Leukemia diagnosis in murine bone marrow transplantation models

Flow cytometric characterization of acute leukemia reveals a distinctive "blast gate" of murine T-lymphoblastic leukemia/lymphoma

Immunophenotypic analysis using multiparameter flow cytometry is an indispensable tool for diagnosis and management of acute leukemia. Mouse models have been widely used for medical research for more than 100 years and are indispensable for leukemia research. However, immunophenotypic analysis of murine leukemia was not always performed in published studies, and blast gating for isolation of blasts was shown only in very few studies. No systemic characterization of all types of murine acute leukemia in large cohorts by flow cytometry has been reported. In this study, we used flow cytometry to comprehensively characterize murine acute leukemia in a large cohort of mice. We found that murine T-lymphoblastic leukemia/lymphoma (T-ALL) exhibits a distinctive “blast gate” (CD45^bright) with CD45/side scatter gating that differs from the “blast gate” (CD45^dim) of human T-ALL. By contrast, murine B-lymphoblastic leukemia and acute myeloid leukemia show the same blast region (CD45^dim) as human leukemia. Using blast cell gating, we for first time detected T-ALL development in FLT3-ITD knock-in mice (incidence: 23%). These leukemic cells were selectively killed by the FLT3 inhibitors crenolanib and midostaurin in vitro. These data suggest that FLT3-ITD plays a potential role in the pathogenesis of T-ALL and that FLT3-ITD inhibition is a therapeutic option in the management of patients with T-ALL. Our gating strategy for immunophenotypic analysis can be used for leukemogenesis and preclinical gene therapy studies in mice and may improve the quality of such analyses.

Analyzing the Genotoxicity of Retroviral Vectors in Hematopoietic Cell Gene Therapy

Retroviral vectors, including those derived from gammaretroviruses and lentiviruses, have found their way into the clinical arena and demonstrated remarkable efficacy for the treatment of immunodeficiencies, leukodystrophies, and globinopathies. Despite these successes, gene therapy unfortunately also has had to face severe adverse events in the form of leukemias and myelodysplastic syndromes, related to the semi-random vector integration into the host cell genome that caused deregulation of neighboring proto-oncogenes. Although improvements in vector design clearly lowered the risk of this insertional mutagenesis, analysis of potential genotoxicity and the consequences of vector integration remain important parameters for basic and translational research and most importantly for the clinic. Here, we review current assays to analyze biodistribution and genotoxicity in the pre-clinical setting and describe tools to monitor vector integration sites in vector-treated patients as a biosafety readout.

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.