Characterization of cd34+ cells mobilized to the peripheral blood during the recovery from cyclophosphamide chemotherapy

Sources of Human Hematopoietic Stem Cells for Transplantation–A Review

Transplantation of hematopoietic stem cells provides a means of replacing a defective hematopoietic system in patients with a wide range of malignant and nonmalignant disorders that affect the blood forming tissue. The same procedure has also allowed dose-escalation of standard chemotherapy and radiotherapy in the treatment of malignant disease of nonhematological origin. Until recently, bone marrow has been the sole source of hematopoietic stem cells, but limitations of conventional bone marrow transplantation have stimulated a search for alternative sources and uses of stem cells. Fetal tissues (especially liver) are a recognized source of transplantable stem cells and offer the great advantage of reduced immunogenicity, potentially removing the problems of tissue type matching. Umbilical cord blood is also a rich source of stem cells and, although it contains alloreactive cells, it is readily available without special ethical constraints. Both fetal tissue and cord blood suffer the disadvantages of limited numbers of stem cells per donation, and there is much interest in the development of technologies for the safe and reliable expansion and/or pooling of stem and progenitor cells. The observation that small numbers of stem cells are found in the peripheral blood of adults has led to the exploitation of the blood as a further source of stem cells. The ability to mobilize these cells from the medullary compartment into the periphery by the use of chemotherapy and/or recombinant hematopoietic growth factors has enabled the collection of sufficient numbers of cells for transplantation purposes. All of these advances are increasing the options and the range of choices available to clinicians and patients in the arena of hematopoietic stem cell transplantation.

Filgrastim-mobilized peripheral-blood stem cells can be stored at 4 degrees and used in autografts to rescue high-dose chemotherapy

We studied 21 filgrastim (G-CSF)-mobilized peripheral blood stem cells (PBSC) apheresis products obtained from seven patients, and stored at 4 degrees C for periods of up to 96 hr prior to their reinfusion, to rescue high-dose chemotherapy. The apheresis products contained a median of 106 x 10(8)/L mononuclear cells (MNC), 14.6% of them displaying the CD34 antigen; the viability was over 90% in all samples studied at 24, 48, and 72 hr after harvesting. These PBSC were successfully used to rescue high-dose chemotherapy; patients received a median of 4.8 x 10(8)/Kg MNC; the median time to achieve > 500 granulocytes was 14 days (range 11-26) and the median time to achieve > 20,000 platelets was 20 days (range 11-40). Since autologous transplants with nonfrozen PBSC are feasible and less costly than those using frozen PBSC, restrictions to PBSC autotransplant programs may be overcome and costs may be diminished.

Sequential transplants using mobilized peripheral blood progenitor cells

Modest success has been achieved with the use of high-dose cytotoxic therapy and bone marrow transplantation in solid tumors. Patient outcome can potentially be improved with further intensification of the therapy. The rapid hematologic recovery achieved with mobilized peripheral blood progenitor cells (PBPC) may reduce the toxicity of transplantation enabling the use of sequential courses of myeloablative therapy. We report on 42 patients with solid tumors enrolled in a tandem transplant protocol involving the use of PBPC mobilized with cyclophosphamide (4 g/m2), etoposide (1 g/m2), and granulocyte-colony-stimulating factor (G-CSF: 10 micrograms/kg/day). This regimen significantly increased the number of circulating progenitor cells; only 1-2 aphereses were sufficient to collect 2.5 x 10(8)/kg mononuclear cells, our goal for each transplant course. The median number of circulating colony-forming units (CFU) and CD34+ cells obtained for each transplant course were 70.3 x 10(4)/kg, and 11.7 x 10(6)/kg, respectively. There was a significant correlation between the numbers of CD34+ cells and CFU measured in the apheresis product (r = 0.49, P = .003). The first transplant regimen given to 38 patients consisted of thiotepa, carboplatin, and cyclophosphamide. The second transplant regimen given to 29 patients consisted of busulfan and etoposide. Hematologic recovery was comparable after each of the two transplant courses. The median time to neutrophil recovery over 0.5 x 10(9)/L and to platelet transfusion independence was 9 and 8 days, respectively. There was no difference in engraftment rates after transplant with PBPC only (n = 28 courses) compared to transplant with PBPC plus bone marrow (n = 39 courses).(ABSTRACT TRUNCATED AT 250 WORDS)

Is our current strategy in manipulating hemopoiesis in autologous transplantation correct?

Autologous hemopoietic stem cell rescue following high-dose chemoradiotherapy is increasingly used in the treatment of lymphohemopoietic malignancy and selected solid tumors. While encouraging disease control has been reported in acute leukemia, lymphoma, multiple myeloma and breast carcinoma, such an approach suffers from a number of limitations. This review addresses a number of issues that may lead to better stem cells for transplant: which stem cell rescue provides the most rapid hemopoietic reconstitution, how can we get sufficient high quality stem cells for transplant to ensure complete and sustained reconstitution, what are the predictors of rapid and sustained hemopoietic reconstitution, what impact on hemopoietic reconstitution purging and positive selection technology may have, and how can we abrogate the obligatory delay to blood count recovery.

Peripheral blood stem cell transplantations: past, present and future

Since the first successful attempt in 1985, peripheral blood stem cell transplants are increasingly performed worldwide and should now be considered as an essential therapeutic weapon against onco-hematological diseases. Their development has benefited greatly from a rapid concomitant advance of experimental knowledge regarding the nature of hematopoietic progenitor cells. For this reason and also for technical ones, until now these transplants generally have been autotransplants. Although one of the main reasons to use blood rather than bone marrow-derived stem cells was that they might carry less risk of relapse than autologous bone marrow cells, the lack of clinical randomized trials and/or the short follow-up make conclusions difficult so far in terms of disease-free and overall survival. Probably the risk of relapse also depends on the type of disease, on prior chemotherapies, on the type of peripheral stem cell mobilization regimen and on the number of blood-derived cells transplanted. Nevertheless, there are several major clinical indications for autologous blood stem cell transplant: acute nonlymphoblastic leukemias (ANLL), low-grade non-Hodgkin's lymphomas, multiple myeloma, some solid tumors, and even chronic myeloid leukemia. Now well-demonstrated advantages add a socioeconomic interest to this technique. The speed of post-transplant hematopoietic recovery induces a briefer hospitalization and a lower cost of the procedure, which represents "per se" important progress. Furthermore, the increasing use of hematopoietic growth factor(s) at time of blood-derived cell mobilization should increase the safety of the procedure. Also new trends are currently being developed: autotransplants with purified peripheral CD34+ cells; addition of adjuvant immunotherapy to induce graft-versus-tumor effect, which is lacking in autotransplant; and transplants using allogenic umbilical cord blood progenitors. Allogenic blood cell transplants might also be developed, provided that blood cells would be less likely to cause graft-versus-host disease (GVHD) than bone marrow, which is still not verified. Finally, the use of blood-derived cells as a vehicle for gene therapy should develop greatly in the near future.

Peripheral blood stem cell transplantation

Haematopoietic stem cells are usually sessile within the bone marrow microenvironment. However, small numbers do circulate in the peripheral blood of normal individuals, and following chemotherapy and/or intravenous growth factors, a substantial transient rise in circulating stem cells occurs. Leukocytes harvested by cytapheresis at this time can be used for autologous reconstitution of the haematopoietic and lymphoid systems following high dosage chemo/radiotherapy for the treatment of malignant disease. Peripheral blood stem cell transplants give rise to similar disease response rates as autologous bone marrow transplants, but have the advantage of more rapid haematopoietic reconstitution, and in addition can be offered to patients in whom marrow harvest is not feasible due to bone marrow damage or infiltration. This article reviews the theoretical and historical background to haematopoietic stem cell research, current clinical practice in peripheral blood stem cell mobilisation and harvesting, addresses the potential advantages and disadvantages compared to bone marrow transplantation, and assesses current experience of comparative efficacy.