Despite great values in many applications, heavy chain-only antibodies (HcAbs) are naturally only produced in camelids and sharks, which are not easy to access and handle. Production of the type of antibodies in small laboratory animals would remarkably facilitate their applications. We previously reported a mouse line in which the CH1 exon of mouse γ1 was deleted that could express heavy chain-only IgG1 antibodies. However, these mice showed an extremely weak IgG1 response to specific antigens when immunized, and we could only achieve single VH domains with low affinity to antigens using these mice. One possibility is that the mouse germline VH repertoire was not sufficient to support the expression of functional heavy chain-only antibodies. In this study, we report the generation of a rat line in which the CH1 exon of the γ2a gene was removed and the γ1 and γ2b genes were silenced. Although the genetically modified rats expressed heavy chain-only IgG2a, they also exhibited a very weak IgG2a response to antigen immunization. Panning of a phage library constructed using IgG2a VH segments amplified from immunized rats identified antigen-specific single VH antibodies, which also exhibited much lower affinity than that of commercial mAbs. Together with our previous report, this study suggests that the simple genetic removal of the CH1 exon does not guarantee the successful expression of functional heavy chain-only antibodies.

中文翻译：

---

CH1外显子的遗传去除导致大鼠功能低下的仅重链IgG2a的产生。

尽管在许多应用中具有很高的价值，但仅重链抗体（HcAb）自然仅在骆驼科动物和鲨鱼中产生，它们不易接近和处理。在小型实验动物中产生这类抗体会极大地促进其应用。我们先前曾报道过一个小鼠系，其中删除了小鼠γ1的CH1外显子，它可以表达仅重链IgG1抗体。但是，这些小鼠在免疫后对特定抗原的IgG1反应非常弱，使用这些小鼠我们只能获得对抗原的亲和力低的单个VH结构域。一种可能性是小鼠种系VH谱库不足以支持仅功能性重链抗体的表达。在这个研究中，我们报道了一条大鼠系的生成，其中删除了γ2a基因的CH1外显子，并使γ1和γ2b基因沉默。尽管转基因大鼠只表达重链IgG2a，但它们对抗原免疫的IgG2a反应也很弱。淘选使用从免疫大鼠中扩增的IgG2a VH片段构建的噬菌体文库，可以鉴定出抗原特异性的单个VH抗体，该抗体的亲和力也比市售mAb低得多。与我们以前的报告一起，这项研究表明，CH1外显子的简单遗传去除不能保证功能性仅重链抗体的成功表达。淘选使用从免疫大鼠中扩增的IgG2a VH片段构建的噬菌体文库，可以鉴定出抗原特异性的单个VH抗体，该抗体的亲和力也比市售mAb低得多。与我们以前的报告一起，这项研究表明，CH1外显子的简单遗传去除不能保证功能性仅重链抗体的成功表达。淘选使用从免疫大鼠中扩增的IgG2a VH片段构建的噬菌体文库，可以鉴定出抗原特异性的单个VH抗体，该抗体的亲和力也比市售mAb低得多。与我们以前的报告一起，这项研究表明，CH1外显子的简单遗传去除不能保证功能性仅重链抗体的成功表达。