Hidden immune cells in the lung could lead to better flu vaccines
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Influenza continues to cause major illness each year in the United States, leading to more than 35,000 deaths annually. Children, older adults, pregnant individuals, people with weakened immune systems and those with chronic conditions such as heart disease, metabolic disorders and cancer are especially vulnerable.
Vaccination remains the most effective way to prevent flu infection, but current vaccines do not always stop the virus from taking hold in the respiratory tract. Now, new research appearing in Nature Immunology suggests that a previously overlooked group of immune cells in the lungs may help change that.
Rethinking how the immune system 'remembers' infection
After infection or vaccination, the immune system forms long-lived "memory" cells that can respond quickly if the virus returns. In the lungs, a specialized type of immune cell called tissue-resident memory T cells acts as a first line of defense at the site where viruses enter the body.
"These cells are positioned right where infection begins, so they can react immediately and help limit viral spread," said Minsoo Kim, Ph.D., a professor of microbiology and immunology at University of Rochester Medicine and lead author of the study. "They are a central goal for next-generation vaccine design because they provide fast, local protection in the respiratory tract."
However, most current flu vaccines—especially those given by injection—do not reliably build strong immune memory in the airways, leaving a gap in protection against initial infection and transmission.
Immune cells that stay behind to help
In the new study, researchers focused on how the immune system builds and maintains these protective memory T cells. They discovered that a subset of monocytes, a type of immune cell normally thought to be short-lived, can persist in the lungs for months after influenza infection.
These long-lasting cells behave differently than expected. Instead of disappearing, they appear to support the formation of immune memory by helping memory T cells survive and function in the lung.
"Our work identified a long-lived monocyte-derived population in the lung that provides essential support for durable T cell immunity," Kim said. "This challenges the traditional view that immune memory is driven only by T and B cells, and shows that innate immune cells also play a lasting role."
A key molecule that strengthens immune memory
The research also uncovered how these monocyte-derived cells communicate with T cells. They produce a protein called galectin-1, which helps activate and sustain tissue-resident memory T cells.
When galectin-1 was added to an experimental nasal flu vaccine in mice, the immune response in the lungs became significantly stronger.
The finding opens the door to new vaccine strategies. "We identified galectin-1 as a powerful immune signal that can be used as a vaccine adjuvant to enhance mucosal immunity. This is a completely new approach for improving how vaccines work in the respiratory tract," Kim said.
Why current vaccines fall short—and what could come next
Most flu vaccines today are injected into the muscle and are very effective at preventing severe illness, but they do not consistently prevent infection in the nose and lungs. Nasal vaccines aim to solve this problem by targeting immunity at the site where viruses first enter, but their effectiveness has been inconsistent.
"Existing nasal vaccines often fail to generate strong or durable protection," Kim said. "This tells us we need new strategies that can better activate immune memory in the airways."
The study suggests that enhancing interactions between innate immune cells and memory T cells could be one such strategy.
Toward a new generation of vaccines
Beyond influenza, the findings may have implications for other respiratory viruses, including those that cause seasonal illness and pandemics.
"We now see that innate immune cells are not just first responders—they can also shape long-term immune memory," Kim said. "This opens up the possibility of designing vaccines that intentionally reprogram these cells to improve protection."
A potential new direction for flu prevention
While the results are promising, they were demonstrated in animal models, and further work is needed before clinical use in humans. Researchers are now working to develop more stable forms of galectin-1 that could be safely used as a vaccine additive.
If these findings translate successfully to humans, they could reshape how respiratory vaccines are designed. Instead of focusing only on antibody responses or circulating immune cells, future vaccines may also target the long-term behavior of immune cells that live in the lungs themselves.
By harnessing this newly discovered "helper" population of immune cells, researchers hope to build vaccines that not only prevent severe disease but also stop infection earlier and more effectively at the point of entry.
Publication details
Galectin-1High monocyte-derived subset provides innate immune help in generating functional T cell memory, Nature Immunology (2026). DOI: 10.1038/s41590-026-02638-9
Journal information: Nature Immunology
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Common illnesses & PreventionInfectious diseasesAllergy and immunology Provided by University of Rochester Medical Center Who's behind this story?
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