DR5–Lig3 Feedback Loop Explains Why MSI Colorectal Tumors Respond to Immunotherapy

Overview

• A peer‑reviewed study published July 16, 2026, found that loss of the Mlh1 repair gene in mouse colorectal tumors triggers ER stress and DR5‑mediated apoptosis that starts a sustaining immune response.
• Researchers showed nuclear Lig3 produces extrachromosomal circular DNA (eccDNA) from dying tumor cells and that eccDNA amplifies immune activation, creating a positive DR5–Lig3 feedback loop.
• Analysis of human colorectal tumor gene‑expression datasets found that higher DR5 and Lig3 activity correlated with better responses to immune checkpoint inhibitors, but those human data are correlative.
• The authors propose two translational paths: test drugs that activate DR5 or boost eccDNA release to sensitize tumors, and evaluate DR5/Lig3 activity as a predictive biomarker, with preclinical human cell and organoid work planned next.
• The finding builds on the known immunogenicity of MSI/dMMR cancers, was published in Gastroenterology with partial NIH support, and will require safety testing because activating death‑receptor pathways could harm normal tissues.