CD34 cells in somatic, regenerative and cancer stem cells: Developmental biology, cell therapy, and omics big data...

The transmembrane phosphoglycoprotein protein CD34 has conventionally been regarded as a marker for hematopoietic progenitors. Its expression on these cells has been leveraged for cell therapy applications in various hematological disorders. More recently, the expression of CD34 has also been reported on cells of nonhematopoietic origin. The list includes somatic cells such as endothelial cells, fibrocytes and interstitial cells and regenerative stem cells such as corneal keratocytes, muscle satellite cells, and muscle-derived stem cells. Furthermore, its expression on some cancer stem cells (CSCs) has also been reported. Till date, the functional roles of this molecule have been implicated in a multitude of cellular processes including cell adhesion, signal transduction, and maintenance of progenitor phenotype. However, the complete understanding about this molecule including its developmental origins, its embryonic connection, and associated functions is far from complete. Here, we review our present understanding of the structure and putative functions of the CD34 molecule based upon our literature survey. We also probed various biological databases to retrieve data related to the expression and associated molecular functions of CD34. Such information, upon synthesis, is hence likely to provide the suitability of such cells for cell therapy. Moreover, we have also covered the existing cell therapy and speculated cell therapy applications of CD34⁺ cells isolated from various lineages. We have also attempted here to speculate the role(s) of CD34 on CSCs. Finally, we discuss number of large-scale proteomics and transcriptomics studies that have been performed using CD34⁺ cells.