The use of rhIL-3 for mobilization of peripheral blood The International Journal of Cell Cloning in previously treated patients with lymphoid malignancies

Mobilization of hematopoietic stem cells for use in autologous transplantation

Autologous hematopoietic stem cell transplantation (HSCT) is a potentially curative therapeutic approach for various malignant hematologic and lymphoid diseases. Hematopoietic stem cells (HSCs) may be collected from the blood or the bone marrow. HSCs are capable of self-renewal and give rise to progenitor cells, multipotent cells that differentiate and proliferate into the mature cells of the blood and immune system. HSCs and progenitor cells are released from the bone marrow into the peripheral blood through a process called mobilization. HSCs then are collected from the blood in a process called apheresis and cryopreserved for administration following the high-dose preparative regimen. This article reviews stem cell biology, current mobilization strategies, use of novel mobilization agents, and nursing care of patients during the mobilization phase of autologous HSCT. Understanding the biology and process of HSC mobilization is critical for transplantation nurses to deliver and coordinate care during this complex phase of autologous HSCT.

The whys and hows of hematopoietic progenitor and stem cell mobilization

Intentional mobilization of hematopoietic/stem cells into the circulation has improved the efficiency of their collection. Transplantation of mobilized blood stem cells to patients with marrow aplasia results in a faster pace of hematopoietic recovery than transplantation of marrow-derived stem cells. Autologous and allogeneic hematopoietic stem cell transplantation are increasingly performed with blood-derived cells. Donors of both autologous and allogeneic blood stem cells do not always respond well to therapies designed to produce mobilization. Autologous donors may respond poorly as a result of myelotoxic damage inflicted by prior antitumor therapy, but this explanation is not valid for allogeneic donors. The mechanism(s) involved in the process of mobilization are incompletely understood. Until these mechanisms are elucidated, methods to improve mobilization vigor on a rational basis will not be obvious. In the meanwhile, clinical observations may provide some hints regarding the whys and hows of mobilization and permit incremental improvements in this process.

Interleukin-3: Promises and Perspectives

Interleukin-3 (IL-3) is a multipotent hematopoietic growth factor produced by activated T-cells, monocytes/macrophages and stroma cells. Human IL-3 gene is located on chromosome 5 near segment 5q31. The high affinity receptor for human IL-3 is composed of alpha and beta subunits. IL-3 shares common beta subunit with GM-CSF and IL-5 which has been mapped to chromosome 22q13.1. The biological effects of IL-3 have been studied in human and murine hematopoietic cell lines and normal human bone marrow cells. Addition of IL-3 to the culture medium induces proliferation, maturation and probably self renewal of pluripotent hematopoietic stem cells and cells of myeloid, erythroid and megakaryocytic lineages. Various clinical trials have assessed the in vivo potential of recombinant human interleukin 3 (rhIL-3). Initial results of phase I/II studies of IL-3 at a dose of 5-10 ug/kg subcutaneous (s/c) daily for 5-10 days in patients with relapsed lymphomas, small cell lung cancer, breast cancer and ovarian cancer have shown that post-chemotherapy application of IL-3 reduces chemotherapy delays and induces faster regeneration of granulocytes and platelets. However, these results were not confirmed in phase III studies. The role of IL-3 alone in the treatment of myelodysplastic syndromes (MDS), aplastic anemia (AA) and other bone marrow failure disorders have also been disappointing. However, preliminary studies of IL-3 in combination with chemotherapeutic agents and immunosuppression have demonstrated encouraging results in patients with MDS and aplastic anemia respectively. The therapeutic potential of IL-3 in peripheral blood stem cell harvesting and priming of stem cells before harvest is beginning to be identified. Initial results of IL-3 in combination with granulocyte macrophage colony stimulating factor (GM-CSF) or later acting growth factor like granulocyte colony stimulating factor (G-CSF) have yielded larger amounts of peripheral blood stem cells during PBSC harvesting. This approach and application of IL-3 with cocktail of other cytokines for ex-vivo expansion of stem cells, dendritic cell development and gene transfer requires further evaluation. The role of IL-3 in murine models of antiphospholipid syndrome (APLS) for prevention of recurrent abortion remains experimental and warrants careful assessment of adverse effects of IL-3 therapy on pregnant woman and fetus. The exact therapeutic role of IL-3 in oncology and nononcology patients is beginning to be identified. It appears that future application of IL-3 in combination with other cytokines is an attractive way forward in the prevention of treatment related mortality and morbidity in oncology patients. It also holds prospects for development of new therapeutic strategies for dose escalation and immune modulation for relapsed cancer patients.

IL-3 in the clinic

Since the cloning of human interleukin 3 (IL-3) in 1986 [1] and the demonstration of its proliferative effects on multiple hematopoietic progenitor cells, IL-3 has been widely studied to treat different states of bone marrow failure or hematologic malignancies, to mobilize or expand hematopoietic progenitor cells for transplantation, and to support engraftment after bone marrow transplantation. However, no condition for the clinical use of IL-3 has been established so far despite its theoretical advantages as an early-acting cytokine and in contrast to erythropoietin (EPO), G-CSF, or GM-CSF all of which have already been approved for several clinical modalities. Here we shortly review our current knowledge about the effects of IL-3 on the molecular and cellular level, summarize recent clinical studies with IL-3, and discuss further perspectives for the use of this cytokine.

Recombinant cytokines and hematopoietic growth factors in allogeneic and autologous bone marrow transplantation

Use of recombinant hematopoietic growth factors in the course of bone marrow transplantation has revolutionized this modality by significantly improving the safety of the procedure. It is anticipated that use of cytokines in combination and the introduction of newer agents will further reduce costs and improve antitumor responses as well.

The Nebraska experience

Autologous peripheral stem cell transplantation was initiated at the University of Nebraska Medical Center to provide hematopoietic rescue for patients who were candidates for high-dose therapy but had marrows that were unfit for autografting. From 1984 until 1991, the cells were collected during steady state without mobilization. These cells restored hematopoietic function at a rate similar to that of autologous marrow in patients not treated with total body irradiation. Patients who received total body irradiation experienced slower hematopoietic recovery. When growth factors became generally available in the United States in 1991, mobilization with cytokines became standard at Nebraska. In recent years, the function of cells other than hematopoietic progenitors contained in a peripheral stem cell apheresis product has been studied. Detection of tumor cells using cell culture, immunocytochemical and polymerase chain reaction techniques has revealed that such collections are less likely to contain, or contain fewer, tumor cells than autologous bone marrow harvests. More antitumor cytotoxic activity was found in cells in peripheral stem cell collections than in marrow cell collections. The immunocompetent lymphocyte population is larger in peripheral stem cell collection than in marrow harvests, and immunologic recovery after peripheral stem cell transplant has differed compared to recovery following bone marrow transplantation. The future of peripheral stem cell transplantation is likely to include engineering of the graft products specific for the patient and disease being treated. Determining the function of accessory cells in a peripheral stem cell collection will be important to provide the best engineered product for the patient.

Stem cell factor enhances in vivo effects of granulocyte colony stimulating factor for stimulating mobilization of peripheral blood progenitor cells

Granulocyte colony stimulating factor (G-CSF) has been shown to increase peripheral blood progenitor cells (PBPC) which have an enhanced engraftment potential in autologous transplantation compared with bone marrow cells. The data presented in this study demonstrate the ability of low doses of stem cell factor (SCF) to synergize with G-CSF to enhance the mobilization of PBPC, compared with G-CSF alone, in both mouse and primate models. In the mouse model the combination of SCF plus G-CSF stimulated an absolute increase in cells with in vivo repopulating potential. These studies suggest a possible role for SCF plus G-CSF in the clinical setting for increased mobilization of PBPC, giving rise to increased phoresis yields and enhanced engraftment for support of high-dose chemotherapy.

Cytokine enhancement of peripheral blood stem cells

The use of cytokines to improve peripheral blood stem cell enhancement and recruitment has recently received close attention. Three main cytokines have been, or are still being, investigated in this way in human clinical trials so far: recombinant human granulocyte-macrophage colony stimulating factor (rhGM-CSF), granulocyte CSF (rhG-CSF) and interleukin 3 (IL-3). While cytokines used alone appear undoubtedly capable of a marked peripheral blood stem cell (PBSC) enhancement, their combination with a chemotherapy priming often increases this phenomenon. This is particularly evident with rhIL-3, which is an earlier acting cytokine than rhGM-CSF and rhG-CSF. rhIL-3 priming alone leads to only a minor elevation of circulating progenitor cells, while its combination with chemotherapy and/or a late acting cytokine may allow enhancement and recruitment of large amounts of PBSC. The effect of cytokines on PBSC enhancement may also be at least partially thwarted by various factors. Additionally, their adequate dosage often remains uncertain. So it is presently too early to determine what is actually the most appropriate cytokine or cytokine combination to improve PBSC enhancement. Also the risk of stimulation of tumor clonogenic cells in some malignant diseases remains, and the experimenters should be as cautious as possible to not jeopardize the patients' safety.

IL-3 and peripheral blood stem cell harvesting

Transplantation of blood-derived stem cells is increasingly performed because when used alone or when combined with autologous bone marrow grafting, it can demonstrably shorten myelosuppression following multi-agent chemotherapy. Hematopoietic growth factors can mobilize peripheral blood stem cells from the bone marrow to therapeutically intervene in accelerating hematologic recovery. Interleukin 3 (IL-3), whose hematopoietic activities were first described some ten years ago, is one of several candidate growth factors that may prove useful in enhancing this mobilization in order to obtain adequate yields of circulating stem cells for transplantation. IL-3 used in conjunction with synergistically acting cytokines such as granulocyte-macrophage colony stimulating factor (GM-CSF) or granulocyte CSF (G-CSF) have already yielded interesting results, while new factors like stem cell factor are in the process of clinical evaluations and appear promising. However, further issues remain to be clarified to confirm the general applicability of cytokine-augmented peripheral blood stem cells in improving on-schedule delivery of high-dose myelosuppressive chemotherapy in patients with malignancies.

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.

Effect of systemic interleukin-3 administration on epithelial cell proliferation in mouse intestine

The effect of interleukin-3 (IL-3) on the crypt cell production rate (CCPR) in the intestine of mice was studied using a stathmokinetic technique combined with crypt microdissection. Interleukin-3 (0.71 micrograms/injection) was administered subcutaneously (s.c.) as two injections per day for 7 successive days and small mucosal pieces (duodenum, jejunum, ileum and colon) removed at necropsy were organ cultured in the presence of the metaphase arrest agent vincristine sulfate for two hours. The number of metaphases was enumerated in dissected crypts and CCPR calculated. The results demonstrated that the CCPR was significantly increased in all mucosal segments in the IL-3 treated animals compared to saline injected controls. These results suggest that the growth promoting properties of IL-3 are not restricted to hematopoietic cells when used in vivo and may directly or indirectly increase epithelial cell turnover in gut mucosa.

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.