If you were given a choice of vaccine delivery method, would you rather a needle or a skin cream? Thought so. Well, the latter might be a viable option soon, as Stanford scientists have used a topical cream to strongly vaccinate mice against tetanus.
The key is a bacteria that’s almost certainly living on your skin right now: Staphylococcus epidermidis. It’s thought to be mostly harmless, but in previous research the team found that it sparks a strong immune response in people. It seems to be a pre-emptive defense against the microbe entering the bloodstream through everyday cuts and scratches that break the skin.
“We got blood from human donors and found that their circulating levels of antibodies directed at S. epidermidis were as high as anything we get routinely vaccinated against,” said Michael Fischbach, senior author of the new study.
They first conducted experiments on mice, who don’t normally have S. epidermidis on their skin. When it was dabbed onto their heads, levels of antibodies against the bacteria climbed over the next six weeks to levels higher than regular vaccines deliver.
The team wondered if this mechanism could be hijacked as a non-invasive vaccination method against more dangerous pathogens. They found that a protein called Aap on the bacterium’s surface is responsible for triggering antibody production, so the researchers tweaked it to display a tetanus toxin.
They repeated the experiment, giving some mice a tetanus-enhanced version of S. epidermidis, and others the regular kind. After a few doses on the skin across six weeks, their antibody levels were tested, and sure enough, those receiving the bioengineered bacteria showed extremely high levels of tetanus-targeting antibodies.
The final test was to inject the mice with lethal doses of tetanus. All mice that received the bioengineered bacteria stayed symptom-free. Even when given six times the lethal dose of tetanus, they survived. Meanwhile, all those given the natural version of S. epidermidis succumbed to the infection.
In even better news, it seems that this mechanism can be applied to a wide range of pathogens. In another test, they swapped the tetanus toxin for diphtheria, and found it also generated a powerful immune response in mice. This could end up being a brand new delivery method for many types of vaccines, which saves us more than the pain of the needle.
“We think this will work for viruses, bacteria, fungi and one-celled parasites,” said Fischbach. “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.”
As intriguing as the research is, it’s important to note that it’s still early days. The next step is to test it in monkeys, the team says, and if that works then human clinical trials would begin in two or three years’ time.
The research was published in the journal Nature.
Source: Stanford University
