Expansion effect of romiplostim on hematopoietic stem and progenitor cells versus other thrombopoietin receptor agonists

Romiplostim, a thrombopoietin (TPO) receptor agonist, is a clinically approved drug that is clearly effective in reconstituting hematopoiesis in refractory aplastic anemia and　idiopathic thrombocytopenic purpura. However, the mechanism underlying its biological effect is unknown, and its difference with other TPO receptor agonists remains unclear. Therefore, we determined the in vitro expansion effect of romiplostim on human CD34+ hematopoietic stem and progenitor cells (HSPCs) versus recombinant human TPO (rhTPO) and another clinically available drug eltrombopag. We also performed single-cell RNA-seq to define the effect of romiplostim on CD34+ HSPCs at the molecular level. The maximum expansion effect of romiplostim on total CD34+ cells, CD34+CD38+ progenitor cells, and CD34+CD38− immature cells was comparable to that of rhTPO, but higher than that of eltrombopag, particularly on CD34+CD38− immature cells. Single-cell RNA-seq analysis revealed that both romiplostim and eltrombopag induced signatures driven by rhTPO, but romiplostim induced molecular changes related to RHOA signaling at the most primitive subsets in HSPCs that were partially or not driven by eltrombopag. Additionally, romiplostim lacked the ability to induce TFRC expression observed by eltrombopag. In conclusion, romiplostim expands and affects human HSPCs similar to rhTPO but partially different from eltrombopag in terms of induction of gene expression.