Cytogenetic studies in dogs after total body irradiation and allogeneic transfusion with cryopreserved blood mononuclear cells: observations in long-term chimeras

Peripheral Blood Stem Cell Transplantation: Critical Review

Autologous blood stem cell transplantations have been increasingly performed worldwide for almost ten years in place of autologous bone marrow transplantation and even of allogenic bone marrow transplantation. Several crucial issues were the subjects of impassioned controversies. Some of them are now satisfactorily answered while others still remain unresolved. First, it is now possible to conclude today that peripheral blood stem cells (PBSC) are undoubtedly capable of restoring short term hematopoiesis when reinfused after myeloablative therapy as well and even more rapidly than bone marrow stem cells, provided that they have been previously collected in sufficient amounts. On the opposite, it is still impossible to firmly prove that their very immature CD34+ cell subset, although in vitro functionally and phenotypically almost identical to their marrow counterpart, is actually responsible for sustained long term hematopoietic recovery, even if it is likely that these cells play a key role.

Most of the time, using chemotherapy alone or a combination of chemotherapy and cytokine(s), mobilizing regimens allow collection of appropriate yields of PBSC with only a small number of apheresis cycles, provided that a sufficient number of residual stem cells remains to be stimulated, when, on the contrary, collection in steady-state is time-consuming and does not provide further accelerated post transplant hematopoietic recovery.

It was initially hypothesized that PBSC could have a lower likelihood of tumoral contamination compared with bone marrow. In fact, biological as well as clinical data are discordant and probably depend largely on the type of disease, its evolutive history and its way of dissemination. Furthermore, the respective impact on the development of further relapse of graft contamination and of residual tumor cells into patient remains to be determined.

Finally, although it has often been claimed that the cost of mobilization, collection and cryopreservation of PBSC would be much higher than the cost of bone marrow harvesting, it is now possible to assert that the whole ABSCT procedure, including this preliminary phase, as well as the post-transplant period, allows an indisputable saving compared with ABMT.

These advantages are already sufficient reasons “per se” to propose ABSCT in place of ABMT or alloBMT in many indications even if their clinical benefit, in terms of disease-outcome, remains to be prospectively explored.

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.

Peripheral blood progenitor cell transplantation

Peripheral blood progenitor cells (PBPCs) have become increasingly popular over the last 15 years as the source of hematopoietic stem cells for transplantation. In the early 1990s, PBPCs replaced bone marrow (BM) as the preferred source of autologous stem cells, and recently the same phenomenon is seen in the allogeneic setting. Under steady-state conditions, the concentration of PBPCs (as defined by CFU-GM and/or CD34+ cells) is very low, and techniques were developed to increase markedly this concentration. Such mobilization techniques include daily injections of filgrastim (G-CSF) or a combination of chemotherapy and growth factors. Leukapheresis procedures allow the collection of large numbers of circulating white blood cells (and PBPCs). One or two leukapheresis procedures are often sufficient to obtain the minimum number of CD34+ cells considered necessary for prompt and consistent engraftment (i.e., 2.5-5.0 x 10(6)/kg). As compared to BM, autologous transplants with PBPCs lead to faster hematologic recovery and have few, if any, disadvantages. In the allogeneic arena, PBPCs also result in faster engraftment, but at a somewhat higher cost of chronic graft-versus-host disease (GvHD). This may be a double-edged sword leading to both increased graft-versus-tumor effects and increased morbidity. The rapid advances in the study of hematopoietic, and even earlier, stem cells will continue to shape the future of PBPC transplantation.

Transplantation of unmanipulated allogeneic PBSC: preliminary report on 24 patients

To explore the feasibility and potential advantages of PBSC in allogeneic transplantation, we grafted 24 patients (age 16-57, median 37) with different hematologic diseases (ALL = 10, AML = 5, MM = 4, NHL = 2, CML = 1, MDS = 1, AA = 1), 23 HLA-identical to their siblings and 1 partially matched. Cells were collected from donors by apheresis after G-CSF 10 to 16 mg/kg/day for 4 to 5 days, and stored at 4 degrees C until infusion. The patients were conditioned with chemotherapy regimens including busulfan and cyclophosphamide in the majority of cases and received GVHD prophylaxis with CSA-MTX in all but two. The graft consisted of PBSC alone, with a median of 143.5 (range 18.1-358.9) x 10(4)/kg CFU-GM, 9.0 (range 3.3-18.0) x 10(6)/kg CD34+ cells and 2.8 (range 1.2 to 8.6) x 10(8)/kg CD3+ and cells. An ANC >0.0.5 x 10(9)/L was recovered on (median) day 13 (range 11-17), and a platelet count >50 x 10(9)/L on (median) day 13 (range 12-55) post graft. There was no correlation between CD34+ cells or CFU-GM number in the inoculum and time to hematologic reconstitution. Acute GVHD (grade II-IV) occurred in 10 out of 22 (45%), chronic GVHD in 10 out of 18 evaluable (55%) patients. We found no relationship between occurrence of acute or chronic GVHD and number of CD3+ cells in the graft. Four patients relapsed and 7 died after transplantation. Fifteen patients are currently alive and disease-free 67 to 710 (median 286) days from the graft. Allogeneic transplantation with unmanipulated PBSC ensures a fast and stable engraftment. Acute GVHD incidence and severity seems comparable to that of bone marrow transplantation, but there may be an increase in chronic GVHD, mainly of the extensive form.

Hematopoietic transplantation: state of the art

Bone marrow transplantation has developed from an experimental therapy for a small group of patients to a well-established form of treatment with well-defined indications for a large group of patients with hematological and non-hematological neoplasia. The availability of suitable donors has more than doubled due to large registries of persons volunteering for marrow donation. With improved techniques for histocompatibility typing, it has become possible to study the role of specific histoincompatibilities for graft-versus-host disease and graft-versus-leukemia reactions. The source of hematopoietic stem cells now comprises not only bone marrow, but also stem cells mobilized into the peripheral blood and stem cells from cord blood. Hematopoietic growth factors have found a large distribution in the mobilization of stem cells and support for hematological reconstitution. They are studied for the expansion of pools of stem cells. Reconstitution of antileukemia and antiviral activity has been achieved by adoptive immunotherapy using lymphocytes and dendritic cells cultured in vitro. The way from transplantation of bone marrow to cellular and genetic engineering leads to new indications such as treatment of severe autoimmune disease. Hematopoietic transplantation has come a long way and it still has possible new areas of application.

CD34 positive blood cells for allogeneic progenitor and stem cell transplantation

The transplantation of allogeneic peripheral blood progenitor cells (PBPC) provides complete and sustained hematopoietic and lymphopoietic engraftment. In healthy donors, large amounts of PBPC can be mobilized with hematopoietic growth factors. However, the high content of immunocompetent T-cells in apheresis products may expose recipients of allogeneic PBPC to an elevated risk of acute and chronic graft-versus-host disease. Thus, the use of appropriate T-cell reduction, but not depletion might reduce this risk. The hazards of graft rejection and a higher relapse rate can be avoided by maintaining a portion of the T-cells in the graft. The positive selection of CD34+ cells from peripheral blood preparations simultaneously provides an approximately 1000-fold reduction of T-cells. These purified CD34+ cells containing committed and pluripotent stem cells are suitable for allogeneic transplantation and can be used in the following instances: 1. As hematopoietic stem and progenitor cell transplantation instead of bone marrow cells, from HLA-identical family donors; 2. for increasing the stem cell numbers from HLA-mismatched or three HLA-loci different family donors in order to reduce the incidence of rejection but without increasing the T-cell number; 3. boosting of poor marrow graft function with stem cells from the same family donors; 4. transplantation from volunteer matched unrelated donors; 5. split transplantation of CD34+ and T-cells; 6. addition of ex vivo expanded CD34+ cells to blood cell or bone marrow transplantation; 7. generation of antigen specific immune effector cells and antigen presenting cells for cell therapy.

Peripheral blood stem cell collection from healthy donors for allogeneic transplantation

There is great interest in the use of peripheral blood stem cells (PBSC) for allogeneic transplantation, based on the good results seen with autologous PBSC infusion. Reasonable caution exists regarding the use of allogeneic PBSC for transplantation because of donor toxicities due to rhG-CSF administration and the risk of graft-versus-host-disease (GVHD) in the recipient because of the large number of T-cell infused. We present preliminary data on allogeneic PBSC collections and transplantation in ten patients affected by advanced leukemia (eight patients), severe aplastic anemia (one patient) and sickle cell anemia (one patient). Seven donors were HLA-identical siblings, while the other three were mismatched for three, two and one locus, respectively. All donors received rhG-CSF at a dose of 12 micrograms/kg for a mean of 5 days. Leukaphereses were performed with the aim of collecting a minimum of 5 x 10(6)/kg (recipient's weight) CD 34+ cells. Collection timing was determined by monitoring CD 34+ cells in the donor's peripheral blood from the second day of rhG-CSF therapy. The PBSC collections yielded a mean of 10.05 x 10(8) MNCs/kg and of 10.48 x 10(6) CD 34+ cells/kg (recipient's weight). PBSC were immediately infused after collection in patients given myeloablative therapy. Engraftment was observed in each patient at a mean of 13.2 days for an absolute neutrophil count (ANC) more than 0.5 x 10(9)/L and of 26.5 days for a platelet count of more than 20 x 10(9)/L. Eight patients experienced no or moderate acute GVHD, whereas two patients died of grade 4 GVHD, notwithstanding GVHD prophylaxis with cyclosporine and prednisone. Two other patients died of viral and fungal infections, respectively, despite prophylaxis. The remaining six patients are alive between 58 and 430 days after transplant. Our results document that allogeneic PBSC are capable of engraftment after a myeloablative regimen. Controlled trials are necessary to compare the potential benefits of this approach with the results obtained in allogeneic bone marrow transplantation.

CD34+Thy-1+Lin- stem cells from mobilized peripheral blood

Over the last ten years there has been increasing use of mobilized peripheral blood (MPB) progenitor cells as grafts for autologous transplantation. Among the cells comprising these MPB autografts is a subpopulation of CD34+Thy-1+Lineage (Lin)- cells, which is enriched for hematopoietic stem cell (HSC) activity. The percentage of CD34+ cells which express Thy-1 is higher in some samples of MPB than in bone marrow (BM). Using myeloid and erythroid cell depletion prior to high speed cell sorting, it is possible to purify sufficient numbers of CD34+Thy-1+Lin-HSCs from a MPB leukapheresis sample for use as an autograft. CD34+Thy-1+Lin-cells will potentially provide a tumor-depleted autograft for cancer patients. This HSC population is also being studied as a potential target for gene transfer for the treatment of patients with HIV, cancer and a variety of genetic disorders.

Transplantation of allogeneic peripheral blood stem cells mobilized by recombinant human granulocyte colony stimulating factor

Recombinant G-CSF has been given to over 150 normal donors for the collection of allogeneic or syngeneic peripheral blood stem cells (PBSC). G-CSF was found to be well-tolerated with mild-moderate bone pain, edema and mild thrombocytopenia being the observed side effects. To date, approximately 90 unmodified primary PBSC transplants from HLA-identical related donors have been performed with engraftment that is, in general, considerably more rapid than marrow. Acute graft-versus-host-disease (GVHD), grades II-IV occurred in 47% of patients and grades III-IV in 17%. Despite the infusion of one to two logs more T cells, these results are not remarkably different than would be expected with marrow transplantation. There have also been successful reports of using G-CSF mobilized allogeneic PBSC following second transplants for graft rejection or relapse. Allogeneic PBSC have been infused without reconditioning for correction of graft failure and unmodified or CD34 selected PBSC have also been given with marrow to augment the dose of hematopoietic cells. Further studies are needed to define the role of allogeneic PBSC for transplantation, refine PBSC mobilization and collection techniques and to evaluate the long-term effects of cytokines in normal donors.

Blood stem cell transplantation: from preclinical to clinical models

This introductory statement to the International Symposium "Ten Years of Blood Stem Cell Transplantation in Heidelberg" provides the opportunity to review the experimental work that was necessary to set the stage for the first successful clinical studies to use blood-derived stem cells to treat hemopoietic and other malignancies. The Ulm University research group used the preclinical canine model to systematically and extensively explore the possibilities and limitations of the therapeutic use of blood-derived hemopoietic stem and progenitor cells. It became clear that blood stem cells are physiological elements of the circulating blood, that their concentration can be drastically increased by chemical and biological means, that they do not lose their function during appropriate cryopreservation, and that they can be "purified" and used successfully to restore hemopoiesis after myeloablative conditioning both in the autologous and allogeneic situation. If compared to fetal liver-derived stem cells, there is excellent experimental evidence that fetal liver-derived stem cells may have even more potential in their ability to restore hemopoiesis, and it is evident that much more experimental work is needed.

Blood stem cell transplantation and gene therapy of cancer

Based on the concept of circulating hematopoietic stem cells with indefinite self-renewal capacity that gives rise to all three cell lineages, peripheral blood progenitor cells (PBPCs) have widely replaced the use of bone marrow (BM) progenitors for autologous transplantation purposes in patients with malignant hematological disorders and selected solid tumors. Ex vivo purification of normal CD34+ cell subsets contained in the patient's apheresis product possibly eliminates clonogenic tumor cells, but also serves as a target cell population for gene transduction. Genetic tagging of PBPC autografts has proven that: 1) NEOR gene expression is sustained for more than 18 months and 2) clonogenic tumor cells contaminating the autograft contribute to relapse. A second generation of gene transduction studies includes new treatment strategies such as the induction of chemoprotection (multidrug resistance gene-1), chemotherapy sensitization (p53), cancer vaccination and genetic chemosensitization. Most recently allogeneic PBPC transplantation has successfully been introduced with the intention of improving the graft-versus-leukemia effect without inducing a higher incidence or more severe graft-versus-host disease (GVHD) than what is expected after BM transplantation. Introducing the herpes virus thymidine kinase cDNA into activated donor T cells makes them susceptible to gangciclovir, thus allowing the in vivo inactivation of GVHD-inducing T cells. With the close interaction of molecular genetics and clinical oncology/hematology, genetic engineering of stem cell grafts will lead into a new stage of stem cell transplantation technology.

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.