Abstract
Abstract The therapeutic anti-IgE monoclonal antibodies (mAbs), which have a unique set of binding specificities to human IgE, are designed for neutralizing free IgE and inhibiting IgE production for the treatment of allergic diseases that are caused by type I hypersensitivity reaction. While anti-IgE antibody, omalizumab, has been approved in most major countries to treat patients with severe allergic asthma, the pharmacological mechanisms of anti-IgE have not been well understood. In this thesis research, we have established an in vitro re-constituted model to study the potential contribution of the rapidly accumulated IgE: anti-IgE immune complexes to the efficacious pharmacological effects of omalizumab especially in the initial few weeks after anti-IgE treatment. The results demonstrate that immune complexes comprised of omalizumab and allergen-specific IgE are capable of trapping allergen molecules to inhibit their cross-linking Fc□RI-bound IgE and the consequential activation of the basophils bearing Fc□RI. The results may also explain that some patients respond to omalizumab treatment after the first or second administration of omalizumab and that atopic dermatitis patients with serum IgE many times of 700IU/ml respond well with doses of omalizumab used for patients with IgE below 700IU/ml. The other important pharmacological mechanism investigated in this research is whether anti-IgE can modulate mIgE-expressing B cells, including IgE B lymphoblasts and memory B cells, to achieve the ultimate effects of blocking new IgE synthesis. For this goal, we have established a transgenic mouse strain “human IgE Ch2-Ch4 mouse strain”, in which the genomic segment spanning CH2 to CH4 of the mouse own □ immunoglobulin gene has been swapped by the corresponding gene segment of human □ gene by site-specific gene knock-in techniques. We have employed this mouse model to investigate the pharmacological effects of omalizumab-like, mouse anti-human IgE mAb, named ASG 16, on the modulation of IgE-committed mIgE+ B cells in vivo. The results indicate that ASG 16 can inhibit m□ RNA transcription of mIgE B cells in vivo and that ASG 16 can cause antibody-dependent cellular cytotoxicity of mIgE-expressing B cells in the presence of IgG-Fc□R-bearing accessory cells in in vitro culture.. The human m□ chain, the heavy chain of mIgE, contains a 52-a.a. segment, referred to as C□mX, between CH4 and the C-terminal membrane-anchoring segment. C□mX, which is derived from the alternative splicing of the □ chain RNA transcript, thus provides an attractive antigenic site for the immunological targeting, either by way of a specific monoclonal antibody or a vaccine-like immunogen containing the C□mX domain, of mIgE-B cells for controlling IgE production. Because only humans and Primates species contain C□mX in their mIgE-expressing B cells, this thesis research has endeavored to construct a transgenic mouse strain to insert human C□mX in mouse mIgE. After several years of research, I have constructed “C□mX transgenic mouse strain” for evaluating the efficacy of anti-C□mX mAbs in targeting mIgE-expressing B cells.