During vertebrate embryonic development, the endothelial and hemopoietic systems are the first system to be specified. In this review, we will summarize recent findings about the molecular mechanisms responsible for the successive steps of the development of these systems: the differentiation of mesodermal cells to endothelial and hemopoietic cells, their proliferation and their interactions to form the vascular system.

Langerhans cell histiocytosis is an uncommon clonal disorder. Its reactional or genetic nature is debated.

Cytokines (cyto:cell; kine:factor) are produced by cells and serve as chemical messengers for one type of intracellular communication. Cytokines play a central role in host defense mechanisms. Defense against infectious and tumoral disease depends on nonspecific myelomonocyte defenses in conjunction with specific immune processes. Both systems are regulated by various leukocytes in the blood and tissue. All these cell components are produced in the bone marrow from hematopoietic stem cells. Cytokines are soluble messengers allowing deployment and coordination of all cell systems. Despite the complexity of the cytokine network, we now have a better understanding of the interactions between the different components determining secretion and activity of these mediators. This knowledge may hold the promise of better control of immune and inflammatory responses. Experimental data shows that the cytokine balance can be modulated in auto-immune, immune deficiency, and malignant diseases, opening up new perspectives for therapy and perhaps vaccination.

Characterization of a new family of G protein-coupled receptors is reported. Expression of these receptors is associated with endothelial lineage. Cloning of the Xenope X-msr receptor allowed to show that embryonic expression of this receptor occurred in the heart and developing primary blood vessels. Furthermore, within these cardiovascular structures, expression was restricted to the endothelial layer. Because structural similarities with the human orphan receptor h-APJ were found, the msr/apj receptor was cloned in mice. This showed that embryonic expression of this receptor was also confirmed to endothelial precursors. Thus, this receptor is the orthological equivalent in mice to the amphibian receptor X-msr. Molecular phylogenesis studies showed that the X-msr, msr/apj, and h-APJ receptors shared considerable homology with two CXC chemokine receptors, namely LCR1, whose name was recently changed to CXCR4, and RDC1, which is structurally similar to the CXCR2 receptor. The human h-APJ receptor is a co-receptor for entry of the HIV into T cells, a property associated only with CXC chemokine receptors in the lymphocyte population. These data suggest that this new signaling system may participate in endothelial precursor migration during developmental angiogenesis and in endothelial cell migration and proliferation during neoangiogenesis in adults.

Whereas the origin and migration of endothelial cells (ECs) have been studied primarily in the avian embryo, the molecular mechanisms governing these events in birds and mammals were unraveled following the identification of specific growth factors and of their receptors. In particular, analytic and experimental studies of vascular endothelial growth factor (VEGF) and its receptors have provided significant insights into the developmental biology of the vascular system. VEGFR2 is the earliest marker expressed by EC precursors in chickens and mice. Based on the localization of VEGFR2-positive cells in the avian embryo and on findings from clonal culture experiments, two types of EC precursors can be differentiated as early as the gastrulation stage, namely posterior mesoderm hemangioblasts capable of differentiating into both ECs and hematopoietic cells and anterior angioblasts capable of yielding only ECs.

The avian model provides an experimental approach for dissecting the origin, migrations, and differentiation of cell lineages in early embryos. In this model, the endothelial network was shown to stem from both the somites and the splanchnopleural mesoderm. The somite line age produces only endothelial cells, whereas the splanchnopleural line age also produces hematopoietic stem cells. Potentialities of the mesoderm are determined by a positive influence from the endoderm and a negative influence from the ectoderm. A novel mode of blood-borne angiogenesis is also described.

We report hereby the results of the french multicentric randomized PEGASE 04 protocol established to evaluate the impact on survival of high-dose chemotherapy over conventional chemotherapy for MBC patients.

A study of cancellous bone in the femoral upper metaphysis was performed using a micro-camera. In osteoporotic disease, a qualitative disorganization of bone and vessels occurs. Bone lamellae break off or fracture. Lacunae fine down some bone plates. Connective tissue replaces part or the totality of the hard structure. Some vessels are functional, some are not. Some walls disappear and flux runs out of their lumen, producing hematomae. Quantitative bone loss results in cavities. Adipocyte cells fill in the gaps. Browish deposits settle on the lamellae. It is suggested that these are either settling stem pigments from the breakdown of hemoglobin or micro-thrombuses.

Allogeneic peripheral blood hematopoietic stem cell transplantation is being evaluated in a randomized French study comparing the use of peripheral blood stem cells vs. bone marrow graft stem cells. In order to standardize immunohematological (IH) assessment and transfusion practices within our protocol, we made suggestions to 25 allo-transplantation French centers on the following elements: pre-inclusion IH assessment, IH exclusion criteria, transfusion rules, post-transplantation IH surveillance and treatment of hemolysis. The analysis of their responses to our suggestions led us to elaborate recommendations which were approved and implemented by the French Bone Marrow Transplantation Society (SFGM). These recommendations concern the transfusion practice in the general framework of allogeneic hematopoietic stem cell transplantation and can therefore be considered as referential.

To evaluate the improvement of the ocular surface after limbal autograft in patients with unilateral limbal stem cell deficiency related to chemical burns.

A comprehensive understanding of the radiobiological bases of total body irradiation (TBI) is made difficult by the large number of normal and malignant tissues that must be taken into account. In addition, tissue responses to irradiation are also sensitive to associated treatments, type of graft and a number of patient characteristics. Experimental studies have yielded a large body of data, the clinical relevance of which still requires definite validation through randomized trials. Fractionated TBI schemes are able to reduce late normal tissue toxicity, but the ultimate consequences of the fractional dose reduction do not appear to be equivocal. Thus, leukemia and lymphoma cells are probably more radiobiologically heterogeneous than previously thought, with several cell lines displaying relatively high radioresistance and repair capability patterns. The most primitive host-type hematopoietic stem cells are likely to be at least partly protected by TBI fractionation and may hamper late engraftment. Similarly, but with possibly conflicting consequences on the probability of engraftment, the persistence of a functional marrow stroma may also be fractionation-sensitive, while higher rejection rates have been reported after T-depletion grafts and fractionated TBI. In clinical practice (as for the performance of relevant clinical trials), the influence of these results are rather limited by the heavy logistic constraints created by a sophisticated and time-consuming procedure. Lastly, clinicians are now facing an increasing incidence of second cancers, at least partly induced by irradiation, which jeopardize the long-term prospects of otherwise cured patients.

Adhesion molecules play a major role in the regulation of normal hematopoiesis. Precursor/cell matrix/endothelial interactions determine retainment or release of hematopoietic cells from the bone marrow microenvironment. Consequently, changes in the affinity or quantitative expression of adhesion molecules on either the bone marrow stroma or the cell precursor component during a malignant process will affect cell attachment. Adhesion molecules, therefore, are modulator molecules which alter the biological behavior of leukemic cells in terms of migration and localization properties. Several membrane-bound adhesion molecules and, in some instances, their soluble counterparts which may be biologically active, have been described in acute myeloid leukemia. The panel of receptors expressed demonstrates heterogeneity between various cases of acute myeloid leukemia. There is generally no correlation between the adhesion receptor phenotype and the morphologic or clinical features of acute leukemia. These receptors function in interactions of leukemic blasts with the cellular and matrix components of the marrow microenvironment. Adhesive interactions may influence the proliferation and survival of leukemic cells. However, the precise role that these molecules play in the generation and sustenance of the leukemic state remains undetermined.

The newborn immune system differs quantitatively and functionally from adults. At birth, the immune system is partially immature, resulting in deficiency in cell-mediated cytolysis, immunoglobulin synthesis and cytokine production. The most clearly defined deficit in neonatal phagocytosis defenses is diminished neutrophil storage. T cell function is diminished, including T cell-mediated cytotoxicity and T cell help for B cell differentiation. Selective decreases in cytokine production by T cells may contribute to all of these deficits. One of the fundamental differences between adults and newborns for T cell functions resides in whether or not the patient had prior exposure to antigens. Significant immune responses to antigens can be obtained in the neonatal period. These responses are qualitatively different from those induced in adults with a predominance of TH2 pattern.

GENERAL DATA: Human herpesvirus 6 (HHV-6) infects 90% of the human population before the age of 4 years, recognized as a childhood disease (sixth disease) or with no clinical manifestation. HHV-6 DNA has partial homogly with cytomegalovirus DNA. Two variants, A and B, are known. The main target cells are CD4+ T cells and macrophages via a partially elucidated mechanism. Primary infection is followed by a latency period and episodes of reactivation. Truly protective targets of the immune response are unknown. POORLY UNDERSTOOD NATURAL HISTORY: In organ transplant or hematopoietic stem cell recipients, the natural history of HHV-6 infection is difficult to establish because of small sample size in certain series, the lack of controls both for patients and samples and differences in the sensitivity of diagnostic tests. Serology is non-specific and cannot be used to study reinfection. Different studies have relied on culture and isolation, detection of viral antigens with monoclonal antibodies and PCR using mononucleated cells, serum and plasma.

MOLECULAR CYTOGENETICS: New fluorescent in situ hybridization (FISH) techniques have been developed using fluorescent non-radioactive DNA probes. FISH: Based on the complementary of nucleotides FISH enables visualization and localization of a DNA fragment on chromosomes by hybridizing the complementary DNA sequence, the probe. Many types of tissues can be analyzed, for example hematopoietic cells in blood or bone marrow, amniotic cells, trophoblasts, fibroblasts, gamete or tumoral cells.

Gene transfer in hematopoietic cells is intended to treat patients with malignant disease and inherited monogenic (hematological, immunological, and metabolic) disorders. Hematopoietic progenitor or stem cells are a favoured target for gene therapy because these cells are easily withdrawn from the patient, expanded and genetically modified ex vivo and then reinjected into the organism. Retroviral vectors allow an efficient transfer of the genes of interest. Transduction of stem cells leads to a stable expression of the transgene for long periods of time. However, we are at the beginning of this new therapeutic application, the technique was being already successful in very few cases. Problems to be solved are mainly in the understanding of the physiology of the hematopoietic stem cell and in the improvement of technical qualities of the vectors for a targeted gene transfer in vivo.

Transferrin receptor is a key protein for the cellular uptake of transferrin iron. The highest number of transferrin receptors is on the surface of erythroblasts. The released iron is used for hemoglobinosynthesis. Regulation occurs at mRNA level depending on the intracellular iron concentration. The synthesis of ferritin and transferrin receptor are regulated in an opposite manner. Serum transferrin receptor is a truncated monomeric form of the cellular receptor. Most of the circulating receptors come from erythroid marrow precursors. Its level mirrors the total tissue receptor mass, it depends on the rate of erythropoiesis and on the iron status. Serum transferrin receptor is easily measured by Elisa methods but the lack of standardization triggers large differences in the results. Unlike ferritin, the concentration of serum transferrin receptors is unaffected in inflammatory diseases, infections, malignancies or cytolysis. In these conditions its measurement is particularly valuable for assessing an associated iron deficiency. It is a very useful tool for the diagnosis of different causes of anemia. In chronic renal failure serum transferrin receptor can predict whether patients will respond to rHu EPO therapy.