Reversible adult-onset cyclic haematopoiesis with a cycle length of 100 days

Modelling Hematopoiesis Mediated by Growth Factors With Applications to Periodic Hematological Diseases

Hematopoiesis is a complex biological process that leads to the production and regulation of blood cells. It is based upon differentiation of stem cells under the action of growth factors. A mathematical approach of this process is proposed to understand some blood diseases characterized by very long period oscillations in circulating blood cells. A system of three differential equations with delay, corresponding to the cell cycle duration, is proposed and analyzed. The existence of a Hopf bifurcation at a positive steady-state is obtained through the study of an exponential polynomial characteristic equation with delay-dependent coefficients. Numerical simulations show that long-period oscillations can be obtained in this model, corresponding to a destabilization of the feedback regulation between blood cells and growth factors, for reasonable cell cycle durations. These oscillations can be related to observations on some periodic hematological diseases (such as chronic myelogenous leukemia, for example).

Idiopathic cyclic thrombocytopenia

Cyclic thrombocytopenia (CTP) is an uncommon disorder characterized by periodic fluctuations in platelet counts, typically resulting in episodes of thrombocytopenia alternating with normal platelet counts. While some CTP cases are associated with a primary hematologic disease, most are idiopathic. Patients with CTP are frequently misdiagnosed as idiopathic thrombocytopenic purpura (ITP) because CTP has clinical features very similar to ITP. When evaluating patients with suspected ITP, CTP should always be included in the differential diagnoses because CTP generally does not respond to standard ITP treatments, including corticosteroids, splenectomy, and intravenous immunoglobulin. Two clinical features relatively unique to CTP besides periodic thrombocytopenia are rebound thrombocytosis unrelated to recent splenectomy and platelet nadirs occurring during menses. When a diagnosis of CTP is made, patients must be offered a period of observation, as many may not require treatment. If treatment is clinically indicated, the literature suggests that hormonal therapy provides the best response.

Occurrence of periodic oscillations in the differential blood counts of congenital, idiopathic, and cyclical neutropenic patients before and during treatment with G-CSF

Using techniques developed in astrophysics to deal with unequally sampled data sets, we have analyzed serial differential cell counts from 45 congenital, idiopathic, and cyclic neutropenic patients before and during treatment with recombinant human G-CSF (rhG-CSF). Our results show that the occurrence of significant cycling in the absolute neutrophil count (ANC) of neutropenics not classified as cyclical is much more prevalent than had been previously thought, and that not all the patients classified as cyclic show significant ANC periodicity. In these patients, cycling in more than one cell line may be involved. The range of periods encountered in these patients is much broader (between 11 and 52 days) than is usually associated with classical cyclical neutropenia, and there is no obvious connection between the range of periods and the patient's diagnostic category. Administration of rhG-CSF is able to induce significant cycling in neutropenic patients that were not cycling prior to treatment. In patients who had significant cycling before treatment, rhG-CSF may either decrease the period to between 11 and 14 days, or may obliterate any statistical evidence of cycling.

Cyclical Neutropenia and Other Periodic Hematological Disorders: A Review of Mechanisms and Mathematical Models

Although all blood cells are derived from hematopoietic stem cells, the regulation of this production system is only partially understood. Negative feedback control mediated by erythropoietin and thrombopoietin regulates erythrocyte and platelet production, respectively, but the regulation of leukocyte levels is less well understood. The local regulatory mechanisms within the hematopoietic stem cells are also not well characterized at this point. Because of their dynamic character, cyclical neutropenia and other periodic hematological disorders offer a rare opportunity to more fully understand the nature of these regulatory processes. We review the salient clinical and laboratory features of cyclical neutropenia (and the less common disorders periodic chronic myelogenous leukemia, periodic auto-immune hemolytic anemia, polycythemia vera, aplastic anemia, and cyclical thrombocytopenia) and the insight into these diseases afforded by mathematical modeling. We argue that the available evidence indicates that the locus of the defect in most of these dynamic diseases is at the stem cell level (auto-immune hemolytic anemia and cyclical thrombocytopenia seem to be the exceptions). Abnormal responses to growth factors or accelerated cell loss through apoptosis may play an important role in the genesis of these disorders.

© 1998 by The American Society of Hematology.

Cyclical Neutropenia and Other Periodic Hematological Disorders: A Review of Mechanisms and Mathematical Models

Although all blood cells are derived from hematopoietic stem cells, the regulation of this production system is only partially understood. Negative feedback control mediated by erythropoietin and thrombopoietin regulates erythrocyte and platelet production, respectively, but the regulation of leukocyte levels is less well understood. The local regulatory mechanisms within the hematopoietic stem cells are also not well characterized at this point. Because of their dynamic character, cyclical neutropenia and other periodic hematological disorders offer a rare opportunity to more fully understand the nature of these regulatory processes. We review the salient clinical and laboratory features of cyclical neutropenia (and the less common disorders periodic chronic myelogenous leukemia, periodic auto-immune hemolytic anemia, polycythemia vera, aplastic anemia, and cyclical thrombocytopenia) and the insight into these diseases afforded by mathematical modeling. We argue that the available evidence indicates that the locus of the defect in most of these dynamic diseases is at the stem cell level (auto-immune hemolytic anemia and cyclical thrombocytopenia seem to be the exceptions). Abnormal responses to growth factors or accelerated cell loss through apoptosis may play an important role in the genesis of these disorders.

© 1998 by The American Society of Hematology.