Retinal dystrophies are rarely curable diseases and several avenues of research are being pursued, such replacement therapies and pharmacological treatment. Among them, the transplantation of functional retinal cells has been envisaged in order to restore vision in patients who have these diseases by repopulating the damaged retina and/or by rescuing retinal neurons from further degeneration. Over the past few years, identification and characterization of stem cells has opened new avenues in cell-replacement therapy. Since retinal stem cells are already present during embryonic development, they persist in the adult mammalian eye only in the ciliary marginal zone, even a stem cell potential has been described for the Müller glia in the retina. This result opened possibilities of regeneration by mobilizing endogenous stem cells to respond to injury. Regarding the transplantation studies, in all experiments using different types of stem cells (retinal progenitors, neural stem cells, bone marrow-derived stem cells and ES cells), despite their incorporation within the host's retina, the transplanted cells failed to express retina-specific markers and to establish synaptic connections. Therefore, the true potential of the different stem cells in retina repair can only be realized with more information about mechanisms that regulate their proliferation and differentiation; and by development of techniques that allow their prospective identification and enrichment.

Graft vs host disease is a serious immunological complication of allogeneic haematopoietic cell transplantation, leading to a significant morbidity and mortality. It occurs when donor T lymphocyte react to foreign host cells. The physiopathology is a more complex process implicating host tissues damage caused by the conditioning regimen, cytokines, cellular effectors implicated in the immune response such as donor lymphocytes T, antigen presenting cells and mechanisms of apoptosis. This review focuses on the physiopathological basis, risk factors, clinical aspects; prevention and current management strategies to treat graft vs host disease. Recent developments in our understanding of this bone marrow transplantation complication have profoundly influenced the practice of allogeneic haematopoietic cell transplantation. There is a growing realisation of the importance of a graft vs leukaemia effect, strategy, which has encouraged the development of less conditioning regimens. Segregation between graft vs host effect and graft vs leukaemia effect is a key challenge, and could lead to new efficient and specific immunotherapy.

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During the last two decades, improvements in the induction and consolidation treatment phases in patients with high-risk neuroblastoma have not translated into significant increases in survival rates. Efforts to improve outcome have used high-dose chemotherapy with stem cell rescue and more recently, differentiating (retinoids) and antiangiogenic agents. In parallel, immunotherapy has become an increasingly important part of the treatment of high-risk neuroblastoma. We review here the biological concepts underlying these new approaches and their clinical applications, with a particular emphasis on applications that manipulate the immune system, including monoclonal antibodies, gene-modified tumor cells (vaccines) or immune effectors.

The discovery of circulating endothelial progenitors (EPCs) in human blood has completely modified the concept of post natal angiogenesis. Many studies have further confirmed the existence of EPCs, their medullar origin and capacity to be integrated in vascular structures at the sites of neoangiogenesis. They suggest that EPCs could be naturally involved in the prevention of ischemia by participating directly to the formation of collateral vessels. These cells have a high tropism for the sites of angiogenesis. They may thus be used as a powerful tool to prevent or treat ischemic diseases and constitute an alternative to the risky local injection of pro-angiogenic growth factors. The efficiency of bone marrow cells autologous transplantation was recently proved by the first clinical trials. Bone marrow mononuclear cells locally injected to patients with limb or cardiac ischemia have been shown to improve reperfusion in ischemic tissues. These trials are still preliminary: they were performed with heterogeneous cells only on few patients and were not randomized. However they raise important questions, essentially on the necessity of cell purification prior to injection and on the nature of the bone marrow cells which are really involved in ischemic tissue regeneration. Further investigations are then required to improve the cell therapy outcome by 1) using more defined cell population, 2) clearly demonstrating the long term improvement of vascular function and 3) performing extensive analysis of the possible side effects.

Using quail-chick parabiosis and the QH1 monoclonal antibody, specific for the endothelial and hematopoietic cells of the quail species, as a marker, we identified circulating endothelial cells in the embryo. In normal conditions, these cells could integrate endothelia in many tissues but their number remained low. When artificial angiogenic responses were created, i.e., in grafting experiments on the chorioallantoic membrane or wound healing, the circulating endothelial cells were rapidly mobilized to reach the embryonic regions submitted to these processes and their number dramatically increased. Interestingly, 1) on one hand, these circulating endothelial cells were present early in ontogeny, before the third embryonic day in the quail embryo; 2) on the other hand, their mobilization was not dependent on the presence of the bone marrow since it was effective before the differentiation of this tissue.

In the vertebrate embryo, the ventral wall of the aorta is the major site of Haematopoietic Stem Cell (HSC) production. HSC, which are at the basis of the adult blood cells hierarchy, are generated from Endothelial Cells (EC) through a complex cascade of molecular events. The transcription factor RUNX1/AML1 and its cofactor CBFbeta, disrupted in 20 % of acute myeloid leukaemia cases, are thought to control this process. A detailed gene expression analysis of RUNX1 and its associated factors in the chick embryo, prompted us to speculate on the molecular cascades involved in HSC production. The function of RUNX1 is however tightly regulated at several levels, rendering analysis through classical genetic approaches very difficult to manage. To offer new possibilities of investigation, we have designed a technique to target the blood forming system in vivo. Gene transfer was achieved by lipofection following delivery by intra-cardiac injection in the avian embryo. This method was optimised to allow a wide range of functional analysis, either by gain or loss of function, in a simple and efficient manner. In combination with experimental advantages of the avian embryo, this new system of genetic analysis allows us to perform a detailed study of RUNX1 function in HSC production from EC.

Intra-aortic haematopoiesis is a transient phenomenon, present in all the vertebrate species examined. Aorta-associated haematopoiesis produces Haematopoietic Stem Cells (HSC) that emerge from the ventral aortic endothelium through endothelial cells (EC) that switch to HSC. HSC emergence is followed by the colonization of definitive haematopoietic organs. Since intra-aortic haematopoiesis is born from EC of the aortic floor, we wondered how vascular integrity was maintained during haematopoietic production. Transplantation experiments have brought about evidence according to which two distinct endothelial lineages contribute to the embryonic vasculature. One comes from the splanchnic mesoderm and gives rise to EC and haematopoietic cells (HC). The other originates from the somite and is restricted to EC differentiation. We have used interspecific quail/chick grafts to study aortic organogenesis during the course of haematopoiesis. We demonstrate that: 1) before haematopoiesis, the aorta, originally entirely of splanchnic origin, is colonized by EC from the somite. This colonization contributes to create a new roof and sides, which are hence formed by somite-derived EC whereas the floor is contributed by splanchnopleural-derived EC; 2) as haematopoiesis proceeds, somite-derived EC begin to colonize the aortic floor and are found beneath HSC clusters; 3) after haematopoiesis, aortic hemangioblasts disappear from the endothelium and are replaced by somite-derived EC. At this stage, the whole aortic endothelium is derived from somitic cells; 4) we have identified a new cell population from the somite that contributes to the vascular smooth muscle cells (VSMC). This population appears distinct from the somite-derived EC. Using lineage tracing with non-replicative retroviral vectors, we show that EC do not give rise to VSMC as previously thought. Taken together, our results bring about new lights on aorta morphogenesis and the time-restricted production of haematopoiesis.

Erythroid differentiation involves the transcription factor GATA-1 that positively regulates promoters of erythroid genes (including haemoglobin, glycophorin, erythropoietin receptor) and of erythropoietin. Terminal erythroid differentiation is characterized by major morphological changes that include chromatin condensation and cell size reduction. The morphological changes are partially similar at least to those observed during apoptosis. The production of red cells depends on the apoptosis rate of erythroid progenitors and precursors. Upon erythropoietin starvation or engagement of the death receptor Fas, caspases are activated in erythroid precursors and cleave GATA-1, thus inducing maturation arrest and apoptosis of immature erythroblasts. We have recently demonstrated that, upon erythropoietin stimulation, caspase-3 was also activated, an event required for human terminal erythroblast maturation. Proteins cleaved by caspases in erythroid cells undergoing terminal differentiation include Lamin B and Acinus, which are involved in chromatin condensation. In contrast, despite caspase-3 activation neither GATA-1 degradation nor apoptosis was observed. Thus, the fate of erythroid precursors is determined downstream of caspase activation by the pattern of cleaved targets. Therefore, there are some mechanisms underlying the selective protection of caspase-3 targets during erythropoiesis. This model in which caspases activation is required for differentiation may apply to other haematopoietic or non haematopoietic cellular systems which are described in this review.

The feasibility and complication rate of central venous totally implantable access ports (TIAP), used for delivering high-dose chemotherapy (HDC) with autologous stem cell transplantation, have not been fully investigated to date, due to the almost exclusive use of external catheters (EC) in this clinical setting.

Epithelial, stromal or endothelial diseases can generate corneal opacity. A lake of corneal epithelial cells leads to corneal opacity and low visual acuity. In these cases, corneal epithelial stem cells from the limbus of the healthy eye or from relatives or other people must be grafted to regenerate corneal epithelium. It is also possible to cultivate corneal stem cells harvested from the sick eye, the healthy eye (autologous culture) or from relatives (allotypic culture). Renewing epithelial cells is not always sufficient to restore corneal transparency. It can also be necessary to replace a part or the entire corneal stroma. We can use today surgical lamellar graft technics to replace only stromal corneal layers involved in the disease we cure.

The human hair follicle is a unique appendage which results from epithelio-mesenchymal interactions initiated around the 3rd month of development. This appendage has a very complex structure, with a dermal compartment and an epithelial compartment. The dermal compartment comprises the connective tissue sheath and the dermal papilla, both of which are irrigated by microvessels. The epithelial compartment is made of highly replicating matrix cells giving rise to three concentrical domains, namely the outer root sheath, the inner root sheath and the hair shaft. The pigmentation unit, responsible for hair color, is made of fully active melanocytes located on top of the dermal papilla. Altogether a hair follicle contains more than 20 different cell types, engaged in different differentiation pathways and/or interacting with each other. This complex appendage has a unique behavior in mammals since, after a hair production phase, it involutes in place before entering a resting phase after which it renews itself under a cyclical but stochastic way, out of a double reservoir of pluripotent stem cells able to also regenerate epidermis. For yet unknown reasons, this well ordered process can be disturbed, provoking alopecia. The pigmentation unit also renews itself under a cyclical way, out of a melanocyte progenitor reservoir which progressively declines with time, provoking the hair whitening process. Finally, the shape of the hair shaft is programmed from the bulb. What makes this appendage unique and fascinating is its high degree of autonomy, its incredibly complex though stable structure, the number of different cell types interacting under an equilibrated way and its potential of regeneration. It represents a true paradigm of tissue homeostasis, exemplifying in a small living cylinder all the fundamental laws of cell-cell and tissue interactions. This life is revealed in this short synthesis.

Treatment of patients with multiple myeloma has shown considerable progress these last two decades. While autologous stem cell transplantation seems to be agreed as the "gold standard" of front-line treatment in the young patients, the result of IFM99-06 prospective study would probably lead to a change regarding treatment of elderly as patients who received the thalidomide-melphalan-prednison association had better overall survival than those who received either the standard melphalan-prednison association or an intensive treatment. The best innovative therapeutic concept is illustrated by the new molecules that target both the myeloma cells and the bone marrow microenvironment. Thus, thalidomide and derivatives (Revlimid and the Actimid) and Velcade have transformed considerably the history of multiple myeloma. They have not to be considered as competitors but rather complementary whose impact will probably come of their combination and their association with the intensive treatments. The issues of maintenance therapy and allogeneic stem cell transplantation in the treatment of patients with myeloma remain to be addressed.

Hematopoietic stem cell transplantation is the sole curative therapy for sickle cell anemia (SCA). This treatment is restricted to severe forms of disease. Lack of HLA-identical sibling donor is the major limiting factor for delivering this therapy. Conditioning regimen should be myeloablative. Post transplantation immunosuppressive medication is necessary for both graft tolerance and graft-versus-host disease (GvHD) control. For the majority of patients, bone marrow is source of stem cells. Alternative sources including related cord blood stem cells are under evaluation and promising. Outcome for 250 grafted patients worldwide is excellent. More than 85 % survive free of SCA and have a good quality of life although GvHD remains the main complication.