Role of a single haemopoietic growth factor in multiple proliferative disorders of haemopoietic and related cells

Autonomous and interleukin-2-responsive growth of leukemic cells in adult T-cell leukemia (ATL): a review of the clinical significance and molecular basis of ATL cell growth

Since the initial report of adult T-cell leukemia (ATL) in 1976, a number of investigators have described the basic biologic aspects of this disease. However, the precise mechanism of leukemogenesis remains unclear. Primary ATL cells demonstrate autonomous and IL-2 responsive growth in vitro. The autonomous growth of the cells is thought to be mediated by IL-2 in an autocrine manner, at least in part. These growth activities are related inversely to survival, and may be useful prognostic determinants. The viral Tax protein stimulates IL-2 and IL-2 receptor alpha expression via nuclear transfer factor NF-kappaB induction. We showed that marked activation of the Tax-NF-kappaB pathway is seen only in acute-type ATL patients. Recent studies show that mutations of p16 and p53 are also found in acute and lymphoma-type ATL. These appear to be late events in ATL leukemogenesis. The relationship between activation of Tax-NF-kappaB pathway and mutations of p53 and p16 genes is unknown. A few other genetic events may be involved in earlier stages of the entire process of ATL leukemogenesis, leading to smoldering and chronic-type ATL. These gene mutations may be accumulated by Tax protein during the long process from the time of HTLV-I infection to the onset of ATL.

Megakaryoblastic transformation of myelofibrosis with expression of the c-sis oncogene

We describe a case of primary myelofibrosis which terminated in an acute megakaryoblastic leukaemia with massive marrow fibrosis and osteosclerosis. The megakaryocyte lineage of the terminal phase was confirmed by ultrastructural and surface marker studies of the blast cells. The leukaemic phase was associated with the presence of large numbers of progressively more immature megakaryocyte progenitors in the peripheral blood. The expression of c-sis mRNA in these blast cells was significantly higher than in normal mononuclear cells. Activation of the c-sis protooncogene leading to increased production of platelet-derived growth factor could be related to the progressive fibrosis observed.

The stem cell concept revisited: self-renewal capacity is a dynamic property of hemopoietic cells

A rigid developmental program of stem cell division and progressive maturation into blood cells is challenged. It is proposed that the capacity for self-renewal is not limited to pluripotent stem cells but is shared by committed progenitors and even cells of later compartments. The relative probability of self-replication vs maturation in mitotic cells is controlled by extracellular influences. At the cell population level, the balance between proliferation and maturation and between compartments is regulated by feedback interactions. Inducibility of maturation in response to regulatory signals is smaller at earlier stages; consequently, at steady state primitive cells self-renew while their more differentiated progeny are forced to be transitory. The proposed dynamic linkage between compartments can be destabilized in a number of ways, resulting in defective hemopoiesis or leukemia. At all stages hemopoietic cells are able to change their patterns of gene expression, in an inheritable manner, in response to changes in their microenvironment. In particular, the capacity for self-renewal itself can vary even within a conventionally-defined compartment. On this basis of adaptive differentiation and self-renewal it is possible to account for the progression of chronic myelocytic leukemia and its "blastic conversion"; to analyse the hemopoietic system's response to various physiological and experimental perturbations; and to re-interpret the excessive phenotypic plasticity and apparent "lineage infidelity" manifested by leukemic cells and cell lines.

Myelodysplastic syndromes: pathogenesis, functional abnormalities, and clinical implications

The myelodysplastic syndromes represent a preleukaemic state in which a clonal abnormality of haemopoietic stem cell is characterised by a variety of phenotypic manifestations with varying degrees of ineffective haemopoiesis. This state probably develops as a sequence of events in which the earliest stages may be difficult to detect by conventional pathological techniques. The process is characterised by genetic changes leading to abnormal control of cell proliferation and differentiation. Expansion of an abnormal clone may be related to independence from normal growth factors, insensitivity to normal inhibitory factors, suppression of normal clonal growth, or changes in the immunological or nutritional condition of the host. The haematological picture is of peripheral blood cytopenias: a cellular bone marrow, and functional abnormalities of erythroid, myeloid, and megakaryocytic cells. In most cases marrow cells have an abnormal DNA content, often with disturbances of the cell cycle: an abnormal karyotype is common in premalignant clones. Growth abnormalities of erythroid or granulocyte-macrophage progenitors are common in marrow cultures, and lineage specific surface membrane markers indicate aberrations of differentiation. Progression of the disorder may occur through clonal expansion or through clonal evolution with a greater degree of malignancy. Current attempts to influence abnormal growth and differentiation have had only limited success. Clinical recognition of the syndrome depends on an acute awareness of the signs combined with the identification of clonal and functional abnormalities.

Refractory anaemia terminating in a combined lymphoproliferative and myeloproliferative disorder

We report a case of non-sideroblastic refractory anaemia which evolved to a double lymphomyeloproliferative disorder. At presentation, bone marrow appearances and peripheral blood pancytopenia without myelomonocytosis were consistent with a diagnosis of non-sideroblastic refractory anaemia. Subsequently, the patient developed pronounced myelomonocytosis and lymphocytosis with prolymphocytes. Light and transmission electron microscopy as well as surface marker studies were compatible with a diagnosis of prolymphocytic transformation of chronic lymphocytic leukaemia/prolymphocytic leukaemia associated with myelomonocytic leukaemia. The pathogenesis of such double lympho-myeloproliferative disorders is discussed in the light of the evidence for common lymphoid and myeloid progenitor cells and some recent advances in the immunology of the myelodysplastic syndromes.

In vitro induction of CFU-S proliferation by a non viral splenic activity from myeloproliferative sarcoma virus infected mice

The myeloproliferative sarcoma virus (MPSV) induces a myeloproliferative syndrome in DBA/2 mice. It is characterized by a considerable increase in the number (100-fold) and in the concentration (10-fold) of pluripotent hematopoietic stem cells detected in vivo (CFU-S) in the spleens of infected animals. Prior studies have shown the presence of a mixed-colony promoting activity (MPA) in neoplastic spleens. In the presence of a small quantity of erythropoietin, MPA induces the proliferation and differentiation of pluripotent hematopoietic stem cells, detected in vitro (Mix-CFU). We tested the effect of factors produced by neoplastic spleen cells on the proliferation of day 10 CFU-S and their entry into the cell cycle. This was done by comparing the number of day 10 CFU-S present in suspensions of normal bone marrow cells incubated for 2 days on agar underlays containing cells from either normal or neoplastic spleens. Our results show the existence of an activity secreted by cells from the spleens of MPSV-infected animals which starts CFU-S cycling and which is physically distinct from MPSV. The presence of this activity, whose identity with MPA remains to be proven, would enable us to explain the proliferation of CFU-S in the course of the disease.