V(D)J recombination generates mature B cells that express huge repertoires of primary antibodies as diverse immunoglobulin (Ig) heavy chain (IgH) and light chain (IgL) of their B cell antigen receptors (BCRs). Cognate antigen binding to BCR variable region domains activates B cells into the germinal center (GC) reaction in which somatic hypermutation (SHM) modifies primary variable region-encoding sequences, with subsequent selection for mutations that improve antigen-binding affinity, ultimately leading to antibody affinity maturation. Based on these principles, we developed a humanized mouse model approach to diversify an anti-PD1 therapeutic antibody and allow isolation of variants with novel properties. In this approach, component Ig gene segments of the anti-PD1 antibody underwent de novo V(D)J recombination to diversify the anti-PD1 antibody in the primary antibody repertoire in the mouse models. Immunization of these mouse models further modified the anti-PD1 antibodies through SHM. Known anti-PD1 antibodies block interaction of PD1 with its ligands to alleviate PD1-mediated T cell suppression, thereby boosting antitumor T cell responses. By diversifying one such anti-PD1 antibody, we derived many anti-PD1 antibodies, including anti-PD1 antibodies with the opposite activity of enhancing PD1/ligand interaction. Such antibodies theoretically might suppress deleterious T cell activities in autoimmune diseases. The approach we describe should be generally applicable for diversifying other therapeutic antibodies.

V(D)J 重组产生成熟的 B 细胞，这些细胞表达大量一抗，如其 B 细胞抗原受体 (BCR) 的不同免疫球蛋白 (Ig) 重链 (IgH) 和轻链 (IgL)。同源抗原结合 BCR 可变区结构域激活 B 细胞进入生发中心 (GC) 反应，其中体细胞超突变 (SHM) 修饰初级可变区编码序列，随后选择提高抗原结合亲和力的突变，最终产生抗体亲和力成熟。基于这些原则，我们开发了一种人源化小鼠模型方法，使抗 PD1 治疗性抗体多样化，并允许分离具有新特性的变体。在这种方法中，抗 PD1 抗体的 Ig 基因片段进行了从头 V(D)J 重组，使小鼠模型中一抗中的抗 PD1 抗体多样化。这些小鼠模型的免疫通过 SHM 进一步修饰了抗 PD1 抗体。已知的抗 PD1 抗体阻断 PD1 与其配体的相互作用，以减轻 PD1 介导的 T 细胞抑制，从而增强抗肿瘤 T 细胞反应。通过使一种这样的抗 PD1 抗体多样化，我们衍生出许多抗 PD1 抗体，包括具有增强 PD1/配体相互作用的相反活性的抗 PD1 抗体。理论上，此类抗体可能会抑制自身免疫性疾病中的有害 T 细胞活性。我们描述的方法应该普遍适用于其他治疗性抗体的多样化。