The most commonly used traditional adjuvants are aluminium salts; however, a biodegradable adjuvant, MCT®, was developed for application in the niche area of allergy immunotherapy (AIT), also in combination with a TLR-4 adjuvant—Monophosphoryl Lipid A (MPL®)—producing the first adjuvant system approach for AIT in the clinic. The gene discussed is TLR4; the disease is allergic disease.