The hunt for a cat allergy treatment is back on at Regeneron Pharmaceuticals.
In a new Phase 3 study, a single injection of allergen-blocking antibodies reduced eye itch and redness in patients with moderate to severe cat allergy who were exposed to their allergen.
The trial involved 64 cat-allergic adults randomly assigned to receive an injection of REGN1908 and REGN1909, a combination of two lab-created antibodies, or placebo. The antibodies target Fel d1, the major cat allergen.
A week later, participants had drops containing cat dander extract placed in their eyes to provoke an allergic reaction.
Those who received the active treatment had 52 percent lower eye itch scores and a 39 percent reduction in eye redness compared with those who received the placebo shot. Their skin test reactivity to Fel d1 was also 44 percent lower.
The differences were seen within moments of exposure to cat allergen.
“There was robust suppression of itch as well as redness,” says Dr. Jennifer Maloney, a study author and Regeneron therapeutic area lead. “Skin tests were also robustly suppressed for cat.”
How Regeneron Therapy Works
The Regeneron antibodies bind to the cat protein Fel d1. This binding prevents IgE antibodies in the blood and on mast cells from attaching to the protein. By stopping that interaction, the lab-made antibodies block the cascade that leads to symptoms of allergic reaction.
Previous studies suggested the antibody cocktail also eased other allergy symptoms, including nasal congestion and wheezing.
In a Phase 2 trial, cat-allergic adults with asthma had less wheezing for up to three months after a single dose of the antibodies. Other research similarly found that the antibody mix reduced symptoms of nasal congestion and runny nose.
Yet for a time it looked like development of the cat allergy treatment had stalled. After a Phase 2 trial in participants with asthma in 2022, Regeneron announced it was shelving the research.
Maloney says the new research for the antibodies is focused this time on eye-related symptoms. An additional Phase 3 study to support an FDA submission for approval is planned to start later this year.
“We designed our recently completed Phase 3 trial to focus on assessing outcomes in key areas of concern for patients, particularly ocular symptoms,” Maloney says. Even though the eye study only went to Day 8, the earlier trials suggest eye symptom relief could last as long as 85 days, Maloney says.
Upcoming trials will confirm how frequently injections would need to be given. Injections can be administered to the upper arms, thighs or abdomen.
Plenty to Sneeze At
At least 12 percent of the U.S. population is allergic to cats. Fel d1 is particularly potent because of its persistence. The protein is excreted in a cat’s skin, saliva and urine. Cats spread it onto their fur while grooming, then shed it with their fur and dried skin particles.
Avoiding the allergen can be like herding cats. Fel d1 is tiny and buoyant. It remains suspended in the air even after a cat leaves the room. The protein also sticks to surfaces like drapes, carpets, furniture, bedding, clothing, and even walls. Vacuuming helps, but doesn’t dislodge all of it.
Even Cat-Free Zones May Not Be
Research has shown the allergen can persist in homes even when no cat has been present for several months. In schools, children can carry enough Fel d1 on their clothes and backpacks to trigger symptoms in their allergic classmates.
A new survey of 1,510 cat-allergic adults found that many struggle to avoid cat allergen, and accidental exposures are common.
In the survey conducted by Regeneron scientists, 64 percent said they were “highly avoidant” of cats and cat dander. The other 36 percent considered themselves “less avoidant.”
When asked how hard they tried to avoid cats or cat dander, the highly avoidant group rated their efforts an 8 or higher on a 10-point scale.
Cat Allergy Study: Hard to Avoid
Exposures to cats were common and largely accidental. About 84 percent in the highly avoidant group said they encountered cat allergen while visiting friends or family with a cat in the past year.
About 62 percent said they were exposed while visiting a significant other. Meantime, about 69 percent were exposed in homes that previously had a cat.
Cat dander also infiltrated commuting. About 55 percent of the highly avoidant reported exposures while using public transportation or rideshares. Work or school exposures affected 54 percent, while 61 percent reported cat allergen in public spaces from shops and cafes to vacation rentals.
“We saw that even people who were highly avoidant still experienced severe cat allergy symptoms, leading to greater impairment in their daily lives than in those who were less avoidant,” said lead study author Slade Schneider, PharmD, a clinical scientist at Regeneron. “The results highlight that the burden of cat allergy is both substantial and multi-dimensional.”
Exposures, and worrying about reactions, impacted quality of life. About 15 percent of the highly avoidant said their cat allergy severely interfered with social events. As well, 13 percent said it affected work or school productivity. Seventeen percent said the allergy severely affected their mental well-being and 13 percent said it strained their finances.
“The unpredictability of when or where they will encounter cat allergens can lead to worry and anxiety,” Schneider says. “People feel that their ability to attend social events, be productive at work or school, and travel is substantially impacted, which can take a significant toll on their overall well-being.”
Schneider says this is first national survey in people with cat allergy who do not live with a cat.
Itchy Eyes, Running Noses, Wheezing
Those in the highly avoidant group reported severe eye, nasal, and lower respiratory symptoms when exposed.
Severe eye symptoms to cat exposures were the most common, with 49 percent reporting itching, 43 percent reporting tearing and 36 percent swelling. About 40 percent reported severe nasal symptoms, including sneezing and running nose.
Severe respiratory symptoms were also common. About 30 percent experienced wheezing, 29 percent had difficulty breathing, 27 percent had chest tightness, and 25 percent reported coughing.
“Even people who do their best to avoid cats still experience severe symptoms related to their eyes, nose, and breathing,” he says.
Birch Allergy Treatment
Regeneron also reported results from a Phase 3 trial of an antibody to block BETv1, the major birch pollen allergen. One week after treatment, eye itch was reduced by 51 percent, eye redness by 46 percent and skin prick reactivity by 44 percent.
Dr. George Yancopoulos, Regeneron’s president and chief scientific officer, said in a statement that the Phase 2 and 3 trials “provide compelling evidence that our first-in-class approach can have the potential to provide profound allergy relief – rapidly and durably after a single treatment.”
“We see significant relief … lasting for over three months, in both our cat and birch allergy programs,” Yancopoulos says.
There were no serious treatment related adverse events in either the cat or birch allergy study leading to study dropouts.
The Regeneron research was presented at the 2026 American Academy of Allergy, Asthma and Immunology annual meeting in Philadelphia.
Related Reading:
Can Cat Allergy Develop in Adult Life?
All About Eye Allergy: The Itch, the Blur and Condition Confusion
Nothing to Sneeze At: Emerging Strategies for Controlling Cat Allergy
