Vaccines Against Allergies

Identification of adjuvants that enhance the therapeutic antibody response to host IgE

In the development of a novel vaccine against atopic allergies, we have screened for adjuvants that enhance the therapeutic antibody response against self immunoglobulin E (IgE). The response against self IgE is induced by administration of a vaccine antigen, which contains both self and non-self IgE regions, together with an adjuvant. We evaluated five commonly used adjuvants; Freund's, aluminium hydroxide, ISCOMs, Montanide ISA 51 and Montanide ISA 720, and found that the mineral oil-based adjuvants; Montanide ISA 51 and Freund's induced at least 5-10-fold higher anti-self IgE titers than any of the other candidates. However, with one exception, Alum, the immune responses against the carrier, i.e. the non-self regions, were similar for all adjuvants, indicating that the ability to induce responses against self and non-self antigens differ among adjuvants. The responses against non-self IgE were more than 50-fold higher than antibody responses against self IgE in both the Freund's and Montanide 51-administered animals, indicating that the response against self molecules is markedly inhibited by tolerance-inducing mechanisms. Co-administration of Montanide ISA 51 with immuno-stimulatory substances from bacteria; muramyldipeptide (MDP), monophosphoryl-lipid A (MPL) or a formyl-methionine-containing tripeptide (fMLP), did not elevate the anti-self IgE response. Hence, adjuvants based on pure mineral oil without additional immuno-stimulatory substances appear to be the best adjuvant candidates in therapeutic vaccines aimed at regulating the in vivo levels of self-proteins.

Generation of therapeutic antibody responses against IgE through vaccination

IgE is the central mediator in atopic allergies such as hay fever, eczema, and asthma; therefore, it is a prime target in the development of allergen-independent preventive treatments. We describe an active immunization strategy that has the potential to reduce IgE to a clinically significant extent. The active vaccine component is a chimeric IgE molecule, Cepsilon2-Cepsilon3-Cepsilon4. The receptor-binding target domain, Cepsilon3, is derived from the recipient species, whereas the flanking domains, Cepsilon2 and Cepsilon4, are derived from an evolutionarily distant mammal. The flanking domains have dual functions, acting both as structural support for the Cepsilon3 domain and to break T cell tolerance by providing foreign T cell epitopes. The efficacy of the vaccine was studied in an ovalbumin-sensitized rat model. Vaccination resulted in antibody responses against IgE in all rats and in a substantial reduction in serum IgE levels in three out of four strains. The skin reactivity upon allergen challenge was significantly reduced in vaccinated animals. The vaccine appears to be safe to use as an antigen. No cross-linking activity was observed in sera of vaccinated animals, and the response to vaccination was reversible with time. Our results suggest that active immunization against IgE has the potential to become a therapeutic method for humans.