CD34 Cell Culture: Clinical Needs and Applications
I. INTRODUCTION Stem cell transplantation has undergone a dramatic change over the past few years both in the numbers of transplants and in the way that these transplants are being done. Stem cell transplants are increasing at a rate of more than 20% per year with current estimates showing that more than 40,000 transplants were done in 1997. The drivers of this increase include the effectiveness of high-dose chemotherapy in lymphoma and some early studies suggesting a similar remission and/or survival advantage in patients with breast cancer and myeloma (1-3). In addition, the discovery and use of hematopoietic growth factors both to treat patients posttransplant and to mobilize CD34 cells to the peripheral blood where they can be harvested by apheresis has also affected the increase in stem cell transplants. Peripheral blood stem cell (PBSC) transplants have been used primarily in the autologous setting and eliminate the need for general anesthesia to harvest stem cells as is required for bone marrow transplants. In the United States, the cost of a transplant has decreased from the $150,000 range to $60,000-$70,000 because of the use of autologous PBSCs. Although decreased cost has been a factor in the increase in stem cell transplants, the primary reason for this trend is the observed decrease in engraftment time. Neutrophil recovery time has been reduced to approximately 10 days and platelet recovery time to approximately 15 days (4-6). This is a dramatic decrease from prolonged engraftment times with bone marrow where platelet recovery could take 4-6 weeks. Although most stem cell transplants have been autologous to date, allogeneic PBSC transplants are now being evaluated in many centers. Most of these use stem cells from matched related donors where CD34 cells have been mobilized with growth factors. Currently, the emphasis of stem cell transplantation is to support high-dose chemotherapy, although its application
is potentially much broader. Other therapeutic applications include both the use of allogeneic CD34 cells to treat patients with congenital and acquired blood cell deficiencies or autologous CD34 cells as target cells for gene therapy.