It took a global pandemic to accomplish one of the most significant advances in the history of vaccinology: widespread, commercial deployment of vaccines derived from nucleic acids. As of this writing, hundreds of millions of people have been vaccinated against SARS-CoV-2, the virus that causes COVID-19. And most of those shots have been the Pfizer-BioNTech and Moderna offerings, which are both of a type known as an mRNA (messenger RNA) vaccine.
Conceived decades ago but released to the public for the first time during the pandemic, mRNA vaccines so far are living up to their promise. Both the Pfizer and Moderna vaccines have proven to be about 95 percent effective against the novel coronavirus. In addition, this kind of vaccine can be tweaked with relative ease to target new variants of a virus, and its production does not rely on items that can be difficult to produce quickly in enormous quantities. And yet, a couple of drawbacks of mRNA vaccines have also been widely noted over the past six months: They depend on deep-freeze supply chains and storage, and they can produce significant side effects such as fever, chills, and muscle aches.
So hopes remain high for another kind of nucleic-acid vaccine, one that makes use of DNA rather than mRNA. DNA-based vaccines have most of the advantages of mRNA vaccines, yet they produce no significant side effects—and, crucially, they don't need to be refrigerated. These attributes could make these vaccines a boon to rural and low-resource regions. “If we really have to vaccinate 7 billion people, we might just need every possible technology," says Margaret Liu, chairman of the board of the International Society for Vaccines.
Inovio's device uses a technique called electroporation to sneak a DNA vaccine into cells. Kate Broderick, Inovio's senior vice president of R&D, has been working on this technique for years, but the pandemic provided both motivation and funding to accelerate development.
DNA vaccines come with a major challenge, however. When administered with an ordinary hypodermic needle, they've conferred only weak immunity, at best, in many human studies. But if a small, ambitious Pennsylvania company backed by the U.S. Department of Defense succeeds in its clinical trials, DNA vaccines—enabled by a new delivery technology—could soon join the fight against COVID-19, and a host of other viral illnesses.
The company, Inovio Pharmaceuticals, is using a technique known as electroporation, in which an electrical pulse applied to the skin briefly opens channels in cells to allow the vaccine to enter. After a standard vaccine injection, Inovio's electroporation device, which looks like an electric toothbrush, is held against the skin. At the press of a button, a weak electric field pulses into the arm, opening channels into the cells. The tool gives DNA vaccines the boost they need to work in humans—or so the company says. It's an engineering solution to a biological problem.
With its overseas warfighters in mind, the U.S. Department of Defense (DOD) has backed Inovio's approach with a US $71 million contract to scale up the manufacturing of its electroporation device, and an undisclosed sum to cover phase 2 and 3 studies of the company's COVID-19 vaccine. And the Bill and Melinda Gates Foundation gave the company $5 million as part of an effort to increase equitable access to COVID-19 vaccines.
Inovio is now finishing phase 2 studies that are testing the vaccine's safety and efficacy on relatively small groups in the United States and China, and those results are imminent. In the meantime, the company has ramped up manufacturing with a plan to supply hundreds of millions of COVID-19 vaccine doses to the global population, should the vaccine prove successful.
But here's the rub: The electroporation tool is essential to Inovio's vaccine, but it also adds a layer of complication. It's both an enabler and a handicap. Inovio must manufacture not only the vaccine but also the device and its disposable tips. Any vaccination site planning to administer Inovio's vaccine will need not only the device but also people who know how to use it. The public will have to develop trust in a new apparatus. And all of this will have to happen during a pandemic and a frenzied vaccine rollout characterized by rampant misinformation and, in some quarters, an unwillingness to be vaccinated.
Given that backdrop, the idea of complicating mass vaccinations with an electric device has drawn skepticism. “This is not standard methodology for giving vaccines," notes John Moore, an immunologist at Weill Cornell Medicine, in New York City. The technique might work, but “how practical it is is another question entirely," he says.
Neither the skeptics nor tough questions from regulators have deterred Inovio. Nor has the fact that, despite more than a decade of research and development in other disease areas, the company has yet to bring a DNA vaccine to market. These are hardly normal times. The coronavirus has propelled many other novel technologies, medicines, and vaccines into the mainstream, and in the process has created massive business success stories. Inovio is betting that its technology will make it into that elite group of pandemic-era winners.
Nucleic-acid-based vaccines have captivated scientists for decades because they can be quickly designed and easily manufactured. These vaccines are typically made with either DNA, the double-stranded molecule that carries the genetic code for living organisms, or messenger RNA (mRNA), a single-stranded molecule that is complementary to DNA and carries instructions from DNA for synthesizing proteins. DNA and mRNA vaccines can be thought of as blueprints that instruct a cell to produce a specific protein from the virus that will trigger an immune response.
Inovio's vaccine contains a snippet of DNA that codes for the production of a coronavirus protein. If the body is exposed to a real virus later, the immune system will recognize that protein and mount a defense. The DNA is first amplified in bacterial cells (top) and then purified (bottom).
In making a nucleic-acid vaccine, scientists first sequence the virus's genome. Next, they figure out which of its proteins is the most important and most recognizable by the human immune system. Then they manufacture either DNA or mRNA that codes for the production of that protein and formulate it into a vaccine. That genetic material gets injected into the body, where nearby cells take it in and start following their new instructions for making a viral protein. To the immune system, this looks like a viral infection, and it mounts a response. Now, should the real virus ever appear, the immune system is primed and ready to attack.
Altering the design of a nucleic-acid vaccine is as easy as plugging in a new code. That's incredibly important when facing a virus that mutates frequently. Indeed, several highly contagious variants of SARS-CoV-2, the virus that causes COVID-19, have already emerged globally, and scientists have warned that the currently available vaccines may be less effective against some of them.
Despite the allure of nucleic-acid vaccines, none had been approved for commercial use in humans by medical regulators prior to the pandemic. In fact, most nucleic-acid-based vaccines hadn't made it past midstage clinical trials. The problem: Human cells don't readily take in foreign DNA or mRNA. After injection, much of the vaccine would remain inert in the body and eventually break down, without prompting much of an immune response.
Developers of mRNA vaccines recently resolved the issue by packaging the vaccine with chemicals. In one approach, researchers encapsulate mRNA within fat droplets called lipid nanoparticles, which fuse with the cell membrane and help the vaccine get inside.
Companies such as BioNTech, Moderna, and CureVac were in the midst of testing various mRNA vaccines against other viruses when the COVID-19 pandemic hit. Market pressure and billions of dollars from governments helped companies finish the job, and quickly. The mRNA vaccine from BioNTech, through a collaboration with Pfizer, was first to market in the United States and Europe, followed swiftly by the one from Moderna.
But the delivery strategies used for mRNA vaccines haven't worked out for DNA vaccines. That challenge has led to an outpouring of creative development and the eventual adoption of an electrical engineering approach.
The first human studies of DNA vaccines, which began in the mid-1990s, “were a complete flop," says Kate Broderick, senior vice president of R&D at Inovio. The vaccine just didn't prompt much of an immune response. “It was a big surprise and disappointment," adds Jeffrey Ulmer, who was head of preclinical R&D at the pharma giant GSK until last year and is now an industry consultant. “Despite very good data in a wide variety of animal models for a wide variety of different disease targets, it just did not seem to translate into humans," he says.
The problem was getting the DNA, which is a big molecule, to penetrate not only through the cell's outer layers but also through the cell's nuclear membrane into the nucleus. Unlike an mRNA vaccine, which can function in parts of the cell outside the nucleus, a DNA vaccine can function only inside the nucleus. Some researchers reasoned that DNA vaccines worked well in small animals because the injection needle created pressure that damaged many surrounding cells, allowing DNA molecules to enter. But in the larger bodies of humans, the needle generates relatively little pressure, and fewer cells take in the vaccine.
So scientists began experimenting with more physical ways to deliver vaccines and increase cellular uptake. “It's common sense: Instead of saying 'Please, open a little window and let me get in,' you have a violent approach where you break the door," says Shan Lu, an immunologist at the University of Massachusetts Medical School.
To that end, researchers engineered all sorts of creative methods to physically force vaccines into the body. They tried sonoporation, which uses sound waves to permeate a cell's outer layer, and pressurized injections, whereby a piston pushed by a sudden release of energy delivers a narrow, high-pressure stream of liquid. They experimented with micro shock waves, in which a spark generated by electrodes causes a microexplosion, sending a wave of energy that forces a vaccine through the skin without a needle. They tried gene guns that propel DNA-coated gold particles into cells and microneedles that were laced with vaccine and engineered into skin patches.
The newest Inovio device, the Cellectra 3PSP, is currently manufactured at Inovio's facility in San Diego. The handheld Cellectra delivers about a hundred doses on a single battery charge. Its electrodes administer a series of electrical pulses that cause nearby cells to open channels through which the vaccine can enter.
Among all these contenders, electroporation stood out as particularly promising. “Electroporation was arguably the technology that allowed DNA vaccines to really reemerge as a technology that could be deployed," says Amy Jenkins, a biological technologies program manager at the U.S. military's research arm, DARPA, which has invested in both mRNA- and DNA-based vaccines.
Researchers have used electroporation routinely for decades to transfer genetic material into cells in the lab. Doctors have also used a high-voltage version of electroporation to break up cancerous masses in humans as part of a surgical technique. So adapting it to vaccines wasn't a radical step.
Inovio's newest electroporation device, the Cellectra 3PSP, is handheld and battery operated. It can deliver about a hundred doses on a single charge and has a life-span of about 5,000 uses, due to battery limitations. Each use requires a disposable tip. As with more conventional vaccines, the injection site is the upper arm. Vaccination starts with an intradermal injection of the vaccine dose—a shot that's only skin deep. Then, the tip of the Cellectra device is pressed against the skin, directly over the location of the shot. Electrodes about 3 millimeters in length administer a series of four square-wave electrical pulses that last 42 milliseconds each, at 0.2 amperes.
The recipient feels a brief twinge, similar to the level of pain people experience from a flu shot, according to a clinical study by Inovio. Recipients rated it at an average of about 2.5 on a 0-to-10 pain scale—although the feeling is said to be like a buzzing sensation, rather than the prick and pressure of a shot.
The pulses cause nearby cells to temporarily open channels through which the vaccine can enter. As soon as the electrical pulses finish, those channels close. “Now this DNA molecule is trapped inside the cells," says Inovio's Broderick. The DNA then “acts like a code, so your cells become a factory for producing the vaccine," she explains. Electroporation is generally 10 to 100 times as efficient at provoking an immune response as the same DNA vaccine given by a conventional needle injection alone, says Lu of the University of Massachusetts.
Over the last decade, Inovio's DNA vaccines have been tested against HIV, Ebola, MERS, Lassa fever, and human papillomavirus (HPV), each delivered with some form of electroporation. In total, more than 3,000 people have received one of Inovio's electroporated medicines, largely through phase 1 and 2 studies, Broderick says.
In a phase 1 study involving 40 volunteers, Inovio's COVID-19 vaccine, which is given in two doses, proved safe and generated an immune response. The results don't tell us much about how well the vaccine will protect against COVID-19 in real life. That will be clearer following the completion of a phase 2 study of 400 volunteers in the United States, which is currently underway. The company is also conducting a phase 2 study of 640 volunteers in China, where it has partnered with biotech company Advaccine Biopharmaceuticals Suzhou Co. to commercialize the vaccine.
During the pandemic, some vaccine developers have been linking the different phases of their clinical trials in an effort to speed up the process. But Inovio can't start on a phase 3 trial in the United States yet—first it has to answer questions from the U.S. Food and Drug Administration about the Cellectra 3PSP device. In September, the FDA notified Inovio of a partial “clinical hold" on trials, a tactic the agency uses when its reviewers find issues with safety or product quality that have not been addressed by the drug developer. Inovio's vaccine comes with a separate novel device, so that requires additional, independent oversight by the FDA's device reviewers, says Dennis Klinman, a former senior reviewer of vaccines at the FDA, and now a consultant. The additional device oversight is likely the reason for the clinical hold, he says.
Inovio says it plans to answer the FDA's questions using data from the phase 2 study, but it would not disclose the specifics of the agency's queries. “It was nothing about the safety or the use of the device in the clinic," Broderick says. “It's more logistical areas for us to clarify."
In addition to Inovio, at least three other companies— Genexine, Takis, and OncoSec—are conducting human studies of an electroporated DNA vaccine against COVID-19. Other companies, such as Ichor Medical Systems and IGEA Clinical Biophysics, have developed electroporation devices that they license to pharma companies for DNA vaccine delivery against other diseases. Not everyone thinks electroporation is the solution for DNA vaccines, however. Some groups continue to work on alternative delivery methods, hoping the surge of interest from the pandemic will push their strategies over the finish line too.
In Inovio's two-step process, the DNA vaccine is first administered via a syringe. Then the Cellectra device is pressed against the skin for electroporation of the cells.
Introducing a new, unfamiliar device to the vaccination process, particularly during a pandemic, undoubtedly brings logistical challenges. The devices must be mass produced and delivered, which will add to the cost of the vaccine. Medical personnel must be trained to operate the Cellectra. The extra step (the zap after the shot) adds time to each vaccination. Considering that people have been lining up by the thousands in miles-long car lines to get their COVID-19 vaccines, these inconveniences are not trivial.
“I don't know that [Inovio's vaccine] is going to get used" during this pandemic, says Moore, the immunologist at Weill Cornell. “It's not among the most potent, and it's among the most inconvenient to deliver, so in the end people will vote with their feet—or their arms, as it may be," he says. Liu of the International Society for Vaccines adds: “We don't even have enough people trained in the U.S. to give enough syringe injections." Complicating things with a new device and new administration method “is going to be hard to do," she says.
And then there's the issue of consumer acceptance of an unfamiliar device that zaps the skin. “I think the device presents a much larger problem, not from a logistical perspective but from a marketing perspective," says Bruce Goodwin, who currently leads research on enabling biotechnologies at the U.S. DOD's Joint Program Executive Office for Chemical, Biological, Radiological, and Nuclear Defense (JPEO–CBRND). “A device that [looks] basically [like] a mix between a sonicator and a stun gun isn't necessarily the kind of PR people are looking to put out there unless there's no other choice."
On the other hand, the COVID-19 vaccines available right now can't reach large swaths of the world. Pfizer's and Moderna's vaccines initially had to be transported and stored in freezers at about –80 °C and –25 °C, respectively. (In February, Pfizer revised its storage guidelines to allow for storage at
–25 °C for up to two weeks.) The COVID-19 vaccines developed by Johnson & Johnson, AstraZeneca, and Novavax as well as those deployed in China and Russia don't need ultracold freezers, but they all need refrigeration.
In many poor and remote parts of the world, this complicated supply chain of refrigerators or freezers simply doesn't exist. Even in more developed and urbanized countries, stories of mishaps abound. Poor temperature control spoiled 12,000 doses en route to Michigan. An unplugged freezer killed 2,000 doses at a hospital in Massachusetts. Widespread power outages in Texas halted deliveries and left officials scrambling to administer thousands of doses before they went bad.
A vaccine that can be stored at room temperature would avoid these pitfalls and “greatly facilitate distribution of the vaccine globally," says Ulmer, the former GSK researcher. “It's a big advantage." Inovio's vaccine is stable for a year at room temperatures of about 19 °C to 25 °C, and for at least a month in hot climates, according to the company.
Pfizer's and Moderna's mRNA vaccines also tend to trigger flulike side effects, such as fever, chills, headache, muscle pain, nausea, and fatigue. Some of those reactions have been incredibly strong, says Barbara Felber, a senior investigator in the vaccine branch of the National Cancer Institute. For example, within hours of getting an mRNA COVID-19 vaccine, Felber's 25- year-old son was trembling and shivering head to toe while wearing all the blankets in his apartment. “He had such a bad reaction that we were on the phone with him all night," Felber says. Of course, most people don't have this kind of reaction, she adds, and the side effects are transient. “It is better to have [side effects] than to get infected by SARS-CoV-2," she stresses.
The United States' Centers for Disease Control and Prevention (CDC) tracks adverse events of COVID-19 vaccines via a smartphone-based tool called
V-safe, which recipients can use to self-report their symptoms. About 25 percent of people who have participated have reported fevers, and 42 percent have reported headaches after taking the second dose of the Pfizer vaccine. “I have not heard of anybody who got a DNA injection with electroporation who had any of these types of side effects," Felber says.
For Inovio's DNA vaccine, the only side effect is that momentary buzzing twinge at the injection site, says Broderick, the company's R&D head.
The upsides of DNA vaccines, plus the ease of manufacturing and its low cost per dose, were enough to convince the DOD to invest heavily in Inovio early in the pandemic. In June 2020 the agency awarded $71 million to scale up the manufacturing of the Cellectra device for COVID-19 vaccines. The DOD will also pay for phase 2 and 3 studies of Inovio's clinical trials, says Nicole Dorsey, director of technology selection and evaluation at the DOD's JPEO-CBRND, which oversees the funding. “The electroporation device is probably the less appealing part of a DNA vaccine," but deploying it is a lot easier than maintaining cold-chain transportation overseas, she says.
The logistics of a new device seem quite manageable for the military. “Trying to roll out these [Cellectra] 3PSP devices for 300 million people at every Walgreens on every corner—man, it's a logistical problem that probably just isn't soluble," says Chris Earnhart, chief technology officer of the enabling biotechnologies program at JPEO-CBRND. “In the DOD's case, it's easily soluble, because we have a very specific population and the numbers are just lower."
Even if Inovio's technology and vaccines don't get adopted in the civilian world during this pandemic, they may prove useful in the long run. “The investments we're making now are related to the COVID response, but in a lot of ways, we're also preparing for the next event," says Earnhart. “That could be a biowarfare event, or it could be another endemic outbreak."
And perhaps it's time for a tech upgrade. Inovio's Broderick notes that people first began administering medicine via syringe around 1650, when goose quills were used for needles. “It's actually a really antiquated modality," she says. “At a time when we carry more computing power around in our pockets than what went to the moon, we should be open to newer technologies for vaccine delivery."
This article appears in the June 2021 print issue as “Vaccines Go Electric."