COVID-19 nasal spray vaccine in the works at Stanford Medicine

A single sniff may one day be all it takes to immunize yourself against COVID-19.

Ramasamy Paulmurugan, PhD, and Tarik Massoud, MD, PhD, both professors of radiology, are leading an effort to stop the coronavirus at its most frequent point of entry: the nose.

“The gold standard for vaccination is through an intramuscular shot to the arm,” Massoud said. “But that’s really a roundabout way to achieve a barrier against a respiratory virus. We thought, theoretically, that administering protection at the site of infection could produce a more robust response.”

So far, the team’s aerosolized vaccine has been delivered only in the snouts of mice, but it’s shown promise in protecting against a pseudovirus that closely resembles SARS-CoV-2.

Powering the intranasal spray’s protection are gold nanoparticles carrying bits of harmless, virus-mimicking DNA that trigger a generation of antibodies — protective soldiers of the immune system — and other immune cells that remember the invader so they can quickly spot and neutralize the threat.

In addition to conjuring robust immunity, the molecules generated by the spray act as a physical blockade against viral infection, limiting the amount of virus that can settle into the nasal passages and travel into the lungs, potentially reducing transmission to others.

The goal, said Paulmurugan, is to create a stable, long-lasting intranasal COVID-19 vaccine that can be shipped globally and self-administered — no medical workers required. Although the initial results are exciting, he said, it’s too soon for the public to think about swapping a shot for a spray. But he and Massoud are optimistic that a human trial may be on the not-too-distant horizon.

A paper describing the study published in ACS Nano Oct. 27. Paulmurugan and Massoud are co-senior authors. Postdoctoral scholar Uday Kumar, PhD, is the lead author.

From brain tumors to vaccines

Paulmurugan and Massoud aren’t immunologists by training, nor did they set out to create a new type of COVID-19 immunization. In the spring of 2020, just as offices were locking up and toilet paper was running out, the two were diligently pursuing a treatment for glioblastoma, a type of brain tumor, that hinged on their gold nanoparticle research.

They had been working on a way to deliver molecules across the blood-brain barrier — a notoriously picky neurological sieve that keeps unwanted molecules out of the brain — and had landed on tiny, inhalable gold particles as their vehicle of choice.

“In our experiments, we anesthetized the mice and placed the treatment nanoparticles in the nose; the particles are then absorbed by nerves in the nasal passage and ferried to the brain,” said Massoud. But during one of these experiments, Paulmurugan noticed something odd. In mice that were breathing more quickly, the nanoparticles trafficked to the lungs, not to the brain.

“We were at the beginning of the pandemic, and we thought, ‘Wow, this would be amazing if we could swap the glioblastoma therapeutic for a SARS-CoV-2 spike protein,’” said Massoud. “It was a completely fortuitous event, complete serendipity that it happened that way.”

Some 18 months later, the two have demonstrated in mice the feasibility of a nasal spray vaccination for COVID-19 that relies on gold nanoparticles and DNA. (While there are a few other researchers that are pursuing an intranasal COVID-19 vaccine, none, to the researchers’ knowledge, use gold nanoparticles to deliver DNA.)

All aboard the gold nanoparticle

One of the advantages of the gold nanoparticles, aside from their innocuous nature, is that they’re light, floating easily from the nasal passage to the lungs. Each one attaches to many copies of a DNA sequence that codes for a specific part of SARS-CoV-2 — the spike proteins that pierce healthy cells to gain entry during infection. The DNA sequence is picked up by cells’ protein manufacturing machinery, which then churns out the spike protein. The immune system regards the spike, while harmless on its own, as suspicious, and it dutifully creates antibodies, which help eliminate foreign molecules.

The results we’re seeing with the intranasal vaccine are incredibly encouraging.

The researchers tested the immune protection of 10 intranasally vaccinated mice by exposing them to the SARS-CoV-2 pseudovirus and saw that the serum, a component of blood, from every mouse was able to neutralize the virus. About 18 weeks later, the researchers saw antibody and immune cell levels wane, so they administered a booster spray, renewing antibody protection that surpassed the levels originally generated.

“So far, the results we’re seeing with the intranasal vaccine are incredibly encouraging,” said Paulmurugan.

The scientists are turning to RNA to see if it too creates a robust immune response; they’re comparing its protection with that of the DNA-based spray. Another advantage to the gold nanoparticle approach is its flexibility — scientists can easily swap out the cargo the nanoparticles carry — which is helpful in preparing for variants. “You could combine vaccines, in that you could inoculate against the standard spike protein from the original virus, plus as many variants as you want all on the same particle,” said Paulmurugan.

The researchers added that a nasal spray might encourage people who are not yet vaccinated — for fear of needles, for instance — to be inoculated.

Once they have run head-to-head comparisons between a DNA-based and RNA-based vaccine, the researchers plan to hold clinical trials to test how well it works in people.

Other Stanford Medicine authors are researcher Rayhaneh Afjei and Katherine Ferrara, PhD, professor of radiology.

This study was funded by the Gary Glazer-GE Fund and the National Institutes of Health (grant S10OD023518-01A1).

Stanford’s Department of Radiology also supported the work.