Meir Lahav

G-CSF induces stem cell mobilization by decreasing bone marrow SDF-1 and up-regulating CXCR4

Granulocyte colony-stimulating factor (G-CSF)–induced hematopoietic stem cell mobilization is widely used for clinical transplantation; however, the mechanism is poorly understood. We report here that G-CSF induced a reduction of the chemokine stromal cell–derived factor 1 (SDF-1) and an increase in its receptor CXCR4 in the bone marrow (BM), whereas their protein expression in the blood was less affected. The gradual decrease of BM SDF-1, due mostly to its degradation by neutrophil elastase, correlated with stem cell mobilization. Elastase inhibition reduced both activities. Human and murine stem cell mobilization was inhibited by neutralizing CXCR4 or SDF-1 antibodies, demonstrating SDF-1–CXCR4 signaling in cell egress. We suggest that manipulation of SDF-1–CXCR4 interactions may be a means with which to control the navigation of progenitors between the BM and blood to improve the outcome of clinical stem cell transplantation.

Induction of the chemokine stromal-derived factor-1 following DNA damage improves human stem cell function

The chemokine stromal-derived factor-1 (SDF-1) controls many aspects of stem cell function. Details of its regulation and sites of production are currently unknown. We report that in the bone marrow, SDF-1 is produced mainly by immature osteoblasts and endothelial cells. Conditioning with DNA-damaging agents (ionizing irradiation, cyclophosphamide, and 5-fluorouracil) caused an increase in SDF-1 expression and in CXCR4-dependent homing and repopulation by human stem cells transplanted into NOD/SCID mice. Our findings suggest that immature osteoblasts and endothelial cells control stem cell homing, retention, and repopulation by secreting SDF-1, which also participates in host defense responses to DNA damage.

Thrombotic complications in essential thrombocythemia with relatively low platelet counts

Essential thrombocythemia (ET) is often associated with thrombotic and hemorrhagic complications, mostly at platelet counts exceeding 600 × 109/L. There are, however, a few reports of such complications in ET at considerably lower platelet levels and the therapeutic approach to affected patients with relatively low platelet counts is still controversial. In the present study, the first to directly address the issue of hemostatic manifestations at relatively low platelet counts, we have determined the lowest platelet counts associated with such manifestations in 56 consecutive ET patients. Clinical manifestations related to ET were recorded in 46 (82%) patients. Of the symptomatic patients, 32 (70%) had symptoms at platelet counts lower than 600 × 109/L, 23 (50%) at counts lower than 500 × 109/L, 10 (22%) at counts lower than 400 × 109/L, and 6 patients (13%) at platelet counts as low as 300–350 × 109/L. Severe complications occurred at platelet counts lower than 600 × 109/L in 10 patients (22%), lower than 500 × 109/L in 7 (15%), and at lower than 400 × 109/L in 2 (4%). Thrombotic neurologic symptoms were the most common (31 patients, 67%), followed by peripheral vascular symptoms (17 patients, 37%); hemorrhagic complications were relatively rare (3 patients, 7%). In most cases, cessation or improvement of clinical manifestations was observed only after further reduction in platelet counts. In conclusion, thrombotic manifestations, including severe ones, are not uncommon in ET at relatively low platelet counts. We recommend that symptomatic patients with relatively low platelet counts be treated and the platelet counts further reduced well into the lower normal range. Am. J. Hematol. 56:168–172, 1997.

Telomere dynamics in arteries and mononuclear cells of diabetic patients: effect of diabetes and of glycemic control.

Telomeres serve as a mitotic clock and biological marker of senescence. Diabetes mellitus (DM) is associated with damage to target organs and premature aging. We assessed the effect of glycemic control on telomere dynamics in arterial cells of 58 patients undergoing coronary artery bypass and in mononuclear blood cells of other diabetic (32 type I and 47 type II) patients comparing well controlled to uncontrolled patients. All were compared to age-dependent curve of healthy controls. Telomeres were significantly shorter in the arteries of diabetic versus non-diabetic patients (p=0.049) and in mononuclear cells of both type I and type II diabetes. In all study groups good glycemic control attenuated shortening of the telomeres. In arterial cells good glycemic control attenuated, but not abolished, the telomere shortening. In type II DM the mononuclear telomere attrition was completely prevented by adequate glycemic control. Telomere shortening in mononuclear cells of type I diabetic patients was attenuated but not prevented by good glycemic control. Results of this study suggest that diabetes is associated with premature cellular senescence which can be prevented by good glycemic control in type II DM and reduced in type I DM.

Late-Onset Neutropenia After Rituximab Treatment Case Series and Comprehensive Review of the Literature

Rituximab is a chimeric monoclonal antibody against CD20 that is used mainly for the treatment of CD20-positive lymphoma. Recently, its use has been expanded to include treatment of other nonmalignant diseases such as rheumatologic diseases and autoimmune cytopenia. Correlating with the increased use of rituximab has been an increased number of reports of its late adverse effects. One of these is late-onset neutropenia (LON). Most investigators define LON as grade III-IV neutropenia occurring 3-4 weeks after the last treatment with rituximab, in the absence of an alternative explanation for the neutropenia. We report 6 cases of LON identified in our institution. Four patients were treated for diffuse large B-cell lymphoma, and 2 patients for follicular lymphoma. Median patient age was 68 years (range, 33-83 yr); LON appeared after a median interval of 77 days (range, 42-153 d) and lasted for a median of 5 days (range, 1-45 d). Five of the 6 patients presented with infectious complications, and 4 patients experienced recurrent episodes of neutropenia. One patient presented with LON and concomitant subacute pulmonary disease that was attributed to rituximab therapy. In addition to our own case series we present a systematic review of the literature, which we performed to compile data to describe better the syndrome of LON. Systematic studies, case series, and case reports were extracted. Most studies dealing with LON are retrospective by design and are limited by the heterogeneous populations included in the analysis. The incidence of LON is generally reported to be in the range of 3%-27%. Data regarding populations at risk are not consistent, and in some instances are conflicting. Patients considered at increased risk of LON include patients after autologous stem cell transplantation, patients treated for acquired immunodeficiency syndrome (AIDS)-related lymphoma, and patients treated with purine analogues. Patients who received previous cytotoxic treatment as well as those treated with more intensive chemotherapy or with chemotherapy in combination with radiotherapy are also considered to be at risk of LON. In addition, advanced stages of disease and having received multiple doses of rituximab are risk factors for LON. The mechanism of LON is poorly understood. Direct toxicity is very unlikely. Some speculate that there may be an infectious etiology involved, as well as an antibody-mediated process, but these ideas have not been substantiated. The concept of a lymphocyte subpopulation imbalance leading to LON has been presented based on the demonstration of T-LGL in peripheral blood and bone marrow of patients with LON. Perturbations in stromal-derived factor-1 and in the BAFF cytokine have also been discussed as potential players in the pathogenesis of LON. A recent study correlated specific polymorphism in the immunoglobulin G Fc receptor FC&ggr;RIIIa 158 V/F with increased rates of LON. The clinical significance of LON is important because it may affect treatment strategies. Of note, infectious complications are not very frequent and not very severe. Pooling data from the major retrospective studies reveals an infection rate of 16.9%. Most infections were mild and resolved promptly. One death occurred from infection during neutropenia. Repeated episodes of LON are not uncommon, but it is so far impossible to identify those patients at risk of these relapsing episodes of LON. Re-treatment with rituximab after LON may result in recurrent episodes, but the implications and risks are uncertain at the present time. The role of growth factors once LON appears is ill defined, and the decision to use them should be made on a case-by-case basis. Abbreviations: ACVB = adriamycin, cyclophosphamide, vindesine, and bleomycin, AIDS = acquired immunodeficiency syndrome, ASCT = autologous stem cell transplantation, CT = computed tomography, DLBCL = diffuse large B-cell lymphoma, G-CSF = granulocyte colony-stimulating factor, LON = late-onset neutropenia, NHL = non-Hodgkin lymphoma, R-CHOP = rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone, R-DA-EPOCH = dose-adjusted etoposide, prednisone, vincristine, cyclophosphamide, and hydroxydaunorubicin with rituximab, SDF-1 = stromal-derived factor 1, T-LGL = T-cell large granulocyte lymphocyte.

Imatinib mesylate (Gleevec) downregulates telomerase activity and inhibits proliferation in telomerase-expressing cell lines

Imatinib mesylate (IM) is a tyrosine kinase inhibitor, which inhibits phosphorylation of downstream proteins involved in BCR-ABL signal transduction. It has proved beneficial in treating patients with chronic myeloid leukaemia (CML). In addition, IM demonstrates activity against malignant cells expressing c-kit and platelet-derived growth factor receptor (PDGF-R). The activity of IM in the blastic crisis of CML and against various myeloma cell lines suggests that this drug may also target other cellular components. In the light of the important role of telomerase in malignant transformation, we evaluated the effect of IM on telomerase activity (TA) and regulation in various malignant cell lines. Imatinib mesylate caused a dose-dependent inhibition of TA (up to 90% at a concentration of 15 μM IM) in c-kit-expressing SK-N-MC (Ewing sarcoma), SK-MEL-28 (melanoma), RPMI 8226 (myeloma), MCF-7 (breast cancer) and HSC 536/N (Fanconi anaemia) cells as well as in ba/F3 (murine pro-B cells), which do not express c-kit, BCR-ABL or PDGF-R. Imatinib mesylate did not affect the activity of other DNA polymerases. Inhibition of TA was associated with 50% inhibition of proliferation. The inhibition of proliferation was associated with a decrease in the S-phase of the cell cycle and an accumulation of cells in the G2/M phase. No apoptosis was observed. Inhibition of TA was caused mainly by post-translational modifications: dephosphorylation of AKT and, to a smaller extent, by early downregulation of hTERT (the catalytic subunit of the enzyme) transcription. Other steps of telomerase regulation were not affected by IM. This study demonstrates an additional cellular target of IM, not necessarily mediated via known tyrosine kinases, that causes inhibition of TA and cell proliferation.

Early Invasive Pulmonary Aspergillosis in a Leukemia Patient Linked to Aspergillus Contaminated Marijuana Smoking

46-year-old patient with acute myeloid leukemia (AML) whose disease manifested as fever, chills and dry cough is reported here. Despite broad antibiotic coverage he remained acutely ill with spiking fever, shaking chills, and hypoxemia. His initial chest radiograph was normal but chest computed tomography (CT) scan disclosed bilateral focal infiltrates. Hypoxemia and severe thrombocytopenia precluded invasive diagnostic procedures. A thorough epidemiological investigation revealed that before becoming acutely ill the patient smoked daily tobacco mixed with marijuana from a “hookah bottle”. While waiting for tobacco and “hookah water” cultures, we started antifungal therapy. Resolution of fever and hypoxemia ensued after 72 hours. Tobacco cultures yielded heavy growth of Aspergillus species. We suggest that habitual smoking of Aspergillus-infested tobacco and marijuana caused airway colonization with Aspergillus. Leukemia rendered the patient immunocompromised, and allowed Aspergillus to infest the lung parenchyma with early occurrence of invasive pulmonary aspergillosis. Physicians should be aware of this potentially lethal complication of “hookah” and marijuana smoking in immunocompromised hosts.

The heme biosynthetic pathway in lymphocytes of patients with malignant lymphoproliferative disorders

The metabolism of heme is impaired in lymphocytes of patients with malignant lymphoproliferative disorders (MLPO). Two of the enzymes of the heme biosynthetic pathway, delta-aminolevulinic acid dehydrase (ALAD) (EC 4.2.1.24) and ferrochelatase (FC) (EC 4.99.1.1) are markedly reduced. The activity of porphobilinogen deaminase (PBGD) (EC 4.3.1.8) is increased. The rate-limiting enzyme of heme biosynthesis in the liver, aminolevulinate synthase (ALAS) (EC 2.3.1.37) remains unchanged although the concentration of total heme in the lymphocytes is markedly reduced. This might reflect a lack of negative feedback inhibition by heme on ALAS activity in this system.

Neutropenia after rituximab treatment: new insights on a late complication.

Purpose of reviewLate-onset neutropenia (LON) after rituximab administration may be encountered in various clinical settings. The identification of neutropenia after rituximab treatment may have immediate implications for the clinical management of the patient and on subsequent treatment strategies. Although the pathogenesis of LON is incompletely understood, various putative mechanisms are suggested. These may be of special importance in the advent of the newer monoclonal anti-CD20 antibodies. Recent findingsThe incidence of LON varies with the clinical setting in which rituximab is administered. Administration of rituximab in the setting of stem cell transplantation significantly increases the risk for LON. The timing of rituximab administration after transplantation may affect the risk and severity of neutropenia. Recent data suggest that in rheumatologic diseases, the incidence of LON is comparable to that in the hematologic population. Suggested mechanisms for LON include humoral and cellular immune mechanisms as well processes that stem from B-cell recovery and its impact on neutrophil kinetics. Recently, an association between specific polymorphism in the immunoglobulin G Fc receptor FC&ggr;RIIIa 158 V/F and LON was demonstrated. SummaryLON is an increasingly recognized late adverse event of rituximab therapy. Acquaintance with the incidence, risk factors, natural history, and expected complications of LON may improve proper clinical management. Many aspects in the clinical management of LON remain to be answered during further studies aimed at this goal.

Lymphoma and Leukemia Cells Possess Fractal Dimensions That Correlate with Their Biological Features

Background: Living cells can be viewed as complex adaptive systems that exhibit non-linear dynamics and fractal features. We investigated the fractal qualities of normal and malignant hematological cells and their potential as a tool for characterizing cell phenotype and clinical behavior. Methods: A mathematical algorithm and an optic tool for fractal analysis of nuclei were developed. A total of 4,713 lymphoid cells derived from 66 patients of five distinct diagnostic groups (normal and reactive lymphocytes, low-grade lymphomas and an aggressive lymphoma) were assessed for their fractal dimension. In addition, in 19 patients fractal analysis of leukemia cells was compared to clinical endpoints. Results: After validating our method, hematological cells possessed fractal dimensions corresponding to their clinical entity. There was a highly significant overall difference in fractal dimensions between various types of hematological malignancies. A preliminary correlation was found between the fractal dimension and the clinical outcome of leukemia patients. Conclusions: Hematological cells possess fractal dimensions that correlate with their biological properties. Measurement of fractal dimension seems to be a sensitive method to assess the hematological cell phenotype and to define a clinical group. This tool may be potentially useful for the evaluation of clinical behavior of hematological diseases.