G-CSF-induced remission in two cases of acute myeloid leukemia.

We report on two elderly patients with newly diagnosed acute myeloid leukemia (AML) who were treated in palliative intention because of comorbidities and intermediate or poor risk cytogenetics. Both received G-CSF to reduce the risk of infection related to neutropenia. Interestingly, one patient achieved a full hematological remission and the other a peripheral remission with dramatic reduction of the bone marrow blast count. Although a direct therapeutic effect of myeloid growth factors seems to be unusual in AML, the use of G-CSF or GM-CSF may be recommended in patients such as elderly patients who are not suited for intensive chemotherapy.

Neuropeptide Y and corticotropin-releasing hormone in CSF mark response to antidepressive treatment with citalopram.

Neuropeptides appear to play a role in the pathophysiology of depression and electroconvulsive treatment and lithium affect these compounds in human cerebrospinal fluid (CSF) and rodent brain. Consequently, we investigated whether long-term treatment with the selective serotonin reuptake inhibitor (SSRI) citalopram (Cit) would also affect neuropeptides in CSF of depressed patients. Changes in CSF monoamine metabolites were also explored. CSF concentrations of corticotropin-releasing hormone (CRH)-like immunoreactivity (-LI), neuropeptide Y (NPY)-LI, and Cit were determined in 21 patients with major depression. Lumbar puncture was performed in the morning at baseline and was repeated after at least 4 wk of Cit treatment (40 mg/d). The severity of depression was assessed by the Hamilton Rating Scale for Depression (HAMD). Cit treatment was associated with a significant increase in NPY-LI and decrease in CRH-LI. An evaluation of the relationship between changes in concentrations of NPY-LI, CRH-LI, and the clinical response showed significant correlations between these parameters. Significant NPY and CRH changes in CSF following treatment as well as correlations to changes in HAMD support the hypothesis that these two peptides play a role in affective disorders and are markers of therapeutic response.

Impact of round-the-clock CSF Gram stain on empirical therapy for suspected central nervous system infections.

The impact of round-the-clock cerebrospinal fluid (CSF) Gram stain on overnight empirical therapy for suspected central nervous system (CNS) infections was investigated. All consecutive overnight CSF Gram stains between 2006 and 2011 were included. The impact of a positive or a negative test on empirical therapy was evaluated and compared to other clinical and biological indications based on institutional guidelines. Bacterial CNS infection was documented in 51/241 suspected cases. Overnight CSF Gram stain was positive in 24/51. Upon validation, there were two false-positive and one false-negative results. The sensitivity and specificity were 41 and 99 %, respectively. All patients but one had other indications for empirical therapy than Gram stain alone. Upon obtaining the Gram result, empirical therapy was modified in 7/24, including the addition of an appropriate agent (1), addition of unnecessary agents (3) and simplification of unnecessary combination therapy (3/11). Among 74 cases with a negative CSF Gram stain and without formal indication for empirical therapy, antibiotics were withheld in only 29. Round-the-clock CSF Gram stain had a low impact on overnight empirical therapy for suspected CNS infections and was associated with several misinterpretation errors. Clinicians showed little confidence in CSF direct examination for simplifying or withholding therapy before definite microbiological results.

CSF lactate for accurate diagnosis of community-acquired bacterial meningitis.

CSF lactate measurement is recommended when nosocomial meningitis is suspected, but its value in community-acquired bacterial meningitis is controversial. We evaluated the diagnostic performance of lactate and other CSF parameters in a prospective cohort of adult patients with acute meningitis. Diagnostic accuracy of lactate and other CSF parameters in patients with microbiologically documented episodes was assessed by receiver operating characteristic (ROC) curves. The cut-offs with the best diagnostic performance were determined. Forty-five of 61 patients (74%) had a documented bacterial (n = 18; S. pneumoniae, 11; N. meningitidis, 5; other, 2) or viral (n = 27 enterovirus, 21; VZV, 3; other, 3) etiology. CSF parameters were significantly different in bacterial vs. viral meningitis, respectively (p < 0.001 for all comparisons): white cell count (median 1333 vs. 143/mm(3)), proteins (median 4115 vs. 829 mg/l), CSF/blood glucose ratio (median 0.1 vs. 0.52), lactate (median 13 vs. 2.3 mmol/l). ROC curve analysis showed that CSF lactate had the highest accuracy for discriminating bacterial from viral meningitis, with a cutoff set at 3.5 mmol/l providing 100% sensitivity, specificity, PPV, NPV, and efficiency. CSF lactate had the best accuracy for discriminating bacterial from viral meningitis and should be included in the initial diagnostic workup of this condition.

CSF biomarkers for the differential diagnosis of Alzheimer's disease: A large-scale international multicenter study.

INTRODUCTION: The aim of this study was to test the diagnostic value of cerebrospinal fluid (CSF) beta-amyloid (Aβ1-42), phosphorylated tau, and total tau (tau) to discriminate Alzheimer's disease (AD) dementia from other forms of dementia. METHODS: A total of 675 CSF samples collected at eight memory clinics were obtained from healthy controls, AD dementia, subjective memory impairment, mild cognitive impairment, vascular dementia, Lewy body dementia (LBD), fronto-temporal dementia (FTD), depression, or other neurological diseases. RESULTS: CSF Aβ1-42 showed the best diagnostic accuracy among the CSF biomarkers. At a sensitivity of 85%, the specificity to differentiate AD dementia against other diagnoses ranged from 42% (for LBD, 95% confidence interval or CI = 32-62) to 77% (for FTD, 95% CI = 62-90). DISCUSSION: CSF Aβ1-42 discriminates AD dementia from FTD, but shows significant overlap with other non-AD forms of dementia, possibly reflecting the underlying mixed pathologies.

Bradykinin in blood and cerebrospinal fluid after acute cerebral lesions: correlations with cerebral edema and intracranial pressure.

Abstract Bradykinin (BK) was shown to stimulate the production of physiologically active metabolites, blood-brain barrier disruption, and brain edema. The aim of this prospective study was to measure BK concentrations in blood and cerebrospinal fluid (CSF) of patients with traumatic brain injury (TBI), subarachnoid hemorrhage (SAH), intracerebral hemorrhage (ICH), and ischemic stroke and to correlate BK levels with the extent of cerebral edema and intracranial pressure (ICP). Blood and CSF samples of 29 patients suffering from acute cerebral lesions (TBI, 7; SAH,: 10; ICH, 8; ischemic stroke, 4) were collected for up to 8 days after insult. Seven patients with lumbar drainage were used as controls. Edema (5-point scale), ICP, and the GCS (Glasgow Coma Score) at the time of sample withdrawal were correlated with BK concentrations. Though all plasma-BK samples were not significantly elevated, CSF-BK levels of all patients were significantly elevated in overall (n=73) and early (≤72 h) measurements (n=55; 4.3±6.9 and 5.6±8.9 fmol/mL), compared to 1.2±0.7 fmol/mL of controls (p=0.05 and 0.006). Within 72 h after ictus, patients suffering from TBI (p=0.01), ICH (p=0.001), and ischemic stroke (p=0.02) showed significant increases. CSF-BK concentrations correlated with extent of edema formation (r=0.53; p<0.001) and with ICP (r=0.49; p<0.001). Our results demonstrate that acute cerebral lesions are associated with increased CSF-BK levels. Especially after TBI, subarachnoid and intracerebral hemorrhage CSF-BK levels correlate with extent of edema evolution and ICP. BK-blocking agents may turn out to be effective remedies in brain injuries.

Statin use and peripheral blood progenitor cells mobilization in patients with multiple myeloma.

PURPOSE: Statins have beneficial effects in patients after myocardial infarction and at least part of the benefit results from mobilization of marrow endothelial progenitors to repopulate damaged myocardial tissues. This study examines if statins may have the same effect in mobilizing marrow progenitors to be harvested and subsequently used in high-dose chemotherapy with progenitor cell rescue in multiple myeloma. METHODS: From 2006 to 2012, 86 patients with multiple myeloma were mobilized with the use of G-CSF and were retrospectively analyzed. Patients with other malignancies or mobilized with the use of chemotherapy or with plerixafor were excluded. RESULTS: The median age of the patients was 60 years. 72 patients had received one line of chemotherapy and 14 patients two or more lines of chemotherapy. Twenty patients were taking statins at the time of the harvest while 66 patients were not. In the group of patients taking statins the success rate of first leukapheresis (obtaining the target number of 4 × 10(6) CD34+ cells/kg) was 85 % while in the group not taking statins this rate was 63.6 %. Despite the comparatively small number of patients this difference approached statistical significance (χ (2) = 0.07). CONCLUSION: This retrospective analysis of 86 patients shows for the first time a possible benefit of statins for peripheral blood progenitor cells mobilization in patients with multiple myeloma. Larger studies would be required to clarify the issue. If their effectiveness is confirmed, statins could be a safe and cheaper addition to chemotherapy and plerixafor for peripheral hematopoietic stem cell mobilization.

Characteristics of infections associated with external ventricular drains of cerebrospinal fluid.

OBJECTIVES: Manifestations of external ventricular drain (EVD) - associated infections overlap with those of the underlying neurosurgical conditions. We analyzed characteristics of EVD-associated infections. METHODS: We included patients aged ≥18 years with EVD-associated infections from 1997 to 2008, using modified CDC criteria for nosocomial infections. Hospital charts were reviewed retrospectively and the in-hospital outcome was evaluated. RESULTS: Forty-eight patients with EVD-associated infections were included (median age, 52 years, range 20-74 years). The median EVD-indwelling time was 7 days (range, 1-39 days) and EVD-associated infection occurred 6 days after insertion (range, 1-17 days). In 23% of patients, meningitis occurred 1-10 days after EVD removal. Fever >38 °C was present in 79% of patients, but Glasgow Coma Scale (GCS) scores were reduced in only 29%, and headache, vomiting and/or neck stiffness were present in only 31%. The median cerebrospinal fluid (CSF) leukocyte count was higher at onset of EVD-associated infection than at EVD insertion (175 × 10(6)/l versus 46 × 10(6)/l, p = 0.021), but other CSF parameters did not differ significantly. The most commonly implicated organisms were coagulase-negative staphylococci (63%) and Propionibacterium acnes (15%). CONCLUSIONS: Fever and increased CSF leukocytes should raise the suspicion of EVD-associated infection, which may occur up to 10 days after removal of EVD.

Nitric oxide synthase 2 is required for conversion of pro-fibrogenic inflammatory CD133+ progenitors into F4/80+ macrophages in experimental autoimmune myocarditis.

AIMS: Experimental autoimmune myocarditis (EAM) model mirrors important mechanisms of inflammatory dilated cardiomyopathy (iDCM). In EAM, inflammatory CD133(+) progenitors are a major cellular source of cardiac myofibroblasts in the post-inflammatory myocardium. We hypothesized that exogenous delivery of macrophage-colony-stimulating factor (M-CSF) can stimulate macrophage lineage differentiation of inflammatory progenitors and, therefore, prevent their naturally occurring myofibroblast fate in EAM. METHODS AND RESULTS: EAM was induced in wild-type (BALB/c) and nitric oxide synthase 2-deficient (Nos2(-/-)) mice and CD133(+) progenitors were isolated from inflamed hearts. In vitro, M-CSF converted inflammatory CD133(+) progenitors into nitric oxide-producing F4/80(+) macrophages and prevented transforming growth factor-β-mediated myofibroblast differentiation. Importantly, only a subset of heart-infiltrating CD133(+) progenitors expresses macrophage-specific antigen F4/80 in EAM. These CD133(+)/F4/80(hi) cells show impaired myofibrogenic potential compared with CD133(+)/F4/80(-) cells. M-CSF treatment of wild-type mice with EAM at the peak of disease markedly increased CD133(+)/F4/80(hi) cells in the myocardium, and CD133(+) progenitors isolated from M-CSF-treated mice failed to differentiate into myofibroblasts. In contrast, M-CSF was not effective in converting CD133(+) progenitors from inflamed hearts of Nos2(-/-) mice into macrophages, and M-CSF treatment did not result in increased CD133(+)/F4/80(hi) cell population in hearts of Nos2(-/-) mice. Accordingly, M-CSF prevented post-inflammatory fibrosis and left ventricular dysfunction in wild-type but not in Nos2(-/-) mice. CONCLUSION: Active and NOS2-dependent induction of macrophage lineage differentiation abrogates the myofibrogenic potential of heart-infiltrating CD133(+) progenitors. Modulating the in vivo differentiation fate of specific progenitors might become a novel approach for the treatment of inflammatory heart diseases.

Mutations in the colony stimulating factor 1 receptor (CSF1R) gene cause hereditary diffuse leukoencephalopathy with spheroids.

Hereditary diffuse leukoencephalopathy with spheroids (HDLS) is an autosomal-dominant central nervous system white-matter disease with variable clinical presentations, including personality and behavioral changes, dementia, depression, parkinsonism, seizures and other phenotypes. We combined genome-wide linkage analysis with exome sequencing and identified 14 different mutations affecting the tyrosine kinase domain of the colony stimulating factor 1 receptor (encoded by CSF1R) in 14 families with HDLS. In one kindred, we confirmed the de novo occurrence of the mutation. Follow-up sequencing identified an additional CSF1R mutation in an individual diagnosed with corticobasal syndrome. In vitro, CSF-1 stimulation resulted in rapid autophosphorylation of selected tyrosine residues in the kinase domain of wild-type but not mutant CSF1R, suggesting that HDLS may result from partial loss of CSF1R function. As CSF1R is a crucial mediator of microglial proliferation and differentiation in the brain, our findings suggest an important role for microglial dysfunction in HDLS pathogenesis.

Cerebrospinal fluid antimicroglial antibodies in Alzheimer disease: a putative marker of an ongoing inflammatory process.

Immunocompetent microglia play an important role in the pathogenesis of Alzheimer's disease (AD). Antimicroglial antibodies in the cerebrospinal fluid (CSF) in clinically diagnosed AD patients have been previously recorded. Here, we report the results of the analysis of the CSF from 38 autopsy cases: 7 with definite AD; 14 with mild and 10 with moderate Alzheimer's type pathology; and 7 controls. Antimicroglial antibodies were identified in 70% of patients with definite AD, in 80% of patients with moderate and in 28% of patients with mild Alzheimer's type pathology. CSF antimicroglial antibodies were not observed in any of the control cases. The results show that CSF antimicroglial antibodies are present in the majority of patients with definite AD and also in cases with moderate Alzheimer's type changes. They may also indicate dysregulation of microglial function. Together with previous observations, these findings indicate that compromised immune defense mechanisms play an important role in the pathogenesis of AD.

Real-time PCR for type-specific identification of herpes simplex in clinical samples: evaluation of type-specific results in the context of CNS diseases.

BACKGROUND: HSV-1 and HSV-2 cause CNS infections of dissimilar clinico-pathological characteristics with prognostic and therapeutic implications. OBJECTIVES: To validate a type-specific real-time PCR that uses MGB/LNA Taqman probes and to review the virologico-clinical data of 25 eligible patients with non-neonatal CNS infections. RESULTS: This real-time PCR was evaluated against conventional PCR (26 CSF and 20 quality controls), and LightCycler assay (51 mucocutaneous, 8 CSF and 32 quality controls) and culture/immunofluorescence (75 mucocutaneous) to assess typing with independent methods. Taqman real-time PCR detected 240 HSV genomes per ml CSF, a level appropriate for the management of patients, and provided unambiguous typing for the 104 positive (62 HSV-1 and 42 HSV-2) out the 160 independent clinical samples tested. HSV type diagnosed by Taqman real-time PCR predicted final diagnosis (meningitis versus encephalitis/meningoencephalitis, p<0.001) in 24/25 patients at time of presentation, in contrast to clinical evaluation. CONCLUSIONS: Our real-time PCR, as a sensitive and specific means for type-specific HSV diagnosis, provided rapid prognostic information for patient management.

Aseptic meningoencephalitis mimicking transient ischaemic attacks.

PURPOSE: To highlight meningoencephalitis as a transient ischaemic attack (TIA) mimic and suggest clinical clues for differential diagnosis. METHODS: This was an observational study of consecutively admitted patients over a 9.75-year period presenting as TIAs at a stroke unit. RESULTS: A total of 790 patients with TIAs and seven with TIA-like symptoms but a final diagnosis of viral meningoencephalitis were recognised. The most frequent presentations of meningoencephalitis patients were acute sensory hemisyndrome (6) and cognitive deficits (5). Signs of meningeal irritation were minor or absent on presentation. Predominantly lymphocytic pleocytosis, hyperproteinorachia and a normal cerebrospinal fluid (CSF)/serum glucose index (in 5 out of 6 documented patients) were present. Meningeal thickening on a brain magnetic resonance imaging (MRI) scan was the only abnormal imaging finding. Six patients received initial vascular treatment; one thrombolysed. Finally, six patients were treated with antivirals and/or antibiotics. Although neither bacterial nor viral agents were identified on extensive testing, viral meningoencephalitis was the best explanation for all clinical and laboratory findings. CONCLUSIONS: Aseptic meningoencephalitis should be part of the differential diagnosis in patients presenting as TIA. The threshold for a lumbar puncture in such patients should be set individually and take into account the presence of mild meningeal symptoms, age and other risk factors for vascular disease, the results of brain imaging and the basic diagnostic work-up for a stroke source.

Antibody-mediated status epilepticus: a retrospective multicenter survey.

Background: In recent years, an increasing number of auto-antibodies (AB) have been detected in the CSF and serum of patients with new onset epilepsy. Some of these patients develop convulsive or nonconvulsive status epilepticus (AB-SE), necessitating intensive medical care and administration of multiple antiepileptic and immunomodulatory treatments of uncertain effectiveness. Objectives: In this retrospective multicenter survey we aimed to determine the spectrum of gravity, the duration and the prognosis of the disorder. In addition, we sought to identify the antibodies associated with this condition, as well as determine whether there is a most effective treatment regime. Methods: 12 European Neurology University Clinics, with extensive experience in the treatment of SE patients, were sent a detailed questionnaire regarding symptoms and treatment of AB-SE patients. Seven centers responded positively, providing a total of 13 patients above the age of 16. Results: AB-SE affects mainly women (12/13, 92%) with a variable age at onset (17-69 years, median: 25 years). The duration of the disease is also variable (10 days to 12 years, median: 2 months). Only the 3 oldest patients died (55-69 years). Most patients were diagnosed with anti NMDAR encephalitis (8/13) and had oligoclonal bands in the CSF (9/13). No specific treatment regimen (antiepileptic, immunomodulatory) was found to be clearly superior. Most of the surviving 10 patients (77%) recovered completely or nearly so within 2 years of index poststatus. Conclusion: AB-SE is a severe but potentially reversible condition. Long duration does not seem to imply fatal outcome; however, age older than 50 years at time of onset appears to be a risk factor for death. There was no evidence for an optimal antiepileptic or immunomodulatory treatment. A prospective multicenter study is warranted in order to stratify the optimal treatment algorithm, determine clear risk factors of unfavorable outcome and long-term prognosis.

The role of Pten in the Hematopoietic System and the Hematopoietic Stem Cells

Résumé Identification, localisation et activation des cellules souches hématopoiétiques dormantes in vivo Les cellules souches somatiques sont présentes dans la majorité des tissus régénératifs comme la peau, l'épithélium intestinal et le système hématopoiétique. A partir d'une seule cellule, elles ont les capacités de produire d'autres cellules souches du même type (auto-renouvellement) et d'engendrer un ensemble défini de cellules progénitrices différenciées qui vont maintenir ou réparer leur tissu hôte. Les cellules souches adultes les mieux caractérisées sont les cellules souches hématopoiétiques (HSC), localisées dans la moelle osseuse. Un des buts de mon travail de doctorat était de caractériser plus en profondeur la localisation des HSCs endogènes in vivo. Pour ce faire, la technique "label retaining assay", se basant sur la division peu fréquentes et sur la dormance des cellules souches, a été utilisée. Après un marquage des souris avec du BrdU (analogue à l'ADN) suivi d'une longue période sans BrdU, les cellules ayant incorporés le marquage ("label retaining cells" LCRs) ont pu être identifiées dans la moelle osseuse. Ces cellules LCRs étaient enrichies 300 fois en cellules de phenotype HSC et, en utilisant de la cytofluorométrie, il a pu être montré qu'environ 15% de toutes les HSCs d'une souris restent dormantes durant plusieures semaines. Ces HSCs dormantes à long terme ne sont probablement pas impliquées dans la maintenance de 'hématopoièse. Par contre, on assiste à l'activation rapide de ces HSCs dormantes lors d'une blessure, comme une ablation myéloide. Elles re-entrent alors en cycle cellulaire et sont essentielles pour une génération rapide des cellules progénitrices et matures qui vont remplacer les cellules perdues. De plus, la détection des LCRs, combinée avec l'utilisation du marqueur de HSCs c-kit, peut être utilisée pour la localisation des HSCs dormantes présentes dans la paroi endostéale de la cavité osseuse. De manière surprenante, les LCRs c-kit+ ont surtout étés trouvées isolées en cellule unique, suggérant que le micro-environement spécifique entourant et maintenant les HSCs, appelé niche, pourrait être très réduit et abriter une seule HSC par niche. Rôles complexes du gène supresseur de tumeur Pten dans le système hématopoiétique La phosphatase PTEN disparaît dans certains cancers héréditaires ou sporadiques humains, comme les gliomes, les cancers de l'utérus ou du sein. Pten inhibe la voie de signalisation de la PI3-kinase et joue un rôle clé dans l'apoptose, la croissance, la prolifération et la migration cellulaire. Notre but était d'étudier le rôle de Pten dans les HSC normale et durant la formation de leucémies. Pour ce faire, nous avons généré un modèle murin dans lequel le gène Pten peut être supprimé dans les cellules hématopoiétiques, incluant les HSCs. Ceci a été possible en croissant l'allèle conditionnelle ptenflox soit avec le transgène MxCre inductible par l'interféron α soit avec le transgène Scl-CreERt inductible par le tamoxifen. Ceci permet la conversion de l'allèle ptenflox en l'allèle nul PtenΔ dans les HSCs et les autres types cellulaires hématopoiétiques. Les souris mutantes Pten développent une splénomégalie massive causée par une expansion dramatiques de toutes les cellules myéloides. De manière interessante, alors que le nombre de HSCs dans la moelle osseuse diminue progressivement, le nombre des HSCs dans la rate augmente de manière proportionnelle. Etrangement, les analyses de cycle cellulaire ont montrés que Pten n'avait que peu ou pas d'effet sur la dormance des HSCs ou sur leur autorenouvellement. En revanche, une augmentation massive du niveau de la cytokine de mobilisation G-CSF a été détéctée dans le serum sanguin, suggérant que la suppression de Pten stimulerait la mobilisation et la migration des HSC de la moelle osseuse vers la rate. Finallement, la transplantation de moelle osseuse délétée en Pten dans des souris immuno-déficientes montre que Pten fonctionnerait comme un suppresseur de tumeur dans le système hématopoiétique car son absence entraîne la formation rapide de leucémies lymphocytaires. Summary Identification, localization and activation of dormant hematopoietic stun cells in vivo Somatic stem cells are present in most self-renewing tissues including the skin, the intestinal epithelium and the hematopoietic system. On a single cell basis they have the capacity to produce more stem cells of the same phenotype (self-renewal) and to give rise to a defined set of mature differentiated progeny, responsible for the maintenance or repair of the host tissue. The best characterized adult stem cell is the hematopoietic stem cell (HSC) located in the bone marrow. One goal of my thesis work was to further characterize the location of endogenous HSCs in vivo. To do this, a technique called "label retaining assay» was used which takes advantage of the fact that stem cells (including HSCs) divide very infrequently and can be dormant for months. After labeling mice with the DNA analogue BrdU followed by a long BrdU free "chase", BrdU "label retaining cells" (CRCs) could be identified in the bone marrow. These CRCs were 300-fold enriched for phenotypic HSCs and by using flow cytometry analysis it could be shown that about 15% of all HSCs in the mouse are dormant for many weeks. Our results suggest that these long-term dormant HSCs are unlikely to be involved in homeostatic maintenance. However they are rapidly activated and reenter the cell cycle in response to injury signals such as myeloid ablation. In addition, detection of LRCs in combination with the HSC marker c-Kit could be used to locate engrafted dormant HSCs close to the endosteal lining of the bone marrow cavities. Most surprisingly, c-Kit+LRCs were found predominantly as single cells suggesting that the specific stem cell maintaining microenvironment, called niche, has limited space and may house only single HSCs. Complex roles of the tumor suppressor gene Pten in the hematopoietic system. The phosphatase PTEN is lost in hereditary and sporadic forms of human cancers, including gliomas, endometrial and breast cancers. Pten inhibits the PI3-kina.se pathway and plays a key role in apoptosis, cell growth, proliferation and migration. Our aim was to study the role of Pten in normal HSCs and during leukemia formation. To do this, we generated a mouse model in which the Pten gene can be deleted in hematopoietic cells including HSCs. This was achieved by crossing the conditional ptenflox allele with either the interferona inducible MxCre or the tamoxifen inducible Scl-CreERT transgene. This allowed the conversion of the ptenflox allele into a pterr' null allele in HSCs and other hematopoietic cell types. As a result Pten mutant mice developed massive splenomegaly due to a dramatic expansion of all myeloid cells. Interestingly, while the number of bone marrow HSCs progressively decreased, the number of HSCs in the spleen increased to a similar extent. Unexpectedly, extensive cell cycle analysis showed that Pten had little or no effect on HSC dormancy or HSC self-renewal. Instead, dramatically increased levels of the mobilizing cytokine G-CSF were detected in the blood serum suggesting that loss-of Pten stimulates mobilization and migration of HSC from the BM to the spleen. Finally, transplantation of Pten deficient BM cells into immuno-compromised mice showed that Pten can function as a tumor suppressor in the hematopoietic system and that its absence leads to the rapid formation of T cell leukemia.