The first signs of itchy eyes or a runny nose can send allergy sufferers running to the drugstore for over-the-counter relief. Yet these medicines only alleviate allergy symptoms and do nothing to address the root cause: our immune system' overreaction to harmless substances. The sole cure is a series of injections that desensitize the body with small doses of allergens over months or years. But many patients avoid these shots because of possible severe side effects—including anaphylaxis.

That dilemma has led Stephen Miller of Northwestern University and Lonnie Shea of the University of Michigan on a mission to develop a safer method—one that briefly hides the contents of allergy shots from the immune system’s attacks.

To teach the immune system what is and is not the enemy, it is necessary to acquaint developing immune cells in the liver and spleen with the harmless proteins they should leave alone later. The problem is that mature immune cells will sometimes attack allergens in an injection before they reach these learning centers. So Miller, an immunologist, and Shea, a biomedical engineer, have designed a Trojan horse delivery method: an allergen enveloped in a nanoparticle. These particles are about the same size as fragments of dying blood cells, so the immune system registers them as normal debris and lets them pass through the bloodstream to the liver and spleen. There the particle casing dissolves, releasing the allergens.

As reported in a new paper in the Proceedings of the National Academy of Sciences USA, the researchers tested this idea in mice allergic to ovalbumin, a protein found in eggs. The scientists first loaded nanoparticles with egg proteins, which would trigger a severe allergic reaction on their own, and then injected the nanoparticles into five mice. The mice showed no reaction. And later, when the researchers injected them with straight ovalbumin to see if they were still allergic, they showed no signs of airway inflammation. Furthermore, blood tests revealed increased numbers of regulatory T cells, which dampen the immune system. These results indicate that the nanoparticle-cloaked allergens slipped through the body’s defenses undetected—and that the immune system subsequently learned that these allergens were not the bad guys.

The use of nanoparticles in allergy treatments could offer a powerful tool to combat a range of allergies and even autoimmune disorders such as multiple sclerosis, according to Kari Nadeau, director of the Sean N. Parker Center for Allergy & Asthma Research at Stanford University. That is because the nanoparticle shells can be filled with immune triggers from many different substances, including pollen and dust mites. Other researchers have already seen positive results in experimenting with nanoparticles to treat peanut allergies. Next, Miller and Shea plan to run a clinical trial for celiac disease, a condition in which the immune system overreacts to wheat proteins.