The pathology of murine myelogenous leukemias

A Critical Review of Animal Models Used in Acute Myeloid Leukemia Pathophysiology

Acute myeloid leukemia (AML) is one of the most frequent, complex, and heterogeneous hematological malignancies. AML prognosis largely depends on acquired cytogenetic, epigenetic, and molecular abnormalities. Despite the improvement in understanding the biology of AML, survival rates remain quite low. Animal models offer a valuable tool to recapitulate different AML subtypes, and to assess the potential role of novel and known mutations in disease progression. This review provides a comprehensive and critical overview of select available AML animal models. These include the non-mammalian Zebrafish and Drosophila models as well as the mammalian rodent systems, comprising rats and mice. The suitability of each animal model, its contribution to the advancement of knowledge in AML pathophysiology and treatment, as well as its advantages and limitations are discussed. Despite some limitations, animal models represent a powerful approach to assess toxicity, and permit the design of new therapeutic strategies.

Morphology and quantitative composition of hematopoietic cells in murine bone marrow and spleen of healthy subjects

Laboratory mice play an outstanding role in modeling human development and disease. In contrast to human leukemia, the spleen is involved in almost all cases, and the bone marrow is only variably involved in murine models. Although mice have been used for medical research for over 100 years, there are only few reports with a small number of cases looking at morphology and quantitative composition of murine hematopoietic cells in the bone marrow of non-transplanted animals of most strains. To our knowledge, there is not even a single report describing the splenogram in C57BL/6J mice, one of the most commonly used strains for medical research. The present study illustrates the morphology of the hematopoietic cells in the bone marrow and spleen of non-treated C57BL/6J mice and establishes the murine myelogram from the largest healthy C57BL/6J cohort reported to date. Furthermore, we present the first murine splenogram described for C57BL/6J mice. Our study supports the acceptance of the presence of >5 % blast cells as providing clear evidence of abnormality in bone marrow like in humans. In addition, we are the first to show <1 % blast cells in the normal spleen. Interestingly, classical dysplastic changes were rare in normal healthy mice. Our study of the bone marrow and spleen of healthy non-transplanted animals provides reference ranges of each cell type and for the myeloid/erythroid ratio, which can be used to interpret preclinical gene therapy data, leukemogenesis, and hematopoiesis studies, and may improve the quality of such analyses.

Cytological characterization of murine bone marrow and spleen hematopoietic compartments for improved assessment of toxicity in preclinical gene marking models

Gene therapy has proven its potential to cure diseases of the hematopoietic system, but potential adverse reactions related to insertional mutagenesis by integrating gene vectors and chromosomal instability in long-lived repopulating cells have emerged as a major limitation. Preclinical gene therapy in murine models is a powerful model for assessment of gene marking efficiency and adverse reactions. However, changes in the hematologic composition after transplantation with retrovirally modified hematopoietic stem cells have not been well investigated in large cohorts of animals by systematic cytological analyses. In the present study, cytological analyses of bone marrow and spleen were performed in a large cohort (n = 58) of C57BL/6J mice over an extended observation period after gene marking. Interestingly, we observed hematological malignancies in four out of 30 animals transplanted with dLNGFR (truncated form of the human p75 low-affinity nerve growth factor receptor) and tCD34 modified stem/progenitor cells. Our data demonstrate that cytological analysis provides important information for diagnosis of hematological disorders and thus should be included in preclinical studies and performed in each investigated animal. Together with histological analysis, flow cytometric analysis, and other analyses, the quality and predictive value of preclinical gene therapy studies will be improved.

Retroviral integration at the Epi1 locus cooperates with Nf1 gene loss in the progression to acute myeloid leukemia

Juvenile myelomonocytic leukemia (JMML) is a disease that occurs in young children and is associated with a high mortality rate. In most patients, JMML has a progressive course leading to death by virtue of infection, bleeding, or progression to acute myeloid leukemia (AML). As it is known that children with neurofibromatosis type 1 syndrome have a markedly increased risk of developing JMML, we have previously developed a mouse model of JMML through reconstitution of lethally irradiated mice with hematopoietic stem cells homozygous for a loss-of-function mutation in the Nf1 gene (D. L. Largaespada, C. I. Brannan, N. A. Jenkins, and N. G. Copeland, Nat. Genet. 12:137-143, 1996). In the course of these experiments, we found that all these genetically identical reconstituted mice developed a JMML-like disorder, but only a subset went on to develop more acute disease. This result strongly suggests that additional genetic lesions are responsible for disease progression to AML. Here, we describe the production of a unique tumor panel, created using the BXH-2 genetic background, for identification of these additional genetic lesions. Using this tumor panel, we have identified a locus, Epi1, which maps 30 to 40 kb downstream of the Myb gene and appears to be the most common site of somatic viral integration in BXH-2 mice. Our findings suggest that proviral integrations at Epi1 cooperate with loss of Nf1 to cause AML.