Researchers identify immune “off switch” exploited by cancer cells

Mayo Clinic researchers have identified a molecular mechanism that enables cancer cells and disease-causing pathogens to weaken T-cell responses, potentially explaining why immune defenses fail in a wide range of cancers, viral infections and inflammatory diseases. The study, published in the Journal of Clinical Investigation, describes how a previously obscure protein variant called TRAILshort functions as an immune “off switch.” In experimental models, blocking TRAILshort restored T-cell activity and improved the ability of immune cells to attack diseased targets, raising the possibility that the protein could become a therapeutic target for cancer immunotherapy and chronic infections.

TRAILshort is an alternatively spliced form of the TRAIL gene. The best-known TRAIL proteins participate in programmed cell death, a process through which immune cells eliminate infected or malignant cells. TRAILshort, however, has a distinct structure and biological behavior. Mayo Clinic scientists first identified it while investigating HIV nearly 15 years ago, and later found that cancer cells can also produce it. Until now, its precise effect on immune signaling had remained unclear. The new research shows that TRAILshort does more than interfere with cell death: it directly disrupts the signaling machinery that allows T cells to recognize and respond to danger.

T cells rely on the T-cell receptor, or TCR, to detect molecular fragments displayed by infected or abnormal cells. Once the receptor is engaged, a chain of phosphorylation events activates signaling proteins that reorganize the cell, promote cytokine production and enable the T cell to kill its target. The Mayo Clinic team found that TRAILshort interrupts this process by activating SHP-1, a protein tyrosine phosphatase. SHP-1 removes phosphate groups from key signaling molecules, effectively applying a biochemical brake before the T cell can complete its activation program.

The result is a form of immune tolerance that benefits diseased cells. When TRAILshort levels are elevated, T cells may encounter cancer cells or infected cells but fail to generate a sufficiently strong response. This mechanism was detected in melanoma, lung, breast, pancreatic and ovarian cancers, as well as Hodgkin lymphoma. Elevated TRAILshort was also associated with infectious diseases including HIV, COVID-19, tuberculosis and hepatitis C. The broad distribution of the protein suggests that it may represent a shared pathway of immune dysfunction rather than a mechanism restricted to a single tumor type or pathogen.

The researchers used highly specific antibodies and engineered preclinical models to examine the protein’s activity. When TRAILshort was blocked, T cells regained signaling capacity and showed improved functional responses against diseased cells. These findings are significant because immune failure in cancer and chronic infection is often attributed to a combination of suppressive signals within the tissue environment. TRAILshort appears to be one of those signals, acting at an early stage of T-cell receptor signaling and potentially preventing immune cells from entering a fully active state.

The study also examined chimeric antigen receptor T-cell therapy, or CAR-T therapy. In this treatment, a patient’s T cells are genetically modified to express synthetic receptors that recognize specific cancer-associated molecules. Although CAR-T therapy can produce durable remissions in some blood cancers, its effectiveness can be limited when tumor cells create an immunosuppressive environment. In preclinical experiments, TRAILshort reduced the ability of CAR-T cells to control tumors. Removing or blocking the protein restored CAR-T activity, indicating that TRAILshort may be an important barrier to the success of cellular immunotherapies.

A therapy directed against TRAILshort could therefore be used alongside CAR-T cells, immune checkpoint inhibitors or other treatments designed to activate antitumor immunity. The protein might also serve as a biomarker. Tumors with high TRAILshort expression could be more likely to resist immune-based treatments, while patients whose tumors show lower levels might respond differently. Before such applications can be considered in humans, researchers will need to determine how TRAILshort is produced, how it moves through the tumor microenvironment and whether blocking it causes excessive inflammation or autoimmune complications.

The mechanism may also be relevant to viral disease. Chronic infections such as HIV and hepatitis C can drive prolonged immune stimulation, followed by T-cell exhaustion and functional decline. During COVID-19 and tuberculosis, immune regulation can become similarly unbalanced, with inadequate pathogen control in some patients and damaging inflammation in others. Because TRAILshort appears in several of these conditions, researchers are investigating whether it contributes to a common pattern of immune suppression. If so, carefully timed TRAILshort inhibition could potentially strengthen antiviral or antimicrobial responses, although such an approach would require precise control to avoid worsening immunopathology.

The same biology could have an opposite therapeutic use in autoimmune disease and transplantation. In cancer and persistent infection, researchers may seek to reduce TRAILshort activity and release the brake on T cells. In lupus, Crohn’s disease or transplant rejection, increasing TRAILshort activity could theoretically dampen harmful immune responses without broadly suppressing the immune system. This two-directional strategy remains experimental, and additional studies are needed to establish whether the protein can be safely manipulated in patients. The discovery nevertheless provides a defined molecular target for regulating T-cell behavior across cancer, infection and immune-mediated disease.

Web References: Mayo Clinic; Journal of Clinical Investigation: https://www.jci.org/articles/view/194449

References: Journal of Clinical Investigation, “TRAIL splice variant TRAILshort disrupts T cell receptor signaling and promotes immune tolerance in vivo,” published 3 August 2026.