Long‑lived monocyte‑derived cells in the lung may help close the gap between injectable flu shots and true mucosal protection, according to a new study published in Nature Immunology. The CDC estimates that the 2024‑2025 influenza season produced roughly 51 million illnesses, 710 000 hospitalizations and 45 000 deaths in the United States, highlighting the need for better immunity at the site where the virus first enters the body.
New Cell Population Identified
Scientists at the University of Rochester Medical Center set out to determine how tissue‑resident memory CD8⁺ T cells (TRM cells) are sustained after an influenza infection. Using a mouse model, they followed CCR2‑positive monocytes that migrated into the lung during the acute phase of disease. Rather than disappearing after the virus was cleared, a portion of those cells transformed into a memory‑stage population that persisted for more than four months.
The senior author, Minsoo Kim, PhD, emphasized that this finding challenges the long‑standing belief that only adaptive lymphocytes can provide lasting protection. “Our work identified a long‑lived monocyte‑derived population in the lung that provides essential support for durable T‑cell immunity,” Kim said in a news release.
Role of Galectin‑1 in T‑Cell Support
When the investigators selectively eliminated these persistent monocyte‑derived cells, the number of lung CD8⁺ TRM cells fell sharply and the mice lost protection against a heterosubtypic influenza strain. Further analysis revealed that the remaining cells positioned themselves next to TRM cells and released galectin‑1, a protein that directly activated CD8⁺ T cells and amplified their response to transforming growth factor‑β, a cytokine that promotes tissue residency.
Kim noted that the galectin‑1 signal offers a concrete, targetable mechanism for TRM maintenance. “We identified galectin‑1 as a powerful immune signal that can be used as a vaccine adjuvant to enhance mucosal immunity,” he explained.
These observations illustrate a broader principle: innate immune cells can be reprogrammed to support adaptive memory, a concept that may apply to other respiratory pathogens beyond influenza.
Potential for Nasal Vaccine Enhancement
To explore therapeutic relevance, the team administered recombinant galectin‑1 intranasally together with an experimental live‑attenuated influenza vaccine. Mice that received the galectin‑1‑adjuvanted vaccine displayed markedly stronger memory CD8⁺ T‑cell responses in the lung than those given the vaccine alone.
“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 approach could help address the historical inconsistency of mucosal immunity achieved by current intranasal formulations.
While the data are encouraging, the work was performed exclusively in animal models. Further development of stable galectin‑1 formulations and human trials will be required before this strategy can be applied clinically. The same innate‑adaptive crosstalk might inform vaccine design for future pandemics, according to the authors.
For health‑care professionals who counsel patients on immunizations, the study signals that upcoming respiratory vaccines may look different: they could rely on mucosal delivery and harness innate‑derived signals rather than relying solely on intramuscular injection. This shift may be especially important for vulnerable patients who struggle to mount strong systemic responses.
Human trials are still needed.
