It sounds a bit like something out of science fiction, but a topical vaccine that is rubbed on the skin is now closer to reality than ever before. In a new study led by Stanford University scientists, researchers engineered a common skin bacteria to express a tetanus toxin on their surfaces. When mice were colonized by these bacteria, they developed immunity to tetanus that prevented them from dying or showing symptoms when later exposed to the toxin.
In a separate experiment, the technique also enabled mice to develop antibodies against diphtheria toxin. The results were published in Nature on Dec. 11.
The researchers next hope to see whether the engineered skin bacteria can provoke an immune response out of primates before turning to human trials within two to three years, according to a Dec. 11 release.
The scientists harnessed a harmless skin bacteria called Staphylococcus epidermidis, which “reside on every hair follicle of virtually every person on the planet,” lead author Michael Fischbach, Ph.D., a bioengineer at Stanford, said in the release.
Previous work had found that these microbes, despite their abundance and generally genial nature, induce a T-cell immune response in mice and primates. Fischbach and colleagues determined that B cells, too, are involved in the immune response to S. epidermidis; mice swabbed on the head with the bacteria generated antibodies against accumulation-associated protein (Aap), a large protein that sits on the surface of the bacteria.
Swapping fragments of Aap with antigens from tetanus and diphtheria toxins and then letting the bacteria colonize mice skin led the rodents’ B cells to generate antibodies targeting the pathogens. Even six times the lethal dose of tetanus toxin didn’t kill the immunized mice.
“We think this will work for viruses, bacteria, fungi and one-celled parasites,” Fischbach said in the release. “Most vaccines have ingredients that stimulate an inflammatory response and make you feel a little sick. These bugs don’t do that. We expect that you wouldn’t experience any inflammation at all.”
Mice already colonized by normal S. epidermidis still showed an immune response when engineered cells were applied to their skin, suggesting the abundance of S. epidermidis on human skin wouldn’t interfere with the technique.