The hematopoietic system is the adult cellular model in which the biology of the stem cells is the best known and may be a model for numerous other tissues. This model is theoretically based on a hierarchy of cells, which begin on a stem cell that differentiates into mature cells through a large number of cellular stages including hematopoietic progenitors. Hematopoietic stem cells have three ain properties: (1) Self-renewal capacities. However, in transplantation experiments this property is limited and may be regulated by the stem cell niche. (2) Multipotentiality. Hematopoietic stem cells are capable of differentiation towards all myeloid and lymphoid lineages. However, recent experiments suggest that, like other somatic stem cells, hematopoietic stem cells are capable

The hematopoietic system is the adult cellular model in which the biology of the stem cells is the best known and may be a model for numerous other tissues. This model is theoretically based on a hierarchy of cells, which begin on a stem cell that differentiates into mature cells through a large number of cellular stages including hematopoietic progenitors. Hematopoietic stem cells have three main properties: (1) Self-renewal capacities. However, in transplantation experiments this property is limited and may be regulated by the stem cell niche. (2) Multipotentiality. Hematopoietic stem cells are capable of differentiation towards all myeloid and lymphoid lineages. However, recent experiments suggest that, like other somatic stem cells, hematopoietic stem cells are capable of differentiating towards non-hematopoietic lineages. The mechanisms of call commitment towards one cell lineage are beginning to be understood and involve competition between transcription factors. (3) Migration. Stem cells are able to travel through the blood. These migration capacities may be an important but underestimated role in the function of hematopoietic stem cells. Mobilization of stem cells by growth factors is now clinically used for hematopoietic transplantation in man. CXCR4 and its ligand, the SDF-1 chemokine, play an important role in stem cell chemotaxis and in their retention in the marrow.

Allogeneic transplantation of hematopoietic stem cells (HSC) is a curative treatment for hematological malignancies aiming to eradicate the malignant clone using the immunological conflict inherent to donor HSC installation in the recipient. The different possible sources of HSCs (bone marrow, blood, and cord blood) and better knowledge of HLA typing has led to the development of new transplantation techniques and modalities (transplantations after non-myeloablative conditioning, haploidentical transplantations, etc.), which should improve patient survival and extend allograft indications. HSC allografting is subject to immunological reactions stemming from the histocompatibility discrepancy between donor and recipient. For the most part, these are reactions of the graft against the host (graft-versus-host disease: GVHD) and graft rejection (host-versus-graft: HVG). This immunological conflict can also be responsible for recognizing and destroying the recipient's residual tumor cells, which carry specific tumor antigens and/or minor antigens of histocompatibility (graft-versus-leukemia effect, GVL or graft-versus-malignancy effect, GVM). The posttransplantation period can also be riddled with various complications such as veno-occlusive disease, endocrine complications, as well as complications arising from infections and secondary neoplasms because of a more or less substantial and durable immune deficiency. Acute and chronic leukemias are the major indications for HSC allogeneic transplantation, for which the results are variable and closely related to the patient status, the hematological disease, and the transplant procedure. Other hematological diseases are also indications for allogeneic transplantation but are rarer, for which allogeneic transplantation remains nevertheless the only curative treatment, despite an overly high level of toxicity. Improvement in the results of unrelated transplantations, use of peripheral HSC or cord blood cells, development of non-myeloablative conditioning regimens, and techniques of ex vivo manipulation of the graft have allowed HSC allogeneic transplantation indications to be extended. The antitumor efficacy of donor lymphocytes infusion for relapses after transplantation mirrors the GVL effect and is the first stage in a targeted cellular immunotherapy using sensitized lymphocytes or dendritic cells.

Economic evaluation of autologous peripheral blood stem cell (PBSC) transplantation certainly played a role in the very fast substitution from bone marrow to BC autograft. Economic evaluation is still ongoing about the optimization of the procedure by assessing the cost-effectiveness ratio of each new improvement of the technique. Among these improvements we present the administration of high dose CD34+ cells, the delayed administration of G-CSF and the outpatient management of post-graft follow-up. It is still very rare in the field of health economics to notice such an early and ongoing economic evaluation of an innovation.

This article summarizes the different clinical results of the IFM trials: high dose therapy supported with autologous stem cells improves survival, melphalan 200 mg/m2 is the best preparative regimen, unpurged peripheral blood stem cells are the recommended source of stem-cells to support high dose therapy, tandem transplants significantly improve survival. However, despite these encouraging results, long term survival needs inovative strategies evaluated with the current IFM 99 protocol.

Despite surgery, post-operative irradiation and adjuvant conventional chemotherapy, prognosis of high-grade gliomas remains poor. Carmustine (BCNU) has been shown to have limited activity at conventional dosage but is still the standard chemotherapy. Activity of chemotherapy is limited by the blood-brain barrier impermeability and high levels of expression of multidrug resistance proteins on tumor and/or endothelial cells. Despite high response rates, development of intra-arterial chemotherapy remains limited because of frequent acute brain toxicity related to drug administration. High-dose intravenous chemotherapy rescued by autologous hemopoietic stem cell transplantation is an alternative that might increase drug delivery through the blood-brain barrier and tumor control. Several phase I-II trials using high-dose BCNU were published. The maximum tolerated dose seems to be 800 mg/m2 and interstitial pneumonitis and hepatitis are dose-limiting toxicities. Few phase I-II trials of high-dose therapy were published using drug combinations. High response rates in patients with progressive tumor were observed and in adjuvant setting, encouraging results in terms of median survival time and long survivors were published. No phase III trial was reported to date. Future investigations should include randomized trials comparing high-dose and conventional-dose chemotherapy and development of new high-dose regimens that incorporate new drugs such as temozolomide.

Small cell lung cancer accounts for 20% of the primitive lung carcinomas. The pronostic is unfavourable, since two thirds of the patients present with extensive stage at diagnosis. The median survival without treatment is less than 3 months. Chemotherapy is the standard front line therapy. In selected patients, chest irradiation and so-called prophylactic cerebral irradiation are current options. Small cell lung cancer is a chemosensitive disease. Indeed, the response rate is around 80-95% of in limited disease patients of which 50-60% are complete responses. Despite these results, the median survival does not exceed 16 months. Early recurrences after initial response probably reflect various resistances mechanisms. Furthermore, small cell lung cancer is associated with a high fraction of dividing cells. It is a clinical model where the dose-response relationship concept is worth testing, and dose-intensity may be integrated into the therapeutic strategies. Therefore, many clinical trials have assessed these principles during the past 20 years. We present here the different methods of therapeutic intensification in small cell lung cancer: with or without hematopoïetic supports, using initial high dose of cytotoxic drugs, either at the beginning or at the end of induction treatment, or by increasing the dose-density.

Peripheral blood stem cells transplantation after high dose chemotherapy is increasingly used for the treatment of hematological malignancies and solid tumors. Autologous transplantation are now used as first line therapy. The use of hematopoïetic growth factors allowed to collect peripheral hematopoietic progenitors in quantity large enough for several autologous reinfusions. As for bone marrow, peripheral blood stem cells allow fast and long-term hematopoietic reconstitution. The fast regeneration is strictly correlated to the number of hematopoietic progenitors infused. Some questions are still opened anyway, notably about the tumoral contamination of the graft which has been clearly demonstrated. Even if residual tumor cells are clearly shown to participate to relapse, the interest of ex vivo purging is still matter of debate. Several techniques of positive selection are now available, selecting normal stem cells thanks to the CD34+ antigen. Negative selection is also available either using clinical purging or monoclonals antibodies against tumoral antigens. Endly, ex vivo expansion of hematopoietic stem cells is under investigation using medical progress in the field of growth factors. Therefore, improvement of mobilisation protocols, of technology for positive or negative selection, as well as the strategy for ex vivo expansion will be the tools for the development of the treatment of some hematological malignancies and solid tumors reducing the hematopoietic and extra hematopoietic toxicity.

We report four cases of non-synchronous antiphospholipid syndrome (APS) and malignant lymphoma, which highlight the complex relationship that seems to exist between these illnesses.

IMMUNOSUPPRESSIVE THERAPY: Intravenous immunoglobulins have demonstrated their value for highly immunized cross-match positive transplantation candidates. Graft rejection during the first two post-transplantation weeks can be avoided with CMPATH-1H, humanized anti-CD52 monoclonal antibody, which produces major and persistent T- and B-cell as well as monocyte depletion. FTY 720 is well tolerated and has demonstrated its efficacy in preventing acute rejection. Sirolimus would have an antiatheromatous effect. Attempts to minimize immunosuppression should be followed for several months. OTHER NEW DEVELOPMENTS: There has been considerable interest in Langerhans islet transplantation. Work also concerns follow-up techniques used to diagnosis rejection. FUNDAMENTAL SCIENCE: New advances in basic science that should have an impact on transplantation have been made in the area of lymphocyte activation, toll-like receptor structures, and germinal and stem cells, as well as in the areas of essay methods and gene therapy.

The general properties of chemokines and their receptors are described, and the perspectives raised for cellular therapy are discussed. Specific examples are provided in the cases of the CXC chemokine SDF1 and of chemokines ligands of CCR5.

This text describes, in an epistemological perspective, the development of the concept of cellular therapy applied to the treatment of type 1 diabetes. Emphasis is put on three recent papers describing the success of islet allograft in diabetic patients, the development of neo-islets from stem cells isolated from the pancreas of adult mice, and the effect of hepatic cell transfection with an adenovirus bearing the gene coding for PDX-1, a transcription factor involved in the maturation of islets of Langerhans. This text tries to delineate some factors which may be involved in the chances for these techniques to reach the real world of human therapeutics.

Articular cartilage has a very poor capacity for repair. In order to get a normal functional efficacy, the replaced tissue has to reproduce the structure, composition and physico-chemical properties of native cartilage tissue. The transplantation of cultured autologous chondrocytes into chondral defects is currently applicable only in the case of young sportive people with a limited lesion in an otherwise relatively normal joint. Recent experimental studies have shown that pluripotent mesenchymal cells from bone marrow could also repair experimental osteochondral defects. An advantage of this grafting procedure is that large areas of cartilage surface could be covered. Bone marrow cells are not so difficult to get, they have a high potency to divide and they can develop in vitro as chondrogenic, osteogenic or adipogenic cells. The present ways of research are: to characterize one or several growth factors capable to specifically induce the chondrogenic lineage; to determine nutrient and environmental conditions allowing the cultured chondrogenic cells to undergo a maturation process within the cell pellet; to elaborate three-dimensional synthetic, biodegradable polymeric scaffolds assessed with respect to chondrogenic cell adhesion, proliferation, maturation and cartilage matrix secretion; finally, to elaborate a mixed biomaterial composed of chondrogenic and osteogenic cells selectively distributed within polymeric scaffolds in order to get a better adherence of the implanted cells to the lesion sites.

Dendritic cells constitute a family of antigen presenting cells defined by their morphology and their capacity to initiate primary immune response. Langerhans cells are paradigmatic dendritic cells, described in 1868 by a young medical student, Paul Langerhans in Berlin. Langerhans cells are present with epithelial cells in the epidermis, bronchi and mucosae. After antigenic challenge, Langerhans cells migrate into the T cell areas of proximal lymph nodes where they act as professional antigen-presenting cells. Langerhans cells originate in the bone marrow and CD34+ hematopoïetic progenitors are present in cord blood or circulating blood. They are actively involved in skin lesions of allergic contact dermatitis or atopic dermatitis, in cancer immunosurveillance and are infected by HIV in AIDS. Since 1992, Langerhans cells may be generated in vitro from CD34+ cord blood or circulating blood progenitors by culture with GM-CSF and TNF alpha, as well as from peripheral blood monocytes by culture with GM-CSF, IL4 and TGF beta 1. The possibility to obtain from the blood, the circulating progenitors of dendritic cells and the subsequent possibility to harvest a large number of these cells through in vitro culture using growth factors, have given rise to several very interesting therapeutic perspectives, especially in the field of anti-cancer immunotherapy. In dermatology advanced studies have concerned malignant melanomas. Anti-melanoma immunization trials were performed in patients, through dendritic cells charged with melanoma antigens. Side effects appear to be limited. Injections of antigenically charged dendritic cells were performed subcutaneously, intravenously or in the lymph nodes. Positive clinical responses were obtained with, in some cases, complete remission of the metastasis. These results open a particularly interesting perspective in the field of cancer treatment.

The success of HSCT from HLA partially disparate donors depends on the development of new strategies able to efficiently prevent GVHD and to protect patients from infections and relapse. Using an immunotoxin (IT) directed against the alpha-chain (p55) of the human IL-2r (RFT5-SMPT-dgA), we have previously shown that it is possible to kill mature T cells activated towards a specific HLA complex by a one-way MLR. We designed a clinical trial assessing the effect of infusing increasing doses of T lymphocytes in the setting of children recipients of non HLA genetically identical HSCT. Thirteen patients have been enrolled from September 1998 to April 2000 and fourteen HSCT have been realized in 13 patients (pts). Donors were MUD in 3 cases and familial HLA partially disparate in the remaining cases. Allodepleted donor T cells were injected between day +14 and day +30 provided that ATG was undetectable in the serum and blood PMN counts was > 500/microliter. The mean age of these patients was 17 months (range 1 to 42). Diagnosis included immune deficient and malignant hemopathies. Three patients received 1 x 10(5) allodepleted T cell/kg, 7 patients received 4 x 10(5)/kg and 4 patients received 6 x 10(5)/kg allodepleted T cells. Full inhibition of MLR was achieved in 12 out of 14 cases. In two cases, a residual T cell reactivity to the recipient was observed (4 to 5%) and patients developed grade II aGVHD. aGVHD occurred in 4 out of 11 grafted patients (all grade II). No chronic GVHD has developed, so far. Three patients died from severe VOD or PHT at day +34, day 51 and day +166, while one infected patient by VZV, CMV and EBV before HSCT died 6 months after transplantation from meningoencephalitis and another patient died from relapse at day +291. The patient for which there was no engraftment died at day +48 from staphylococcus infection. Overall survival is 54%, with a median follow up of 8 months; the mean time to reach a blood lymphocyte count > 500 was 41 days, to reach a CD3 count > 300 microliters 63 days (20-111), CD4 > 200 microliters 97 days and positive mitogen-induced proliferation 90 days. In three patients, a tetanus-toxoid positive proliferation was detected before immunization. From this intermediate analysis, we conclude that 1) specific allodepletion is an effective approach to prevent aGVHD in a haploincompatible setting, 2) data on immunological reconstitution suggest that infused T cells do survive and expand. A higher number of patients must be enrolled to determine the optimal number of T cells to infuse.

Fetal neural allografts have already proven their therapeutic value in several hundreds of patients with Parkinson's disease, and have very recently provided promising results for patients with Huntington's disease in our center. Fetal neurons integrate readily into the neural parenchyma of the adult hosts, differentiate into mature neurons and substitute, anatomically and functionally for lost host neurons. Notable clinical improvements have been obtained using this procedure. Nevertheless, a major obstacle hampers the development of the technique, that provoked by the logistic difficulty in retrieving and preparing the tissue. Indeed, this requires, for each surgical session, the organization of a chain of expertise which cannot be taken up by an external provider (e.g. a biotech company). This is difficult to organize outside of specialized research centers. The future of the technique relies, therefore, upon the design of alternative sources of tissue. Two different ways are currently explored very actively, namely xenografting of neurons of porcine origin and human stem cells, in particular derived from ES cells. In both cases, but in different ways, the goal of both techniques is to allow the organisation of cell banking systems, relieving the constraints of obtaining the collaboration of specialized obstetricians and biologists. Obstacles foreseen for these two alternative ways of fetal neurons to be are identified and research laboratories are actively exploring ways to overcome them.

Regenerative medicine can be defined as the possibility to replace aged/damaged cells by genetically similar young and functional cells. This could be reached by using human embryonic stem cells, eventually from cloned human embryos, or pluripotent adult stem cells. The range of the possible differentiation fates of these latter cells has recently been shown to be strikingly large. Although considerable works remains necessary to develop this new type of medicine, to assure its efficacy and safety, it nevertheless represents one of the major medical breakthroughs expected for the future.

When proceeding normally, embryonic morphogenesis begins with germ layer formation through the process of gastrulation. Each primordial germ layer gives rise to a particular set of lineages. Until recently, it was considered that fate switches between germ layers were impossible. In the last two or three years however, a fair number of such switches have been described (Table I), the most spectacular of which entails the differentiation of neural stem cells into various derivatives. This unexpected plasticity opens important prospects for cell therapy. Stem cells, which are the cells that display this plasticity, are defined by the two properties of self renewal and pluripotency. They are set apart during ontogeny and are responsible for maintaining the homeostasis of a tissue. This notion, first established in the case of hematopoietic stem cells was later extended to other fast renewing cells, such as those in the intestinal epithelium or epidermis, and more recently to cells reputedly non-renewable, i.e. neurons. A new strategy has been described, which has the interesting feature that it can be applied to the isolation of stem cells from various lineages. It consists in sorting out cells on the basis of the efflux of Hoechst 33342 dye (Goodell et al., 1996). When a cell suspension stained with this dye is examined under two distinct wave lengths, a "side population" (SP), characterized by weak fluorescence, can be identified and sorted out. The dye efflux property of these cells is due to the activity of the mdr (multidrug resistance) gene, which encodes a protein responsible for the building of a canal which serves to extrude toxins from the cells. A means of distinguishing a truly multipotent stem cell from a progenitor committed to a specific lineage has been reported. This consists in the expression of the Pax7 gene. Pax7-/- mouse muscles have no satellite cells, i.e. they miss the cells normally responsible for the regeneration of muscle. In contrast they do have an SP population. These SP cells are incapable of differentiating into muscle, but give rise to 10 times more hematopoietic colonies, when cloned in vitro, than SP cells from wild type muscle do. Thus Pax7 appears to be a commitment gene, in the absence of which stem cells cannot become specified to the muscle lineage. As a conclusion, this review emphasizes various features of the recent findings: 1) the unexpected plasticity uncovered in recent years is restricted to the stem cells of each tissue; 2) the switch in phenotype has to be "forced" on these stem cells by drastic experimental conditions enforced in the host: often sublethal irradiation is superimposed on a genetic deficiency. Progress in this field, concerning both conceptual and applied aspects, will require the identification of the factors characterizing the niches which promote integration and fate switches of stem cells, probably a combination of growth factors and intercellular interactions. Finally a key issue, before any therapeutical applications can be considered, is how to control the proliferation of transplanted stem cells in their new environment.