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A Safer Way to Vaccinate
Vaccines usually consist of inactivated viruses that prompt the immune system to remember the invader and launch a strong defense if it later encounters the real thing. However, this approach can be too risky with certain viruses, including human immunodeficiency virus (HIV).
In recent years, scientists have been exploring DNA as a potential alternative vaccine. About 20 years ago, DNA coding for viral proteins was found to induce strong immune responses in rodents, but so far, tests in humans have failed to duplicate that success.
In a study published online in Nature Materials, researchers at the Massachusetts Institute of Technology (MIT) have described a new type of vaccine-delivery film that holds promise for improving the effectiveness of DNA vaccines. If such vaccines could be successfully delivered to humans, they could overcome not only the safety risks of using viruses to vaccinate against diseases, such as HIV infection, but they would also be more stable, making it possible to ship and store them at room temperature, the researchers say.
This type of vaccine delivery would also eliminate the need to inject vaccines by syringe, according to Dr. Darrell Irvine. “You just apply the patch for a few minutes, take it off, and it leaves behind these thin polymer films embedded in the skin,” he said.
The researchers created a patch made of many layers of polymers embedded with the DNA vaccine. These polymer films are implanted under the skin using microneedles that penetrate about half a millimeter into the skin — deep enough to deliver the DNA to immune cells in the epidermis, but not deep enough to cause pain in the nerve endings of the dermis.
Once under the skin, the films degrade as they come in contact with water, releasing the vaccine over days or weeks. As the film breaks apart, the DNA strands become tangled up with pieces of the polymer, which protect the DNA and help it get inside cells.
The researchers can control how much DNA is delivered by tuning the number of polymer layers. They can also control the rate of delivery by altering how hydrophobic the film is. DNA injected on its own is usually broken down very quickly, before the immune system can generate a memory response. When the DNA is released over time, the immune system has more time to interact with it, boosting the vaccine’s effectiveness.
The polymer film also includes an adjuvant — a molecule that helps to boost the immune response. In this case, the adjuvant consists of strands of RNA that resemble viral RNA, which provokes inflammation and recruits immune cells to the area.
Source: MIT; January 27, 2013.