PURPOSE OF THE STUDY:
Cats are found in 25% of US households, and 10% of humans are allergic to them. Most cat-allergic subjects make IgE antibody to the major cat allergen Fel d 1. If environmental control measures and medication fail to provide sufficient control of allergic symptoms, allergen immunotherapy can be beneficial. What about immunizing the cat instead?
The cats received a series of 3 intramuscular injections at 3-week intervals of a conjugate vaccine consisting of recombinant Fel d 1 and a virus-like particle (VLP) carrier (Fel-CuMVTT). The VLP does not contain viral genetic material but does represent a pathogen-associated structural pattern and also carries RNA from the bacterial production strain, which is a ligand for Toll-like receptors 7 and 8 and is a pathogen-associated molecular pattern, thus providing an immunostimulatory vehicle. Anti–Fel d 1 IgG was measured in the cats after immunization, as was the amount of Fel d 1 in the cats’ tears.
Before immunization, there was no detectable anti–Fel d 1. Fel d 1–specific IgG was detected on day 22 after a single immunization, increased further after the second immunization, and was maintained after the third immunization for 282 days (last blood sample collection). There was a significant mean reduction of Fel d 1 in cat tears by a factor of 2.7 that was maintained up to 84 days (last tear sample collection). No signs of toxicity were seen in the cats.
Cat vaccination with Fel-CuMVTT induces neutralizing antibodies, and this could be a novel method to address allergic symptoms in cat owners.
This is a very ingenious approach to cat allergy. Rather than injecting cat-allergic humans with Fel d 1 to make IgG, we may be able to inject the cat with Fel d 1 to make IgG, resulting in less Fel d 1 expression by the cat and fewer symptoms in the owner. Future studies will need to determine whether this approach decreases Fel d 1 production in sebaceous glands and dander and ultimately airborne levels, and whether this leads to sufficient reduction of human symptoms. Presumably, because the cats themselves are not allergic to Fel d 1, they do not need to sit in the waiting room for 30 minutes after each injection.