A New Suction Technique for Delivering DNA Vaccines

Nucleic acid-based therapies: The future

Nucleic acid-based medicines involve treating a disease, or preventing a disease, by targeting the underlying genetic code. While their development has been ongoing for several decades, recent advances in next-generation sequencing technologies and other molecular biology research methods have seen these therapeutics move closer towards the clinic. Most recently, Pfizer–BioNTech's COVID-19 vaccine, BNT162b2, became the first mRNA-based vaccine approved for human use.

Nucleic acid-based therapeutics are projected to "change the standard of care for many diseases and actualize personalized medicine". For this to be realized, there are hurdles associated with nucleic acid-based therapeutics and preventatives that must be overcome.

"Nucleic-acid medicine works when synthetic or engineered nucleic acids enter host cells and, using the cellular machinery, direct the production of encoded proteins. For a nucleic acid vaccine, the proteins then leave the cell and prompt an immune response," says Hao Lin, professor in mechanical and aerospace engineering at Rutgers School of Engineering. "The process of transferring RNA or DNA from outside of muscle or skin cells to the inside is called transfection," he adds.

Successful transfection is fundamental for a nucleic acid-based therapeutic to fulfil its purpose. Currently, there are a number of different approaches used, and these differ for RNA and DNA. Jonathan Singer, assistant professor in the department of mechanical and aerospace engineering, and co-author on the paper, explains: "For DNA there are two methods that have been used to induce cellular transfection. These include electroporation that uses an electric field current and air-jet microdroplet delivery." Electrical fields are most commonly used, however they are associated with adverse reactions such as inflammation and tissue damage.

RNA, on the other hand, degrades quickly and so is delivered in a carrier molecule, such as a lipid nanoparticle. These nanoparticles protect against degradation and also aid the transfection of RNA into the cell. Thus, while DNA is more stable than RNA upon injection, it is harder to deliver it to target cells for transfection.

A suction method for delivering DNA

Lin and colleagues have been working on novel methods to improve DNA delivery. In a new study published in Science Advances, they outline a suction-based technique in which a moderate negative pressure is applied to the skin after DNA injection. The method can be likened to "cupping therapy", an ancient practise in which cups are applied to the skin and a vacuum is created to draw the skin into the cup.

Lin and colleagues first tested their method in rat models, using green fluorescence protein (GPF) to analyze the transfection of pure DNA. Next, they conducted a proof-of-concept study in which they analyzed host immune responses in rats following injection of a candidate DNA vaccine followed by the suction technique. "Injection followed by suction induced seroconversion in 80% of rats by two weeks and 100% by four weeks. Notably, immune responses in rats who received a single injection followed by suction were not statistically different from those who received two injections, suggesting that this method of DNA vaccine delivery may provide clear benefits," the authors write.

There were no observable adverse effects or tissue damage when using the suction method. The device used to apply suction is likened to a blackhead remover, with a similar pressure range.

Based on these initial study results, the technology has been licensed for use in human clinical trials of a COVID-19 vaccine, which has advanced to Phase II. Preliminary results from a Phase I study conducted in Korea has reported that the use of suction was very well tolerated, Lin says.

How does the suction-based method work?

On a molecular level, how does applying a negative pressure trigger the uptake of DNA molecules by skin cells? Lin and colleagues don't know with full certainty, but they have some hypotheses. "One [hypothesis] is that the stretching–relaxation of the cells under suction triggers certain molecular mechanisms to take in the extra membranes that are created during such a process," Joel Maslow, developer of gene-based therapies and vaccines and co-author of the paper, says. If DNA molecules are in the vicinity of these "extra membranes" they will be taken in together. "However, we emphasize that this is strictly a hypothesis and much more work is required to validate it," he adds.

A portable, battery-powered suction device for human clinical trials. Credit: Rutgers University.

The researchers believe that the effect of adding suction to aid transfection is local. However, in the case of the COVID-19 vaccine study, once the antigens are produced and an immune response is triggered, the effect is systemic.

Overcoming vaccine access issues

The most challenging aspect of this work, the researchers say, was to carefully define the conditions required to optimize DNA expression. They believe that the suction device will greatly advance the ability to deliver vaccines throughout the world, particularly to remote areas with limited resources.

"The suction device has numerous advantages relative to other devices for DNA vaccine and therapeutics delivery," says Lin. "First, it is very inexpensive and easy to use, requiring minimal training. Second, the device is run from a battery that is easily rechargeable. Third, is the high degree of patient acceptance as the device will help deliver DNA vaccines and therapeutics without pain or discomfort. Fourth, unlike the significant set up times with other devices, this only requires changing out a cap and then pressing the power button; the machine will turn off in a few seconds," he adds.

Next, the researchers plan to work on identifying the molecular mechanisms that lead to suction-induced endocytosis and will focus on optimizing the protocol such that it is even more effective and convenient.

Hao Lin, Jonathan Singer and Joel Maslow were speaking to Molly Campbell, Science Writer for Technology Networks.

Reference: Lallow EO, Jhumur NC, Ijaz A, et al. Novel suction-based in vivo cutaneous DNA transfection platform. Sci Adv. 2021;7(45):eabj0611. doi: 10.1126/sciadv.abj0611.