BACKGROUND: Whether umbilical cord blood (UCB) quality is maintained during decades of cryopreservation is critical for public banking policy. We analyzed post-thaw quality of 1129 UCB units cryopreserved for up to 19 years at Korea's largest public cord blood bank and examined implications for shelf-life policy. METHODS: UCB units manually volume-reduced and cryopreserved between 2006 and 2025 underwent pre-transplant testing using their attached integral segments (median storage 6.5 years; range 16 days-19.0 years). Associations between storage duration and 19 quality indicators and 13 paired pre-/post-thaw complete blood count parameters were analyzed by Spearman correlation (ρ) before and after adjusting for era effects (processing and testing dates) to separate genuine storage effects from longitudinal analytical variation. Predictors of colony-forming unit (CFU) were ranked by univariate correlation and a Random Forest machine-learning model. Compliance with German/FACT-NetCord pre-transplant criteria was assessed. RESULTS: Associations between storage duration and quality indicators were modest before adjustment (|ρ| ≤ 0.4) and were largely abolished once differences in testing era were taken into account: the storage-duration correlations for viable CD45+ and viable CD34+ both lost significance, as did CFU/CD34 + (P = .327). The post-thaw CD34+ count was the strongest predictor of CFU. Testing date, although ranked only seventh by simple correlation, rose to second in the Random Forest model, indicating an era effect not captured by pairwise analysis. The composite pre-transplant criteria pass rate was 96.2%, remaining above 93% across all storage bins. CONCLUSIONS: After up to 19 years of cryopreservation, per-CD34+ colony-forming capacity is preserved. A test-based shelf-life policy is more evidence-based than a predetermined expiration limit.

Background: Acute erythroid leukemia (AEL) or AML-M6 predominantly affects older adults and is rare in childhood. Compared with other AML subtypes, AEL remains relatively understudied because of its rarity. We established LS-CHM, a novel AEL cell line derived from the ascitic fluid of a patient with congenital leukemia. Interestingly, leukemic cells persisted in the ascitic fluid even after successful eradication from the bone marrow and extramedullary sites. Method: Leukemia cells from the ascites fluid exhibited robust proliferation in culture independent of cytokine requirement and were further characterized by flow cytometric immunophenotyping, cytogenetics, cell cycle and doubling time analysis, colony formation, genome and RNA sequencing, myeloid gene next generation sequencing, and cytotoxicity analysis. Results: LS-CHM displayed CD36, partial CD235a, CD31, CD43, and CD71 expression and demonstrated in vitro robust growth and high sensitivity to chemotherapeutic agents. A PDX mouse model showed development of leukemia. Genomic analysis revealed a frameshift BCOR mutation in the absence of additional mutations and downregulated TP53 expression with an exonic non-deleterious mutation. RNA sequencing of LS-CHM cells revealed upregulation of two cohesin complex genes, RAD21 and SMC3, whose high levels are associated with hematopoietic stem cell differentiation into erythroid lineage. Conclusions: LS-CHM represents the first congenital AEL-derived cell line, in contrast to the predominantly adult-origin and often secondary erythroid leukemia cell lines available currently. Thus, LS-CHM provides a unique pediatric and extramedullary AEL model, expanding the existing spectrum of AEL cell lines and offering valuable opportunities for biologic and therapeutic investigations.

ABSTRACTStem cell niches are complex multi‐signalling networks comprised of molecular cues and physical interactions, orchestrated by niche‐resident cells and the extracellular factors they produce. The bone niche specifically houses haematopoietic stem cells (HSCs), a critical cell type responsible for producing all blood and immune cells throughout life. Currently, how niches facilitate an ideal environment with simultaneously coordinating both intrinsic and extrinsic cellular signals is unknown. Studies presented here identify the existence of unique extracellular vesicle (EV)‐defined niches within the haematopoietic system of human individuals. Bridging studies using proteomic signatures, nanoparticle characterization at single‐vesicle resolution and machine learning‐based techniques reveal that EVs can be grouped by blood, bone marrow and trabeculae within a human individual. Stem cell assays demonstrate that these niche‐defined EVs impart functional effects on stem cells/progenitors based on location within the haematopoietic system. Finally, using single‐cell transcriptomic analyses, results identify for the first time how niche‐sourced EVs differentially affect the most primitive human HSCs and progenitors. This study highlights the significance of nanoparticles on human immunity and blood production and provides evidence for a new role for EVs, namely the demarcation of distinct nano‐niches within biological systems.