Blood cells最新文献

Study of the mechanisms regulating stem cells would be significantly facilitated if a purified population of stem cells were available. During the last 4 years, our laboratory has been engaged in enrichment of murine marrow cells for primitive hemopoietic progenitors. We primarily used marrow cells from mice treated with 150 mg/kg of 5-fluorouracil (5-FU), and our assay for the primitive progenitors was formation of multilineage colonies supported by a combination of interleukin-3 (IL-3) and IL-6. First, we found that post-5-FU marrow cells with a density of 1.0631-1.0770 g/cm3, negative for lineage-specific markers and positive for Ly-6A/E are routinely enriched for multipotential progenitors by approximately 800-fold. We then observed that J11d.2 and c-kit are additional useful markers for further enrichment of the primitive hemopoietic progenitors. Cell cycle-dormant primitive progenitors are primarily in the J11d.2+ fraction, whereas more mature progenitors are J11d.2-. The primitive progenitors express relatively low levels of c-kit, while more mature, actively cycling progenitors express high levels of c-kit. Combinations of these markers may be useful in enrichment of marrow cells of normal mice for primitive hemopoietic progenitors.

Interaction with stromal cells is known to be crucial for growth and differentiation of hematopoietic cells. To characterize adhesion molecules involved in this interaction, we examined adhesion of a panel of lymphoid, myeloid, and mast cell lines with stromal cells. We found that very late antigen-4 (VLA-4) and vascular cell adhesion molecule 1 (VCAM-1) were major adhesion molecules in lymphoid and myeloid cells, whereas myeloma cells adhered to stromal cells through hyaluronate. We investigated regulation of VLA-4 during differentiation of myeloid cells using a neutrophil precursor cell line, L-G3. Differentiation of neutrophils induced by granulocyte colony-stimulating factor was accompanied with down-regulation of VLA-4. Induced L-G3 cells adhered to stromal cells in proportion to the expression of VLA-4. Mast cells used two mechanisms to adhere to fibroblasts and stromal cells. They adhered to fibronectin through VLA-5 when stimulated with steel factor and also directly to membrane-anchored steel factor through c-kit.

Several studies on the gelation and oxygenation state of sickle red blood cells have been done under conditions of equilibrium. The kinetics of sickle hemoglobin (HbS) polymerization have also been studied extensively in fully deoxygenated HbS solutions. The issue of the relevance of these investigations to the physiological in vivo situation has not been addressed. Here, we use a theoretical model to compare theoretical equilibrium predictions of HbS polymer concentration and cellular oxygen content, previously validated against equilibrium data, with the corresponding values under physiologic oxygen unloading conditions. We also use the model to simulate polymerization in almost completely deoxygenated sickle erythrocytes, validate the theoretical polymerization curves against published data, and compare them with the corresponding curves from the dynamic oxygen unloading analyses. Our model shows that equilibrium predictions severely overestimate intracellular polymer concentrations and underestimate cellular oxygen content, during the unloading of oxygen. Also, the delay times to significant polymerization in the physiologic situation are substantially longer than the corresponding values measured in completely deoxygenated HbS solutions. These results indicate that in vivo HbS polymerization is strongly influenced by the rate of oxygen desaturation. Equilibrium estimates of intracellular polymer content, or polymerization kinetic data from fully deoxygenated solutions, could be misleading and should be used in the proper perspective.

Primitive human hematopoietic progenitors containing a high proportion of long-term culture-initiating cells (LTCICs) are found in the 34+DR- fraction of bone marrow mononuclear cells (BMMNCs). These progenitors adhere selectively to the 33/66-kD binding domain of fibronectin and to the FN-CHII binding site, unlike more committed progenitors, which adhere less selectively to fibronectin components. These differences in adhesion to stromal components may explain selective homing and release of progenitors at varying levels of differentiation from the marrow compartment. In additional studies, we demonstrate that cultivation of primitive progenitors in a stroma noncontact long-term culture allows both differentiation of primitive progenitors and conservation of LTCICs. These observations (1) demonstrate that expansion of primitive progenitors does not require stromal contact, (2) shed light on the regulatory role of stroma in myeloid differentiation, and (3) suggest strategies for both ex vivo myeloid progenitor expansion and retrovirus gene insertion. Finally, we demonstrate that a natural killer cell population can be derived from primitive hematopoietic progenitors in a modified long-term culture model. Our findings suggest an important role for marrow stroma in lymphoid differentiation from primitive progenitors and in expression of CD2, a lymphoid marker ordinarily associated with passage of T-lymphocyte progenitors through the thymus.

The ability to insert a gene into hematopoietic stem cells and achieve lineage specific expression of the transferred gene within hematopoietic organs following bone marrow transplantation would create the potential to effectively treat many genetic and acquired diseases. The use of retroviral vectors to achieve this purpose has been investigated extensively in animal models and most recently, in humans. In the murine model, about 20-30% of repopulating stem cells can be genetically modified with a retroviral vector. Peripheral blood stem cells, mobilized by cytokine administration in splenectomized animals, are readily transduced and are capable of long-term reconstitution of transplant recipients with genetically modified cells. Similar protocols have been utilized to transduce highly purified stem cells from rhesus monkeys. Although long-term repopulation with cells that persistently express the transferred gene has been achieved, the frequency of cells containing the vector genome is only about 1-2%. Genetic marking of human bone marrow and peripheral blood cells has been utilized to investigate their potential for contributing to long-term reconstitution following autologous transplantation. Future work will focus on improving gene transfer efficiencies for specific therapeutic applications.

We have taken advantage of the permissive environment of the preimmune fetus to achieve engraftment of hematopoietic stem cells (HSC) from fetal and postnatal human sources in sheep. The resulting chimeric lambs exhibited long-term multilineage (erythroid, myeloid, lymphoid) expression of donor cells that remained responsive to human-specific cytokines. The small size of the fetus allowed the assessment of the engraftment potential of relatively small numbers of highly characterized human HSC populations, while the large size of the chimeric sheep permitted the long-term evaluation of the HSC activity and response in vivo. The human/sheep xenograft may offer a useful large animal model for the assay and long-term study of the human HSC subsets.

Recent studies in our laboratory have shown striking differences in the functional properties of candidate hematopoietic stem cells purified from fetal, neonatal, and adult human tissues. These differences include the ability to produce CD34+ cells, the turnover rate, and the fraction of cells that respond to a mixture of cytokines. All these parameters decrease with the age of the cell donor, and some of these observations are summarized here. Extensive qualitative changes in hematopoietic cells from various stages of development should be taken into account in the design of novel therapeutic strategies.

Cord blood transplant has been performed in children with malignant and nonmalignant hematological disorders. Most often, the donor was an HLA-identical or a partially mismatched sibling. The results seem to demonstrate that one cord blood contains enough hematopoietic stem cells to reconstitute the marrow in a child, the incidence of graft vs. host disease (GVHD) has been very low in matched transplants, and the immune reconstitution has not been different from a bone marrow transplant. In Paris, seven children have received an HLA-identical sibling cord transplant; five are alive and well, and two had no engraftment. Several questions remain: results in adults, use of cord blood for mis-matched or matched unrelated transplants, standardization of methods of collection, cryopreservation, and banking. A European cord blood banking group has been created to coordinate this research.