Clusters of Differentiation/CD

From Wikipedia

CD34 molecule is a cluster of differentiation molecule present on certain cells within the human body. It is a cell surface glycoprotein and functions as a cell-cell adhesion factor. It may also mediate the attachment of stem cells to bone marrow extracellular matrix or directly to stromal cells. CD34 is the human gene encoding it.[1]
Cells expressing CD34 (CD34+ cell) are normally found in the umbilical cord and bone marrow as hematopoeitic cells, endothelial progenitor cells, endothelial cells of blood vessels but not lymphatics (except pleural lymphatics), mast cells, a sub-population dendritic cells (which are factor XIIIa negative) in the interstitium and around the adnexa of dermis of skin, as well as cells in soft tissue tumors like DFSP, GIST, PNSTs etc.
Clinical applications
CD34+ cells may be isolated from blood samples using immunomagnetic or immunofluorescent methods.
Antibodies are used to quantify and purify hematopoietic progenitor stem cells for research and for clinical bone marrow transplantation. However, counting CD34+ mononuclear cells may overestimate myeloid blasts in bone marrow smears due to hematogones and CD34+ megakaryocytes.
Cells observed as CD34+ and CD38- are of an undifferentiated, primitive form; i.e. they are pluripotential hemopoietic stem cells. Thus, because of their CD34+ expression, such undifferentiated cells can be sorted out.
In tumors, CD34 is found in alveolar soft part sarcoma, preB-ALL (positive in 75%), AML (40%), AML-M7 (most), dermatofibrosarcoma protuberans, gastrointestinal stromal tumors, giant cell fibroblastoma, granulocytic sarcoma, Kaposi’s sarcoma, liposarcoma, malignant fibrous histiocytoma, malignant peripheral nerve sheath tumors, mengingeal hemangiopericytomas, meningiomas, neurofibromas, schwannomas, and papillary thyroid carcinoma.