Imagine a new type of vaccine that does not require a needle to be injected into the muscle during vaccination. It only requires the application of a cream on the skin, which is painless to use and does not cause fever, swelling, redness, or arm pain. People do not need to wait in line for vaccination, and its price is low. According to the latest issue of Nature magazine, this vision is expected to become a reality thanks to the improvement of a common bacteria present on human skin by researchers at Stanford University School of Medicine in the United States. Researchers say that for most single celled organisms, the skin is a harsh living environment. This place is extremely dry, but there are still some stubborn microorganisms that make it their home, including Staphylococcus epidermidis. This type of skin symbiotic bacteria is usually harmless and can be found in almost everyone's hair follicles. In recent years, scientists have found that the immune system's response to Staphylococcus epidermidis is much more intense than expected. This time, researchers conducted an experiment in which Staphylococcus epidermidis was applied to the skin on the heads of mice, and their antibody response was monitored for 6 consecutive weeks. The results showed that the antibody response of mice to Staphylococcus epidermidis was "shocking", with antibody levels continuously increasing and reaching and maintaining levels higher than expected after routine vaccination at 6 weeks. Similar situations naturally occur in humans as well. Subsequently, researchers successfully transformed Staphylococcus epidermidis into a locally applicable "ready to use" live vaccine. They found that the Aap protein in Staphylococcus epidermidis is a key component that triggers a strong immune response. Its huge tree like structure is enough to extend the "branches" from the bacterial cell wall, exposing the outer layer to the immune system's "sentinel" cells and triggering antibody responses. Researchers used bioengineering methods to replace the gene encoding tetanus toxin fragments into the "branches and leaves" of Aap, and successfully induced extremely high levels of antibodies against tetanus toxin in mice. Mice vaccinated with an improved version of Staphylococcus epidermidis survived and showed no symptoms after receiving lethal doses of tetanus toxin. This vaccine only needs to be applied 2-3 times to obtain a life-saving antibody response in mice. In addition, the study also demonstrated that even if Staphylococcus epidermidis was previously present on the skin of mice, it would not interfere with the ability of experimental treatments to elicit strong antibody responses. (New Society)