ABSTRACT

A major asset of many monoclonal antibody (mAb)-based biologics is their persistence in circulation. The MHC class I family Fc receptor, FCGRT, is primarily responsible for this extended pharmacokinetic behavior. Engagement of FCGRT with the crystallizable fragment (Fc) domain protects IgG from catabolic elimination, thereby extending the persistence and bioavailability of IgG and related Fc-based biologics. There is a need for reliable in vivo models to facilitate the preclinical development of novel IgG-based biologics. FcRn-humanized mice have been widely accepted as translationally relevant surrogates for IgG-based biologics evaluations. Although such FCGRT-humanized mice, especially the mouse strain, B6.Cg-Fcgrt^tm1Dcr Tg(FCGRT)32Dcr (abbreviated Tg32), have been substantially validated for modeling humanized IgG-based biologics, there is a recognized caveat – they lack an endogenous source of human IgG that typifies the human competitive condition. Here, we used CRISPR/Cas9-mediated homology-directed repair to equip the hFCGRT Tg32 strain with a human IGHG1 Fc domain. This replacement now results in mice that produce human IgG1 Fc-mouse IgG Fab₂ chimeric antibodies at physiologically relevant levels, which can be further heightened by immunization. This endogenous chimeric IgG1 significantly dampens the serum half-life of administered humanized mAbs in an hFCGRT-dependent manner. Thus, such IgG1-Fc humanized mice may provide a more physiologically relevant competitive hFCGRT-humanized mouse model for the preclinical development of human IgG-based biologics.

摘要

许多基于单克隆抗体 (mAb) 的生物制剂的主要资产是它们在循环中的持久性。MHC I 类家族 Fc 受体 FCGRT 主要负责这种扩展的药代动力学行为。FCGRT 与可结晶片段 (Fc) 结构域的结合保护 IgG 免于分解代谢消除，从而延长 IgG 和相关 Fc 生物制剂的持久性和生物利用度。需要可靠的体内模型来促进新型 IgG 生物制剂的临床前开发。FcRn 人源化小鼠已被广泛接受为基于 IgG 的生物制剂评估的翻译相关替代物。尽管这种 FCGRT 人源化小鼠，尤其是小鼠品系，B6.Cg-Fcgrt ^tm1DcrTg(FCGRT)32Dcr（缩写为 Tg32）已被充分验证用于模拟基于人源化 IgG 的生物制剂，但有一个公认的警告——它们缺乏代表人类竞争条件的人类 IgG 的内源性来源。在这里，我们使用 CRISPR/Cas9 介导的同源定向修复为 hFCGRT Tg32 菌株配备了人类IGHG1 Fc 域。这种替换现在导致小鼠产生人 IgG1 Fc-小鼠 IgG Fab ₂生理相关水平的嵌合抗体，可以通过免疫进一步增强。这种内源性嵌合 IgG1 以 hFCGRT 依赖性方式显着抑制了施用的人源化 mAb 的血清半衰期。因此，此类 IgG1-Fc 人源化小鼠可为基于人 IgG 的生物制剂的临床前开发提供更具生理相关性的竞争性 hFCGRT 人源化小鼠模型。