid Structures (TLSs) are the lymph node-like structures in non-lymphoid tissue and are known to be predictive markers for cancer immunotherapy. TLSs in the tumor are formed by the interaction between Lymphoid Tissue Inducer (Lti) cells, High Endothelial Venules (HEVs), stroma, Follicular Helper T (Tfh) cells, and B cells. M1-like macrophages are reported to be one of the Lti cell populations. In this study, we explored the involvement of tertiary lymphoid structure formation in the anti-tumor activity of 5DEX-0509R. Methods: To clarify the effect of 5DEX-0509R on the tumor immune microenvironment, we analyzed the gene expression in mouse tumors by RNA sequencing. We then focused on genes related to the formation of TLSs. TLSs in the tumor ultimately support plasma cell maturation, which expresses antibodies against tumor antigens. Next, we evaluated the anti-tumor activity of 5DEX-0509R in a lymphoid cell-depleted condition using a mouse model. Results: 5DEX-0509R increased the expression of Cxcl12, Cxcl13, Ccl19, Icam1, Vcam1, Il21, Lta, and Ltb in EMT6 tumors. Cxcl13 is reported to induce Lti cell and HEV formation. Vcam, Icam, and Ccl19 are reported to be expressed on HEVs. Lta and Ltb are reported to be important inducers of TLSs. Il21 is known to be secreted by Tfh cells. Additionally, dosing of 5DEX-0509R increased the number of CD19+ B cells in the tumor, as shown by IHC analysis. These data suggest that 5DEX-0509R administration may induce the early formation of TLSs in the tumor microenvironment. In a tumor model using nude mice, the anti-tumor activity of 5DEX-0509R was attenuated. Furthermore, CD19 depletion in a mouse tumor model attenuated the anti-tumor activity of 5DEX-0509R. These data suggest that B cells are involved in the anti-tumor activity of 5DEX-0509R. Conclusion: These data suggest that the strong polarization of TAMs into an M1-like phenotype by 5DEX-0509R triggers the change of the tumor immune microenvironment towards the formation of early TLSs. Furthermore, B cells in the tumor contribute to the anti-tumor activity of 5DEX-0509R. We believe our 5DEX-0509R would be a novel treatment option for cancer patients. Citation Format: Yosuke Ota, Kimiya Matsuda, Hiroki Umehara, Hitoshi Ban. Increased expression of tertiary lymphoid structure related genes contributes the strong anti-tumor activity of 5DEX-0509R that is dextran conjugated TLR7 agonist targeting TAM [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_2):Abstract nr LB125.