Skin-friendly bacteria could revolutionize vaccinations

Imagine a world where vaccines are creams applied to the skin by health care workers instead of needles inserted into muscles. Even better, it's completely pain-free and is not accompanied by fever, swelling, redness, or arm pain. No need to stand in long lines to get it. Plus, it's cheap.

That vision could become a reality, thanks to researchers at Stanford University who have domesticated a species of bacteria that lives on the skin of people around the world.

We all hate needles -; everyone does. There is not a single person who does not like the idea that you can replace the shot with cream. ”

Dr. Michael Fischbach, Liu Family Professor, Professor of Bioengineering

According to Fischbach, the skin is a scary place to live. “It's incredibly dry, too salty for most single-celled organisms, and there's not much to eat. I can't imagine anything wanting to live there.”

However, a small number of hardy microorganisms make it their home. Among them are Staphylococcus epidermidisa generally harmless bacterial species that colonizes the skin.

“These bugs are present in every hair follicle of virtually every person on the planet,” Fischbach said.

Fischbach said the bacteria that colonize our skin are probably ignored by immunologists because they don't seem to contribute much to our health. “We thought there wasn't much going on there.”

That turns out to be a mistake. In recent years, Fischbach and his colleagues have discovered that the immune system mounts a much more aggressive response to bacteria. Staphylococcus epidermidis More than anyone expected.

In a study to be published on December 11th, natureFischbach and his colleagues focused on key aspects of the immune response. Antibody production. These specialized proteins attach to specific biochemical features of invading microorganisms, often allowing them to successfully enter cells or travel through the bloodstream to places they shouldn't. This prevents Individual antibodies are very picky about what they attach to. Each antibody molecule typically targets a specific biochemical characteristic belonging to a single microbial species or strain.

Fischbach, postdoctoral fellow Dr. Jennette Boosbein (senior and first author of the study, respectively), and their colleagues wanted to know: Immunity in mice whose skin is not normally colonized by bacteria. What will happen to the system? Staphylococcus epidermidisIf a microorganism appears there, will an antibody reaction against that microorganism occur?

Unprovoked (antibody) levels?

Bousbaine's first experiment was simple. Dip a cotton swab into a vial containing: Staphylococcus epidermidis. Gently rub the cotton swab on the head of a normal mouse – no need to shave, rinse or wash. Then return the mouse to the cage. Over the next six weeks, we draw blood at set points and ask: Did this mouse's immune system produce antibodies that:? Staphylococcus epidermidis?

The mouse antibody response is Staphylococcus epidermidis “It was shocking,” Fischbach said. “Those antibody levels increased slowly, then increased further, and then increased again.” After six weeks, they reached concentrations higher than expected from routine vaccinations. -; and they stayed at that level.

“It's like vaccinating mice,” Fischbach said. Their antibody responses were strong and specific, as if they were responding to a pathogen.

“The same thing seems to happen naturally in humans,” Fischbach said. “When we took blood from human donors, we found that their circulating antibody levels were directed against: Staphylococcus epidermidis It was as expensive as what we routinely get vaccinated against. ”

That's puzzling, he says. “Our ferocious immune responses to these commensal bacteria that roam beyond the all-important antimicrobial barrier we call our skin seem to serve no purpose.”

what happened? It may boil down to a line scrawled by early 20th century poet Robert Frost: “Good fences make good neighbors.” Fischbach said most people thought the fence was skin. But it's far from perfect. Without the help of the immune system, it can quickly break through.

“The best fences are antibodies. Antibodies are the immune system's way of protecting us from the inevitable cuts, scrapes, cuts and scratches that we accumulate in our daily lives,” he said. .

Antibody responses to infectious pathogens begin only after the pathogen enters the body; Staphylococcus epidermidis It happens pre-emptively, before a problem occurs. This allows your immune system to respond as needed. For example, when there is a break in the skin and a normally harmless insect enters and tries to pass through our bloodstream.

Develop a live vaccine

Fischbach's team changed direction one step at a time. Staphylococcus epidermidis It will be a plug-and-play live vaccine that can be applied topically. They said that part Staphylococcus epidermidis The biggest culprit in blocking a strong immune response is a protein called Aap. This giant tree-like structure, five times the size of the average protein, protrudes from the bacterial cell wall. They periodically crawl through the skin, sample the hair follicles, and snatch samples of what's fluttering in Aap's “leaves” and return them inside for the rest of the immune system to see, and then take part of its outermost mass. They believe that the body may be exposed to the sentinel cells of the immune system. Cells responsible for creating the appropriate antibody response aimed at that item.

(Mr. Fischbach is a co-author of a study led by Dr. Yasmin Belkaid, director of the Pasteur Institute, and a co-author of the Fischbach team's study, which will be published in the same issue.) nature. This related research identifies sentinel immune cells called Langerhans cells that alert the rest of the immune system to the presence of bacteria. Staphylococcus epidermidis On your skin. )

Aap triggers a surge of blood-borne antibodies, known to immunologists as IgG, as well as other antibodies called IgA, which reach the mucous lining of the nostrils and lungs.

“We're inducing IgA in the nostrils of the mice,” Fischbach said. “Respiratory pathogens that cause colds, flu, and COVID-19 tend to enter the body through the nostrils. Regular vaccines cannot prevent this. It only becomes effective once it gets into the bloodstream, so a vaccine would be much better at stopping it from getting there in the first place. ”

Once scientists identified Aap as the main target for antibodies, they looked for ways to make it work.

“Genet did some smart engineering,” Fischbach said. “She substituted a gene that encodes part of the tetanus toxin for a gene fragment that encodes a component that normally appears in the leaves of this giant tree-like protein. Now, it's this fragment. -; a harmless mass of highly toxic bacterial protein -; swaying in the wind. “Will the mouse's immune system 'recognize' it and develop a specific antibody response against it?”

The researchers repeated the soaking and swabbing experiment, but this time they used the raw version. Staphylococcus epidermidis or bioengineered Staphylococcus epidermidis Encodes tetanus toxin fragment. They administered several applications over a six-week period. The mice were wiped down with a bioengineered substance. Staphylococcus epidermidisdeveloped very high levels of antibodies targeting tetanus toxin, while others did not. The researchers then injected the mice with a lethal dose of tetanus toxin, which gave the mice natural tetanus toxin. Staphylococcus epidermidis Everything gave in. Mice given the modified version remained asymptomatic.

Similar experiments in which the researchers inserted the gene for diphtheria toxin in place of the gene for tetanus toxin into an Aap “cassette player” also induced large concentrations of antibodies targeting diphtheria toxin.

The researchers ultimately discovered that just a few applications were enough to generate a life-saving antibody response in mice.

By colonizing very young mice, they also Staphylococcus epidermidisfound that the pre-existing presence of bacteria on the skin of these mice (which is typical in humans but not mice) did not impede the treatment's ability to stimulate a strong antibody response. I did. This means our species has virtually a 100% skin colonization rate, Fischbach said. Staphylococcus epidermidis There are no problems using this construct on humans.

Look, Mom, there are no limits.

In a change of strategy, the researchers produced fragments of tetanus toxin in a bioreactor and chemically stapled them to the Aap in a dotted manner. Staphylococcus epidermidissurface. To Fischbach's surprise, this turned out to generate a surprisingly strong antibody response. Fischbach initially reasoned that each time the bacteria divided, the amount of toxins lingering on the surface would be further diluted, gradually weakening the immune response. Just the opposite happened. When applied topically, the worms produced enough antibodies to protect mice from six times the lethal dose of tetanus toxin.

“We know it works in mice,” Fischbach said. “Next, we need to show that it works in monkeys, and that's what we're trying to do.”Hopefully, this vaccination approach will enter clinical trials within two to three years. He predicts.

“We think this will also be effective against viruses, bacteria, fungi and single-celled parasites,” he said. “Most vaccines contain ingredients that stimulate an inflammatory response and make you feel a little sick. These bugs don't do that. We're confident that you won't experience any symptoms. I look forward to it.” inflammation not at all. ”

Researchers at the University of California, Davis. National Human Genome Research Institute. National Institute of Allergy and Infectious Diseases. and the National Institute of Arthritis and Musculoskeletal and Skin Diseases contributed to the research.

This research was supported by the National Institutes of Health (grants 5R01AI175642-02, 1K99AI180358-01A1, P51OD0111071, and F32HL170591-01), the Leona M. and Harry B. Helmsley Charitable Trust, the Chan Zuckerberg Biohub, and the Bill and Melinda Gates Foundation. Funded. , Open Philanthropy and Stanford microbiome therapy initiative.