Feline allergies are a common source of allergens, affecting up to 15% of adults and children and causing symptoms such as rhinoconjunctivitis and severe asthma [1-3]. Data from the U.S. National Health and Nutrition Examination Survey indicates that over 5 million asthma attacks occur each year, with ~350,000 emergency room visits attributed to patients sensitized and exposed to feline allergens [4].
Sensitization to the major feline allergen, Fel d 1 (Felis domesticus allergen 1), elicits IgE responses in >90% of cat-allergic individuals [5]. Feline allergens are produced by the sebaceous, salivary, and lacrimal glands of cats, and the highest Fel d 1 levels are found in saliva. When cats groom themselves, Fel d 1 is transferred from saliva to their hair, and cat dander containing Fel d 1 allergen is then spread to the environment as small airborne particles [6-11].
Furthermore, the small size and structure of Fel d 1 allows it to be easily and continuously airborne for long periods of time, making it one of the easiest allergens to inhale. Its molecular structure also allows it to adhere to fabrics, carpets, and upholstered furniture [11, 13-16]. These factors can make it difficult to remove Fel d 1 from homes, and allow it to travel on clothing and other items from cat-owning households to places where no cat is present. Fel d 1 can be found in homes and buildings without cats, especially in communities where cat owners live [17], causing serious cat allergic problems.
Despite the prevalence and potential severity of feline allergic disease, current treatments merely address the allergic symptoms (e.g., antihistamines) or have demonstrated inconsistent results (e.g., feline allergen immunotherapy [18, 19]).
Outside the laboratory building of our team lives a Cat called "Dean". He is so cute and tsundere, attracting students to stop to admire his charmable appearance, and sometimes also touch him, to feed him some cat strips and cat cans. One member of the iGEM team this year is a devoted cat lover, but can only watch from a distance with envy because she is allergic to cat.
During the brainstorming phase, we realized that by preventing cat allergies, we could give more people who want to own a cat a chance. Under this idea, we investigated the existing treatment and prevention methods in the market, considered the feasibility of using antibodies for treatment and the benefits of commercialization, and finally confirmed the theme of this year's project.
The name of our project is C.A.T: Cat Allergic Therapy. As the name suggests, we hope to use synthetic biology to address the problem of people who want to own cats but they couldn't because of suffering from allergies. Our project targets the cat itself. By treating with our products, cats will have fewer allergens, then making the people who are allergic to cats can also keep them at ease.
Colonization
This module enables our engineered bacteria to live in the cat's mouth for an extended period of time. Hsa, a protein that the Streptococcus gordonii str. Challis uses to stick to the teeth, is used in this part [20]. By recognizing components containing sialic acid, Hsa makes our engineered bacteria adhere to the saliva pellicle [21].
Regulation and Blocking
As a quorum sensing(QS) signaling molecule, 3,5-Dimethyl-Pyrazin-2-OL (DPO)'s concentration can be sensed by the engineered bacteria through the membrane protein VqmA [22, 23]. Once the concentration reaches a certain level, the colonization module is closed while the blocking module is opened, avoiding the excessive biofilm formation. Blocking module consists mainly of two single-chain fragment variables (scFvs) secreted outside the cell [24]. These scFvs block the immune response caused by the antigen and prevent allergies.
Sterilization
This module is based on the two-component quorum sensing system of Streptococcus mutans, ComDE, and bactericidal proteins specific to S. mutans [25]. S. mutans is the main pathogen in dental plaque [26]. In order to prevent the biofilm formed by engineered bacteria on teeth from being used by S. mutans, engineered bacteria use the ComDE two-component system (TCS) to sense S. mutans' ability to competence-stimulating peptide (CSP) production when S. mutans concentration is high, and affects the downstream loop to express ClyR [27, 28], which destroys the biofilm on the tooth surface and kills S. mutans.
Suicide
Our project adds a suicide module to prevents our engineered bacteria from leaking into the environment and prevent engineered bacteria from entering the cat's body through the digestive tract. If engineered bacteria get out of the environment it's supposed to be in, the suicide module turns on.
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