Hmatopoietische Stammzellen, d. h. Progenitorzellen, die bereits in Richtung einer bestimmten Zellreihe festgelegt sind, lassen sich immunzytochemisch durch Nachweis der membranstndigen Expression von CD 34 darstellen. Aufgrund dieser Eigenschaft ist es mglich geworden, Vorluferzellen durch unterschiedliche Zellseparationsverfahren anzureichern und genauer zu charakterisieren. Neuere Untersuchungen zeigen, da CD 34-positive (CD 34+-) Stammzellen des Blutes einer relativ uniformen Zellpopulation angehren. Zytologisch deuten sie in Routinefrbungen Aspekte sog. lymphoider Reizformen bzw. Virozyten an. Ultrastrukturelle Untersuchungen besttigen den relativ organellenarmen Charakter der Progenitorzellen. Vergleichsweise stellt sich die entsprechende Zellpopulation aus dem Knochenmark als wesentlich heterogeneres Zellgemisch dar. Sowohl die CD 34+-Stammzellen des Blutes wie des Knochenmarks weisen eine Expression von CD 43 (MT1) und CD 45 (LCA) auf. Weiterhin zeigen Subpopulationen in Abhngigkeit von ihrem Vorkommen (Peripherie/Knochenmark) und in unterschiedlicher Ausprgung linienspezifische Marker. Die krzlich entwickelten, v. a. immunomagnetischen Anreicherungsverfahren fr CD 34+-Stammzellen stellen bedeutende Perspektiven fr die moderne Onkologie dar. Sie sind insbesondere fr die Therapie hmatologischer Neoplasien und fortgeschrittener maligner Tumoren im Rahmen von Stammzelltransplantationen, von grter klinischer Bedeutung.
Pluripotential haematopoietic stem cells and their progeny, the so-called committed precursor cells, i. e., progenitor cells which are already lineage-restricted, may be identified by the membrane-bound expression of CD 34. In accordance with this peculiar property it became possible to enrich and characterize primitive precursor cells by using different methods of cell separation techniques, which involved fluorescence staining or ferro-magnetic particles bound to CD 34 antibodies. Recently conducted studies demonstrate that CD 34-positive (CD 34+) stem cells of the peripheral blood represent a relatively uniform cell population with almost round nuclei, a finely dispersed chromatin pattern and a small portion of weakly basophilic cytoplasm. From the cytological viewpoint they resemble so-called large stimulated lymphocytes (virocytes). Ultrastructural studies are compatible with a paucity of organelles and a lymphoid character of these progenitors. In comparison, the stem cell population, derived from the bone marrow consists of more heterogeneous elements. These are generally larger and reveal an admixture of fairly immature as well as more differentiated cells, sharing bean-shaped or indented nuclei with prominent nucleoli and a more extended cytoplasm. CD 34+ progenitors from the peripheral blood and those from the bone marrow display a co-expression of CD 43 (MT1) and CD 45 (LCA). Furthermore, different subpopulations exhibit dependent on their origin (blood/bone marrow) and to a various extent lineage-restricted markers like CD 33, CD 38, CD 61, CD 20, CD 11a/c, glycophorin C und CD 15 (LeuM 1). The recently developed immuno- and ferromagnetic enrichment methods for CD 34+ progenitor cells are considered innovative tools for modern oncology. These techniques play an important role in the treatment of haematological malignancies and advanced tumours in the context of autologous and, although so far rarely applied, heterologous stem cell transplantation procedures.