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Updated: Aug 14, 2025

Analysis of Human T Cell Activity in an Allogeneic Co-Culture Setting of Pre-Treated Tumor Cells
Published on: March 7, 2025
TLR5 agonists enhance anti-tumor immunity and overcome resistance to immune checkpoint therapy
Caleb Gonzalez1, Sarah Williamson1, Seth T Gammon1
1Department of Cancer Systems Imaging, University of Texas MD Anderson Cancer Center, Houston, TX, 77030, USA.
Abstract:
Primary and adaptive resistance to immune checkpoint therapies (ICT) represent a considerable obstacle to achieving enhanced overall survival. Innate immune activators have been actively pursued for their antitumor potential. Herein we report that a syngeneic 4T1 mammary carcinoma murine model for established highly-refractory triple negative breast cancer showed enhanced survival when treated intra-tumorally with either the TLR5 agonist flagellin or CBLB502, a flagellin derivative, in combination with antibodies targeting CTLA-4 and PD-1. Long-term survivor mice showed immunologic memory upon tumor re-challenge and a distinctive immune activating cytokine profile that engaged both innate and adaptive immunity. Low serum levels of G-CSF and CXCL5 (as well as high IL-15) were candidate predictive biomarkers correlating with enhanced survival. CBLB502-induced enhancement of ICT was also observed in poorly immunogenic B16-F10 melanoma tumors. Combination immune checkpoint therapy plus TLR5 agonists may offer a new therapeutic strategy to treat ICT-refractory solid tumors.
Insights
Combining immune checkpoint therapies (ICT) with toll-like receptor 5 (TLR5) agonists like flagellin or CBLB502 improved survival in refractory triple-negative breast cancer and melanoma models. This strategy may overcome resistance to current cancer immunotherapies.
Area of Science:
- Immunology
- Oncology
- Pharmacology
Background:
- Primary and adaptive resistance to immune checkpoint therapies (ICT) limit patient survival.
- Innate immune activators offer potential for enhancing anti-tumor immunity.
Purpose of the Study:
- To investigate the efficacy of combining TLR5 agonists with ICT in refractory cancer models.
- To identify potential biomarkers for predicting response to combination therapy.
Main Methods:
- Utilized a syngeneic 4T1 mammary carcinoma murine model for triple-negative breast cancer and a B16-F10 melanoma model.
- Administered intra-tumoral flagellin or CBLB502 in combination with anti-CTLA-4 and anti-PD-1 antibodies.
- Analyzed survival, immunologic memory, cytokine profiles, and serum biomarker levels (G-CSF, CXCL5, IL-15).
Main Results:
- Combination therapy significantly enhanced survival in both 4T1 and B16-F10 models.
- Long-term survivors exhibited immunologic memory and a distinct cytokine profile activating innate and adaptive immunity.
- Low G-CSF and CXCL5, along with high IL-15, were identified as candidate predictive biomarkers for enhanced survival.
Conclusions:
- Combination of TLR5 agonists with ICT represents a promising therapeutic strategy for ICT-refractory solid tumors.
- This approach engages both innate and adaptive immune responses for improved anti-tumor activity.
- Biomarker analysis suggests potential for personalized treatment selection in future clinical applications.
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