Use of CpG oligonucleotides in treatment of asthma and allergic disease.

In the last several decades, there has been a marked increase in the prevalence of atopic disorders including asthma in "Western" societies; a relationship has been identified between lack of early-life exposure to microbes or microbial products and increased susceptibility to atopic disorders. The innate immune system is activated by early microbial exposures, many of which utilize one of the Toll-like receptors, and there has been significant interest in studying how ligation of TLRs may be therapeutically useful. CpG oligonucleotides (CpG-ODN, resembling bacterial DNA) engage TLR-9 on B-cells, dendritic cells and other cell types, resulting in a cascade that includes induction of Th1-type and T-regulatory-type immune responses. Preclinical models of asthma have demonstrated that CpG-ODN are potent inhibitors of atopic responses, suppressing Th2 cytokine and, reducing airway eosinophilia, systemic levels of IgE, and bronchial hyperreactivity-in short the critical attributes of the asthmatic phenotype. In models of chronic allergen exposure, CpG-ODN are also effective at preventing the development of airway remodeling. In established asthma, CpG-ODN can reverse manifestations of disease, both when used alone or in combination with allergen immunotherapy. Early clinical trials have had mixed results, including a significant benefit when CpG-ODN were conjugated to ragweed allergen in an allergic rhinitis immunotherapy study, but only limited efficacy seen when administered prior to allergen challenge in asthmatics. Further study of CpG-ODNs for the treatment of asthma and other atopic disorders is warranted by existing data.