DR5-Lig3 Feedback Loop May Shape Immunotherapy Response in dMMR Colorectal Cancer

Researchers have identified a death receptor 5 (DR5)/ligase 3 (Lig3) feedback loop that may help sustain immune recognition of mismatch repair–deficient colorectal cancer, according to an experimental study published in Gastroenterology. The findings connect tumor-cell death and extrachromosomal circular DNA (eccDNA) release with immune activation, but they remain primarily preclinical.¹

“We’ve gathered enough evidence to suggest that this feedback loop is an important piece of the puzzle,” said lead author Lin Zhang, PhD, professor of medicine at the Keck School of Medicine of USC. “Our hope is that these findings can someday help make cancers more visible to the immune system and more responsive to immunotherapy treatment.”²

Microsatellite instability (MSI) and deficient DNA mismatch repair (dMMR) can make tumors more recognizable to the immune system because defective DNA repair increases tumor-associated genetic abnormalities. These cancers tend to respond better to immune checkpoint inhibitors than cancers without these characteristics, although the biological factors governing individual responses remain incompletely understood.²

How was the colorectal cancer mechanism studied?

The researchers created a mouse model of dMMR colorectal cancer by disabling a DNA repair gene in tumor cells and implanting the altered cells into immunocompetent mice. They then evaluated immune responses alongside changes in cellular signaling, behavior, and gene activity.¹

DR5 and Lig3 emerged as central components of the proposed mechanism. According to the investigators, the DNA repair defect increased DR5 activity, promoting tumor-cell death. Dying cells subsequently released eccDNA, with greater release observed when Lig3 activity was elevated. The eccDNA then stimulated a broader immune response, establishing a positive feedback loop that perpetuated immune pressure against the tumor.¹

The experiment was designed to define biological causality rather than to evaluate a therapeutic regimen. No investigational drug, clinical comparator, dosing schedule, or prospective efficacy end point was reported. Consequently, the results do not establish that pharmacologically manipulating DR5, Lig3, or eccDNA will improve treatment outcomes.

What did the feedback loop show in human tumors?

The investigators also analyzed gene-expression and outcome data from patients with colorectal cancer. Tumors with higher DR5 and Lig3 activity were more likely to respond to immune checkpoint inhibitor treatment, according to the report.¹,² However, numerical response rates, survival outcomes, sample size, and adjusted effect estimates were not provided in the institutional summary.

“One of the most encouraging parts of the study was seeing that the same signals showed up in patient tumors,” Zhang said. “That suggests we’re uncovering a mechanism that could be clinically relevant.”²

The human findings provide correlative support for the mouse experiments, but they do not establish DR5 or Lig3 as validated predictive biomarkers. It also remains unclear whether expression of either gene adds predictive value beyond established MSI or dMMR testing.

Clinically, the study addresses an important question within the immunotherapy landscape: why some MSI or dMMR tumors respond more effectively than others despite sharing a broadly immunogenic phenotype. The proposed loop could help explain response heterogeneity, but the research did not compare the mechanism across current colorectal cancer treatment strategies or define its role in treatment resistance.

What must be established before clinical translation?

The researchers plan to investigate whether activating DR5 or increasing eccDNA release can enhance immune checkpoint inhibition. They also intend to assess whether DR5 and Lig3 expression could support treatment selection. Studies using human colorectal tumor cells are required before either strategy advances to clinical testing.²

Additional work will need to determine the safety of intensifying DR5-mediated cell death or eccDNA-associated immune signaling, identify reproducible biomarker thresholds, and prospectively validate associations with response and survival. Whether the mechanism applies to MSI or dMMR endometrial, ovarian, or other cancers also remains unresolved.

The study was supported by National Institutes of Health grants and Keck School of Medicine of USC start-up funding. The authors reported no conflicts of interest.¹

References

1. Hao S, Sato Y, Battaglin F, et al. (2026 Jul 16). A DR5/ligase 3-mediated feedback loop perpetuates immunogenicity in mismatch repair deficient colorectal cancer. Gastroenterology. https://www.gastrojournal.org/article/S0016-5085(26)07034-4/fulltext
2. Researchers at the Keck School of Medicine of USC have identified a biological feedback loop that helps explain why certain colorectal cancers respond better to immunotherapy. (2026 Jul 16). EurekAlert. https://www.eurekalert.org/news-releases/1136118