Abstract 2044: High TLR3 transcript levels correlate with high TIM3 and VISTA checkpoints, but not with outcome after immune checkpoint blockade

Abstract Introduction: The Nobel Prize-winning discovery of Toll-like Receptors (TLR) in 2011 sparked the exploration of TLR3 as a key target in cancer pathogenesis and immunotherapy treatment. Upon activation by double-stranded RNAs, TLR3 stimulates the production of cytokines and chemokines that augment inflammation and cell death, which are risk-factors in several cancers including colorectal cancer (CRC). Despite the growing interest in TLR3, its specific role in influencing patient outcomes and interactions with other immune checkpoints remains inadequately understood. In this study, we evaluated the association between TLR3 RNA expression levels and clinical outcomes to determine its potential role as a biomarker in cancer prognosis and immune checkpoint inhibitor (ICI) treatment response. Methods: RNA expression levels of TLR3 and other immune checkpoints were evaluated in 514 tumors (489 patients with full clinical outcome annotation) in a clinical-grade laboratory and categorized as “High” (75-100 percentile) or “Not-High” (0-74 percentile). Univariate logistic regression assessed the association between high TLR3 expression, patient characteristics, immune markers, and cancer subtypes, followed by multivariable logistic regression for variables with p ≤ 0.05. Survival analyses was conducted through the Kaplan-Meier method on patients with available survival data. Overall survival (OS) and progression-free survival (PFS) were stratified by TLR3 expression (“High” vs “Not-High”) and compared using the log-rank test. Results: High expression of TLR3 RNA was seen in 90/514 (17%) among all patients and 11/140 (8%) in CRC patients. The highest proportion of high TLR3 expressors were seen in liver and bile duct cancers (7/19, 36.8%), pancreatic cancer (16/55, 29.1%), and ovarian cancer (12/43, 27.9%). High TLR3 RNA expression was significantly correlated with high VISTA (OR = 2.12, p = 0.004) and TIM3 (OR = 2.10, p = 0.026) RNA levels, and was lower in CRC (OR = 0.39, p = 0.008). CRC was the only cancer subtype in logistic regression analyses with a statistically significant correlation with high TLR3 RNA expression. In survival analyses of all cancer patients and CRC patients, high TLR3 RNA expression did not significantly correlate with OS and PFS, regardless of ICI treatment status. Conclusion: High TLR3 RNA expression was associated with higher levels of VISTA and TIM3 RNA; CRC had lower TLR3 levels than other cancers. However, TLR3 expression was not a statistically significant predictive biomarker for better outcomes (OS and PFS) in cancer patients, regardless of ICI treatment. Citation Format: Marvin Hsieh, Daisuke Nishizaki, Taylor J. Jensen, Sarabjot Pabla, Jeffrey M. Conroy, Paul DePietro, Shumei Kato, Razelle Kurzrock. High TLR3 transcript levels correlate with high TIM3 and VISTA checkpoints, but not with outcome after immune checkpoint blockade [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 2044.