The generation of haematopoietic stem cells (HSCs) from human pluripotent stem cells (hPSCs) is a major goal for regenerative medicine. During embryonic development, HSCs derive from haemogenic endothelium (HE) in a NOTCH- and retinoic acid (RA)-dependent manner. Although a WNT-dependent (WNTd) patterning of nascent hPSC mesoderm specifies clonally multipotent intra-embryonic-like HOXA⁺ definitive HE, this HE is functionally unresponsive to RA. Here we show that WNTd mesoderm, before HE specification, is actually composed of two distinct KDR⁺ CD34^neg populations. CXCR4^negCYP26A1⁺ mesoderm gives rise to HOXA⁺ multilineage definitive HE in an RA-independent manner, whereas CXCR4⁺ ALDH1A2⁺ mesoderm gives rise to HOXA⁺ multilineage definitive HE in a stage-specific, RA-dependent manner. Furthermore, both RA-independent (RAi) and RA-dependent (RAd) HE harbour transcriptional similarity to distinct populations found in the early human embryo, including HSC-competent HE. This revised model of human haematopoietic development provides essential resolution to the regulation and origins of the multiple waves of haematopoiesis. These insights provide the basis for the generation of specific haematopoietic populations, including the de novo specification of HSCs.

从人类多能干细胞（hPSC）生成造血干细胞（HSC）是再生医学的一个主要目标。在胚胎发育过程中，HSC 以 NOTCH 和视黄酸 (RA) 依赖性方式源自造血内皮 (HE)。尽管新生 hPSC 中胚层的 WNT 依赖性 (WNTd) 模式指定了克隆多能的胚胎内样HOXA ⁺确定性 HE，但该 HE 在功能上对 RA 没有反应。在这里，我们表明，在 HE 规范之前的 WNTd 中胚层实际上是由两个不同的 KDR ⁺ CD34 ^neg群体组成。CXCR4 ^neg CYP26A1 ⁺中胚层以与 RA 无关的方式产生HOXA ^{+多谱系最终 HE，而 CXCR4 +} ALDH1A2 ⁺中胚层以阶段特异性、RA 依赖性方式产生HOXA ^{+多谱系最终 HE。}此外，RA 独立性 (RAi) 和 RA 依赖性 (RAd) HE 都与早期人类胚胎中发现的不同群体（包括具有 HSC 能力的 HE）具有转录相似性。这种修订后的人类造血发育模型为造血多波的调节和起源提供了重要的解决方案。这些见解为特定造血群体的产生提供了基础，包括 HSC 的从头规范。