Mechanisms of cell commitment in myeloid cell differentiation

The hematopoietic developmental hierarchy originates with a rare population of lymphohematopoietic stem cells that are capable of extensive self-renewal as well as the continuous generation of more developmentally restricted progeny. The generation of mature blood cells from these pluripotent hematopoietic stem cells involves the highly regulated progression through successive stages involving commitment to a specific cell lineage, terminal differentiation of lineage-restricted progenitors, and growth arrest. Although the differentiation commitment of stem cells may be intrinsically determined, it is apparent that a wide variety of external and internal stimuli can influence and modulate lineage choice and differentiation. These factors cooperate with cellular transcription factors to activate or repress the expression of genes responsible for lineage choice, diverse mature phenotypes, and cell cycle progression. The extrinsic and genetic mechanisms that orchestrate the differentiation commitment and myeloid lineage restriction of pluripotent stem cells are of fundamental importance in the regulation of hematopoiesis. The elucidation of these mechanisms of normal myeloid differentiation has provided instrumental insights into the biology of leukemia and other hematopoietic disorders.

Growth factor-mediated terminal differentiation of chronic myeloid leukemia

Expression of the BCR-ABL chimeric gene in chronic myeloid leukemia results in the inhibition of apoptosis, a genetically programmed process of autonomous cell death. BCR-ABL and other genetic factors that suppress apoptosis confer cross-resistance to cytotoxic agents with diverse mechanisms of action. Eradication of the chronic myeloid leukemia clone requires strategies that circumvent this inherent resistance to cytotoxic therapy. We have determined that BCR-ABL expression augments the sensitivity of hematopoietic cells to growth factor-mediated signals of differentiation; hematopoietic growth factors induce the selective terminal differentiation of chronic myeloid leukemia progenitors at concentrations that allow optimal growth of normal progenitors. Hematopoietic growth factors may be an effective strategy for the elimination of cytotoxic therapy-resistant leukemic cells by inducing their terminal differentiation while allowing concomitant expansion of coexistent normal hematopoietic progenitors.

Inhibition of apoptosis by BCR-ABL in chronic myeloid leukemia

BCR-ABL expression is presumed to effect clonal expansion in chronic myeloid leukemia (CML) by deregulation of cell proliferation. However, most studies have found that relative rates of cell proliferation are not increased in CML. Moreover, we found that CML progenitors display a normal proliferative response to growth factors and do not manifest greater proliferative potential than normal progenitors. Growth of malignancies depends on an imbalance between the rate of cell production and the rate of cell death. We found that BCR-ABL expression inappropriately prolongs the growth factor-independent survival of CML myeloid progenitors and granulocytes by inhibiting apoptosis, a genetically programmed process of active cell death; inhibition of BCR-ABL expression by antisense oligonucleotides reversed the suppression of apoptosis as well as the enhancement of survival. The decreased rate of programmed cell death appears to be the primary mechanism by which BCR-ABL effects expansion of the leukemic clone in CML.

Biology of chronic myeloid leukemia and its relevance to autologous bone marrow transplantation

Because of the relative resistance of chronic myeloid leukemia (CML) progenitors to most standard cytotoxic agents, marrow-ablative doses of drugs or radiotherapy followed by allogeneic bone marrow transplantation (BMT) remain the only curative option for patients with CML. However, the effectiveness of allogeneic BMT is limited by the toxicity of graft-versus-host disease and the lack of histocompatible donors for most patients. Although it avoids these major obstacles of allogeneic BMT, autologous BMT has not been effective in CML because of the inability to purge CML from the autologous graft and the absence of the allogeneic immunologic antitumor activity. Techniques that allow the clinical isolation of normal stem cells from CML marrow combined with novel posttransplantation immunotherapeutic approaches should make autologous BMT a curative treatment for CML in the near future.

A tool to fill the gap. Developing a wound risk assessment chart for children

1. Consistent monitoring and assessment of wounds is vital in children as well as adults. 2. There are anatomic, physiological and psychological differences between adults and children, of which nurses should be aware. 3. To date, the practice of paediatric risk assessment is an unknown entity. 4. A pressure sore risk assessment chart was developed specifically for use with children.

Isolation and analysis of eight exe genes and their involvement in extracellular protein secretion and outer membrane assembly in Aeromonas hydrophila

The exeE gene of Aeromonas hydrophila has been shown to be required for the secretion of most if not all of the extracellular proteins produced by this bacterium. In addition, an exeE::Tn5-751 insertion mutant of A. hydrophila was found to be deficient in the amounts of a number of its major outer membrane proteins (B. Jiang and S. P. Howard, J. Bacteriol. 173:1241-1249, 1991). The exeE gene and the exeF gene were previously isolated as part of a fragment which complemented this mutant. In this study, we have isolated and sequenced a further eight exe genes, exeG through exeN, which constitute the 3' end of the exe operon. These genes have a high degree of similarity with the extracellular secretion operons of a number of different gram-negative bacteria. Marker exchange mutagenesis was used to insert kanamycin resistance cassettes into three different regions of the exe operon. The phenotypes of these mutants showed that in A. hydrophila this operon is required not only for extracellular protein secretion but also for normal assembly of the outer membrane, in particular with respect to the quantities of the major porins. Five of the Exe proteins contain type IV prepilin signal sequences, although the prepilin peptidase gene does not appear to form part of the exe operon. Limited processing of the ExeG protein was observed when it was expressed in Escherichia coli, and this processing was greatly accelerated in the presence of the prepilin peptidase of Pseudomonas aeruginosa.

BCR-ABL gene rearrangement and expression of primitive hematopoietic progenitors in chronic myeloid leukemia

Chronic myeloid leukemia (CML) is characterized by an initial chronic phase of expanded yet orderly clonal hematopoiesis that is distinguished by the BCR-ABL gene rearrangement. We found that although the mature myeloid compartment in patients with CML was expanded and entirely derived from the dominant leukemic clone, the primitive hematopoietic progenitor compartment did not show a corresponding expansion and was substantially enriched for cells without the BCR-ABL gene rearrangement. More importantly, primitive progenitors exhibiting the BCR-ABL gene rearrangement did not express either the BCR-ABL hybrid mRNA or fusion protein (P210). Expression of P210 protein and BCR-ABL mRNA increased with myeloid commitment in vivo as well as with growth factor-induced proliferation and differentiation of the primitive CML progenitors in vitro. This differential expression of BCR-ABL between primitive and mature CML progenitors may explain the expansion of the leukemic clone at the level of mature myeloid progenitors and granulocytes without a concomitant expansion of primitive CML progenitors. Because BCR-ABL mRNA is minimally expressed or may be absent in primitive CML progenitors, these cells may escape detection by reverse transcriptase-polymerase chain reaction and eradication by antisense oligonucleotides targeted against BCR-ABL mRNA.

Short-term focused cognitive therapy of panic disorder with aerophobia: a case report

The efficacy of focused cognitive therapy was evaluated in the short-term treatment of a flight instructor suffering from panic disorder with aerophobic and agoraphobic symptoms. A modified panic induction technique (hyperventilation) was used in session to activate the specific bodily sensations he typically experienced during panic attacks. The patient was then asked to articulate his catastrophic interpretations of the physiological sensations he was experiencing and taught to re-interpret them in a non-catastrophic manner, which enabled him to reduce his symptoms to a more manageable level. After four sessions of focused cognitive therapy, the patient's panic and phobic symptoms were significantly reduced and no longer interfered with his daily functioning. Posttreatment follow-up at 6 and 9 months revealed that the patient was completely free of panic while flying.

Impact of therapeutic management on use of seclusion and restraint with disruptive adolescent inpatients

Use of seclusion and restraint on three inpatient adolescent psychiatric units was examined during two five-month periods before and after implementation of a "therapeutic management" protocol. Under the protocol, staff classified disruptive behaviors into four stages and provided verbal and behavioral interventions to control behavior at each stage. Patients who required seclusion and restraint had significant latitude to determine the timing of their release from the interventions and met with staff one hour and 24 hours after their release to explore alternatives to aggression. The number of episodes of seclusion and restraint fell by 64 percent after the protocol was adopted, and the number of patients who required those interventions dropped by 39 percent. The mean duration of episodes of seclusion and restraint was reduced by 59 percent. Therapeutic management provides a corrective experience by addressing the developmental needs, deficient cognitive skills, and poor internalized controls of disruptive adolescents.