Effective mRNA vaccines by Moderna and BioNTech have proven their worth against COVID-19, but shots using DNA to code for the vaccine antigen still haven’t reached the market.
Now, researchers at Taiwan’s National Health Research Institutes have developed a DNA COVID-19 vaccine that’s delivered into cells with some extra help from an electrical pulse. The candidate induced high levels of antibody response in animals and protected hamsters against the disease, according to results published in the journal PLOS Neglected Tropical Diseases.
The team argues their DNA vaccine, dubbed pSARS2-S, could potentially offer a more stable option against COVID compared with mRNA shots, which require ultralow temperatures for transportation and storage.
Using DNA to code for a vaccine antigen is a logical approach. But DNA vaccines have only been approved for veterinary use so far, as their immune responses in humans are often not enough to offer clinically meaningful protection. That’s partly because of poor efficiency of DNA delivery into cells for antigen expression.
For its candidate, the Taiwanese team resorted to a technology called electroporation, which uses electrical pulse to open up temporary pores in the cell membrane to allow the vaccine’s DNA material to pass through. In the current study in animals, immunization was followed by a treatment with an electroporator device.
Like many other existing COVID vaccines, the team designed the shot to code for the spike protein of the SARS-CoV-2 coronavirus behind the disease.
In both mice and hamsters, the vaccine induced strong antibody responses against the spike protein. The antibodies peaked at eight weeks after immunization, but the levels remained high at Week 20.
The researchers further evaluated the vaccine’s efficacy by challenging hamsters with the SARS-CoV-2 virus at Week 7 after the animals were immunized twice three weeks apart. While animals that got a dummy shot lost about 11% of body weight after six days as a sign of COVID disease, those vaccinated with the DNA vaccine were protected from weight loss and showed significantly reduced viral RNA in their lungs.
Compared with other vaccine platforms, not many research groups have chosen the DNA pathway for developing COVID vaccines. One leader in that race, Inovio, recently suffered a setback as the U.S. federal government pulled back funding on a phase 3 trial for the company’s DNA candidate, INO-4800, citing rapid deployment of existing FDA-authorized shots. The shot is also based on electroporation for delivery, but concerns have targeted the Cellectra 2000 device that Inovio uses.
The Taiwanese team suggests a DNA vaccine may still be a useful approach for controlling COVID-19 given the long-lasting antibody response observed with its candidate. “The DNA vaccine is an ideal vaccine platform with several advantages, including easy design and production, stability at a range of temperatures, and low production cost,” the scientists noted in the study.