Characteristics and clinical correlates of MPL 515W>L/K mutation in essential thrombocythemia

Among 994 patients with essential thrombocythemia (ET) who were genotyped for the MPLW515L/K mutation, 30 patients carrying the mutation were identified (3.0%), 8 of whom also displayed the JAK2V671F mutation. MPLW515L/K patients presented lower hemoglobin levels and higher platelet counts than did wild type (wt) MPL; these differences were highly significant compared with MPLwt/JAK2V617F–positive patients. Reduced hemoglobin and increased platelet levels were preferentially associated with the W515L and W515K alleles, respectively. MPL mutation was a significant risk factor for microvessel disturbances, suggesting platelet hyperreactivity associated with constitutively active MPL; arterial thromboses were increased only in comparison to MPLwt/JAK2wt patients. MPLW515L/K patients presented reduced total and erythroid bone marrow cellularity, whereas the numbers of megakaryocytes, megakaryocytic clusters, and small-sized megakaryocytes were all significantly increased. These data indicate that MPLW515L/K mutations do not define a distinct phenotype in ET, although some differences depended on the JAK2V617F mutational status of the counterpart.     

Allogeneic hematopoietic stem cell transplantation for myelofibrosis

Fifty-six patients, 10 to 66 years of age, with idiopathic myelofibrosis (IMF) or end-stage polycythemia vera or essential thrombocythemia received allogeneic hematopoietic cell transplants from related (n = 36) or unrelated (n = 20) donors. Forty-four patients were prepared with busulfan plus cyclophosphamide and 12 with total body irradiation plus chemotherapy. The source of stem cells was marrow in 33 and peripheral blood in 23 patients. All but 3 patients achieved engraftment. While 50 patients showed complete donor chimerism, 3 patients were found to be mixed chimeras at 26, 48, and 86 months after transplantation, respectively. Two patients died from relapse/progressive disease, and 18 died from other causes. There are 36 patients surviving at 0.5 to 11.6 (median, 2.8) years, for a 3-year Kaplan-Meier estimate of 58% (CI, 43%-73%). Dupriez score, cytogenetic abnormalities, and degree of marrow fibrosis were the most significant risk factors for posttransplantation mortality. Patients conditioned with a regimen of busulfan targeted to plasma levels of 800 to 900 ng/mL plus cyclophosphamide had a higher probability of survival (76% [CI, 62%-91%]) than other patients. Results with unrelated donors were comparable with those with HLA-identical sibling transplants. Thus, allogeneic hematopoietic cell transplantation offers long-term relapse-free survival for patients with myelofibrosis.     

Allogeneic hematopoietic stem cell transplantation for myelofibrosis

PURPOSE OF REVIEW: This review summarizes the current status and new developments in allogeneic hemopoietic stem cell transplantation strategies for patients with myelofibrosis with myeloid metaplasia, focusing on novel concepts of allogeneic transplantation with reduced-intensity conditioning. RECENT FINDINGS: No substantial progress has been made in the conventional management of myelofibrosis with myeloid metaplasia. Allogeneic hemopoietic stem cell transplantation represents the only treatment modality with proven curative potential. Standard-dose conditioning regimes followed by allogeneic transplantation are associated with a relatively high transplant-related mortality. Reduced-intensity conditioning regimens have substantially reduced treatment-related mortality. This result is from three studies on myelofibrosis with myeloid metaplasia including more than 60 patients overall. The optimal conditioning regimen for this condition is unknown, in particular the utility of using T-cell depleted stem cells to reduce graft versus host disease is not documented. Emerging concepts include new risk classification for a better provision of the transplant outcome, and splenectomy before transplantation for reducing tumor burden. SUMMARY: The data on hemopoietic stem cell transplantation with reduced-intensity conditioning in myelofibrosis with myeloid metaplasia are encouraging. An accurate risk stratification is a pivotal procedure for selecting patients who will receive the greatest benefit for transplantation. Reduced-intensity conditioning should be further evaluated within clinical trials, in particular for assessing the role of splenectomy and for testing the optimal conditioning regimen.     

Co-culture of hematopoietic stem cells with mesenchymal stem cells increases VCAM-1-dependent migration of primitive hematopoietic stem cells

Hematopoietic stem cells (HSC) lose their capacity for engraftment during ex vivo cytokine expansion. It has been shown that mesenchymal stem cells (MSC) improve HSC transplantability; however, the molecular mechanisms responsible for this effect have not yet been completely elucidated. This paper reports that expanding HSC in co-culture with MSC enhances a vascular cell adhesion molecule (VCAM-1)-dependent pro-migratory phenotype. MSC did not regulate the HSC expression of CD49d (VCAM-1 counter-receptor molecule), but did decrease the cytokine-induced HSC VCAM-1-mediated pro-adhesive phenotype. Co-culture with MSC reduced the expression of the inactive conformation of lymphocyte function-associated antigen (LFA-1) at the HSC uropod, and induced higher expression of an LFA-1 activation epitope. Interestingly, VCAM-1-dependent HSC migration was modulated by targeting this LFA-1 high affinity form, suggesting integrin cross-regulation. VCAM-1-mediated HSC transmigration appeared to favor the more primitive HSC immunophenotype. Our results suggested that co-culture with MSC improved VCAM-1-dependent migration of primitive HSC, which was affected in ex vivo cytokine-expanded HSCs by a mechanism involving LFA-1 modulation.     

Cyclic hematopoiesis: disorders of primitive hematopoietic stem cells

Utilizing both in vivo and in vitro techniques, a great deal of information has been obtained on the structure and regulation of the hematopoietic cell lineages. A number of hematopoietic stem cells and regulators have now been well characterized and their possible physiologic relevance at least in part established. More recently, new "alternative" or primitive stem cells have been described which may provide important insights into the nature of hematopoietic regeneration and regulation. These include late CFUs, high proliferative potential colony-forming cells, colony-forming unit diffusion chamber and both bipotent and blast colonies assayed in in vitro culture systems. Regulators active at these stem cell levels are also under study and in large part appear to be produced by monocytes or lymphocytes. Cyclical hematopoiesis can be viewed as a genetic abnormality at the multipotent stem cell level with defective cell production. At present however, details of the defect await further investigation possibly including an evaluation of the role of primitive stem cells and their regulators.     

Development and aging of primitive hematopoietic stem cells in BALB/cBy mice.

Evaluating the function of an individual hematopoietic stem cell (HSC) is a difficult and important problem. The functional ability per HSC, as well as the HSC concentration, was measured with minimal disruption to the cells in vivo using the new competitive dilution assay. Distribution of HSC into recipients was modeled based on Poisson probabilities. Predictions of donor contributions from models assuming different levels of donor HSC functional ability and concentration were compared to actual observations. The model with the least difference between predictions and observations was accepted. In BALB/ cBy (BALB) mice, models assuming equal functional ability of HSC from the same donor fit extremely well with actual observations, suggesting that all HSC are functionally homogeneous at any particular time point during development or aging. Relative HSC functional ability per cell declined during development, so that a fetal HSC had 1.6 to 3.0 times the functional ability of a young adult HSC. The decline continued with age, so that a young adult HSC had 1.6 to 2.0 times the functional ability of an old HSC. Concentrations of HSC that engrafted and functioned were similar among 16-day fetal liver cells and bone marrow cells (BMC) from 3-month and 25 to 28-month-old adult mice. They were either 10 or 4 HSC per million cells when tested in BALB or CByB6F1 recipients, respectively. All HSC were pluripotent and produced lymphoid and myeloid descendants proportionally (r = 0.80 to 0.98, p < 0.01). Fetal and young HSC in both types of recipients maintained clonal stability long term so that percentages of donor cells at 6 and 9 months were strongly correlated (r = 0.72 to 0.93, p < 0.01). Although HSC from aged donors in BALB recipients maintained clonal stability, HSC from the same aged donors failed to show clonal stability in CByB6F1 recipients, perhaps due to the less suitable host environment. All HSC from BALB mice seemed to have equal functional levels at a given stage of life and were gradually exhausted simultaneously through development and aging.     

Concurrent MPL515 and JAK2V617F mutations in myelofibrosis: chronology of clonal emergence and changes in mutant allele burden over time

MPLW515L/K and JAK2V617F can co-exist in myelofibrosis with myeloid metaplasia (MMM).The chronology of clonal emergence was studied in three such cases using serially stored bone marrow. At diagnosis, a major MPL515 mutant clone was accompanied by a minor JAK2V617F clone in all three instances. At 25 time points over a period of 4-8 years, allele burden fluctuated but remained high for MPLW515L/K and low for JAK2V617F. We conclude that MPLW515L/K and JAK2V617F are both early events in MMM and allele burden, rather than the mere presence of these mutations, might be relevant to phenotypic variation in myeloproliferative disorders.     

MPL515 mutations in myeloproliferative and other myeloid disorders: a study of 1182 patients

Recently, a gain-of-function MPL mutation, MPLW515L, was described in patients with JAK2V617F-negative myelofibrosis with myeloid metaplasia (MMM). To gain more information on mutational frequency, disease specificity, and clinical correlates, genomic DNA from 1182 patients with myeloproliferative and other myeloid disorders and 64 healthy controls was screened for MPL515 mutations, regardless of JAK2V617F mutational status: 290 with MMM, 242 with polycythemia vera, 318 with essential thrombocythemia (ET), 88 with myelodysplastic syndrome, 118 with chronic myelomonocytic leukemia, and 126 with acute myeloid leukemia (AML). MPL515 mutations, either MPLW515L (n = 17) or a previously undescribed MPLW515K (n = 5), were detected in 20 patients. The diagnosis of patients with mutant MPL alleles at the time of molecular testing was de novo MMM in 12 patients, ET in 4, post-ET MMM in 1, and MMM in blast crisis in 3. Six patients carried the MPLW515L and JAK2V617F alleles concurrently. We conclude that MPLW515L or MPLW515K mutations are present in patients with MMM or ET at a frequency of approximately 5% and 1%, respectively, but are not observed in patients with polycythemia vera (PV) or other myeloid disorders. Furthermore, MPL mutations may occur concurrently with the JAK2V617F mutation, suggesting that these alleles may have functional complementation in myeloproliferative disease.     

Ultrastructure of primitive hematopoietic stem cells isolated using probes of functional status

The most primitive hematopoietic stem cells capable of longterm reconstitution of the entire hematopoietic system following transplantation are characterized by their ability to exclude both Rhodamine 123 and Hoechst 33342 dyes (Rh/Ho(dull)), and are an appropriate target population for the determination of stem cell ultrastructure. We have used a fluorescence-activated cell sorter to enrich to near purity these rare, highly quiescent cells. Analysis of the in vitro growth characteristics of Rh/Ho(dull) cells demonstrated an obligatory requirement for multiple growth factors, with 62% of the sorted population having the capacity to form colonies in the presence of CSF-1 + IL-1alpha + IL-3 + SCF. The Rh/Ho(dull) cells were small, with profiles having a mean diameter of 4.6 microm. Ultrastructural examination showed numerous ribosomes and several mitochondria in the thin rim of cytoplasm surrounding the nucleus, with other cytoplasmic organelles revealed in serial sections. The cells were generally homogeneous in appearance apart from the nucleus, which had an irregular shape with a single deep indentation. The heterochromatin around the margin was distinctly more pronounced in about 50% of nuclei. The findings provide a basis for studying the structural changes that occur with progressive differentiation of early hematopoietic cells.     

Prognostic value of JAK2, MPL and CALR mutations in Chinese patients with primary myelofibrosis

<正>Objective To evaluate the prognostic value of JAK2,MPL and CALR mutations in Chinese patients with primary myelofibrosis(PMF).Methods Four hundred and two Chinese patients with PMF were retrospectively analyzed.The Kaplan-Meier method,the Log-rank test,the likelihood ratio test and the Cox proportional     

In vivo expansion of purified hematopoietic stem cells transplanted in nonablated W/Wv mice

We have evaluated the in vivo amplification potential of purified murine hematopoietic stem cells, identified as Wheat Germ Agglutinin+ (WGA+), 15-1.1(-) , Rhodamine 123 Dull (Rho-dull) cells, by serial transplantation into stem cell defective nonmyeloablated W/Wv mice. C57BL Rho-dull cells (250/ 500 cells/mouse) permanently engrafted nonablated W/Wv mice as defined by the presence of > 95% red and > 20% white donor-derived circulating cells for at least 1.5 years following transplantation. At this time, approximately 61% of Rho-dull cells and all the Rho-bright progenitor and colony forming cells of the engrafted mice were found to be donor-derived by c-Kit genotyping and by their response to stem cell factor (SCF). Retransplantation of 250-1000 Rho-dull cells from primary into secondary W/Wv recipients generated C57BL hematopoiesis in 40%-64% of animals revealing the presence of donor derived hematopoietic stem cells (HSC) in the bone marrow of the primary recipients. One and half years after transplantation, the bone marrow of the secondary engrafted animals contained C57BL Rho-dull cells approximately = 51% by genotype), which were capable of reconstituting tertiary W/Wv recipients. In this respect, 25% of tertiary mice expressed C57BL hematopoiesis when transplanted with 250-1000 Rhodull cells purified from secondary W/Wv recipients. On the basis of the number of Rho-dull cells purified from a single mouse, we calculate that approximately 7.3x10(4) Rho-dull cells, which are genotypically and functionally defined as C57BL long-term repopulating stem cells, were generated in the marrow of reconstituted primary W/Wv recipients transplanted 1.5 years earlier with 250-500 C57BL Rho-dull cells. We conclude that murine HSC have extensive amplification capacity in nonmyeloablated animals.     

Agnogenic myeloid metaplasia: a clonal proliferation of hematopoietic stem cells with secondary myelofibrosis

The glucose-6-phosphate dehydrogenase (G-6-PD) types and chromosomes of hematopoietic and other tissues were determined in a woman with agnogenic myeloid metaplasia. The patient was heterozygous at the X- linked G-6-PD locus so that both B and A isoenzymes were found in nonhematopoietic cells. In contrast, only one G-6-PD type was found in granulocytes, red cells, and platelets. She also had a distinctive chromosome abnormality in blood cells but not in other tissues. These results indicate that agnogenic myeloid metaplasia is a disorder of a pluripotent stem cell and provide strong evidence that it is of clonal origin. In contrast to blood cells, the patient's cultured marrow "fibroblasts" had normal chromosomes and both B and A G-6-PD types, suggesting that the marrow fibrosis is a secondary abnormality. Thus, at least in this case of agnogenic myeloid metaplasia, the hematopoietic cell proliferation appears to be clonal, and, by inference, possibly neoplastic, whereas the marrow fibrosis is probably not clonal, and therefore appears to be secondary.