Abstract A054: AMP-410: A VEGF-dependent conditional 4-1BB agonist drives localized antitumor immunity with high therapeutic index across multiple tumor types

Abstract Background: 4-1BB agonists show potent antitumor activity but are limited by systemic toxicity. We have developed AMP-410, an anti-VEGF × 4-1BB molecule that confines 4-1BB activation to VEGF-rich tumors, achieving durable efficacy that was well tolerated in preclinical studies. To extend these findings, we investigated temporal and spatial immune mechanisms, local immune activity, and comparative performance of AMP-410 relative to a clinical-stage PD-1 × VEGF bispecific. Methods: AMP-410 was evaluated in human 4-1BB transgenic mice bearing syngeneic MC38 colorectal or B16F10 melanoma tumors and in humanized CD34+ NCG mice bearing A549 non–small cell lung cancer (NSCLC) xenografts. Tumor and peripheral immune cells were profiled by single-cell RNA sequencing (scRNA-seq) at early and late time points and by paired T-cell receptor sequencing (TCR-seq). Serum cytokines, liver immune responses, and histopathology were assessed to monitor systemic activity. Comparative efficacy studies included a PD-1 × VEGF bispecific as a clinical benchmark. VEGF concentrations were measured in interstitial fluid (ISF) and matched serum samples from multiple human tumor types to evaluate translational selectivity. Results: Temporal scRNA-seq revealed progressive remodeling of the tumor microenvironment, from early M1-like macrophage activation to late expansion of cytotoxic and memory-like CD8+ T cells. TCR-seq demonstrated localized clonal expansion within tumors with minimal overlap in draining lymph nodes, confirming spatially restricted immune activation. Despite strong intratumoral engagement, systemic cytokines and hepatic immune signatures remained near baseline, indicating limited peripheral activation. In the A549 humanized model, AMP-410 achieved deeper tumor regression with prolonged survival compared to the PD-1 × VEGF bispecific while maintaining superior peripheral safety, reflected by near-baseline serum IFNγ levels. Across multiple human tumor types, ISF VEGF levels exceeded serum concentrations by more than 100-fold, supporting the translational selectivity of this VEGF-dependent mechanism. Conclusions: The conditional 4-1BB agonist AMP-410 elicits potent, localized antitumor immunity by activating 4-1BB selectively within VEGF-rich tumors. This mechanism maximizes tumor-specific immune activation and tolerability, achieving durable efficacy with a high therapeutic index. These findings support the advancement of AMP-410 for clinical evaluation as a first-in-class tumor-localized 4-1BB immunotherapy. Citation Format: Xiaofei Zhou, Michelle Yen, Joseph R. Brady, Oliver Yvon, Marwa Bsat, Johnny Bray, Sarah Phat, Vishal Kamat, Kyriakos D. Economides, Daniël Blom. AMP-410: A VEGF-dependent conditional 4-1BB agonist drives localized antitumor immunity with high therapeutic index across multiple tumor types abstract. In: Proceedings of the AACR Immuno-Oncology Conference (AACR IO): Discovery and Innovation in Cancer Immunology: Revolutionizing Treatment through Immunotherapy; 2026 Feb 18-21; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Immunol Res 2026;14(2 Suppl):Abstract nr A054.