CD203c is expressed by human fetal hepatoblasts and distinguishes subsets of hepatoblastoma.

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Public Summary:
A flow cytometry based approach was used to screen human liver cells at midgestation for over 300 cell-surface antigens to identify those useful in discriminating among the many cell populations that comprise the developing liver. Indeed, the human liver undergoes profound changes during early development transforming from a primarily an organ that produces red blood cells during the first half of gestation into an organ comprised mostly of large hepatocytes at birth. Blood stem cells and progenitors as well as mature blood cells persist in the adult liver and contribute to the important immune functions of this organ, but in adults the liver is not normally a primary blood cell producing organ. From the onset of liver development until the neonatal period, fetal hepatoblasts grow and mature into hepatocytes exposed to a rapidly changing environment that includes the rise and fall of blood cell production, hormonal changes, and the dramatic changes in blood flow at birth that alter the flow of nutrients and oxygenated blood. Given the unique nature of the prenatal liver, it is not surprising that fetal hepatocytic cells differ from their postnatal counterparts. In our study, a more complete understanding of the proteins and some carbohydrate antigens found on fetal hepatoblasts, LSECs, and hematopoietic cells is presented. A closer focus on hepatoblasts identified many widely expressed antigens as well antigens with differential expression that may be useful in identifying different stages of differentiation, maturation, or functional diversity. Notably, CD203c was a newly identified marker of fetal hepatoblasts with broad expression that was restricted to the hepatoblast population. The uniqueness of fetal hepatoblasts compared to adult parenchymal cells is not only of interest to the study of liver development but also of particular interest to the classification and treatment of pediatric hepatoblastoma. Hepatoblastoma is a paradigm for embryonal cancers – those in which early life (prenatal) factors drive the initiation and biology of the malignancy after birth and later in life. Hepatoblastoma is the most common primary liver tumor diagnosed in children. CD203c expression was found to be a marker of some hepatoblastomas using cell lines consisting of two types consisting of a cholangiocyte-like type that expressed CD203c and CD326 and a hepatocyte-like type with diminished expression of these markers. CD203c was also expressed by some hepatoblastoma tumors and may represent a marker of a less differentiated embryonal component. As such, it is possible that CD203c may offer diagnostic or therapeutic insights in the fight against hepatoblastoma.
Scientific Abstract:
BACKGROUND & AIMS: Hepatocytic cells found during prenatal development have unique features compared to their adult counterparts, and are believed to be the precursors of pediatric hepatoblastoma. The cell-surface phenotype of hepatoblasts and hepatoblastoma cell lines was evaluated to discover new markers of these cells and gain insight into the development of hepatocytic cells and the phenotypes and origins of hepatoblastoma. METHODS: Human midgestation livers and four pediatric hepatoblastoma cell lines were screened using flow cytometry. Expression of over 300 antigens was evaluated on hepatoblasts defined by their expression of CD326 (EpCAM) and CD14. Also analyzed were hematopoietic cells, expressing CD45, and liver sinusoidal-endothelial cells (LSECs), expressing CD14 but lacking CD45 expression. Select antigens were further examined by fluorescence immunomicroscopy of fetal liver sections. Antigen expression was also confirmed on cultured cells by both methods. Gene expression analysis by liver cells, 6 hepatoblastoma cell lines, and hepatoblastoma cells was performed. Immunohistochemistry was used to evaluate CD203c, CD326, and cytokeratin-19 expression on three hepatoblastoma tumors. RESULTS: Antibody screening identified many cell surface markers commonly or divergently expressed by hematopoietic cells, LSECs, and hepatoblasts. Thirteen novel markers expressed on fetal hepatoblasts were identified including ectonucleotide pyrophosphatase/phosphodiesterase family member 3 (ENPP-3/CD203c), which was found to be expressed by hepatoblasts with widespread expression in the parenchyma of the fetal liver. In culture CD203c(+)CD326(++) cells resembled hepatocytic cells with coexpression of albumin and cytokeratin-19 confirming a hepatoblast phenotype. CD203c expression declined rapidly in culture whereas the loss of CD326 was not as pronounced. CD203c and CD326 were co-expressed on a subset of hepatoblastoma cell lines and hepatoblastomas with an embryonal pattern. CONCLUSIONS: CD203c is expressed on hepatoblasts and may play a role in purinergic signaling in the developing liver. Hepatoblastoma cell lines were found to consist of two broad phenotypes consisting of a cholangiocyte-like phenotype that expressed CD203c and CD326 and a hepatocyte-like phenotype with diminished expression of these markers. CD203c was expressed by some hepatoblastoma tumors and may represent a marker of a less differentiated embryonal component.