目的：肝细胞癌（HCC）主要特征是高发生血管侵袭。然而，肝癌门静脉肿瘤栓塞（PVTT）的具体机制仍不清楚。由于髓样细胞发育阻滞，CD71+红细胞祖细胞（EPCs）和髓源性抑制细胞在HCC中起重要作用；但它们在PVTT中的作用仍不清楚。方法：通过形态学、RNA测序、酶联免疫吸附测定和流式细胞术分析评估了CD71+EPCs在HCC肿瘤微环境（TME）中的作用。采用共培养技术评估了CD45+EPCs及其对血管的损害效应。另外，在小鼠模型中探索了CD45+EPCs促进PVTT的功能。结果：HCC组织中的CD45+EPCs表现出增强的髓样细胞特征，包括形态学、表面标记物、转化生长因子（TGF）-β产生和基因表达，与循环中的CD45+EPCs比较起来。因此，CD45+EPCs的大部分，尤其是TME中的EPCs，由红细胞向髓样细胞转分化而来（EDMCs）。此外，表达C-C趋化因子受体2（CCR2）mRNA的CD45+EPCs在TME中上调。HCC组织的肿瘤巨噬细胞诱导CD45+EPCs剂量依赖性迁移。同时，免疫荧光分析结果显示，在TME和循环中这两种细胞类型是正相关的。也就是说，EDMCs主要通过CCR2从循环中的CD45+EPCs被HCC巨噬细胞趋化。此外，与脾脏相比，在TME中CD45+EPCs的FX，FVII，FGB，C4b，CFB和CFH的表达升高。与脾脏相比，来自HCC TME的CD45+EPCs通过TGF-β和FGB促进血管内皮细胞迁移和管道形成的破坏，同时也诱导HCC细胞的迁移。HCC巨噬细胞诱导CD45+EPCs表现出更高水平的FX，FVII，FGB和TGF-β。与此同时，CCAAT/增强子结合蛋白β表达的上调也在TME中诱导CD45+EPCs产生FGB和TGF-β。WTAP作为主要的RNA m6A写入体，在TME中稳定FX和FVII的mRNA，增强它们的核外运输。TME中的CD45+EPCs与PVTT和预后不良呈正相关。脾切除减少了循环和TME中的CD45+EPCs水平，以及微血管侵袭的发生率。将HCC组织的CD45+EPCs移植到脾切除的HCC小鼠中后，微血管侵袭发生率增加。结论：HCC微环境富集的CD45+EPCs是EDMCs，由HCC巨噬细胞诱导从循环迁移到TME。随后，EDMCs通过破坏血管内皮、加重凝血和促进HCC细胞迁移来促进PVTT。©作者。

Rationale: Hepatocellular carcinoma (HCC) is primarily characterized by a high incidence of vascular invasion. However, the specific mechanism underlying portal vein tumor thrombus (PVTT) in HCC remains unclear. As a consequence of myeloid cell developmental arrest, CD71+ erythroid progenitor cells (EPCs) and myeloid-derived suppressor cells play important roles in HCC; however, their roles in PVTT remain unclear. Methods: The role of CD71+ EPCs in the HCC tumor microenvironment (TME) was evaluated via morphological, RNA-sequencing, enzyme-linked immunosorbent assay, and flow cytometric analyses. Co-culture techniques were employed to assess the CD45+ EPCs and their vascular compromising effect. Additionally, the PVTT-promoting function of CD45+ EPCs was explored in vivo in a murine model. Results: The CD45+EPCs in HCC tissues exhibited increased myeloid cell features, including morphology, surface markers, transforming growth factor (TGF)-β generation, and gene expression, compared with those in circulation. Hence, a large proportion of CD45+EPCs, particularly those in TMEs, comprise erythroid-transdifferentiated myeloid cells (EDMCs). Additionally, the expression of C-C chemokine receptor type 2 (CCR2) mRNA was upregulated in CD45+EPCs within the TME. Tumor macrophages from HCC tissues induced substantial migration of CD45+EPCs in a dose-dependent manner. Meanwhile, results from immunofluorescence analyses revealed that these two cell types are positively associated in the TME and circulation. That is, EDMCs are chemoattracted by HCC macrophages mainly via CCR2 from CD45+ EPCs in the circulation. Additionally, the expressions of FX, FVII, FGB, C4b, CFB, and CFH were elevated in CD45+EPCs within the TME compared with those in the spleen. The CD45+EPCs from the HCC TME promoted vessel endothelial cell migration and compromised tube formation through TGF-β and FGB, respectively. Additionally, CD45+EPCs from the TME induced HCC cell migration. HCC macrophage-induced CD45+EPCs to exhibit higher levels of FX, FVII, FGB, and TGF-β. Meanwhile, upregulation of CCAAT/enhancer binding protein beta expression induced FGB and TGF-β generation in CD45+EPCs in the TME. WTAP, a major RNA m6A writer, stabilized FX and FVII mRNA and enhanced their nuclear export in CD45+EPCs from the TME. CD45+EPCs from the TME were positively associated with PVTT and poor prognosis. Splenectomy reduced the level of CD45+EPCs in the circulation and TME, as well as the incidence of microvascular invasion. The incidence of microvascular invasion increased following the transfer of HCC tissue CD45+EPCs to splenectomized HCC-bearing mice. Conclusions: The CD45+EPCs enriched in the HCC microenvironment are EDMCs, which are induced by HCC macrophages to migrate from the circulation to the TME. Subsequently, EDMCs promote PVTT by compromising the blood vessel endothelium, aggravating coagulation, and promoting HCC cell migration.© The author(s).