Polymer film that gradually releases DNA coding for viral proteins could offer an alternative method
Vaccines usually consist of inactivated viruses that prompt the immune system to remember the invader and launch a strong defence if it later encounters the real thing. However, this approach can be too risky with certain viruses, including HIV.
In recent years, scientists have been exploring DNA as a potential alternative vaccine.
In a paper published in the 27 January online issue of Nature Materials, researchers at Massachusetts Institute of Technology (MIT) describe 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, the researchers say they could overcome not only the safety risks of using viruses to vaccinate against diseases such as HIV, but they would also be more stable, making it possible to ship and store them at room temperature.
‘This type of vaccine delivery would also eliminate the need to inject vaccines by syringe,’ says Darrell Irvine, an MIT professor of biological engineering and materials science and engineering. ‘You just apply the patch for a few minutes, take it off and it leaves behind these thin polymer films embedded in the skin.’
Irvine and Paula Hammond, the David H. Koch Professor in Engineering at MIT, are the senior authors of the paper. The lead author is Peter DeMuth, a graduate student in biological engineering.
This type of vaccine delivery would also eliminate the need to inject vaccines by syringe
Scientists have had some recent success delivering DNA vaccines to human patients using electroporation, which requires first injecting the DNA under the skin, then using electrodes to create an electric field that opens small pores in the membranes of cells in the skin, allowing DNA to get inside. However, the process can be painful and give varying results, says Irvine.
‘It‘s showing some promise but it‘s certainly not ideal and it‘s not something you could imagine in a global prophylactic vaccine setting, especially in resource-poor countries.’
Irvine and Hammond took a different approach to delivering DNA to the skin, creating 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 millimetre into the skin.
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.
How much DNA gets delivered by tuning the number of polymer layers can be controlled
The researchers can control how much DNA gets 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 consisting of strands of RNA that resemble viral RNA, which provokes inflammation and recruits immune cells to the area.
In tests with mice, the researchers found that the immune response induced by the DNA-delivering film was as good as or better than that achieved with electroporation.