Calreticulin mutants in mice induce an MPL-dependent thrombocytosis with frequent progression to myelofibrosis.

Frameshift mutations in the calreticulin (CALR) gene are seen in about 30% of essential thrombocythemia and myelofibrosis patients. To address the contribution of the CALR mutants to the pathogenesis of myeloproliferative neoplasms, we engrafted lethally irradiated recipient mice with bone marrow cells transduced with retroviruses expressing these mutants. In contrast to wild-type CALR, CALRdel52 (type I) and, to a lesser extent, CALRins5 (type II) induced thrombocytosis due to a megakaryocyte (MK) hyperplasia. Disease was transplantable into secondary recipients. After 6 months, CALRdel52-, in contrast to rare CALRins5-, transduced mice developed a myelofibrosis associated with a splenomegaly and a marked osteosclerosis. Monitoring of virus-transduced populations indicated that CALRdel52 leads to expansion at earlier stages of hematopoiesis than CALRins5. However, both mutants still specifically amplified the MK lineage and platelet production. Moreover, a mutant deleted of the entire exon 9 (CALRdelex9) did not induce a disease, suggesting that the oncogenic property of CALR mutants was related to the new C-terminus peptide. To understand how the CALR mutants target the MK lineage, we used a cell-line model and demonstrated that the CALR mutants, but not CALRdelex9, specifically activate the thrombopoietin (TPO) receptor (MPL) to induce constitutive activation of Janus kinase 2 and signal transducer and activator of transcription 5/3/1. We confirmed in c-mpl- and tpo-deficient mice that expression of Mpl, but not of Tpo, was essential for the CALR mutants to induce thrombocytosis in vivo, although Tpo contributes to disease penetrance. Thus, CALR mutants are sufficient to induce thrombocytosis through MPL activation.

Thrombospondin-1 is not the major activator of TGF-ß1 in thrombopoietin-induced myelofibrosis.

Transforming growth factor-ß1 (TGF-ß1) is the most important cytokine involved in the promotion of myelofibrosis. Mechanisms leading to its local activation in the bone marrow environment remain unclear. As a recent study has highlighted the role of thrombospondin-1 (TSP-1) in platelet-derived TGF-ß1 activation, we investigated the role of TSP-1 in the TPO(high) murine model of myelofibrosis. Two groups of engrafted mice, WT TPO(high) and Tsp-1-null TPO(high), were constituted. All mice developed a similar myeloproliferative syndrome and an increase in total TGF-ß1 levels in the plasma and in extracellular fluids of marrow and spleen. Surprisingly, we were able to detect the active form of TGF-ß1 in Tsp-1-null TPO(high) mice. Accordingly, these mice developed marrow and spleen fibrosis, with intriguingly a higher grade than in WT TPO(high) mice. Our results show that TSP-1 is not the major activator of TGF-ß1 in TPO-induced myelofibrosis, suggesting the contribution of another mechanism in the megakaryocyte/platelet compartment.

The hematopoietic stem cell compartment of JAK2V617F-positive myeloproliferative disorders is a reflection of disease heterogeneity.

The JAK2V617F somatic point mutation has been described in patients with myeloproliferative disorders (MPDs). Despite this progress, it remains unknown how a single JAK2 mutation causes 3 different MPD phenotypes, polycythemia vera (PV), essential thrombocythemia, and primitive myelofibrosis (PMF). Using an in vivo xenotransplantation assay in nonobese diabetic-severe combined immunodeficient (NOD/SCID) mice, we tested whether disease heterogeneity was associated with quantitative or qualitative differences in the hematopoietic stem cell (HSC) compartment. We show that the HSC compartment of PV and PMF patients contains JAK2V617F-positive long-term, multipotent, and self-renewing cells. However, the proportion of JAK2V617F and JAK2 wild-type SCID repopulating cells was dramatically different in these diseases, without major modifications of the self-renewal and proliferation capacities for JAK2V617F SCID repopulating cells. These experiments provide new insights into the pathogenesis of JAK2V617F MPD and demonstrate that a JAK2 inhibitor needs to target the HSC compartment for optimal disease control in classical MPD.

Pericyte coverage of abnormal blood vessels in myelofibrotic bone marrows.

BACKGROUND AND OBJECTIVES: Myelofibrotic bone marrow displays abnormal angiogenesis but the pathogenic mechanisms of this are poorly understood. Since pericyte abnormalities are described on solid tumor vessels we studied whether vessel morphology and pericyte coverage in bone marrow samples from patients with myelofibrosis differed from that in samples from controls. DESIGN AND METHODS: We assessed the microvascular density (MVD), vessel morphology and pericyte coverage in bone marrows from 19 myelofibrosis patients and nine controls. We also studied the same parameters in two mouse models of myelofibrosis, with genetic alterations affecting megakaryocyte differentiation (i.e. one model with low GATA-1 expression and the other with over-expression of thrombopoietin). RESULTS: In myelofibrotic marrows, MVD was 3.8-fold greater than in controls (p<0.001) and vessels displayed 5.9-fold larger mean perimeters (p<0.001). MVD was 1.8-fold greater in JAK2 V617F-positive than in negative patients (p=0.026). Moreover, 92+/-11 % of vessels in patients with myelofibrosis were pericyte-coated but only 51+/-20 % of vessels in controls (p<0.001). In the two mouse models of myelofibrosis caused by targeting megakaryocytopoesis, wide, pericyte-coated and morphologically aberrant vessels were detected. MVD was significantly greater in bone marrow and spleen samples from animals with myelofibrosis than in wild-type mice. INTERPRETATION AND CONCLUSIONS: We conclude that angiogenesis is similarly abnormal in human and murine myelofibrosis with intense pericyte coating, presumably related to abnormal megakaryocytopoiesis.

Proteasome inhibitor bortezomib impairs both myelofibrosis and osteosclerosis induced by high thrombopoietin levels in mice.

Primary myelofibrosis (PMF) is the most serious myeloproliferative disorder, characterized by clonal myeloproliferation associated with cytokine-mediated bone marrow stromal reaction including fibrosis and osteosclerosis. Current drug therapy remains mainly palliative. Because the NF-kappaB pathway is implicated in the abnormal release of cytokines in PMF, the proteasome inhibitor bortezomib might be a potential therapy. To test its effect, we used the lethal murine model of myelofibrosis induced by thrombopoietin (TPO) overexpression. In this TPO(high) model, the development of the disease is related to a deregulated MPL signaling, as recently described in PMF patients. We first demonstrated that bortezomib was able to inhibit TPO-induced NF-kappaB activation in vitro in murine megakaryocytes. It also inhibited NF-kappaB activation in vivo in TPO(high) mice leading to decreased IL-1alpha plasma levels. After 4 weeks of treatment, bortezomib decreased TGF-beta1 levels in marrow fluids and impaired marrow and spleen fibrosis development. After 12 weeks of treatment, bortezomib also impaired osteosclerosis development through osteoprotegerin inhibition. Moreover, this drug reduced myeloproliferation induced by high TPO level. Finally, bortezomib dramatically improved TPO(high) mouse survival (89% vs 8% at week 52). We conclude that bortezomib appears as a promising therapy for future treatment of PMF patients.

Adenoviral-mediated TGF-beta1 inhibition in a mouse model of myelofibrosis inhibit bone marrow fibrosis development.

Myelofibrosis is characterized by excessive deposits of extracellular matrix proteins, which occur as a marrow microenvironment reactive response to cytokines released from the clonal malignant myeloproliferation. The observation that mice exposed to high systemic levels of thrombopoietin (TPO) invariably developing myelofibrosis has allowed demonstration of the crucial role of transforming growth factor (TGF)-beta1 released by hematopoietic cells in the onset of myelofibrosis. The purpose of this study was to investigate whether TGF-beta1 inhibition could directly inhibit fibrosis development in a curative approach of this mice model. An adenovirus encoding for TGF-beta1 soluble receptor (TGF-beta-RII-Fc) was injected either shortly after transplantation (preventive) or 30 days post-transplantation (curative). Mice were transplanted with syngenic bone marrow cells transduced with a retrovirus encoding for murine TPO. All mice developed a myeloproliferative syndrome. TGF-beta-RII-Fc was detected in the blood of all treated mice, leading to a dramatic decrease in TGF-beta1 level. Histological analysis show that the two approaches (curative or preventive) were successful enough to inhibit bone marrow and spleen fibrosis development in this model. However, lethality of TPO overexpression was not decreased after treatment, indicating that in this mice model, myeloproliferation rather than fibrosis was probably responsible for the lethality induced by the disorder.

Monocyte/macrophage dysfunctions do not impair the promotion of myelofibrosis by high levels of thrombopoietin.

Several lines of evidence indicate that the megakaryocyte/platelet lineage is crucial in myelofibrosis induction. The demonstration that NOD/SCID mice with functionally deficient monocytes do not develop fibrotic changes when exposed to thrombopoietin (TPO) also suggests an important role for monocyte/macrophages. However, in this animal model, the development of myelofibrosis is dependent on the level of TPO. This study was conducted to investigate whether NOD/SCID mice exposed to high TPO levels mediated by a retroviral vector would be refractory to the development of bone marrow fibrosis. We show that TPO and TGF-beta1 in plasma from NOD/SCID and SCID mice engrafted with TPO-overexpressing hemopoietic cells reach levels similar to the ones reached in immunocompetent mice, and all animals develop a myeloproliferative disease associated with a dense myelofibrosis at 8 wk posttransplantation. Monocytes in NOD/SCID mice are functionally deficient to secrete cytokines such as IL-1alpha in response to stimuli, even under TPO expression. Surprisingly, the plasma of these mice displays high levels of IL-alpha, which was demonstrated to originate from platelets. Together, these data suggest that completely functional monocytes are not required to develop myelofibrosis and that platelets are able, under TPO stimulation, to synthesize inflammatory cytokines, which may be involved in the pathogenesis of myelofibrosis and osteosclerosis.

Life-threatening hemophagocytic syndrome related to mycobacterium tuberculosis.

Hemophagocytosis is a classic but uncommon complication of tuberculosis and can lead to a life-threatening condition. We report two cases of severe hemophagocytic syndrome related to mycobacterium tuberculosis. The etiologic diagnosis was made by specific polymerase chain reaction in one patient. These reports illustrate that tuberculosis should be considered for the diagnosis of hemophagocytic syndrome in critically ill patients.

JAK2V617F expression in murine hematopoietic cells leads to MPD mimicking human PV with secondary myelofibrosis.

A JAK2(V617F) mutation is frequently found in several BCR/ABL-negative myeloproliferative disorders. To address the contribution of this mutant to the pathogenesis of these different myeloproliferative disorders, we used an adoptive transfer of marrow cells transduced with a retrovirus expressing JAK2(V617F) in recipient irradiated mice. Hosts were analyzed during the 6 months after transplantation. For a period of 3 months, mice developed polycythemia, macrocytosis and usually peripheral blood granulocytosis. Transient thrombocytosis was only observed in a low-expresser group. All mice displayed trilineage hyperplasia in marrow and spleen along with an amplification of myeloid and erythroid progenitor cells and a formation of endogenous erythroid colonies. After 3 to 4 months, polycythemia regressed, abnormally shaped red blood cells and platelets were seen in circulation, and a deposition of reticulin fibers was observed in marrow and spleen. Development of fibrosis was associated with anemia, thrombocytopenia, high neutrophilia, and massive splenomegaly. These features mimic human polycythemia vera and its evolution toward myelofibrosis. This work demonstrates that JAK2(V617F) is sufficient for polycythemia and fibrosis development and offers an in vivo model to assess novel therapeutic approaches for JAK2(V617F)-positive pathologies. Questions remain regarding the exact contribution of JAK2(V617F) in other myeloproliferative disorders.

A non-randomised dose-escalating phase II study of thalidomide for the treatment of patients with low-risk myelodysplastic syndromes: the Thal-SMD-2000 trial of the Groupe Français des Myélodysplasies.

Patients (n=47) with low-risk myelodysplastic syndrome were treated with thalidomide [200 mg/d, increased by 200 mg/d/4 weeks up to week 16]. Responses were evaluated according to the International Working Group criteria at week 16 for 39 patients who received at least 8 weeks of treatment. Twenty-three (59%) patients showed haematological improvement (HI): four major erythroid response (HI-EM), 15 minor erythroid response, six major neutrophil response, two major platelet response. Side effects caused 22/39 to stop thalidomide before week 16. Nine of 23 responders continued thalidomide after week 16 [19% of trial patients] with sustained response in eight of nine. Six reached week 56, including the four HI-EM patients [13% of trial patients]. Nineteen of 36 red blood cell transfusion-dependent patients (53%) showed erythroid response, but only four became transfusion-independent. Among the 23 responders, the median duration of response was 260 d (range 30-650). Responses were sustained in all patients except one, and were observed between week 4 and week 8 in 85% of patients, at doses ranging from 200 to 400 mg. Only two patients responded at 600 mg/d and none at 800 mg/d. No clinical characteristics of responding versus non-responding patients were identified. The erythroid response rate was identical in all cytogenetic subgroups, including 5q31.1 deletions. Pretreatment vascular endothelial growth factor levels were lower in responders compared with non-responders (P=0.004). Microvessel density (MVD) increased and apoptosis decreased in four of six and in all six responders studied respectively whereas MVD and apoptosis were unchanged in three non-responders.

Pseudouveitis: a clue to the diagnosis of primary central nervous system lymphoma in immunocompetent patients.

Primary oculocerebral non-Hodgkin lymphoma (NHL) of the immunocompetent patient is associated with significant morbidity and mortality, but early diagnosis and follow-up may improve prognosis. The eye, anatomically and embryologically part of the central nervous system (CNS), can be the primary site of the lymphomatous process. In patients with symptoms of atypical uveitis, vitrectomy can be of great help for early diagnosis of primary central nervous system lymphoma. We retrospectively reviewed the diagnostic features, treatment, and evolution of 10 patients with primary central nervous system lymphoma who presented with symptoms of pseudouveitis. The patients complained of chronic vitreal opacities, increasing with time. These symptoms contrasted with the absence of the usual signs of inflammation of the anterior segment or of the retina, which characterize true uveitis. Vitrectomy was proposed after lumbar puncture and cerebral magnetic resonance imaging. Six vitrectomies were carried out, 3 patients had a stereotaxic biopsy, and 1 patient had a cardiac biopsy. A pathologic diagnosis of large B-cell lymphoma was made on vitrectomy specimens in 100% of the patients who had this procedure. The mean time from onset of ocular symptoms to diagnosis was 24 months. This series was characterized by a rare systemic dissemination of the NHL (negative in 80%), a strong preponderance of B-cell NHL, and the absence of association with Epstein-Barr virus (EBV) among these immunocompetent patients. To our knowledge, this series includes the only reported case of oculocardiac lymphoma. Meningeal dissemination appeared to be associated with a poor prognosis. Neurologic complications of treatment combining radiotherapy and methotrexate were significant among patients older than 60 years of age. The current study suggests that primary central nervous system lymphoma should be suspected in patients with pseudouveitis, and that the diagnosis can be established quickly and without side effects by vitrectomy. These patients should be followed carefully in order to detect meningeal dissemination.

Fatal disseminated Kaposi's sarcoma following human herpesvirus 8 primary infections in liver-transplant recipients.

Human herpesvirus 8 (HHV-8) is associated with the development of Kaposi's sarcoma (KS) and rare lymphoproliferative disorders in immunosuppressed patients. The risk of HHV-8 transmission by liver transplantation and the clinical manifestations of primary infection in this setting have yet to be determined. In order to evaluate this risk, we measured the seroprevalence of HHV-8 among 122 liver donors and their respective recipients before and after transplantation. Molecular methods and immunohistochemical analyses were performed to study the features of HHV-8 infection. Antibodies to HHV-8 were detected in sera of 4 donors before transplantation (3.3%) and of 3 recipients (2.4%). None of the 3 recipients, who were HHV-8 seropositive before transplantation, developed a KS during the follow-up. Four primary HHV-8 infections were detected among the 4 HHV-8 seronegative recipients who received a liver from an HHV-8 positive donor. Among these 4 recipients, 2 particularly immunosuppressed patients developed symptomatic diseases and died a few months after transplantation, harboring disseminated KS and HHV-8 positive lymphoproliferation. In these 2 patients, HHV-8 DNA genome sequences were detectable in peripheral blood mononuclear cells and other tissues with high viremia levels before and at the beginning of HHV-8-related diseases. In conclusion, in liver transplantation recipients, HHV-8 primary infection can be associated with fatal outcome. This study raises the question of screening liver donors for HHV-8--even in low HHV-8 infection prevalence countries--not systematically to exclude the graft but to monitor, clinically and biologically, patients who received a graft from an HHV-8-infected donor.

Delayed viral replication and CD4(+) T cell depletion in the rectosigmoid mucosa of macaques during primary rectal SIV infection.

Rectal infection of macaques by SIV is a model for rectal HIV transmission. We focus here on the digestive tract during days 7-14 of primary rectal infection by SIV in 15 rhesus macaques. Surprisingly, we did not detect productively infected cells in the rectosigmoid colon at early stages of viral dissemination. This strongly suggests that there is no massive viral amplification in the rectosigmoid colon prior to viral dissemination. As dissemination proceeds, productively infected T cells are observed in the rectosigmoid colon and small intestine, with rectosigmoid colon showing the heaviest viral load. Lymphoid follicles are infected prior to lamina propria at both sites. When viral dissemination is widespread, inflammatory infiltrates are visible in the rectosigmoid colon, but not in the small intestine. An important decrease in CD4(+) T cells is then observed in the lamina propria of the rectosigmoid colon only.

Stimulation of osteoprotegerin production is responsible for osteosclerosis in mice overexpressing TPO.

Myelofibrosis and osteosclerosis are prominent features arising in mice overexpressing thrombopoietin (TPO). The pivotal role of transforming growth factor beta 1 (TGF-beta 1) in the pathogenesis of myelofibrosis has been documented, but the mechanisms mediating osteosclerosis remain unclear. Here, we used mice deficient in osteoprotegerin (OPG), a secreted inhibitor of bone resorption, to determine whether osteosclerosis occurs through a deregulation of osteoclastogenesis. Marrow cells from opg-deficient mice (opg(-/-)) or wild-type (WT) littermates were infected with a retrovirus encoding TPO and engrafted into an opg(-/-) or WT background for long-term reconstitution. The 4 combinations of graft/host (WT/WT, opg(-/-)/opg(-/-), opg(-/-)/WT, and WT/opg(-/-)) were studied. Elevation of TPO and TGF-beta 1 levels in plasma was similar in the 4 experimental groups and all the mice developed a similar myeloproliferative syndrome associated with severe myelofibrosis. Osteosclerosis developed in WT hosts engrafted with WT or opg(-/-) hematopoietic cells and was associated with increased OPG levels in plasma and decreased osteoclastogenesis. In contrast, opg(-/-) hosts exhibited an osteoporotic phenotype and a growth of bone trabeculae was rarely seen. These findings suggest that osteosclerosis in mice with TPO overexpression occurs predominantly via an up-regulation of OPG in host stromal cells leading to disruption of osteoclastogenesis.

Prominent role of TGF-beta 1 in thrombopoietin-induced myelofibrosis in mice.

Several studies suggest an implication of transforming growth factor-beta1 (TGF-beta1) in the promotion of myelofibrosis associated with hematopoietic malignancies, but the involvement of this cytokine is not fully investigated. To test directly the impact of TGF-beta1 in the pathogenesis of myelofibrosis, bone marrow stem cells from homozygous TGF-beta1 null (TGF-beta1(-/-)) and wild-type (WT) littermates were infected with a retrovirus encoding the murine thrombopoietin (TPO) protein and engrafted into lethally irradiated wild-type hosts for long-term reconstitution. Over the 4 months of follow-up, TPO levels in plasma were markedly elevated in both groups of mice, and animals typically developed a myeloproliferative syndrome characterized by thrombocytosis, leukocytosis, splenomegaly, increased numbers of progenitors in blood, and extramedullary hematopoiesis. Severe fibrosis was observed in spleen and marrow from all the mice engrafted with WT cells. In contrast, none of the mice repopulated with TGF-beta1(-/-) cells (chimerism > 70%) showed deposition of reticulin fibers at any time during the follow-up. In accordance with the development of fibrosis, latent TGF-beta1 levels in plasma and extracellular fluid of the spleen from mice engrafted with WT cells were increased 6-fold and 4-fold, respectively, over levels found in normal hosts, whereas no increase over baseline levels could be demonstrated in animals undergoing transplantation with TGF-beta1(-/-) cells. These data provide evidence that TGF-beta1 produced by hematopoietic cells is pivotal for the pathogenesis of myelofibrosis that develops in mice with TPO overexpression.

Inflammation and cancer, the mastocytoma P815 tumor model revisited: triggering of macrophage activation in vivo with pro-tumorigenic consequences.

Subcutaneous in vivo injections of cells of the mastocytoma line P815 in syngenic DBA/2 mice induce locally fast growing solid tumors. These have been used extensively as a cancer model to analyze and manipulate the relationship between tumor cells and host's immune defenses. We report that progression of P815 tumors in vivo was accompanied by a burst (Days 5-7) of local inflammatory cells recruitment and angiogenesis observed histologically, corroborated in vivo by MRI with gadolinium, overtranscription of macrophage activation marker genes, secretion of TNF-alpha by regional lymph node cells and concomitant systemic inflammation. No substantial overtranscriptions of either VEGF or IL-10 or TGF-beta genes were observed. Induction of COX-2 gene was a late event. To establish a possible relationship between the tumor-induced local, regional and systemic increase of pro-inflammatory mediators and progression of tumors in vivo, we carried out experiments deliberately modulating the inflammatory status of the recipient animals. Pretreatment of recipient animals by i.p. injection of thioglycolate accelerated P815 tumor growth. At the opposite, treatment of mice with either a COX-1 + COX-2 inhibitor (aspirin, 1 mg/day/mouse) or a specific COX-2 inhibitor (celecoxib, 0.13 mg/day/mouse) for 2 weeks after injection of tumor cells, significantly reduced the size and growth rate of tumors compared to control mice. Experiments carried out in vitro indicated that peritoneal macrophages from untreated animals were strongly activated by live P815 cells and by P815 membrane preparations. The tumor-induced inflammatory reaction could establish a local micro environment favoring tumor progression. The P815 tumor model might be helpful to recognize important factors controlling host/tumor relationship.

Fluorescence in situ hybridization study of chromosome 7 aberrations in hepatosplenic T-cell lymphoma: isochromosome 7q as a common abnormality accumulating in forms with features of cytologic progression.

Hepatosplenic gamma delta T-cell lymphoma (HS gamma delta TCL) is a rare and aggressive subtype of peripheral T-cell lymphoma that has been associated cytogenetically with the isochromosome 7q [i(7)(q10)]. The incidence of this aberration and its relevance to pathogenesis of HS gamma delta TCL is still unknown. We investigated the status of chromosome 7 in 12 HSTCL cases, including nine with a typical gamma delta phenotype, one with a so-called T-cell receptor (TCR)-silent phenotype, and two with the variant alpha beta phenotype. We analyzed available fresh and archival material using a dual-color interphase fluorescence in situ hybridization (FISH) approach with 7p and 7q probes. A significant population of cells with predominance of 7q signals was detected in 10 cases (eight gamma delta, one alpha beta, and one TCR silent), and two lymphomas did not show clonal 7p/7q signal imbalances. In four of 10 cases with chromosome 7 aberrations, a hybridization pattern indicative of the presence of one chromosome 7 and one i(7)(q10) was found. In four other cases, the configuration of signals (2 x 7p/3 x 7q) suggested the presence of the i(7)(q10) and additional structural aberrations involving the second chromosome 7. In two cases, including one alpha beta phenotypic variant, a variety of FISH patterns equivalent to two to five copies of i(7)(q10) or numerical and structural aberrations of second chromosome 7 has been detected. These findings support cytogenetic data pointing to a characteristic association of i(7)(q10) with HSTCL, irrespective of the immunophenotype of malignant cells. An increased number of 7q signals was found in three cases with cytologic features of progression, indicating a tendency of HSTCL to multiply the i(7)(q10) chromosome during evolution.