During the last 15 years the retrieval of peripheral blood stem cells (PBSC) has become more and more important as an alternative to haematopoietic stem cells isolated from bone marrow. The application of the growth factor G-CSF stimulates the production of stem cells in the donor’s bone marrow and their release into the peripheral blood . By leukapheresis (meaning withdrawal (Greek apherein) of white (Greek leukós) cells) PBSC can be collected out of the blood. Purification can be achieved by positive or negative selection. Therefore, the cells are labelled with antigen-specific antibodies conjugated to magnetic iron beads. While passing a selection column located in a strong magnetic field immunomagnetic isolation takes place: labelled cells remain on the selection column while unlabeled cells pass the magnetic field.
CD34 positive selection: Stem cells are labelled with antibodies conjugated with iron beads against the stem cell specific CD34 antigen and are enriched in the magnetic field of the CliniMACS system. Highly purified CD34 stem cells remain in the cell collection bag (CCB=graft, see picture below, left).
CD3 or TCRαβ/CD19 depletion: This procedure is a negative selection in which the CD3 or TCRαβ T cells and CD19 B cells are depleted directly from the graft. By labelling CD3 or TCRαβ and CD19 antigens, the T and B cells remain in the magnetic field while all other cells pass the selection column and can be collected (see picture below, right). The cell collection bag contains CD34 stem cells (SZ) and further immunocompetent cells like natural killer (NK) cells and dendritic cells (DZ).