Mayo Clinic Finds Cancer's "Off Switch" for Immune System

Cancer cells have been hiding a master switch that turns off the immune system, and Mayo Clinic researchers just found it.

The discovery centers on a protein called TRAILshort that acts like a stop sign for T cells, the immune system's primary cancer fighters. When cancer cells produce TRAILshort, it prevents T cells from recognizing and destroying them, allowing tumors to grow unchecked.

Published in the Journal of Clinical Investigation, the study reveals for the first time exactly how this immune shutdown happens. TRAILshort activates another protein called SHP-1, which acts as a molecular brake that stops T cells before they can attack diseased cells.

Researchers found elevated levels of TRAILshort in melanoma, lung, breast, pancreatic and ovarian cancers, plus Hodgkin lymphoma. The protein also appears in HIV, COVID-19, tuberculosis, and autoimmune diseases like lupus and Crohn's disease.

Dr. Andrew Badley, the study's senior author, sees enormous potential in this pattern. "TRAILshort appears in almost every condition where the immune system is failing or misfiring. That tells us we may have identified a fundamental switch in human immunity, not just a curiosity in one disease."

The team first discovered TRAILshort while studying HIV 15 years ago, but only now understand its mechanism. Using highly specific antibodies in preclinical models, they proved that blocking TRAILshort restores immune activity against cancer.

Why This Inspires

This discovery matters most for patients receiving CAR-T therapy, one of the most advanced cancer treatments available. Researchers found that TRAILshort significantly weakened CAR-T therapy's ability to control tumors, but blocking the protein restored its effectiveness.

Dr. Saad Kenderian, an oncologist and study co-author, believes this opens new possibilities. "Discovering the role of TRAILshort and how it inhibits CAR-T cells opens the door for a new therapeutic strategy to improve their activity."

The findings could work both ways. In cancer, scientists could use antibodies to remove excess TRAILshort and strengthen immune responses. In autoimmune diseases where the immune system attacks the body, they could potentially deliver more TRAILshort to calm harmful activity without broadly suppressing immunity.

Lead researcher Dr. Shahrzad Jalali emphasizes the novelty of their findings. "This is the first study to show that TRAILshort doesn't just block cell death but also acts as a signaling molecule that directly suppresses T-cell activity."

The research is part of Mayo Clinic's Precure Research initiative, which focuses on detecting and addressing disease before symptoms appear. By identifying this molecular mechanism, scientists now have a defined target and a clear path for developing new therapies.

Additional studies will determine whether blocking TRAILshort is safe and effective in patients, but the discovery gives researchers something they didn't have before: an actionable way to control when the immune system turns on and off.