What is ex vivo purification of autologous stem cells?
Autologous hematopoietic stem cell transplantation is the collection and freezing of one’s own normal hematopoietic stem cells, the administration of high-dose radiation and chemotherapy, and then the reinfusion of previously preserved hematopoietic stem cells.
Because autologous grafts may contain tumor cells such as leukemia cells that cause recurrence of hematologic disease after transplantation, this is the main reason why the recurrence rate is higher after autologous HSCT than allogeneic HSCT. Therefore, ex vivo purification is used to minimize the residual leukemic cells in the graft while preserving normal hematopoietic stem cells intact as much as possible, i.e., ex vivo purification of autologous stem cells.
Currently, ex vivo purification of autologous stem cells mainly uses in vitro sorting of hematopoietic stem cells (CD34-positive cells)
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Because CD34 antigen is selectively expressed in normal hematopoietic stem cells and not or minimally expressed in leukemic cells, normal hematopoietic stem cells can be sorted out by immunomagnetic bead separation. The CD34 monoclonal antibody is combined with magnetic beads, and when peripheral blood hematopoietic stem cell grafts pass through a special separator, they bind to the CD34 monoclonal antibody magnetic beads mentioned above.
Hematologists in many parts of the country have used this approach and have shown that it significantly reduces the amount of leukemic cells in the grafts, and that the time to hematopoietic reconstitution after transfusion is only slightly delayed compared to those without sorting, i.e., there is little effect on normal hematopoietic stem cells.
Re-transplantation after ex vivo purification does not guarantee that relapse will not occur
First, pretreatment before autologous HSCT is mainly with high-dose chemotherapy and/or radiotherapy. High-dose radiotherapy does not completely remove the leukemic cells from the patient’s body, and these residual leukemic cells may be the source of later relapse.
Second, even with ex vivo purification of autologous stem cells, the stem cells may not be completely free of residual leukemia cells as expected, and these residual leukemia cells can increase the risk of leukemia recurrence.