In the field of allergology, desensitization to animals, specifically cats, is rarely prescribed. Has allergen immunotherapy (IT), which has long been considered ineffective, evolved? What other solutions are there for patients who are allergic to cats? These questions were the subject of a presentation at the latest Francophone Congress of Allergology.
Pascal Demoly, MD, PhD, allergist at the University Hospital of Montpellier, Montpellier, France, defended IT. Alain Didier, MD, a pulmonologist at the University Hospital of Toulouse in Toulouse, France, took a more skeptical position. He proposed alternative solutions, some of which were quite original, for living in harmony with one's favorite feline.
Few Conclusive Data
Few clinical trials have tested IT in cat allergy. Twelve have examined the subcutaneous route, and two the sublingual route. The trials have had small populations (eg, 250 patients) and generally yielded negative results, said Demoly. "The only positive trials are those whose efficacy criterion is based on a provocation test, whether nasal, ocular, bronchial, or in an exposure chamber with cat allergens," he said. Demoly noted that this type of study cannot easily be conducted on a large scale, thus limiting regulators' ability to approve a product for the market. But real-life studies can be relied upon, using quality of life as a primary criterion, he said.
Real-Life Data
The EfficAPSI study, of which Demoly was the principal investigator, included more than 100,000 patients in France with allergic rhinitis, with or without asthma, who were treated with sublingual liquid IT and symptomatic medications. In addition, more than 330,000 patients with allergic rhinitis, with or without asthma, were treated only with symptomatic medications.
The study, funded by Stallergenes, spanned from 2006 to 2018 and relied on data from the national health system, SNDS. EfficAPSI covered a wide range of allergens, including dust mites, grass, birch, and ragweed pollens, as well as cat allergens. The results were positive and consistent for all allergens and age groups. IT was associated with a 28% reduced risk for asthma exacerbation, reaching 37% for severe cases. Demoly noted that in a subgroup analysis, the 1902 patients treated with sublingual IT in drop form at a concentration of 100 IR for cat allergy showed particularly interesting results.
Clinical Recommendations
While obtaining positive data from traditional clinical trials would be very difficult, if not impossible, because of methodological challenges (no one will keep their cat locked in a room with them for 8 h/d), real-life data are conclusive and justify the use of desensitization method, including in cat allergy, said Demoly.
He referred to precise international and national recommendations. According to the 2017 recommendations of the European Academy of Allergy and Clinical Immunology, allergen IT for cat allergens is clearly identified as effective in treating allergic rhinitis, alongside desensitization to dust mites and pollens. While the French Society of Allergology remained cautious in 2021 during the revision of its recommendations, allergen IT for cat allergy was mentioned, although with a relatively low level of evidence.
"Although acknowledging that precise research data are rather scarce, allergen IT for cat allergy is indicated in cases that truly require it," said Demoly.
Moreover, the development of more concentrated extracts (such as 300 IR rather than 100 IR) could lead to even more significant effectiveness, as may be demonstrated by real-life data in the years to come, he said.
Negative Trials
As a coauthor of a 2022 literature review on this subject, Didier provided a dissenting voice. He immediately and humorously targeted the cat, which he called a dangerous threat to biodiversity.
France is among the top three countries in Europe, along with Germany and Italy, in terms of cat ownership, said Didier. The feline population in France has recently stabilized.
"A good piece of news," he remarked, not without irony, knowing that cats, along with dogs, are the leading causes of respiratory allergies after dust mites and pollens.
More seriously, Didier outlined three reasons not to desensitize to cats. The first reason is that the efficacy of IT is still to be determined. "Most trials with IT are negative, especially those with the sublingual route," he said. Only one study met his approval: A double-blinded, placebo-controlled Spanish trial. It had few patients, however (25 in each arm at baseline), and a 34% dropout rate.
In this study conducted in an exposure chamber, IT was effective but did not lead to further development. Didier emphasized this point by citing a BVA poll conducted for Stallergenes in 2023, showing that allergists themselves are not very convinced of the usefulness of desensitization through IT when it comes to cats — unlike in the case of dust mites.
'Treating the Cat'
There are other solutions, however, and the second reason not to desensitize to cats, according to the Didier, would be to "make the patient an active participant in their care."
What does this mean? "When you have a cat, you can take steps to reduce your exposure to it," said Didier. The first option is to keep the animal away — a measure that often meets with little success among cat owners. Another possibility is to wash the animal regularly, cover it with products to reduce Fel d 1, the most allergenic substance in cats, or put it under a special hood to limit exposure.
Finally, the third proposal was to "not treat the human but treat the cat," said Didier. "You have several options, such as vaccinating the cat against Fel d 1." As the speaker explains, this vaccine currently in development contains a recombinant protein of Fel d 1 associated with the cucumber mosaic virus. This allows for the stimulation of cats' immune response and the production of anti-Fel d 1 immunoglobulin (Ig) G.
"The results are encouraging. Among cat owners whose animals have been vaccinated with this unique combination, symptoms tend to improve," said Didier.
Another already available solution is to feed the cat a diet rich in IgY produced by chickens and found in eggs. "If the cat's diet is rich in IgY, the presence of Fel d 1 is reduced. This works even better if the cat is a heavy Fel d 1 producer," said Didier.
Purina has developed Pro Plan LiveClear, cat food that reduces allergens on fur and dander by an average of 47% starting from the third week of daily feeding. The product is recommended by the French Association for the Prevention of Allergies.
Patients with cat allergy will choose their strategy.
Demoly disclosed financial ties with laboratories, including Viatris Medical, Stallergenes Greer, Alk, and AstraZeneca. Didier disclosed financial ties with various laboratories, including Novartis, Chiesi, AstraZeneca, Sanofi, Stallergenes Greer, and GlaxoSmithKline.
This story was translated from the Medscape French edition using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.