A comprehensive understanding of human pathophysiology requires the analysis of interindividual variability among healthy individuals. While reference ranges for complete blood counts (CBCs) are routinely used in clinical settings, no such standard reference exists for circulating hematopoietic stem and progenitor cells (cHSPCs) due to their rarity and bone marrow residency. However, technological advances like single-cell RNA sequencing (scRNA-seq) now enable detailed cHSPCs profiling, revealing heterogeneity linked to both disease and age. This was well explained in current study published in nature medicine.
A total of 148 healthy individuals aged 23 to 91 years (median age = 61.5 years, males = 79, females = 69) were included in this study. All participants were recruited from the Weizmann Institute of Science (WIS). Researchers established reference tools and models for projecting new samples, indicating the potential of diagnosis among 73 patients with myelodysplastic syndrome (MDS) or cytopenia.
Researchers analyzed 626,966 CD34+ from 148 partcipants using genotyping and scRNA-seq. A robust model reported diverse cellular states and a consistent cell-state pattern in 47 individuals. But distinct from bone marrow-derived HSPCs, cHSPCs offer a reliable, accessible proxy for discovering human hematopoiesis under steady-state conditions.
The cHSPCs model demonstrated a unique HSC population linked to both lymphoid and myeloid differentiation, marked by hepatic leukemia factor (HLF) and arginine vasopressin (AVP) expression. This suggested that self-renewing HSCs existed in peripheral blood under steady-state conditions. Notably, 14 genes, including HLF and AVP, were expressed at least 1.5 times more in HSCs compared to their immediate differentiation branches. The cHSPC atlas also revealed the presence of basophil-eosinophil-mast cell progenitors (BEMPs) and natural killer T cell and dendritic cell progenitors (NKTDPs) in blood, progenitor types that are rarely found in the bone marrow.
The composition of cHSPC state varied widely across individuals, especially for HSCs and common lymphoid progenitor-like myeloid cells (CLP-Ms), while multipotent progenitor cells (MPPs) and megakaryocyte-erythroid-basophil-eosinophil-mast cell progenitors (MEBEMPs) showed less variability. Longitudinal sampling confirmed that individual cell-state frequencies remained stable over time. This reinforces the finding that interindividual variability in cHSPC composition is substantial, even among healthy individuals.
Circulating HSPC composition correlated with CBC parameters and clonal hematopoiesis (CH). Reduced CLP frequencies were associated with high red-cell distribution width (RDW) and CH. In CH-negative people, aging increased myeloid-to-lymphoid cHSPC ratios in males compared to females. This sex-specific shift may have reflected intrinsic or extrinsic factors, including bone marrow or hormonal microenvironmental changes. Composition-normalized cHSPC gene expression correlated with age, notably through the LMNA signature, which increased in lymphoid progenitors. This underscored the age-related transcriptional changes.
In the context of disease, cHSPC profiling identified distinct MDS subclasses by comparing peripheral blood cell compositions with those of a healthy reference. In silico sorting identified abnormal cell distributions, copy number variations (CNVs), and RDW associations. This approach distinguished MDS from cytopenia and highlighted cHSPC-based diagnostics for subclassifying and understanding the pathophysiology of MDS.
Researchers developed an MDS diagnostic classifier using gene signatures, cHSPC composition, CBCs, and variant allele frequency (VAF) data, achieving high accuracy with an area under the curve (AUC) up to 0.97. Key signatures included major histocompatibility complex class II (MHC-II) and S-phase-related genes. cHSPC profiling also predicted blast fractions and treatment response. This highlighted the potential for noninvasive MDS monitoring, diagnosis, and risk stratification.
This study concluded that the physiology of cHSPC changes with age, and these changes are reflected at the population level. Based on these findings, this study proposed a diagnostic platform to differentiate normal from pathological hematopoiesis. These tools offer a promising approach for tracking the transition from health to disease.
Reference: Furer N, Rappoport N, Milman O, et al. A reference model of circulating hematopoietic stem cells across the lifespan with applications to diagnostics. Nat Med. 2025. doi:10.1038/s41591-025-03716-5
