First in Class Cat, Birch Allergen Blockers Succeed in Phase 3 Trials

Regeneron’s allergen-specific antibody blockers have succeeded in meeting the primary endpoints in 2 phase 3 trials in adults with moderate-to-severe cat or birch allergies.1

“Millions suffer from the debilitating effects of allergies, which can cause severe symptoms in the eyes, nose, skin and even trigger asthma. To try to alleviate this suffering, millions undergo allergy desensitization shots, often several times a week for several years, and often with disappointing results. The purpose of these burdensome allergy shots is to try to build up allergen-blocking antibodies in the body. We wondered whether we could instead manufacture and directly provide allergen-blocking antibodies,” George D. Yancopoulos, MD, PhD, Board co-Chair, President and Chief Scientific Officer at Regeneron, and a co-inventor of this new approach to allergy, said in a statement.1 “These recent Phase 3 allergen challenge trials, together with our earlier Phase 2 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 – decreasing ocular, nasal and even asthma measures. We see significant relief at the earliest assessment timepoint, and lasting for over 3 months, in both our cat and birch allergy programs.”

In the 2 ocular allergen challenge trials, patients received direct ocular instillation of either cat dander or birch pollen at day 8 following a single subcutaneous administration of the allergen-blocking antibodies. Investigators assessed signs and symptoms of ocular allergy after allergen instillation.

The cat allergen trial evaluated a FelD1-blocking antibody combination therapy of REGN1908 and REGN1909, 2 fully human monoclonal antibodies (mAbs). FelD1 is the most dominant cat allergen which clings to clothes, shoes and furniture. Participants with a cat allergy received the combination therapy (n = 33) or placebo (n = 31).

The trial met its primary endpoint of ocular itch and both key secondary endpoints of conjunctival redness and skin prick testing, with the combination therapy significantly reducing itch by 52% (P <.0001), conjunctival redness by 39% (P <.0001) and skin prick reactivity by 44% (P <.0001) 1 week after therapy.1

Furthermore, reductions in ocular itch and conjunctival redness were greater in patients whose cat allergy was more specifically driven by FelD1 (the majority of patients; ocular itch reduction of 64% and conjunctival redness reduction of 49%), in a post-hoc exploratory analysis.1

In the birch allergy trial, participants were randomized to receive a single dose of the BetV1-blocking antibody combination (REGN5713 and REGN5715, n=27) or placebo (n=27). Investigators similarly found significant reductions in itch by 51% (P <.0001), conjunctival redness by 46% (P <.0001), and skin prick reactivity by 44% (P <.0001) 1 week after treatment.1

In terms of safety, the allergen therapies were generally well-tolerated. There were no serious treatment-related adverse events (AEs) or AEs leading to trial discontinuation reported in either trial. The cat allergen trial is ongoing for further safety follow-up and additional Phase 3 development for both trials is planned to begin in the first half of 2026.

These latest trials continue to demonstrate efficacy of the 2 allergen-specific antibody blockers, which has previously been seen in nasal allergen challenge trials for both cat and birch allergy.2,3 Regeneron will present more detailed data from the ocular challenge trials at future scientific meetings.

References

1. Regeneron Advances Allergy Pipeline with Two Positive Phase 3 Trials Evaluating First-in-Class Antibody-Blockers of Cat and Birch Allergies. News release. Regeneron. September 8, 2025. https://finance.yahoo.com/news/regeneron-advances-allergy-pipeline-two-103000615.html

2. Gevaert P, De Craemer J, De Ruyck N, et al. Novel antibody cocktail targeting Bet v 1 rapidly and sustainably treats birch allergy symptoms in a phase 1 study. J Allergy Clin Immunol. 2022;149(1):189-199. doi:10.1016/j.jaci.2021.05.039

3. Orengo JM, Radin AR, Kamat V, et al. Treating cat allergy with monoclonal IgG antibodies that bind allergen and prevent IgE engagement. Nat Commun. 2018;9(1):1421. Published 2018 Apr 12. doi:10.1038/s41467-018-03636-8