Human hematopoietic stem cells (HSCs) emerge in the aorta-gonad-mesonephros (AGM) region during Carnegie stages (CS) 14–17. Although we previously reported that these HSCs can generate no less than 300 daughter HSCs, their actual number has never been established. Here, we show that a single human AGM region HSC can generate 600–1,600 functional daughter HSCs. The presence of HSCs in the CS 17 liver in one case gave us a unique opportunity to describe a reduction of HSC self-renewal potential after liver colonization. From a clinical perspective, the efficacy of long-term hematopoietic regeneration depends on HSC self-renewal capacity. We quantitatively show that this capacity dramatically declines in the umbilical cord blood compared with HSCs in the AGM region. A full appreciation of the vast regenerative potential of the first human embryo-derived HSCs sets a new bar for generation of clinically useful HSCs from pluripotent stem cells.

在卡内基阶段（CS）14-17期间，人类造血干细胞（HSC）出现在主动脉-性腺-中肾（AGM）地区。尽管我们以前曾报道过这些HSC可以生成不少于300个子HSC，但它们的实际数量尚未确定。在这里，我们表明单个人类AGM区域HSC可以产生600–1,600个功能性子HSC。在一个案例中，CS 17肝中HSC的存在为我们提供了独特的机会来描述肝脏定植后HSC自我更新潜能的降低。从临床角度看，长期造血再生的功效取决于HSC的自我更新能力。我们定量地显示，与AGM地区的HSC相比，脐带血中的这种能力急剧下降。