No abstract

Asthma is a respiratory disorder characterized by airway hyperreactivity (AHR) and inflammation and is associated with high serum IgE and overproduction of IL-4, IL-5, and IL-13 by allergen-specific Th2 cells. Our previous studies demonstrated that heat-killed Listeria monocytogenes (HKL) as an adjuvant in immunotherapy successfully reversed ongoing Ag-specific Th2-dominated responses toward Th1-dominated responses, but it was unclear if such immune modulation could reverse ongoing, established disease in target organs such as the lung. In this paper we show that a single dose of Ag plus HKL as adjuvant significantly reduced AHR in a murine model for asthma and reversed established AHR when given late after allergen sensitization. HKL as adjuvant also dramatically inhibited airway inflammation, eosinophilia, and mucus production, significantly reduced Ag-specific IgE and IL-4 production, and dramatically increased Ag-specific IFN-γ synthesis. The inhibitory effect of HKL on AHR depended on the presence of IL-12 and CD8+ T cells and was associated with an increase of IL-18 mRNA expression. Thus, our results demonstrate that HKL as an adjuvant for immunotherapy mediates immune deviation from a pathological Th2-dominated response toward a protective immune response in peripheral lymphoid tissues and in the lungs and may be clinically effective in the treatment of patients with established asthma and allergic disease.

The BALB/cByJ mouse strain displays an immunodominant T cell response directed at the same CD4+ T cell epitope peptide region in human IFN-β, as detected in a human population-based assay. BALB/cByJ mice also recognize a second region of the protein with a lesser magnitude proliferative response. Critical residue testing of the immunodominant peptide showed that both BALB/cByJ mice and the human population response were dependent on an isoleucine residue at position 129. A variant IFN-β molecule was constructed containing the single amino acid modification, I129V, in the immunodominant epitope. The variant displayed 100% of control antiproliferation activity. Mice immunized with unmodified IFN-β responded weakly in vitro to the I129V variant. However, BALB/cByJ mice immunized with the I129V variant were unable to respond to either the I129V variant or the unmodified IFN-β molecule by either T cell proliferation or Ag-specific IgG1 Ab production. This demonstrates that a single amino acid change in an immunodominant epitope can eliminate an immune response to an otherwise intact therapeutic protein. The elimination of the immunodominant epitope response also eliminated the response to the subdominant epitope in the protein. Modifying functionally immunodominant T cell epitopes within proteins may obviate the need for additional subdominant epitope modifications.

We investigated the capacity of heat-killed Listeria monocytogenes (HKL), a potent stimulator of the innate immune system, as a vaccine adjuvant to modify both primary and secondary Ag-specific immune responses. Mice immunized with the Ag keyhole limpet hemocyanin (KLH) mixed with HKL generated a KLH-specific primary response characterized by production of Th1 cytokines and large quantities of KLH-specific IgG2a Ab. Moreover, administration of KLH with HKL as an adjuvant reversed established immune responses dominated by the production of Th2 cytokines and high levels of KLH-specific IgE and induced a Th1-type response with high levels of IFN-γ and IgG2a and low levels of IgE and IL-4. Neutralization of IL-12 activity at the time of HKL administration blocked the enhancement of IFN-γ and reduction of IL-4 production, indicating that IL-12, induced by HKL, was responsible for the adjuvant effects on cytokine production. These results suggest that HKL as an adjuvant during immunization can successfully bias the development of Ag-specific cytokine synthesis toward Th1 cytokine production even in the setting of an ongoing Th2-dominated response. Thus, HKL may be clinically effective in vaccine therapies for diseases such as allergy and asthma, which require the conversion of Th2-dominated immune responses into Th1-dominated responses.