Regulation of hematopoietic progenitor cell migration, mobilization and homing

Myeloid growth factors in oncology

Within the last decade haemopoietic growth factors have become established in the pharmacopoeia of oncology. In the form of granulocyte colony-stimulating factor (G-CSF), and to a lesser extent granulocyte-macrophage colony-stimulating factor (GM-CSF), these proteins are routinely used to accelerate restoration of neutrophil count after chemotherapy or bone marrow transplant. Their main advance has been the development of mobilisation protocols. Peripheral blood progenitor cells are induced to egress from the bone marrow and re-transfusion after myelosuppressive chemotherapy allows for a simple and more rapid form of autologous transplantation than bone marrow transplantation. This review will give a brief overview of the biology of haemopoiesis in relation to growth factors and the potential lines of further research. Although the established clinical uses of G-CSF will be discussed the main focus will be on the developmental applications, such as ex vivo haemopoiesis, dose intensification schedules and the application of growth factors in the therapy of haematological malignancies. The relevance of novel or more recently introduced recombinant haemopoietic growth factors will also be discussed in relation to these indications.

Mobilization of peripheral blood stem cells with high-dose cyclophosphamide or the DHAP regimen plus G-CSF in non-Hodgkin's lymphoma

Our study analyzes the mobilization of hematopoietic stem cells after two chemotherapeutic regimens in non-Hodgkin's lymphoma (NHL) patients. The study included 72 patients with NHL (42 follicular and 30 large cells). The mean age was 37 years (range 17-60). Sixty-four patients (88.9%) had stage III-IV disease. Forty-eight patients (66.7%) had bone marrow involvement. Systemic B symptoms were present in 42 patients (58.3%). Mobilization chemotherapy regimens were randomly assigned as DHAP in 38 patients (52.7%) or cyclophosphamide (CPM) (5 g/m(2)) in 34 (47.2%) and the results of 132 procedures were analyzed. At the time of PBSC mobilization, 46 patients (63.9%) were considered to be responsive (complete remission, partial remission or sensitive relapse) and 26 (36.1%) not responsive (refractory relapse or refractory to therapy). Pre-apheresis CD34+ blood cell count and number of previous chemotherapy treatments were used to predict the total number of CD34+ cells in the apheresis product. The mobilizing regimens (CPM or DHAP) were similar in achieving the threshold CD34+ cell yield, for optimal engraftment. Since DHAP was very effective as salvage treatment, we suggest using DHAP as a mobilizing regimen in patients with active residual lymphoma at the time of stem cell collection.

The role of blood stem cells in hematopoietic cell renewal

It has been the purpose of this keynote address to review available evidence for the notion that the stem and progenitor cells circulating in the peripheral blood play a decisive role in the homeostasis of blood cell formation distributed throughout dozens of bone marrow units in the skeleton. Furthermore, if this notion is correct, one could speculate that the quantity and quality of stem and progenitor cells in the blood should reflect the functional state of the hematopoietic stem cell system throughout the skeletal bone marrow and provide a new tool for the evaluation of alteration in blood cell production. On this basis, the following questions are considered: A) What do we know about the quality and quantity of blood stem cells in steady state conditions? B) In what way do blood stem cells respond to perturbations of the "steady state" of blood cell formation? C) Which role do blood stem cells play during hemopoietic development assuming that the establishment of bone marrow hemopoiesis requires the "seeding" of blood stem cells into an appropriate cellular environment? D) What is the role of blood stem cells in hemopoietic regeneration after partial body irradiation with a small volume of marrow (and hence stem cells) protected? and E) What are the mechanisms and/or kinetics of hemopoietic recovery if stem cells introduced into the circulation were collected from exogenous (autologous or allogeneic) sources? In this review presentation, experimental work of our group and of other members of the scientific community is summarized. It becomes obvious that blood stem and progenitor cells play a key role in hematopoietic homeostasis. Furthermore, their physiology and pathophysiology deserve rigorous experimental studies in order to develop a novel tool in the diagnosis and prognosis of neoplastic and non-neoplastic disorders of blood cell formation.

Acceleration of hemopoietic recovery in dogs after extended-field partial-body irradiation by treatment with colony-stimulating factors: rhG-CSF and rhGM-CSF

PURPOSE

The influence of treatment with the two colony-stimulating factors, rhG-CSF and rhGM-CSF, on the hemopoietic recovery in aplastic bone marrow sites after extended-field irradiation was studied in a canine model.

METHODS AND MATERIALS

The dogs received irradiation of the cranial part of their body with a single dose of 11.7 Gy, comprising approximately 72% of the total bone marrow mass. Anatomically this type of exposure corresponds to upper body irradiation (UBI) as employed under clinical conditions. Treatment with both the CSFs was employed for 7 days by daily injections of 30 microg/kg, starting 24 hr after irradiation.

RESULTS

Treatment with rhGM-CSF did not completely prevent the initial decrease of the granulocyte counts, but caused an accelerated, though incomplete, recovery in the period from day 5 to day 15. In contrast, treatment with rhG-CSF caused two phases of granulocytosis and an early recovery to normal levels at day 11 after irradiation. Treatment with rhG-CSF, but not with rhGM-CSF, was associated with a strong supra-normal increase of progenitor cells in the blood within the first 8 days and an accelerated hemopoietic recovery in the irradiated sites particularly within the first 7 days after the exposure.

CONCLUSIONS

These results indicate that under conditions of partial-body irradiation short term treatment with G-CSF is superior to GM-CSF in initiating the hemopoietic recovery on the basis of endogenous stem cell seeding.

Differential expression of cell adhesion molecules by human hematopoietic progenitor cells from bone marrow and mobilized adult peripheral blood

The mechanisms responsible for mobilization of hematopoietic progenitor cells (HPC) from the bone marrow into the circulation are unknown. One possibility is that HPC downregulate cell adhesion molecule expression. We studied normal human bone marrow and adult peripheral blood following 4 g/m2 cyclophosphamide and recombinant human granulocyte colony-stimulating factor (rHuG-CSF). Each sample was studied for the coexpression of CD34 and a panel of cell adhesion molecules by dual immunocytometry. Bone marrow HPC express the immunoglobulin gene superfamily members of ICAM-1 (CD54), PECAM-1 (CD31) and LFA-3 (CD58), the integrins VLA-4 (CD49d/CD29), VLA-5 (CD49e/CD29) and LFA-1 (CD11a/CD18), L-Selectin (CD62L), HCAM (CD44) and CD36. Mobilized peripheral blood HPC display less expression of LFA-3 (CD54) and VLA-5 (CD49e). Significant differences in cell adhesion molecule expression do exist between sessile and circulating HPC, but the biological relevance of these observations is currently unclear.