Isolation andfunctional characterization of HO-hMSCs as NK-supportive cells derived from hematopoietic organoids

[Objective] In in vitro systems for differentiating and expanding natural killer (NK) cells, feeder cells provide essential cell-cell contact and paracrine signals that drive precursor proliferation and terminal maturation. However, existing xenogeneic feeder cells or tumor-derived genetically modified feeder cells pose risks of residual immunogenicity and malignant transformation, limiting clinical use. This study aims to develop a humanized mesenchymal-like stromal cell (hematopoietic organoid-derived human mesenchymal stromal cells, HO-hMSCs) derived from iPSC-based hematopoietic organoids, and elucidate its mechanisms of NK-supportive activity to enable a safe, efficient platform for clinical-grade NK cell production. [Methods] Human induced pluripotent stem cells (iPSCs) were differentiated into hematopoietic organoids, from which HO-hMSCs were isolated. Flow-cytometric phenotyping and bulk RNA-sequencing were performed to compare HO-hMSCs with umbilical cord-derived MSCs (UC-hMSCs). The effect of HO-hMSCs on NK cell differentiation efficiency (CD3-CD56+) and effector maturation (CD16 expression) were assessed by co-culture experiments, using UC-hMSCs as control. [Results] 1) Hematopoietic organoid induction and NK differentiation: iPSCs were induced to form hematopoietic organoids using cytokine cocktails, which further differentiated into high-purity CD45+CD56+ NK cells [(82.8%±12.07)% efficiency on day 21]. 2) HO-hMSC characteristics: HO-hMSCs exhibited upregulated expression of Notch pathway ligands (DLL4, JAG1, 4.06-8.04-fold), homeobox genes (HOXA3, HOXA5, log2FC=1.28 and 1.44), and key regulators of NK development (GATA3, BCL11A) and cytokine receptors (IL7R, IL27RA, 6.76 to 13.34-fold increase). 3) Functional validation: Compared to UC-hMSCs, HO-hMSCs co-culture significantly enhanced NK cell proportion by 30.5% (P<0.05) and increased CD16 positivity (+20.5%). [Conclusion] This study for the first time reveals that human hematopoietic organoid-derived HO-hMSCs possess potent hematopoietic niche-supportive activity. It provides a humanized, feeder-free platform for robust clinical-grade NK cell production and expands the translational utility of organoid technologies in cell therapy.