CD34: structure, biology, and clinical utility [see comments]

Abstract

CD34 is a surface glycophosphoprotein expressed on developmentally early lymphohematopoietic stem and progenitor cells,"3 small-vessel endothelial and embryonic fibroblasts6 CD34+ bone marrow (BM) cells comprise only 1.5% of marrow mononuclear cells, but contain precursors for all lymphohematopoietic lineages, as evidenced by the finding that CD34+ cells purified from marrow can reconstitute hematopoiesis of primates, humans, or mice undergoing autologous marrow reinfusion after myeloablative therapy (BM transplant~-~.""C).D 34+ hematopoietic cells obtained from marrow or blood are in clinical use in transplantation and gene therapy studies, including ongoing attempts to expand hematopoietic stedprogenitor cells ex vivo. Despite the importance of CD34 as a marker of early hematopoietic stedprogenitor cells in experimental and clinical hematopoiesis, the function of CD34 is not yet clear. Because of its potential role in such fundamental processes as hematopoietic stedprogenitor cell development and inflammation, studies on the regulation and function of CD34 are being pursued in several laboratories. Recent experiments on the function of CD34 indicate that CD34 expressed on endothelial cells may play a role in leukocyte adhesion and "homing" during the inflammatory process, and it has been hypothesized that CD34 plays a role in stedprogenitor cell localizatiodadhesion in the BM. CD34 may also be involved in maintenance of the hematopoietic stedprogenitor phenotype." This review will concentrate on our current knowledge of the expression, structure, regulation, function, and clinical utility of the CD34 molecule.