Humanization of hFcRn Mice for Physiological Evaluation of Therapeutic Antibodies

描述（申请人提供）：新生儿Fc受体（FcRn）具有4种主要功能：IgG和白蛋白的分解代谢保护、IgG的转胞吞作用和抗原呈递。FcRn在许多组织中发挥作用，对于新生儿通过初乳和乳汁获得母体IgG、IgG的肺分泌以及IgG和免疫复合物跨成人肠上皮的双向转运至关重要。它也参与T细胞抗原呈递。IgG的主要临床成功是作为精确靶向和治疗广泛的人类疾病，特别是癌症和炎性疾病的“魔术子弹”。这一成功部分是由于与其他血清蛋白相比，它们在体内的半衰期较长。与我们 随着对FcRn在该过程中的关键作用的理解，已经出现了解决血清蛋白和小分子半衰期的新的治疗领域。这一新领域的主要参与者是IgG Fc结构域和白蛋白：临床相关分子通过融合与这些连接，延长其功能性体内半衰期。化合物的功能性半衰期延长具有许多临床益处，包括：（i）有效剂量的减少（减少不良反应）;（ii）给药频率的降低（延长的药代动力学）;（iii）生物利用度的提高;以及（iv）生产成本的降低。 IgG和融合化合物的治疗开发的关键是临床前模型，其准确地反映了人类生理学。然而，FcRn在人类和啮齿动物之间表现出种属歧视结合差异。为了克服这一点，开发了缺乏小鼠FcRn并表达人FcRn（hPcRn）的小鼠。尽管有用，但这些模型表达小鼠IgG，其不能被hFcRn和小鼠白蛋白有效保护。这并不反映正常的生理状况。对于白蛋白，目前没有容易获得的模型。为了建立更好地反映人类生理过程的模型，我们建议将小鼠IgG 2b的Fc结构域与人Fc交换，并将小鼠白蛋白基因与人白蛋白替换。为此，我们将使用TAL效应物核酸酶来引入位于感兴趣区域侧翼的异源特异性重组酶靶位点，然后通过重组介导的盒交换来直接遗传工程改造现有人源化FcRn小鼠模型的合子。通过对当前模型进行连续修改来创建这些新菌株，我们将建立在它们以前的使用和声誉（数据）的基础上，加快它们的实施。经过验证后，这些新菌株将通过JAX Mouse Repository分发。我们完全期望这些模型能够更准确地反映人IgG和人白蛋白生物学，从而快速推进药物开发和FcRn生物学。

DESCRIPTION (provided by applicant): The neonatal Fc receptor (FcRn) has four major functions: catabolic protection of IgG and albumin, transcytosis of IgG and antigen presentation. FcRn functions across many tissues and is critical for neonatal acquisition of maternal IgG via colostrum and milk, the pulmonary secretion of IgG and bidirectional transport of both IgG and immune complexes across the adult intestinal epithelium. It is also involved in T cell antigen presentation. A major clinical success of IgGs is as a "magic bullet" precisely targeting and treating a wide array of human disorders, especially cancer and inflammatory diseases. This success is due, in part, to their long half-life in vivo compared to other serum proteins. With our understanding of the critical role of FcRn in this process, a new therapeutic field addressing serum proteins and small molecules half-life has emerged. The major players of this new field are the IgG Fc domain and albumin: clinically relevant molecules are attached to these via fusion extending their functional in vivo half- life. Functional half-life extension of compounds has a number of clinical benefits including: (i) reduction of effective dosage (reducing adverse reactions); (ii) reduced frequency of administration (extended pharmacokinetics); (iii) improved bioavailability; and (iv) a reduction of production costs. Critical for therapeutic development of IgGs and fusion compounds are preclinical models, which accurately reflect human physiology. However, FcRn exhibits species-discrimination binding differences between human and rodents. To overcome this, mice lacking the mouse FcRn and expressing human FcRn (hPcRn) were developed. Although useful, these models express mouse IgGs, which are not effectively protected by hFcRn and mouse albumin. This does not reflect the normal physiological situation. For albumin there is currently no model easily available. To establish models that better reflect the human physiological processes, we propose to exchange the Fc domain of mouse lgG2b with human Fc and to replace the mouse albumin gene with human albumin. To do this, we will use TAL effector nucleases to introduce heterospecific recombinase target sites flanking the region of interest, followed by recombination mediated cassette exchange to directly genetically engineer the zygote of existing humanized FcRn mouse models. By creating these new strains via sequential modification of current models we will build upon their previous use and reputation (data), speeding their implementation. After verification, these novel strains will be distributed via the JAX Mouse Repository. We fully expect these models to more accurately reflect human IgG and human albumin biology and, therefore, rapidly advance drug development and FcRn biology.