NOTUM deletion restores full immunotherapy response in microsatellite-stable colorectal cancer mouse models

The University of Calgary team performed CRISPR knockout screens comparing immunotherapy-sensitive and resistant microsatellite-stable colorectal cancer lines, identifying NOTUM as the key secreted WNT inhibitor that suppresses T-cell infiltration. Gene-edited cells lacking NOTUM lost the ability to secrete this protein, resulting in restored antigen presentation and complete tumor clearance in syngeneic mice even without checkpoint blockade in some arms. This mechanism differs from the more common MSI-high pathway and explains the 85% non-response rate seen clinically.

The work highlights a tumor-intrinsic immune-evasion strategy missed by prior bulk transcriptomic studies that focused on stromal or T-cell exhaustion signatures. Unlike PD-1 inhibitor trials that achieved only modest gains in MSS disease, single-gene deletion produced binary outcomes, suggesting NOTUM acts as a dominant cloak rather than a redundant checkpoint. Similar WNT-modulatory programs appear in pancreatic and lung adenocarcinoma datasets, indicating potential cross-tumor applicability.

Limitations include reliance on transplantable mouse models that lack human microbiome and chronic inflammation contexts. No patient-derived organoid or PDX data were reported, and off-target effects of NOTUM inhibition on intestinal homeostasis remain untested. Next steps require selective small-molecule or antibody validation in humanized models before any clinical translation.