Thouvenel Christopher D, Tipton Christopher M, Yamazaki Yasuhiro, Zhang Ting-Ting, Rylaarsdam Stacey, Hom Jennifer R, Snead Catherine, Zhu Chengsong, Li Quan-Zhen, Lee Yu Nee, Kawai Tomoki, Haque Neshatul, Zimmermann Michael T, Ponnan Sivasankaran Munusamy, Jackson Shaun W, James Rich G, Sanz Ignacio, Notarangelo Luigi D, Torgerson Troy R, Ochs Hans D, Rawlings David J, Allenspach Eric J
Center for Immunity and Immunotherapies, Seattle Children's Research Institute, Seattle, WA, USA.
Lowance Center for Human Immunology, Emory University School of Medicine, Atlanta, GA, USA.
J Clin Immunol. 2025 Jan 15;45(1):66. doi: 10.1007/s10875-024-01849-9.
Reduced function or hypomorphic variants in recombination-activating genes (RAG) 1 or 2 result in a broad clinical phenotype including common variable immunodeficiency (CVID) and even adult-onset disease. Milder RAG variants are less characterized. Here we describe the longitudinal course of a milder combined RAG deficiency in 3 of 7 siblings sharing the same RAG2 mutations over a 50-year study. Whole-genome and repertoire sequencing, bacteriophage immunizations, and deep immunophenotyping were used to compare affected and unaffected family members. The clinical phenotype of three affected siblings with hypomorphic RAG deficiency ranged from combined immunodeficiency and early mortality to a late-onset CID with hyper-IgM phenotype. T cells were remarkably similar across affected siblings, yet CDR3 skewing and regulatory T cell defects were not observed. B cell analysis showed elevated unswitched CD27+ and CD21 cells as well as features of an autoreactive antibody repertoire and presence of secreted autoantibodies, yet no clinical autoimmunity was present. Most striking was an expanded polyclonal marginal zone-like B cell population (IgM+IgD+CD27+) utilizing the self-reactive unmutated VH4-34 receptor demonstrating that hypomorphic RAG deficiency can promote expansion of self-reactive B cells. This process, however, was not sufficient to trigger clinical autoimmunity. Utilizing multiple approaches, we functionally measured the specific RAG2 variant effects and assessed how selection and secondary triggers altered the BCR repertoire and immunophenotype overtime. Overall, we demonstrate a broad disease spectrum in siblings with identical hypomorphic RAG deficiency, highlighting that phenotypic divergence can result from expansion of IgM + memory B cells.
重组激活基因（RAG）1或2功能降低或低表达变异会导致广泛的临床表型，包括常见变异型免疫缺陷（CVID）甚至成人发病疾病。较轻的RAG变异特征较少。在一项为期50年的研究中，我们描述了7名携带相同RAG2突变的兄弟姐妹中3人较轻的联合RAG缺陷的病程。使用全基因组和库测序、噬菌体免疫接种以及深度免疫表型分析来比较受影响和未受影响的家庭成员。三名患有低表达RAG缺陷的受影响兄弟姐妹的临床表型从联合免疫缺陷和早期死亡到具有高IgM表型的迟发性CID不等。受影响的兄弟姐妹之间的T细胞非常相似，但未观察到CDR3偏斜和调节性T细胞缺陷。B细胞分析显示未转换的CD27+和CD21细胞升高，以及自身反应性抗体库特征和分泌性自身抗体的存在，但无临床自身免疫。最引人注目的是一个利用自身反应性未突变VH4-34受体的多克隆边缘区样B细胞群体（IgM+IgD+CD27+）扩增，表明低表达RAG缺陷可促进自身反应性B细胞扩增。然而，这一过程不足以引发临床自身免疫。我们使用多种方法在功能上测量了特定RAG2变异的影响，并评估了选择和二次触发因素如何随时间改变BCR库和免疫表型。总体而言，我们证明了具有相同低表达RAG缺陷的兄弟姐妹存在广泛的疾病谱，突出了IgM+记忆B细胞扩增可导致表型差异。
