THE JEREMIAH METZGER LECTURE NOVEL THERAPEUTIC STRATEGIES OF ALLERGIC AND IMMUNOLOGIC DISORDERS

Abstract

Advances in understanding the immunological basis and mechanisms underlying allergic and immunologic disorders have led to effective but costly long-term and repetitive biologic therapies. Gene therapy is a rapidly advancing technology, in which a single administration of an adeno-associated virus encoding the therapeutic protein or monoclonal antibody may provide effective long-term therapy for allergic and immunologic disorders. In this review, we summarize the recent studies from our laboratory developing gene therapy strategies to treat hereditary angioedema and peanut allergy. The unraveling of the pathogenesis of immune-based disorders, including hereditary deficiencies of components of the immune system and allergic disorders, has led to the development of therapies using parenteral administration of recombinant proteins or monoclonal antibodies (1). While many of these therapies are highly effective, they are limited by the half-life of the therapeutic protein or antibody, requiring repetitive administration of days to weeks (2-15). The focus of recent work in our laboratory has been to solve this problem by substituting protein/monoclonal antibody administration with gene therapy, where current technology allows for a single administration of the gene coding for a protein or antibody to provide persistent expression of effective levels of the therapeutic protein or antibody. Gene therapy is a drug delivery platform which uses genetic material, usually in the form of coding exons of the therapeutic gene, to correct, compensate for, or prevent the development of an abnormal phenotype (16). Originally conceptualized as a strategy to treat rare hereditary disorders, gene therapy is being developed for a wide range of human disorders, including common acquired conditions (17-20). In this review, we will describe how we have adopted gene therapy technology to develop therapies for immune-related disorders, using as examples hereditary angioedema, an inherited autosomal dominant disorder, and peanut allergy, a common acquired allergic disorder.

Fig. 1

Adeno-associated virus (AAV) gene transfer vectors. (A) Components of AAV- based vectors. Example of an expression cassette comprised of AAV2 internal terminal repeats (ITR), encapsidation signal (Ψ), CAG promoter, optimized cDNA of gene to be expressed, and rabbit β-globin polyadenylation signal. The expression cassette is packaged into an AAV serotype-specific capsid to generate the gene therapy vector. (B) Transmission electron microscopy image of purified AAV gene transfer vector.

Fig. 2

Complement cascade in hereditary angioedema. C1-esterase inhibitor (C1EI) binds and inhibits the function of several proteases relevant to the classical complement system and contact cascades, including C1r, C1s and kallikrein. Insufficient C1EI function leads to dysregulation of each of these pathways. Contact pathway dysregulation is largely responsible for the symptoms of hereditary angioedema (HAE) via excess generation of bradykinin. In individuals with C1EI deficiency, excess generation of bradykinin results in vasodilatation, increased vascular permeability, and smooth muscle contraction, leading to the symptoms of HAE.

Fig. 3

Adeno-associated virus serotype 8–mediated persistent expression of human C1EI levels over time following a single intravenous administration (10¹¹ gc) to C57Bl/6 mice. Phosphate-buffered saline (PBS) – administered mice were controls. Values are presented as means ± SEM, n = 5/group. The dashed lines represent the clinical threshold required for effective therapy and the limit of detection of the assay.

Fig. 4

Prevention of peanut-induced anaphylaxis by prior therapy with an adeno-associated virus coding for omalizumab (anti-immunoglobulin E [IgE] monoclonal antibody [mAB]). (A) Schematic of the AAVrh.10anti-hIgE vector with the expression cassette including the cytomegalovirus (CMV) enhancer/chicken β-actin (CAG) promoter, heavy and light chains of the anti-hIgE mAb omalizumab, furin 2A cleavage site, and polyadenylation signal. (B) Persistence of expression of the anti-hIgE antibody over time after a single intravenous administration of AAVrh.10anti-hIgE (10¹¹ genome copies) to NOD-scid IL2Rgamma^null female mice. AAVrh.10IgGcontrol (10¹¹ genome copies) were controls. Values are presented as means ± SEM. (C) Plasma histamine levels 30 minutes after peanut challenge 7 weeks after therapy. (D) Mice after peanut extract challenge 6 weeks after therapy. Top. Mouse treated with a control vector with puffiness around the eyes/snout and pilar erecti, itching/ruffling of fur, and decreased ambulation and respiratory rate after peanut challenge. Bottom, Mouse previously treated with AAVrh.10anti-hIgE appeared normal after peanut challenge. Adapted from Pagovich et al (56).