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H M Kvasnicka

Publications and source records attributed to H M Kvasnicka.

At least 37 records · Page 2Linked to original sources
PubMed2004

Therapy-related changes of the bone marrow in chronic idiopathic myelofibrosis.

In chronic myeloproliferative disorders (CMPDs) a conflict of opinion exists regarding therapy-induced bone marrow (BM) changes and the evolution of myelofibrosis during the lengthy course of the disease. For a more elaborate study of these features chronic idiopathic myelofibrosis (IMF) seems to be a most suitable condition. Therefore this review is focused on this CMPD and amongst other findings analyzes data from a series of 340 patients with a long follow-up including 893 biopsies (median interval of 32 months). The ensuing results were compared with those communicated in the relevant literature. In addition to a control group of 153 patients with IMF who received only symptomatic treatment, therapy groups included busulfan, hydroxyurea, interferon and various combinations. In all groups hypoplasia of a varying degree was a frequent finding (6%) and often accompanied by a patchy arrangement of hematopoiesis. Most conspicuous was a gelatinous edema showing a tendency to develop a discrete reticulin fibrosis (scleredema). Aplasia developed in 7.7% of patients, usually at terminal stages of the disease independently of treatment. Minimal to moderate maturation defects of hematopoiesis involved especially megakaryocytes and erythroid precursors, but overt myelodysplastic features were most prominent following hydroxyurea and busulfan therapy. Acceleration and blastic crisis were characterized not only by increasing dysplastic changes, but also by the appearance of blasts including CD34+ cells. Semiquantitative grading of the fiber content revealed that 183 patients (54%) without or with moderate fibrosis at the beginning showed a significant progression and therefore contrasted with the 66 patients with a stable state. Following this calculation no relevant differences in the evolution of myelofibrosis were evident in the various therapy groups especially not following interferon treatment. In a few patients a regression was found which was accompanied by a severe hypoplasia or aplasia compatible with a myelo-ablative effect. In conclusion, peculiar BM changes, in particular conspicuously expressed myelodysplastic features are consistent with therapy-related lesions. Development of myelofibrosis in IMF is obviously due to disease progression unrelated to stage at diagnosis and not significantly influenced by treatment modalities.

Animals↗
PubMed2003

Chronic myeloproliferative disorders with thrombocythemia: a comparative study of two classification systems (PVSG, WHO) on 839 patients.

A multicenter observational study was performed on 839 adult patients with a chronic myeloproliferative disorder and a platelet count in excess of 600 x 10(9)/l to compare the updated criteria of the Polycythemia Vera Study Group (PVSG) with the recently published WHO classification. Essential thrombocythemia (ET) was diagnosed in 483 patients according to the PVSG; however, when considering histopathology as a major diagnostic feature of the WHO criteria, (true) ET could be established in only 162 patients. The remaining cases were found to represent either initially prefibrotic (184 patients) or early fibrotic (137 patients) chronic idiopathic myelofibrosis (IMF). On the other hand, both classification systems enabled a clear-cut distinction of patients showing overt IMF and polycythemia vera. Follow-up examinations in 140 patients with ET according to the PVSG criteria included also sequential bone marrow biopsies (interval: 38+/-30 months). A transition into mild reticulin fibrosis occurred in only 2 of 49 patients with (true) ET in contrast to 45 of 91 patients with initial and early IMF where a progression into overt myelofibrosis was encountered. Survival patterns for ET displayed significant differences because according to the PVSG a 16.5% disease-specific loss of life expectancy was calculable compared to a value of only 8.9% when following the WHO criteria. Contrasting this finding, initial and early IMF mimicking ET was characteriZed by a reduction of life expectancy ranging between 21.6% and 32.3 %. In conclusion, a more accurate classification of ET is warranted by regarding the WHO criteria that include histopathology as a major feature for diagnosis.

Adult↗
PubMed2003

Bone marrow histopathology following cytoreductive therapy in chronic idiopathic myelofibrosis.

AIMS: To analyse systematically therapy-induced lesions of haematopoiesis in chronic idiopathic myelofibrosis (IMF). METHODS AND RESULTS: A total of 759 sequential bone marrow (BM) biopsies (median interval 32 months) were performed in 261 patients with IMF. Besides a control group (symptomatic treatment), monotherapies included busulfan, hydroxyurea and interferon. In all therapy groups hypoplasia of varying degree was a frequent finding and often accompanied by a patchy distribution of haematopoiesis. Most conspicuous was gelatinous oedema showing a tendency to develop discrete reticulin fibrosis (scleroedema). Minimal to moderate maturation defects of megakaryopoiesis and erythroid precursors occurred, but overt myelodysplastic features were most prominent following hydroxyurea and busulfan therapy. Acceleration and blastic crisis were characterized by the appearance of immature and CD34+ progenitor cells. Concerning the dynamics of fibrosis, no differences were observed between controls and the various therapy groups. In 143 patients (55%) without or with little reticulin at onset, an increase in myelofibrosis was detectable that progressed to overt collagen fibrosis. CONCLUSIONS: Therapy-related bone marrow lesions in IMF comprise a strikingly variable spectrum that may include aplasia with scleroedema and a patchy distribution of myelodysplastic haematopoiesis associated with progressive myelofibrosis.

Aged↗
PubMed2003

Dynamics of fibrosis in chronic idiopathic (primary) myelofibrosis during therapy: a follow-up study on 309 patients.

Controversial issues in chronic idiopathic myelofibrosis (IMP) are amongst others the evolution of the disease process and the influence of therapy on the dynamics of fibrosis. For this reason, a multicenter observational study was performed on 309 patients with IMF that had a long follow-up including 822 bone marrow biopsies at a median interval of 32 months. In addition to a control group (156 patients) with symptomatic treatment, monotherapy consisted of busulfan (30 patients), hydroxyurea (52 patients), interferon (26 patients) and various combinations (48 patients). Density and quality (reticulin/collagen) of fibers was determined by a semiquantitative scoring system. Independent of therapeutic regimens at the time of the last bone marrow biopsy 67% of the patients with grades 0-2 fibrosis revealed a progression, 42% stable state and 6% regression of myelofibrosis. Because of significant differences concerning frequencies of biopsies and endpoints of examinations, individual changes in the grades of fibrosis were evaluated with regard to treatment applied at standardized intervals of 20 months. According to this calculation no relevant differences in the dynamics of myelofibrosis (progression, stable state) was detectable in the control group compared to the other therapeutic modalities. The few patients with a regression of myelofibrosis usually presented with severe hypoplasia compatible with a myelo-ablative effect by aggressive chemotherapy. In conclusion, persuasive evidence has been produced that myelofibrosis in IMF is characterized by a stepwise progression and that this process is not significantly influenced by current treatment strategies.

Biopsy↗
PubMed2003

Mixed chimerism of erythro- and megakaryopoiesis following allogeneic bone marrow transplantation.

Until now, studies on mixed chimerism (MCh) after allogeneic bone marrow transplantation (BMT) have predominantly focused on the B- and T-lymphocyte population, but not on distinct myeloid cell lineages like nucleated erythroid precursors and megakaryocytes. To evaluate the lineage-restricted MCh more explicitly in 10 patients with chronic myelogenous leukemia (CML), a quantitative analysis was performed on bone marrow biopsies following a sex-mismatched host/donor constellation. Techniques included immunophenotyping (antiglycophorin C, CD61) for the identification of erythro- and megakaryopoiesis and a simultaneously conducted genotyping with x- and y-chromosome-specific DNA probes. Normal bone marrow and specimens taken before BMT served as controls. Contrasting a total gender-dependent sex-typing in the latter samples in the early and late posttransplant period (up to 586 days), 3-9% erythroid precursors and about 16% megakaryocytes revealed a host-type origin. This significantly higher number of host megakaryocytes is explained by their polyploidy generating an increased probability to detect positive signals at a certain section level of the corresponding biopsies. A striking conversion of MCh to a recipient cell type was found in leukemic relapse with a more than 90% host-derived erythroid and megakaryocytic cell population in 4 patients approximately 643 days after BMT.

Adult↗
PubMed2003

Dynamics of lineage-restricted mixed chimerism following sex-mismatched allogeneic bone marrow transplantation.

Scant knowledge is available about the dynamics of lineage-specific mixed chimerism (Ch) following bone marrow transplantation (BMT). This review is focused on findings derived from bone marrow (BM) biopsies in patients with chronic myeloid leukemia (CML) including a sex-mismatched host/donor constellation. Appropriate techniques involved immunophenotyping by monoclonal antibodies to identify the various cell lineages, dual color fluorescence in situ hybridization (FISH) with x- and y-chromosome-specific DNA-probes and a proper detection system for a simultaneous labeling of the bcr/abl locus. A significant degree of Ch with more than 20% host CD34+ progenitors was found in the early and late (up to 200 days after BMT) posttransplant period. However, only 10% of these cells harbored the bcr/abl translocation gene. This result fits well with corresponding molecular biological findings of so-called minimal residual disease. Conversion of Ch evolved during leukemic relapse with 90% host progenitors of which 50% revealed the bcr/abl locus. A Ch of nucleated erythroid percursors (5%) and CD68+ macrophages (8%) was expressed to a significantly lower degree. The slightly increased frequency found in CD61+ megakaryocytes (16%) was probably due to the polyploid state of these cells. Similar to the CD34+ progenitor cells abrupt changes from donor to host type was associated with an insidious transformation into recurrent leukemia. The CD34+ endothelial cells showed a minor degree of Ch, because donor-derived elements ranged from 18% to 25%. Leukemic relapse was characterized by an almost complete conversion of the endothelial cells to a host type. These findings point towards a CD34+ progenitor cell origin of the (leukemic) endothelial cell layer and suggests that their dysfunction may contribute to an expansion of the neoplastic clone.

Animals↗
PubMed2003

Diagnostic differentiation of essential thrombocythaemia from thrombocythaemias associated with chronic idiopathic myelofibrosis by discriminate analysis of bone marrow features--a clinicopathological study on 272 patients.

Until now diagnosis of essential thrombocythaemia (ET) is generally performed by following the criteria of the Polycythaemia Vera Study Group (PVSG) that only marginally regards morphological features. Bone marrow biopsies were studied from 272 patients with ET in strict accordance with the PVSG guidelines and also from 35 control patients with reactive thrombocytosis. To define morphological features of distinctive impact more accurately, we performed a stepwise discriminant analysis of 16 morphological parameters based on histochemical staining reactions and semiquantitative grading of standardized features. A clear-cut separation into three distinctive histological patterns was accomplished that showed in more than 96% a correct predicted classification. Variables of significant impact included fibre content, quantity and cytological abnormalities of megakaryopoiesis like bulbous (cloud-like) nuclei, degree of nuclear lobulation and presence of giant forms. These changes were not detectable in the control group. The different constellations of histopathological features could be assigned to true ET (98 patients) and false ET, i.e. 136 patients with prefibrotic and 38 patients with early fibrotic chronic idiopathic myelofibrosis (IMF) accompanied by thrombocythaemia. A re-evaluation of clinical findings was in keeping with this classification into three categories that exerted significant differences to develop myelofibrosis during observation time and also different survival patterns. Contrasting IMF true ET is characterized by a pronounced proliferation of the megakaryocyte lineage showing large to giant cells without maturation defects and no relevant increase in reticulin fibres. Discrimination between these entities is warranted, because of a significant difference in presenting haematological data, follow-up and life expectancy.

Bone Marrow Cells↗
PubMed2002

[Diagnostic spectrum of Philadelphia-chromosome negative leukemic disorders].

The spectrum of Philadelphia-chromosome negative leukemoid disorders displays a large heterogeneity of clinical and morphological findings at presentation. According to the FAB guidelines as well as the WHO classification, independent subtypes with different morphological features can be distinguished. In particular, based on the degree of dysgranulopoiesis, the extent of monocytosis, basophilia and the amount of immature and mature granulocytes in the peripheral blood and the percentage of erythroblasts, most of these cases can be correctly classified as either atypical chronic myeloid leukemia (aCML) or chronic myelomonocytic leukemia (CMML). An increase in immature and dysplastic granulocytes in the blood films at presentation accompanied by granulocytic dysplasia, is the most important diagnostic parameter of aCML. On the other hand, CMML is characterized by absolute monocytosis and, as explicitly outlined by the WHO classification, may show myelodysplastic and myeloproliferative features. However, in the absence of characteristic cytogenetic or molecular abnormalities for both diseases, a minority of patients still remain who are difficult to assign to a distinctive entity, since they either show overlapping features or do not fulfill the whole set of diagnostic criteria. Furthermore, controversy and discussion arise about aCML with monocytosis and its association to CMML. Finally, leukemoid reactions and the very rarely encountered chronic neutrophilic leukemia (CNL) should be considered in patients with chronic leukocytosis. In conclusion, careful morphological analysis of bone marrow histology as well as peripheral blood films and bone marrow smears, enables the identification of patients with different prognosis and therapeutic response.

Biopsy↗
PubMed2002

[Quantification and morphometric analysis of vascular structures in the bone marrow. A critical review].

The important role of angiogenesis for invasion, tumor growth, metastasis and progression of solid tumors is well established. Only recently, the clinical significance of neovascularization in hematological neoplasms has come into the focus of scientific efforts. Emerging data from these studies suggest that the vascular architecture exerts a pivotal role in acute leukemias and multiple myeloma as well as myeloproliferative disorders. Thus, angiogenesis seems to maintain a general condition for malignant growth and the progression of hematological diseases. However, a major shortcoming is that most of the previous studies include only a simple quantitative evaluation of the microvessel density, and applied methods which were developed primarily for the characterization of angiogenesis in solid tumors. In this context it should not be overlooked that solid neoplasms and the bone marrow reveal significant differences regarding the vascular structures and the distribution of microvessels. Therefore, the usually applied, so-called hot-spot techniques, should be amended by an appropriate and more elaborate computer-assisted morphometric analysis of the microvessel structures. This additional spectrum of information regarding quantity and quality of angiogenesis, enables a further understanding of the morphological changes in the course of diseases, and in particular the effect of various therapies on bone marrow vascularization.

Blood Vessels↗
PubMed2002

[Anagrelide-induced changes of megakaryopoiesis during therapy of chronic myeloproliferative disorders with thrombocythemia].

Thrombocythemia in the course of chronic myeloproliferative disorders like chronic idiopathic myelofibrosis (cIMF) and of course essential thrombocythemia (ET), are characterized by life-threatening complications. In a number of clinical trials the recently introduced drug Agrylin((R)) has proven to be very effective. The normalization of the platelet count was related to an interference with megakaryocyte maturation leading to a left-shifting of this cell lineage and/or a reduced proliferation. However, until now no systematic study has been performed on the relationship between development of megakaryopoiesis and proliferative activity. In this investigation we included 10 patients with cIMF and 5 patients with ET that had received Agrylin((R)) for a period ranging between 6 and 70 months. Following therapy this cohort revealed a decrease in the platelet count from 1,104x10(9)/l at diagnosis to 485x10(9)/l. In this context we focused on an immunohistochemical and morphometric analysis of the CD61(+) megakaryopoiesis involving also endomitotic reduplication, by applying a double-immune incubation technique with the proliferating cell nuclear antigen (PCNA). Moreover, we determined the changes of fiber density during observation time. According to our results, the thrombocytopenic effect of Agrylin((R)) is based on an arrest in the dynamics of megakaryocyte maturation towards large (mature) platelet-shedding (polyploid) cells. This pathomechanism causes a significant increase in the number of promegakaryoblasts and megakaryoblasts. On the other hand, the total amount of CD61(+) megakaryocytic cells is not increased. Related to the peculiar cell biology of endomitotic reduplication during the maturation process and its different periods alloted to each single step, PCNA activity (late G1- and S-phase of the cell cycle) is found to be enhanced in the megakaryocyte precursors. Finally, no significant influence of Agrylin((R)) on the evolution of myelofibrosis is detectable and there is a general improvement of hematological data especially in cIMF.

Blood Platelets↗
PubMed2002

[Chimerism of cardiomyocytes and endothelial cells after allogeneic bone marrow transplantation in chronic myeloid leukemia. An autopsy study].

The results of a number of animal experimental studies are in keeping with the finding that hematopoietic progenitors can generate cardiomyocytes and endothelial cells. As a consequence innovative therapeutic strategies have been suggested to possibly ameliorate the outcome of coronary artery disease. However, there is no information available at present whether this pathomechanism is also effective in humans, in particular without prior ischemic lesion of the myocardium. Therefore an autopsy study was performed on cadaver hearts derived from five male patients with chronic myeloid leukemia who received full unmanipulated bone marrow grafts from female donors 21-631 days before death. The purpose of this investigation was to detect and quantify a putative chimerism of cardiomyocytes and endothelial cells (intramural and subepicardial vessels). Genotyping was carried out by applying X- or Y-chromosome-specific DNA probes (fluorescence in-situ hybridisation) on routinely formalin-fixed specimens of the myocardium. To test the sensitivity of our method, cadaver hearts from two males and two females without a history of transplantation served as controls. In contrast to a totally corresponding sex-matched genotyping in 780 cardiomyocytes and 155 endothelial cells of the control group, the five male patients with a previous transplantation revealed significantly different results. A mixed chimerism was identifiable in 57 out of 890 counted cardiomyocytes (6.4%) and in 19 out of 322 endothelial cells (5.8%). These findings support the assumption that in addition to endothelial cells there is also a cardiomyogenic potential of bone marrow stem cells which exists without prior (ischemic) damage to the heart. However, further investigations are necessary to identify, isolate and enrich the cardiomyocytic stem cells more specifically for future curative therapeutic options in patients with severe ischemic cardiomyopathy.

Adult↗
PubMed2002

[Extramedullary initial manifestations of acute myeloid leukemia (AML)].

Extramedullary myeloblastic tumors, so-called myelosarcomas (granulocytic sarcomas, chloromas) have been reported only sporadically in the pertinent literature which reflects their rather infrequent occurrence. These lesions may accompany the initial manifestation or signal relapse of acute myeloid leukemia (AML) or coincide with blastic transformation of a chronic myeloproliferative disorder. However, even more rarely, primary myelosarcomas may precede AML by months or years or may be associated with myelodysplastic syndromes (MDS) that never progress to manifest leukemia. In a retrospective evaluation a clinicopathological study on these latter two variants of isolated extramedullary manifestations of AML was performed to elucidate certain aspects of site involvement and histopathology by application of enzyme and immunohistochemistry. For this reason, we selected 6 patients presenting with a myelosarcoma in combination with MDS and 12 patients revealing only uncharacteristic reactive changes of the bone marrow. Of these patients 8 developed AML following an observation time of up to 2 years. Focal leukemic infiltrates were most often localized in the skin ( n=4), oral mucosa ( n=4), lymph nodes ( n=3), gastrointestinal tract ( n=3) or pleura and retroperitoneum ( n=3 each). Myelosarcomas were usually regarded by the clinicians as putative malignant lymphomas unless further evaluation, especially involving chloroacetate esterase reactions as well as immunostaining with a panel of antibodies reactive with lysozyme, myeloperoxidase, CD68, CD43, CD56, CD117 and CD34 proved their true nature. Although at that time bone marrow findings were inconclusive, a straightforward diagnosis was reached by considering the possibility of a (primary) myelosarcoma in these patients.

Adolescent↗
PubMed2002

[Differentiation of granulomatous lesions in the bone marrow].

Granulomas are an infrequent finding in bone marrow biopsies and may be associated with a broad spectrum of infectious and non-infectious disorders. In this context sarcoidosis generally reveals the highest incidence of such bone marrow lesions. Other granulomas may be encountered in drug-induced secondary changes (toxic myelopathy) and in particular also in HIV myelopathy. In these cases the granulomas are small, ill-defined and difficult to recognize. Special staining methods are required to detect microorganisms. Fibrin ring granulomas (doughnut granulomas) are typical for Q-fever, but may also be seen in reactive conditions, after drug therapy and in the course of other infectious disorders, such as Lyme disease. Therefore a broad serological testing should be performed. In conclusion, in most cases the morphological findings in the bone marrow are not specific so that a synoptical approach regarding histological, clinical and serological data is warranted to reach the correct diagnosis.

Bone Marrow↗
PubMed2002

[Bone marrow manifestation of Niemann-Pick disease. A review of histiocytic proliferations of the bone marrow].

Niemann-Pick disease is an inherited autosomal recessive lysosomal storage disorder of sphingolipids that results in an accumulation of sphingomyelin in the cells of the reticulo-histiocyte system due to an enzyme defect. Type B of this disorder is characterised by a late onset and a variable manifestation of clinical symptoms. In the presented case a bone marrow biopsy was performed because of a pancytopenia and splenomegaly. A suspicious histiocyte proliferation was found in the bone marrow, showing typically large macrophages with foamy cytoplasm. Enzymatic analysis of a fibroblast culture confirmed the diagnosis of Niemann-Pick disease type B, with reduced activity of acid sphingomyelinase. A broad spectrum of disorders is associated with an increase in histiocytic cells within the bone marrow. In particular the differential diagnosis includes typical storage diseases, such as Gaucher's disease, and other metabolic disorders. Furthermore, reactive conditions with secondary increase in bone marrow macrophages have to be considered. In accordance with the presented patient the most common causes of histiocytic disorders involving the bone marrow are reviewed.

Bone Marrow↗
PubMed2002

CD34+ progenitor cells in idiopathic (primary) myelofibrosis: a comparative quantification between spleen and bone marrow tissue.

Previous studies on idiopathic (primary) myelofibrosis (IMF) are in keeping with the finding of an increased number of circulating CD34+ progenitor cells. However, dependent on the fibrosclerotic changes, little knowledge exists about quantitative relationships of this precursor cell population in spleen and bone marrow. The purpose of this study was to determine the number of CD34+ cells at these sites by applying immunohistochemistry and morphometry. In seven patients with IMF and a control group without hematopathology (14 patients), CD34+ progenitors were identified in the red pulp of the spleen and also in bone marrow trephine biopsies by the monoclonal antibody QBEND10. Histological analysis showed no differences regarding size or cytological details of these cells at both sites in patients with IMF as well as in the controls. On the other hand, in the IMF group there was an unequal distribution with an approximate twofold increase in precursor cells in the spleen compared to the bone marrow. This result is opposed to corresponding values of the control group. Considering the quantity of progenitor cells in the normal bone marrow, no significant increase was revealed in IMF, but a marked pooling (more than fourfold of the normal value) in the spleen. In conclusion, our findings are in keeping with a increased number of splenic CD34+ progenitor cells and therefore support the hypothesis of a pronounced filtration and trapping of this precursor cell population by the spleen in IMF.

Aged↗
PubMed2002

Early-stage idiopathic (primary) myelofibrosis--current issues of diagnostic features.

Idiopathic myelofibrosis (IMF) is generally characterized by bone marrow (BM) fibrosis, anemia, splenomegaly and a leuko-erythroblastic blood picture. Although, histopathology is in keeping with the assumption of a stepwise evolution of the disease, little hematological data are available for patients with prefibrotic and early stages of disease. Therefore a clinicopathological study was performed that included firstly an exploratory sample of 68 patients with minor supportive therapy in whom BM biopsies during follow-up (41 +/- 32 months) revealed an evolution of a prefibrotic or very early fibrotic lesion into overt IMF. The validation sample consisted of 556 patients with pretreatment marrow specimens on admission. Diagnostic features and BM lesions were identical compared with the patients of the exploratory sample at their first examination. BM biopsies were processed by routine stainings including silver impregnation (reticulin fibers) and frequently also by immunohistochemistry to identify megakaryocytes and erythroid precursor cells more properly. Apart from minor hemorrhage and peripheral thrombosis patients with early stage IMF presented with non-specific symptoms including varying degrees of leukocytosis (51%), anemia (38%), a platelet count exceeding 600 x 10(9)/l (86%), splenomegaly (15%) and increase in leukocyte alkaline phosphatase (LAP) (24%) and serum lactate dehydrogenase (LDH) (20%). BM histology confirmed a moderate increase in hematopoiesis with a mixed granulocytic and megakaryocytic myeloproliferation, a reduction of erythroid precursors and significant megakaryocytic abnormalities. In keeping with the first BM examination of the exploratory sample no or only a borderline to slight increase in reticulin fibers was detectable, however, in 68 of 134 patients follow-up biopsies revealed a transition into overt IMF (intervals about three years). Median survival of this cohort with early-stage IMF was 129 months thus contrasting manifest IMF with an usually more unfavorable prognosis. Recognition of early stage IMF certainly alters the generally applied diagnostic criteria of this disorder. Regarding patients with associated thrombocytosis, differentiation from essential thrombocythemia is recommended. Moreover, characterization of early stage IMF probably exerts an impact on survival and may influence the decision to perform a BM transplantation.

Adult↗
PubMed2002

CD34+ stem cells in chronic myeloproliferative disorders.

Contrasting the wealth of information that is available about various biological and therapeutic aspects of human CD34+ stem cells, little data exist concerning their quantity and dynamics as well as their mutual relationships with other hematopoietic constituents in the bone marrow of patients with chronic myeloproliferative disorders. In comparison with a control group frequency of progenitors is significantly increased in chronic myeloid leukemia (CML). Following different therapeutic modalities their quantity reflects therapeutic efficacy (responder and non-responder patients) and therefore exerts a predictive value regarding acceleration and blastic crisis. The significant correlations between fiber content and number of these precursors elucidates the complex interactions between stroma and progenitor cell differentiation and maturation. Following allogeneic bone marrow transplantation there is a rapid recovery of the CD34+ stem cell population in the first month. A higher number of these cells is related with graft size, an earlier independence for platelet transfusion and a more extended regeneration of erythro- and megakaryopoiesis. The slight increase in reticulin fibers in these patients may be associated with the complex and so far ill-defined pathomechanism of homing (adherence to the fibrous matrix). In idiopathic myelofibrosis (IMF) an increased number of CD34+ stem cells is found predominantly in the early (prefibrotic or mild fibrotic) hypercellular stages and probably indicates a higher proliferative activity of the precursor cell pool. According to sequential biopsies most patients with early IMF that later evolved into an overt fibrosclerotic stage usually display a reduction of progenitor cells during the development of myelofibrosis. The unequal distribution of CD34+ stem cells in the bone marrow versus spleen in IMF (advanced fibrosclerotic stage) is in support of the currently discussed hypothesis of splenic filtration and concentration of precursor cells as an essential feature of myeloid metaplasia. Regarding prognosis in CML a higher amount of CD34+ stem cells is significantly associated with an unfavorable survival and thus confirms the assumed implication of an accelerated phase of disease at onset. On the other hand, in polycythemia vera (PV) and IMF a low number of progenitors is probably due to a decreased proliferation rate (reduced hematopoietic turnover index) and therefore reflects a reduction in the regenerative capacity of hematopoiesis. For this reason, a presumptive defect in the recovery of normal and clonally transformed stem cells is speculated to add to the worsening of prognosis by causing the well-known bone marrow insufficiency in terminal stage PV and IMF.

Antigens, CD34↗