Distinct Phenotypic and Molecular Characteristics of CD34− and CD34+ Hematopoietic Stem/Progenitor Cell Subsets in Cord Blood and Bone Marrow Samples: Implications for Clinical Applications

<b>Background/Objectives:</b> We aimed to identify the molecular signatures of primitive CD34⁺ and CD34^- hematopoietic stem/progenitor cell (HSC/HPC) subsets in cord blood and bone marrow samples. <b>Methods:</b> CD34⁺ and CD34^- HSC/HPC subsets from cord blood and bone marrow were characterized using flow cytometry, real-time PCR, and proteomic analysis to evaluate their phenotypic and molecular profiles. <b>Results:</b> Our findings revealed a significantly higher percentage of Lin^-CD34^-CD38^Low/- (-/-) cells than of Lin^-CD34⁺CD38^Low/- (+/-) cells in cord blood. Aldehyde dehydrogenase levels were significantly lower in (-/-) than in (+/-) cells. Clonogenic ability was lower in (-/-) than in (+/-) cells. However, CD34^- cells exhibited potent megakaryocyte/erythrocyte differentiation ability. Importantly, the HSC/HPC subsets expressed pluripotency or stemness genes (SOX2, Nanog, and OCT4); however, OCT4 expression significantly increased in (-/-) compared with (+/-) cells. We identified 304 proteins in the HSC/HPC subsets-85.6% had similar expression patterns in the two subsets; only 14.4% were differentially expressed between (-/-) and (+/-) cells. This implies their comparability at the protein level. Certain proteins were implicated in cellular-development-, gene-expression-, and embryonic-development-related signaling networks. <b>Conclusions:</b> Distinct biological and functional characteristics were observed between (-/-) and (+/-) HSC/HPC subsets. Some of the identified proteins may be novel HSC/HPC subsets markers for clinical applications after validation.