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CD30 and its ligand: Possible role in regulation of teratoma stem cells

Like the oocyte, the cells of the early embryo, and primordial germ cells, human teratocarcinoma stem cells are pluripotent, capable of giving rise to a wide range of somatic and extraembryonic tissues. Growth factors which regulate the growth of multipotent stem cells in the mouse have been identified, but none of these have been shown conclusively to have similar effects on human or primate multipotent stem cells. CD30 is a member of the tumour necrosis factor receptor superfamily with a restricted pattern of tissue distribution, limited to immune cells, decidual tissue, and human embryonal carcinoma: in common with other embryonal carcinoma markers, CD30 is found in foci of cells in a sub‐population of seminomas. CD30 ligand is a transmembrane protein, structurally related to tumour necrosis superfamily members TNFα, TNFβ, and CD40. CD30 ligand is expressed by T and B lymphocytes, macrophages, and a variety of normal haematopoietic cells and tumours derived from them, and exerts pleiotropic effects on normal and malignant lymphoid cells, including death, differentiation, or cell division. Studies on cultured cell lines derived from human embryonal carcinomas and yolk sac carcinomas confirm CD30 expression in the former but not the latter, and show that CD30 expression is down‐regulated during stem cell differentiation in vitro. Transcripts for CD30 ligand are found at highest levels in yolk sac carcinoma cell lines, but are also found in embryonal carcinoma. CD30 ligand protein is detected in yolk sac carcinoma and nullipotent embryonal carcinoma cell lines. Exogenous CD30 ligand has no effect on multipotent human stem cell growth in vitro. However, the receptor‐ligand pair may function in autocrine regulation of embryonal carcinoma stem cells. CD30 and its ligand are candidate stem cell identity factors, juxtacrine regulators whose sole function is to identify a cell's position in a developmental hierarchy.