Immune checkpoint therapy, a type of cancer immunotherapy that helps the immune system recognize and attack tumors, has transformed cancer treatment. While these therapies can produce long-lasting benefits for some patients, many cancers either fail to respond or become resistant over time.

One major challenge is the tumor microenvironment —the network of cells and signals surrounding tumors that can weaken immune cells and protect cancer from treatment. This protective environment can act like a shield that prevents immunotherapy from working effectively.

Researchers at University of California San Diego investigated whether microRNAs —small RNA molecules that help control gene activity—play a role in creating this treatment-resistant environment. The team focused on microRNA-25 (miR-25), which stood out after analyses showed that its levels changed in tumors that responded to immunotherapy.