Defining the ontogeny of the human adaptive immune system during embryogenesis has implications for understanding childhood diseases including leukaemias and autoimmune conditions. Using RAG1:GFP human pluripotent stem cell reporter lines, we examined human T-cell genesis from pluripotent-stem-cell-derived haematopoietic organoids. Under conditions favouring T-cell development, RAG1+ cells progressively upregulated a cohort of recognized T-cell-associated genes, arresting development at the CD4+CD8+ stage. Sort and re-culture experiments showed that early RAG1+ cells also possessed B-cell, myeloid and erythroid potential. Flow cytometry and single-cell-RNA-sequencing data showed that early RAG1+ cells co-expressed the endothelial/haematopoietic progenitor markers CD34, VECAD and CD90, whereas imaging studies identified RAG1+ cells within CD31+ endothelial structures that co-expressed SOX17+ or the endothelial marker CAV1. Collectively, these observations provide evidence for a wave of human T-cell development that originates directly from haemogenic endothelium via a RAG1+ intermediate with multilineage potential.

在胚胎发生过程中定义人类适应性免疫系统的个体发育对于理解包括白血病和自身免疫性疾病在内的儿童疾病具有重要意义。使用 RAG1:GFP 人类多能干细胞报告基因系，我们检查了来自多能干细胞衍生的造血类器官的人类 T 细胞发生。在有利于 T 细胞发育的条件下，RAG1+ 细胞逐渐上调一组公认的 T 细胞相关基因，在 CD4+CD8+ 阶段停止发育。分选和再培养实验表明，早期 RAG1+ 细胞也具有 B 细胞、骨髓和红细胞潜能。流式细胞术和单细胞 RNA 测序数据显示，早期 RAG1+ 细胞共表达内皮/造血祖​​细胞标志物 CD34、VECAD 和 CD90，而影像学研究确定了 CD31+ 内皮结构内的 RAG1+ 细胞，这些细胞共表达 SOX17+ 或内皮标记 CAV1。总的来说，这些观察结果为人类 T 细胞发育浪潮提供了证据，该浪潮直接源自造血内皮，通过具有多向谱系潜力的 RAG1+ 中间体。