Synthesis and Function of Antibody Fc Domain Glycoforms

描述（由申请方提供）：免疫球蛋白G（IgG）型单克隆抗体（MAb）是一类重要的治疗性糖蛋白。令人信服的证据表明，Fc结构域保守N-糖基化位点（Asn-297）处聚糖的精细结构负责MAb的独特效应子功能，包括抗体依赖性细胞毒性（ADCC）、补体依赖性细胞毒性（CDC）和细胞凋亡激活。此外，一种特殊的唾液酸化的Fc糖型被鉴定为负责静脉内免疫球蛋白（IVIG）的免疫活性。然而，在理解IgG-Fc糖基化的功能作用方面的进展受到Fc结构域聚糖的巨大结构异质性的阻碍。此外，控制MAb在表达中的糖基化为期望的同质糖型仍然是一项具有挑战性的任务。在本申请中，我们提出探索化学酶促方法来制备均一糖基化IgG-Fc和选择的单克隆抗体糖型的文库。通过进行Fc受体结合研究，我们旨在了解不同的聚糖结构如何微调IgG和IgG-Fc蛋白的效应子功能。我们已经进行了重要的初步研究，表明使用基于内切糖基化酶的转糖基化方法来构建人IgG-Fc的确定的、均一的糖型是可行的。在这一成功的基础上，我们建议实现三个具体目标。目的1：探索一种化学酶法构建各种纯IgG Fc糖型的方法。目的二是评价不同Fc结构域糖型在Fc受体结合中的构效关系，并评价选择性糖基化单克隆抗体的ADCC活性。目的3：合成新型的Fc结构域糖型，以评价IgG-Fc糖基化在抗炎活性中的作用。从所提出的研究中获得的知识将最终促进MAb和IgG-Fc蛋白的新型糖型作为有效治疗剂的开发。

DESCRIPTION (provided by applicant): Monoclonal antibodies (MAbs) of the immunoglobulin G (IgG) type are an important class of therapeutic glycoproteins. Compelling evidence has indicated that the fine structures of the glycans at the conserved N-glycosylation site (Asn-297) of the Fc domain are responsible for the distinct effector functions of MAbs, including antibody-dependent cellular cytotoxicity (ADCC), complement-dependent cytotoxicity (CDC), and activation of apoptosis. In addition, a special sialylated Fc glycoform was identified to be responsible for the antiinflammatory activity of intravenous immunoglobulin (IVIG). However, progress in understanding the functional roles of IgG-Fc glycosylation is hampered by the tremendous structural heterogeneity of Fc domain glycans. In addition, controlling glycosylation of MAbs in expression to a desired homogeneous glycoform is still a challenging task. In this application, we propose to explore a chemoenzymatic method to make a library of homogeneously glycosylated IgG-Fc and selected glycoforms of MAbs. Through performing Fc receptor binding studies, we aim to understand how different glycan structures can fine tune the effector functions of IgG and IgG-Fc protein. We have performed important preliminary studies indicating that it is feasible to use the endoglycosidase-based transglycosylation approach to construct defined, homogeneous glycoforms of human IgG-Fc. Building on this success, we propose to pursue three specific aims. Aim 1 is to explore a chemoenzymatic method for the construction of various pure glycoforms of IgG-Fc. Aim 2 is to evaluate the structure-activity realtionships of different Fc domain glycoforms in Fc receptor binding, and to evaluate ADCC activity of selectively glycoengineered monoclonal antibodies. Aim 3 is to synthesize novel Fc domain glycoforms for evaluating the roles of IgG-Fc glycosylation in anti-inflammatory activity. The knowledge gained from the proposed research will eventually facilitate the development of novel glycoforms of MAbs and IgG-Fc proteins as effective therapeutics.