CD34 + Liver Cancer Stem Cells Were Formed by Fusion of Hepatobiliary Stem/Progenitor Cells with Hematopoietic Precursor-Derived Myeloid Intermediates

Abstract

A large number of cancer stem cells (CSCs) were identified and characterized; however, the origins and formation of CSCs remain elusive. In this study, we examined the origination of the newly identified CD34⁺ liver CSC (LCSC). We found that CD34⁺ LCSC coexpressed liver stem cell and myelomonocytic cell markers, showing a mixed phenotype, a combination of hepatobiliary stem/progenitor cells (HSPCs) and myelomonocytic cells. Moreover, human xenografts produced by CD34⁺ LCSCs and the parental cells, which CD34⁺ LCSC was isolated from, coexpressed liver cancer and myelomonocytic markers, also demonstrating mixed phenotypes. The xenografts and the parental cells secreted albumin demonstrating their hepatocyte origin and also expressed cytokines [interleukin (IL)-1b, IL-6, IL-12A, IL-18, tumor necrosis factor-alpha (TNF-α), and CSF1] and chemokines (IL-8, CCL2, and CCL5). Expression of these cytokines and chemokines responded to the stimuli [interferon-γ (INF-γ), IL-4, and lipopolysaccharide (LPS)]. Furthermore, human xenografts and the parental cells phagocytized Escherichia coli. CD34⁺ LCSC coexpressed CD45, demonstrating that its origin appears to be from a hematopoietic precursor. The percentage of cells positive for OV6, CD34, and CD31, presenting the markers of HSPC, hematopoietic, and myelomonocytic cells, increased under treatment of CD34⁺ LCSC with a drug. Cytogenetic analysis showed that CD34⁺ LCSC contained a greater number of chromosomes. HBV DNA integrations and mutations in CD34⁺ LCSC and the parental cells were identical to those in the literature or the database. Thus, these results demonstrated that CD34⁺ LCSCs were formed by fusion of HSPC with CD34⁺ hematopoietic precursor-derived myeloid intermediates; it appears that this is the first report that human CSCs have been formed by the fusion. Therefore, it represents a significant step toward better understanding of the formation of human CSC and the diverse origins of liver cancers.