A team of Stanford Medicine researchers has created a vaccine that breaks 230 years of vaccine tradition by protecting against multiple respiratory threats simultaneously, rather than targeting one specific pathogen. In a study published in Science, the vaccine protected mice against SARS-CoV-2, other coronaviruses, hospital-acquired bacterial infections, and even common allergens like house dust mites. The vaccine is delivered as a nasal spray and provides broad protection in the lungs for several months, offering a glimpse into what a truly universal vaccine might look like. How Does This Vaccine Work Differently From Traditional Vaccines? Every vaccine since Edward Jenner's smallpox inoculation in the 1790s has relied on the same fundamental principle: teaching the immune system to recognize a specific component of a pathogen, such as the spike proteins on a coronavirus. This approach works well until the virus mutates or a new pathogen emerges, which is why people need new flu shots and COVID-19 boosters every year. The Stanford vaccine takes a radically different approach. Instead of mimicking a pathogen's distinctive features, it mimics the signals that immune cells use to communicate with each other during an actual infection. This novel strategy activates both branches of the immune system, the innate and adaptive responses, creating a feedback loop that sustains broad protection. "What's remarkable about the innate system is that it can protect against a broad range of different microbes," said Bali Pulendran, the Violetta L. Horton Professor II and a professor of microbiology and immunology at Stanford Medicine. Bali Pulendran, Professor of Microbiology and Immunology, Stanford Medicine What Are the Two Key Components That Make This Vaccine Work? The vaccine, currently known as GLA-3M-052-LS+OVA, contains two critical elements working together. First, it includes toll-like receptor stimuli, which are molecules that directly activate innate immune cells in the lungs. These are the generalist defenders of the immune system, including dendritic cells, neutrophils, and macrophages that can recognize and destroy a wide range of pathogens. Second, the vaccine contains a harmless antigen called ovalbumin, an egg protein that recruits specialized T cells into the lungs. These T cells send chemical signals called cytokines that keep the innate immune cells activated for weeks to months, far longer than they would normally remain active. How to Understand the Vaccine's Protective Mechanism - Innate Immune Activation: The vaccine stimulates toll-like receptors on innate immune cells, causing them to become highly alert and ready to destroy any pathogen they encounter in the lungs. - T Cell Recruitment: The harmless antigen in the vaccine attracts specialized T cells to the lungs, where they continuously send activation signals to keep innate immune cells vigilant. - Sustained Protection: This two-part system maintains a heightened immune state in the lungs for months, providing what researchers call a "double whammy" defense against infection. What Did the Study Show in Vaccinated Mice? In the research, mice received drops of the vaccine in their noses, with some receiving multiple doses spaced a week apart. When exposed to respiratory viruses, the results were striking. Vaccinated mice that received three doses were protected against SARS-CoV-2 and other coronaviruses for at least three months. The protection was dramatic. In unvaccinated mice, these viruses caused severe weight loss and often death, with lungs inflamed and full of virus. By contrast, vaccinated mice lost much less weight, all survived, and their lungs were nearly clear of the virus. The vaccine reduced the amount of virus in the lungs by 700-fold through its prolonged innate immune response. For any viruses that managed to slip through this initial defense, the adaptive immune response was extraordinarily swift. Vaccinated mice could launch virus-specific T cells and antibodies in as little as three days, compared to the typical two weeks needed in unvaccinated mice. "The lung immune system is so ready and so alert that it can launch the typical adaptive responses in as little as three days, which is an extraordinarily short length of time," explained Bali Pulendran. Bali Pulendran, Professor of Microbiology and Immunology, Stanford Medicine What Pathogens Did the Vaccine Protect Against? The breadth of protection was one of the most surprising findings. In the study, vaccinated mice were protected against multiple distinct threats, including respiratory viruses like SARS-CoV-2 and other coronaviruses, bacterial infections such as Staphylococcus aureus and Acinetobacter baumannii (both common causes of hospital-acquired infections), and even allergens like house dust mites. This wide-ranging protection suggests the vaccine's approach of activating generalist immune cells may overcome the limitations of traditional antigen-specific vaccines. How Did Researchers Discover This Approach? The breakthrough built on earlier research into the Bacillus Calmette-Guerin (BCG) tuberculosis vaccine, which is given to approximately 100 million newborns every year. Epidemiological studies had long shown that this vaccine could decrease infant mortality from other infections, suggesting cross-protection that lasted months, but the mechanism remained mysterious. In 2023, Pulendran's team published research explaining how the BCG vaccine works. They discovered that T cells recruited to the lungs as part of the adaptive immune response were sending signals to innate immune cells to keep them active for several months, far longer than the typical few days or week. The researchers identified these signals as cytokines that activate pathogen-sensing receptors called toll-like receptors on innate immune cells. "In that paper, we speculated that since we now know how the tuberculosis vaccine is mediating its cross-protective effects, it would be possible to make a synthetic vaccine, perhaps a nasal spray, that has the right combination of toll-like receptor stimuli and some antigen to get the T cells into the lungs," noted Bali Pulendran. Bali Pulendran, Professor of Microbiology and Immunology, Stanford Medicine That speculation became reality in the current study. The research team, led by postdoctoral scholar Haibo Zhang, designed the new vaccine to mimic exactly what they had theorized, and the results in mice confirmed their hypothesis. What Could This Mean for Human Health? If the vaccine translates successfully to humans, the implications could be transformative. Rather than receiving multiple shots every year for seasonal respiratory infections, people could potentially receive a single nasal spray vaccine that provides broad protection. Such a vaccine would also be ready to deploy should a new pandemic virus emerge, without needing months to develop a pathogen-specific vaccine. The researchers emphasized that while the results in mice are encouraging, significant work remains before this vaccine could be tested in humans. However, the fundamental shift in approach, moving away from 230 years of antigen-specific vaccine design toward a strategy that activates the immune system's generalist defenders, represents a conceptual breakthrough in immunology. "We were interested in this idea because it sounded a bit outrageous. I think nobody was seriously entertaining that something like this could ever be possible," said Bali Pulendran. Bali Pulendran, Professor of Microbiology and Immunology, Stanford Medicine
