Nasal immune booster shields mice from flu long before exposure
Researchers at the University of Tokyo tested a nasal adjuvant called K3-SPG, which stimulates innate immune sensors. In mice, the treatment provided temporary protection against respiratory viruses and improved survival after influenza even when given well before exposure, with effects observed up to 100 days later. The study appears in Science Advances and points to trained immunity as a possible stopgap before pathogen-specific vaccines are ready.
K3-SPG is a nanoscale adjuvant pairing a synthetic DNA segment, CpG oligodeoxynucleotide, with schizophyllan, a β-glucan. The DNA component engages TLR9. In mouse experiments, one intranasal dose lessened influenza A severity, improved survival, and remained detectable at 100 days, though it declined. It also helped susceptible mice exposed to SARS-CoV-2.
Delivery by nose outperformed skin or blood routes. The adjuvant did not greatly lower lung viral loads; instead, it appeared to help animals endure infection and reduce tissue injury. Early protection involved macrophages, later innate lymphoid cells, with chromatin-level shifts suggesting durable functional changes. Effects required TLR9 and inflammatory signaling.
If similar effects translate to humans, a broad-acting nasal immune booster could offer temporary protection during early outbreak phases before matched vaccines exist. It may especially matter for older adults, immunocompromised people, healthcare workers, and communities facing respiratory virus surges. Yet mouse results may not predict human outcomes, and durability, safety, and optimal timing remain uncertain. Such an approach could complement, not replace, vaccines tailored to a specific pathogen.