Scientists at Weill Cornell Medicine discovered a previously unknown link between two key pathways that regulate the immune system in mammals – a finding that impacts our understanding of chronic inflammatory bowel diseases (IBD), a family of disorders that severely impacts the health and quality of life of more than 2 million people in the United States.
The immune system has many pathways to protect the body from infection, but sometimes an overactive immune response results in autoimmune diseases including IBD, psoriasis, rheumatoid arthritis and multiple sclerosis. Interleukin-23 (IL-23) is one such immune factor that fights infections but is also implicated in many of these inflammatory diseases. However, it was unknown why IL-23 is sometimes beneficial, and at other times becomes a driver of chronic disease.
In the study, , the team found that IL-23 acts on group 3 innate lymphoid cells (ILC3s), a family of immune cells that are a first line of defense in mucosal tissues such as the intestines and lungs. In response, ILC3s increase activity of CTLA-4, a key regulatory factor that prevents the immune system from attacking the body and beneficial gut microbiota. This identifies ILC3s as a critical link between potent IL-23 driven inflammatory response and checkpoints for immune regulation in the intestine. It also provides clues on how to harness this pathway to fight cancer and alleviate a serious side effect of cancer immunotherapy.
“We were surprised to uncover the unexpected connection between these two major immune pathways that control health, immunity and inflammation,” said senior author , the Henry R. Erle, M.D.-Roberts Family Professor of Medicine, head of basic research in the and a member of the at Weill Cornell Medicine. “Until now, most research on CTLA-4 focused on T cells, another type of immune cell. By uncovering that it is selectively upregulated on ILC3s by IL-23, this demonstrates that we should be thinking about these pathways more broadly to develop more selective therapeutics.”
“IL-23 normally provides tissue protection in the gut, but something changes in chronic inflammatory diseases which makes IL-23 a key driver of tissue pathology, and that’s what we decided to investigate,” said postdoctoral researcher Anees Ahmed, the paper’s lead author.
The investigators used single-cell RNA sequencing to study the effects of IL-23 on different types of immune cells in the healthy intestine. This analysis revealed that IL-23 in the healthy gut potently turns on the CTLA-4 pathway in ILC3s. They then showed that blocking the CTLA-4 pathway in those cells led to severe intestinal inflammation.
To see if their results applied to humans, the investigators turned to the Jill Roberts Institute , which includes deidentified samples from people with IBD as well as healthy individuals. “This unique resource enabled us to quickly confirm that our findings in mice were relevant to IBD patients,” Sonnenberg said.
They then verified this finding in patients through collaboration with , professor of clinical pediatrics and chief of the Division of in the Department of Pediatrics at Weill Cornell Medicine, and a pediatric gastroenterologist at and the .
The group found evidence that this novel immunologic pathway exists in the healthy human intestine and becomes impaired in the inflamed intestine of IBD patients. “This may provide a new explanation of why IL-23 becomes a driver of intestinal inflammation in human IBD,” Sockolow said.
This study also suggests that this pathway may be harnessed to fight cancer and may explain why people receiving certain immunotherapy drugs often experience inflammation in the gut as a side effect. Immunotherapy drugs that block CTLA-4 are used to take the brakes off the immune system – allowing it to fight cancer. These new results suggest that CTLA-4 on ILC3 cells and other related innate or innate-like lymphocytes should be considered in fighting cancer. Further, it suggests that blocking CTLA-4 in ILC3s may lead to severe gut inflammation which can cause patients to discontinue their cancer treatment.
Much more research is needed before these findings can be applied to new treatments. Ahmed said that eventually it may be possible to develop more targeted treatments that avoid ILC3s in the gut or simultaneously block IL-23.
“In the future, we may be able to find ways to selectively block CTLA-4 or IL-23 in specific immune cells,” he said. “If we could manage it, that could lead to a breakthrough in fighting cancer while protecting the gut from inflammation.”
The findings could also have long-term applications in developing new treatments for a range of autoimmune diseases known to be mediated by IL-23. Drugs that target IL-23 already exist, Sonnenberg said, and potentially next-generation therapies that don’t completely block IL-23, but instead control the underlying mechanisms of IL-23-driven chronic inflammatory diseases, could be developed.
This research was supported by grants from the ³Ô¹ÏÍøÕ¾ Institutes of Health; the Burroughs Wellcome Fund; the Meyer Cancer Center Collaborative Research Initiative; the Dalton Family Foundation; the Cancer Research Institute Lloyd J Old STAR Award; and Linda and Glenn Greenberg.
Julie Grisham is a freelance writer for Weill Cornell Medicine.
