Eight to 10 years ago, Bill Gates asked gene therapy pioneer James M. Wilson, MD, PhD, whether his lab’s expertise in using adeno-associated virus (AAV) vectors could be applied toward fighting a pandemic. At the time, the Bill & Melinda Gates Foundation had approached Wilson, director of the Gene Therapy Program (GTP) at the University of Pennsylvania, about using AAVs to deliver antibodies against HIV.

With encouragement from the Foundation, Wilson’s lab and GTP began to study applications of AAV vectors as countermeasures for pandemic respiratory infections such as those caused by influenza viruses. That research sparked a call to Wilson last February from a colleague at the U.S. Department of Health and Human Services, who asked if the AAV approach to fighting pandemic flu—the subject of a GTP collaboration with Janssen Pharmaceuticals—could be applied against COVID-19 as well.

After saying he didn’t see why not, Wilson reached out to several agencies within HHS, as well as developers of antibody therapies against SARS-CoV-2 before connecting with Regeneron Pharmaceuticals, based on its expertise in developing therapeutics based on proteins, especially antibodies.

This week, Penn announced that GTP will partner with Regeneron to explore whether its two-antibody “cocktail” REGEN-COV2 (casirivimab and imdevimab) can prevent COVID-19 infection when delivered as a nasal spray via AAV vectors. REGEN-COV2 received FDA Emergency Use Authorization (EUA) on November 21 as a treatment for adults and youths ages 12 years and older with mild-to-moderate COVID-19.

The partners have signed a sponsored research agreement, with Regeneron retaining an option for rights to the nasal spray antibody cocktail. The partnership will proceed in two phases. The first phase will include validation of the effectiveness of the antibodies delivered via AAV in a large animal model challenge study, where animals will be given the antibody cocktail via AAV and exposed to the novel coronavirus. If that study is successful, the research team will complete studies to support filing of an IND application with the FDA.

Regeneron joins several developers that have disclosed plans to study or develop nasally-administered COVID-19 drugs and vaccines over the past year. The list includes AIM ImmunoTech, Altimmune, AstraZeneca and the University of Oxford, Atossa Therapeutics, Bharat Biotech and partner FluGen, eTheRNA, Intravacc, MediciNova, Sorrento Therapeutics, Tiziana Life Sciences, Tonix Pharmaceuticals, VistaGen Therapeutics.

Go/no-go decision

“We’ve had preliminary discussions with FDA, and hopefully sometime soon after the first of the year, we’ll be in a position to determine whether we want to bring this into the clinic,” said Wilson, who is also director of the Orphan Disease Center at Penn’s Perelman School of Medicine. “We’re well into the preclinical work. We just have an additional set of experiments to do in January, at which time, there’ll be a go-or-no-go [decision].”

Should GTP and Regeneron move forward with clinical trials, Penn would take the lead on the first-in-human studies, with financial and technical support from Regeneron.

“We are interested in scientific collaborations that can maximize the impact of this potential treatment or prevention. Intranasal AAV delivery is one potential way of producing Regeneron’s antibodies in vivo, thus possibly expanding the number of doses that could be delivered to people in need of immediate immunity,” Regeneron spokeswoman Alexandra Bowie said.

REGEN-COV2 consists of casirivimab and imdevimab. Both are designed to bind non-competitively to the receptor-binding domain (RBD) of SARS-CoV-2’s spike protein. REGEN-COV2 is one of 20 “front runners” among more than 300 COVID-19 drug and vaccine candidates on GEN’s COVID-19 DRUG & VACCINE TRACKER.

Soon after testing positive for COVID-19, President Donald Trump began his treatment regimen for the virus with REGEN-COV2 before adding Gilead Sciences’ remdesivir, marketed in the United States as Veklury® and other treatments. President Trump “received a single 8 g dose” of REGEN-COV2, his physician Sean P. Conley, DO, wrote in a letter made public by the White House on October 2.

That is a higher dose than the dosage recommended by the EUA, which is 2.4 g (2,400 mg)—consisting of 1.2 g (1,200 mg) of casirivimab and 1.2 g of imdevimab, administered as a single intravenous infusion. The dosage was changed this fall after data from a clinical trial in ambulatory patients found no significant difference in efficacy between the doses.

In clinical trials thus far, casirivimab and imdevimab are delivered together by intravenous or subcutaneous injection. Wilson and colleagues envision a 1cc syringe that would nebuilize the spray into the nose, reasoning that introducing the antibody cocktail via a single dose of AAV could prevent SARS-CoV-2 infection for longer than the month-long period of antibody levels seen in clinical trials of REGEN-COV2.

They noted that data from Regeneron’s preclinical studies published November 27 in Science showed the antibody cocktail to prevent infection in rhesus macaques believed to model mild COVID-19, and in golden hamsters which model more severe symptoms.

“Our hope and expectation is that we at least get about a six-month window of protection with this approach,” Wilson said. “In mice, when we look at other pathogens, such as flu, we can show protection out to about nine months. And in monkeys, where we only look at expression, we can detect expression out to about six months.”

GTP and Janssen are partnering to develop AAV-based prophylactics against influenza A and B as an alternative to the traditional flu vaccine for seasonal and/or pandemic influenza infections. “That’s an active program that we hope to move into the clinic” Wilson said.

Setback and success

The program arose from GTP’s effort to fight pandemics using AAV. Wilson and colleagues reasoned they could use AAV to express an antibody as opposed to a respiratory pathogen, if they could localize the expression of the antibody at its points of entry, the nose and the pharynx and mouth.

GTP had worked for years to determine how to transfer genes into cells at the proximal airway. That work failed to pan out in cystic fibrosis, where the vector requires distribution throughout the lung at high efficiency.

That setback, Wilson said, prompted additional questions: Where does the respiratory virus get in? Can antibody genes be expressed from an AAV? And how can genes be transferred into the respiratory cells that line the proximal airway?

“We came up with this concept of a bioshield,” Wilson said. “We said, ‘Maybe the best way to achieve this is to essentially aerosolize an AAV vector expressing an antiviral protein such as an antibody into the nose, and then engineer the respiratory cells of the airway… and engineer them to make an antibody.’ They’re not normally immune-modulating cells to express this antibody on the airway surface, so when the respiratory pathogen comes in, it’s stopped dead in its tracks. It’s blocked before it can get any further.”

GTP began to develop an AAV-based vaccine for pandemic flu with support from the Department of Defense. In 2013, Wilson and GTP colleagues published a study in Science Translational Medicine reporting that a single dose of an AAV expressing a broadly neutralizing flu antibody into the nasal passages of mice and ferrets gave them complete protection and substantial reductions in flu replication when exposed to lethal strains of H5N1 from the 1918 flu pandemic and H1N1 from 2009.

“For influenza, the vaccine is very limited to the virus that you vaccinate against. But there are probably neutralizing antibodies against flu, and we showed in mouse and ferret models that you can aerosolize the vector with this broadly neutralizing antibody, and prevent lethal consequences of all the pandemic strains that we had available to us,” Wilson added.

Regeneron launched clinical trials of REGEN-COV2 in June, following a development period that was about half the nine-month company record set when the company developed its three-antibody cocktail for Ebola, Inmazeb^®, which won FDA approval on October 14. REGEN-COV2 advanced into Phase III trials in July.

The company assessed thousands of potential antibodies produced through Regeneron’s monoclonal antibody discovery platform VelocImmune^®, before identifying the two most potent, non-competing, and virus-neutralizing antibodies, casirivimab and imdevimab.

Complementary Targets

According to a paper published in August in Science, casirivimab targets the spike-like loop region on one edge of the ACE2 interface. The fragment antigen-binding region of casirivimab binds the RBD from the top, where it collides with ACE2, while imdevimab only binds to the front or the lower left side of the RBD.

The FDA based its EUA on positive clinical data announced by the company in September and October from the first 799 adults in the Phase II/III portion (NCT04425629) of an adaptive Phase I/II/III trial evaluating the safety, tolerability, and efficacy of REGEN-COV2 in ambulatory adult outpatients with COVID-19. Those data showed that the antibody cocktail met its primary endpoint of significantly reducing viral load, and in the secondary endpoint of medically attended visits related to COVID-19, particularly hospitalizations and emergency room visits within 28 days after treatment.

That trial is one of four late-stage trials in progress for REGEN-COV2. The antibody cocktail is also under study in the Phase II/III portion (NCT04426695) of an adaptive Phase I/II/III trial assessing REGEN-COV2 in hospitalized adult patients with COVID-19. In October, Regeneron paused enrollment of patients requiring high-flow oxygen or mechanical ventilation in that study at the recommendation of the trial’s independent data monitoring committee (IDMC) “based on a potential safety signal and an unfavorable risk/benefit profile” that Regeneron did not disclose.

The other two late-stage trials with which Regeneron is proceeding are:

• A portion of the 15,000-patient open-label, Phase III RECOVERY (Randomized Evaluation of COVid-19 thERapY) trial (NCT04381936) that is examining the effectiveness of the cocktail plus standard of care in at least 2,000 hospitalized COVID-19 patients to be chosen at random in the U.K., and comparing that to another 2,000 patients who already receive standard of care alone.
• A Phase III trial (NCT04452318) designed to assess REGEN-COV2’s ability to prevent infection among uninfected people who have had close exposure to a COVID-19 patient, such as a patient’s housemate. The trial has an estimated enrollment of 2,000 participants.

“We’re really focusing on prevention, not treatment. Once someone’s sick, then the virus has left the nose; it’s in the lung and other organs,” Wilson said. “Our expression is really localized just to the nose. So, the virus comes in, the initial contact, we block it and slow it down. But once you’re sick, systemic delivery of the antibody would make more sense and when you’re really sick, then maybe none of this would work.”

Regeneron has envisioned REGEN-COV2 as being capable of both treating and preventing COVID-19.

“It’s too soon to say if this could ever replace current antibody delivery via intravenous or subcutaneous injection,” Regeneron’s Bowie said. “But we are hopefully that it could one day supplement these methods.”