| Autologous or allogeneic hematopoietic stem/progenitor cell (HSPC) transplantation is an effective approach to treat leukemia and some other malignancies. The diseases, however, may relapse due to the tumor cells remaining in autografts and the Grafts versus Host Disease (GVHD) may occur due to the donor T lymphocytes in allografts.Whether the transplantation is successful or not depends on the number and the quality of the 'seeds' in grafts, which are HSPCs. There is an important marker, CD34 antigen, on the surface of HSPC. CD34+ HSPCs exist in many kinds of hematopoietic tissues, but the percentage of HSPC is very low in nucleated cells (NC). Researches abroad have demonstrated that CD34+ HSPCs could be enriched, CD34- tumor cells and T lymphocytes could be purged if a proper method concerning CD34 antigen was used, which could reduce relapse and GVHD.Two kinds of method can be used to enrich the CD34+ cells. One is so-called the negative selection and the other is the positive selection. The negative selection is a procedure that can enrich CD34+ cells by eliminating CD34- cells in grafts using some proper methods. These methods include density gradient centrifugation, phagocytosis of magnetic beads, nylon-wool adherence, soybean agglutinin lectin and immunomagnetic beads (IMB) method. The positive selection is a procedure that CD34+ HSPCs are selected specifically from grafts by physical orbiologic methods using CD34 monoclonal antibody by means of certain mediators. These methods include avidin-biotin immunoadsorption technique, IMB method etc. Both of the methods can be used to enrich the CD34+ cells and to deplete the tumor cells and the T lymphocytes. Generally, the positive selection can achieve better enrichment than the negative selection. For the positive selection, the effect of IMB method is superior to others. At present, two kinds of magnetic beads can be used for HPSC processing. One is 4.5 um in diameter; the other is 50 nm in diameter. When the former is used to enrich CD34+ cells via positive selection, the beads attached to the cells must be separated before the cells are infused, but it is unnecessary to do so when the latter is used. However, the 50nm beads are more expensive than the 4. 5 um ones so that widely utilization of this kind of beads for clinical transplantation is hindered.Carbonyl iron (CI) is a small particulate of highly purified metallic iron with the diameter of < 5um in size. Its formula is Fe(CO)5. It is very cheap and little toxicity to human body. It can be sterilized by high temperature. It has been used to remove monocytes and macrophages from bone marrow (BM) and peripheral blood before undergoing further experiment, but no data on enriching CD34+ cells using CI have been reported worldwide. Nimgaonker et al reported to use CD15 IMB to achieve up to a 7 log depletion in leukemia and 1-4 log reduction in CD15+ cells. They found that CD34+ cells were enriched following CD15+ cells removal without a significant loss of HSPC. In this study, we tried to eliminate CD34- phagocytes and CD15+ myelomonocytes to enrich CD34+ cells by engaging CD34 negative selection with CI or CD15 IMB or both.Many studies have shown that CD34- tumor cells in autografts and T lymphocytes in allografts can be purged after positive selection with CD34 IMB, but it was hard to evaluate precisely the safety whether the patients could suffer from relapse or GVHD after transplantation due to the poor methodology. It would have reduced the manpower and thefinancial resources greatly if an accurate evaluation method had been employed before transplantation engaged on actual clinical practice.An accurate evaluation of the purging effect depends on the sensitive and reliable methods. Immunocytology staining and polymerase chain reaction (PCR) are the two main methods frequently being used. Due to the discrepancies between the number of tumor cells detected and the actual tumor cells remained by using the above methods, the accuracy of applicability and security of the pur...
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