Columbia researchers identify immune-suppressing cells that shield lung tumors

A team at Columbia University has mapped out one of lung cancer's most effective hiding places: a previously unknown type of cell that actively recruits the immune system's peacekeepers to shield tumors from attack. The discovery, published in Nature Immunology, identifies a specific fibroblast marked by a gene called CHL1 that appears nowhere in healthy lungs but thrives in cancerous ones. For patients, the finding opens a potential new line of attack against a disease that kills more Americans than any other cancer.

The work began with a simpler question: what role do fibroblasts—ordinary-looking cells that cluster around solid tumors—actually play in cancer's survival? Over the past decade, researchers have increasingly recognized that these cells are not passive bystanders. Olivia Ringham, a graduate student at Columbia's Vagelos College of Physicians and Surgeons, led the investigation into lung cancer specifically, a gap in the research landscape. Most prior work had focused on pancreatic tumors. "Much of the earlier work on these cancer-associated fibroblasts has focused on pancreatic cancer, but little is known about the cells in lung cancer," notes Nicholas Arpaia, the study's senior author and Ringham's adviser.

Ringham examined fibroblasts from a mouse model of lung cancer using single-cell transcriptomic profiling, a technique that has matured dramatically over the past decade. The method allowed her to read the genetic activity of individual cells, revealing hidden populations that would have been invisible in bulk tissue analysis. The CHL1 fibroblasts emerged as the anomaly: cells expressing a gene that should not appear in the lungs of healthy animals. The discovery raised an immediate question: what were they doing there?

The answer proved elegant and troubling. The CHL1 fibroblasts recruit regulatory T cells—immune cells whose normal job is to prevent the lungs from overreacting to the constant stream of foreign particles and pathogens that arrive with every breath. Without these regulatory cells, Ringham explains, the immune system would mount an inflammatory response to routine environmental exposure. But in the context of a tumor, this immunosuppression becomes a liability. The regulatory T cells accumulate at the tumor's border, creating a zone of immune tolerance that allows cancer cells to survive and grow unchecked.

The mechanism relies on a signaling protein called CXCL9, which the fibroblasts use to summon the regulatory T cells. When Ringham and her colleagues, working with collaborators at the University of Toronto, blocked this signaling pathway by inactivating the relevant genes in mice, the accumulation of regulatory T cells dropped sharply. The immune system, no longer suppressed, mounted an attack on the tumor. The finding suggested a direct causal link: the fibroblasts' recruitment strategy was essential to the tumor's survival.

The mouse model findings translated to human disease. Using tissue samples and clinical data from Columbia's repository, Ringham identified the same CHL1 fibroblasts in human lung cancers. Patients whose tumors contained higher numbers of these cells showed weaker immune responses against their cancer and lower progression-free survival rates—the time before the disease worsened. The correlation held, suggesting that what the team had discovered in mice reflected a genuine mechanism operating in people.

The therapeutic implications are substantial. Blocking the CXCL9 signaling pathway could theoretically unleash immune responses that current treatments fail to trigger. Because CHL1 fibroblasts do not appear in normal lungs, they also represent a potential direct target, though questions remain about their origin. "Where do these cells come from? How are they formed?" Ringham asks. Understanding that transformation could open another avenue: preventing the fibroblasts from becoming immunosuppressive in the first place. For now, the research points toward a new vulnerability in lung cancer's defenses—and a possible way to exploit it.