Acute lymphoblastic leukemias (ALL) represent malignant clonal proliferations of stem cells committed in lymphoid differentiation, B or T-cell ALL. Clonal chromosomal abnormalities are found in 80% children and 70% adult cases. They are associated with an independent prognostic value which modifies the therapeutic approach and therefore karyotyping at diagnosis is mandatory. Molecular techniques such as FISH and RT-PCR are very helpful too as cryptic chromosomal abnormalities have been described. In this review, numerical and structural abnormalities are described: frequency, diagnosis and prognosis value as well as genes involved in structural abnormalities.

The staging of murine cardiomyocyte specification and determination was investigated in cultures of tissue explants from pre- and postgastrulation embryos and after transplantation of cardiac or cardiogenic tissues from mouse embryos into chick embryos. The development of cultured and transplanted cells in cardiomyocytes was evaluated by testing the expression of several cardiac transcription factor genes (Nkx 2.5, eHAND, dHAND, GATA 4), alpha cardiac actin, and beta myosin heavy chain protein. In vitro analyses showed that cells with the potential to form cardiac muscle were present prior to gastrulation in 6.5-day postconception (dpc) epiblasts. Although, as shown by in vivo experiments, neurectodermal derived structures did not influence cardiogenesis in epiblast transplants, these transplants did not exhibit full cardiogenic cell differentiation in the chicken environment. In in vitro culture, the neurectoderm also had no effect on murine cardiomyogenesis. In contrast, the presence of endoderm in explants between mid- and late streak stages stimulated emerging mesodermal cells to adopt a myocardial pathway. Mesoderm from late streak explants (7.5 dpc) was capable of differentiating into a cardiac phenotype in the avian heterotopic environment, indicating that the specification of cardiac precursors became irreversible around the late streak stage in mouse embryo.

The international standard for histologic classification of lung tumours is that proposed by the WHO/IASLC (1999). Ninety percent of these cancers are distributed in squamous cell carcinoma, adenocarcinoma, small cell carcinoma, and large cell carcinoma, all related to tobacco smoke carcinogens, responsible for 90% of tumours. As a consequence of their derivation from totipotential stem cells, heterogeneity is common. They arise from multifocal preinvasive lesions reflecting the "field cancerization" process of the entire bronchial tree. All together 1999 WHO classification offers a valuable hallmark for clinical, biological, and epidemiological studies, and a solid basis for inclusion of patients in randomized therapeutical trials as well as for interpretation of sensibility or resistance to new therapeutic agents.

The existence of a growth and regeneration cycle makes the hair follicle a true paradigm of tissue homeostasis. Analysis of about 9000 cycles led us to propose a stochastic model of human hair dynamics. The existence of hair cycles implies that stem cells must be cyclically activated and hair melanin unit has to be renewed. Using different markers, we were able to identify two distinct epithelial stem cell reservoirs, located in the upper and lower thirds of the anagen hair follicle outer root sheath. These two reservoirs fuse during the regression phase and individualize again in the new forming anagen hair follicle. Using a set of antibodies specific of melanocyte lineage and melanogenesis, pigmentation unit turnover was followed throughout the entire hair cycle. In the terminal anagen hair, active melanocytes were localized on top of the dermal papilla, while amelanotic melanocytes were identified in the upper third of the outer root sheath (ORS). Those amelanotic melanocytes located in upper ORS probably represented a melanocyte reservoir for successive hair generation, since at the induction of anagen phase, some melanocytes were committed to cell division and melanogenesis was turned on, but only in the nascent hair bulb, close to the dermal papilla.

To study time-scheduled regimens in the treatment of tumours by cytotoxic drugs delivered by IV injection, we propose a mathematical model of the action of a chemotherapy on the population of tumoral cells on the one hand, on a population of fast renewing healthy cells on the other hand. We chose for model parameter identification the treatment by oxaliplatin of Glasgow Osteosarcoma in mice.

The application of stem cell therapy to cure degenerative diseases offers immense possibilities, but the research in this field is the subject of ethical debates raised by the question of destructive research on early human embryos. Stem cells taken in the adult constitute an alternative to human embryonic stem cells, but our knowledge on totipotent or pluripotent cells is currently insufficient. Furthermore, many questions must be solved before selection and differentiation of these cells in a given cellular type can be controlled on a routine basis. What are the molecular characteristics of an adult stem cell? What are the mechanisms involved in cell reprogramming? Which signals control stem cell replication and differentiation? Basic research activities must be carried out in order to clarify all these points. In this context, the regeneration of vertebrate appendages provides a model for this type of research. The regeneration process is defined by both the morphological and functional reconstruction of a part of a living organism, which has previously been destroyed. But why are some vertebrates able to regenerate complex structures and others apparently not? Among most vertebrates, the capacity to regenerate is limited to some tissues. It is however possible to observe the regeneration of appendages (limb, tail, fin, jaw, etc.) among several amphibians and fish. This regeneration leads to re-forming of the amputated part with a complete restoration of its shape, segmentation and function. Why is the amputation of limbs not followed by regeneration in mammals and birds: absence of stem cells, absence of recruitment signals for these cells, or absence of signal receptivity? This review constitutes a report on the current understanding of the basis of on regeneration of legs in tetrapods and of fins in fish with an emphasis in the role of the nervous system in this process.

Systolic heart failure is mainly due to a decreased left ventricular systolic function after myocardial infarction. Despite significant improvements in medical management of heart failure, the prognostic remains poor, with a 5-years survival only of 30%.

The ability to identify, select and manipulate stem cells from tissues opens the way to regenerative medicine. In the field of hematopoiesis, our increasingly precise knowledge of the mechanisms of production and regulation of blood cells should permit in the near future the production of cells in sufficient quantity to be of interest for transfusion. Our present capacity to amplify hematopoietic stem cells and direct their differentiation towards the erythroid line is reviewed here. A procedure is described for the amplification of CD34 + hematopoietic stem cells of placental origin, based on the sequential use of specific combinations of growth factors in a given serum-free medium. Such conditions allowing the terminal maturation in vivo of large numbers of precursors produced ex vivo permit one to envisage important transfusion perspectives. A complementary source of red blood cells would in fact improve our transfusion capacity.

In order to effectively perceive the huge diversity of antigenic determinants to which it is confronted, the immune system uses referring internal images from self. The major histocompatibility complex constitutes the main reference to self, essential to the operating system of T and NK lymphocytes. It is involved in shaping the T operating repertoire in the thymus, where each differentiating thymocyte, with its TCR interacting with the MHC-peptide self complexes exposed by thymic presenting cells, should answer to both questions: Is it really necessary (positive selection) Is not dangerous (negative selection)? Once in periphery, naive T lymphocytes will undergo an homeostatic control helping their survival through the same contacts between TCR and MHC-peptide self complex than those which allowed the thymic positive selection. In a more hypothetic way, it is possible that contact between a T lymphocyte and the rare foreign MHC-peptide complexes spread at the surface of antigen presenting cell, is not sufficient to initiate its activation. Some arguments exist to involve the MHC-peptide self complexes themselves in the activation process.Finally, the MHC also constitutes a quality referential for the NK lymphocytes. When a somatic cell, infected by a virus or transformed, repress the expression of one or more of its class I HLA alleles, this absence of the self is perceived by the NK lymphocytes which proceed to its elimination through cytolysis. This disposition to sanction the non-self is also used for therapeutic purpose in the case of a non HLA identical allogenic hematopoïetic stem cells graft.

Recognition of the importance of immune cells present in a hematopoietic graft has resulted in a significant change in the perception of allogeneic hematopoietic transplantation. Such a transplant modality is now perceived has a very efficient form of adoptive allogeneic immunotherapy unfortunately associated with significant toxicity.

Our increasing knowledge of the mechanisms of blood regulation allows us to envisage the production of cells in quantities sufficient enough to have transfusional interest. We present the state of the art on our capacity to amplify hematopoietic stem cells (HSC) and to force their differentiation into the erythroid lineage. We describe the difficulties met ex vivo for simultaneously reaching a very high level of expansion to have meaningful transfusional interests and obtaining a complete terminal maturation up to enucleation. We describe here a procedure for massively amplifying HSC from human cord blood to produce erythroblastic precursors able to differentiate in vivo into mature red cells after infusion. Although we do not suggest to replace classical blood transfusion, we consider that this approach may become complementary.