Many vaccines are made from either a weakened virus or a protein taken from a virus. But so far, scientists haven’t had much luck developing such vaccines for respiratory syncytial virus (RSV), which causes an infection that is typically mild but can become deadly in infants and older adults.
Icosavax is taking a different route to developing an RSV vaccine. The Seattle startup uses computers to design a molecule that closely resembles the virus, but contains none of its genetic material and therefore can’t cause infection. Icosavax is preparing to test its experimental vaccine in humans, and the company announced Thursday that it has raised $51 million in financing to support its research.
“RSV is a hard one,” says Icosavax CEO Adam Simpson. “There’s no vaccine so we want to get this right.”
Symptoms of RSV infection typically resemble those of a cold. But the infection leads to more than 57,000 hospitalizations a year of children age 5 or younger, according to the Centers for Disease Control and Prevention (CDC). An additional 177,000 older adults are hospitalized annually with RSV infection, which kills about 17,000 of them, the CDC says. RSV infection also poses a risk to those with weakened immune systems.
There’s one FDA-approved RSV product on the market. The AstraZeneca (NYSE: AZN) antibody drug palivizumab (Synagis) was developed to bind to a protein on the surface of the virus in order to prevent infection. Approved more than 20 years ago, the drug—which is not a vaccine—is prescribed to infants and children to reduce their risk of an RSV-related respiratory infection.
Simpson says that the way that the AstraZeneca drug works sparked others to try and develop vaccines that target the virus in a similar way. But he adds that more recent research at the National Institutes of Health has shown that RSV is a shape shifter, changing its structure after it comes in contact with a cell. Simpson says it’s more effective to intervene earlier—before contact with a cell changes the protein’s shape and it loses epitope sites, parts of a protein’s surface that trigger an immune response.
An experimental RSV vaccine developed by the NIH is currently being tested in humans. According to preliminary Phase 1 results released in August, one dose of the vaccine in healthy adults between the ages of 18 and 50 led to increases in RSV-neutralizing antibodies that were sustained for months. The data were published in the journal Science.
Icosavax licensed rights to the RSV antigen developed by the NIH. The company combines that with virus-like particles (VLPs) that it designs. Simpson says the vaccine “self assembles,” with the antigens combining with the VLP. To visualize what it looks like, Simpson says to imagine a black-and-white soccer ball. If that soccer ball represents the Icosavax VLP, the antigens would attach to the ball, looking like poles sticking out of each of the ball’s 20 black hexagons.
Icosavax aims to target older adults whose immune systems may not be as robust, making them vulnerable to RSV infection. So far, the company has tested its vaccine in mice and monkeys. In preclinical data reported in March and published in the journal Cell, the vaccine elicited neutralizing antibodies against the virus. That research was funded primarily by the Bill & Melinda Gates Foundation. Icosavax’s latest financing was led by Qiming Venture Partners USA and joined by Adams Street Partners, Sanofi Ventures, and NanoDimension. Simpson says the new funds will support a Phase 1b study in adults 60 or older.
There are others developing RSV vaccines. Last week, South San Francisco-based Meissa Vaccines raised $30 million to finance Phase 1 tests of its experimental RSV vaccine, developed from a weakened form of the virus. The Meissa technology is based on research from Emory University.
Simpson says that Icosavax’s VLP technology, which was licensed from the University of Washington’s Institute for Protein Design, enables the company to manufacture its vaccines at scale. He adds that the technology can be used to develop other vaccines.
“We will be matching other antigens to the soccer ball, so to speak,” he says.
Image by Icosavax