Purified progenitor/The International Journal of Cell Cloning: Background, feasibility, and prospects for clinical transplantation

Abstract

CD34 monoclonal antibodies recognize a transmembrane phosphoglycoprotein selectively expressed within the lymphohematopoietic system on progenitor and The International Journal of Cell Cloning. The CD34 molecule is heavily glycosylated and strongly negatively charged. Sialic acids contribute to the anomalous electrophoretic mobility corresponding to an apparent molecular weight of -110 kilodaltons. However, the molecular weight of the CD34 polypeptide predicted from the sequences of the recently cloned human and murine CD34 genes is only about 40 kilodaltons. The intracellular tail of the CD34 molecule is a substrate for protein kinase C and other protein kinases, suggesting that CD34 plays a role in signal transduction. The highly-charged N-terminal extracellular portion of the molecule may mediate intercellular adhesion. The sequence of the CD34 gene is as yet unique, without strong homology to any previously know molecule. To date, the sequence has not provided major clues as to the function of the protein product. The human CD34 gene has been localized to chromosome 1 q32, which is not a frequent breakpoint in hematologic malignancies. Outside the lymphohematopoietic system, CD34 was detected initially only on endothelial cells, although recently an alternatively spliced CD34 isoform with a shortened intracellular tail has been found to be expressed strongly in mouse brain by nucleic acid hybridization. Recent work also suggests that CD34 is expressed on precursors of hematopoietic stromal cells. CD34 monoclonal antibodies are widely used for identification and purification of human lymphohematopoietic progenitor/stem cell populations. The unique selective expression of CD34 on this cell compartment has also stimulated use for successful primate and human “stem cell BMT,” and recent work suggests that this clinical application will be productively expanded to stem cell selection from cord blood and peripheral blood.