Congenital and Acquired Neutropenia

Cell biology of membrane trafficking in human disease

Understanding the molecular and cellular mechanisms underlying membrane traffic pathways is crucial to the treatment and cure of human disease. Various human diseases caused by changes in cellular homeostasis arise through a single gene mutation(s) resulting in compromised membrane trafficking. Many pathogenic agents such as viruses, bacteria, or parasites have evolved mechanisms to subvert the host cell response to infection, or have hijacked cellular mechanisms to proliferate and ensure pathogen survival. Understanding the consequence of genetic mutations or pathogenic infection on membrane traffic has also enabled greater understanding of the interactions between organisms and the surrounding environment. This review focuses on human genetic defects and molecular mechanisms that underlie eukaryote exocytosis and endocytosis and current and future prospects for alleviation of a variety of human diseases.

Neutrophil elastase in cyclic and severe congenital neutropenia

Mutations in ELA2 encoding the neutrophil granule protease, neutrophil elastase (NE), are the major cause of the 2 main forms of hereditary neutropenia, cyclic neutropenia and severe congenital neutropenia (SCN). Genetic evaluation of other forms of neutropenia in humans and model organisms has helped to illuminate the role of NE. A canine form of cyclic neutropenia corresponds to human Hermansky-Pudlak syndrome type 2 (HPS2) and results from mutations in AP3B1 encoding a subunit of a complex involved in the subcellular trafficking of vesicular cargo proteins (among which NE appears to be one). Rare cases of SCN are attributable to mutations in the transcriptional repressor Gfi1 (among whose regulatory targets also include ELA2). The ultimate biochemical consequences of the mutations are not yet known, however. Gene targeting of ELA2 has thus far failed to recapitulate neutropenia in mice. The cycling phenomenon and origins of leukemic transformation in SCN remain puzzling. Nevertheless, mutations in all 3 genes are capable of causing the mislocalization of NE and may also induce the unfolded protein response, suggesting that there might a convergent pathogenic mechanism focusing on NE.

Antitumor necrosis factor-induced neutropenia: a case report with double positive rechallenges

A 50-year-old man with ankylosing spondylitis who developed neutropenia after treatment of etanercept, with two positive rechallenges, and after the first infliximab infusion, is described. Although leukopenia and neutropenia related to etanercept and infliximab have been described as rare adverse events from clinical trials data, their mechanism of action are unknown. This patient developed recurrent mild neutropenia after exposition of two different antitumor necrosis factors; therefore, it seems to be an adverse reaction related to the therapeutic group. Doctors should be aware of this potentially severe adverse effect in patients treated with antitumor necrosis factor.

Patient-centred screening for primary immunodeficiency: a multi-stage diagnostic protocol designed for non-immunologists

Efficient early identification of primary immunodeficiency disease (PID) is important for prognosis, but is not an easy task for non-immunologists. The Clinical Working Party of the European Society for Immunodeficiencies (ESID) has composed a multi-stage diagnostic protocol that is based on expert opinion, in order to increase the awareness of PID among doctors working in different fields. The protocol starts from the clinical presentation of the patient; immunological skills are not needed for its use. The multi-stage design allows cost-effective screening for PID within the large pool of potential cases in all hospitals in the early phases, while more expensive tests are reserved for definitive classification in collaboration with an immunologist at a later stage. Although many PIDs present in childhood, others may present at any age. The protocols presented here are therefore aimed at both adult physicians and paediatricians. While designed for use throughout Europe, there will be national differences which may make modification of this generic algorithm necessary.

Drug-associated disease: hematologic dysfunction

Hematologic dysfunction, including thrombocytopenia, anemia, neutropenia, thromboses, and coagulopathy, occur commonly during critical illnesses. A major challenge is to identify drug-induced causes of hematologic dysfunction. Given the wide variety of drug-induced hematologic effects, clinicians always should consider any concomitant drugs in the differential diagnosis of acquired hematologic dysfunction. The most severe effects include drug-induced aplastic anemia, heparin-induced thrombocytopenia, and drug-induced thrombotic microangiopathy. Certain drugs are associated with multiple hematologic effects. For example, cisplatin can cause hemolytic uremia syndrome and erythropoietin deficiency, and quinine can precipitate immune-mediated thrombocytopenia, immune-mediated thrombocytopenia, and thrombotic microangiopathy.

Pathogenesis of neutropenia in large granular lymphocyte leukemia and Felty syndrome

T-cell large granular lymphocyte leukemia (TLGL) is an atypical chronic lymphoproliferative disorder derived from cytotoxic T-cells (CTL). Unlike most forms of leukemia, the pattern of bone marrow infiltration in TLGL may be subtle and the cytopenias are often lineage specific, with neutropenia dominating. Both granulocytic survival and proliferation defects are observed and are mediated by humoral and cell-mediated mechanisms respectively. Splenic production of immune complexes induces a neutrophil survival defect, where as Fas expression by leukemic CTL results in a marrow based proliferation defect. These humoral and cell-mediated pathways induce granulocytic apoptosis through independent intracellular mechanisms which are not mutually exclusive and may be observed concurrently in individual patients with either TLGL or FS. A variety of therapeutic interventions have been utilized in the management of TLGL and Felty syndrome, including methotrexate, cyclosporine A, cyclophosphamide, glucocorticoids, myeloid colony stimulating factors and splenectomy. Their efficacy and mechanisms of action are reviewed.

Large Granular Lymphocyte Leukemia

Clonal disorders of large granular lymphocytes (LGLs) represent a spectrum of biologically distinct lymphoproliferative diseases originating either from mature T cells (CD3+) or natural killer (NK) cells (CD3-). Both subtypes, T-cell and NK-cell LGL leukemia, can manifest as indolent or aggressive disorders. The majority of patients with T-cell LGL leukemia have a clinically indolent course with a median survival time >10 years. Immunosuppressive therapy with low-dose methotrexate, cyclophosphamide, or cyclosporine A can control symptoms and cytopenias in more than 50% of patients, but this approach is not curative. Several cases of an aggressive variant (CD3+ CD56+) of T-cell LGL leukemia with a poor prognosis have also been reported. Aggressive NK-cell LGL leukemia is usually a rapidly progressive disorder associated with Epstein-Barr virus (EBV), with a higher prevalence in Asia and South America. This disease is usually refractory to conventional chemotherapy, with a median survival time of 2 months. Chronic NK-cell leukemia/lymphocytosis is a rare EBV-negative disorder with an indolent clinical course. The malignant origin of this subtype is uncertain because clonality is difficult to determine in LGLs of NK-cell origin.

Neutropenia: Etiology and Pathogenesis

Neutropenia is defined as an absolute neutrophil count <1500 cells/mm(3) and can be graded as mild (1000-1500 cells/mm(3)), moderate (500-1000 cells/mm(3)), or severe (<500 cells/mm(3)). Neutropenia can develop as a result of > or =1 pathologic mechanism, including decreased bone marrow production, the sequestering of neutrophils, and increased destruction of neutrophils in the peripheral blood. The clinical result is increased risk for infection. This risk is directly proportional to the severity and duration of neutropenia. Neutropenia is classified according to the etiology as congenital or acquired, with the latter further defined according to the etiology or pathology. Febrile neutropenia is associated with substantial morbidity and even mortality.

Disorders of Neutrophil Number and Function

This review of disorders of neutrophil number and function will discuss important research advances in the field and then provide a clinical diagnostic approach. The focus will be on two recent clinical developments in the field of phagocyte disorders. First, an important natural history study from the Severe Chronic Neutropenia International Registry has recently quantitated the incidence and risk factors for death from sepsis and for progression to myelodysplastic syndrome and acute myeloid leukemia in a large cohort of severe chronic neutropenia patients, many of whom were followed 10 or more years on treatment with granulocyte colony-stimulating factor. Second, in the past year, a multinational group has announced successful gene therapy of two adults with chronic granulomatous disease, the most common disorder of neutrophil function. However, monitoring of retroviral insertion sites revealed expansion of the multiclonal population of gene-modified cells, raising concerns about eventual leukemogenesis. The review also provides a pragmatic approach to the evaluation of a patient with a suspected disorder of neutrophil number or function.

Chronic lymphoid leukemias other than chronic lymphocytic leukemia: diagnosis and treatment

The World Health Organization classification divides lymphoid malignancies into precursor B-cell and T-cell neoplasms as well as mature B-cell and T-cell neoplasms. Mature B-cell neoplasms comprise more than 85% of non-Hodgkin lymphomas worldwide and can be further subclassified according to the postulated cell of origin by using specific morphologic, immunophenotypic, and molecular characteristics. Similarly, the more uncommon mature T-cell neoplasms have been better characterized to include numerous distinct entities with widely varying natural histories. The distinction between lymphoma and leukemia is somewhat arbitrary and is based on variable involvement of the bone marrow, peripheral blood, and lymphatic system. In this article, we review the diagnostic and clinical features of mature B-cell and T-cell lymphoproliferative disorders that commonly have a leukemic presentation.

How to interpret and pursue an abnormal complete blood cell count in adults

A complete blood cell count (CBC) is one of the most common laboratory tests in medicine. For example, at our institution alone, approximately 1800 CBCs are ordered every day, and 10% to 20% of results are reported as abnormal. Therefore, it is in every clinician's interest to have some understanding of the specific test basics as well as a structured action plan when confronted with abnormal CBC results. In this article, we provide practical diagnostic algorithms that address frequently encountered conditions associated with CBC abnormalities including anemia, thrombocytopenia, leukopenia, polycythemia, thrombocytosis, and leukocytosis. The objective is to help the nonhematologist recognize when a subspecialty consultation is reasonable and when it may be circumvented, thus allowing a cost-effective and intellectually rewarding practice.

Mature T-cell leukemias

Mature T-cell and NK-cell leukemias are a group of relatively uncommon neoplasms derived from mature or postthymic T-cells accounting for a relatively small percentage of lymphoid malignancies. The recent availability of modern immunophenotypic and molecular tools has allowed a better distinction of these disorders from their B-cell counterparts. Similarly, identification of recurrent cytogenetic abnormalities, as well as plausible mechanisms through which these molecular events influence cellular signaling pathways, have created further insight into the pathogenesis of these disorders. Furthermore, the availability of new agents such as alemtuzumab has generated significant interest in devising specific therapeutic strategies for these malignancies. Herein, we review the clinical and pathological features of mature T-cell leukemias.